ABSTRACT
PALMER, TRISHA DENISE. The Role of Land-Surface Hydrology on Small Stream Flash
Flooding in Central North Carolina. (Under the direction of Dr. Sethu Raman and Kermit
Keeter.)
In order to determine the influence of various factors on flash flooding, six case studies during which flash flooding occurred across central North Carolina are examined: 1) 26
August 2002, 2) 11 October 2002, 3) 9-10 April 2003, 4) 16 June 2003, 5) 29 July 2003, and
6) 9 August 2003. Utilizing stream gage data from the United States Geological Survey combined with radar-estimated precipitation from the Weather Surveillance Radar-1988
Doppler (WSR-88D) KRAX near Clayton, NC, several statistical conclusions are drawn.
These conclusions are based on relationships between the inputs – rain rate and precipitation amount – to the stream responses: the amount of time between when the stream began its rise and when the maximum stage was reached, the amount of time between the onset of precipitation and the initial response of the stream, the maximum stage reached, the change in height of the stream, and the rate of change of height of the stream. Results indicate that precipitation rate and amount tend to dominate the influence of stream response; however, in many situations, land-surface characteristics play an important role. The notable situations where precipitation rate and amount do not dominate are along the major rivers, in locations with sandy soils where infiltration is high, and in urban areas, where runoff occurs rapidly and streams thus respond quickly regardless of precipitation rate or amount. In addition, rain rate and precipitation amount do not necessarily have similar relationships with the stream response variables; rain rate has a stronger correlation with rate of change of stream rise, while precipitation amount has a stronger correlation with change in stream height.
However, it is not enough to study rainfall rates and precipitation amounts if a flash flood warning is to be issued. The results of this research show that there is value and necessity in understanding the role of land-surface characteristics when determining if flash flooding is going to occur.
DEDICATION
This work is dedicated to my father, David Edward Brune. His tornado stories and “official” piece of paper (certification to take weather observations) instilled in me this passion for weather. His support and encouragement, along with my mother’s, to strive to be and do my best instilled in me a passion for learning. As a result, Daddy, I'm certain I'm finally allowed to be the one to look out the window and proudly proclaim that it's going to rain. I now have my share of “official” papers.
ii BIOGRAPHY
Trisha Denise Palmer was born 23 May 1980 in Ft. Smith, Arkansas, the third of four children of David and Cassandra Brune. They moved to the small community of Avilla just outside of Little Rock, Arkansas, in 1987, where her parents still reside with her youngest sibling. She spent most of her childhood and teenage years wondering what caused the huge tornado (retroactively classified as an F5) that devastated her father’s hometown of Ruskin
Heights, Missouri, on 20 May 1957. As if that wasn’t enough to pique her interest, a large outbreak in her own backyard of central Arkansas on 1 March 1997 reinforced her decision to go into meteorology. She toured the National Weather Service Weather Forecast Office in
Little Rock and joined the Central Arkansas Chapter of the American Meteorological Society
(AMS)/National Weather Association. After graduating from Bryant High School in May of
1998, she was off to the University of Oklahoma (OU) the following fall.
She thoroughly enjoyed her time at OU, especially when a break in coursework allowed for a storm chase or two. She entered with several scholarships, including the Freshman
Meteorology Scholarship from the OU School of Meteorology (SoM). She was involved in the OU Student Chapter of the AMS all four years, and was elected Vice President her senior year. The Oklahoma Weather Lab (OWL), a forecasting organization modeled after the
National Weather Service, was founded her freshman year, and she immediately volunteered to serve on the leadership committee. By her sophomore year, she was a shift leader, and she became co-President her junior year. For her work with OWL, she was awarded an
Outstanding Service Award from the SoM her junior year. She participated in the National
Collegiate Weather Forecasting Competition throughout her undergraduate career and won
iii both national and local awards. She graduated in May 2002 with a Bachelor of Science in
Meteorology with Special Distinction and a minor in mathematics, not long after notification of being awarded an AMS graduate fellowship sponsored by the National Science
Foundation.
As luck would have it, a student position at WFO Little Rock opened just as she started at
OU. She jumped at the opportunity, beginning in June of 1999 and working there through
June of 2002. While at Little Rock, she trained on most aspects of office functions, launched weather balloons, went on storm surveys, and conducted a radar research project, not to mention several other various duties and tasks.
Trisha married Joshua Palmer, also a meteorology graduate from OU, on 25 May 2002 – they had met during their second week of classes their freshman year. They made the decision to attend graduate school at North Carolina State University, and she was given the opportunity to transfer from a student position at WFO Little Rock to one at WFO Raleigh in
July of 2002. They began graduate school in August 2002.
In November 2003, an Intern position opened at WFO Raleigh. Trisha applied and was hired; in December 2003 her dream of obtaining a career position with the National Weather
Service was accomplished. Her Master’s degree will be completed during the fall of 2004, concurrently with part of her forecaster training.
iv ACKNOWLEDGEMENTS
I would like first to thank my committee members: my advisor, Dr. Sethu Raman, for his
guidance, and also for allowing me the freedom to choose a topic to assist WFO Raleigh; my
NCSU members, Drs. Gary Lackmann and Al Riordan, for their assistance throughout this
project; and finally Kermit Keeter, the Science and Operations Officer (SOO) at WFO
Raleigh, my “technical consultant,” but so much more than that.
At the State Climate Office (SCO), thanks to everyone – Maggie Puryear, Becky Eager,
Mark Brooks, Matt Simpson, just to name a few. But special thanks to Robb Ellis, Pete
Childs, and Ryan Boyles, who have helped me on specific projects. At the United States
Geological Survey, thanks to Ramona Traynor; without her I’d never have my river data.
There are so many people associated with the National Weather Service; I could never
list them all. I need to especially thank Paul Jendrowski, Information Technology Officer
(ITO) at WFO Blacksburg, VA, for his endless help with AMBERGIS, and for installing it here at WFO Raleigh to begin with,. At the Southeast River Forecast Center in Atlanta, GA,
I need to thank Brad Gimmestad, Reggina Garza, and Tom Wallace for their help; at WFO
Greenville-Spartanburg, SC, thanks to Joe Pellisier, Larry Lee, and Pat Tanner for their advice. Finally, right here at WFO Raleigh I need to thank the entire staff, for advice, support, encouragement, comic relief, basically everything that a family would do. A huge thank-you to all the operational staff, for putting up with the “tornado monger” in the corner, and for allowing me the time to research. Many thanks to Jonathan Blaes, ITO, for countless hours devoted to working with me to get AMBERGIS up and running, not to mention the other computer issues he assisted with. Mike Moneypenny and Al Lazo, thank you for
v answering all of my flash flooding questions. Steve Harned, thank you for the many opportunities, and for believing in me. And of course, Kermit, I could never thank you enough, for everything you’ve done.
My family and friends have supported me through everything. Especially my parents – I couldn’t have asked for more from them – throughout high school and college, they’ve been there for me every step of the way. I am the person I am today because of them, and I love them dearly. My friends, both from OU and here at NCSU, have been immensely supportive; we’ve all been through this together, and without each other it would have been far more difficult.
Most of all, though, I must thank my husband, Joshua. He was there at the beginning of this academic journey, he’s supported and assisted me throughout the duration, and he’ll be there with me through our meteorological careers. His unwavering love has been more than I could have ever asked. I look forward to what life has to offer us.
Computing resources at both WFO Raleigh and the SCO were essential in completing this research. This research is supported by the State Climate Office of North Carolina, a one-year AMS/National Science Foundation graduate fellowship, and a federal salary with the National Weather Service.
vi TABLE OF CONTENTS
Page
LIST OF TABLES ...... x
LIST OF FIGURES ...... xii
LIST OF ABBREVIATIONS ...... xxiv
1. INTRODUCTION ...... 1
1.1 Motivation ...... 1 1.2 Flash Floods ...... 3 1.3 Forecasts and Warnings ...... 3 1.3.1 Parameters and Features Associated with Flash Floods ...... 3 1.3.2 Classifications and Pattern Recognition ...... 6 1.3.3 Ingredients for Heavy Rainfall ...... 9 1.3.4 Warnings ...... 11 1.4 Precipitation Estimation ...... 13 1.4.1 Radar ...... 13 1.4.2 Rain Gage ...... 16 1.4.3 Satellite ...... 17 1.5 Land-Surface Hydrology ...... 21 1.5.1 Infiltration ...... 21 1.5.2 Runoff ...... 22 1.6 Objective ...... 24
2. OPERATIONAL FORECASTING TOOLS ...... 38
2.1 Flash Flood Guidance ...... 38 2.2 Areal Mean Basin Estimated Rainfall ...... 41 2.2.1 Introduction ...... 41 2.2.2 Algorithm Overview ...... 42 2.2.3 Operational Use and Limitations ...... 44 2.3 Flash Flood Monitoring and Prediction ...... 46
3. DATA AND METHODOLOGY ...... 58
3.1 Stream ...... 58 3.2 Radar ...... 59 3.3 Soil ...... 62 3.4 Landcover ...... 62 3.5 Analysis Methodology ...... 63
vii
4. CASES STUDIED ...... 75
4.1 Overview ...... 75 4.2 26 August 2002 ...... 77 4.2.1 Antecedent Conditions ...... 77 4.2.2 Operational Summary and Warning Strategies .....78 4.3 11 October 2002 ...... 80 4.3.1 Antecedent Conditions ...... 80 4.3.2 Operational Summary and Warning Strategies .....80 4.4 9-10 April 2003 ...... 83 4.4.1 Antecedent Conditions ...... 83 4.4.2 Operational Summary and Warning Strategies .....84 4.5 16 June 2003 ...... 86 4.5.1 Antecedent Conditions ...... 86 4.5.2 Operational Summary and Warning Strategies .....86 4.6 29 July 2003 ...... 88 4.6.1 Antecedent Conditions ...... 88 4.6.2 Operational Summary and Warning Strategies .....89 4.7 9 August 2003 ...... 90 4.7.1 Antecedent Conditions ...... 90 4.7.2 Operational Summary and Warning Strategies .....91
5. DISCUSSION OF RESULTS ...... 109
5.1 Overview ...... 109 5.1.1 Site Analysis ...... 109 5.1.2 Review of Flash Flooding Situation ...... 112 5.2 Statistical Calculations ...... 114 5.3 Correlations ...... 116 5.3.1 Stream Rise Time ...... 116 5.3.2 Lag Time ...... 117 5.3.3 Maximum Stream Stage ...... 118 5.3.4 Change in Height of Stream Stage ...... 119 5.3.5 Rate of Change of Stream Rise ...... 120 5.4 Confidence Intervals ...... 121
6. CONCLUSIONS AND FUTURE RESEARCH ...... 127
6.1 Conclusions ...... 127 6.2 Future Research ...... 129
7. REFERENCES ...... 131
viii
APPENDIX ...... 136
APPENDIX A. INPUT PRECIPITATION AND STREAM RESPONSES ...... 137
ix LIST OF TABLES
Page
Table 1.1 Features associated with heavy rainfall and atmospheric fields (event characteristics) used to assess the strength (character) of these features ...... 25
Table 1.2 Performance of the Auto-Estimator in various categories of precipitation systems ...... 26
Table 1.3 Major impacts of water-resource-management activities on river-flow regimes ...... 27
Table 3.1 USGS stations in operation across the Raleigh CWA between August 2002 and August 2003, sorted by county. Also listed are landcover classes and soil types corresponding to the location. Asterisks (*) indicate locations included in the final analysis ...... 65
Table 3.2 STATSGO soil textures and associated abbreviations. Data obtained from the National Cartography and GIS Center (1991) ...... 70
Table 3.3 Values of porosity, saturated hydraulic conductivity, air-entry tension (or bubbling pressure), and pore-size distribution index. Values in parentheses are standard deviations ....71
Table 3.4 NCCGIA landcover classes and associated definitions. Data obtained from the National Center for Geographic Information and Analysis (1997) ...... 72
Table 4.1 Warnings issued by the NWS in Raleigh for the 26 August 2002 event. All times are in UTC ...... 93
Table 4.2 Same as Table 4.1, but for the 11 October 2002 event ...... 93
Table 4.3 Same as Table 4.1, but for the 09-10 April 2003 event ...... 94
Table 4.4 Same as Table 4.1, but for the 16 June 2003 event ...... 94
x
Table 4.5 Same as Table 4.1, but for the 29 July 2003 event ...... 95
Table 4.6 Same as Table 4.1, but for the 09 August 2003 event ...... 95
Table 5.1 Means and 95% confidence intervals (CI) for the stream rise times (SRT) and lag times of the sites listed below, in units of hours. The number of total samples from all six events is also listed ...... 122
Table 5.2 Means and 95% confidence intervals (CI) for the maximum stream stage (ft), change in stream stage (ft), and rate of change of stream stage (ft hr-1) of the sites listed below (the site names have been abbreviated from Table 5.1). The number of total samples is the same as in Table 5.1 ...... 123
Table A.1 Conversions of feet to meters and inches to millimeters, for reference in Figs. A.1-A.46 below ...... 137
xi LIST OF FIGURES
Page
FIG. 1.1 (a) Surface pattern for a typical synoptic flash flood event. Potential for heavy rains and flash flooding exists in the boxes. (b) The corresponding 850-hPa flow pattern for a typical synoptic type flash flood event. Winds are in knots with full barb = 10 kt and flag = 50 kt. (c) The corresponding 500-hPa flow pattern for a typical synoptic type flash flood event ...... 28
FIG. 1.2 (a) Surface pattern for a typical frontal event with details as in Fig. 1.1. (b) Corresponding 850-hPa pattern for a typical frontal event. (c) Corresponding 500-hPa pattern for a typical frontal event ...... 29
FIG. 1.3 (a) Surface pattern for a typical mesohigh event with details as in Fig. 1.1. (b) Corresponding 850-hPa pattern for a typical mesohigh event. (c) Corresponding 500-hPa pattern for a typical mesohigh event...... 31
FIG. 1.4 Schematic illustration of the time variation of water vapor input (cross hatched area) and the precipitation output (vertical bars) over the lifetime of a precipitation system. The units are arbitrary, so the system being portrayed can be any precipitation process with a developing phase (time = 0-3 units), a mature phase (time = 3-6 units), and a dissipating phase (time = 6-10 units). For this example, the areas under the respective curves give a precipitation efficiency of about 44%...... 33
FIG. 1.5 Schematic showing how different types of convective systems with different motions affect the rainfall rate (R) at a point (indicated by) a circled dot) as a function of time; contours and shading indicate radar reflectivity. For case (a) a convective line is passing the point with a motion nearly normal to the line; for case (b) the line is moving past the point with a large component tangent to the line itself;
xii for case (c) the line has a trailing region of moderate precipitation but is otherwise similar to (b), and for case (d) the motion of the line has only a small component normal to the line but is otherwise similar to (c). Total rainfall experienced at the point is the shaded area under the R vs. time graphs ...... 34
FIG. 1.6 Soil-texture triangle, showing the textural terms applied to soils with various fractions of sand, silt, and clay ...... 35
FIG. 1.7 Ranges of porosity, field capacities, and permanent wilting points for soils of various textures ...... 36
FIG. 1.8 Hydraulic conductivity, Kh, vs. degree of saturation, S, for soils of three different textures. Note that the vertical axis gives the base-10 logarithm of the hydraulic conductivity, expressed in cm s-1 ...... 37
FIG. 2.1 Gridded 1-hour FFG from the SERFC for the Raleigh CWA. The “holes” in the product are from problems in the software used to create the FFG (T. Wallace 2004, personal Communication). Note that in operations, the AWIPS display default background color is black and has been inverted in all figures to white .....48
FIG. 2.2 Basin-averaged FFG from the SERFC for the Raleigh CWA. Otherwise, details as in Fig. 2.1 ...49
FIG. 2.3 Representation of basins within the AMBER algorithm. Basins are defined by 1 degree by 1 km radar data points ...... 50
FIG. 2.4 Interface to monitor AMBER alerts. Top section changes color, green, yellow, or red, to indicate highest Alert Status detected from all basins ...... 50
FIG. 2.5 Sample 4 p-panel AMBER BRA and ABR display on D2D with AMBER basins as a map overlay ...... 51
FIG. 2.6 Sample AMBER ArcView GIS display. The AMBER display consists of an Area of Responsibility
xiii view and one or more detailed basin views. Selecting a basin in the detailed view will bring up a graph as shown in Fig. 2.7 ...... 52
FIG. 2.7 Sample graph of ABR (line with solid circles), FFG (heavy line) and BRA (blue line) for a 6 hour period with ABR and BRA in inches and BRA in in/hr. Plotted numbers ABR for the six Alert Time Periods. Area under the ABR curve is Shaded green, yellow, and red in the actual display based on the Alert Status to indicate Alert Status category ...... 53
FIG. 2.8 Flash Flood Monitoring and Prediction. Counties are sorted in the FFMP Threat Table by whichever column the user has highlighted, in this case the ratio of precipitation to FFG; Montgomery County’s 0.75-hr precipitation is 103% that of its FFG. Clicking with the left mouse button on the county name in the Area_Id column will zoom in, as in Fig. 2.9. The screen displays, in this case, precipitation accumulation ...... 54
FIG. 2.9 Flash Flood Monitoring and Prediction, zoomed into Montgomery County. This allows the forecaster to see where the heaviest rainfall is occurring and which basins are being impacted. Clicking with the right-most mouse button on the Area_Id number will bring up a basin graph as in Fig. 2.10 ...... 55
FIG. 2.10 Graph of ABR(dotted line), BRA (blue line), and FFG (purple line) for Nichols Run basin in Montgomery County. Note the similarity to the AMBER graph in Fig. 2.7...... 56
FIG. 2.11 The Forced FFG GUI available in AWIPS. The user has the option of providing FFG values across the entire CWA, for a specific county, or for a specific basin within a county. In this example, in order to provide a 1 Hr FFG value of 1.0 in (25.4 mm) for Wake County, the user would need to simply click on “NC,WAKE” with the right mouse button, and subsequently click “apply all” with the left mouse button on the lower right hand side of the GUI...... 57
xiv FIG. 3.1 USGS stream gages (as listed in Table 3.1) within the Raleigh CWA in operation at the time of this research. Major river basins, from west to east, are: Yadkin/Pee Dee, Lumber, Cape Fear, Neuse, Tar, and Lower Roanoke ...... 74
FIG. 3.2 STATSGO dissolved soil textures for central North Carolina. Counties within the Raleigh CWA are outlined. Data obtained from the National Cartography and GIS Center (1991)...... 75
FIG. 4.1 NWS Raleigh hand-performed surface analysis valid 0900 UTC 26 August 2002 ...... 96
FIG. 4.2 KRAX WSR-88D estimated precipitation for the 24-hour period between 1200 UTC 26 August and 1200 UTC 27 August 2002. As in the AWIPS images from section 2, the default background color has been inverted from black to white ...... 97
FIG. 4.3 Same as Fig. 4.1, except valid 1500 UTC 11 October 2002 ...... 98
FIG. 4.4 KRAX WSR-88D estimated precipitation for the 18-hour period between 2300 UTC 10 October and 1700 UTC 11 October 2002. ASOS 24-hour rainfall reports are plotted on the image as well ...... 99
FIG. 4.5 Hydrometeorological Prediction Center surface Analysis valid 0900 UTC 9 April 2003 ...... 100
FIG. 4.6 KRAX WSR-88D estimated precipitation for the 24-hour period between 1200 UTC 09 April and 1200 UTC 10 April 2003. ASOS 24-hour rainfall reports are plotted on the image as well ...... 101
FIG. 4.7 Same as Fig. 4.6, but for 10-11 April 2003 ...... 102
FIG. 4.8 Same as Fig. 4.5, except valid 0600 UTC 16 June 2003 ...... 103
FIG. 4.9 Same as Fig. 4.6, but for 16-17 June 2003 ...... 104
FIG. 4.10 Same as Fig. 4.5, except valid 2100 UTC 29 July 2003 ...... 105
FIG. 4.11 Same as Fig. 4.6, but for 29-30 July 2003 ...... 106
xv
FIG. 4.12 Same as Fig. 4.5, except valid 0900 UTC 9 August 2003 ...... 107
FIG. 4.13 Same as Fig. 4.6, but for 09-10 August 2003 ...... 108
FIG. 5.1 Number of USGS sites for each case that experienced various conditions. Shown are the sites that rose above flood stage (including both floods and flash floods), those that qualified as flash floods, those that experienced a rapid rise but did not rise above flood stage, and those that experienced a rapid rise but did not have a pre-determined flood stage ...... 124
FIG. 5.2 Precipitation and stream response for the USGS site at Crabtree Creek at Ebenezer Church Road in Raleigh during the 11 October 2002 event. Flood stage is 19 ft for this location. Graphically, the methodology to determine stream rise time (SRT) (the amount of time between when the stream began its rise and when the maximum stage was reached), the lag time (the amount of time between onset of precipitation and the initial response of the stream), the maximum stage, the change in height (∆H) of the stream, and the rate of change of stream rise (∆H/∆t) is displayed ...... 125
FIG. 5.3 Correlations between rain rate and precipitation accumulation to stream rise time (SRT) (hr), lag time (hr), maximum stream stage (ft), change in stream stage (∆H) (ft), and rate of change of stream stage (∆H/∆t) (ft hr-1)...... 126
FIG. A.1 a) Haw River at Haw River on 11 October 2002. Flood stage is 18 ft. b) Same as in a, except for 16 June 2003. c) Same as in a, except for 9 August 2003 ...... 138
FIG. A.2 a) Buckhorn Creek near Corinth on 26 August 2002. No pre-determined flood stage. b) Same as in a, except for 11 October 2002. c) Same as in a, except for 9-10 April 2003. d) Same as in a, except for 16 June 2003. e) Same as in a,
xvi except for 29 July 2003. f) Same as in a, except for 9 August 2003 ...... 139
FIG. A.3 a) Tick Creek near Mount Vernon Springs on 11 October 2002. No pre-determined flood stage. b) Same as in a, except for 9-10 April 2003. c) Same as in a, except for 16 June 2003. d) Same as in a, except for 29 July 2003 ...... 142
FIG. A.4 a) Abbotts Creek at Lexington on 11 October 2002. Flood stage is 17 ft. b) Same as in a, except for 16 June 2003. c) Same as in a, except for 29 July 2002 ...... 144
FIG. A.5 a) Mountain Creek at SR1617 near Bahama on 26 August 2002. No pre-determined flood stage. b) Same as in a, except for 11 October 2002. c) Same as in a, except for 9-10 April 2003. d) Same as in a, except for 16 June 2003 ...... 146
FIG. A.6 a) Flat River at Bahama on 26 August 2002. Flood stage is 12 ft. b) Same as in a, except for 11 October 2002. c) Same as in a, except for 9-10 April 2003. d) Same as in a, except for 9 August 2003 ...... 148
FIG. A.7 a) Eno River near Durham on 26 August 2002. Flood stage is 20 ft. b) same as in am except for 11 October 2002. c) Same as in a, except for 9-10 April 2003. d) Same as in a, except for 16 June 2003. e) Same as in a, except for 9 August 2003 ...... 150
FIG. A.8 a) Little River at SR1461 near Orange Factory on 26 August 2002. No pre-determined flood stage. b) Same as in a, except for 11 October 2002. c) Same as in a, except for 9-10 April 2003. d) Same as in a, except for 9 August 2003 ...... 152
FIG. A.9 a) Tar River at NC97 at Rocky Mount on 26 August 2002. Flood Stage is 18 ft. b) Same as in a, except for 11 October 2002. c) Same as in a, except for 29 July 2003 ...... 154
FIG. A.10 a) East Fork Deep River near High Point on 11 October 2002. No pre-determined flood stage.
xvii b) Same as in a, except for 9-10 April 2003. c) Same as in a, except for 16 June 2003. d) Same as in a, except for 29 July 2003. e) Same as in a, except for 9 August 2003 ...... 156
FIG. A.11 a) Horsepen Creek at US220 near Greensboro on 11 October 2002. Flood stage is 11 ft. b) Same as in a, except for 9-10 April 2003. c) Same as in a, except for 16 June 2003. d) Same as in a, except for 29 July 2003. e) Same as in a, except for 9 August 2003 ...... 158
FIG. A.12 a) North Buffalo Creek at Westover Terrace at Greensboro on 11 October 2002. Flood stage is 10 ft. b) Same as in a, except for 9-10 April 2003. c) Same as in a, except for 16 June 2003. d) Same as in a, except for 29 July 2003. e) Same as in a, except for 9 August 2003 ...... 161
FIG. A.13 a) North Buffalo Creek at Church Street at Greensboro on 26 August 2002. Flood stage is 14 ft. b) Same as in a, except for 11 October 2002. c) Same as in a, except for 9-10 April 2003. d) Same as in a, except for 16 June 2003. e) Same as in a, except for 29 July 2003. f) Same as in a, except for 9 August 2003 ...... 163
FIG. A.14 a) North Buffalo Creek near Greensboro on 11 October 2002. Flood stage is 13 ft. b) Same as in a, except for 9-10 April 2003. c) Same as in a, except for 16 June 2003. d) Same as in a, except for 29 July 2003. e) Same as in a, except for 9 August 2003 ...... 166
FIG. A.15 a) Ryan Creek below US220 at Greensboro on 11 October 2002. Flood stage is 10 ft. b) Same as in a, except for 9-10 April 2003. c) Same as in a, except for 16 June 2003. d) Same as in a, except for 29 July 2003. e) Same as in a, except for 9 August 2003 ...... 169
FIG. A.16 a) South Buffalo Creek near Greensboro on 11 October 2002. Flood stage is 10 ft. b) Same as in a, except for 9-10 April 2003. c) Same as in a, except for 16 June 2003. d) Same as
xviii in a, except for 29 July 2003. e) Same as in a, except for 9 August 2003 ...... 171
FIG. A.17 a) South Buffalo Creek at US220 near Greensboro on 11 October 2002. Flood stage is 14 ft. b) Same as in a, except for 9-10 April 2003. c) Same as in a, except for 16 June 2003. d) Same as in a, except for 29 July 2003. e) Same as in a, except for 9 August 2003 ...... 174
FIG. A.18 a) Brush Creek at Fleming Road at Greensboro on 11 October 2002. Flood stage is 9 ft. b) Same as in a, except for 9-10 April 2003. c) Same as in a, except for 16 June 2003. d) Same as in a, except for 29 July 2003. e) Same as in a, except for 9 August 2003 ...... 176
FIG. A.19 a) Buffalo Creek at SR2819 near McLeansville on 11 October 2002. Flood stage is 17 ft. b) Same as in a, except for 29 July 2003. c) Same as in a, except for 9 August 2003 ...... 179
FIG. A.20 a) Reedy Fork near Oak Ridge on 11 October 2002. Flood stage is 10 ft. b) Same as in a, except for 9-10 April 2003. c) Same as in a, except for 16 June 2003. d) Same as in a, except for 29 July 2003. e) Same as in a, except for 9 August 2003 ...... 180
FIG. A.21 a) South Buffalo Creek near Pomona on 11 October 2002. Flood stage is 10 ft. b) Same as in a, except for 9-10 April 2003. c) Same as in a, except for 16 June 2003. d) Same as in a, except for 29 July 2003. e) Same as in a, except for 9 August 2003 ...... 183
FIG. A.22 a) Flat Creek near Inverness on 9-10 April 2003. Flood stage is 7 ft. b) Same as in a, except for 16 June 2003. c) Same as in a, except for 29 July 2003 ...... 185
FIG. A.23 a) Little River near Star on 9-10 April 2003. Flood stage is 11 ft. b) Same as in a, except for 29 July 2003. c) Same as in a, except for 9 August 2003 ...... 187
FIG. A.24 a) Dutchmans Creek near Uwharrie on 11 October
xix 2002. No pre-determined flood stage. b) Same as in a, except for 9-10 April 2003. c) Same as in a, except for 16 June 2003. d) Same as in a, except for 29 July 2003. e) Same as in a, except for 9 August 2003 ...... 188
FIG. A.25 a) Morgan Creek near Chapel Hill on 11 October 2002. No pre-determined flood stage. b) Same as in a, except for 9-10 April 2003. c) Same as in a, except for 16 June 2003. d) Same as in a, except for 9 August 2003 ...... 191
FIG. A.26 a) Cane Creek near Orange Grove on 11 October 2002. No pre-determined flood stage. b) Same as in a, except for 9-10 April 2003. c) Same as in a, except for 16 June 2003 ...... 193
FIG. A.27 a) Morgan Creek near White Cross on 11 October 2002. No pre-determined flood stage. b) Same as in a, except for 9-10 April 2003. c) Same as in a, except for 16 June 2003 ...... 194
FIG. A.28 a) Eno River near Hillsborough on 26 August 2002. Flood stage is 16 ft. b) Same as in a, except for 11 October 2002. c) Same as in a, except for 9-10 April 2003. d) Same as in a, except for 16 June 2003. e) Same as in a, except for 29 July 2003. f) Same as in a, except for 9 August 2003 ...... 196
FIG. A.29 a) Mayo Creek near Bethel Hill on 9-10 April 2003. Flood stage is 8 ft. b) Same as in a, except for 16 June 2003. c) Same as in a, except for 9 August 2003 ...... 199
FIG. A.30 a) Deep River at Ramseur on 11 October 2002. Flood stage is 20 ft. b) Same as in a, except for 9-10 April 2003. c) Same as in a, except for 29 July 2003. d) Same as in a, except for 9 August 2003 ...... 200
FIG. A.31 a) Deep River near Randleman on 11 October 2002. Flood stage is 24 ft. b) Same as in a, except for 9-10 April 2003. c) Same as in a, except for 29 July 2003. d) Same as in a, except for 9 August 2003 ...... 202
xx FIG. A.32 a) Big Bear Creek near Richfield on 26 August 2002. No pre-determined flood stage. b) Same as in a, except for 11 October 2002. c) Same as in a, except for 9-10 April 2003. d) Same as in a, except for 16 June 2003. e) Same as in a, except for 29 July 2003 ...... 204
FIG. A.33 a) Crabtree Creek at Ebenezer Church Road near Raleigh on 26 August 2002. Flood stage is 19 ft. b) Same as in a, except for 11 October 2002. c) Same as in a, except for 9-10 April 2003. d) Same as in a, except for 16 June 2003. e) Same as in a, except for 29 July 2003 ...... 207
FIG. A.34 a) Swift Creek near McCullars Crossroads on 11 October 2002. Flood stage is 12 ft. b) Same as in a, except for 9-10 April 2003. c) Same as in a, except for 16 June 2003. d) Same as in a, except for 29 July 2003. e) Same as in a, except for 9 August 2003 ...... 209
FIG. A.35 a) Marsh Creek near New Hope on 26 August 2002. No pre-determined flood stage. b) Same as in a, except for 11 October 2002. c) Same as in a, except for 9-10 April 2003. d) Same as in a, except for 16 June 2003. e) Same as in a, except for 29 July 2003 ...... 212
FIG. A.36 a) Crabtree Creek at US 1 at Raleigh on 26 August 2002. Flood stage is 18 ft. b) Same as in a, except for 11 October 2002. c) Same as in a, except for 9-10 April 2003. d) Same as in a, except for 16 June 2003. e) Same as in a, except for 29 July 2003. f) Same as in a, except for 9 August 2003 ...... 214
FIG. A.37 a) Pigeon House Creek at Cameron Village at Raleigh on 26 August 2002. No pre-determined flood stage. b) Same as in a, except for 11 October 2002. c) Same as in a, except for 9-10 April 2003. d) Same as in a, except for 16 June 2003. e) Same as in a, except for 29 July 2003. f) Same as in a, except for 9 August 2003 ...... 217
FIG. A.38 a) Rocky Branch below Pullen Drive at Raleigh
xxi on 26 August 2002. No pre-determined flood stage. b) Same as in a, except for 11 October 2002. c) Same as in a, except for 9-10 April 2003. d) Same as in a, except for 16 June 2003. e) Same as in a, except for 29 July 2003. f) Same as in a, except for 9 August 2003 ...... 220
FIG. A.39 a) Walnut Creek at Sunnybrook Drive near Raleigh on 26 August 2002. No pre-determined flood stage. b) Same as in a, except for 11 October 2002. c) Same as in a, except for 9-10 April 2003. d) Same as in a, except for 16 June 2003. e) Same as in a, except for 29 July 2003. f) Same as in a, except for 9 August 2003 ...... 223
FIG. A.40 a) Crabtree Creek at Hwy. 70 at Raleigh on 26 August 2002. Flood stage is 18 ft. b) Same as in a, except for 11 October 2002. c) Same as in a, except for 9-10 April 2003. d) Same as in a, except for 16 June 2003. e) Same as in a, except for 29 July 2003. f) Same as in a, except for 9 August 2003 ...... 226
FIG. A.41 a) Unnamed Tributary to Swift Creek near Yates Mill Pond on 11 October 2002. No pre- determined flood stage. b) Same as in a, except for 9-10 April 2003. c) Same as in a, except for 16 June 2003. d) Same as in a, except for 29 July 2003. e) Same as in a, except for 9 August 2003 ...... 229
FIG. A.42 a) Crabtree Creek at Anderson Drive at Raleigh on 26 August 2002. Flood stage is 18 ft. b) Same as in a, except for 11 October 2002. c) Same as in a, except for 9-10 April 2003. d) Same as in a, except for 16 June 2003. e) Same as in a, except for 29 July 2003. f) Same as in a, except for 9 August 2003...... 231
FIG. A.43 a) Crabtree Creek at Old Wake Forest Road at Raleigh on 26 August 2002. Flood stage is 13 ft. b) Same as in a, except for 11 October 2002. c) Same as in a, except for 9-10 April 2003. d) Same as in a, except for 16 June 2003. e) Same as in a, except for 29 July
xxii 2003. f) Same as in a, except for 9 August 2003 ...... 234
FIG. A.44 a) Swift Creek near Apex on 11 October 2002. No pre-determined flood stage. b) Same as in a, except for 9-10 April 2003. c) Same as in a, except for 16 June 2003. d) Same as in a, except for 29 July 2003. e) Same as in a, except for 9 August 2003 ...... 237
FIG. A.45 a) Nahunta Swamp near Pikeville on 26 August 2002. No pre-determined flood stage. b) Same as in a, except for 11 October 2002. c) Same as in a, except for 9-10 April 2003. d) Same as in a, except for 29 July 2003. e) Same as in a, except for 9 August 2003 ...... 240
FIG. A.46 a) Contentnea Creek near Lucama on 11 October 2002. Flood stage is 11 ft. b) Same as in a, except for 29 July 2003. c) Same as in a, except for 9 August 2003 ...... 242
xxiii LIST OF ABBREVIATIONS
Abbreviation Description ABR Average Basin Rainfall ADAPS Automated Data Processing System A-E Auto-Estimator AFD Area Forecast Discussion AMBER Areal Mean Basin Estimated Rainfall AMBERGIS AMBER for Geographic Information System ASOS Automated Surface Observing System AWIPS Advanced Weather Interactive Processing System BRA Basin Rate of Accumulation COMET Cooperative Program for Operational Meteorology, Education, and Training CPC Climate Prediction Center CWA County Warning Area DHR Digital Hybrid Reflectivity FB Forecast Branch (of the NMC) FFA Flood Watch FFG Flash Flood Guidance FFMP Flash Flood Monitoring and Prediction FFW Flash Flood Warning FLS Flood Statement FS Flood Stage H-E Hydro-Estimator HPC Hydrometeorological Prediction Center IFFA Interactive Flash Flood Analyzer LFC Level of Free Convection LSR Local Storm Report NBD National Basin Delineation NCCGIA North Carolina Center for Geographic Information Analysis NCDC National Climatic Data Center NCEP National Centers for Environmental Prediction NESDIS National Environmental Satellite, Data, and Information Service NMC National Meteorological Center NOAA National Oceanic and Atmospheric Administration NRCS National Resource Conservation Service NSSL National Severe Storms Laboratory NWS National Weather Service NWSRFS NWS River Forecast System OB Operational Build OHP One Hour Precipitation ORPG Open Radar Product Generation PDF Precipitation Detection Function PPS Precipitation Processing System
xxiv PW Precipitable Water RFC River Forecast Center SAB Satellite Analysis Branch SCO State Climate Office (of North Carolina) SERFC Southeast River Forecast Center SPENES Satellite Precipitation Estimates from NESDIS SRT Stream Rise Time STATSGO State Soil Geographic STP Storm Total Precipitation THP Three Hour Precipitation USGS United States Geological Survey WFO Weather Forecast Office WSR-88D Weather Surveillance Radar-1988 Doppler
xxv 1. INTRODUCTION
1.1 Motivation
North Carolina is home to a plethora of weather phenomena. Its location relative to the
Atlantic Ocean and the Gulf Stream makes it vulnerable to tropical and coastal cyclones.
The Appalachian Mountains along the western border complicate forecasting by adding the
possibility of cold-air damming year round. Far enough north for significant winter weather,
but yet still susceptible to tornado outbreaks, the forecast process can be quite complicated.
However, much like the United States as a whole, flooding, and especially flash flooding, is a
major concern. Indeed, little in the way of local research has been conducted on the topic, and as a result forecasters at the National Weather Service (NWS) in Raleigh, NC, have identified flash flooding as one of its most significant forecast difficulties.
The NWS in Raleigh, which is responsible forecasts and warnings for 31 counties in central North Carolina, has several resources and tools available for use in the monitoring and prediction of flash floods, many of which have improved upon the forecasting and warning of flash floods. The basic requirements of any forecaster includes the need to know, in real-time, where it is raining, how much rain is falling and at what rate, and what basins are being/have been impacted. This can be done with current technology (section 2 will provide more detail on these operational tools). However, it is important for the forecaster to understand what meteorological and hydrological parameters are included or excluded in the current technology, and what parameters not included are equally important in understanding the behavior of a flash flood.
1 The purpose, then, of this research was to determine which of those meteorological and
hydrological parameters (e.g., rainfall rate, soil moisture), or what combination of
parameters, is most significant in the evolution of a flash flood. An observational analysis
was conducted to determine the correlation between precipitation (including precipitation
rate) and small stream response for various soil types, general terrain variations,
vegetation/landuse categories, and antecedent soil moisture conditions.
To carry out this analysis, six events in which flash flooding occurred within the Raleigh
County Warning Area (CWA) were chosen (see section 4) during the period of August 2002-
August 2003. The events were selected such that soil moisture conditions varied greatly. In
August 2002, central North Carolina was in a severe to exceptional drought. According to a
NOAA Press Release from 14 August 2002, the 12-month period from August 2001-July
2002 was the driest on record for the state (NOAA News Online 2004a). A year later, the 14
August 2003 NOAA Press Release reported that many eastern states had recorded the wettest or second wettest preceding three months (NOAA News Online 2004b). By that same date, the Piedmont-Triad International Airport in Greensboro, NC, was well on its way to setting the annual precipitation record; 46.51 in (1181.4 mm) had fallen. By the end of the year,
Greensboro recorded 62.32 in (1582.9 mm), breaking the previous record of 56.51 in (set in
1975).
Results obtained from this study will be provided to the forecasters at the NWS office in
Raleigh for use in operations. The objective is that these results will improve flash flood operations, specifically the timeliness and accuracy of warnings associated with small stream flash flooding.
2 1.2 Flash floods
A flash flood is defined as a flood which occurs within six hours or less of the causative
event (Helble 2002). The water must rise rapidly to a pre-determined flood stage and must
pose a threat to life and property. Local criteria can be applied to this definition, which will
be elaborated upon in Section 1.2.4.
During the 30 years from 1974-2003, an average of 107 lives have been lost to floods
(both flash floods and river floods) every year in the United States. While the 10-year
average over the past decade ending with 2003 has decreased with an average of 84 fatalities
a year, floods have still claimed more lives than lightning, tornadoes, hurricanes, extreme
cold, and winter storms; only extreme heat has resulted in more fatalities per year (NWS
Office of Meteorology 2004). In North Carolina, between the years 1995 and 2003, flash
flooding alone claimed an average of five lives a year (the eight-year total was 39 deaths; 24
of those occurred in 1999).
1.3 Forecasts and warnings
1.3.1 Parameters and features associated with flash floods
Konrad (1997), Funk (1991), and LaPenta (1994) all discussed mesoscale and synoptic
scale parameters, values, and characteristics that have been tied to flash flood events. Those discussed by Konrad (1997) are included in Table 1.1. Some of the others are listed below.
• Pre-existence of convective storms;
• High surface dewpoint temperatures (see below);
3 • Large moisture contents (near-saturation) throughout a deep layer (greater than 300
hPa) in the atmosphere;
• Weak to moderate vertical wind shear throughout the cloud depth.
Other elements that are useful for a forecaster or operational meteorologist to inspect in
the event of a flash flood forecasting situation are:
• Light environmental winds;
• High ambient and/or inflow moisture, with;
• K-index values above 30 and precipitable water (PW) values above one inch, and;
• Surface dewpoints exceeding 170C and 850 hPa dewpoints approaching or exceeding
120C in warm seasons;
• Dynamic uplift forced by upper-tropospheric jet streaks;
• Middle-tropospheric shortwave immediately upstream of the heavy rain area;
• Presence of moisture ridges at 850 hPa and other levels in the atmosphere;
• Low-level (surface and 850 hPa) inflow and convergence;
1 • θe ridge axis at 850 hPa;
• Diffluent 1000-500 hPa thickness isopleths.
Built upon these atmospheric variables and years of experience interpreting them, the former National Meteorological Center (NMC), now the National Centers for Environmental
Prediction (NCEP), developed several “Rules of Thumb” to assist forecasters in determining flood potential (Funk 1991). Those that apply to the region in this study are listed:
• “500 hPa vorticity minimum ridge axes often mark the location of heavy convection
and maximum rainfall.
1 Holton (1992) defines the equivalent potential temperature, θe, as the potential temperature a parcel of air would have if all its moisture were condensed and the resulting latent heat used to warm the parcel.
4 • Strong convection can occur behind a weak shortwave when moist, unstable inflow
continues to be directed toward a low level boundary.
• When a well-defined connection of mid- and high-level tropical moisture is observed in
water vapor imagery, the potential exists for heavier rainfall amounts than would
normally be expected given the synoptic situation.
• Models are subject to “convective feedback,” whereby they develop deep convection
and generate high values of vorticity through strong vertical velocities and latent heat
release.”
Funk (1991) describes several other rules of thumb, but they pertain to the Plains and western
Gulf of Mexico and not to the area of interest in this research.
In addition to atmospheric variables, one must remember topography and geography.
Upslope flow frequently helps to produce or enhance heavy rainfall due to forced ascent of
air. Differential heating due to changes in terrain or land use can induce vertical motions.
Small river and stream basins with highly variable topography are conducive to large runoff
over short periods of time. Troughing in the lee of the Appalachians or Rockies can be a
forcing mechanism, and sea/lake breeze fronts can generate uplift as well. Along the Atlantic
coast, winds along the sea breeze fronts advecting moisture from the ocean combined with
the immediate variability in topography and resulting uplift of the moist air can also serve to cause convection.
Konrad (1994) diagnosed moisture trajectories in the Appalachian region associated with heavy rainfall. As might be expected, but confirmed through the scientific process, southeasterly to southerly trajectories of moisture are most commonly associated with heavy rainfall along the eastern slopes of the Appalachians and adjacent Piedmont areas.
5 Geography is an important factor in this finding, as moisture from the Atlantic Ocean easily condenses when orographically uplifted.
Because of all of these parameters and characteristics, it is extremely important for the operational meteorologist to accurately assess the atmosphere. According to Maddox (1979), on synoptic maps, forecasters should locate low-level jets, moisture and temperature ridges, areas of significant instability, regions of high moisture content and weak vertical wind shear, and middle-level shortwave troughs. On the surface map, forecasters should accurately locate fronts, drylines, pressure systems, and squall lines, and they should monitor the movement of these features. Further, forecasters should watch for thunderstorm outflow boundaries, mesoscale pressure systems, and moist regions that might develop.
The atmosphere is only one part of the flash flood process. Hydrology plays a fundamental role as well. Factors such as soil moisture, antecedent precipitation, surface runoff characteristics, basin size, and even soil type can all have a significant impact upon the land’s response to a flooding scenario.
1.3.2 Classifications and pattern recognition
A much-used practice in operational forecasting is that of pattern recognition. While many argue against it, including notable researchers (e.g., Doswell et al. 1996), operational meteorologists profess repeatedly the value of pattern recognition. Elsner et al. (1989) stated that “the operational value of pattern recognition…is that it provides forecasters a means for an initial assessment of the potential for a given weather problem such as heavy rainfall.”
Funk (1991) stressed that “pattern recognition is extremely important and is the foundation for forecasting heavy precipitation in the FB [Forecast Branch of the NMC].” He went on to
6 say that the skills of pattern recognition regarding heavy rainfall are built upon 1) a thorough knowledge and understanding of climatology, and 2) conscious recall of previous events. In many Weather Forecast Offices (WFOs) across the country, including Raleigh, seasonal training includes reminding forecasters of recurring patterns and the physical processes that support them. This combination of pattern recognition and the physical processes supporting them provides conceptual models essential for the forecast process. A certain pattern might be indicative of a major tornado outbreak, while another might bespeak quiescent weather.
Opitz et al. (1994) outlined procedures, techniques, computer software and new technology that could be used in identifying flood scenarios, many of which focused on pattern recognition.
Maddox et al. (1979) identified four synoptic classifications for flash flood events: synoptic, frontal, mesohigh, and western. Since the focus of this research includes only portions of North Carolina, the western classification will not be elaborated upon. Maddox
(1979) provided further details about these four classifications and described forecast procedures and parameters of which forecasters should be aware. According to Funk (1991), the NMC uses these classifications in their forecasts.
LaPenta et al. (1994) discussed synoptic classifications relevant to the NWS’s Eastern
Region, which extends from Maine to South Carolina. While this study is obviously more current, it seems less thorough than Maddox et al. (1979), as the classifications consist of: S, surface front; E, extratropical cyclone; T, tropical cyclone; C, combined tropical and extratropical; and U, for unknown. While some of the characteristics outlined in LaPenta et al. (1994) are similar to those of Maddox et al. (1979), they were not as detailed. The three relevant classifications from Maddox et al. (1979) are discussed below.
7 Synoptic events (Fig. 1.1) are generally associated with large-scale weather systems and
strong tropospheric wind fields. A large trough at 500 hPa lies west of the threat center and is usually moving slowly to the east or northeast while the storms usually develop and remain on the warm side of a quasistationary front, in the moist sector. As is the case in many flood situations, the storms typically repeatedly develop or “train” over the same area. During a typical synoptic event, small disturbances often move along the front, helping to force low- level convergence and trigger initiation of heavy rain. Due to the fact that the synoptic events are usually associated with a relatively intense synoptic scale cyclone or frontal system, these events are the easiest, comparatively, for operational meteorologists to identify.
Unlike the synoptic events, frontal events (Fig. 1.2) typically develop on the cool side of the surface front as warm unstable air “overruns” the cooler air on the opposite side of the east-west oriented frontal zone. These fronts are usually quasistationary, and are typically embedded within a quiescent large-scale pattern. Maddox et al. (1979) and Maddox (1979) both state that typically, a meso-α scale shortwave (on the order of 1000 km) is associated.
With such a situation, calculated indices, such as the Total-totals (TT) index
TT = T 850mb + T 850mb − 2(T 500mb ) d [1.1]
or the K index (KI)
850mb 500mb 850mb 700mb 700mb KI = (T − T ) + Td − (T − Td ) [1.2]
are useful. The Total-totals index measures severe weather intensities; for example a value
of 44 would imply isolated to widely scattered non-severe thunderstorms, while a value of 56
would imply numerous thunderstorms with scattered severe storms and perhaps scattered
tornadoes. The K index measures thunderstorm potential based on the lapse rate and
moisture at 850 and 700-hPa; values less than 20 indicate little to no coverage of storms,
8 while values greater than 35 indicate numerous storms. Typically, frontal events are nocturnal in character.
Mesohigh events (Fig. 1.3) can be in close proximity to a frontal system of some sort, but are associated with cool outflow boundaries, which are artifacts of prior convective activity.
Typically these outflow boundaries move very slowly while the winds aloft parallel the boundary, and thus the heavy rainfall is quasistationary as convection trains over the same area. As with frontal events, a meso-α scale shortwave is usually associated. Since thunderstorms that would normally leave such outflow boundaries characteristically develop in the afternoon, mesohigh flooding events are also noticeably nocturnal, and forecasters and operational meteorologists should be aware of the possibility through the afternoon and evening hours if thunderstorms have occurred and plentiful moisture is available.
1.3.3 Ingredients for heavy rainfall
Doswell (1994) and Doswell et al. (1996) admit that pattern recognition, rules of thumb, and other personal forecasting preferences might have their own “virtues and vices,” but they believe that “an ingredients-based methodology is a logical choice for the application of scientific understanding to the forecasting task.” They first outlined the ingredients for flash floods, then the meteorological processes linking those ingredients together, understanding that basically, “the heaviest precipitation occurs where the rainfall rate is the highest for the longest time.”
The total precipitation produced by a storm can be described by a simple formula:
P = RD , [1.3]
9 where P is the total precipitation, R is the average rainfall rate, and D is the duration of the rainfall. Rainfall rates are also extremely important in deducing the possibility of flash flooding. R, the instantaneous rainfall rate, is proportional to the magnitude of the vertical moisture flux, wq, where q is the mixing ratio of air rising with vertical velocity w. The precipitation efficiency E (Fig. 1.4) is the coefficient of proportionality that relates the rainfall rate to the moisture flux:
R = Ewq [1.4]
(Doswell et al. 1996).
Another ingredient significant for flash floods is deep, moist convection. According to
Doswell et al. (1996), in order to produce the needed buoyancy and deep convection, 1) the environmental lapse rate must be conditionally unstable, 2) sufficient moisture must be available such that a rising parcel has a level of free convection (LFC) when lifted along a moist adiabat, and 3) there must be a lifting mechanism such that the parcel may reach its
LFC. Determining if these three criteria are met would be the purpose of a meteorological analysis.
As mentioned previously, the duration of the event is an important factor, which in turn itself is related to the character of the storm. The duration of the heavy precipitation in any given location is related to 1) the system movement speed, 2) system size, and 3) within- system variations in rainfall intensity (Fig. 1.5). Long duration is associated with systems that move slowly, have a large area of high rainfall rates along their direction of movement, or both of these.
The types of storms that typically produce these flash floods were classified in Doswell et al. (1996) as follows: multicell and supercell convection; squall lines; mesoscale convective
10 systems (MCSs); and nonconvective precipitation systems. However, another operational difficulty is brought to light; forecasting the type of system that will produce a flash flood.
Each of these classifications of flash flood-producing systems has further complicating characteristics, and difficulties that can compound quickly.
1.3.4 Warnings
In the realm of warnings, a Flash Flood Warning (FFW) is issued in the Raleigh CWA as outlined in the Raleigh NWS Hydrology Station Duty Manual, and is based on the following forecast/impact criteria (as long as the flooding meets the definition of a flash flood):
• “Immediate action to protect lives and property, includes urban and small stream
locations;
• Urban areas;
• Convective rainfall;
• Tropical rainfall;
• Dam or levee failure;
• Forecast of flash flooding based on Flash Flood Guidance (FFG) exceedance.”
A local time criterion is that the flooding occurs typically within six hours after the bulk of the heavy rain has fallen. Flash flooding in the Raleigh CWA is characteristically thought of as a “wall of water” that affects areas with somewhat variable terrain. Urban flooding is only considered a flash flood if it poses a threat to life and property and meets the above time criterion. In addition, if the meteorologist expects that the rainfall will meet or exceed FFG within the next three to six hours, a FFW should be issued. In contrast, a FFW is far different
11 from an Urban and Small Stream Flood Advisory, issued as a Flood Statement (FLS), where the forecast/impact criteria include:
• “Nuisance flooding of streams and ponding of water on roads in urban areas,
warranting public notification, but NOT a warning;
• Minor impacts are forecast or occurring.”
The local time criterion for the Urban/Small Stream Flood Advisories is that minor flooding is forecast or imminent within six hours or less of the causative event. These may be upgraded to a FFW if:
• “Moderate or major flooding is developing; or
• Flooding becomes a threat to life.”
A forecaster may also issue an area or county-based flood warning (FLW), for flooding which is long in duration, and slow to rise from generally stratiform rain. The forecast/impact criteria for this type of FLW (note that this is not a river-based FLW) include:
• “Widespread flooding forecast/imminent for streams or counties. Relatively slow to
rise.
• Moderate or greater impacts forecast or imminent.”
These floods generally occur more than six hours after the causative precipitation.
Forecasters do have the option of issuing a Flood Watch (abbreviated as FFA), which covers all types of flooding events, covering less than 36 hours (this may be expanded to 48 hours for extreme events). Flash flooding is covered in a FFA in two general circumstances:
• “Headline Flash Flooding – Convective rainfall resulting in rapid runoff, or tropical
rainfall;
12 • Threatening dam or levee failure impacting lives and property, but failure is NOT
deemed imminent.”
1.4 Precipitation estimation
1.4.1 Radar
Operational meteorologists at NWS offices typically use precipitation estimates from the
Weather Surveillance Radar-1988 Doppler (WSR-88D) when monitoring flash flooding.
WSR-88D precipitation estimation is carried out by the Precipitation Processing System
(PPS), which uses a set methodology to produce graphics of precipitation totals, as outlined by Fulton et al. (1998).
The PPS begins with collecting reflectivity data and quality control of those data.
Reflectivity data for the 0.5o elevation angle are collected in 1.0 km range bins approximately every 1o in azimuth. A quality-control process is employed after the data are gathered, and then the necessary algorithms are run. Fulton et al. (1998) outline five subalgorithms: 1) preprocessing, 2) rate, 3) accumulation, 4) adjustment, and 5) products. After these subalgorithms are run, scientists monitoring radar products at the NWS office in question can pull up graphical displays of the data, including but not limited to one-hour precipitation
(OHP), three-hour precipitation (THP), and storm total precipitation (STP). These products are reset when the PPS does not detect precipitation for a period of 1 hr.
Radar estimation of precipitation can have significant advantages over rain gage estimates. For example, according to Rinehart (1997), the typical area covered by a single
13 pulse of radar is 150 m long and can be 1000 m across. His estimation is that the sample area of radar is more than 2 million times larger than that of a rain gage.
However, the radar scans above the surface, which depending on the exact bin’s range from the radar itself, can be a significant level above ground. Evaporation can be a problem
(hence the radar would result in an overestimation of the rainfall), and where the beam overshoots precipitation, significant growth of raindrops by accretion at lower levels of a storm can cause the radar to underestimate true rainfall rates at the surface (Austin 1987).
The presence of a “bright band,” where frozen precipitation melts to liquid form at the freezing level, can also influence estimations because of the increase in reflectivity within the band. Austin (1987) states that radar indications of surface rainfall become unreliable if the radar beam encounters a portion of the melting layer. Blockage of the radar beam is a concern to those using radar estimates as well.
Yet another disadvantage with estimation of precipitation by the WSR-88D is the fact that each volume scan can take anywhere from five to ten minutes. During that time span, considerable changes in rainfall rate can occur, and the radar would not detect the differences, as the 0.5o elevation angle is the lowest sampled. Doviak and Zrnić (1993)
(hereafter referred to as D&Z93) outlined nine significant sources of error, summarized as follows: 1) horizontal winds, 2) attenuation, 3) reflectivity enhancement in the melting layer
(as mentioned above), 4) incomplete beam filling, 5) evaporation, 6) beam blockage, 7) rain rate gradients, 8) polarization effects, and 9) vertical air motion. The last of these can have a significant impact on the rain rate estimation, as changes in updraft/downdraft strength and intensity can cause significant over- or underestimations of the rainfall rate.
14 As outlined by D&Z93, the reflectivity factor method of estimating precipitation (a single-parameter measurement) incorporates the usage of the reflectivity factor Z to estimate rainfall rate R. As stated by D&Z93, Austin (1987), Wilson et al. (1979), Fulton et al.
(1998), Baeck and Smith (1998), Cataneo (1969), and several other authors, there is no set relationship between reflectivity factor Z and rainfall rate R that can be used universally, mainly due to the inherent variability in drop size distributions from event to event. Many studies have been done to determine relationships for different precipitation types (stratiform, convective, etc.) and different locations. For decades, the relationship between reflectivity and rain rate has been extensively studied. The general format for the Z-R relationship is
Z = aR b [1.5] where Z is the standard reflectivity factor, R is the rain rate, in mm h-1, and a and b are constants dependent upon precipitation type. A commonly-used Z-R relationship was determined by Marshall and Palmer (1948), and has been proven to work well for stratiform rain:
Z = 200R1.6 . [1.6]
The current default equation for the WSR-88D (Fulton et al. 1998), which is also known as the “standard relation,” is:
Z = 300R1.4 . [1.7]
Moreover, tropical environments might use (Fulton et al. 1998)
Z = 250R1.2 . [1.8]
According to Austin (1987), common standard relationships between Z and R in different convective types are listed below:
Average or ordinary rainfall: Z = 230R1.4 ;
15 Intense convective cells: Z = 400R1.3 ;
Noncellular rain: Z = 100R1.4 .
Choosing the best Z-R relationship for the precipitation type can be a difficult process.
Austin (1987) and D&Z93 suggest that rainfall rate estimates would have significantly less error if the Z-R relationships used to calculate the rainfall rate could change within the algorithms, as they change within storms and from storm to storm, as well as between different locations. Though an obvious solution, such a process might be difficult to achieve operationally. See section 2.2 for further discussion on this topic.
Operational meteorologists are often concerned about “contaminated” rainfall accumulations in thunderstorms where hail is likely occurring. For this reason, the WSR-
88D PPS is equipped with a “hail cap” threshold (Fulton et al. 1998). The default setting for this threshold is at 53 dBz; any dBz value higher than 53 will automatically be set to 53 when calculating rainfall rates. In arid regions, the setting is generally adjusted to 50 dBz, while in more tropical environments, such as along the Gulf Coast states, it is adjusted upwards to 56 dBz. According to Fulton et al. (1998), this value is somewhat arbitrary, but few studies have been conducted to determine more accurate thresholds. Therefore, although the threshold can be adjusted in an operational setting, it is difficult for a forecaster to know what, if any, value might be better than the default value.
1.4.2 Rain gage
Since the spatial resolution of rain gage networks is not sufficient for the purpose of this research (see section 3.1), rain gage data will not be utilized. However, such data can be used to verify other precipitation estimates and are often considered to be “ground truth” and
16 therefore an understanding of the basic limitations is necessary. Various rain gage networks are spread throughout the United States, operated by many agencies, including the NWS, the
US Army Corps of Engineers, the US Air Force Geophysical Laboratories (Austin 1987), and state climate offices. The NWS Automated Surface Observing System (ASOS) sites use a tipping bucket to measure rainfall, where every 0.01 in (0.254 mm) of rainfall collected fills one side of the bucket, and literally “tips” it to the other side. There are errors inherent in this measurement process. During extremely high rainfall rates, the tipping bucket can sometimes tip too fast or too often, as momentum builds with increasing rainfall intensity, which would lead to an overestimation of the actual rainfall amount. In addition, not only is rain falling as the bucket tips, but water can splash out of the bucket, both leading to an underestimate. The opening at the top of the rain gage usually ranges from 8 to 10 in
(Rinehart 1997), also limiting the estimation. If any amount of wind is present, it is likely that the true amount of rainfall is greater than the amount measured by the rain gage, especially the manual gages that are less likely to be protected by the wind. The restrictions in spatial coverage that most rain gage networks have, including those official climate stations maintained by the NWS, limits the estimation of wide ranges of precipitation.
1.4.3 Satellite
Although satellite precipitation estimates provide yet another method by which forecasters monitor rainfall, such estimates are rarely favored over radar and rain gage estimates. However, they can be extremely useful when radar data are unavailable or as a supplement to radar data, and they are a practical method by which to verify radar estimates during a heavy rainfall event. Satellite precipitation estimates used operationally in
17 NWSWFOs originate from the Satellite Analysis Branch (SAB) of the NOAA’s National
Environmental Satellite, Data, and Information Service (NESDIS). The SAB produces both graphical and text products (available online at http://www.ssd.noaa.gov/PS/PCPN/index.html), of which the text products are sent to the
WFOs via the Advanced Weather Interactive Processing System (AWIPS). The text precipitation estimates are disseminated to the WFOs under AWIPS header SPENES
(Satellite Precipitation Estimates – NESDIS) (U.S. Department of Commerce 1999, 2002).
The SAB produces three-hour estimated totals every 30 minutes, six-hour totals every hour, and 24-hour totals every day at 1200 UTC (U.S. D.O.C. 1999, 2002, Borneman 2000,
2002, 2003, Fortune 1998). Many operational meteorologists feel that these estimates either are not timely enough, as opposed to the five- or six-minute estimates that can be obtained by
WSR-88D, or one-minute data obtained by the ASOS sites (K. Keeter 2003, personal communication). In addition, often the discussion on the SPENES text product does not refer to one’s particular area of interest, and until the Auto- and, more recently, Hydro-Estimator became operational, the meteorologists at the SAB could only analyze one or two meteorological systems across the country at any given time (Fortune 1998).
Until June of 2000, the Interactive Flash Flood Analyzer (IFFA) technique was used operationally; it was initially developed by Roderick Scofield and V. J. Oliver in 1977 and updated by Scofield in 1980 and 1987 (Fortune 1998). It became fully operational in 1983
(Borneman 2000). The IFFA consisted of a labor-intensive flowchart method based on the meteorologist’s experience, and because of its time-consuming process, the SAB meteorologists were limited to one or two heavy precipitation regions of the country at any time. SPENES messages were limited in number due to the meteorologists’ time constraints.
18 The initial version developed in 1977 considered cloud top temperature and growth, overshooting tops, and cloud mergers. After 1980, divergence aloft, saturated environment, and moisture correction factors were added to the technique (Scofield 1987).
The need for an automatic method of precipitation estimation was apparent; many areas experiencing moderate rain were overlooked in deference to areas experiencing heavy rain when using the IFFA technique. The Auto-Estimator (A-E) technique that became operational in June of 2000 (Borneman 2002) is described in detail by Vicente et al. (1998).
The A-E computes rainfall rates based on a power-law relationship between radar estimated rainfall rates and cloud-top temperature. The relationship is given by
11 −2 1.2 R = 1.1183∗10 exp[− 3.6382 ∗10 Tc ], [1.9]
-1 where Tc is the cloud-top temperature in Kelvin, and R is the rainfall rate in mm h .
After the rainfall rates are initially computed, the A-E corrects for parallax and, sometimes, orography. It also uses a correction factor based on Eta model relative humidity
(RH) and PW to scale the rainfall rates depending on atmospheric moisture values. This moisture correction factor was carried over from the IFFA technique (Fortune 1998).
Another concept carried over from IFFA is the growth factor, which reduces rainfall rates for clouds that decreased in area between two consecutive images. The A-E also applies a gradient correction which identifies overshooting tops; this concept in its entirety was not applied in IFFA, but a similar idea was taken into account in the flowchart.
Although the A-E technique is arguably better than IFFA, if only because it is automated and SAB meteorologists are not limited to analyzing only one or two systems across the country, it still has its individual strengths and weaknesses. These are summarized in Table
1.2. Fortune (1998) provides a more detailed summary of these strengths and weaknesses,
19 and in addition, provides several recommendations, through the implementation of which the
A-E might be improved.
The Hydro-Estimator (H-E) became operational in September of 2002 (Borneman 2003).
The developers of the H-E acted on some of the recommendations listed in Fortune (1998), and are briefly summarized as follows (U.S. D.O.C. 2002):
1) radar is not used to discriminate between rain/no rain;
2) H-E uses a new screening technique that separates raining and non-raining pixels; and
3) H-E has separate adjustments for PW and RH that improve handling of stratiform
events with embedded convection.
In addition, for warm-topped convection, the H-E uses an equilibrium level adjustment derived from the Eta model.
Meteorologists at the SAB have the option of using H-E, reverting to A-E, or performing the more labor-intensive IFFA method to obtain satellite precipitation estimates, depending on the meteorological situation and the particular meteorologist’s experience level. The graphical and text products are then disseminated to the WFOs to be used in monitoring flood situations as deemed necessary. For the most part, the A-E and H-E are used operationally today. IFFA estimates were used to produce three-, six-, and 24-hour precipitation estimates. However, the A-E and H-E methods update one- and three-hour totals every half hour, six-hour totals every hour, and like IFFA, produce 24-hour totals every morning at 1200 UTC. Temporally, the A-E and H-E estimates have a much higher resolution than IFFA, and since the former two are completely automated, the meteorologists can spend more time on interpretation of the output, rather than development of the output
(Borneman 2000).
20
1.5 Land-surface hydrology
Understanding the movement of water is necessary in order to accurately forecast and warn for a flash flood. However, from an operational point of view, little is understood in this realm. Infiltration, the movement of water from the soil surface into the soil (Dingman
2002), must be thoroughly understood, as water that does not infiltrate becomes overland flow, or surface runoff, and moves toward a stream. Both of these variables, infiltration and runoff, are dependent upon various properties of the soil, which in turn are primarily dependent upon soil texture. Fig. 1.6 illustrates the scheme developed by the U.S.
Department of Agriculture for defining soil textures. Shown in Fig. 1.7 is the range of porosities, wilting points, and field capacities for different textures. Dingman (2002) defines porosity as the proportion of pore spaces in a volume of soil; the wilting point is the point on the moisture-characteristic curve at which transpiration ceases and plants wilt due to the lack of water content in the soil; and the field capacity is the water content below which further water drainage occurs at a negligible rate. Hydraulic conductivity, the rate at which water moves through a porous medium under a unit potential-energy gradient, is shown in Fig 1.7.
The saturated value is determined primarily by grain size. This will be discussed further in section 5.1.
1.5.1 Infiltration
According to Dingman (2002), when there is no ponding of water at the surface, then the infiltration rate equals the rate at which water is being input into the soil. However, when ponding is present, there are two methods by which this occurs; saturation from above and
21 saturation from below. The former is typically from snowmelt or rainfall, while the latter is due to a high water table in which case the entire soil is saturated. Dingman (2002) outlines six factors that determine the infiltration rate:
1. “(a) the rate at which the water arrives from above as rainfall, snowmelt, or irrigation;
or (b) the depth of ponding on the surface;
2. the saturated hydraulic conductivity of the soil profile;
3. the degree to which soil pores are filled with water when the process begins;
4. the inclination and roughness of the soil surface;
5. the chemical characteristics of the soil surface;
6. the physical and chemical properties of the water.”
There are several factors by which the pore size, and thus the value of saturated hydraulic conductivity, which has been shown to be equal to the minimum value of infiltration in the soil, can be altered. This includes organic surface layers, frost, swelling and drying, rain compaction, and human modification of the soil surface, including urbanization. Antecedent conditions are also important; wet soils at the onset of a rainfall event will be more likely to saturate and less likely to infiltrate, increasing runoff potential. Rugged terrain and steeper slopes increases the runoff potential and decreases infiltration as well; however, overland flow also decreases with increasing roughness (Dingman 2002).
1.5.2 Runoff
Dingman (2002) states that streamflow is determined by (1) spatially and temporally varying rainfall rates; (2) the travel time between when the raindrop hits the ground surface and when it reaches the stream; and (3) the travel time between when the water reaches the
22 stream and when it reaches the gage site. In very small watersheds (less than 50 km2), the last of these three is negligible. The hydrograph (stream response) is largely dependent on the hyetograph (input precipitation) shape. In addition, the more tributaries in the stream network, the longer the lag time (section 5.2).
Unless chemical and isotope components of the stream water are analyzed, there is no way to determine with absolute certainty if water associated with a flood wave is that from input precipitation. Therefore, when conducting flood analyses, one must estimate to the best of one’s ability the separation between the flood wave and the base flow of the stream.
Dingman (2002) explained that with a linear watershed model, larger watersheds have larger response times (this is a generic variable and could represent any specific stream response, such as those in section 5.2). In addition, watersheds with low surface hydraulic conductivities (e.g., clay soils) have smaller response times than those with high values of the same (e.g., sandy soils). Steeper slopes in a watershed result in smaller response times, and watersheds with extensive municipal development have smaller response times as well due to large areas of impermeability and many storm sewers.
The two types of surface runoff, or overland flow, which occur on a sloping surface are
Hortonian overland flow and saturation overland flow (Dingman 2002). The former is runoff which results from saturation from above, while the latter occurs from saturation from below.
Saturation overland flow is the common mechanism, except in arid or semi-arid regions or on human-developed and impermeable areas, where Hortonian overland flow is more common.
Table 1.3 provides a summary of the ways humans have altered river and stream flow regimes. While in some cases, such as damming, adding levees, and diverting streams, humans have acted to reduce flooding, in other cases, such as urbanization and deforestation,
23 human activity has only served to increase flood frequency. Some of this will be addressed in sections 5 and 6.
1.6 Objective
The goal of this research is to understand the role of various parameters such as soil type and landuse on flash floods in central North Carolina. It has been learned through the forecasting operations (section 5) that urban areas tend to flood more quickly, and that rainfall thresholds need to be adjusted downwards where and when rain has fallen previously.
In addition, given the current state of the science (section 2), it is apparent that more factors contribute to flash flooding than the basic parameter of soil moisture state, but it is not apparent by how much. This research will examine the gaged streams across the Raleigh
CWA, in order to analyze stream response to various amounts of precipitation under different antecedent conditions. After comparing stream response to not only rain rate and total precipitation amount but landcover and soil type as well, the impact of each of these variables on stream response will be evaluated.
24
Table 1.1. Features associated with heavy rainfall and the atmospheric fields (event characteristics) used to assess the strength (character) of these features (courtesy of Konrad 1997).
25
Table 1.2. Performance of the Auto-Estimator in various categories of precipitation systems (courtesy of Fortune 1998).
26
Table. 1.3. Major impacts of water-resource-management activities on river-flow regimes. Image courtesy of Dingman (2002).
27
FIG. 1.1a. Surface pattern for a typical synoptic type flash flood event. Potential for heavy rains and flash flooding exists in the boxes. Image courtesy of Maddox et al. (1979).
FIG. 1.1b. The corresponding 850-hPa flow pattern for a typical synoptic type flash flood event. Winds are in knots with full barb = 10 kt and flag = 50 kt. Image courtesy of Maddox et al. (1979).
28 FIG. 1.1c. The corresponding 500-hPa flow pattern for a typical synoptic type flash flood event. Image courtesy of Maddox et al. (1979).
FIG. 1.2a. Surface pattern for a typical frontal event with details as in Fig. 1.1. Image courtesy of Maddox et al. (1979).
29 FIG. 1.2b. Corresponding 850-hPa pattern for a typical frontal event. Image courtesy of Maddox et al. (1979).
FIG. 1.2c. Corresponding 500-hPa pattern for a typical frontal event. Image courtesy of Maddox et al. (1979).
30 FIG. 1.3a. Surface pattern for a typical mesohigh event with details as in Fig 1.1. Image courtesy of Maddox et al. (1979).
FIG. 1.3b. Corresponding 850-hPa pattern for a typical mesohigh event. Image courtesy of Maddox et al. (1979).
31 FIG. 1.3c. Corresponding 500-hPa pattern for a typical mesohigh event. Image courtesy of Maddox et al. (1979).
32 FIG. 1.4. Schematic illustration of the time variation of water vapor input (cross hatched area) and the precipitation output (vertical bars) over the lifetime of a precipitation system. The units are arbitrary, so the system being portrayed can be any precipitating process with a developing phase (time = 0-3 units), a mature phase (time = 3-6 units), and a dissipating phase (time = 6-10 units). For this example, the areas under the respective curves give a precipitation efficiency of about 44%. Image courtesy of Doswell et al. (1996).
33 FIG. 1.5. Schematic showing how different types of convective systems with different motions affect the rainfall rate (R) at a point (indicated by a circled dot) as a function of time; contours and shading indicate radar reflectivity. For case (a) a convective line is passing the point with a motion nearly normal to the line; for case (b) the line is moving past the point with a large component tangent to the line itself; for case (c) the line has a trailing region of moderate precipitation but is otherwise similar to (b), and for case (d) the motion of the line has only a small component normal to the line but is otherwise similar to (c). Total rainfall experienced at the point is the shaded area under the R vs. time graphs. Image courtesy of Doswell et al. (1996).
34 FIG 1.6. Soil-texture triangle, showing the textural terms applied to soils with various fractions of sand, silt, and clay. Image courtesy of Dingman (2000).
35 FIG 1.7. Ranges of porosities, field capacities, and permanent wilting points for soils of various textures. Image courtesy of Dingman (2000).
36
FIG 1.8. Hydraulic conductivity, Kh, vs. degree of saturation, S, for soils of three different textures. Note that the vertical axis gives the base-10 logarithm of the hydraulic conductivity, expressed in cm s-1. Image courtesy of Dingman (2000).
37 2. OPERATIONAL FORECASTING TOOLS
NWS forecasters use a number of tools in the operational forecasting, warning, and
monitoring of flash floods. Although some of these tools have been available for years and
are quite familiar to forecasters, others are relatively new and have only been widely used in
the operational process since the implementation of AWIPS in 1998/99. This section will
outline some of the tools available to forecasters for use in operations. One may notice that
land-surface information is markedly absent in these tools; however, once an understanding
of the land-surface hydrology is obtained, combining that understanding with these tools will
only serve to improve flash flood operations.
2.1 Flash Flood Guidance
Flash Flood Guidance (FFG) is used in a WFO as a principle criterion for issuing FFWs
and as an indicator for soil moisture conditions (NWSRFS User Manual II.9.2). FFG for a specific county or basin is issued by the River Forecast Center (RFC)2 overseeing that particular county or basin. Some WFOs have three or four RFCs issuing products for their
CWA, as RFC boundaries are based on major river basins rather than political boundaries
(Helble 2004). The Southeast RFC (SERFC), for example, issues all FFG products for the
Raleigh WFO, while WFO Greenville-Spartanburg, SC, receives products from the SERFC as well as from the Lower Mississippi RFC.
FFG arrives at the WFO in three forms: areal (or county), headwater, and gridded
guidance. Areal FFG is a numerical estimate of the average rainfall over a specified area and
2 “RFCs provide river forecasts and hydrologic guidance to their partners, which consist of WFOs, NCEP [National Centers for Environmental Prediction] service centers, other RFCs, and cooperating water-related agencies. The forecasts and guidance are used for the protection of life and property associated with flooding, and to provide water resource information to support commerce and economic decisions” (Helble 2003a).
38 time interval required to initiate flooding on small streams. Gridded FFG (Fig. 2.1), instead of over a specified area, is over a set of pre-defined grid areas; while headwater FFG is for a specified small stream basin (Helble 2003b). In addition, an option is available in AWIPS for basin-averaged FFG (Fig. 2.2). FFG is to be used by the WFO as an aid in the warning process; when estimated rainfall exceeds FFG, the forecaster may choose to issue a FFW
(Sweeney 1992, 1999). FFG is computed for 1-, 3- and 6-hour intervals, and in some RFCs,
12- and 24-hour intervals as well (NWSRFS User Manual II.9.2). It is issued at the SERFC at 1200, 1800, and 0000 UTC, and during critical hydrologic events when the SERFC is on
24-hour operations, FFG is also issued at 0600 UTC (B. Gimmestad 2003, personal communication).
FFG is computed using the current soil moisture state and the threshold runoff (Sweeney
1999). Soil moisture state itself is simulated by the NWS River Forecast System (NWSRFS).
Parameters depicting soil moisture state within the NWSRFS convert precipitation and any snowmelt (depending on atmospheric and ground temperatures) to runoff, which is then verified by observed values of stream levels. With the model interpretations of soil moisture
(and any snowmelt), several combinations of rainfall and runoff are computed and combined to produce a rainfall-runoff curve for each forecast basin. (NWSRFS User Manual II.9.2)
In some cases, rainfall intensity dominates over soil moisture state in the computation of
FFG. This is especially true in very dry parts of the country or under drought conditions, in areas with high soil permeabilities where interflow and baseflow are the only modes of runoff generation when investigation a large basin, and in impervious areas such as urban locations. Unfortunately, in current NWS models, surface infiltration is not modeled, and
39 therefore runoff in dry or drought conditions is under-computed (NWSRFS User Manual
II.9.2).
Threshold runoff is the amount of rainfall needed to fill a stream to just over bankfull
(NWSRFS User Manual II.9.2). It is not computed for basins greater than 775 mi2 (2007.2
km2), as rainfall over larger areas would rarely be uniform, and larger areas would not retain
the characteristics of a flash flood (NWSRFS User Manual II.9.5). A detailed explanation of
the computation of threshold runoff is available in the NWSRFS User Manual in Section
II.9.5.
Within the NWSRFS, the equation used to compute FFG can be written as:
Rt = FFG ∗ I + f (FFG)∗ (1− I) [2.1] where FFG is in inches, I is the percent impervious area, f is an internal function, and Rt is the total runoff in inches. Rt and I are provided as inputs, and the equation is subsequently solved internally for FFG. There are two main adjustments that can be made, one for high flow, or threshold runoff (the above equation assumes low flow), and one for intensity. The threshold runoff computation is, again, explained in detail in the NWSRFS User Manual
Section II.9.5. The intensity adjustment, mentioned above, can be done two ways. One may adjust threshold runoff Rh, or one may assign FFG a specific value, independent of soil
moisture conditions.
Rh = Rh ∗ INTEN [2.2]
or
FFG = INTEN , [2.3]
where INTEN is the intensity factor. (NWSRFS User Manual II.9.3)
40 While FFG from the SERFC is updated typically every six hours with the exception of
the overnight period, the operational forecaster must remember that if a rainfall event occurs
within that period, the soil moisture state has changed. This will not be accounted for until
the next official update, and therefore the WFO forecasters must adjust FFG accordingly,
especially if more rainfall is expected.
2.2 Areal Mean Basin Estimated Rainfall
2.2.1 Introduction
The Areal Mean Basin Estimated Rainfall (AMBER) algorithm uses radar-based
precipitation data to monitor the amount of precipitation that has fallen within a certain basin,
to assist in flash flood operations. AMBER computes Average Basin Rainfall (ABR) and
can compare these values to FFG as well as alert forecasters to basins in which ABR is
approaching and has exceeded FFG. Unless otherwise noted, all source information for this
section is from “The AMBER Flash Flood Algorithm” by Paul Jendrowski (available at
http://www.erh.noaa.gov/rnk/amber/).
The AMBER algorithm was first developed by Robert Davis at WFO Pittsburgh, PA, in
the early 1980s, and was updated through the mid-1990s for the WSR-88D system by Davis
and Paul Jendrowski. The updated algorithm uses the Digital Hybrid Reflectivity (DHR)
product as precipitation input. In 1998, it was adapted for use with a Geographic Information
System (GIS) to allow for the more accurate derivation of basins as well as display output.
In tandem with the modernization of the NWS, the newest version dubbed AMBERGIS was
further upgraded in 1999 to be used and displayed in AWIPS.
41
2.2.2 Algorithm overview
The primary input for AMBER is the 1 azimuth degree by 1 km DHR product, although
one can incorporate rain gage data for radar-gage comparisons at a single bin. AMBER can
ingest the DHR product either in real-time, checking every 20 seconds for new data, or in
“playback” mode. The DHR product is required when running AMBER in playback mode and is usually created from radar data in the Level II format (section 3.2). A utility available as part of the AMBER software is used to create the DHR product. An explanation of this utility is provided in section 3.2.
AMBER allows for the adjustment of certain processing settings via a text file containing adaptation data. For example, as discussed in section 1.4.1, the standard or default WSR-
88D Z-R relationship (Fulton et al. 1998),
Z = 300R1.4 [2.4] is provided (where Z and R are as in section 1.4.1), but the user may adjust the relationship as
needed, such as to the tropical relationship,
Z = 250R1.2 , [2.5] without necessarily adjusting the relationship at the Open Radar Product Generation (ORPG) console. An advantage of this capability is that it would allow the forecaster to recognize whether or not the radar is accurately estimating precipitation without affecting surrounding
WFOs or the RFC(s).
AMBER computes the scan-to-scan accumulation for each bin as is done in the WSR-
88D preprocessing algorithms (described in Fulton et al. 1998), except AMBER retains the
1o × 1 km radial and 0.5 dBz resolution of the DHR product. Fulton et al. (1998) state that
42 the WSR-88D preprocessing calculates rain rates on a 1o × 1 km polar grid, but averaging is performed on adjacent bins to result in a polar grid of 1o × 2 km. The AMBER scan-to-scan accumulations, in units of inches, are then calculated as
(R + R ) Accum = T ∗ t t−1 , [2.6] 2 where T is the time difference from the previous scan to the current scan, R is the rain rate as in equation 1.5, and the subscript t denotes the current scan. The scan-to-scan accumulations for each bin are then mapped to basins (Fig. 2.3), and the accumulations for all bins in a basin are summed and averaged over the area of the basin to produce ABR. A Basin Rate of
Accumulation (BRA) product is also computed, which is simply a rate of ABR over a volume scan period.
AMBER uses input FFG by converting county, or areal, FFG into basin FFG. In the same file as the basin FFG numbers are the alert time periods, which can be any six time periods ranging from 15 to 720 minutes. ABR accumulations are calculated for these six intervals and subsequently compared to FFG. The user can input FFG directly from the
RFC, or the user can adjust the FFG values as necessary. Forecasters must remember that the county FFG from the RFC will be the same for every basin in the county, regardless of landuse. Therefore, the user may wish to adjust some of the FFG values, such as for urban areas, and use a static value of, for example, 0.5 inches in one hour, whereas the RFC FFG may be much higher, such as up to 2 inches in one hour, for the urban basins.
Small watershed basins were defined and then distributed to each WFO by the National
Basin Delineation (NBD) Project at the National Severe Storms Laboratory (NSSL) throughout 2002. It was recommended that each WFO then customize those watersheds to correct errors and add any enhancements that the WFO deemed necessary to improve flash
43 flood operations (Arthur et al. 2003). The NBD Project basins were those used to create the
AMBER basins used in this research, although a digital elevation model and a GIS could have been used to derive basins manually. The AMBER algorithm will support nine basin types; the example provided in the software lists headwater, stream, and river basins. The added advantage of integrating AMBER with the GIS is that basins can be nested within one another; that is, a major river basin encompasses a small stream basin, yet within a small stream exists a headwater basin. Each basin type is assigned an identifying number, and the basins are subsequently assigned to a county. For each of these basins, a FFG value will be listed for each alert time period, and finally, ABR will be computed.
2.2.3 Operational use and limitations
AMBER compares the computed ABR to FFG for each basin, and computes an Alert
Status,
AlertStatus = 100 ∗ (ABR FFG), [2.7] which can be interpreted as the percentage of FFG reached (or exceeded if greater than 100) in that particular basin. The user specifies “yellow” and “red” alert thresholds (in percents, for example, 60 and 90 percent, respectively) in the same adaptation file as the Z-R relationship. AMBER will alert the forecaster when either category has been exceeded (Fig.
2.4). The basins are then color-coded by alert status on either the AWIPS (D2D) or GIS display for easy identification of problem areas (Figs. 2.5 and 2.6, respectively). ABR and
BRA can be looped just as any other radar product, and graphs of ABR, BRA, and FFG curves for any basin are available for any scan (Fig. 2.7). These are all accessible for use in the warning decision process and have proved invaluable in areas prone to flash flooding.
44 As with any radar rainfall estimates, care must be taken when relying solely upon them for warning decisions, for the reasons listed in section 1.4.1. Forecasters must always verify that the estimates corroborate with ground truth. Arthur (2000) reiterates this, as well as recommending that forecasters remain aware of FFG limitations in one’s WFO. In addition, her study found that examining not only time series of ABR accumulations but ABR rates
(BRA) was very effective, with the latter actually being a more accurate indicator of flash flooding. Customized basins, allowing for smaller watersheds with a minimum drainage area of 2 mi2 (5.2 km2), would be a significant advantage as well (Arthur 2000, Arthur et al.
2003). Arthur (2000) also recommends determining threshold accumulations and rates, and incorporating that information with hydrologic information unique to the basin such as terrain, infiltration, and antecedent moisture conditions. AMBER can be used with case studies in playback mode, as in this research, to implement that recommendation. ABR,
BRA, and Alert Status are output to a text file, identified by scan and basin, which can easily be saved for use in post-processing and for case studies. This could be extremely worthwhile if one decides to undertake a project to improve flash flood operations as recommended above.
In addition, especially when considering flash flooding, one must take into account rounding errors. While the AMBER output is in inches to a precision of hundredths of inches, all values are stored internally as integer tenths of millimeters. Therefore during short alert time periods, significant rounding errors can occur (P. Jendrowski 2004, personal communication). There is also a time weighting to the ABR accumulations. At the time of this research, the WSR-88D scanning options were either 5-, 6-, or 10-minute intervals
(Fulton et al. 1998), depending on the Volume Coverage Pattern (VCP). If then the AMBER
45 alert time period is, for example, every 15 minutes, while the radar is scanning every six minutes, it would be impossible to obtain a true 15-minute accumulation without some form of interpolation. Therefore, in this example, the 15-minute accumulation would then be the sum of the scan-to-scan accumulations completely contained within the 15-minute window, plus the contribution from the scan that spans the rest of the 15-minute period. The contribution of the partial scan is calculated using the entire accumulation from the scan and weighting it by how long it is in the 15-minute window versus how long the scan is itself, to the nearest second:
∆tscan Contribution = Accum ∗ window [2.8] ∆t scan
(P. Jendrowski 2004, personal communication).
2.3 Flash Flood Monitoring and Prediction
Flash Flood Monitoring and Prediction (FFMP) is an AWIPS application with AMBER- like functionality. The first version of FFMP was released with AWIPS 4.1 during the winter of 1998/99 (Smith et al. 1999), and has been continuously updated ever since. According to the NWS’s Meteorological Development Laboratory (2004), FFMP 2.0, released with
AWIPS 5.1.2 during the winter of 2001/02, was the first version that closely matched the
AMBER functionality, calculating ABR and comparing those calculations to FFG. Fig. 2.8 is the main display seen when FFMP is first invoked at Raleigh, and Fig. 2.9 illustrates what is seen when a specific county is chosen. FFMP also has includes the capability to graph
ABR, BRA, and FFG for any basin in which rainfall is detected by radar (Fig. 2.10). FFMP in AWIPS Operational Build (OB) 2 was released with a “forced FFG” option, allowing user-defined FFG values rather than utilizing only RFC-defined FFG (Fig. 2.11). This is
46 done in the most recent OB by opening a terminal window on the AWIPS workstation and typing the command “ForcedFFG.tcl.” A Graphical User Interface (GUI) will subsequently appear where the user can adjust the FFG values by CWA, by county, or by basin as desired.
If the AWIPS DHR products are saved from a certain event, FFMP can be run in Displaced
Real-Time (DRT) mode for case studies.
While FFMP is not as customizable as AMBERGIS, nor does it have the same post- processing capabilities, it does come packaged with AWIPS; that is, it is not necessary to install it at the WFO separately. Every WFO has access to FFMP, which has been shown to improve the warning process (Davis 2003). It was for FFMP that the NBD project was undertaken (Arthur et al. 2003), and a basin customization course was developed by the
Cooperative Program for Operational Meteorology, Education, and Training (COMET) in
Boulder, CO.
FFMP has allowed for easier monitoring of flash floods, and has arguably improved the accuracy of FFWs in general (M. Moneypenny 2004, personal communication). Forecasters at the Raleigh WFO feel that FFMP has greatly improved their individual ability to more accurately warn on flash floods (P. Badgett 2004, personal communication). However, the fact remains that in order to properly use the tools currently available, especially the new
Forced FFG application, the forecasters must have an understanding of the land-surface hydrology and how various parameters influence flash flooding.
47 FIG 2.1. Gridded 1-hour FFG from the SERFC for the Raleigh CWA. The “holes” in the product are from problems in the software used to create the FFG (T. Wallace 2004, personal communication). Note that in operations, the AWIPS display default background color is black and has been inverted in all figures to white.
48 FIG 2.2. Basin-averaged 1-hour FFG from the SERFC for the Raleigh CWA. Otherwise, details as in Fig. 2.1.
49 FIG 2.3. Representation of basins within the AMBER algorithm. Basins are defined by 1 degree by 1 km radar data points. Image courtesy of Jendrowski (2001), http://www.erh.noaa.gov/rnk/amber/doc/amber_awipsweb.htm.
FIG 2.4. Interface to monitor AMBER alerts. Top section changes color, green, yellow or red, to indicate highest Alert Status detected from all basins. Image courtesy of Jendrowski (2001), http://www.erh.noaa.gov/rnk/amber/doc/amber_awipsweb.htm.
50 FIG 2.5. Sample 4 p-panel AMBER BRA and ABR display on D2D with AMBER basins as a map overlay. Image courtesy of Jendrowski (2001), http://www.erh.noaa.gov/rnk/amber/doc/amber_awipsweb.htm.
51 FIG. 2.6. Sample AMBER ArcView GIS display. The AMBER display consists of an Area of Responsibility view and one or more detailed basin views. Selecting a basin in the detailed view will bring up a graph as shown in Fig. 2.7. Image courtesy of Jendrowski (2001), http://www.erh.noaa.gov/rnk/amber/doc/amber_awipsweb.htm.
52 FIG. 2.7. Sample graph of ABR (line with solid circles), FFG (heavy line) and BRA (blue line) for a 6 hour period with ABR and FFG in inches and BRA in in/hr. Plotted numbers are ABR for the six Alert Time Periods. Area under the ABR curve is shaded green, yellow and red in the actual display based on the Alert Status to indicate Alert Status category. Image courtesy of Jendrowski (2001), http://www.erh.noaa.gov/rnk/amber/doc/amber_awipsweb.htm.
53 FIG 2.8. Flash Flood Monitoring and Prediction. Counties are sorted in the FFMP Threat Table by whichever column the user has highlighted, in this case the ratio of precipitation to FFG; Montgomery County’s 0.75-hour precipitation is 103% that of its FFG. Clicking with the left mouse button on the county name in the Area_Id column will zoom in, as in Fig. 2.9. The screen displays, in this case, precipitation accumulation.
54 FIG 2.9. Flash Flood Monitoring and Prediction, zoomed into northeast Montgomery County. This allows the forecaster to see where the heaviest rainfall is occurring and which basins are being impacted. Clicking with the right-most mouse button on the Area-Id number will bring up a basin graph as in Fig. 2.10.
55 FIG 2.10. Graph of ABR (dotted line), BRA (blue line), and FFG (purple line) for the Nichols Run basin in Montgomery County. Note the similarity to the AMBER graph in Fig. 2.7.
56
FIG 2.11. The Forced FFG GUI available in AWIPS. The user has the option of providing FFG values across the entire CWA, for a specific county, or for a specific basin within a county. In this example, in order to provide a 1 Hr FFG value of 1.0 in (25.4 mm) for Wake County, the user would need to simply click on “NC,WAKE” with the right mouse button, and subsequently click “apply all” with the left mouse button on the lower right hand side of the GUI.
57 3. DATA AND METHODOLOGY
Numerous data sources were used in the course of this research. These include stream gage height, radar, soil, and landcover data. These data were obtained using a variety of resources, which will be outlined in detail in the following section. In addition, the methodology used to process the data will be described.
3.1 Stream
Six major river basins are contained within the Raleigh CWA: the Lower Roanoke, Tar,
Neuse, Cape Fear, Lumber, and Yadkin/Pee Dee basins. The major river basins are of course made up of smaller stream basins, and so on. The United States Geological Survey (USGS) maintains a number of gages along streams across the CWA; these gages measure gage height (ft) and streamflow (cubic feet per second). Some USGS stream gages measure precipitation, water temperature, air temperature, and a number of other parameters. These are available at the USGS website (http://waterdata.usgs.gov/nc/nwis/dv). This site was queried to determine the number of gage sites in existence across the CWA at the time of this research , as well as the respective location of each of those sites. Latitude and longitude coordinates were pulled from the site and loaded into a GIS. Fig. 3.1 shows the locations of the 93 resulting gage sites, and one can see the concentration of sites in the Triangle
(Raleigh, Durham, and Chapel Hill) and Greensboro areas. However, the gage height and streamflow available online are only at a temporal resolution of one day, which is not a sufficient increment to study flash flooding. It is known, though, with the USGS data ingested into the AWIPS, that these gages report in increments of 15-minutes. However, the
58 only access to these archives is through the USGS itself. With the amount of data needed for this study (for any given event, there were around 90 working USGS stream gages in operation across the CWA), it was necessary to learn how to access the USGS’s system in order to personally obtain the data.
Utilizing the USGS’s Automated Data Processing System (ADAPS), one can pull data for the desired station by the USGS station identification, and subsequently by desired parameter or descriptor (e.g., discharge, gage height, precipitation, etc.). ADAPS also contains daily data quality flags (marked by an “e”); flagged data indicate a possible equipment malfunction, or perhaps that conditions at the site compromised accurate readings
(R. Traynor 2003, personal communication). One must query ADAPS by site, by descriptor, and by date, so it was far simpler to pull data for a time period of just over a year, rather than for the individual cases listed below. ADAPS writes all the data to one file, in columns by site identification number and in rows by date. Once this was done, and the file with the quality control flags accessed and saved, it was a simple matter to then separate this file by site and case for use in analyses.
Table 3.1 lists the 93 USGS stations by county, as well as the soil type and the landcover class (see below) corresponding to the sites. The sites with the asterisks (*) beside them are those that were included for final analysis.
3.2 Radar
The National Climatic Data Center (NCDC) provides the full period of digital record of
WSR-88D Levels II and III data free to the public (available online at http://has.ncdc.noaa.gov/plclimprod/plsql/HAS.DsSelect), although one must have the proper
59 software (e.g., Warning Decision Support System) to be able to use the data. For this study,
Level II data, which contain the basic reflectivity fields, were downloaded for the dates
discussed in section 4.
AMBERGIS is equipped with a software utility to create the DHR product from Level II
data, specifically for the purpose of running the main program in “playback” mode. The
utility, “pps_pdf,” is formulated after the WSR-88D precipitation processing algorithm
described in Fulton et al. (1998). Unless otherwise noted, all source information relating to
pps_pdf is from Jendrowski (1997).
The user must create a text file listing the volume scans and the path to the directory in
which they are located. It is recommended that the scans themselves remain compressed, as
pps_pdf will uncompress them and store them to a temporary directory, deleting them
upon completion of the run. Before running the program, the user must edit an input file,
which in effect tells pps_pdf which products to create. The program is able to create a
number of products, including but not limited to the OHP, STP, THP, and, of course, the
DHR product. In this file the user also specifies what Z-R relationship to use and numerous thresholds, such as minimum and maximum precipitation rates, minimum time in an hour for a missing period, minimum clutter area, et cetera. The clutter area thresholds, used to
suppress ground clutter and necessary for the precipitation detection function (PDF), are
typically set at low values to force precipitation accumulations, but if the actual values from
the event are known, it is recommended that the event values be used. In addition, the user
must also specify the radar latitude, longitude, height (MSL), and identification (e.g.,
KRAX).
60 The operational PDF processes the lowest four elevations to determine if precipitation
exists. If the area of an echo with a precipitation rate exceeds a threshold area, then the PDF
has detected precipitation. However, since in playback mode one cannot choose different
VCPs as can be done operationally, pps_pdf uses the “hybrid scan”, with only one rate and area threshold, to determine if precipitation exists. The hybrid scan consists of the lowest elevation angle for each polar grid point that is at least 150 m above the ground but as close to 1.0 km above the radar level as possible, unless there is more than 50% beam blockage by terrain (Fulton et al. 1998).
Once the DHR product has been created, it is written to the current directory (as well as any other product the user specifies). To then run AMBERGIS in order to obtain text precipitation output by basin, the user must list the DHR products in a text file, along with the path pointing to the directory in which the DHR products are located. Creating a valid
FFG file is the next step; one may either use the RFC’s FFG or use one’s own values. The user must point to the file in which the DHR products are listed after entering the playback command, and AMBERGIS will subsequently print to the screen the output by basin, listing the ABR, FFG, and alert status.
AMBERGIS creates an “alert” directory in the current directory in which the text files for post-processing are located. Each text file represents a scan, and within the file is a list of basins, one on each line, along with the precipitation accumulation for the alert time period, the FFG, the alert status, and the ABR.
It was necessary for this study to reorganize the alert files such that each file contained data for one basin and multiple scans, rather than vice versa. Robb Ellis, Climate Services
Assistant at the State Climate Office (SCO) of North Carolina, developed a Perl script to
61 perform this function. This allowed for the straightforward processing of the files by basin, with the 15-minute precipitation accumulation, a temporal resolution adequate for flash flooding, of particular interest for this study. In particular, basins in which USGS stream gages were located were identified, so that the 15-minute precipitation accumulations could be compared to the 15-minute gage heights to measure stream response. This will be discussed in more detail below.
3.3 Soil
Soil data used in this study include datasets associated with soil type. The State Climate
Office (SCO) of North Carolina obtained the State Soil Geographic (STATSGO) dataset for
North Carolina from the National Resource Conservation Service (NRCS). The 102 different soil textures had been dissolved by Robb Ellis, using a GIS into a more manageable number of 21. The resulting textures are listed in Table 3.2, and Fig. 3.2 displays the soils across central North Carolina, with the counties within the Raleigh CWA highlighted. This dissolved dataset was then used to obtain the soil type for the USGS stations across the
CWA, and then parameters corresponding to that soil type were collected from Dingman
(2002). Table 3.3 lists the values of various parameters for several different soil textures.
3.4 Landcover
Much like the dataset containing information on soil type, the SCO obtained a landuse dataset from the North Carolina Center for Geographic Information Analysis (NCCGIA).
This statewide land cover dataset originated from the Earth Satellite Corporation (EarthSat).
19 different landcover classes are enumerated in the dataset, and are defined in Table 3.4. As
62 with the soil type dataset, the landuse dataset was loaded into a GIS, along with the USGS
stations, and the landuse category was determined for each of the USGS stations.
3.5 Analysis methodology
After the radar data for the cases discussed in section 4 were collected, they were
processed through AMBERGIS using the alert time periods of 15, 30, 45, 60, 75, and 90
minutes. Nevertheless, only the 15-minute increment was relevant to the study, as the
comparison between 15-minute stream gage readings and 15-minute precipitation
accumulation was the first objective. However, as discussed in section 1.4.1, the WSR-88D
scans at increments of 5-, 6-, or 10-minutes. Therefore, while the USGS stream gages report
every 15 minutes, on the exact 15-minute increment of :00, :15, :30, and :45, there is no guarantee that the AMBERGIS 15-minute accumulations will end on those same increments.
What was henceforth done was to take the one or two full scans completely within the 15- minute accumulation period, and a time-weighted average of the other(s) as necessary, very similar to what was described in section 2.2.3. These 15-minute accumulations were then plotted against stream gage heights, as will be discussed further in section 5.1.1.
If there was no response of the stream to the input precipitation, that is, if no flood wave was evident, then the event or perhaps even the site, was not considered in the analysis and results. However, the most likely cause was determined if possible, which, too, will be discussed in section 5.1.1. In addition, if the response to precipitation did not occur as expected, that is, if the response was overwhelmingly extreme, it was likely that water from upstream was likely contributing, and thus the site, or at least the particular event for that location was not considered. There were a few other reasons for which sites were not
63 considered for analysis, but those particular reasons are part of the results, and will be discussed in section 5.1.1. Once a final set of sites was decided upon, statistical conclusions were drawn to determine relationships between different variables and responses in order to facilitate the forecasting of flash floods. These statistical results will also be covered in section 5.
64 Table 3.1. USGS sites across the CWA in operation between August 2002 and August 2003, sorted by county. Also listed are landcover classes and soil types corresponding to the sites. Asterisks (*) indicate locations included in the final analysis.
USGS Site Name County Landcover Soil *HAW RIVER AT HAW RIVER, NC Alamance Low intensity developed SL ROCKY RIVER NEAR NORWOOD, NC Anson Cultivated CN-SIL *BUCKHORN CREEK NR CORINTH, NC Chatham Southern yellow pine L *TICK CREEK NEAR MOUNT VERNON SPRINGS, NC Chatham Mixed hardwoods CN-SIL HAW RIVER NEAR BYNUM, NC Chatham Mixed hardwoods SL B. EVERETT JORDAN LAKE AT DAM NR MONCURE, NC Chatham Southern yellow pine FSL HAW R BELOW B. EVERETT JORDAN DAM NR MONCURE, NC Chatham High intensity developed FSL CAPE FEAR RIVER AT FAYETTEVILLE, NC Cumberland High intensity developed LS LITTLE RIVER AT MANCHESTER, NC Cumberland Southern yellow pine LS *ABBOTTS CREEK AT LEXINGTON, NC Davidson Mixed hardwoods SL NEW HOPE CREEK NEAR BLANDS, NC Durham Southern yellow pine FSL NORTHEAST CREEK AT SR1100 NR GENLEE, NC Durham Mixed hardwoods FSL FLAT RIVER AT DAM NEAR BAHAMA, NC Durham Southern yellow pine SL *MOUNTAIN CREEK AT SR1617 NR BAHAMA, NC Durham Mixed hardwoods SL *FLAT RIVER AT BAHAMA, NC Durham Mixed hardwoods SL *ENO RIVER NEAR DURHAM, NC Durham Mixed hardwood/conifer FSL Bottomland LITTLE R BL LITTLE R TRIB AT FAIRNTOSH, NC Durham hardwood/swamp L *LITTLE RIVER AT SR1461 NEAR ORANGE FACTORY, NC Durham Deciduous shrubland SL Bottomland FLAT RIVER TRIB NR WILLARDVILLE, NC Durham hardwood/swamp SIL Bottomland FISHING CREEK NEAR ENFIELD, NC Edgecombe hardwood/swamp L TAR RIVER AT TARBORO, NC Edgecombe High intensity developed LS *TAR RIVER AT NC 97 AT ROCKY MOUNT, NC Edgecombe High intensity developed SL
65 Table 3.1. Continued FISHING CREEK AT NC 97 NEAR LEGGETT, NC Bottomland Edgecombe hardwood/swamp MUCK Bottomland TOWN CREEK AT US 258 NEAR PINETOPS, NC Edgecombe hardwood/swamp MUCK Bottomland CONETOE CREEK AT CONETOE, NC Edgecombe hardwood/swamp FSL Bottomland SWIFT CREEK AT NC 97 NEAR LEGGETT, NC Edgecombe hardwood/swamp MUCK TAR R AT US 401 AT LOUISBURG, NC Franklin Mixed hardwood/conifer SL Bottomland TAR RIVER NEAR TAR RIVER, NC Granville hardwood/swamp SL *EAST FORK DEEP RIVER NEAR HIGH POINT, NC Guilford Mixed hardwoods L REEDY FORK NEAR GIBSONVILLE, NC Guilford Mixed hardwoods L *HORSEPEN CREEK AT US 220 NR GREENSBORO, NC Guilford Mixed hardwoods L *N BUFFALO CR AT WESTOVER TERRACE AT GREENSBORO, NC Guilford Mixed hardwoods L *NORTH BUFFALO CREEK AT CHURCH ST AT GREENSBORO, NC Guilford Low intensity developed L *NORTH BUFFALO CREEK NEAR GREENSBORO, NC Guilford Mixed hardwoods L *RYAN CREEK BELOW US 220 AT GREENSBORO, NC Guilford Managed herbaceous cover L *SOUTH BUFFALO CR NEAR GREENSBORO, NC Guilford Managed herbaceous cover L *SOUTH BUFFALO CREEK AT US 220 AT GREENSBORO, NC Guilford High intensity developed L *BRUSH CREEK AT FLEMING ROAD AT GREENSBORO, NC Guilford Mixed hardwoods L *BUFFALO CREEK AT SR2819 NR MCLEANSVILLE, NC Guilford Mixed hardwoods L *REEDY FORK NEAR OAK RIDGE, NC Guilford Mixed hardwoods L *SOUTH BUFFALO CREEK NR POMONA, NC Guilford Mixed hardwoods L Bottomland LITTLE FISHING CREEK NEAR WHITE OAK, NC Halifax hardwood/swamp LS ROANOKE RIVER AT ROANOKE RAPIDS, NC Halifax Mixed hardwood/conifer L
66 Table 3.1. Continued ROANOKE RIVER AT HALIFAX, NC Bottomland Halifax hardwood/swamp L ROANOKE RIVER NEAR SCOTLAND NECK, NC Halifax Evergreen shrubland L CAPE FEAR RIVER AT LILLINGTON, NC Harnett High intensity developed L *FLAT CREEK NEAR INVERNESS, NC Hoke Southern yellow pine LS Bottomland ROCKFISH CREEK AT RAEFORD, NC Hoke hardwood/swamp MK-L Bottomland NEUSE RIVER NEAR CLAYTON, NC Johnston hardwood/swamp LS Bottomland MIDDLE CREEK NEAR CLAYTON, NC Johnston hardwood/swamp LS Bottomland LITTLE RIVER NEAR PRINCETON, NC Johnston hardwood/swamp MUCK NEUSE RIVER AT SMITHFIELD, NC Johnston Low intensity developed SL DEEP RIVER AT MONCURE, NC Lee Managed herbaceous cover SL *LITTLE RIVER NEAR STAR, NC Montgomery Deciduous shrubland LS *DUTCHMANS CREEK NR UWHARRIE, NC Montgomery Mixed hardwood/conifer CN-SIL Bottomland SWIFT CREEK AT HILLIARDSTON, NC Nash hardwood/swamp SL Bottomland TAR R BL TAR R RESERVOIR NR ROCKY MOUNT, NC Nash hardwood/swamp SL TAR RIVER AT US 301 BYPASS AT ROCKY MOUNT, NC Nash Evergreen shrubland SL *MORGAN CREEK NEAR CHAPEL HILL, NC Orange Mixed hardwood/conifer FSL *CANE CREEK NEAR ORANGE GROVE, NC Orange Mixed hardwoods SL Bottomland *MORGAN CREEK NEAR WHITE CROSS, NC Orange hardwood/swamp SCL SEVENMILE CREEK NR EFLAND, NC Orange High intensity developed SL *ENO RIVER AT HILLSBOROUGH, NC Orange Low intensity developed SIL *MAYO CR NR BETHEL HILL, NC Person Managed herbaceous cover FSL
67 Table 3.1. Continued
HYCO R BL ABAY D NR MCGEHEES MILL, NC Person Southern yellow pine SL HYCO LAKE AT DAM NR ROXBORO, NC Person High intensity developed L Bottomland AFTERBAY RESERVOIR AT DAM NR MCGEHEES MILL, NC Person hardwood/swamp SL Bottomland *DEEP RIVER AT RAMSEUR, NC Randolph hardwood/swamp SL *DEEP RIVER NEAR RANDLEMAN, NC Randolph Mixed hardwoods L DROWNING CREEK NEAR HOFFMAN, NC Richmond Southern yellow pine S Bottomland PEE DEE R NR ROCKINGHAM, NC Richmond hardwood/swamp L BLACK RIVER NEAR TOMAHAWK, NC Sampson Southern yellow pine S Bottomland BIG SHOE HEEL CREEK NR LAURINBURG, NC Scotland hardwood/swamp LS Bottomland *BIG BEAR CR NR RICHFIELD, NC Stanly hardwood/swamp SL ROCKY R AT SR1300 NR CRUTCHFIELD CROSSROADS, NC Wake Managed herbaceous cover SL Bottomland WHITE OAK CR AT GREEN LEVEL, NC Wake hardwood/swamp FSL Bottomland *CRABTREE CR AT EBENEZER CHURCH RD NR RALEIGH, NC Wake hardwood/swamp L NEUSE RIVER NEAR FALLS, NC Wake High intensity developed L Bottomland *SWIFT CREEK NEAR MCCULLARS CROSSROADS, NC Wake hardwood/swamp L *MARSH C NR NEW HOPE, NC Wake High intensity developed L *CRABTREE CREEK AT US 1 AT RALEIGH, NC Wake High intensity developed L Bottomland *PIGEON HOUSE CR AT CAMERON VILLAGE AT RALEIGH, NC Wake hardwood/swamp L Bottomland *ROCKY BRANCH BELOW PULLEN DRIVE AT RALEIGH, NC Wake hardwood/swamp L *WALNUT CREEK AT SUNNYBROOK DRIVE NR RALEIGH, NC Wake Mixed hardwood/conifer L
68 Table 3.1. Continued
*CRABTREE CREEK AT HWY 70 AT RALEIGH, NC Wake High intensity developed L *UNNAMED TRIB TO SWIFT CR NR YATES MILL POND, NC Wake Managed herbaceous cover L FALLS LAKE ABOVE DAM NR FALLS, NC Wake High intensity developed L *CRABTREE CREEK AT ANDERSON DRIVE AT RALEIGH, NC Wake Low intensity developed L *CRABTREE CR AT OLD WAKE FOREST RD AT RALEIGH, NC Wake High intensity developed L Bottomland *SWIFT CREEK NEAR APEX, NC Wake hardwood/swamp L Bottomland NEUSE RIVER NEAR GOLDSBORO, NC Wayne hardwood/swamp MUCK Bottomland *NAHUNTA SWAMP NEAR PIKEVILLE, NC Wayne hardwood/swamp SL Bottomland *CONTENTNEA CREEK NEAR LUCAMA, NC Wilson hardwood/swamp MUCK
69 Table 3.2. STATSGO soil textures and associated abbreviations. Data obtained from the National Cartography and GIS Center (1991).
Soil Texture Abbreviation Clay Loam CL Channery-Fine Sandy Loam CN-FSL Channery-Loam CN-L Channery-Silt Loam CN-SIL Fine Sand FS Fine Sandy Loam FSL Gravel Loam GL Loam L Loamy Fine Sand LFS Loamy Sand LS Mucky Loam MK-L Muck MUCK Sand S Sandy Clay Loam SCL Silt Loam SIL Sandy Loam SL Stony-Loam ST-L Stony-Sandy Loam ST-SL Very Stony-Loam STV-L Unweathered Bedrock UWB Variable VAR
70
Table 3.3. Values of porosity, saturated hydraulic conductivity, air-entry tension (or bubbling pressure), and pore-size distribution index. Values in parentheses are standard deviations. Image courtesy of Dingman (2000).
71 Table 3.4. NCCGIA landcover classes and associated definitions. Data obtained from the National Center for Geographic Information and Analysis (1997).
Landcover Class Definition High Intensity More than 80% coverage by synthetic land cover. Developed Low Intensity Between 50% and 80% coverage by synthetic land cover. Developed Cultivated Areas of land that are occupied by row and root crops that are cultivated in distinguishable rows and patterns. Managed Herbaceous Areas used for the production of grass and other forage crops, Cover and other actively managed areas of herbaceous cover, including golf courses, cemeteries, etc. Upland Herbaceous Areas covered by herbaceous vegetation that is not characteristic of riverine and estuarine environments. Riverine/Estuarine Areas of herbaceous cover in salt, brackish, and freshwater Herbacous marshes in riverine and estuarine environments. Evergreen Shrubland Areas where evergreen vegetation is dominated by shrubs and/or woody plants below 3 meters in height. Deciduous Shrubland Areas where deciduous vegetation is dominated by shrubs and/or woody plants below 3 meters in height. Mixed Shrubland Areas where neither evergreen or deciduous vegetation is dominated by shrubs and/or woody plants below 3 meters in height. Mixed Hardwoods Areas where deciduous dominant woody vegetation is above 3 meters in height. Crown density is at least 25%. Bottomland Areas where deciduous dominant woody vegetation is above 3 Hardwoods/Hardwood meters in height, as well as occurring in lowland and wet areas. Swamp Crown density is at least 25%. Other Broadleaf Areas where deciduous dominant woody vegetation is above 3 Deciduous Forests meters in height, but do not fit in either of the previous categories. Crown density is at least 25%. Needleleaf Deciduous Forest class including cypress stands, mixed gum/cypress forests, and maritime swamp forests dominated by cypress. Mountain Conifers Areas where stocking of trees is 75% evergreen needleleaf or broad leaf species, including the following forest types: white pine, hemlock, and spruce-fir. Southern Yellow Pine Areas where stocking of trees is 75% evergreen needleleaf or broad leaf species, including the following forest types: longleaf pine, loblolly-slash pine, other yellow pine, and pond pine. Other Needleleaf Areas where stocking of trees is 75% evergreen needleleaf or Evergreen Forests broad leaf species, including the following forest types: Atlantic
72 Table 3.4 (continued). White Cedar, other needle leaf species such as red cedar, and other forest areas that cannot be classified as either mountain or southern yellow pine. Broadleaf Evergreen Areas where stocking of trees is 75% broad leaf evergreen Forest species characteristic of Carolina Bays and pocosins, as well as maritime evergreen broadleaf forests and bay forests, stocked predominantly by broadleaf trees that do not seasonally lose their leaves. Mixed Forest land with at least a 25% intermixture of deciduous and Hardwoods/Conifers evergreen species. This classification commonly occurs in Piedmont and mountain areas in which hardwoods (mainly oak) constitute a plurality of stocking but pines also account for 25 to 50% of the stocking. Oak/Gum/Cypress Bottomland forests in which tupelo, blackgum, sweetgum, or cypress, singly or in combination, constitute a plurality of the stocking. These stands are classified in this subcategory when cypress constitutes at least 25% of the stocking but less than 75%. Water Bodies Areas of all surface water with no or minimal, emergent vegetation. Unconsolidated Sandy or silty areas abutting tidal areas, and inland lakes and Sediment upland sand areas with little or no established vegetation. Exposed Rock Areas where bedrock is exposed at the surface or where a layer of soil exists that is not thick enough to support significant vegetation. Indeterminate Land will be assigned to this category in cases where the cover type does not logically fall into a previously defined land cover type. Municipal Areas Areas covered by urban development, including residential, commercial, industrial, transportation and utility infrastructure, and other developed land exclusive of agricultural land.
73 Person Granville Vance Warren Franklin
Guilford Alamance Orange Durham Halifax
Forsyth
Davidson Edgecombe
Chatham Nash Randolph Wilson
Stanly Wake
Lee Wayne
Moore Johnston
Montgomery Harnett
Anson Sampson
Richmond Scotland Hoke Cumberland
FIG 3.1. USGS stream gages (as listed in Table 3.1), within the Raleigh CWA in operation at the time of this research. Major river basins, from west to east, are: Yadkin/Pee Dee, Lumber, Cape Fear, Neuse, Tar, and Lower Roanoke.
74
FIG 3.2. STATSGO dissolved soil textures for central North Carolina. Counties within the Raleigh CWA are outlined. Data obtained from the National Cartography and GIS Center (1991).
75 4. CASES STUDIED
4.1 Overview
The main objective of this research was to determine the influence of land-surface
hydrological factors on flash flooding, and in addition to assist the NWS at Raleigh with their
flash flood operations. To accomplish this objective, several case studies within the Raleigh
CWA in which flash flooding occurred were identified. Initially, eight cases were chosen
between August 2002 and August 2003; however, due to inconsistencies in radar data from
the Raleigh WSR-88D (KRAX), the source of rainfall estimates, two cases during the spring
of 2003 had to be removed from consideration. The six remaining cases are as follows: 26
August 2002, 11 October 2002, 9-10 April 2003, 16 June 2003, 29 July 2003, and 9 August
2003. The events, and especially the warning strategies and flash flooding reports, will be
discussed below. If upper-air and surface data for the events were saved in the event folders
(see below), then the synoptic and mesoscale features will be described as well. In addition, a surface map is included for each event; for the 2003 events, the maps were obtained from a local archive of NCEP surface analyses. However, NCEP analyses were not available for the
2002 events, and thus hand analyses are included for those events. Each of these events had a considerable impact either on life or property, as will also be discussed below.
As stated in section 1.1, this one-year time period from August 2002 to August 2003 saw
North Carolina recover from an extreme drought, and then experience one of the wettest springs on record. This was an ideal situation for studying flash flooding in the CWA; antecedent soil moisture conditions ranged from extremely dry to extremely moist. While
75 soil moisture data were available from the State Climate Office of NC, close analysis of these data proved inconclusive, and therefore it was decided to omit their inclusion.
The NWS at Raleigh has long followed a practice of making “event folders” for significant weather events. These event folders contain hardcopies of watches, warnings,
Local Storm Reports (LSRs), verification logs, newspaper articles, surface and upper-air analyses, and anything else that is deemed noteworthy for future reference. For the more extreme events, case studies were performed, and some of these case studies are available at the NWS Raleigh collaboration webpage (http://www.meas.ncsu.edu/nws/www/cases/).
More recently, during the spring and summers of 2004, this practice has been expanded, and forecasters have begun writing “rapid response” event summaries of significant weather events in addition to making the event folders; these summaries outline the synoptic and mesoscale features surrounding the event, as well as the forecast and warning strategies undertaken as the event unfolded, and are typically completed within 24 hours following the event. It is from the event folders, available at the Raleigh NWS, and when applicable the online case studies, that most of the data for this section were gathered.
In addition, the NWS at Raleigh monitors daily climate data for the ASOS sites at the
Piedmont Triad International Airport near Greensboro, the Raleigh-Durham International
Airport, and the Fayetteville Regional Airport. 30-year climate normals are available for the former two (the period of record is not long enough at the Fayetteville Regional Airport for climate normals to have been computed), and records and daily values are kept on-station for the three sites.
Finally, it is the practice at the NWS at Raleigh to archive the 24-hour precipitation accumulation at 1200 UTC each morning. Through 2002, this occurred when rainfall was
76 observed, but since 2003, this has been a daily activity. The archives for the events have been included in this section.
In comparing these events to the Maddox classifications, it is difficult to find resemblances. Maddox et al. (1979) specifically did not include events influenced by tropical systems, so the 11 October 2002 event cannot be compared. In looking at surface and upper-air data from the other event and comparing those data to Figs. 1.1-1.3 from section 1, only the 16 June 2003 event seems to match any of the patterns; a frontal event.
Many of the others resemble a frontal event at the surface, but a synoptic-type event aloft. It is interesting to note that in analyzing their case studies, Maddox et al. (1979) state that flash flooding seems to be especially rare in the southeastern United States during the summer months. Perhaps since their sample did not include many flash flooding events in the area encompassing North Carolina, it may be that many events in the Carolinas may not match the
Maddox classifications very well.
4.2 26 August 2002
4.2.1 Antecedent conditions
By 25 August 2002, the Piedmont Triad International Airport (hereafter referred to as
GSO) had received 19.84 in (503.9 mm) of precipitation for the year, which was 8.95 in
(227.33 mm) below normal. The Raleigh-Durham International Airport (hereafter referred to as RDU) received 22.15 in (562.61 mm); 6.69 in (169.93 m) below normal. The Fayetteville
Regional Airport (FAY) had received 19.32 in (490.73 mm). Recall from section 1.1 that the
12-month period ending in July 2002 was the driest on record for the state. In July 2002
77 most of the CWA was under the Climate Prediction Center’s (CPCs) category of exceptional drought, while the far westernmost and far easternmost sections were under extreme drought.
Many reservoirs across the CWA had only a few months of water left (Lazo 2002a). This event was thus classified as a “dry” event with regards to antecedent soil conditions.
4.2.2 Operational summary and warning strategies
An upper level low pressure system was located over the southeastern United States at
0000 UTC 26 August. At the surface, an area of low pressure was centered near FAY at
0300 UTC 26 August 2002 and propagated slowly northward overnight. A cold front trailed southwest into South Carolina, toward Columbia, while a warm front stretched toward the
Outer Banks. No significant convection developed along this boundary during the event.
However, weak convection did develop over Vance County, NC, around 0400 UTC. The
0900 UTC hand-analyzed surface map is shown in Fig. 4.1, where the surface cyclone can be seen in the coastal plain, and heavy rainfall is evident over Vance County.
At 0637 UTC, the Hydrometeorological Prediction Center issued their excessive rainfall potential outlook, in which they stated that rainfall was not expected to exceed FFG values.
The FFG for Vance County, for example, was three inches in one hour and five inches in three hours. Soon after the one-hour threshold was exceeded, a call from Vance County 911 was received, confirming that flooding was already ongoing. The first FFW was issued immediately thereafter, at 0839 UTC. Table 4.1 lists all the warnings issued for 26 August
2002, including the valid times and locations.
At approximately 0905 UTC, a drowning fatality occurred in Vance County along
Highway 39 across Nutbush Creek. Water was flowing across the road at that time; the
78 vehicle was in the creek near the highway while the body was discovered a few hundred feet
away.
Radar rainfall estimates through the event ranged up to eight inches (203 mm) in some
areas. A six-foot deep sinkhole developed in a road in Vance County, the fire department in
the city of Wilson was flooded and several people had to be evacuated from the town after
six inches (152 mm) of rain fell, and over two feet of water covered roads in Nash County.
In addition, in Wake County, Raleigh Creek overflowed its banks, flooding apartments and
vehicles. By the end of the day, all waters had receded, and none of the mainstem rivers (i.e.,
the Neuse, Tar, etc.) experienced any flooding.
It was determined that flooding had begun before radar estimates and FFMP indicated
that rainfall had reached FFG. Part of this is due to the way FFG is calculated; for example,
hypothetically, if the soil is infinitely dry, it would take an infinite amount of rain to saturate
the soil. However, a cap for dry conditions can be put in place using the intensity factor
discussed in section 2.1. This was likely done, but a suggested practice for the Raleigh WFO first employed during this event was to consider warning at two-thirds of the FFG value under dry conditions. Additionally, regarding the Wake County flash flood, a suggestion made was to consider using a universal FFG value of one inch per hour for urban areas.
The 24-hour precipitation ending at 1200 UTC 26 August, which would include the heavy rainfall that occurred around 0900 UTC, was unfortunately not archived. Fig. 4.2 is the 24-hour accumulation ending at 1200 UTC 27 August, and while it does not display the heaviest rain over Vance County, it does still provide one with a general understanding of the amount of rain that did fall with this event.
79 It was noted that this rainfall improved the drought conditions in central North Carolina only marginally. Areas in eastern parts of the CWA previously under the “exceptional” category were downgraded to “severe,” and the areal extent of the exceptional drought decreased while the extent of the extreme drought increased (Lazo 2002b).
4.3 11 October 2002
4.3.1 Antecedent conditions
While September 2002 received slightly above normal rainfall, which provided some relief to water supplies, it did little to solve the prolonged drought (Lazo 2002c). By 9
October 2002, GSO had received 27.20 in (690.88 mm) of rain for the year, 7.72 in (196.08 mm) below normal. RDU was at 29.40 in (746.76 mm) for the year, which was 5.51 in
(139.95 mm) below normal. FAY had received 29.98 in (761.49 mm). Soils were still very dry, and rivers and streams were still extremely low; the rainfall that occurred over the preceding two months had prevented the situation from worsening, but was not enough to improve the rainfall deficit by any considerable amount. This event was therefore classified as a “dry” event as well.
4.3.2 Operational summary and warning strategies
At 0000 UTC 10 October, high pressure was located off the southeastern coast of the
United States at all levels of the atmosphere, allowing moist air to follow a southerly trajectory at lower levels, with a more southwesterly flow at upper levels. An upper-level jet stretching from New England to the Ohio Valley provided a mechanism for lift in the lower
80 Mississippi River Valley, being located in the jet’s right rear quadrant. By 1200 UTC 10
October, moisture was overspreading the Mid-Atlantic states at lower levels, while the upper-
level jet had shifted further east to place parts of Tennessee and North Carolina in the right
entrance region. A 500-hPa shortwave over Texas was slowly moving east and into an
extremely moist environment. A surface ridge extended down the Piedmont, and a trough
was quickly moving onshore from the Atlantic. This trough had moved well inland by 1800
UTC. Little had changed in the upper levels by 0000 UTC 11 October; the moisture
remained firmly entrenched, the jet streak was marginally stronger, and the 500-hPa
shortwave had progressed only slightly to the north and east. The Greensboro and Morehead
City soundings had PW values of 1.75 and 1.80 inches (44.45 and 45.72 mm), respectively,
with easterly flow at the lowest levels, indicating both strong veering in the lowest layers and
a moist Atlantic inflow. At 1200 UTC 11 October, the 850-hPa analysis indicated speed and
directional convergence over North Carolina, strong RH advection with Atlantic inflow, and
dewpoints in the teens (13-17 0C, with near-zero dewpoint depressions). At 700-hPa, a sharp
RH gradient was evident, as well as a wind maximum over North Carolina due both in part to an approaching shortwave from the southwest and to Tropical Storm Kyle located off the southeastern coast of the United States. Finally, the 500-hPa shortwave previously in Texas
was now over the lower Mississippi River valley, and North Carolina was very favorably
located with respect to the upper-level jet. Fig. 4.3 shows the surface analysis at 1500 UTC
11 October, indicating the location of Tropical Storm Kyle and the circulation around it, the
surface ridge, and the areas of deepest moisture.
The forecasters at Raleigh noted that the extremely moist airmass, a tropical connection
as indicated on water vapor imagery, the surface-based coastal trough, the low-level
81 convergence, and the upper-level jet were likely the most critical factors in the production of heavy rainfall. It was also noted that Tropical Storm Kyle, moving north-northeast along the southeastern coast, did not itself contribute rainfall to the event, although moisture from Kyle most likely enhanced the event. It may be, also, that Kyle contributed wind shear to make the environment more favorable for tornadic development; indeed, two tornadoes touched down in the Raleigh CWA, with more reports further east.
At 0805 UTC 11 October, the SAB sent a SPENES message for central North Carolina and south central Virginia discussing a baroclinic leaf satellite cloud signature and high moisture. The SAB forecaster discussed that although the A-E did have a maximum of precipitation over central NC, the forecaster believed that the amounts were underestimated and felt that they should be increased by at least a factor of 1.5. The 6-hour maximum given over central NC by the A-E was 1.0 in (25.4 mm). The forecaster did indicate that WFOs should be on guard for increased flash flood potential through the rest of the day.
A comparison of 24-hour KRAX WSR-88D precipitation estimates to standard 8-inch gage estimates across the CWA on the morning of 11 October (just after 1200 UTC) indicated that where the precipitation was heaviest, the radar tended to underestimate in general, but not always. This is something to consider in section 5. The 18-hour precipitation accumulation ending at 1700 UTC 11 October is shown in Fig. 4.4. ASOS precipitation reports are plotted on the figure as well. One can see that the radar indeed underestimated, in general, where the heaviest precipitation fell. Note that no 24-hour precipitation accumulation image was saved for this date.
Flash flooding was reported in several counties across central North Carolina: Durham,
Franklin, Granville, Person, and Wake. Many roads were reported flooded, cars were
82 submerged, and several creeks flooded, the most notable being Crabtree Creek in Wake
County. Crabtree Creek along Old Wake Forest Road crested 4.18 ft (1.27 m) above flood
stage. Tornadoes were reported in Edgecombe, Wilson, and Johnston Counties (the latter
two reports were from one tornado). More information on the tornadoes, including damage
pictures, is available at the NWS Raleigh case study website
(http://www4.ncsu.edu/~nwsfo/storage/cases/20021011/). Table 4.2 lists the warnings issued for this event.
The rainfall caused the Haw River to flood at the towns of Haw River and Bynum, the
Neuse River flooded at Clayton and Smithfield, and the Tar River exceeded flood stage at
Louisburg and Rocky Mount. The rain also brought streams and reservoirs across the CWA to near normal levels by mid-month. In addition, by the end of October 2002, the Climate
Prediction Center downgraded the drought from extreme and exceptional to moderate and severe levels throughout the CWA (Lazo 2002d).
4.4 9-10 April 2003
4.4.1 Antecedent conditions
The months prior to April 2003 were wetter than normal. In March 2003, many river forecast points, locations for which the RFC issues forecasts (detailed information can be found in Helble 2003b), in the CWA exceeded flood stage, and a few surrounding areas suffered damage as a result. By the end of March 2003, the North Carolina State Drought
Monitoring Council officially declared that the drought was over, with rivers remaining at
above-normal levels (Lazo 2003a). By March 7, GSO recorded 15.60 in (396.24 mm) of
83 rain, 4.29 in (108.97 mm) above normal. Meanwhile, RDU was at 12.89 in (327.41 mm) for
the year, which was 0.68 in (17.27 mm) above the yearly normal. Finally, FAY recorded
8.24 in (209.30 mm) for the year. This event was therefore classified as a “moist” event.
4.4.2 Operational summary and warning strategies
A very moist airmass was in place before the event occurred, with a series of 500-hPa vorticity maxima approaching North Carolina. In addition, around 0800 UTC 8 April 2003, a stationary front was located south of the Raleigh CWA, and several areas of low pressure were forecast to move northeast along the front through 9 April. Finally, a low pressure system that developed in the Gulf of Mexico moved up the coast and across eastern North
Carolina on 9 April (Fig 4.5).
A Flood Potential Outlook was issued on 7 April to discuss the possibility of heavy
rainfall and flooding along mainstem rivers. The first flood watch (FFA) was issued at 0830
UTC 8 April and updated at 1531 UTC 8 April. This particular watch expired by 1520 UTC
9 April, but with a caution that an upper level disturbance over the Mississippi Valley would
bring more rainfall on 10 April. The next FFA was issued at 1915 UTC 9 April, valid until
0300 UTC 11 April. Note from Table 4.3 that all the warnings issued were FLWs, rather
than FFWs. This indicates that the forecasters reasoned that the criteria for issuing a FFW
would not be met, that is, the rapid rise of water, or the immediate threat to life or property.
This will be discussed briefly in section 5.3.3.
The SAB sent a SPENES message at 1905 UTC 10 April; in it the forecaster stated that
due to the warm cloud tops, the H-E estimates were low, and thus they were reverting to the
IFFA method (section 1.4.3). For central North Carolina, specifically Montgomery, Moore,
84 and Lee Counties northward to Forsyth and Stokes Counties, the hourly rates were estimated as 0.3 to 0.8 in (7.62-20.32 mm), with totals of 0.7 to 0.9 in (17.78-22.86 mm) between 1515 and 1815 UTC. The forecaster noted that these totals approached or exceeded FFG for flooding threats in some areas.
One of the major complications with this case, aside from the widespread flooding, was the pre-saturated soils; it took very little wind to begin receiving reports of trees down in some counties, including Harnett and Wake Counties. The substantial flooding rendered numerous roads impassable and inundated bridges, basements, and homes, requiring the rescue of several people. Stanly County 911 was quoted as asserting that there were “not enough traffic cones;” in other words, so many roads were flooded that the county did not have the cones necessary to block the roads to traffic.
Figs. 4.6 and 4.7 show the 24-hour precipitation accumulations ending at 1200 UTC 10
April and 1200 UTC 11 April 2003, respectively. The widespread nature of the rain can be seen. In addition, discrepancies between the rain gage reports and the radar estimates can be seen in Fig. 4.7, although the radar estimates in Fig. 4.7 seem to be much closer to the gage reports than those in Fig. 4.6.
Many of the mainstem rivers flooded: the Haw at Haw River and Bynum; the Cape Fear at Moncure; the Lower Little River at Fort Bragg; the Tar at Louisburg, Rocky Mount and
Tarboro; Fishing Creek at Enfield; the Lower Roanoke at Roanoke Rapids and Scotland
Neck; the Neuse at Clayton, Smithfield and Goldsboro; the Yadkin at Yadkin College; and the Rocky River at Norwood crested around 15 ft (4.57 m) above flood stage. The Neuse at
85 Goldsboro flooded a few days later and crested at 20.4 ft (6.22 m), or 6.4 ft (1.95 m) above
flood stage3, inundating roads in the area. (Lazo 2003b)
4.5 16 June 2003
4.5.1 Antecedent conditions
May 2003 was the fourth month in a row of above-normal rainfall, with river and stream
levels remaining above normal as well (Lazo 2003c). However, the heavy rainfall events in
May 2003 were typically convective in nature rather than stratiform as the events of March
and April had been. Hence, river levels, while still high, were as not high as in April.
Nonetheless, by 14 June 2003, GSO received a total of 30.70 in (779.78 mm) of rainfall, a full 11.23 in (285.24 mm) above normal. RDU, however, was at 22.19 in (563.63 mm), only
2.51 in (63.75 mm) above the yearly normal. FAY received 20.59 in (522.99 mm). This event is consequently classified as a “moist” event.
4.5.2 Operational summary and warning strategies
As with the April 2003 event, a very humid airmass was in place over the southeastern
United States. A slow-moving cold front stretched east-west across the Mid-Atlantic states would provide the lift necessary to trigger numerous showers and thunderstorms across the state, and as it moved slowly southward, thunderstorm cells trained along it in an ideal flash flood-producing situation. In addition, a weak quasi-stationary frontal boundary over central
North Carolina would serve as an additional focusing mechanism (Fig. 4.8).
3 Effective 21 January 2004, the flood stage at the Neuse River at Goldsboro (GLDN7) was 18 ft (5.49 m), adjusted from the previous value of 14 ft (4.27 m).
86 A Flood Potential Outlook was issued at 0920 UTC 15 June and updated at 1900 UTC,
and the first flood watch was issued at 2101 UTC 15 June, which included the northern
Piedmont and northern Coastal Plain. A SPENES message from the SAB at 2119 UTC 15
June explained that the boundary discussed above would continue to be the focus. The cells
along the boundary were estimated to have hourly rainfall rates of 1.25 to 1.75 in (31.75-
44.45 mm), but with cell mergers taking place, an additional enhancement of 0.5 in (12.7
mm) could be expected. However, that particular FFA was cancelled at 0709 UTC 16 June,
with a message stating that another watch would be issued for the afternoon hours of 16 June.
Indeed, another FFA was issued by 0845 UTC 16 June for the Sandhills and southern
Piedmont, valid until 0300 UTC 17 June. By the issuance time the boundary had stalled along the southern tier of central North Carolina, as was outlined in the FFA. Given the heavy rainfall the day before and the additional rain expected in the afternoon, small streams would likely overflow their banks. The cold front located in Virginia around 0900 UTC was forecast to move into the northern Piedmont later that afternoon, triggering further showers and thunderstorms. At 1945 UTC 16 June, the FFA was extended through 1000 UTC 17
June as a result of the cold front moving into and through the area. All warnings issued
during this event are listed in Table 4.4.
Another SPENES message from the SAB at 2352 UTC 16 June pointed out that merging
cells along the frontal boundary currently in Stanly County were producing torrential rainfall;
half-hourly amounts approached 2 in (50.8 mm). They indicated that as this feature
continued to track eastward, continued mergers and training cells would bring a high flash
flood threat across southern counties in the Raleigh CWA.
87 The 24-hour precipitation accumulation ending at 1200 UTC 17 June is displayed in Fig.
4.9. The heavy rainfall that impacted areas of southern Stanly County is clearly visible; this convective line apparently extended across southern sections of the CWA, as was outlined in the last SPENES message.
Several small creeks overflowed their banks during this event, and many roads were flooded and subsequently closed. Homes were evacuated in Cumberland County in the town of Hope Mills, other homes were damaged in Burlington in Alamance County, and some businesses in Oakboro in Stanly County were inundated with up to 3 ft (0.91 m) of water.
Just before 0030 UTC on 17 June, four fatalities occurred in Cottonville in southeast Stanly
County; a vehicle attempting to cross Hardy Creek near Norwood was washed off the bridge by the high water. Three adults and a nine-year-old boy were in the vehicle at the time, and the bodies were all found away from the vehicle.
The Rocky River at Norwood is the only RFC forecast river that flooded after this event.
Other mainstem rivers flooded at different times of the month and caused minor damage to nearby areas (Lazo 2003d), but this event was mainly a flash flood-producing event, rather than a flood-producing one.
4.6 29 July 2003
4.6.1 Antecedent conditions
June and July 2003 were the fifth and sixth consecutive months of above-normal rainfall
(Lazo 2003d, e). However, again, convective cells dominated the majority of events during these months. By 28 July 2003, GSO recorded 35.63 in (905.00 mm) of rainfall, 10.19 in
88 (258.83 mm) above normal. RDU was at 27.75 in (704.85 mm) for the year, which was 2.33 in (59.18 mm) above the normal rainfall. FAY reported 34.31 in (871.47 mm) by that date.
This event, too, is classified as “moist.”
4.6.2 Operational summary and warning strategies
On the 1200 UTC 29 July maps, a positively-tilted upper-level trough stretched from the
Great Lakes to the middle Mississippi Valley. An upper-level jet over the New England states once again placed North Carolina in the right entrance region, favorable for lift. A stalled frontal boundary at the surface was draped across the southern and eastern sections of the CWA during the late morning and afternoon hours of 29 July (Fig. 4.10). This along with diurnal heating would provide focus for showers and thunderstorms during the afternoons.
Particularly on the afternoon of 29 July, as the boundary shifted slowly north and a shortwave, located in Nebraska at 1200 UTC, rounded the base of the longwave trough, with a warm and humid airmass already in place (dewpoints were in the lower to mid 70s), conditions were favorable for heavy rain. In addition, with the shortwave approaching and the nearby frontal boundary, there existed a potential for severe thunderstorms as well.
A severe thunderstorm watch was issued at 1905 UTC 29 July for much of the western two-thirds of the CWA. Not long after the watch issuance, the first FFW was issued at 1930
UTC for Wake County, with strong thunderstorms in several counties across the CWA.
Heavy rain fell from many of these storms; at the WFO in Raleigh, 3.21 in (81.53 mm) of rain were recorded in less than 1.5 hr. Unfortunately, no SPENES messages were saved from this event. The Wake County FFW was issued using a lower threshold than FFG itself (D.
Schneider 2004, personal communication), but it is unknown if the FFW was issued using the
89 recommendation that arose from the 26 August 2002 case, which was to use a universal value of one inch per hour as a FFG value for urban areas. Table 4.5 lists the warnings issued.
The 24-hour precipitation accumulation ending at 1200 UTC 30 July is shown in Fig.
4.11. However, KRAX was not in operation on 29 July until the volume scan beginning at
1443 UTC, and therefore if any rain did occur between 1200-1443 UTC, the 24-hour image does not include it. Since the bulk of the rain, and the flash flooding, took place during the afternoon hours, the gap in radar data is not a significant concern.
In Winston-Salem, Forsyth County, anywhere from two to three feet of water covered
Stratford and Haynes Mall Roads near the Interstate 40 underpass. Stranded motorists had to be rescued from their cars in Lexington in Davidson County. Several creeks in different counties were reported out of their banks, and many roads were submerged under water and had to be closed. A few streets in Wake County had over four feet of water covering them; roads were closed, and traffic had to be re-routed. Commuters during the afternoon rush hour had to wait several hours before roads were passable again. (Lazo 2003e)
4.7 9 August 2003
4.7.1 Antecedent conditions
Yet again, rainfall leading up to this event was above normal and typically convective in nature (Lazo 2003e, f). GSO’s annual rainfall total on August 7 was 42.65 in (1083.31 mm), which was 15.94 in (404.88 mm) above normal. Note that GSO was a mere two months away from tying the annual rainfall record of 56.51 in (1435.35 mm), set in 1975. Recall from section 1.1 that GSO broke this record by 5.81 in (147.57 mm), with an annual total of
90 62.32 in (1582.93 mm). RDU totaled 30.90 in (784.86 mm) by 7 August, which was 4.22 in
(107.19 mm) above the yearly normal. FAY reported 40.51 in (1028.95 mm) by the same date. Like the previous two events, this event was also classified as “moist.”
4.7.2 Operational summary and warning strategies
There were no synoptic or mesoscale data saved in the event folder for this particular case; however, the Area Forecast Discussions4 (AFD) from the morning of 9 August indicated an upstream shortwave at 500-hPa over the Savannah Basin approaching the area and a jet streak aloft placing North Carolina in the right entrance region. In addition, diffluent flow aloft would enhance convection. By 1044 UTC 9 August, a weak low pressure trough stretched down the Piedmont (Fig. 4.12), but the strongest moisture convergence was to the east. By 0155 UTC 10 August, water vapor imagery indicated that the upper level jet was providing the energy to sustain significant convection over the Piedmont, and that a vorticity maximum would pass over the area after 0400 UTC. Training cells and cell mergers on saturated soil from rainfall that occurred the previous morning combined to produce flash flooding.
Although there was a flood watch out for the early morning hours of 9 August, the last one was cancelled at 1300 UTC. No other watches were issued during the event. A
SPENES message was saved from 0544 UTC 10 August stating that although cloud tops were warm, heavy rain was expected to linger. H-E three-hourly estimates over Randolph
County were 1.0 to 1.5 in (25.4-38.1 mm), but the forecaster added a message indicating that while the location was probably good, the amounts were likely too low and should probably
4 The AFD, issued with each forecast, is used to explain the scientific rationale behind the forecast and to convey watch/warning/advisory information (Young 2003). AFDs issued by the NWS at Raleigh are available online at http://www.erh.noaa.gov/rah/data/RDUAFDRAH.html.
91 be closer to 2.0 to 3.0 in (50.8-76.2 mm). The forecaster also pointed out that on water vapor
imagery a well-defined short wave was rounding the base of the longwave trough over
Mississippi and would likely increase the rain threat again to central North Carolina later that day. The bulk of the heavy rain that caused the major flooding problems fell overnight between 9-10 August, but more rain did indeed fall on the evening of 10 August, causing additional problems in counties that had seen substantial amounts of rain the night before.
As before, warnings issued during the event are listed in Table 4.6.
Fig. 4.13 illustrates the 24-hour precipitation ending 1200 UTC 10 August 2003.
Emphasizing the SPENES message, the radar estimates over southern Randolph County were between 6-8 in (152.4-203.2 mm). Recall from Fig. 3.1 that there are no stream gages located in that area of Randolph County; the only gages in the county are located along the
Deep River, further north and east.
Upstream of the Little River along one of its tributaries in Randolph County, the historic
Pisgah Covered Bridge, 92 years old, was washed away during the early morning hours of 10
August. It was only one of two covered bridges left in the state. Crane Creek in Moore
County rose to unprecedented levels; the operators on Woodlake Dam, which contains runoff from Crane Creek, were forced to open all gates in order to avoid the dam’s collapse.
Downstream, where the runoff from this creek met the Little River whose waters were also overflowing its banks, residents in the town of Lobelia had to be evacuated by boat. 35 homes sustained moderate water damage, and cars were submerged up to their windows.
(Lazo 2003f)
92
Table 4.1. Warnings issued by the NWS in Raleigh during the 26 August 2002 event. All times are in UTC.
County Warning Type Valid Time (UTC) Vance FFW 0839 – 1200 26 August Vance FFW 1147 – 1500 26 August Franklin FFW 1147 – 1500 26 August Warren FFW 1147 – 1500 26 August Wilson FFW 1219 – 1515 26 August Nash FFW 1219 – 1515 26 August Edgecombe FFW 1241 – 1515 26 August
Table 4.2. Same as Table 4.1, but for the 11 October 2002 event.
County Warning Type Valid Time (UTC) Durham FLW 0218 – 0400 11 October Granville FLW 1009 – 1300 11 October Person FLW 1009 – 1300 11 October Durham FFW 1100 – 1300 11 October Durham FFW 1250 – 1515 11 October Granville FFW 1250 – 1515 11 October Randolph FFW 1250 – 1515 11 October Chatham FFW 1250 – 1515 11 October Wake FFW 1448 – 1800 11 October Vance FFW 1448 – 1800 11 October Durham FFW 1502 – 1800 11 October Granville FFW 1502 – 1800 11 October Edgecombe TOR 1713 – 1800 11 October Wake FFW 1748 – 2015 11 October Franklin FFW 1748 – 2015 11 October Johnston FFW 1748 – 2015 11 October Wilson TOR 1805 – 1845 11 October Wake FFW 2053 – 2400 11 October Durham FFW 2053 – 2400 11 October Granville FFW 2053 – 2400 11 October
93 Table 4.3. Same as Table 4.1, but for the 09-10 April 2003 event.
County Warning Type Valid Time (UTC) Alamance FLW 1614 – 1900 Chatham FLW 1614 – 1900 Davidson FLW 1614 – 1900 Forsyth FLW 1614 – 1900 Guilford FLW 1614 – 1900 Lee FLW 1614 – 1900 Montgomery FLW 1614 – 1900 Moore FLW 1614 – 1900 Randolph FLW 1614 – 1900 Durham FLW 1705 – 2100 Orange FLW 1705 – 2100 Wake FLW 1705 – 2100 Anson FLW 1800 – 2100 Stanly FLW 1800 – 2100
Table 4.4. Same as Table 4.1, but for the 16 June 2003 event.
County Warning Type Valid Time (UTC) Sampson SVR 2038 – 2115 16 June Moore FFW 2135 – 2330 16 June Montgomery FFW 2145 – 2345 16 June Sampson FFW 2200 – 0100 16 June Stanly FFW 2205 – 0030 16 June Hoke FFW 2315 – 0115 16 June Cumberland FFW 0000 – 0300 17 June Anson FFW 0003 – 0300 17 June Montgomery FFW 0003 – 0300 17 June Southern Stanly FFW 0035 – 0330 17 June
94
Table 4.5. Same as Table 4.1, but for the 29 July 2003 event.
County Warning Type Valid Time (UTC) Wake FFW 1930 – 2100 29 July Forsyth FFW 2245 – 0045 29 July Stanly SVR 2310 – 2345 29 July Davidson FFW 2327 – 0130 29 July Stanly SVR 2346 – 0825 29 July Montgomery SVR 0017 – 0045 30 July Wayne FFW 0047 – 0245 30 July Richmond FFW 0057 – 0230 30 July Cumberland FFW 0140 – 0345 30 July
Table 4.6. Same as Table 4.1, but for the 09 August 2003 event.
County Warning Type Valid Time (UTC) Eastern Moore FFW 2215 – 2345 09 August Southern Moore FFW 2345 – 0100 09 August Alamance FFW 2358 – 0200 09 August Orange FFW 0016 – 0215 10 August Durham FFW 0142 – 1115 10 August Davidson FFW 0156 – 0330 10 August Randolph FFW 0417 – 0615 10 August Montgomery FFW 0435 – 0630 10 August Montgomery FFW 0615 – 0900 10 August Randolph FFW 0615 – 0900 10 August Wake FFW 1550 – 1745 10 August Southern Moore FFW 2133 – 2300 10 August Harnett FFW 2143 – 2345 10 August
95 FIG 4.1. NWS Raleigh hand-performed surface analysis valid 0900 UTC 26 August 2002.
96 FIG 4.2. KRAX WSR-88D estimated precipitation for the 24-hour period between 1200 UTC 26 August and 1200 27 August 2002. As in the AWIPS images from section 2, the default background color as been inverted from black to white.
97 FIG 4.3. Same as Fig. 4.1, except valid 1500 UTC 11 October 2002.
98 FIG 4.4. KRAX WSR-88D estimated precipitation for the 18-hour period between 2300 UTC 10 October and 1700 11 October 2002. ASOS 24-hour rainfall reports are plotted on the image as well.
99
FIG 4.5. Hydrometeorological Prediction Center surface analysis valid 0900 UTC 9 April 2003.
100 FIG 4.6. KRAX WSR-88D estimated precipitation for the 24-hour period between 1200 UTC 09 April and 1200 10 April 2003. ASOS 24-hour rainfall reports are plotted on the image as well.
101 FIG 4.7. Same as Fig. 4.6, but for 10-11 April 2003.
102 FIG 4.8. Same as Fig. 4.5, except valid 0600 UTC 16 June 2003.
103 FIG 4.9. Same as Fig. 4.6, but for 16-17 June 2003.
104 FIG 4.10. Same as Fig. 4.5, except valid 2100 UTC 29 July 2003.
105 FIG 4.11. Same as Fig. 4.6, but for 29-30 July 2003.
106 FIG 4.12. Same as Fig. 4.5, except valid 0900 UTC 9 August 2003.
107
FIG 4.13. Same as Fig. 4.6, but for 09-10 August 2003.
108 5. DISCUSSION OF RESULTS
5.1 Overview
5.1.1 Site analysis
Section 1.5 discussed the mechanisms of infiltration and runoff, which one must
reference with respect to this entire section, especially section 5.3. As discussed in section
3.1, 93 USGS stream gage sites were used in the course of this research. After the radar data
were processed for each event, plots were made of the precipitation (hyetograph) and the
stream gage height (response hydrograph). As was outlined in section 3.5, if the stream did
not respond to the input precipitation, the case was not analyzed. Also, if it was evident that
water from upstream was the primary cause of the rise at that particular site, the case was not
analyzed. This was done by visually analyzing the hydrograph with respect to the
hyetograph; typically it was obvious when the flood wave in question was caused by input
precipitation. In many cases, especially on larger streams, a certain length of time later there
was a second flood wave due to water from tributaries upstream reaching the site. The only
way to fully conduct such an analysis would be to separate the chemical and isotope
components of the water (Dingman 2002) which would be difficult to do in any situation, so
a visual separation is arguably the best method of analysis.
Other analysis methods were subjective in various instances. For some cases,
precipitation occurred in several pulses. If the stream responded to each pulse of
precipitation, it was a matter of visual analysis, as discussed above. However, if the stream
responded only to the first pulse of precipitation, or if the opposite occurred and there was
109 steady precipitation and yet the stream oscillated, the case was typically disregarded. If onset
was weak and response was slow, basin size or drainage area had to be considered in addition
to rain rates themselves. A table was constructed of all sites, indicating which cases were
analyzed, and if two or fewer cases were analyzed, the entire site was disregarded for the
overall results.
It is interesting to note which sites were ignored. All sites along major rivers (i.e., the
Neuse, Tar, Cape Fear, Haw, Yadkin, Pee Dee, Lumber, and Roanoke), except two fell into
this category. The Tar River at NC97 at Rocky Mount was the only Tar River site included in the analysis, and the Haw River at Haw River in Alamance County, one of the “flashy rivers” (i.e., water levels tend to rise quickly) in the CWA, was also included. This is likely because it took a large amount of precipitation for these major rivers to respond; rather, any river response was likely due to water from upstream. Indeed, during only one case, 11
October 2002, did many of these rivers respond to the precipitation, and for this case many of the gages along these rivers received over six inches of precipitation in a matter of a few hours.
In addition, referring to Table 3.1, neither of the two sites with sandy soil were kept. Of the nine loamy sand sites, two remained for analysis. Of nine fine sandy loam sites, only three remained; out of 23 sandy loam sites, 13 were disregarded. The one site with sandy clay loam soil was included in the final analysis. In summary, out of 44 total sites with sand content in the soil, 16 (36%) remained in the final analysis, and 11 of those contained less sand than loam, or in one case, clay loam. Investigating the response of the sites to the precipitation, the main reason most of the sites were not analyzed was because the streams simply did not respond to the precipitation. Indeed, the sites with sandy soil did not flood
110 during these six cases, and the sites with loamy sand that had predetermined flood stages did
not flood either, no matter how significant the precipitation. Dingman (2000) defines
hydraulic conductivity as “the rate at which water moves through a porous medium under a
unit potential energy gradient.” This is determined under saturated conditions by the size of
the soil grains. Sandy soils have the highest saturated hydraulic conductivity values (see Fig.
3.5), and thus water moves through these soils at a higher rate than others (e.g., soils with
high clay contents have very low values of the same). This would lead one to conclude that
the precipitation simply infiltrated quickly and thus the streams did not receive as much of
the precipitation in these areas as in areas with different soil types. Unfortunately, this did
not allow for any analysis in the Sandhills region; however, the knowledge that even with
significant precipitation that these sites responded little if at all for these six cases is quite useful in an operational setting. One must remember, however, that this conclusion is only
valid for these six cases for the sites studied, and does not represent the entire spectrum of
possibilities.
It must also be noted that the sites in urban locations, such as those in Greensboro,
Raleigh, and Durham, responded very quickly to the precipitation. This will be discussed further below. Additionally, regardless of the size of the stream, no site immediately downstream from a controlled dam was included in the analysis, as although instantaneous precipitation does somewhat determine gage heights at those sites, reservoir releases are
typically what control the stages. The 46 sites that were therefore left to analyze are
indicated by an asterisks (*) in Table 3.1. The number of actual precipitation/stream
response samples for each site varied, ranging from three to 17.
111 5.1.2 Review of flash flooding situation
Of the 46 sites left, 29 (63%) have a flood stage (FS) determined. No sites rose above FS for the 26 August 2002 case; unfortunately, there were no gages located where the heaviest
rainfall occurred during the worst of the event. Four sites (9%) experienced a rapid rise, but
did not flood, and two sites (4%) experienced a rapid rise but have no FS determined. For
the 11 October 2002 case, six sites (13%) experienced flood conditions, and of those six, four
of them (66%) qualified as flash floods, while the others met the definition of a flood. Nine
sites (20%) rose rapidly, but did not reach flood stage, although in some cases the water was
literally inches from that level. Eight (17%) sites rose rapidly due to the heavy rainfall but
did not have a pre-determined flood stage.
During the 9-10 April 2003 event, only four (9%) of the 46 sites left for analysis rose
above flood stage, and only one of those four (25%) could qualify as a flash flood. Of the
sites that did not reach their FS, five (11%) sites underwent a rapid rise. Similarly, nine sites
rose rapidly but had no determined FS. For 16 June 2003, none of the sites in the analysis
rose above flood stage, although the Rocky River near Norwood in Stanly County, which
was not left in the final analysis due to the lack of events analyzed, did experience a flash
flood. During this event, 14 sites (30%) experienced a rapid rise, but did not reach FS, and
nine sites (20%) experienced a rapid rise, but did not have a pre-determined FS.
Similarly, in the 29 July 2003 case, no sites rose above flood stage. However, 20
locations (43%) underwent a rapid rise of water. 10 sites (22%) experienced a rapid water
rise, but had no flood stage determined for those locations. And for the 9 August 2003 case,
two sites flooded, but neither of them experienced the kind of rise that would qualify as a
flash flood. Again, 20 sites (43%) experienced a rapid rise of water but did not reach FS, and
112 eight sites (17%) experienced the same rapid rise, but had no pre-determined FS. Fig. 5.1 gives this information in graphical format.
It is known that in some cases, the most serious flash flooding, or the flash flooding with the most significant impacts, occurred where there was no USGS stream gage. For example, the 26 August 2002 flash flooding occurred in the northeast parts of the CWA, in Vance and
Warren Counties, with no gages nearby. The 16 June 2003 fatalities occurred along a small creek in Stanly County; the nearest gage is the Rocky River near Norwood, and as a result of the elimination process, that particular site was not included in the final analysis. The Pisgah
Covered Bridge, washed out during the 9 August 2003 event, was constructed over a tributary of the Little River in Randolph County. As was noted in section 4.7.2, the nearest stream gage to this location is the Deep River at Ramseur, to the north and east.
The first two cases, 26 August and 11 October 2002, occurred during extreme to exceptional drought conditions. The last four cases, those during the spring and summer of
2003, occurred with very high antecedent soil moisture conditions, when the area was experiencing above-normal rainfall. The two events with the most extreme antecedent conditions were 26 August 2002, the driest, and 9-10 April 2003, the wettest. Clay soil is that texture which often has the most variability; under very dry conditions it will crack, allowing more infiltration, yet it will harden at the surface, inhibiting infiltration. However, once a raindrop hits clay soil, the soil swells, thereby further inhibiting infiltration (Dingman
2002). Loam and silt have a similar process, albeit each less extreme than clay. During the
26 August 2002 event, the drought-hardened soils across most of the Raleigh CWA seemed to behave much like clay soils, allowing very little water to infiltrate. The extremely moist
113 soils during the 9-10 April 2003 event also allowed very little water to infiltrate, simply because they were near saturation.
5.2 Statistical calculations
Several variables were investigated after the final list of sites was established. Both the rain rate and the actual precipitation amount for each distinct rise in the stream were determined. The amount of time between when the stream began its rise and when the maximum stage was reached was determined as well and was designated as the stream rise time (SRT). The amount of time between the onset of precipitation and the initial response of the stream was described as the lag time. In addition, not only was the maximum stage attained by the stream determined, but the change in height (∆H) of the stream was recorded as well, as some rises were logically more significant than others. Finally, the rate of change of stream rise (∆H/∆t), to ascertain how rapid the stream’s response was to the precipitation, was computed as well. Fig. 5.2, an input precipitation hyetograph and a stream response hydrograph, gives a graphical example of how these variables were computed. More of these figures, but without the computations, are given in Appendix A.
Means, standard deviations, and 95% confidence intervals on the means of these variables (that is, maximum stage, SRT, lag time, ∆H, and ∆H/∆t) for all 46 sites were calculated, as well as correlations between these variables to rain rate and precipitation amount (Fig. 5.3, see below). The correlations were computed as
1 n ()x − x ()y − y n −1∑ i i r = i=i , [5.1] σ xσ y where
114 n 1 2 σ = ∑(xi − x) [5.2] n −1 i=1
(Tamhane and Dunlop 2000). Correlations (positive or negative) between 0 and 0.29 are classified as “weak,” those between 0.3 and 0.69 are considered “moderate,” and those that fall above 0.7 are considered “strong.” The correlations were then analyzed with respect to landcover and soil type. It must be remembered that correlation does not necessarily imply causation; however, in these cases, it is understood that a stream responds to either input precipitation or to water flowing from upstream. Those situations where rises were possibly due to the latter situation, although a flash flood can occur under those conditions, were not included in the analysis, and therefore it is felt that correlations can indeed describe a cause- and-effect relationship for this type of research. The two-sided 95% confidence interval is computed using what is known from the normal distribution; if µ is the population mean, then there is a 95% probability that the sample mean X will fall within a distance of
1.96σ√n from µ (Tamhane and Dunlop 2000):
⎡ σ σ ⎤ P⎢µ −1.96 ≤ X ≤ µ +1.96 ⎥ = 0.95 . [5.3] ⎣ n n ⎦
Fig. 5.3 illustrates the weak, moderate, and strong negative and positive correlations between the variables listed above: the inputs, rain rate and precipitation amount to the stream responses, SRT, lag time, maximum stage, ∆H, and ∆H/∆t. The first set of correlations are those between rain rate and SRT, and displayed are the number of sites with strong negative, moderate negative, weak negative, weak positive, moderate positive, and strong positive correlations, respectively. Following rain rate and SRT are the correlations between precipitation amount and SRT, after which are the same for rain rate/precipitation
115 amount and lag time, and so on. If the correlations in the moderate categories are concentrated toward either the weak or strong side, it will be mentioned below.
5.3 Correlations
5.3.1 Stream rise time
One must consider aspects such as drainage area or basin size that might factor into this variable. Of all sites, 26 had a correlation between rain rate and SRT less than -0.5.
However, only three sites had correlations less than -0.5 between precipitation amount and
SRT. Most of the sites (32) had positive correlations between the latter two, whereas only two sites had positive correlations between rain rate and SRT. The number of weak, moderate, and strong relationships can be seen graphically in Fig. 5.3. Therefore, one can conclude from these data that higher rates of rainfall will, in general, lead to a stream in the
Raleigh CWA reaching its maximum stream stage more quickly. However, large amounts of precipitation do not necessarily mean that there will be a small SRT.
There seemed to be no distinct pattern between the soil types or landcover classes for the correlations between rain rate and SRT. Geographically, all of the USGS sites along
Crabtree Creek in Wake County had similar correlations, between -0.1 and -0.4, but sites along North and South Buffalo Creeks in Guilford County did not. It is interesting to note all the sites in urban locations (i.e., those with “high-” or “low-intensity developed” landcover classes, as in Table 3.1, and those surrounded by developed areas although their individual class was not considered developed, hereafter referred to as “quasi-developed”) have positive correlations between precipitation amount and SRT. In addition, 85% of the sites with loamy
116 soil fall into this same category of correlations between precipitation amount and SRT. Both sites with channery-silt loam5 soil had a correlation between rain rate and SRT near -0.7; hence a significant amount of rock in the soil, a higher rainfall rate would likely mean a smaller SRT.
5.3.2 Lag time
In this situation, 15 sites had correlations less than -0.5 between rain rate and lag time, while only four had the same between precipitation amount and lag time. Moderate to strong negative relationships were noted between rain rate and lag time in 63% of the sites, while
52% of the sites had a weak (positive and negative) relationship between precipitation amount and lag time (Fig 5.3). Again, one can conclude that high rates of precipitation will lead to rapid stream responses. However, again, this is not necessarily true with the actual precipitation amount. This may lead one to investigate further to determine the cause.
Inspecting the data for sites with the weak correlations, one can see that these specific streams responded quickly to any amount of precipitation, although as was mentioned above higher rates seemed to influence response time. It was also noted that many of these streams with weak correlations are located in urban areas; 25% of the weak-relationship sites have developed landcover classes, while 38% of the sites were in quasi-developed. Runoff, then, from these areas, notably Raleigh, Durham, and Greensboro, would reach these streams quickly, and thus the lag time would understandably be small, regardless of the amount of precipitation. There seemed to be no distinct relationship between soil type and these correlations.
5 Channery soil is by volume at least 15% thin fragments of shale, sandstone, slate, limestone, or other flat rock.
117
5.3.3 Maximum stream stage
Correlations between rain rate and maximum stream stage, and precipitation amount and maximum stage were quite different. For the former, 72% of sites had negative correlations, while 89% of correlations were positive for the latter. There were 10 sites with correlations below -0.5 between rain rate and maximum stage, while 26 sites had correlations above 0.5 between precipitation amount and the same. Weak, strong, and moderate relationships are again shown in Fig 5.3. One can conclude that maximum stage is far more dependent upon the amount of precipitation than the rate of rainfall. However, one may ask why higher rainfall rates might mean a lower maximum stream stage; investigating the data, the lowest rainfall rates were typically seen during the 9-10 April 2003 event. However, stream stages were initially high (section 4.4.1), and therefore the maximum stages reached during this event were some of the highest stages reached for all six events. Therefore, while this event may skew the data somewhat, it does add the information that with high initial stream levels, even small precipitation rates and amounts can cause streams to overflow their banks.
Most of the sites with developed or quasi-developed landcover classes (15 sites total) had correlations above 0.5 between precipitation amount and maximum stream stage.
However, there seemed to be no specific relationship between the landcover and the correlation between rain rate and maximum stage. Five (50%) of the sandy loam sites had correlations less than 0.2 (ranging to -0.9) between precipitation amount and maximum stage, and all of the sites with loamy soil had positive correlations between the same. No other significant relationship between soil and these correlations was determined.
118 5.3.4 Change in height of stream stage
Much like the maximum stream stage correlations, the change in stream height (∆H) correlations were significantly different between rain rate and precipitation amount. There were negative correlations seen between rain rate and ∆H for 54% of the sites, while 93% of the correlations between precipitation amount and ∆H are positive. Between the latter, 80% of the correlations are above 0.5. Refer to Fig. 5.3 for the number of weak, moderate, and strong relationships. This leads us to the understanding that while the rate of rainfall has little influence on the amount of change in stream rise, the amount of precipitation does, and a significant influence at that. That is, a forecaster expecting a large amount of precipitation can therefore expect any one of the streams across the CWA to rise by a considerable amount. However, a forecaster must remember that unless the banks of a particular stream are quite steep, the ∆H will increase only slightly once a stream floods.
It is interesting to note that of the urban (developed and quasi-developed) locations, sites along Crabtree Creek in Wake County have a stronger relationship between precipitation amount and ∆H than do those along North and South Buffalo Creeks in Guilford County. In general, the urban sites in Durham County also have a stronger relationship to ∆H than those in Guilford County. Another interesting observation is that the locations with stronger positive relationships between rain rate and ∆H are closer to the headwaters of the stream on which they are located: Rocky Branch below Pullen Drive at Raleigh (Wake County), South
Buffalo Creek near Pomona (Guilford County), Unnamed Tributary to Swift Creek near
Yates Mill Pond (Wake County), North Buffalo Creek at Westover Terrace at Greensboro
(Guilford County), Pigeon House Creek at Cameron Village at Raleigh (Wake County), and
Crabtree Creek at Highway 70 at Raleigh (Wake County), just to name a few. It is likely that
119 since these locations have a smaller drainage area, a higher rainfall rate, regardless of the duration, can indeed mean a large ∆H; this is something for forecasters to bear in mind.
The two sites with channery-silt loam soil had similar correlations between precipitation amount and ∆H, between 0.65 and 0.7. In addition, three sites with fine sandy loam soil were analyzed, all of which had correlations between the same of 0.7 to 0.81. No other significant relationships between soil type and the correlations were evident.
5.3.5 Rate of change of stream rise
Mostly positive correlations were computed between the rate of change of stream rise and both rain rate and precipitation amount. 80% of the former were positive, while 91% of the latter were positive. However, 52% of the correlations between rain rate and ∆H/∆t were above 0.5, while 41% of the correlations between precipitation amount and ∆H/∆t were above that value. Again, Fig. 5.3 displays the number of weak, moderate, and strong relationships. One can see that more strong relationships were found between rain rate and
∆H/∆t than between precipitation amount and ∆H/∆t. Considering this information along with the correlations computed in section 5.2.4, one might say that precipitation amount is more significant in the amount of stream rise, but precipitation rate is more significant in determining the rate of stream rise. The latter is not considerably more significant than precipitation amount for ∆H/∆t, but at least somewhat more so.
Considering landcover classes against the correlations in both cases, there were no noteworthy relationships; even the urban areas had both weak and strong correlations. In addition, the soil types had no notable relationships. Therefore, the conclusions to be drawn
120 from these correlations are only general ones about the CWA as a whole, rather than from specific landcover areas or soil types.
5.4 Confidence intervals
More will be discussed regarding this topic in section 6.2, with respect to the possibilities of future research. However, given the largest unknown associated with this research – the fact that several of the USGS gage sites have no flood stage determined – perhaps some of the confidence interval calculations can be of use to the forecasters at the NWS in Raleigh in determining when some of these particular streams may be reaching their actual inundation or flood stages. Impacts are, of course, also a determining factor, but these data may at least assist in the NWS mission of protecting life and property. Tables 5.1 and 5.2 list these sites with undetermined flood stages, the number of samples involved, the means for the five variables outlined above, and the 95% confidence intervals. Given these values, along with the figures in Appendix A, operational meteorologists may now have a general idea as to when problems may be occurring along these creeks, especially when compared to known flood stages along other streams.
121 Table 5.1. Means and 95% confidence intervals (CI) for the stream rise times (SRT) and lag times of the sites listed below, in units of hours. The number of total samples from all six events is also listed. USGS Site Name Samples SRT Mean SRT CI Lag Mean Lag CI BUCKHORN CREEK NR CORINTH, NC 10 5.33 2.98,7.68 0.60 0.42,0.78 TICK CREEK NEAR MOUNT VERNON SPRINGS, NC 7 6.54 3.70,9.38 0.68 0.33,1.03 MOUNTAIN CREEK AT SR1617 NR BAHAMA, NC 8 3.28 2.33,4.23 0.66 0.25,1.07 LITTLE RIVER AT SR1461 NEAR ORANGE FACTORY, NC 8 6.38 3.14,9.62 0.78 0.47,1.09 EAST FORK DEEP RIVER NEAR HIGH POINT, NC 9 5.69 3.24,8.14 0.83 0.49,1.17 DUTCHMANS CREEK NR UWHARRIE, NC 11 4.41 2.90,5.92 1.18 0.81,1.55 MORGAN CREEK NEAR CHAPEL HILL, NC 6 5.17 1.24,9.10 0.67 0.34,1.00 CANE CREEK NEAR ORANGE GROVE, NC 6 7.63 4.16,11.10 0.83 0.30,1.36 MORGAN CREEK NEAR WHITE CROSS, NC 6 6.46 4.10,8.82 0.75 0.20,1.30 BIG BEAR CR NR RICHFIELD, NC 9 4.92 3.18,6.66 1.06 0.54,1.58 MARSH C NR NEW HOPE, NC 12 3.44 2.26,4.62 0.33 0.24,0.42 PIGEON HOUSE CR AT CAMERON VILLAGE AT RALEIGH, NC 16 1.20 0.70,1.70 0.38 0.20,0.56 ROCKY BRANCH BELOW PULLEN DRIVE AT RALEIGH, NC 17 1.41 0.80,2.02 0.50 0.26,0.74 WALNUT CREEK AT SUNNYBROOK DRIVE NR RALEIGH, NC 7 10.43 5.23,15.63 1.29 0.77,1.81 UNNAMED TRIB TO SWIFT CR NR YATES MILL POND, NC 12 1.88 1.31,2.45 0.35 0.21,0.49 SWIFT CREEK NEAR APEX, NC 10 6.30 4.05,8.55 0.83 0.27,1.39 NAHUNTA SWAMP NEAR PIKEVILLE, NC 7 7.68 1.98,13.38 0.64 0.23,1.05
122
Table 5.2. Means and 95% confidence intervals (CI) for the maximum stream stage (ft), change in stream stage (ft), and rate of -1 change of stream stage (ft hr ) of the sites listed below (the site names have been abbreviated from Table 5.1). The number of tota l samples is the same as in Table 5.1. USGS Site Name Max Stage Mean Max Stage CI ∆H Mean ∆H CI ∆H/∆t Mean ∆H/∆t CI BUCKHORN CREEK 4.31 2.61,6.01 1.33 0.19,2.47 0.21 0.03,0.39 TICK CREEK 6.16 5.05,7.27 2.97 1.85,4.09 0.55 0.35,0.75 MOUNTAIN CREEK 6.41 4.53,8.29 1.95 0.15,3.75 0.23 0.09,0.37 LITTLE RIVER 4.43 2.30,6.56 2.20 0.30,4.10 0.28 0.06,0.50 EAST FORK DEEP RIVER 7.08 5.53,8.63 3.82 2.44,5.20 0.87 0.54,1.20 DUTCHMANS CREEK 4.42 3.39,5.45 2.43 1.56,3.30 0.86 0.23,1.49 MORGAN CREEK NEAR CHAPEL HILL 7.41 4.67,10.15 2.83 0.43,5.23 0.54 0.38,0.70 CANE CREEK 3.68 2.04,5.32 1.98 0.68,3.28 0.23 0.11,0.35 MORGAN CREEK NEAR WHITE CROSS 6.11 3.94,8.28 2.71 1.04,4.38 0.42 0.12,0.72 BIG BEAR CR 6.95 3.67,10.23 4.54 1.83,7.25 0.94 0.27,1.61 MARSH C 6.19 4.78,7.60 2.39 0.96,3.82 0.84 0.40,1.28 PIGEON HOUSE CR 2.97 2.00,3.94 1.30 0.40,2.20 1.43 0.31,2.55 ROCKY BRANCH 5.23 4.59,5.87 1.21 0.55,1.87 1.24 0.56,1.92 WALNUT CREEK 6.69 4.95,8.43 3.61 1.91,5.32 0.42 0.26,0.58 UNNAMED TRIB TO SWIFT CR 1.73 1.56,1.90 0.39 0.21,0.57 0.27 0.12,0.42 SWIFT CREEK 7.78 6.32,9.24 4.35 2.84,5.86 0.74 0.55,0.93 NAHUNTA SWAMP 6.34 4.61,8.07 1.35 0.61,2.09 0.20 0.15,0.25
123 Flash Flooding Overview
25
20 Rose above flood stage (both flood and flash flood) 15 Flash flooded
Rose rapidly, did not reach 10 flood stage er of USGS Sites b Rose rapidly, no determined flood stage Num 5
0 26 11 9-10 16 June 29 July 9 August October April 2003 2003 August 2002 2002 2003 2003 Event
FIG. 5.1. Number of USGS sites for each case that experienced various conditions. Shown are the sites that rose above flood stage (including both floods and flash floods), those that qualified as flash floods, those that experienced a rapid rise but did not rise above flood stage, and those that experienced a rapid rise but did not have a pre-determined flood stage.
124 Time vs. Precipitation, Gage Height (Crabtree Creek @ Ebenezer Church Road near Raleigh 10-11 Oct 2002) 1.00 20 Precipitation FS = 19ft Maximum stage 18 Gage Height 16
) 0.75 n
i ∆H (divide 14 (ft) (
by SRT to t n
12 h get ∆H/ ∆t) g io i t e a 0.50 10 it H e ip Lag time 8 c SRT g e a
r 6 G P 0.25 4 2 0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 :1 :1 :1 :1 :1 :1 :1 :1 :1 :1 :1 :1 :1 3 6 5 8 6 8 1 00 0 0 09 12 1 1 21 00 03 0 09 12 15 1 2 Local Time (15 min)
FIG. 5.2. Precipitation and stream response for the USGS gage site at Crabtree Creek at Ebenezer Church Road in Raleigh during the 11 October 2002 event. Flood stage is 19 ft for this location. Graphically, the methodology to determine stream rise time (SRT) (the amount of time between when the stream began its rise and when the maximum stage was reached), the lag time (the amount of time between the onset of precipitation and the initial response of the stream), the maximum stage, the change in height (∆H) of the stream, and the rate of change of stream rise (∆H/∆t) is displayed.
125
Correlations between Rain Rate, Precipitation Accumulation and Computed Variables
30 -1.0 to -0.7 25 -0.69 to -0.3 20 -0.29 to 0 15 0 to 0.29 0.3 to 0.69 10 0.7 to 1.0 Number of Sites 5
0
e me g RRT Time ta , , RRT Ti S Stage ip g x
Prec p, La , Ma ci Rain Rate Rate, Lagre ecip, Max in P Rate r a in P R a R Correlations
FIG. 5.3. Correlations between rain rate and precipitation accumulation to stream rise time (SRT) (hr), lag time (hr), maximum stream stage (ft), change in stream stage (∆H) (ft), and rate of change of stream stage (∆H/ ∆t) (ft hr-1).
126 6. CONCLUSIONS AND FUTURE RESEARCH
6.1 Conclusions
One must bear in mind that with only six cases studied, a comprehensive climatology of flash flooding cannot be compiled for the Raleigh CWA. However, based upon the analysis of the 46 sites, the information gathered from the sites left out of the final analysis, and the case studies themselves, the following conclusions can be drawn regarding stream responses:
• Flash flooding does not tend to occur on the mainstem rivers, unless the site is near
the headwater of the river.
• Flash flooding does not tend to occur immediately downstream from a controlled
dam, regardless of stream size.
• Sites with higher sand content in the soil tend to respond little if at all to precipitation,
as infiltration is high and runoff is low.
• In extremely dry areas, some soil types tend to become more impervious, especially
those soils with higher clay content. Runoff is increased in these situations.
• High rainfall rates generally lead to small time periods between when the stream
begins to rise and when the maximum stage is reached (stream rise time).
• High rainfall rates generally lead to rapid stream responses (lag time).
• Sites with higher rock content (channery) in the soils tend to have a lower stream rise
time.
• In urban areas, typically any amount of precipitation has a rapid stream response.
• Larger amounts of precipitation, regardless of the period of time in which it falls,
generally lead to higher stream levels.
127 • Small rainfall rates can lead to very high stream levels if antecedent conditions are
extremely moist.
• Larger amounts of precipitation generally lead to larger changes in stream height,
whereas the precipitation rate has less of an influence.
• Sites near the headwaters of a stream tend to have a stronger relationship between
precipitation and change in stream height than those downstream.
• Rain rate tends to be more significant when considering rate of change of stream rise,
but when considering the amount of stream rise itself, precipitation amount tends to
have a stronger relationship.
• In the higher-impact basins of Crabtree Creek and North and South Buffalo Creeks,
all sites along Crabtree Creek tend to have similar responses to each other during each
event, while sites in the Buffalo Creek basins can have very dissimilar responses
during any given event.
Given these conclusions, it is imperative, then, for forecasters to monitor the basin graphs of ABR and BRA in FFMP during a flash flood situation, as well as the stream responses. If in an urban and extremely dry areas, adjusting thresholds downward, as has typically been done, should continue to be a practice, and it might be advantageous to remember the importance of infiltration in sandy soils during a heavy rainfall event.
Unfortunately, fewer conclusions than expected were drawn regarding soil type and landcover. This may be partly because all soil types in the remaining 46 sites consisted of some version of loam. However, it is evident that streams in urban locations respond more quickly than those in non-urban locations.
128 6.2 Future research
Had time permitted, it would have been beneficial to perform sensitivity tests utilizing a
hydrological model in order to study in greater detail the influence of hydrological factors on stream response. If a three-dimensional model were available, especially one with overland flow or river routing (the capability to model flow from upstream), many other factors could be incorporated into the study, including terrain. Such a study would assist in determining exactly what land-surface factors are most conducive to flash flooding across the CWA.
With the 95% confidence intervals computed for the means of the variables discussed in section 5 (maximum stage, SRT, lag time, ∆H, and ∆H/∆t), future work would include
expanding that information for the prediction of the same for a future event based on past
cases. Forecasters could then anticipate the outcome of these variables given what they
know (input precipitation or rainfall rate). In addition, this might easily be expanded; if one
uses a sample including one specific soil type or landcover category, the confidence interval
would represent the likelihood of the variable (i.e., lag time, ∆H, etc.) occurring for that soil
type or landcover category. Samples could also be created based on ranges of precipitation
totals or rainfall rates, and confidence intervals for the above variables for any one site, or a
series of sites along a basin, could be studied. The option of utilizing the above mentioned
hydrological model in conjunction with such studies could also be useful. Numerous options
are available to assist the forecasters at the NWS in Raleigh in their flash flood operations;
these are just a few. The result of the above confidence interval analyses would be an
extensive database for locations across the Raleigh CWA that would guide forecasters to
make conclusions regarding flooding severity based on any combination of the
aforementioned variables.
129 The Forced FFG application now available as part of FFMP allows the user to adjust FFG
from the RFC by a certain amount or the user may input a new value to replace the RFC’s
value. However, this is an arbitrary process; it is difficult to know by how much the FFG
should be adjusted, or what the new value should be. Further research, especially with a
hydrological model, utilizing soil moisture and perhaps including additional case studies
would perhaps provide forecasters with enough information to be able to adjust these values
with higher levels of confidence.
Since AMBERGIS is now combined with a GIS, the user has the capability of integrating
any spatial information desired into the flash flood monitoring process. If run in an
operational setting, it would be advantageous to include landcover and soil type, especially if any one certain category of either is more prone to flash flooding, when AMBER is run.
Smith (2002) describes how the Western Region of the NWS along with the Colorado Basin
RFC collaborated on a project to create a Flash Flood Potential Index – a small-stream basin level index based on factors such as soil type, landuse, terrain, and the amount of rock in the soil to indicate a static relative flash flood potential. This might also include information regarding vegetation canopy, as canopy interception might also play a role in flash flooding.
Such a project could be done for the Raleigh CWA and could be incorporated into
AMBERGIS such that the forecasters would be alerted earlier than they might otherwise be based on a higher flash flood potential. These proposals and indeed this research play a part in the objective outlined in the NWS mission statement: to protect lives and property.
130 REFERENCES
Arthur, Ami, and K. W. Howard, 2000. Evaluation of the Areal Mean Basin Estimated Rainfall (AMBER) flash flood algorithm at the Tulsa, OK and Sterling, VA NWSFOs. Preprints, Precipitation Extremes: Prediction, Impacts, and Responses, Seattle, WA, Amer. Metr. Soc., P2.39.
____, R. S. Davis, and P. Jendrowski, 2003. Why customize Flash Flood Monitoring and Prediction watersheds? Preprints, 17th Conference on Hydrology, Long Beach, CA, Amer. Metr. Soc., CD-ROM, JP3.10.
Austin, Pauline M., 1987: Relation between measured radar reflectivity and surface rainfall. Mon. Wea. Rev., 115, 1053–1053.
Baeck, Mary L., and J. A. Smith, 1998: Rainfall estimation by the WSR-88D for heavy rainfall events. Wea. Forecasting, 13, 416–436.
Borneman, Richard, 2000: Satellite rainfall estimates in SAB: Moving from IFFA heavy rainfall estimates to the automatic estimator. Presented at the National Weather Association Annual Meeting, October 2000.
_____, 2002: 2001 summary of the precipitation program in SAB. NOAA-NESDIS Memo, 13 pp. [Available online at http://www.ssd.noaa.gov/PS/PCPN/2001SUMMARYforDist.pdf.]
_____, 2003: 2002 summary of the precipitation program in SAB. NOAA-NESDIS Memo, 14 pp. [Available online at http://www.ssd.noaa.gov/PS/PCPN/2002PrecipSummary.pdf.]
Cataneo, Robert, 1969: A method for estimating rainfall rate-radar reflectivity relationships. J. Appl. Meteor., 8, 815–819.
Davis, Robert S., 2003. Some practical applications of FFMP. Preprints, 17th Conference on Hydrology, Long Beach, CA, Amer. Metr. Soc., CD-ROM, JP4.7.
Dingman, S. L., 2002: Physical Hydrology. 2d ed. Prentice Hall, 646 pp.
Doswell, Charles A. III, 1994: Flash flood-producing convective storms: Current understanding and research. Report of the Proceedings (1994) of the U.S.-Spain Workshop on Natural Hazards, Barcelona, Spain, pp. 97-107. [Available from the Iowa Institute of Hydraulic Research, University of Iowa, Iowa City, Iowa 52421.]
_____, H. E. Brooks, and R. A. Maddox, 1996: Flash flood forecasting: An ingredients- based methodology. Wea. Forecasting, 11, 560-581.
131 Doviak, R. J. and D. S. Zrnić, 1993: Doppler Radar and Weather Observations. 2d ed. Academic Press, 562 pp.
Elsner, James B., W. H. Drag, and J. K. Last, 1989: Synoptic weather patterns associated with the Milwaukee, Wisconsin flash flood of 6 August 1986. Wea. Forecasting, 4, 537-554.
Fortune, Michael A., 1998: Automated satellite-based estimates of precipitation: an assessment of accuracy. NOAA-NESDIS Tech. Rep. 90, 42 pp.
Fulton, Richard A., J. P. Breidenbach, D. J. Seo, D. A. Miller, and T. O’Bannon, 1998: The WSR-88D rainfall algorithm. Wea. Forecasting, 13, 377–395.
Funk, Theodore W., 1991: Forecasting techniques utilized by the Forecast Branch of the National Meteorological Center during a major convective rainfall event. Wea. Forecasting, 6, 548-564.
Helble, T., 2002. Definitions and general terminology. National Weather Service Instruction 10-950, 3 pp. [Available online at http://www.nws.noaa.gov/directives/010/pd01009050a.pdf.]
____, 2003a. River Forecast Center operations. National Weather Service Instruction 10- 911, 8 pp. [Available online at http://www.nws.noaa.gov/directives/010/pd01009011b.pdf.]
____, 2003b. River Forecast Center products specification. National Weather Service Instruction 10-912, 20 pp. [Available online at http://www.nws.noaa.gov/directives/010/pd01009012b.pdf.]
____, 2004. Geographic areas of responsibility. National Weather Service Instruction 10- 903, 11 pp. [Available online at http://www.nws.noaa.gov/directives/010/pd01009003c.pdf.]
Holton, James R., 1992: An Introduction to Dynamic Meteorology, 3d ed. Academic Press, 511 pp.
Jendrowski, Paul, 1997: pps_pdf. NWS.
____, 2001, cited 2004: The Areal Mean Basin Estimated Rainfall (AMBER) flash flood algorithm as an AWIPS local application. [Available online at http://www.erh.noaa.gov/rnk/amber/doc/amber_awipsweb.htm]
Konrad II, Charles E., 1994: Moisture trajectories associated with heavy rainfall in the Appalachian region of the United States. Physical Geography, 15, 227-248.
132 ____, 1997: Synoptic-scale features associated with warm season heavy rainfall over the interior Southeastern United States. Wea. Forecasting, 12, 557-571.
LaPenta, Kenneth D., B. J. McNaught, S. J. Capriola, L. A. Giordano, C. D. Little, S. D. Hrebenach, G. M. Carter, M. D. Valverde, and D. S. Frey, 1994: The challenge of forecasting heavy rain and flooding throughout the Eastern Region of the National Weather Service. Part I: characteristics and events. Wea. Forecasting, 10, 78-90.
Lazo, A. F., 2002a. Monthly report of river/flood conditions: July 2002. NWS Form E-5, U.S. Department of Commerce, 1 pp. [Available from the National Weather Service in Raleigh, NC.]
____, 2002b. Monthly report of river/flood conditions: August 2002. NWS Form E-5, U.S. Department of Commerce, 1 pp. [Available from the National Weather Service in Raleigh, NC.]
____, 2002c. Monthly report of river/flood conditions: September 2002. NWS Form E-5, U.S. Department of Commerce, 1 pp. [Available from the National Weather Service in Raleigh, NC.]
____, 2002d. Monthly report of river/flood conditions: October 2002. NWS Form E-5, U.S. Department of Commerce, 1 pp. [Available from the National Weather Service in Raleigh, NC.]
____, 2003a. Monthly report of river/flood conditions: March 2003. NWS Form E-5, U.S. Department of Commerce, 1 pp. [Available from the National Weather Service in Raleigh, NC.]
____, 2003b. Monthly report of river/flood conditions: April 2003. NWS Form E-5, U.S. Department of Commerce, 1 pp. [Available from the National Weather Service in Raleigh, NC.]
____, 2003c. Monthly report of river/flood conditions: May 2003. NWS Form E-5, U.S. Department of Commerce, 1 pp. [Available from the National Weather Service in Raleigh, NC.]
____, 2003d. Monthly report of river/flood conditions: June 2003. NWS Form E-5, U.S. Department of Commerce, 1 pp. [Available from the National Weather Service in Raleigh, NC.]
____, 2003e. Monthly report of river/flood conditions: July 2003. NWS Form E-5, U.S. Department of Commerce, 1 pp. [Available from the National Weather Service in Raleigh, NC.]
133 ____, 2003f. Monthly report of river/flood conditions: August 2003. NWS Form E-5, U.S. Department of Commerce, 2 pp. [Available from the National Weather Service in Raleigh, NC.]
____, and M. Moneypenny, 2004. Raleigh hydrology station duty manual, National Weather Service, Raleigh, NC, 23 pp. [Available from the National Weather Service in Raleigh, NC.]
Maddox, Robert A., 1979: Methodology for forecasting heavy convective precipitation and flash flooding. Natl. Wea. Dig, 4, 30-42.
____, C. F. Chappell, and L. R. Hoxit, 1979: Synoptic and meso-alpha scale aspects of flash flood events. Bull. Amer. Meteor. Soc., 60, 115-123.
Marshall, J. S., and W. M. Palmer, 1948: The distribution of raindrops with size. J. Meteor., 5, 165-166.
National Cartography and GIS Center, 1991: State Soil Geographic (STATSGO) data base data use information. National Soil Survey Center Miscellaneous Publication Number 1492, Natural Resources Conservation Service, United States Department of Agriculture, 113 pp. [Available from the U.S. Department of Agriculture, Natural Resources Conservation Service, P.O. Box 6567, Fort Worth, TX 76115-0657.]
NOAA News Online, cited 2004a. Drought affects half of the contiguous States; Temperatures much warmer than 100-year average in July. [Available online at http://www.noaanews.noaa.gov/stories/s965.htm.]
____, cited 2004b. NOAA reports July cooler, wetter than average in the East, hot in the West. [Available online at http://www.noaanews.noaa.gov/stories/s2011.htm.]
North Carolina Center for Geographic Information and Analysis, 1997: Land cover – 1996, raster metadata. [Available online at http://www.cgia.state.nc.us/cgdb/lc96ras.html]
NWS Meteorological Development Laboratory, cited 2004: Flash Flood Monitoring and Prediction (FFMP). [Available online at http://www.nws.noaa.gov/mdl/ffmp/.]
NWS Office of Hydrologic Development, cited 2004: NWSRFS user manual documentation. [Available online at http://www.nws.noaa.gov/oh/hrl/nwsrfs/users_manual/htm/formats.php.]
NWS Office of Meteorology, cited 2004: 64-Year list of severe weather fatalities. [Available online at http://www.nws.noaa.gov/om/severe_weather/64yrstat.pdf.]
Opitz, Harold H., S. G. Summer, D. A. Wert, W. R. Snyder, R. J. Kane, R. H. Brady, P. M. Stokols, S. C. Kuhl, and G. M. Carter, 1994: The challenge of forecasting heavy rain
134 and flooding throughout the Eastern Region of the National Weather Service. Part II: forecast techniques and applications. Wea. Forecasting, 10, 91-104.
Rinehart, Ronald E., 1997: Radar for Meteorologists. Rinehart Publications, 428 pp.
Scofield, Roderick A., 1987: The NESDIS operational convective precipitation estimation technique. Mon. Wea. Rev., 115, 1773-1792
Smith, Greg, 2002: Flash Flood Guidance issues: CBRFC/Western Region flash flood analysis project. Presented to SVR WX/FF WDM – COMET, September 2002.
Smith, Stephan, S. K. Goel, M. T. Filiaggi, M. E. Churma, and L. Xin, 1999. Overview and status of the AWIPS System for Convective Analysis and Nowcasting – SCAN. Preprints, 14th International Conf. on Interactive Information and Processing Systems, Dallas, TX, Amer. Meteor. Soc., 326-329.
Sweeney, Timothy L. 1992: Modernized areal Flash Flood Guidance. NOAA Tech. Memo. NWS Hydro 44, 21 pp.
____, and T. F. Baumgardner, 1999: Modernized Flash Flood Guidance. NWS Office of Hydrology. [Available online at http://www.nws.noaa.gov/oh/hrl/ffg/modflash.htm.]
Tamhane, Ajit C., and D. D. Dunlop, 2000: Statistics and Data Analysi:, from Elementary to Intermediate. Prentice Hall, 722 pp.
Vicente, Gilberto A., R. A. Scofield, and W. P. Menzel, 1998: The operational GOES infrared rainfall estimation technique. Bull. Amer. Meteor. Soc., 79, 1183-1898.
Wilson, James W., and E. A. Brandes, 1979: Radar measurement of rainfall—A summary. Bull. Amer. Meteor. Soc., 60, 1048–1060.
U.S. Department of Commerce, 1999: GOES products and services catalog. 2d ed. NOAA-NESDIS, Camp Springs, MD.
____, 2002: GOES products and services catalog. 4h ed. NOAA-NESDIS, Camp Springs, MD.
Young, D., 2003: WFO public weather forecast products specification. National Weather Service Instruction 10-503, 82 pp. [Available online at http://www.nws.noaa.gov/directives/010/pd01005003a.pdf.]
135
APPENDIX
136 APPENDIX A: INPUT PRECIPITATION AND STREAM RESPONSES
Input precipitation hyetographs and stream response hydrographs from the 46 stream sites included in the final analysis are included below. Some streams included all six events in the analysis; others had only three events analyzed, while most fell in between. Those figures included are those that were analyzed. As in Table 3.1, the sites are organized by county, and subsequently by date. As the USGS gages report in increments of feet, and the
WSR-88D provides precipitation estimates in increments of inches, generic conversions are provided in Table A1 below.
Table A.1. Conversions of feet to meters and inches to millimeters, for reference in Figs. A.1-A.46 below. Feet Meters Inches Millimeters 0.50 0.1524 0.01 0.254 1.00 0.3048 0.02 0.508 2.00 0.6096 0.05 1.270 3.00 0.9144 0.10 2.540 4.00 1.2192 0.15 3.810 5.00 1.5240 0.20 5.080 6.00 1.8288 0.25 6.350 7.00 2.1336 0.30 7.620 8.00 2.4384 0.35 8.890 9.00 2.7432 0.40 10.160 10.00 3.0480 0.50 12.700 15.00 4.5720 0.60 15.240 20.00 6.0960 0.70 17.780
137 Time vs. Precipitation, Gage Height (Haw River @ Haw River 10-11 October 2002) 1.00 25 Precipitation Gage Height 20 ) 0.75 n
i FS = 18ft (ft) ( t n 15 h g io i t
a 0.50 it He e ip 10 c g e a r G P 0.25 5
0.00 0
5 15 15 15 15 :15 :15 15 15 15 15 15 15 1 15 15 15 6: 9: 5: 8: 00: 03: 0 0 12 15 18: 21: 00: 03: 06: 09: 12: 1 1 21: Local Time (15 min)
FIG A.1a. Haw River at Haw River on 11 October 2002. Flood stage is 18 ft.
Time vs. Precipitation, Gage Height (Haw River @ Haw River 15-16 June 2003) 1.00 16 Precipitation 14 Gage Height
) 0.75 12 n i (ft) ( t
n 10 h g io i t
a 0.50 8 it He e ip
c 6 g e a r G P 0.25 4 2 0.00 0
5 15 15 15 15 :15 :15 15 15 15 15 15 15 1 15 15 15 6: 9: 5: 8: 00: 03: 0 0 12 15 18: 21: 00: 03: 06: 09: 12: 1 1 21: Local Time (15 min)
FIG A.1b. Same as in a, except for 16 June 2003.
138 Time vs. Precipitation, Gage Height (Haw River @ Haw River 9-10 August 2003) 1.00 12 Precipitation Gage Height 10
) 0.75 n i (ft) ( 8 t n h g io i t
a 0.50 6 it He e ip c g
e 4 a r G P 0.25 2
0.00 0
5 15 15 15 15 :15 :15 15 15 15 15 15 15 1 15 15 15 6: 9: 5: 8: 00: 03: 0 0 12 15 18: 21: 00: 03: 06: 09: 12: 1 1 21: Local Time (15 min)
FIG A.1c. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (Buckhorn Creek near Corinth 25-26 August 2002) 1.00 1.4 Precipitation 1.2 Gage Height
) 0.75 n
i 1 (ft) ( t n h g
io 0.8 i t
a 0.50 it 0.6 He e ip c g e a r 0.4 G P 0.25 0.2
0.00 0
5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Time (15 min)
FIG A.2a. Buckhorn Creek near Corinth on 26 August 2002. No pre-determined flood stage.
139 Time vs. Precipitation, Gage Height (Buckhorn Creek near Corinth 10-11 October 2002) 1.00 7 Precipitation 6 Gage Height
) 0.75 n
i 5 (ft) ( t n h g
io 4 i t
a 0.50 it 3 He e ip c g e a r 2 G P 0.25 1
0.00 0
15 15 15 15 :15 :15 :15 15 15 15 15 15 15 15 15 :15 2: 5: 8: 00: 03: 06: 09: 12 15 18 21: 00: 03: 06: 09: 1 1 1 21 Local Time (15 min)
FIG A.2b. Same as in a, except for 11 October 2002.
Time vs. Precipitation, Gage Height (Buckhorn Creek near Corinth 8-10 April 2003) 1.00 12 Precipitation Gage Height 10
) 0.75 n i (ft) ( 8 t n h g io i t
a 0.50 6 it He e ip c g
e 4 a r G P 0.25 2
0.00 0
5 5 15 15 15 15 15 15 :15 15 :15 15 15 15 15 15 1 15 15 1 15 15 15 15 15 15 3: 9: 9: 8: 00: 0 06: 0 12: 15: 18 21: 00 03: 06: 09: 12: 15: 18: 21: 00: 03: 06: 0 12: 15: 1 21: Local Time (15 min)
FIG A.2c. Same as in a, except for 9-10 April 2003.
140 Time vs. Precipitation, Gage Height (Buckhorn Creek near Corinth 15-16 June 2003) 1.00 3
2.5
) 0.75 n i (ft) ( 2 t n h g io i t
a 0.50 1.5 it Precipitation He e ip c g
e 1 Gage Height a r G P 0.25 0.5
0.00 0
5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Time (15 min)
FIG A.2d. Same as in a, except for 16 June 2003.
Time vs. Precipitation, Gage Height (Buckhorn Creek near Corinth 29-30 July 2003) 1.00 1.8 1.6 1.4 ) 0.75 n i (ft) ( Precipitation 1.2 t n h g io Gage Height
1 i t
a 0.50 it
0.8 He e ip c g
e 0.6 a r G P 0.25 0.4 0.2 0.00 0
5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Time (15 min)
FIG A.2e. Same as in a, except for 29 July 2003.
141 Time vs. Precipitation, Gage Height (Buckhorn Creek near Corinth 9-10 August 2003) 1.00 8 7
) 0.75 6 n i (ft)
( Precipitation t
n 5 h g io Gage Height i t
a 0.50 4 it He e ip
c 3 g e a r G P 0.25 2 1 0.00 0
15 15 15 15 :15 :15 :15 15 15 15 15 15 15 15 15 :15 2: 5: 8: 00: 03: 06: 09: 12 15 18 21: 00: 03: 06: 09: 1 1 1 21 Local Time (15 min)
FIG A.2f. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (Tick Creek near Mount Vernon Springs 10-11 October 2002) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) ( t
n 5 h g io i t
a 0.50 4 it He e ip
c 3 g e a r G P 0.25 2 1 0.00 0
15 15 15 15 :15 :15 :15 15 15 15 15 15 15 15 15 :15 2: 5: 8: 00: 03: 06: 09: 12 15 18 21: 00: 03: 06: 09: 1 1 1 21 Local Time (15 min)
FIG A.3a. Tick Creek near Mount Vernon Springs on 11 October 2002. No pre- determined flood stage.
142 Time vs. Precipitation, Gage Height (Tick Creek near Mount Vernon Springs 8-10 April 2003) 1.00 9 Precipitation 8 Gage Height 7 ) 0.75 n i (ft) ( 6 t n h g io
5 i t
a 0.50 it
4 He e ip c g
e 3 a r G P 0.25 2 1 0.00 0
5 5 15 15 15 15 15 15 :15 15 15 :15 15 15 15 15 1 1 15 15 15 15 15 15 :15 :15 3: 6: 5: 6: 9: 00: 0 0 09: 12: 1 18 21: 00: 03 06: 09: 12: 15: 18: 21: 00: 03: 0 0 12: 15: 18 21 Local Time (15 min)
FIG A.3b. Same as in a, except for 9-10 April 2003.
Time vs. Precipitation, Gage Height (Tick Creek near Mount Vernon Springs 15-16 June 2003) 1.00 4.5 Precipitation 4 Gage Height 3.5 ) 0.75 n i (ft) ( 3 t n h g io
2.5 i t
a 0.50 it
2 He e ip c g
e 1.5 a r G P 0.25 1 0.5 0.00 0
5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Time (15 min)
FIG A.3c. Same as in a, except for 16 June 2003.
143 Time vs. Precipitation, Gage Height (Tick Creek near Mount Vernon Springs 29-30 July 2003) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) ( t
n 5 h g io i t
a 0.50 4 it He e ip
c 3 g e a r G P 0.25 2 1 0.00 0
15 15 15 15 :15 :15 :15 15 15 15 15 15 15 15 15 :15 2: 5: 8: 00: 03: 06: 09: 12 15 18 21: 00: 03: 06: 09: 1 1 1 21 Local Time (15 min)
FIG A.3d. Same as in a, except for 29 July 2003.
Time vs. Precipitation, Gage Height (Abbotts Creek @ Lexington 10-11 October 2002) 1.00 12 Precipitation Gage Height 10
) 0.75 n i (ft) ( 8 t n h g io i t
a 0.50 6 it He e ip c g
e 4 a r G P 0.25 2
0.00 0
5 15 15 15 15 :15 :15 15 15 15 15 15 15 1 15 15 15 6: 9: 5: 8: 00: 03: 0 0 12 15 18: 21: 00: 03: 06: 09: 12: 1 1 21: Local Time (15 min)
FIG A.4a. Abbotts Creek at Lexington on 11 October 2002. Flood stage is 17 ft.
144 Time vs. Precipitation, Gage Height (Abbotts Creek @ Lexington 15-16 June 2003) 1.00 5 4.5 4 ) 0.75 n
i 3.5 (ft)
( Precipitation t n 3 h g io Gage Height i t
a 0.50 2.5 it He e ip 2 c g e a
r 1.5 G P 0.25 1 0.5 0.00 0
5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Time (15 min)
FIG A.4b. Same as in a, except for 16 June 2003.
Time vs. Precipitation, Gage Height (Abbotts Creek @ Lexington 29-30 July 2003) 1.00 10 Precipitation 9 Gage Height 8 ) 0.75 n
i 7 (ft) ( t n 6 h g io i t
a 0.50 5 it He e ip 4 c g e a
r 3 G P 0.25 2 1 0.00 0
5 15 15 15 15 :15 :15 15 15 15 15 15 15 1 15 15 15 6: 9: 5: 8: 00: 03: 0 0 12 15 18: 21: 00: 03: 06: 09: 12: 1 1 21: Local Time (15 min)
FIG A.4c. Same as in a, except for 29 July 2003.
145 Time vs. Precipitation, Gage Height (Mountain Creek @ SR1617 near Bahama 25-26 August 2002) 1.00 6 Precipitation Gage Height 5
) 0.75 n i (ft) ( 4 t n h g io i t
a 0.50 3 it He e ip c g
e 2 a r G P 0.25 1
0.00 0
15 15 15 15 :15 :15 :15 15 15 15 15 15 15 15 15 :15 2: 5: 8: 00: 03: 06: 09: 12 15 18 21: 00: 03: 06: 09: 1 1 1 21 Local Time (15 min)
FIG A.5a. Mountain Creek at SR1617 near Bahama on 26 August 2002. No pre- determined flood stage.
Time vs. Precipitation, Gage Height (Mountain Creek @ SR1617 near Bahama 10-11 October 2002) 1.00 14 Precipitation 12 Gage Height
) 0.75 n
i 10 (ft) ( t n h g
io 8 i t
a 0.50 it 6 He e ip c g e a r 4 G P 0.25 2
0.00 0
5 15 15 15 15 :15 :15 15 15 15 15 15 15 1 15 15 15 6: 9: 5: 8: 00: 03: 0 0 12 15 18: 21: 00: 03: 06: 09: 12: 1 1 21: Local Time (15 min)
FIG A.5b. Same as in a, except for 11 October 2002.
146 Time vs. Precipitation, Gage Height (Mountain Creek @ SR1617 near Bahama 8-10 April 2003) 1.00 10 Precipitation 9 Gage Height 8 ) 0.75 n
i 7 (ft) ( t n 6 h g io i t
a 0.50 5 it He e ip 4 c g e a
r 3 G P 0.25 2 1 0.00 0
5 5 15 15 15 15 15 15 :15 15 :15 15 15 15 15 15 1 15 15 1 15 15 15 15 15 15 3: 9: 9: 8: 00: 0 06: 0 12: 15: 18 21: 00 03: 06: 09: 12: 15: 18: 21: 00: 03: 06: 0 12: 15: 1 21: Local Time (15 min)
FIG A.5c. Same as in a, except for 9-10 April 2003.
Time vs. Precipitation, Gage Height (Mountain Creek @ SR1617 near Bahama 15-16 June 2003) 1.00 5 4.5 4 ) 0.75 n
i 3.5 (ft)
( Precipitation t n 3 h g io Gage Height i t
a 0.50 2.5 it He e ip 2 c g e a
r 1.5 G P 0.25 1 0.5 0.00 0
5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Time (15 min)
FIG A.5d. Same as in a, except for 16 June 2003.
147 Time vs. Precipitation, Gage Height (Flat River @ Bahama 25-26 August 2002) 1.00 1 Precipitation 0.9 Gage Height 0.8 ) 0.75 n
i 0.7 (ft) ( t n 0.6 h g io i t
a 0.50 0.5 it He e ip 0.4 c g e a
r 0.3 G P 0.25 0.2 0.1 0.00 0
5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Time (15 min)
FIG A.6a. Flat River at Bahama on 26 August 2002. Flood stage is 12 ft.
Time vs. Precipitation, Gage Height (Flat River @ Bahama 10-11 October 2002) 1.00 12 Precipitation Gage Height 10
) 0.75 n i (ft) ( 8 t n h g io i t
a 0.50 6 it He e ip c g
e 4 a r G P 0.25 2
0.00 0
5 15 15 15 15 :15 :15 15 15 15 15 15 15 1 15 15 15 6: 9: 5: 8: 00: 03: 0 0 12 15 18: 21: 00: 03: 06: 09: 12: 1 1 21: Local Time (15 min)
FIG A.6b. Same as in a, except for 11 October 2002.
148 Time vs. Precipitation, Gage Height (Flat River @ Bahama 8-10 April 2003) 1.00 9 Precipitation 8 Gage Height 7 ) 0.75 n i (ft) ( 6 t n h g io
5 i t
a 0.50 it
4 He e ip c g
e 3 a r G P 0.25 2 1 0.00 0
5 5 15 15 15 15 15 15 :15 15 15 :15 15 15 15 15 1 1 15 15 15 15 15 15 :15 :15 3: 6: 5: 6: 9: 00: 0 0 09: 12: 1 18 21: 00: 03 06: 09: 12: 15: 18: 21: 00: 03: 0 0 12: 15: 18 21 Local Time (15 min)
FIG A.6c. Same as in a, except for 9-10 April 2003.
Time vs. Precipitation, Gage Height (Flat River @ Bahama 9-10 August 2003) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) ( t
n 5 h g io i t
a 0.50 4 it He e ip
c 3 g e a r G P 0.25 2 1 0.00 0
15 15 15 15 :15 :15 :15 15 15 15 15 15 15 15 15 :15 2: 5: 8: 00: 03: 06: 09: 12 15 18 21: 00: 03: 06: 09: 1 1 1 21 Local Time (15 min)
FIG A.6d. Same as in a, except for 9 August 2003.
149 Time vs. Precipitation, Gage Height (Eno River near Durham 25-26 August 2002) 1.00 2.5 Precipitation Gage Height 2 ) 0.75 n i (ft) ( t n 1.5 h g io i t
a 0.50 it He e ip 1 c g e a r G P 0.25 0.5
0.00 0
5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Time (15 min)
FIG A.7a. Eno River near Durham on 26 August 2002. Flood stage is 20 ft.
Time vs. Precipitation, Gage Height (Eno River near Durham 10-11 October 2002) 1.00 20 Precipitation 18 Gage Height 16 ) 0.75 n
i 14 (ft) ( t n 12 h g io i t
a 0.50 10 it He e ip 8 c g e a
r 6 G P 0.25 4 2 0.00 0
5 15 15 15 15 :15 :15 15 15 15 15 15 15 1 15 15 15 6: 9: 5: 8: 00: 03: 0 0 12 15 18: 21: 00: 03: 06: 09: 12: 1 1 21: Local Time (15 min)
FIG A.7b. Same as in a, except for 11 October 2002.
150 Time vs. Precipitation, Gage Height (Eno River near Durham 8-10 April 2003) 1.00 16 Precipitation 14 Gage Height
) 0.75 12 n i (ft) ( t
n 10 h g io i t
a 0.50 8 it He e ip
c 6 g e a r G P 0.25 4 2 0.00 0
5 5 15 15 15 15 15 15 :15 15 :15 15 15 15 15 15 1 15 15 1 15 15 15 15 15 15 3: 9: 9: 8: 00: 0 06: 0 12: 15: 18 21: 00 03: 06: 09: 12: 15: 18: 21: 00: 03: 06: 0 12: 15: 1 21: Local Time (15 min)
FIG A.7c. Same as in a, except for 9-10 April 2003.
Time vs. Precipitation, Gage Height (Eno River near Durham 15-16 June 2003) 1.00 4 Precipitation 3.5 Gage Height
) 0.75 3 n i (ft) ( t
n 2.5 h g io i t
a 0.50 2 it He e ip
c 1.5 g e a r G P 0.25 1 0.5 0.00 0
5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Time (15 min)
FIG A.7d. Same as in a, except for 16 June 2003.
151 Time vs. Precipitation, Gage Height (Eno River near Durham 9-10 August 2003) 1.00 12 Precipitation Gage Height 10
) 0.75 n i (ft) ( 8 t n h g io i t
a 0.50 6 it He e ip c g
e 4 a r G P 0.25 2
0.00 0
5 15 15 15 15 :15 :15 15 15 15 15 15 15 1 15 15 15 6: 9: 5: 8: 00: 03: 0 0 12 15 18: 21: 00: 03: 06: 09: 12: 1 1 21: Local Time (15 min)
FIG A.7e. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (Little River @ SR1461 near Orange Factory 25-26 August 2002) 1.00 1.2 Precipitation Gage Height 1
) 0.75 n i (ft) ( 0.8 t n h g io i t
a 0.50 0.6 it He e ip c g
e 0.4 a r G P 0.25 0.2
0.00 0
5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Time (15 min)
FIG A.8a. Little River at SR1461 near Orange Factory on 26 August 2002. No pre- determined flood stage.
152 Time vs. Precipitation, Gage Height (Little River @ SR1461 near Orange Factory 10-11 October 2002) 1.00 10 Precipitation 9 Gage Height 8 ) 0.75 n
i 7 (ft) ( t n 6 h g io i t
a 0.50 5 it He e ip 4 c g e a
r 3 G P 0.25 2 1 0.00 0
5 15 15 15 15 :15 :15 15 15 15 15 15 15 1 15 15 15 6: 9: 5: 8: 00: 03: 0 0 12 15 18: 21: 00: 03: 06: 09: 12: 1 1 21: Local Time (15 min)
FIG A.8b. Same as in a, except for 11 October 2002.
Time vs. Precipitation, Gage Height (Little River @ SR1461 near Orange Factory 8-10 April 2003) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) ( t
n 5 h g io i t
a 0.50 4 it He e ip
c 3 g e a r G P 0.25 2 1 0.00 0
5 5 15 15 15 15 15 15 :15 15 15 :15 15 15 15 15 1 1 15 15 15 15 15 15 :15 :15 3: 6: 5: 6: 9: 00: 0 0 09: 12: 1 18 21: 00: 03 06: 09: 12: 15: 18: 21: 00: 03: 0 0 12: 15: 18 21 Local Time (15 min)
FIG A.8c. Same as in a, except for 9-10 April 2003.
153 Time vs. Precipitation, Gage Height (Little River @ SR1461 near Orange Factory 9-10 August 2003) 1.00 7 Precipitation 6 Gage Height
) 0.75 n
i 5 (ft) ( t n h g
io 4 i t
a 0.50 it 3 He e ip c g e a r 2 G P 0.25 1
0.00 0
15 15 15 15 :15 :15 :15 15 15 15 15 15 15 15 15 :15 2: 5: 8: 00: 03: 06: 09: 12 15 18 21: 00: 03: 06: 09: 1 1 1 21 Local Time (15 min)
FIG A.8d. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (Tar River @ NC97 @ Rocky Mount 25-26 August 2002) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) ( t
n 5 h g io i t
a 0.50 4 it He e ip
c 3 g e a r G P 0.25 2 1 0.00 0
15 15 15 15 :15 :15 :15 15 15 15 15 15 15 15 15 :15 2: 5: 8: 00: 03: 06: 09: 12 15 18 21: 00: 03: 06: 09: 1 1 1 21 Local Time (15 min)
FIG A.9a. Tar River at NC97 at Rocky Mount on 26 August 2002. Flood stage is 18 ft.
154
Time vs. Precipita tion, Gage Height (Tar River @ NC97 @ Rocky Mount 10-11 October 2002) 1.00 7 Precipitation 6 Gage Height ) 0.75 n
i 5 (ft) ( t n
h g
io 4 i t a 0.50 it 3 He e ip c g
e a r 2 G P 0.25 1
0.00 0
15 15 15 15 :15 :15 :15 15 15 15 15 15 15 15 15 :15 2: 5: 8: 00: 03: 06: 09: 12 15 18 21: 00: 03: 06: 09: 1 1 1 21 Local Tim e (15 min)
FIG A.9b. Same as in a, except for 11 October 2002.
Time vs. Precipitation, Gage Height (Tar River @ NC97 @ Rocky Mount 29-30 July 2003) 1.00 5 4.5 4 ) 0.75 n
i 3.5 (ft)
( Precipitation t n 3 h g io Gage Height i t
a 0.50 2.5 it He e ip 2 c g e a
r 1.5 G P 0.25 1 0.5 0.00 0
5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Time (15 min)
FIG A.9c. Same as in a, except for 29 July 2003.
155
Time vs. Precipita tion, Gage Height (East Fork Deep River near High Point 10-11 October 2002) 1.00 10 Precipitation 9 Gage Height 8 ) 0.75 n
i 7 (ft) ( t n 6 h g io i t a 0.50 5 it He e ip 4 c g
e a
r 3 G P 0.25 2
1 0.00 0 5 15 15 15 15 :15 :15 15 15 15 15 15 15 1 15 15 15 6: 9: 5: 8: 00: 03: 0 0 12 15 18: 21: 00: 03: 06: 09: 12: 1 1 21: Local Tim e (15 min)
FIG A.10a. East Fork Deep River near High Point on 11 October 2002. No pre- determined flood stage.
Time vs. Precipitation, Gage Height (East Fork Deep River near High Point 8-10 April 2003) 1.00 12 Precipitation Gage Height 10
) 0.75 n i (ft) ( 8 t n h g io i t
a 0.50 6 it He e ip c g
e 4 a r G P 0.25 2
0.00 0
5 5 15 15 15 15 15 15 :15 15 :15 15 15 15 15 15 1 15 15 1 15 15 15 15 15 15 3: 9: 9: 8: 00: 0 06: 0 12: 15: 18 21: 00 03: 06: 09: 12: 15: 18: 21: 00: 03: 06: 0 12: 15: 1 21: Local Time (15 min)
FIG A.10b. Same as in a, except for 9-10 April 2003.
156
Time vs. Precipita tion, Gage Height (East Fork Deep River near H igh Point 15-16 June 2003) 1.00 3
2.5 ) 0.75 n
i (ft) ( Precipitation 2 t n
h g io Gage Height i t a 0.50 1.5 it He e ip c g
e 1 a r G P 0.25 0.5
0.00 0 5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Tim e (15 min)
FIG A.10c. Same as in a, except for 16 June 2003.
Time vs. Precipitation, Gage Height (East Fork Deep River near High Point 29-30 July 2003) 1.00 10 Precipitation 9 Gage Height 8 ) 0.75 n
i 7 (ft) ( t n 6 h g io i t
a 0.50 5 it He e ip 4 c g e a
r 3 G P 0.25 2 1 0.00 0
5 15 15 15 15 :15 :15 15 15 15 15 15 15 1 15 15 15 6: 9: 5: 8: 00: 03: 0 0 12 15 18: 21: 00: 03: 06: 09: 12: 1 1 21: Local Time (15 min)
FIG A.10d. Same as in a, except for 29 July 2003.
157
Time vs. Precipita tion, Gage Height (East Fork Deep River near H igh Point 9-10 August 2003) 1.00 9 Precipitation 8 Gage Height 7 ) 0.75 n
i (ft) ( 6 t n
h g io
5 i t a 0.50 it 4 He e ip c g
e 3 a r G P 0.25 2
1
0.00 0
15 15 15 15 :15 :15 :15 15 15 15 15 15 15 15 15 :15 2: 5: 8: 00: 03: 06: 09: 12 15 18 21: 00: 03: 06: 09: 1 1 1 21 Local Tim e (15 min)
FIG A.10e. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (Horsepen Creek @ US220 near Greensboro 10-11 October 2002) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) ( t
n 5 h g io i t
a 0.50 4 it He e ip
c 3 g e a r G P 0.25 2 1 0.00 0
15 15 15 15 :15 :15 :15 15 15 15 15 15 15 15 15 :15 2: 5: 8: 00: 03: 06: 09: 12 15 18 21: 00: 03: 06: 09: 1 1 1 21 Local Time (15 min)
FIG A.11a. Horsepen Creek at US220 near Greensboro on 11 October 2002. Flood stage is 11 ft.
158
Time vs. Precipita tion, Gage Height (Horsepen Creek @ US220 near Greensboro 8-10 April 2003) 1.00 10 Precipitation 9 Gage Height 8 ) 0.75 n
i 7 (ft) ( t n 6 h g io i t a 0.50 5 it He e ip 4 c g
e a
r 3 G P 0.25 2
1 0.00 0 5 5 15 15 15 15 15 15 :15 15 :15 15 15 15 15 15 :1 15 15 1 15 15 15 15 15 15 3: 9: 8 9: 8: 00: 0 06: 0 12: 15: 18 21: 00 03: 06: 09: 12: 15: 1 21: 00: 03: 06: 0 12: 15: 1 21: Local Tim e (15 min)
FIG A.11b. Same as in a, except for 9-10 April 2003.
Time vs. Precipitation, Gage Height (Horsepen Creek @ US220 near Greensboro 15-16 June 2003) 1.00 4 Precipitation 3.5 Gage Height
) 0.75 3 n i (ft) ( t
n 2.5 h g io i t
a 0.50 2 it He e ip
c 1.5 g e a r G P 0.25 1 0.5 0.00 0
5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Time (15 min)
FIG A.11c. Same as in a, except for 16 June 2003.
159
Time vs. Precipita tion, Gage Height (Horsepen Creek @ US220 near Greensboro 29-30 July 2003) 1.00 8 Precipitation 7 Gage Height ) 0.75 6 ) t n f i ( (
n 5 ght io i t e a 0.50 4
it H ip
c 3 ge e a
G Pr 0.25 2
1 0.00 0
15 15 15 15 :15 :15 :15 15 15 15 15 15 15 15 15 :15 2: 5: 8: 00: 03: 06: 09: 12 15 18 21: 00: 03: 06: 09: 1 1 1 21 Local Tim e (15 min)
FIG A.11d. Same as in a, except for 29 July 2003.
Time vs. Precipitation, Gage Height (Horsepen Creek @ US220 near Greensboro 9-10 August 2003) 1.00 9 Precipitation 8 Gage Height 7 ) 0.75 n i (ft) ( 6 t n h g io
5 i t
a 0.50 it
4 He e ip c g
e 3 a r G P 0.25 2 1 0.00 0
15 15 15 15 :15 :15 :15 15 15 15 15 15 15 15 15 :15 2: 5: 8: 00: 03: 06: 09: 12 15 18 21: 00: 03: 06: 09: 1 1 1 21 Local Time (15 min)
FIG A.11e. Same as in a, except for 9 August 2003.
160
Time vs. Precipita tion, Gage Height (N. Buffalo Creek @ Westover Terrace @ Greensboro 10-11 October 2002)
1.00 9 Precipitation 8 Gage Height 7 ) 0.75 ) t n f i ( ( 6 t n h io
5 ig t e a 0.50 it
4 H ip e c g
e 3 a G Pr 0.25 2 1 0.00 0
15 15 15 15 :15 :15 :15 15 15 15 15 15 15 15 15 :15 2: 5: 8: 00: 03: 06: 09: 12 15 18 21: 00: 03: 06: 09: 1 1 1 21 Local Tim e (15 min)
FIG A.12a. North Buffalo Creek at Westove r Terrace at Greensboro on 11 October 2002. Flood stage is 10 ft.
Time vs. Precipitation, Gage Height (N. Buffalo Creek @ Westover Terrace @ Greensboro 8-10 April 2003) 1.00 12 Precipitation Gage Height FS = 10ft 10
) 0.75 n i (ft) ( 8 t n h g io i t
a 0.50 6 it He e ip c g
e 4 a r G P 0.25 2
0.00 0
5 5 15 15 15 15 15 15 :15 15 :15 15 15 15 15 15 1 15 15 1 15 15 15 15 15 15 3: 9: 9: 8: 00: 0 06: 0 12: 15: 18 21: 00 03: 06: 09: 12: 15: 18: 21: 00: 03: 06: 0 12: 15: 1 21: Local Time (15 min)
FIG A.12b. Same as in a, except for 9-10 April 2003.
161
Time vs. Precipita tion, Gage Height (N. Buffalo Creek @ Westover Terra ce @ Greensboro 15-16 June 2003) 1.00 3 Precipitation Gage Height 2.5 ) 0.75 n
i (ft) ( 2 t n
h g io i t a 0.50 1.5 it He e ip c g
e 1 a r G P 0.25 0.5
0.00 0 5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Tim e (15 min)
FIG A.12c. Same as in a, except for 16 June 2003.
Time vs. Precipitation, Gage Height (N. Buffalo Creek @ Westover Terrace @ Greensboro 29-30 July 2003) 1.00 9 Precipitation 8 Gage Height 7 ) 0.75 n i (ft) ( 6 t n h g io
5 i t
a 0.50 it
4 He e ip c g
e 3 a r G P 0.25 2 1 0.00 0
15 15 15 15 :15 :15 :15 15 15 15 15 15 15 15 15 :15 2: 5: 8: 00: 03: 06: 09: 12 15 18 21: 00: 03: 06: 09: 1 1 1 21 Local Time (15 min)
FIG A.12d. Same as in a, except for 29 July 2003.
162
Time vs. Precipita tion, Gage Height (N. Buffalo Creek @ Westover Terrac e @ Greensboro 9-10 August 2003) 1.00 4 Precipitation 3.5 Gage Height ) 0.75 3 n
i (ft) ( t
n 2.5
h g io i t a 0.50 2 it He e ip
c 1.5 g
e a r G P 0.25 1 0.5
0.00 0 5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Tim e (15 min)
FIG A.12e. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (North Buffalo Creek @ Church Street @ Greensboro 25-26 August 2002) 1.00 3 Precipitation Gage Height 2.5
) 0.75 n i (ft) ( 2 t n h g io i t
a 0.50 1.5 it He e ip c g
e 1 a r G P 0.25 0.5
0.00 0
5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Time (15 min)
FIG A.13a. North Buffalo Creek at Church Street at Greensboro on 26 August 2002. Flood stage is 14 ft.
163
Time vs. Precipita tion, Gage Height (North Buffalo Creek @ Church Street @ Greensboro 10-11 October 2002) 1.00 14 Precipitation 12 Gage Height ) 0.75 n
i 10 (ft) ( t n
h g
io 8 i t a 0.50 it 6 He e ip c g
e a r 4 G P 0.25 2
0.00 0 5 15 15 15 15 :15 :15 15 15 15 15 15 15 1 15 15 15 6: 9: 5: 8: 00: 03: 0 0 12 15 18: 21: 00: 03: 06: 09: 12: 1 1 21: Local Tim e (15 min)
FIG A.13b. Same as in a, except for 11 October 2002.
Time vs. Precipitation, Gage Height (North Buffalo Creek @ Church Street @ Greensboro 8-10 April 2003) 1.00 14 Precipitation 12 Gage Height
) 0.75 n
i 10 (ft) ( t n h g
io 8 i t
a 0.50 it 6 He e ip c g e a r 4 G P 0.25 2
0.00 0
5 5 15 15 15 15 15 15 :15 15 :15 15 15 15 15 15 1 15 15 1 15 15 15 15 15 15 3: 9: 9: 8: 00: 0 06: 0 12: 15: 18 21: 00 03: 06: 09: 12: 15: 18: 21: 00: 03: 06: 0 12: 15: 1 21: Local Time (15 min)
FIG A.13c. Same as in a, except for 9-10 April 2003.
164
Time vs. Precipita tion, Gage Height (North Buffalo Creek @ Church Stre et @ Greensboro 15-16 June 2003) 1.00 4.5 Precipitation 4 Gage Height 3.5 ) 0.75 n
i (ft) ( 3 t n
h g io
2.5 i t a 0.50 it 2 He e ip c g
e 1.5 a r G P 0.25 1
0.5
0.00 0 5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Tim e (15 min)
FIG A.13d. Same as in a, except for 16 June 2003.
Time vs. Precipitation, Gage Height (North Buffalo Creek @ Church Street @ Greensboro 29-30 July 2003) 1.00 10 Precipitation 9 Gage Height 8 ) 0.75 n
i 7 (ft) ( t n 6 h g io i t
a 0.50 5 it He e ip 4 c g e a
r 3 G P 0.25 2 1 0.00 0
5 15 15 15 15 :15 :15 15 15 15 15 15 15 1 15 15 15 6: 9: 5: 8: 00: 03: 0 0 12 15 18: 21: 00: 03: 06: 09: 12: 1 1 21: Local Time (15 min)
FIG A.13e. Same as in a, except for 29 July 2003.
165
Time vs. Precipita tion, Gage Height (North Buffalo Creek @ Church Street @ Greensboro 9-10 August 2003) 1.00 6 Precipitation Gage Height 5 ) 0.75 n
i (ft) ( 4 t n
h g io i t a 0.50 3 it He e ip c g
e 2 a r G P 0.25 1
0.00 0
15 15 15 15 :15 :15 :15 15 15 15 15 15 15 15 15 :15 2: 5: 8: 00: 03: 06: 09: 12 15 18 21: 00: 03: 06: 09: 1 1 1 21 Local Tim e (15 min)
FIG A.13f. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (North Buffalo Creek near Greensboro 10-11 October 2002) 1.00 14 Precipitation 12 Gage Height
) 0.75 n
i 10 (ft) ( t n h g
io 8 i t
a 0.50 it 6 He e ip c g e a r 4 G P 0.25 2
0.00 0
5 15 15 15 15 :15 :15 15 15 15 15 15 15 1 15 15 15 6: 9: 5: 8: 00: 03: 0 0 12 15 18: 21: 00: 03: 06: 09: 12: 1 1 21: Local Time (15 min)
FIG A.14a. North Buffalo Creek near Greensboro on 11 October 2002. Flood stage is 13 ft.
166
Time vs. Precipita tion, Gage Height (North Buffalo Creek near G reensboro 8-10 April 2003) 1.00 14 Precipitation 12 Gage Height ) 0.75 n
i 10 (ft) ( t n
h g
io 8 i t a 0.50 it 6 He e ip c g
e a r 4 G P 0.25 2
0.00 0 5 5 15 15 15 15 15 15 :15 15 :15 15 15 15 15 15 :1 15 15 1 15 15 15 15 15 15 3: 9: 8 9: 8: 00: 0 06: 0 12: 15: 18 21: 00 03: 06: 09: 12: 15: 1 21: 00: 03: 06: 0 12: 15: 1 21: Local Tim e (15 min)
FIG A.14b. Same as in a, except for 9-10 April 2003.
Time vs. Precipitation, Gage Height (North Buffalo Creek near Greensboro 15-16 June 2003) 1.00 4 Precipitation 3.5 Gage Height
) 0.75 3 n i (ft) ( t
n 2.5 h g io i t
a 0.50 2 it He e ip
c 1.5 g e a r G P 0.25 1 0.5 0.00 0
5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Time (15 min)
FIG A.14c. Same as in a, except for 16 June 2003.
167
Time vs. Precipita tion, Gage Height (North Buffalo Creek near G reensboro 29-30 July 2003) 1.00 6 Precipitation Gage Height 5 ) 0.75 n
i (ft) ( 4 t n
h g io i t a 0.50 3 it He e ip c g
e 2 a r G P 0.25 1
0.00 0
15 15 15 15 :15 :15 :15 15 15 15 15 15 15 15 15 :15 2: 5: 8: 00: 03: 06: 09: 12 15 18 21: 00: 03: 06: 09: 1 1 1 21 Local Tim e (15 min)
FIG A.14d. Same as in a, except for 29 July 2003.
Time vs. Precipitation, Gage Height (North Buffalo Creek near Greensboro 9-10 August 2003) 1.00 3.5 Precipitation 3 Gage Height
) 0.75 n
i 2.5 (ft) ( t n h g
io 2 i t
a 0.50 it 1.5 He e ip c g e a r 1 G P 0.25 0.5
0.00 0
5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Time (15 min)
FIG A.14e. Same as in a, except for 9 August 2003.
168
Time vs. Precipita tion, Gage Height (Ryan Creek below US220 @ G reensboro 10-11 October 2002) 1.00 9 Precipitation 8 Gage Height 7 ) 0.75 n
i (ft) ( 6 t n
h g io
5 i t a 0.50 it 4 He e ip c g
e 3 a r G P 0.25 2
1
0.00 0
15 15 15 15 :15 :15 :15 15 15 15 15 15 15 15 15 :15 2: 5: 8: 00: 03: 06: 09: 12 15 18 21: 00: 03: 06: 09: 1 1 1 21 Local Tim e (15 min)
FIG A.15a. Ryan Creek below US220 at Greensboro on 11 October 2002. Flood stage is 10 ft.
Time vs. Precipitation, Gage Height (Ryan Creek below US220 @ Greensboro 8-10 April 2003) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) ( t
n 5 h g io i t
a 0.50 4 it He e ip
c 3 g e a r G P 0.25 2 1 0.00 0
5 5 15 15 15 15 15 15 :15 15 15 :15 15 15 15 15 1 1 15 15 15 15 15 15 :15 :15 3: 6: 5: 6: 9: 00: 0 0 09: 12: 1 18 21: 00: 03 06: 09: 12: 15: 18: 21: 00: 03: 0 0 12: 15: 18 21 Local Time (15 min)
FIG A.15b. Same as in a, except for 9-10 April 2003.
169
Time vs. Precipita tion, Gage Height (Ryan Creek below US220 @ Greensboro 15-16 June 2003) 1.00 1 Precipitation 0.9 Gage Height 0.8 ) 0.75 n
i 0.7 (ft) ( t n 0.6 h g io i t a 0.50 0.5 it He e ip 0.4 c g
e a
r 0.3 G P 0.25 0.2
0.1 0.00 0 5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Tim e (15 min)
FIG A.15c. Same as in a, except for 16 June 2003.
Time vs. Precipitation, Gage Height (Ryan Creek below US220 @ Greensboro 29-30 July 2003) 1.00 7 Precipitation 6 Gage Height
) 0.75 n
i 5 (ft) ( t n h g
io 4 i t
a 0.50 it 3 He e ip c g e a r 2 G P 0.25 1
0.00 0
15 15 15 15 :15 :15 :15 15 15 15 15 15 15 15 15 :15 2: 5: 8: 00: 03: 06: 09: 12 15 18 21: 00: 03: 06: 09: 1 1 1 21 Local Time (15 min)
FIG A.15d. Same as in a, except for 29 July 2003.
170
Time vs. Precipita tion, Gage Height (Ryan Creek below US220 @ G reensboro 9-10 August 2003) 1.00 1.2 Precipitation Gage Height 1 ) 0.75 n
i (ft) ( 0.8 t n
h g io i t a 0.50 0.6 it He e ip c g
e 0.4 a r G P 0.25 0.2
0.00 0 5 5 15 15 15 15 15 :15 :15 15 15 15 1 1 15 15 15 :15 3: 6: 8: 00: 0 0 09: 12: 15 18 21: 00: 03: 06: 09: 12: 15: 1 21 Local Tim e (15 min)
FIG A.15e. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (South Buffalo Creek near Greensboro 10-11 October 2002) 1.00 14 Precipitation 12 Gage Height
) 0.75
n 10 i FS = 10ft (ft) ( t n 8 h io g t i a 0.50 e it
6 H ip e c g e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.16a. South Buffalo Creek near Greensboro on 11 October 2002. Flood stage is 10 ft.
171 Time vs. Precipitation, Gage Height (South Buffalo Creek near Greensboro 8-10 April 2003) 1.00 16 Precipitation 14 Gage Height
) 0.75 12 n i (ft) (
FS = 10ft 10 t n h io g t i a 0.50 8 e it H ip 6 e c g e a G Pr 0.25 4 2 0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 :1 15 :1 15 :1 :1 :15 :1 :15 :1 :15 :15 :1 :15 :1 :15 :15 :1 :15 9: 8: 0: 00 03 06 0 12 15 1 21 0 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.16b. Same as in a, except for 9-10 April 2003.
Time vs. Precipitation, Gage Height (South Buffalo Creek near Greensboro 15-16 June 2003) 1.00 4.5 Precipitation 4 Gage Height 3.5 ) 0.75 n i 3 (ft) ( t n h io 2.5 g t i a 0.50 e
it 2 H ip e c g
e 1.5 a G Pr 0.25 1 0.5 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.16c. Same as in a, except for 16 June 2003.
172 Time vs. Precipitation, Gage Height (South Buffalo Creek near Greensboro 29-30 July 2003) 1.00 10 Precipitation 9 Gage Height 8
) 0.75 n
i 7 (ft) ( t n
6 h io g t i a 0.50 5 e it H ip 4 e c g e 3 a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.16d. Same as in a, except for 29 July 2003.
Time vs. Precipitation, Gage Height (South Buffalo Creek near Greensboro 9-10 August 2003) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) (
5 t n h io g t i a 0.50 4 e it H ip 3 e c g e a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.16e. Same as in a, except for 9 August 2003.
173 Time vs. Precipitation, Gage Height (South Buffalo Creek @ US220 near Greensboro 10-11 October 2002) 1.00 14 Precipitation 12 Gage Height
) 0.75
n 10 i (ft) ( t n 8 h io g t i a 0.50 e it
6 H ip e c g e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.17a. South Buffalo Creek at US220 near Greensboro on 11 October 2002. Flood stage is 14 ft.
Time vs. Precipitation, Gage Height (South Buffalo Creek @ US220 near Greensboro 8-10 April 2003) 1.00 14 Precipitation 12 Gage Height
) 0.75
n 10 i (ft) ( t n 8 h io g t i a 0.50 e it
6 H ip e c g e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 :1 15 :1 15 :1 :1 :15 :1 :15 :1 :15 :15 :1 :15 :1 :15 :15 :1 :15 9: 8: 0: 00 03 06 0 12 15 1 21 0 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.17b. Same as in a, except for 9-10 April 2003.
174 Time vs. Precipitation, Gage Height (South Buffalo Creek @ US220 near Greensboro 15-16 June 2003) 1.00 3
2.5
) 0.75 n i Precipitation 2 (ft) ( t n Gage Height h io g t i a 0.50 1.5 e it H ip e c g
e 1 a G Pr 0.25 0.5
0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.17c. Same as in a, except for 16 June 2003.
Time vs. Precipitation, Gage Height (South Buffalo Creek @ US220 near Greensboro 29-30 July 2003) 1.00 9 Precipitation 8 Gage Height 7 ) 0.75 n i 6 (ft) ( t n h io 5 g t i a 0.50 e
it 4 H ip e c g
e 3 a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.17d. Same as in a, except for 29 July 2003.
175 Time vs. Precipitation, Gage Height (South Buffalo Creek @ US220 near Greensboro 9-10 August 2003) 1.00 10 Precipitation 9 Gage Height 8
) 0.75 n
i 7 (ft) ( t n
6 h io g t i a 0.50 5 e it H ip 4 e c g e 3 a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.17e. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (Brush Creek @ Fleming Road @ Greensboro 10-11 October 2002) 1.00 7 Precipitation 6 Gage Height
) 0.75
n 5 i (ft) ( t n 4 h io g t i a 0.50 e it
3 H ip e c g e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.18a. Brush Creek at Fleming Road at Greensboro on 11 October 2002. Flood stage is 9 ft.
176 Time vs. Precipitation, Gage Height (Brush Creek @ Fleming Road @ Greensboro 8-10 April 2003) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) (
5 t n h io g t i a 0.50 4 e it H ip 3 e c g e a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 :1 :1 15 15 :1 :1 15 :15 :1 :15 :15 :1 :1 :15 :15 :1 :1 :15 :15 :1 :1 5: 8: 3: 00 03 06 09 12 1 1 21 00 0 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.18b. Same as in a, except for 9-10 April 2003.
Time vs. Precipitation, Gage Height (Brush Creek @ Fleming Road @ Greensboro 15-16 June 2003) 1.00 3.5 Precipitation 3 Gage Height
) 0.75
n 2.5 i (ft) ( t n 2 h io g t i a 0.50 e it
1.5 H ip e c g e 1 a G Pr 0.25 0.5
0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.18c. Same as in a, except for 16 June 2003.
177 Time vs. Precipitation, Gage Height (Brush Creek @ Fleming Road @ Greensboro 29-30 July 2003) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) (
5 t n h io g t i a 0.50 4 e it H ip 3 e c g e a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.18d. Same as in a, except for 29 July 2003.
Time vs. Precipitation, Gage Height (Brush Creek @ Fleming Road @ Greensboro 9-10 August 2003) 1.00 7 Precipitation 6 Gage Height
) 0.75
n 5 i (ft) ( t n 4 h io g t i a 0.50 e it
3 H ip e c g e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.18e. Same as in a, except for 9 August 2003.
178 Time vs. Precipitation, Gage Height (Buffalo Creek @ SR2819 near McLeansville 10-11 October 2002) 1.00 18 FS = 17ft 16 14 ) 0.75 n i Precipitation 12 (ft) ( t n Gage Height h io 10 g t i a 0.50 e
it 8 H ip e c g
e 6 a G Pr 0.25 4 2 0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.19a. Buffalo Creek at SR2819 near McLeansville on 11 October 2002. Flood stage is 17 ft.
Time vs. Precipitation, Gage Height (Buffalo Creek @ SR2819 near McLeansville 29-30 July 2003) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) (
5 t n h io g t i a 0.50 4 e it H ip 3 e c g e a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.19b. Same as in a, except for 29 July 2003.
179 Time vs. Precipitation, Gage Height (Buffalo Creek @ SR2819 near McLeansville 9-10 August 2003) 1.00 6 Precipitation Gage Height 5
) 0.75 n i 4 (ft) ( t n h io g t i a 0.50 3 e it H ip e c g
e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.19c. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (Reedy Fork near Oak Ridge 10-11 October 2002) 1.00 7 Precipitation 6 Gage Height
) 0.75
n 5 i (ft) ( t n 4 h io g t i a 0.50 e it
3 H ip e c g e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.20a. Reedy Fork near Oak Ridge on 11 October 2002. Flood stage is 10 ft.
180 Time vs. Precipitation, Gage Height (Reedy Fork near Oak Ridge 8-10 April 2003) 1.00 10 Precipitation 9 Gage Height 8
) 0.75 n
i 7 (ft) ( t n
6 h io g t i a 0.50 5 e it H ip 4 e c g e 3 a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 :1 15 :1 15 :1 :1 :15 :1 :15 :1 :15 :15 :1 :15 :1 :15 :15 :1 :15 9: 8: 0: 00 03 06 0 12 15 1 21 0 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.20b. Same as in a, except for 9-10 April 2003.
Time vs. Precipitation, Gage Height (Reedy Fork near Oak Ridge 15-16 June 2003) 1.00 4.5 4 3.5 ) 0.75 n i Precipitation 3 (ft) ( t n Gage Height h io 2.5 g t i a 0.50 e
it 2 H ip e c g
e 1.5 a G Pr 0.25 1 0.5 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.20c. Same as in a, except for 16 June 2003.
181 Time vs. Precipitation, Gage Height (Reedy Fork near Oak Ridge 29-30 July 2003) 1.00 9 Precipitation 8 Gage Height 7 ) 0.75 n i 6 (ft) ( t n h io 5 g t i a 0.50 e
it 4 H ip e c g
e 3 a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.20d. Same as in a, except for 29 July 2003.
Time vs. Precipitation, Gage Height (Reedy Fork near Oak Ridge 9-10 August 2003) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) (
5 t n h io g t i a 0.50 4 e it H ip 3 e c g e a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.20e. Same as in a, except for 9 August 2003.
182 Time vs. Precipitation, Gage Height (South Buffalo Creek near Pomona 10-11 October 2002) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) (
5 t n h io g t i a 0.50 4 e it H ip 3 e c g e a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.21a. South Buffalo Creek near Pomona on 11 October 2002. Flood stage is 10 ft.
Time vs. Precipitation, Gage Height (South Buffalo Creek near Pomona 8-10 April 2003) 1.00 10 Precipitation 9 Gage Height 8
) 0.75 n
i 7 (ft) ( t n
6 h io g t i a 0.50 5 e it H ip 4 e c g e 3 a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 :1 15 :1 15 :1 :1 :15 :1 :15 :1 :15 :15 :1 :15 :1 :15 :15 :1 :15 9: 8: 0: 00 03 06 0 12 15 1 21 0 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.21b. Same as in a, except for 9-10 April 2003.
183 Time vs. Precipitation, Gage Height (South Buffalo Creek near Pomona 15-16 June 2003) 1.00 1.6 Precipitation 1.4 Gage Height
) 0.75 1.2 n i (ft) (
1 t n h io g t i a 0.50 0.8 e it H ip 0.6 e c g e a G Pr 0.25 0.4 0.2 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.21c. Same as in a, except for 16 June 2003.
Time vs. Precipitation, Gage Height (South Buffalo Creek near Pomona 29-30 July 2003) 1.00 7 Precipitation 6 Gage Height
) 0.75
n 5 i (ft) ( t n 4 h io g t i a 0.50 e it
3 H ip e c g e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.21d. Same as in a, except for 29 July 2003.
184 Time vs. Precipitation, Gage Height (South Buffalo Creek near Pomona 9-10 August 2003) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) (
5 t n h io g t i a 0.50 4 e it H ip 3 e c g e a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.21e. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (Flat Creek near Inverness 8-10 April 2003) 1.00 3 Precipitation Gage Height 2.5
) 0.75 n i 2 (ft) ( t n h io g t i a 0.50 1.5 e it H ip e c g
e 1 a G Pr 0.25 0.5
0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 15 :1 15 :1 15 :1 :15 :1 :15 :1 :15 :1 :15 :1 :15 :1 :15 :1 :15 9: 5: 1: 3: 00 03 06 0 12 1 18 2 00 0 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.22a. Flat Creek near Inverness on 9-10 April 2003. Flood stage is 7 ft.
185 Time vs. Precipitation, Gage Height (Flat Creek near Inverness 15-16 June 2003) 1.00 1.8 Precipitation 1.6 Gage Height 1.4 ) 0.75 n i 1.2 (ft) ( t n h io 1 g t i a 0.50 e
it 0.8 H ip e c g
e 0.6 a G Pr 0.25 0.4 0.2 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.22b. Same as in a, except for 16 June 2003.
Time vs. Precipitation, Gage Height (Flat Creek near Inverness 29-30 July 2003) 1.00 1.6 Precipitation 1.4 Gage Height
) 0.75 1.2 n i (ft) (
1 t n h io g t i a 0.50 0.8 e it H ip 0.6 e c g e a G Pr 0.25 0.4 0.2 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.22c. Same as in a, except for 29 July 2003.
186 Time vs. Precipitation, Gage Height (Little River near Star 8-10 April 2003) 1.00 12 Precipitation Gage Height 10
) 0.75 n i 8 (ft) ( t n h io g t i a 0.50 6 e it H ip e c g
e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 :1 15 :1 15 :1 :1 :15 :1 :15 :1 :15 :15 :1 :15 :1 :15 :15 :1 :15 9: 8: 0: 00 03 06 0 12 15 1 21 0 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.23a. Little River near Star on 9-10 April 2003. Flood stage is 11 ft.
Time vs. Precipitation, Gage Height (Little River near Star 29-30 July 2003) 1.00 3.5 Precipitation 3 Gage Height
) 0.75
n 2.5 i (ft) ( t n 2 h io g t i a 0.50 e it
1.5 H ip e c g e 1 a G Pr 0.25 0.5
0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.23b. Same as in a, except for 29 July 2003.
187 Time vs. Precipitation, Gage Height (Little River near Star 9-10 August 2003) 1.00 18 Precipitation 16 Gage Height 14 ) 0.75 n i 12 (ft) ( t n
FS = 11ft h io 10 g t i a 0.50 e
it 8 H ip e c g
e 6 a G Pr 0.25 4 2 0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.23c. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (Dutchmans Creek near Uwharrie 10-11 October 2002) 1.00 7 Precipitation 6 Gage Height
) 0.75
n 5 i (ft) ( t n 4 h io g t i a 0.50 e it
3 H ip e c g e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.24a. Dutchmans Creek near Uwharrie on 11 October 2002. No pre-determined flood stage.
188 Time vs. Precipitation, Gage Height (Dutchmans Creek near Uwharrie 8-10 April 2003) 1.00 7 Precipitation 6 Gage Height
) 0.75
n 5 i (ft) ( t n 4 h io g t i a 0.50 e it
3 H ip e c g e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 :1 :1 15 15 :1 :1 15 :15 :1 :15 :15 :1 :1 :15 :15 :1 :1 :15 :15 :1 :1 5: 8: 3: 00 03 06 09 12 1 1 21 00 0 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.24b. Same as in a, except for 9-10 April 2003.
Time vs. Precipitation, Gage Height (Dutchmans Creek near Uwharrie 15-16 June 2003) 1.00 6 Precipitation Gage Height 5
) 0.75 n i 4 (ft) ( t n h io g t i a 0.50 3 e it H ip e c g
e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.24c. Same as in a, except for 16 June 2003.
189 Time vs. Precipitation, Gage Height (Dutchmans Creek near Uwharrie 29-30 July 2003) 1.00 3 Precipitation Gage Height 2.5
) 0.75 n i 2 (ft) ( t n h io g t i a 0.50 1.5 e it H ip e c g
e 1 a G Pr 0.25 0.5
0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.24d. Same as in a, except for 29 July 2003.
Time vs. Precipitation, Gage Height (Dutchmans Creek near Uwharrie 9-10 August 2003) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) (
5 t n h io g t i a 0.50 4 e it H ip 3 e c g e a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.24e. Same as in a, except for 9 August 2003.
190 Time vs. Precipitation, Gage Height (Morgan Creek near Chapel Hill 10-11 October 2002) 1.00 14 Precipitation 12 Gage Height
) 0.75
n 10 i (ft) ( t n 8 h io g t i a 0.50 e it
6 H ip e c g e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.25a. Morgan Creek near Chapel Hill on 11 October 2002. No pre-determined flood stage.
Time vs. Precipitation, Gage Height (Morgan Creek near Chapel Hill 8-10 April 2003) 1.00 14 Precipitation 12 Gage Height
) 0.75
n 10 i (ft) ( t n 8 h io g t i a 0.50 e it
6 H ip e c g e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 :1 15 :1 15 :1 :1 :15 :1 :15 :1 :15 :15 :1 :15 :1 :15 :15 :1 :15 9: 8: 0: 00 03 06 0 12 15 1 21 0 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.25b. Same as in a, except for 9-10 April 2003.
191 Time vs. Precipitation, Gage Height (Morgan Creek near Chapel Hill 15-16 June 2003) 1.00 6 Precipitation Gage Height 5
) 0.75 n i 4 (ft) ( t n h io g t i a 0.50 3 e it H ip e c g
e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.25c. Same as in a, except for 16 June 2003.
Time vs. Precipitation, Gage Height (Morgan Creek near Chapel Hill 9-10 August 2003) 1.00 6
5
) 0.75 n i Precipitation 4 (ft) ( t n Gage Height h io g t i a 0.50 3 e it H ip e c g
e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.25d. Same as in a, except for 9 August 2003.
192 Time vs. Precipitation, Gage Height (Cane Creek near Orange Grove 10-11 October 2002) 1.00 6 Precipitation Gage Height 5
) 0.75 n i 4 (ft) ( t n h io g t i a 0.50 3 e it H ip e c g
e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.26a. Cane Creek near Orange Grove on 11 October 2002. No pre-determined flood stage.
Time vs. Precipitation, Gage Height (Cane Creek near Orange Grove 8-10 April 2003) 1.00 7 Precipitation 6 Gage Height
) 0.75
n 5 i (ft) ( t n 4 h io g t i a 0.50 e it
3 H ip e c g e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 :1 :1 15 15 :1 :1 15 :15 :1 :15 :15 :1 :1 :15 :15 :1 :1 :15 :15 :1 :1 5: 8: 3: 00 03 06 09 12 1 1 21 00 0 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.26b. Same as in a, except for 9-10 April 2003.
193 Time vs. Precipitation, Gage Height (Cane Creek near Orange Grove 15-16 June 2003) 1.00 1.6 1.4
) 0.75 1.2 n i Precipitation (ft) (
1 t n Gage Height h io g t i a 0.50 0.8 e it H ip 0.6 e c g e a G Pr 0.25 0.4 0.2 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.26c. Same as in a, except for 16 June 2003.
Time vs. Precipitation, Gage Height (Morgan Creek near White Cross 10-11 October 2002) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) (
5 t n h io g t i a 0.50 4 e it H ip 3 e c g e a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.27a. Morgan Creek near White Cross on 11 October 2002. No pre-determined flood stage.
194 Time vs. Precipitation, Gage Height (Morgan Creek near White Cross 8-10 April 2003) 1.00 10 Precipitation 9 Gage Height 8
) 0.75 n
i 7 (ft) ( t n
6 h io g t i a 0.50 5 e it H ip 4 e c g e 3 a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 :1 15 :1 15 :1 :1 :15 :1 :15 :1 :15 :15 :1 :15 :1 :15 :15 :1 :15 9: 8: 0: 00 03 06 0 12 15 1 21 0 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.27b. Same as in a, except for 9-10 April 2003.
Time vs. Precipitation, Gage Height (Morgan Creek near White Cross 15-16 June 2003) 1.00 3.5 Precipitation 3 Gage Height
) 0.75
n 2.5 i (ft) ( t n 2 h io g t i a 0.50 e it
1.5 H ip e c g e 1 a G Pr 0.25 0.5
0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.27c. Same as in a, except for 16 June 2003.
195 Time vs. Precipitation, Gage Height (Eno River @ Hillsborough 25-26 August 2002) 1.00 1.4
1.2
) 0.75
n 1 i Precipitation (ft) ( t n Gage Height 0.8 h io g t i a 0.50 e it
0.6 H ip e c g e 0.4 a G Pr 0.25 0.2
0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.28a. Eno River at Hillsboro on 26 August 2002. Flood stage is 16 ft.
Time vs. Precipitation, Gage Height (Eno River @ Hillsborough 10-11 October 2002) 1.00 18 Precipitation FS = 16ft 16 Gage Height 14 ) 0.75 n i 12 (ft) ( t n h io 10 g t i a 0.50 e
it 8 H ip e c g
e 6 a G Pr 0.25 4 2 0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.28b. Same as in a, except for 11 October 2002.
196 Time vs. Precipitation, Gage Height (Eno River @ Hillsborough 8-10 April 2003) 1.00 18 Precipitation FS = 16ft 16 Gage Height 14 ) 0.75 n i 12 (ft) ( t n h io 10 g t i a 0.50 e
it 8 H ip e c g
e 6 a G Pr 0.25 4 2 0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 :1 15 :1 15 :1 :1 :15 :1 :15 :1 :15 :15 :1 :15 :1 :15 :15 :1 :15 9: 8: 0: 00 03 06 0 12 15 1 21 0 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.28c. Same as in a, except for 9-10 April 2003.
Time vs. Precipitation, Gage Height (Eno River @ Hillsborough 15-16 June 2003) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) (
5 t n h io g t i a 0.50 4 e it H ip 3 e c g e a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.28d. Same as in a, except for 16 June 2003.
197 Time vs. Precipitation, Gage Height (Eno River @ Hillsborough 29-30 July 2003) 1.00 2.5 Precipitation
Gage Height 2
) 0.75 n i (ft) ( t n
1.5 h io g t i a 0.50 e it H ip 1 e c g e a G Pr 0.25 0.5
0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.28e. Same as in a, except for 29 July 2003.
Time vs. Precipitation, Gage Height (Eno River @ Hillsborough 9-10 August 2003) 1.00 14 Precipitation 12 Gage Height
) 0.75
n 10 i (ft) ( t n 8 h io g t i a 0.50 e it
6 H ip e c g e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.28f. Same as in a, except for 9 August 2003.
198 Time vs. Precipitation, Gage Height (Mayo Creek near Bethel Hill 8-10 April 2003) 1.00 9 Precipitation FS = 8ft 8 Gage Height 7 ) 0.75 n i 6 (ft) ( t n h io 5 g t i a 0.50 e
it 4 H ip e c g
e 3 a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 :1 :1 15 15 :1 :1 15 :15 :1 :15 :15 :1 :1 :15 :15 :1 :1 :15 :15 :1 :1 5: 8: 3: 00 03 06 09 12 1 1 21 00 0 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.29a. Mayo Creek near Bethel Hill on 9-10 April 2003. Flood stage is 8 ft.
Time vs. Precipitation, Gage Height (Mayo Creek near Bethel Hill 15-16 June 2003) 1.00 4.5 4 3.5 ) 0.75 n i Precipitation 3 (ft) ( t n Gage Height h io 2.5 g t i a 0.50 e
it 2 H ip e c g
e 1.5 a G Pr 0.25 1 0.5 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.29b. Same as in a, except for 16 June 2003.
199 Time vs. Precipitation, Gage Height (Mayo Creek near Bethel Hill 9-10 August 2003) 1.00 4.5 Precipitation 4 Gage Height 3.5 ) 0.75 n i 3 (ft) ( t n h io 2.5 g t i a 0.50 e
it 2 H ip e c g
e 1.5 a G Pr 0.25 1 0.5 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.29c. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (Deep River @ Ramseur 10-11 October 2002) 1.00 25
FS = 20ft 20 ) 0.75 n i Precipitation (ft) ( t n
15 h Gage Height io g t i a 0.50 e it H ip 10 e c g e a G Pr 0.25 5
0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.30a. Deep River at Ramseur on 11 October 2002. Flood stage is 20 ft.
200 Time vs. Precipitation, Gage Height (Deep River @ Ramseur 8-10 April 2003) 1.00 25 Precipitation
Gage Height FS = 20ft 20
) 0.75 n i (ft) ( t n
15 h io g t i a 0.50 e it H ip 10 e c g e a G Pr 0.25 5
0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 :1 15 :1 15 :1 :1 :15 :1 :15 :1 :15 :15 :1 :15 :1 :15 :15 :1 :15 9: 8: 0: 00 03 06 0 12 15 1 21 0 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.30b. Same as in a, except for 9-10 April 2003.
Time vs. Precipitation, Gage Height (Deep River @ Ramseur 29-30 July 2003) 1.00 4 Precipitation 3.5 Gage Height
) 0.75 3 n i (ft) (
2.5 t n h io g t i a 0.50 2 e it H ip 1.5 e c g e a G Pr 0.25 1 0.5 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.30c. Same as in a, except for 29 July 2003.
201 Time vs. Precipitation, Gage Height (Deep River @ Ramseur 9-10 August 2003) 1.00 9 Precipitation 8 Gage Height 7 ) 0.75 n i 6 (ft) ( t n h io 5 g t i a 0.50 e
it 4 H ip e c g
e 3 a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.30d. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (Deep River near Randleman 10-11 October 2002) 1.00 16 Precipitation 14 Gage Height
) 0.75 12 n i (ft) (
10 t n h io g t i a 0.50 8 e it H ip 6 e c g e a G Pr 0.25 4 2 0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.31a. Deep River near Randleman on 11 October 2002. Flood stage is 24 ft.
202 Time vs. Precipitation, Gage Height (Deep River near Randleman 8-10 April 2003) 1.00 25 Precipitation
Gage Height 20
) 0.75 n i (ft) ( t n
15 h io g t i a 0.50 e it H ip 10 e c g e a G Pr 0.25 5
0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 :1 15 :1 15 :1 :1 :15 :1 :15 :1 :15 :15 :1 :15 :1 :15 :15 :1 :15 9: 8: 0: 00 03 06 0 12 15 1 21 0 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.31b. Same as in a, except for 9-10 April 2003.
Time vs. Precipitation, Gage Height (Deep River near Randleman 29-30 July 2003) 1.00 7 Precipitation 6 Gage Height
) 0.75
n 5 i (ft) ( t n 4 h io g t i a 0.50 e it
3 H ip e c g e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.31c. Same as in a, except for 29 July 2003.
203 Time vs. Precipitation, Gage Height (Deep River near Randleman 9-10 August 2003) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) (
5 t n h io g t i a 0.50 4 e it H ip 3 e c g e a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.31d. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (Big Bear Creek near Richfield 25-26 August 2002) 1.00 0.5 Precipitation 0.45 Gage Height 0.4
) 0.75 n
i 0.35 (ft) ( t n
0.3 h io g t i a 0.50 0.25 e it H ip 0.2 e c g e 0.15 a G Pr 0.25 0.1 0.05 0.00 0
5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 15 :1 :15 :1 :15 :1 :15 :1 :15 :1 :15 9: 5: 00 03 06 0 12 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.32a. Big Bear Creek near Richfield on 26 August 2002. No pre-determined flood stage.
204 Time vs. Precipitation, Gage Height (Big Bear Creek near Richfield 10-11 October 2002) 1.00 10 Precipitation 9 Gage Height 8
) 0.75 n
i 7 (ft) ( t n
6 h io g t i a 0.50 5 e it H ip 4 e c g e 3 a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.32b. Same as in a, except for 11 October 2002.
Time vs. Precipitation, Gage Height (Big Bear Creek near Richfield 8-10 April 2003) 1.00 14 Precipitation 12 Gage Height
) 0.75
n 10 i (ft) ( t n 8 h io g t i a 0.50 e it
6 H ip e c g e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 :1 15 :1 15 :1 :1 :15 :1 :15 :1 :15 :15 :1 :15 :1 :15 :15 :1 :15 9: 8: 0: 00 03 06 0 12 15 1 21 0 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.32c. Same as in a, except for 9-10 April 2003.
205 Time vs. Precipitation, Gage Height (Big Bear Creek near Richfield 15-16 June 2003) 1.00 14 Precipitation 12 Gage Height
) 0.75
n 10 i (ft) ( t n 8 h io g t i a 0.50 e it
6 H ip e c g e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.32d. Same as in a, except for 16 June 2003.
Time vs. Precipitation, Gage Height (Big Bear Creek near Richfield 29-30 July 2003) 1.00 4 Precipitation 3.5 Gage Height
) 0.75 3 n i (ft) (
2.5 t n h io g t i a 0.50 2 e it H ip 1.5 e c g e a G Pr 0.25 1 0.5 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.32e. Same as in a, except for 29 July 2003.
206 Time vs. Precipitation, Gage Height (Crabtree Cr. @ Ebenezer Church Rd. near Raleigh 25-26 August 2002) 1.00 4.5 Precipitation 4 Gage Height 3.5 ) 0.75 n i 3 (ft) ( t n h io 2.5 g t i a 0.50 e
it 2 H ip e c g
e 1.5 a G Pr 0.25 1 0.5 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.33a. Crabtree Creek at Ebenezer Church Road near Raleigh on 26 August 2002. Flood stage is 19 ft.
Time vs. Precipitation, Gage Height (Crabtree Cr. @ Ebenezer Church Rd. near Raleigh 10-11 October 2002) 1.00 20 Precipitation 18 Gage Height 16
) 0.75 n
i 14 (ft) ( t n
12 h io g t i a 0.50 10 e it H ip 8 e c g e 6 a G Pr 0.25 4 2 0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.33b. Same as in a, except for 11 October 2002.
207 Time vs. Precipitation, Gage Height (Crabtree Cr. @ Ebenezer Church Rd. near Raleigh 8-10 April 2003) 1.00 14 Precipitation 12 Gage Height
) 0.75
n 10 i (ft) ( t n 8 h io g t i a 0.50 e it
6 H ip e c g e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 :1 15 :1 15 :1 :1 :15 :1 :15 :1 :15 :15 :1 :15 :1 :15 :15 :1 :15 9: 8: 0: 00 03 06 0 12 15 1 21 0 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.33c. Same as in a, except for 9-10 April 2003.
Time vs. Precipitation, Gage Height (Crabtree Cr. @ Ebenezer Church Rd. near Raleigh 15-16 June 2003) 1.00 7 Precipitation 6 Gage Height
) 0.75
n 5 i (ft) ( t n 4 h io g t i a 0.50 e it
3 H ip e c g e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.33d. Same as in a, except for 16 June 2003.
208 Time vs. Precipitation, Gage Height (Crabtree Cr. @ Ebenezer Church Rd. near Raleigh 29-30 July 2003) 1.00 6 Precipitation Gage Height 5
) 0.75 n i 4 (ft) ( t n h io g t i a 0.50 3 e it H ip e c g
e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.33e. Same as in a, except for 29 July 2003.
Time vs. Precipitation, Gage Height (Swift Creek near McCullars Crossroads 10-11 October 2002) 1.00 12
10
) 0.75 n i Precipitation 8 (ft) ( t n Gage Height h io g t i a 0.50 6 e it H ip e c g
e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.34a. Swift Creek near McCullars Crossroads on 11 October 2002. Flood stage is 12 ft.
209 Time vs. Precipitation, Gage Height (Swift Creek near McCullars Crossroads 8-10 April 2003) 1.00 12 Precipitation Gage Height 10
) 0.75 n i 8 (ft) ( t n h io g t i a 0.50 6 e it H ip e c g
e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 :1 15 :1 15 :1 :1 :15 :1 :15 :1 :15 :15 :1 :15 :1 :15 :15 :1 :15 9: 8: 0: 00 03 06 0 12 15 1 21 0 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.34b. Same as in a, except for 9-10 April 2003.
Time vs. Precipitation, Gage Height (Swift Creek near McCullars Crossroads 15-16 June 2003) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) (
5 t n h io g t i a 0.50 4 e it H ip 3 e c g e a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.34c. Same as in a, except for 16 June 2003.
210 Time vs. Precipitation, Gage Height (Swift Creek near McCullars Crossroads 29-30 July 2003) 1.00 6 Precipitation Gage Height 5
) 0.75 n i 4 (ft) ( t n h io g t i a 0.50 3 e it H ip e c g
e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.34d. Same as in a, except for 29 July 2003.
Time vs. Precipitation, Gage Height (Swift Creek near McCullars Crossroads 9-10 August 2003) 1.00 12
10
) 0.75 n i Precipitation 8 (ft) ( t n Gage Height h io g t i a 0.50 6 e it H ip e c g
e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.34e. Same as in a, except for 9 August 2003.
211 Time vs. Precipitation, Gage Height (Marsh Creek near New Hope 25-26 August 2002) 1.00 12 Precipitation Gage Height 10
) 0.75 n i 8 (ft) ( t n h io g t i a 0.50 6 e it H ip e c g
e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.35a. Marsh Creek near New Hope on 26 August 2002. No pre-determined flood stage.
Time vs. Precipitation, Gage Height (Marsh Creek near New Hope 10-11 October 2002) 1.00 14 Precipitation 12 Gage Height
) 0.75
n 10 i (ft) ( t n 8 h io g t i a 0.50 e it
6 H ip e c g e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.35b. Same as in a, except for 11 October 2002.
212 Time vs. Precipitation, Gage Height (Marsh Creek near New Hope 8-10 April 2003) 1.00 7 Precipitation 6 Gage Height
) 0.75
n 5 i (ft) ( t n 4 h io g t i a 0.50 e it
3 H ip e c g e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 :1 :1 15 15 :1 :1 15 :15 :1 :15 :15 :1 :1 :15 :15 :1 :1 :15 :15 :1 :1 5: 8: 3: 00 03 06 09 12 1 1 21 00 0 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.35c. Same as in a, except for 9-10 April 2003.
Time vs. Precipitation, Gage Height (Marsh Creek near New Hope 15-16 June 2003) 1.00 7 Precipitation 6 Gage Height
) 0.75
n 5 i (ft) ( t n 4 h io g t i a 0.50 e it
3 H ip e c g e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.35d. Same as in a, except for 16 June 2003.
213 Time vs. Precipitation, Gage Height (Marsh Creek near New Hope 29-30 July 2003) 1.00 5 Precipitation 4.5 Gage Height 4
) 0.75 n
i 3.5 (ft) ( t n
3 h io g t i a 0.50 2.5 e it H ip 2 e c g e 1.5 a G Pr 0.25 1 0.5 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.35e. Same as in a, except for 29 July 2003.
Time vs. Precipitation, Gage Height (Crabtree Creek @ US1 @ Raleigh 25-26 August 2002) 1.00 5 Precipitation 4.5 Gage Height 4
) 0.75 n
i 3.5 (ft) ( t n
3 h io g t i a 0.50 2.5 e it H ip 2 e c g e 1.5 a G Pr 0.25 1 0.5 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.36a. Crabtree Creek at US 1 at Raleigh on 26 August 2002. Flood stage is 18 ft.
214 Time vs. Precipitation, Gage Height (Crabtree Creek @ US1 @ Raleigh 10-11 October 2002) 1.00 16 Precipitation 14 Gage Height
) 0.75 12 n i (ft) (
10 t n h io g t i a 0.50 8 e it H ip 6 e c g e a G Pr 0.25 4 2 0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.36b. Same as in a, except for 11 October 2002.
Time vs. Precipitation, Gage Height (Crabtree Creek @ US1 @ Raleigh 8-10 April 2003) 1.00 12 Precipitation Gage Height 10
) 0.75 n i 8 (ft) ( t n h io g t i a 0.50 6 e it H ip e c g
e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 :1 15 :1 15 :1 :1 :15 :1 :15 :1 :15 :15 :1 :15 :1 :15 :15 :1 :15 9: 8: 0: 00 03 06 0 12 15 1 21 0 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.36c. Same as in a, except for 9-10 April 2003.
215 Time vs. Precipitation, Gage Height (Crabtree Creek @ US1 @ Raleigh 15-16 June 2003) 1.00 4.5 Precipitation 4 Gage Height 3.5 ) 0.75 n i 3 (ft) ( t n h io 2.5 g t i a 0.50 e
it 2 H ip e c g
e 1.5 a G Pr 0.25 1 0.5 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.36d. Same as in a, except for 16 June 2003.
Time vs. Precipitation, Gage Height (Crabtree Creek @ US1 @ Raleigh 29-30 July 2003) 1.00 7 Precipitation 6 Gage Height
) 0.75
n 5 i (ft) ( t n 4 h io g t i a 0.50 e it
3 H ip e c g e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.36e. Same as in a, except for 29 July 2003.
216 Time vs. Precipitation, Gage Height (Crabtree Creek @ US1 @ Raleigh 9-10 August 2003) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) (
5 t n h io g t i a 0.50 4 e it H ip 3 e c g e a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.36f. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (Pigeon House Creek @ Cameron Village @ Raleigh 25-26 August 2002) 1.00 1.8 1.6 1.4 ) 0.75 n i Precipitation 1.2 (ft) ( t n Gage Height h io 1 g t i a 0.50 e
it 0.8 H ip e c g
e 0.6 a G Pr 0.25 0.4 0.2 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.37a. Pigeon House Creek at Cameron Village at Raleigh on 26 August 2002. No pre-determined flood stage.
217 Time vs. Precipitation, Gage Height (Pigeon House Creek @ Cameron Village @ Raleigh 10-11 October 2002) 1.00 7 Precipitation 6 Gage Height
) 0.75
n 5 i (ft) ( t n 4 h io g t i a 0.50 e it
3 H ip e c g e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.37b. Same as in a, except for 11 October 2002.
Time vs. Precipitation, Gage Height (Pigeon House Creek @ Cameron Village @ Raleigh 8-10 April 2003) 1.00 3 Precipitation Gage Height 2.5
) 0.75 n i 2 (ft) ( t n h io g t i a 0.50 1.5 e it H ip e c g
e 1 a G Pr 0.25 0.5
0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 15 :1 15 :1 15 :1 :15 :1 :15 :1 :15 :1 :15 :1 :15 :1 :15 :1 :15 9: 5: 1: 3: 00 03 06 0 12 1 18 2 00 0 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.37c. Same as in a, except for 9-10 April 2003.
218 Time vs. Precipitation, Gage Height (Pigeon House Creek @ Cameron Village @ Raleigh 15-16 June 2003) 1.00 3.5 Precipitation 3 Gage Height
) 0.75
n 2.5 i (ft) ( t n 2 h io g t i a 0.50 e it
1.5 H ip e c g e 1 a G Pr 0.25 0.5
0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.37d. Same as in a, except for 16 June 2003.
Time vs. Precipitation, Gage Height (Pigeon House Creek @ Cameron Village @ Raleigh 29-30 July 2003) 1.00 9 Precipitation 8 Gage Height 7 ) 0.75 n i 6 (ft) ( t n h io 5 g t i a 0.50 e
it 4 H ip e c g
e 3 a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.37e. Same as in a, except for 29 July 2003.
219 Time vs. Precipitation, Gage Height (Pigeon House Creek @ Cameron Village @ Raleigh 9-10 August 2003) 1.00 7 Precipitation 6 Gage Height
) 0.75
n 5 i (ft) ( t n 4 h io g t i a 0.50 e it
3 H ip e c g e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.37f. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (Rocky Branch below Pullen Drive @ Raleigh 25-26 August 2002) 1.00 5 4.5 4
) 0.75 n i Precipitation 3.5 (ft) ( t n Gage Height 3 h io g t i a 0.50 2.5 e it H ip 2 e c g e 1.5 a G Pr 0.25 1 0.5 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.38a. Rocky Branch below Pullen Drive at Raleigh on 26 August 2002. No pre- determined flood stage.
220 Time vs. Precipitation, Gage Height (Rocky Branch below Pullen Drive @ Raleigh 10-11 October 2002) 1.00 9 Precipitation 8 Gage Height 7 ) 0.75 n i 6 (ft) ( t n h io 5 g t i a 0.50 e
it 4 H ip e c g
e 3 a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.38b. Same as in a, except for 11 October 2002.
Time vs. Precipitation, Gage Height (Rocky Branch below Pullen Drive @ Raleigh 8-10 April 2003) 1.00 6 Precipitation Gage Height 5
) 0.75 n i 4 (ft) ( t n h io g t i a 0.50 3 e it H ip e c g
e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 :1 :1 15 15 :1 :1 15 :15 :1 :15 :15 :1 :1 :15 :15 :1 :1 :15 :15 :1 :1 5: 8: 3: 00 03 06 09 12 1 1 21 00 0 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.38c. Same as in a, except for 9-10 April 2003.
221 Time vs. Precipitation, Gage Height (Rocky Branch below Pullen Drive @ Raleigh 15-16 June 2003) 1.00 6
5
) 0.75 n i 4 (ft) ( t n h io g t i a 0.50 3 e it
Precipitation H ip e c g
e 2 Gage Height a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.38d. Same as in a, except for 16 June 2003.
Time vs. Precipitation, Gage Height (Rocky Branch below Pullen Drive @ Raleigh 29-30 July 2003) 1.00 10 Precipitation 9 Gage Height 8
) 0.75 n
i 7 (ft) ( t n
6 h io g t i a 0.50 5 e it H ip 4 e c g e 3 a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.38e. Same as in a, except for 29 July 2003.
222 Time vs. Precipitation, Gage Height (Rocky Branch below Pullen Drive @ Raleigh 9-10 August 2003) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) (
5 t n h io g t i a 0.50 4 e it H ip 3 e c g e a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.38f. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (Walnut Creek @ Sunnybrook Drive near Raleigh 25-26 August 2002) 1.00 6 Precipitation Gage Height 5
) 0.75 n i 4 (ft) ( t n h io g t i a 0.50 3 e it H ip e c g
e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.39a. Walnut Creek at Sunnybrook Drive near Raleigh on 26 August 2002. No pre- determined flood stage.
223 Time vs. Precipitation, Gage Height (Walnut Creek @ Sunnybrook Drive near Raleigh 10-11 October 2002) 1.00 12 Precipitation Gage Height 10
) 0.75 n i 8 (ft) ( t n h io g t i a 0.50 6 e it H ip e c g
e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.39b. Same as in a, except for 11 October 2002.
Time vs. Precipitation, Gage Height (Walnut Creek @ Sunnybrook Drive near Raleigh 8-10 April 2003) 1.00 9 Precipitation 8 Gage Height 7 ) 0.75 n i 6 (ft) ( t n h io 5 g t i a 0.50 e
it 4 H ip e c g
e 3 a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 :1 :1 15 15 :1 :1 15 :15 :1 :15 :15 :1 :1 :15 :15 :1 :1 :15 :15 :1 :1 5: 8: 3: 00 03 06 09 12 1 1 21 00 0 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.39c. Same as in a, except for 9-10 April 2003.
224 Time vs. Precipitation, Gage Height (Walnut Creek @ Sunnybrook Drive near Raleigh 15-16 June 2003) 1.00 7 Precipitation 6 Gage Height
) 0.75
n 5 i (ft) ( t n 4 h io g t i a 0.50 e it
3 H ip e c g e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.39d. Same as in a, except for 16 June 2003.
Time vs. Precipitation, Gage Height (Walnut Creek @ Sunnybrook Drive near Raleigh 29-30 July 2003) 1.00 9 Precipitation 8 Gage Height
) 7
) 0.75 n i 6 (ft) ( t n h
5 g io i t
0.50 e a
it 4 H e ip g c 3 a e G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.39e. Same as in a, except for 29 July 2003.
225 Time vs. Precipitation, Gage Height (Crabtree Creek @ Hwy70 @ Raleigh 25-26 August 2002) 1.00 6
5
) 0.75 n i 4 (ft) ( t n h io g t i a 0.50 3 e it
Precipitation H ip e c g
e 2 Gage Height a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.40a. Crabtree Creek at Hwy. 70 at Raleigh on 26 August 2002. Flood stage is 18 ft.
Time vs. Precipitation, Gage Height (Crabtree Creek @ Hwy70 @ Raleigh 10-11 October 2002) 1.00 20 Precipitation FS = 18ft 18 Gage Height 16
) 0.75 n
i 14 (ft) ( t n
12 h io g t i a 0.50 10 e it H ip 8 e c g e 6 a G Pr 0.25 4 2 0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.40b. Same as in a, except for 11 October 2002.
226 Time vs. Precipitation, Gage Height (Crabtree Creek @ Hwy70 @ Raleigh 8-10 April 2003) 1.00 16 Precipitation 14 Gage Height
) 0.75 12 n i (ft) (
10 t n h io g t i a 0.50 8 e it H ip 6 e c g e a G Pr 0.25 4 2 0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 :1 15 :1 15 :1 :1 :15 :1 :15 :1 :15 :15 :1 :15 :1 :15 :15 :1 :15 9: 8: 0: 00 03 06 0 12 15 1 21 0 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.40c. Same as in a, except for 9-10 April 2003.
Time vs. Precipitation, Gage Height (Crabtree Creek @ Hwy70 @ Raleigh 15-16 June 2003) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) (
5 t n h io g t i a 0.50 4 e it H ip 3 e c g e a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.40d. Same as in a, except for 16 June 2003.
227 Time vs. Precipitation, Gage Height (Crabtree Creek @ Hwy70 @ Raleigh 29-30 July 2003) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) (
5 t n h io g t i a 0.50 4 e it H ip 3 e c g e a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.40e. Same as in a, except for 29 July 2003.
Time vs. Precipitation, Gage Height (Crabtree Creek @ Hwy70 @ Raleigh 9-10 August 2003) 1.00 9 8 7 ) 0.75 n i Precipitation 6 (ft) ( t n Gage Height h io 5 g t i a 0.50 e
it 4 H ip e c g
e 3 a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.40f. Same as in a, except for 9 August 2003.
228 Time vs. Precipitation, Gage Height (Unnamed Tributary to Swift Cr. near Yates Mill Pond 10-11 October 2002) 1.00 3 Precipitation Gage Height 2.5
) 0.75 n i 2 (ft) ( t n h io g t i a 0.50 1.5 e it H ip e c g
e 1 a G Pr 0.25 0.5
0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.41a. Unnamed Tributary to Swift Creek near Yates Mill Pond on 11 October 2002. No pre-determined flood stage.
Time vs. Precipitation, Gage Height (Unnamed Tributary to Swift Cr. near Yates Mill Pond 8-10 April 2003) 1.00 2.5 Precipitation Gage Height 2
) 0.75 n i (ft) ( t n
1.5 h io g t i a 0.50 e it H ip 1 e c g e a G Pr 0.25 0.5
0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 15 :1 15 :1 15 :1 :15 :1 :15 :1 :15 :1 :15 :1 :15 :1 :15 :1 :15 9: 5: 1: 3: 00 03 06 0 12 1 18 2 00 0 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.41b. Same as in a, except for 9-10 April 2003.
229 Time vs. Precipitation, Gage Height (Unnamed Tributary to Swift Cr. near Yates Mill Pond 15-16 June 2003) 1.00 2 Precipitation 1.8 Gage Height 1.6
) 0.75 n
i 1.4 (ft) ( t n
1.2 h io g t i a 0.50 1 e it H ip 0.8 e c g e 0.6 a G Pr 0.25 0.4 0.2 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.41c. Same as in a, except for 16 June 2003.
Time vs. Precipitation, Gage Height (Unnamed Tributary to Swift Cr. near Yates Mill Pond 29-30 July 2003) 1.00 1.6 Precipitation 1.4 Gage Height
) 0.75 1.2 n i (ft) (
1 t n h io g t i a 0.50 0.8 e it H ip 0.6 e c g e a G Pr 0.25 0.4 0.2 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.41d. Same as in a, except for 29 July 2003.
230 Time vs. Precipitation, Gage Height (Unnamed Tributary to Swift Cr. near Yates Mill Pond 9-10 August 2003) 1.00 1.8 Precipitation 1.6 Gage Height 1.4 ) 0.75 n i 1.2 (ft) ( t n h io 1 g t i a 0.50 e
it 0.8 H ip e c g
e 0.6 a G Pr 0.25 0.4 0.2 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.41e. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (Crabtree Creek @ Anderson Drive @ Raleigh 25-26 August 2002) 1.00 4 Precipitation 3.5 Gage Height
) 0.75 3 n i (ft) (
2.5 t n h io g t i a 0.50 2 e it H ip 1.5 e c g e a G Pr 0.25 1 0.5 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.42a. Crabtree Creek at Anderson Drive at Raleigh on 26 August 2002. Flood stage is 18 ft.
231 Time vs. Precipitation, Gage Height (Crabtree Creek @ Anderson Drive @ Raleigh 10-11 October 2002) 1.00 20 Precipitation FS = 18ft 18 Gage Height 16
) 0.75 n
i 14 (ft) ( t n
12 h io g t i a 0.50 10 e it H ip 8 e c g e 6 a G Pr 0.25 4 2 0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.42b. Same as in a, except for 11 October 2002.
Time vs. Precipitation, Gage Height (Crabtree Creek @ Anderson Drive @ Raleigh 8-10 April 2003) 1.00 16 Precipitation 14 Gage Height
) 0.75 12 n i (ft) (
10 t n h io g t i a 0.50 8 e it H ip 6 e c g e a G Pr 0.25 4 2 0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 :1 15 :1 15 :1 :1 :15 :1 :15 :1 :15 :15 :1 :15 :1 :15 :15 :1 :15 9: 8: 0: 00 03 06 0 12 15 1 21 0 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.42c. Same as in a, except for 9-10 April 2003.
232 Time vs. Precipitation, Gage Height (Crabtree Creek @ Anderson Drive @ Raleigh 15-16 June 2003) 1.00 6 Precipitation Gage Height 5
) 0.75 n i 4 (ft) ( t n h io g t i a 0.50 3 e it H ip e c g
e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.42d. Same as in a, except for 16 June 2003.
Time vs. Precipitation, Gage Height (Crabtree Creek @ Anderson Drive @ Raleigh 29-30 July 2003) 1.00 7 Precipitation 6 Gage Height
) 0.75
n 5 i (ft) ( t n 4 h io g t i a 0.50 e it
3 H ip e c g e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.42e. Same as in a, except for 29 July 2003.
233 Time vs. Precipitation, Gage Height (Crabtree Creek @ Anderson Drive @ Raleigh 9-10 August 2003) 1.00 10 Precipitation 9 Gage Height 8
) 0.75 n
i 7 (ft) ( t n
6 h io g t i a 0.50 5 e it H ip 4 e c g e 3 a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.42f. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (Crabtree Creek @ Old Wake Forest Road @ Raleigh 25-26 August 2002) 1.00 4 Precipitation 3.5 Gage Height
) 0.75 3 n i (ft) (
2.5 t n h io g t i a 0.50 2 e it H ip 1.5 e c g e a G Pr 0.25 1 0.5 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.43a. Crabtree Creek at Old Wake Forest Road at Raleigh on 26 August 2002. Flood stage is 13 ft.
234 Time vs. Precipitation, Gage Height (Crabtree Creek @ Old Wake Forest Road @ Raleigh 10-11 October 2002) 1.00 20 Precipitation 18 Gage Height 16
) 0.75 n
i 14 (ft) (
FS = 13ft t n
12 h io g t i a 0.50 10 e it H ip 8 e c g e 6 a G Pr 0.25 4 2 0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.43b. Same as in a, except for 11 October 2002.
Time vs. Precipitation, Gage Height (Crabtree Creek @ Old Wake Forest Road @ Raleigh 8-10 April 2003) 1.00 14 Precipitation 12 Gage Height
) 0.75
n 10 i (ft) ( t n 8 h io g t i a 0.50 e it
6 H ip e c g e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 :1 15 :1 15 :1 :1 :15 :1 :15 :1 :15 :15 :1 :15 :1 :15 :15 :1 :15 9: 8: 0: 00 03 06 0 12 15 1 21 0 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.43c. Same as in a, except for 9-10 April 2003.
235 Time vs. Precipitation, Gage Height (Crabtree Creek @ Old Wake Forest Road @ Raleigh 15-16 June 2003) 1.00 4 Precipitation 3.5 Gage Height
) 0.75 3 n i (ft) (
2.5 t n h io g t i a 0.50 2 e it H ip 1.5 e c g e a G Pr 0.25 1 0.5 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.43d. Same as in a, except for 16 June 2003.
Time vs. Precipitation, Gage Height (Crabtree Creek @ Old Wake Forest Road @ Raleigh 29-30 July 2003) 1.00 5 Precipitation 4.5 Gage Height 4
) 0.75 n
i 3.5 (ft) ( t n
3 h io g t i a 0.50 2.5 e it H ip 2 e c g e 1.5 a G Pr 0.25 1 0.5 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.43e. Same as in a, except for 29 July 2003.
236 Time vs. Precipitation, Gage Height (Crabtree Creek @ Old Wake Forest Road @ Raleigh 9-10 August 2003) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) (
5 t n h io g t i a 0.50 4 e it H ip 3 e c g e a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.43f. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (Swift Creek near Apex 10-11 October 2002) 1.00 14 Precipitation 12 Gage Height
) 0.75
n 10 i (ft) ( t n 8 h io g t i a 0.50 e it
6 H ip e c g e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.44a. Swift Creek near Apex on 11 October 2002. No pre-determined flood stage.
237 Time vs. Precipitation, Gage Height (Swift Creek near Apex 8-10 April 2003) 1.00 12 Precipitation Gage Height 10
) 0.75 n i 8 (ft) ( t n h io g t i a 0.50 6 e it H ip e c g
e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 :1 15 :1 15 :1 :1 :15 :1 :15 :1 :15 :15 :1 :15 :1 :15 :15 :1 :15 9: 8: 0: 00 03 06 0 12 15 1 21 0 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.44b. Same as in a, except for 9-10 April 2003.
Time vs. Precipitation, Gage Height (Swift Creek near Apex 15-16 June 2003) 1.00 9 Precipitation 8 Gage Height 7 ) 0.75 n i 6 (ft) ( t n h io 5 g t i a 0.50 e
it 4 H ip e c g
e 3 a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.44c. Same as in a, except for 16 June 2003.
238 Time vs. Precipitation, Gage Height (Swift Creek near Apex 29-30 July 2003) 1.00 8 Precipitation 7 Gage Height
) 0.75 6 n i (ft) (
5 t n h io g t i a 0.50 4 e it H ip 3 e c g e a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.44d. Same as in a, except for 29 July 2003.
Time vs. Precipitation, Gage Height (Swift Creek near Apex 9-10 August 2003) 1.00 10 Precipitation 9 Gage Height 8
) 0.75 n
i 7 (ft) ( t n
6 h io g t i a 0.50 5 e it H ip 4 e c g e 3 a G Pr 0.25 2 1 0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.44e. Same as in a, except for 9 August 2003.
239 Time vs. Precipitation, Gage Height (Nahunta Swamp near Pikeville 25-26 August 2002) 1.00 6 Precipitation Gage Height 5
) 0.75 n i 4 (ft) ( t n h io g t i a 0.50 3 e it H ip e c g
e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.45a. Nahunta Swamp near Pikeville on 26 August 2002. No pre-determined flood stage.
Time vs. Precipitation, Gage Height (Nahunta Swamp near Pikeville 10-11 October 2002) 1.00 6 Precipitation Gage Height 5
) 0.75 n i 4 (ft) ( t n h io g t i a 0.50 3 e it H ip e c g
e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.45b. Same as in a, except for 11 October 2002.
240 Time vs. Precipitation, Gage Height (Nahunta Swamp near Pikeville 8-10 April 2003) 1.00 12 Precipitation Gage Height 10
) 0.75 n i 8 (ft) ( t n h io g t i a 0.50 6 e it H ip e c g
e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 5 5 5 5 5 :1 :1 :1 15 :1 :1 15 :1 15 :1 :1 :15 :1 :15 :1 :15 :15 :1 :15 :1 :15 :15 :1 :15 9: 8: 0: 00 03 06 0 12 15 1 21 0 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.45c. Same as in a, except for 9-10 April 2003.
Time vs. Precipitation, Gage Height (Nahunta Swamp near Pikeville 29-30 July 2003) 1.00 6 Precipitation Gage Height 5
) 0.75 n i 4 (ft) ( t n h io g t i a 0.50 3 e it H ip e c g
e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.45d. Same as in a, except for 29 July 2003.
241 Time vs. Precipitation, Gage Height (Nahunta Swamp near Pikeville 9-10 August 2003) 1.00 7 Precipitation 6 Gage Height
) 0.75
n 5 i (ft) ( t n 4 h io g t i a 0.50 e it
3 H ip e c g e 2 a G Pr 0.25 1
0.00 0
5 5 5 5 5 5 5 5 :1 :1 :1 :1 15 15 15 :15 :15 :15 :15 :15 :1 :1 :1 :1 2: 5: 8: 00 03 06 09 1 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.45e. Same as in a, except for 9 August 2003.
Time vs. Precipitation, Gage Height (Contentnea Creek near Lucama 10-11 October 2002) 1.00 4 Precipitation 3.5 Gage Height
) 0.75 3 n i (ft) (
2.5 t n h io g t i a 0.50 2 e it H ip 1.5 e c g e a G Pr 0.25 1 0.5 0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.46a. Contentnea Creek near Lucama on 11 October 2002. Flood stage is 11 ft.
242 Time vs. Precipitation, Gage Height (Contentnea Creek near Lucama 29-30 July 2003) 1.00 2.5 Precipitation
Gage Height 2
) 0.75 n i (ft) ( t n
1.5 h io g t i a 0.50 e it H ip 1 e c g e a G Pr 0.25 0.5
0.00 0
5 5 5 5 5 5 5 5 5 5 :1 :1 15 :1 :1 15 15 :1 :1 :15 :1 :1 :15 :15 :1 :1 6: 5: 8: 00 03 0 09 12 1 1 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.46b. Same as in a, except for 29 July 2003.
Time vs. Precipitation, Gage Height (Contentnea Creek near Lucama 9-10 August 2003) 1.00 12 Precipitation Gage Height 10
) 0.75 n i 8 (ft) ( t n h io g t i a 0.50 6 e it H ip e c g
e 4 a G Pr 0.25 2
0.00 0
5 5 5 5 5 5 5 5 :1 :1 15 15 15 15 :1 :1 :1 :15 :15 :15 :1 :1 :1 :15 6: 9: 2: 5: 00 03 0 0 1 1 18 21 00 03 06 09 12 15 18 21 Local Time (15 min)
FIG A.46c. Same as in a, except for 9 August 2003.
243