Flood of October 1996 in Southern Maine by Glenn Hodgkins and Gregory J. Stewart
U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 97-4189
Prepared in cooperation with the FEDERAL EMERGENCY MANAGEMENT AGENCY
uses Augusta, Maine science for a changing world 1997 U.S. DEPARTMENT OF THE INTERIOR
Bruce Babbitt, Secretary
U.S. GEOLOGICAL SURVEY
Mark Schaefer, Acting Director
For additional information Copies of this report can contact: be purchased from:
Chief, Maine District USGS Information Services U.S. Geological Survey Box 25286 26 Ganneston Drive Denver, CO 80225 Augusta, Me 04330 Telephone: (303) 202-4200 Telephone: (207) 622-8201 CONTENTS
Abstract 1 Introduction 1 Purpose and Scope 1 Acknowledgments 2 Antecedent Hydrologic Conditions 2 Streamflows 2 Rainfall 2 Storm Characteristics 2 Rainfall Amounts 4 Rainfall Frequency 5 Description of Flood 6 Peak Water-Surface Elevations 6 Peak Flows 6 Peak-Flow Frequency 20 Extrapolation of Peak-Flow Frequency 21 Reservoir Storage 22 Flood Damages 23 Historical Perspective on Flood 23 Historical Peak Flows 24 Historical Peak Water-Surface Elevations 25 Summary and Conclusions 26 References Cited 27
FIGURES
1. Map showing location of study area and selected points 3 2. Graph showing daily rainfall totals from September 1, 1996 to October 19, 1996 at Portland International Jetport 4 3. Graph showing cumulative rainfall from October 20-22, 1996 at Portland International Jetport 5 4. Photograph showing aerial view of Presumpscot River at Route 302 in Westbrook, Maine on October 22, 19967 5. Photograph showing Presumpscot River at Route 302 in Westbrook, Maine on October 22, 19967 6. Photograph showing flooding at Winona Avenue in the Ocean Park area of Old Orchard Beach, Maine on October 22, 1996 8 7. Photograph showing Stroudwater River at Saco Street in Westbrook, Maine on October 22, 19968 8. Photograph showing Cascade Brook (Stuart Brook) at Old Blue Point Road in Scarborough, Maine on October 22, 1996 9 9. Map showing total rainfall isolines and location of sites where peak water-surface elevations were determined for October 1996 southern Maine flood 10
Flood of October 1996 in Southern Maine USGS WRIR 97-4189 jjj 10. Map showing total rainfall isolines and location of sites where peak flows and recurrence intervals were determined for October 1996 southern Maine flood 19 11. Graph showing relation between recurrence interval of peak flows and basin-average rainfall for October 1996 southern Maine flood 22 12. Graph showing Crippen and Bue region 1 envelope curve with data from October 1996 southern Maine flood 25
TABLES
1. Peak water-surface elevations for October 1996 southern Maine flood 11 2. Peak-flow data for October 1996 flood and previous floods in southern Maine 18 3. Recurrence intervals, exceedance probabilities, and peak flows for the Presumpscot River at the S. D. Warren bridge in Westbrook, Maine 20 4. Elevation and usable storage data for Sebago Lake 23 5. Significant historical peak flows on the Presumpscot River in Westbrook, Maine 24 6. Flood flows that defined Crippen and Bue region 1 envelope curve 25 7. Historical peak water-surface elevations on the Presumpscot River in Maine 26
CONVERSION FACTORS
Multiply By To obtain
Length inch (in) 25.40 millimeter foot (ft) 0.3048 meter mile (mi) 1.609 kilometer Area square mile (mi2) 2.590 square kilometer Volume cubic foot (ft3) 0.02832 cubic meter
Flow cubic foot per second (ft3/s) 0.02832 cubic meter per second
VERTICAL DATUM
In this report, all elevations are referenced to the National Geodetic Vertical Datum of 1929, a geodetic datum derived from a general adjustment of the first-order level nets of both the United States and Canada. It was formerly called Sea Level Datum of 1929.
jV Flood of October 1996 in Southern Maine USGS WRIR 97-4189 Flood of October 1996 in Southern Maine
By Glenn Hodgkins and Gregory J. Stewart
ABSTRACT Documented flood data are valuable to many people. Peak flows, recurrence intervals of peak flows, and Up to 19.19 inches of rain were recorded in southern peak water-surface elevations (associated with the peak Maine from October 20-22, 1996. This rainfall caused flows) are used to establish, assess, and verify the severe flooding that resulted in one death, damage to accuracy of Federal Emergency Management Agency more than 2,100 homes and businesses, and the (FEMA) flood insurance study 100-year and 500-year destruction of bridges and dams in 8 communities. floodplain limits and flood profiles. These flood Peak flows, with estimated recurrence intervals of insurance studies are used to promote sound flood plain greater than 500 years, were recorded on 3 streams. management by local, State, and Federal officials. The peak flow on the Presumpscot River in Westbrook, Flood information is also important in the design of Maine was 68 percent larger than any other flow at that hydraulic structures (such as bridges, culverts, and location in the last 102 years. dams), helping to ensure the safety and cost effectiveness of the structures. This report provides a detailed description of the October 1996 flood in southern Maine. It presents peak streamflows for 13 sites, peak-flow recurrence intervals Extraordinary amounts of rain fell in southern Maine for 12 of these 13 sites, and peak water-surface from October 20-22, 1996. Record-breaking elevations for 74 sites; describes hydrologic conditions streamflows and consequent flooding caused one death, prior to the October 20-22 storm; provides a method damage to more than 2,100 homes and businesses, and for estimating the recurrence intervals of peak flows at destruction of bridges and dams in 8 communities. The sites where peak flows were not determined (for this U.S. Geological Survey (USGS) in cooperation with flood); and reports a significant amount of historical the Federal Emergency Management Agency (FEMA), flood data for the Presumpscot River. made observations and measurements to describe and document the October 1996 flood. INTRODUCTION Purpose And Scope Typically, the most important factor contributing to extreme flood flows on streams in Maine is rainfall. This report provides a detailed description of the Total rainfall amounts, rainfall intensity, and the spatial October 1996 .flood in southern Maine (fig. 1). The distribution of rainfall in a drainage basin are all meteorological characteristics of the October 20-22 important in determining the magnitude of flood flows. storm are summarized and the rainfall amounts from Other significant contributing factors include the the storm and their associated frequencies are given. antecedent hydrologic conditions (the conditions prior Hydrologic conditions (streamflow and rainfall) in the to a flood, such as soil moisture and streamflows) and area, prior to the storm, are described. This report gives the physical characteristics of the drainage basin in peak water-surface elevations for 74 sites, peak question (such as drainage area and stream slope). streamflows for 13 sites, and peak-flow recurrence Factors such as snowmelt and dam breaks, in certain intervals for 12 of these 13 sites from the October 1996 situations, can also be important. Extreme water- flood. This report also describes a method for surface elevations are typically caused by extreme estimating the recurrence intervals of peak flows at flood flows, but can be aggravated or caused by ice sites where peak flows were not determined (for this jams, debris jams, and other factors. flood). Reservoir storage data for Sebago Lake are given, flood damages in southern Maine are described,
Flood of October 1996 in Southern Maine USGS WRIR 97-4189 1 and a significant amount of historical peak flow and The daily mean flow on October 19, 1996 at the Royal peak water-surface elevation data, mostly for the lower River gaging station was 52 cubic feet per second s) Presumpscot River, are presented. (ft /s) and was receding from a small peak on October 10, 1996. Eighteen percent of all the daily mean flows Acknowledgments at the Royal River gaging station from October 1, S. D. Warren Co. provided historical streamflow and 1949, to September 30, 1996, were less than 52 ft3/s o peak water-surface elevation data for the Presumpscot and 50 percent were less than 120 ft /s. Thirty nine River and provided information on the Presumpscot percent of all the October daily mean flows from River and Sebago Lake for the October 1996 southern October 1, 1949, to October 31, 1995, were less than o o Maine flood. Meteorological data were provided by the 52 ft /s and 50 percent were less than 61 ft /s. The National Weather Service. Central Maine Power Co. streamflow at the Royal River gaging station prior to provided streamflow data for the lower Saco River. the October 1996 southern Maine flood was a typical October flow. This report is the culmination of an intensive effort by dedicated personnel of the U.S. Geological Survey Rainfall (USGS). The following USGS employees provided significant help collecting the data, analyzing the data, The National Weather Service operates a recording rain preparing the final report, and/or reviewing the final gage at the Portland International Jetport (fig. 1). The report: William P. Bartlett, Jr., James M. Caldwell, daily rainfall totals at the Jetport from September 1, Andrew R. Cloutier, Gary D. Firda, Richard A. 1996 to October 19, 1996 are shown in figure 2. The Fontaine, William H. Kirby, Robert G. Lippert, Gloria total rainfall for September 1996 was 3.54 inches and L. Morrill, Joseph P. Nielsen, Scott A. Olson, Perry N. the total rainfall from October 1 through October 19, Silverman, and Chester Zenone. 1996, was 1.68 inches. Using data from 1961 to 1990, daily normal rainfall amounts were computed ANTECEDENT HYDROLOGIC (National Oceanic and Atmospheric Administration, 1990). The normal rainfall total for September is CONDITIONS 3.09 inches. The normal rainfall total for October 1 to The hydrologic conditions in a watershed prior October 19 is 2.21 inches. The total rainfall in the (antecedent) to a storm can be important in weeks prior to the October 1996 southern Maine flood determining the severity of flooding. For example, high was near normal. streamflows prior to extreme rainfall would result in higher flood flows than if prior streamflows were low. STORM CHARACTERISTICS Prior to the extreme rainfall on October 20-22, 1996, which caused the flooding in southern Maine, only Very large amounts of rain fell in southern Maine from minimal antecedent condition data are available. the afternoon of October 20, 1996, to early in the Information that is available on streamflows and morning of October 22. The maximum recorded rainfall is presented in this section. rainfall from this storm was 19.19 inches in the Camp Ellis area of Saco, Maine (fig. 1). This record-breaking precipitation was caused by a combination of several Streamflows meteorological factors. On Sunday, October 20, a The Royal River in Yarmouth, Maine (fig. 1, site 74 in strong coastal low pressure system (northeaster) was this report) was the closest active long-term streamflow located near Washington, D. C. At the same time, gaging station to the severely flooded area of southern Hurricane Lili was located about 900 miles southeast Maine in October 1996. The flow conditions at this site of Portland, Maine, and a strong high pressure system just prior to the October 1996 flood are assumed to be was centered over Labrador. The high pressure system generally representative of flow conditions at other acted as a block, preventing other systems from streams in the area shown in figure 1. moving. The northeaster remained nearly stationary for about 36 hours while moisture from Hurricane Lili became entrained into the large circulation created by
2 Flood of October 1996 in Southern Maine USGS WRIR 97-4189 70°45' JO'301 70° 15'
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Base from U.S. Geological Survey Portland, 0 SCALE SMILES and Kittery quadrangles 1:100,000,1985
0 5 KILOMETERS Figure 1 . Location of study area and selected points.
Flood of October 1996 in Southern Maine USGS WRIR 97-4189 3 10 15 20 25 30 10 15 9 SEPTEMBER OCTOBER 1996
Figure 2. Daily rainfall totals from September 1,1996 to October 19,1996 at Portland International Jetport (National Oceanic and Atmospheric Administration, 1996a). the northeaster. This "conveyor belt" of moisture from The National Weather Service rain gage at the Portland Hurricane Lili, combined with the slow movement of Internationa] Jetport was the only recording rain gage the northeaster, resulted in the tremendous rainfall in southern Maine during the October 20-22, 1996 totals in Maine (Tom Hawley, National Weather storm. Figure 3 is a graph of the cumulative rainfall Service, written commun., 1996). amounts at the Jetport from October 20-22, 1996 and is based on hourly rainfall data from the Jetport gage Rainfall Amounts (National Oceanic and Atmospheric Administration, 1996b). Maximum rainfall totals for different time The rainfall totals from the October 20-22, 1996 storm periods were calculated using this same hourly rainfall are shown with lines of equal rainfall (rainfall isolines) data. The maximum 48-hour, 24-hour, 12-hour, 6-hour, in figure 9 (page 10). These isolines were computed by and 2-hour rainfall totals at the Jetport were 14.65 the National Weather Service (NWS), based on rainfall inches, 13.32 inches, 8.86 inches, 4.81 inches, and 2.06 totals from NWS observers in southern Maine. The inches, respectively. largest recorded totals were: 19.19 inches in the Camp Ellis area of Saco, 19.00 inches in Gorham, 17.62 The data in figure 3 show that most of the rain at the inches in Westbrook, 16.00 inches in South Windham, Jetport from this storm fell in a 26-hour period from and 15.52 inches in Scarborough (Tom Hawley, written October 20 at 8:00 p.m. to October 21 at 10:00 p.m. commun., 1997). The relatively uniform slope in this figure indicates
Flood of October 1996 in Southern Maine USGS WRIR 97-4189 that most of the rain at the Jetport fell at a relatively totals. The n-year (where n equals 100, 50, 25, 10, 5, constant rate. and 2), 1-day and 2-day rainfall recurrence intervals for Portland were interpolated from these maps. The At the Jetport, the total rainfall for October 20-22, 1996 recurrence interval is the average period of time was 14.65 inches and the maximum 24-hour total was between rainfalls that are greater than, or equal to, a 13.32 inches. This 24-hour total shattered the previous specified magnitude. As an example of recurrence 24-hour record of 7.83 inches set during Hurricane Bob interval, the 100-year rainfall is the rainfall that, on in August 1991. Rainfall records for Portland have long-term average, would be equaled or exceeded once been kept since 1871 (Tom Hawley, oral commun., every 100 years. Conversely, this means that there is a 1997). The total rainfall isolines in figure 9, indicate one percent chance, every year, that a rainfall of this that the 13.32-inch 24-hour rainfall at the Jetport was magnitude will be equaled or exceeded. exceeded at other locations. The 48-hour, n-year rainfall amounts for Portland were Rainfall Frequency computed by applying the adjustment factor from the Atlas of Precipitation Extremes for the Northeastern The Atlas of Precipitation Extremes for the United States and Southeastern Canada to the 2-day Northeastern United States and Southeastern Canada rainfall totals. The 24-hour rainfalls were computed by (Wilks and Cember, 1993) contains maps with applying the adjustment factor to the I-day rainfalls. recurrence-interval isolines for 1 -day and 2-day rainfall
16
14
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12am 4am Sam 12pm 4pm 8pm 12am 4am Sam 12pm 4pm 8pm 12am 4am Sam 12pm 4pm 8pm 12am
October 20, 1996 October 21, 1996 October 22, 1996 Figure 3. Cumulative rainfall from October 20-22, 1996 at Portland International Jetport.
Flood of October 1996 in Southern Maine USGS WRIR 97-4189 The 48-hour and 24-hour adjustment factors in the Peak water-surface elevations were based on high- Atlas were obtained from Hershfield (1961). The 12- water marks which were identified using the hour, 6-hour, and 2-hour rainfalls were computed by techniques of Benson and Dalrymple (1967). These applying adjustment factors to the I-day rainfall totals. marks were surveyed to the National Geodetic Vertical These adjustment factors in the Atlas are originally Datum of 1929. At each site, personnel would typically from Huff and Angel (1992) and correspond closely to identify three or more high-water marks on the those in Hershfield (Wilks and Cember, 1993). upstream side of a structure and three or more marks on the downstream side of the structure. High-water The Portland International Jetport rainfall totals from marks can include seed, conifer needle, and mud lines the October 20-22, 1996 storm were compared to the n- on trees and buildings; and debris and wash lines on year recurrence interval rainfall totals. The 48-hour, 24- the ground. The elevations listed in table 1 are the best hour, and 12-hour rainfall totals were greater than 100- estimates of the true peak water-surface elevations year recurrence interval events. The 6-hour rainfall from the October 1996 flood. These elevations are total was a 50-year recurrence interval event and the 2- based on the quality of the individual flood marks at hour rainfall total was a 2- to 5-year event. The 2-hour each site. It is possible for individual flood marks to be recurrence interval shows that the October 20-22 storm lower or higher than the true peak flood elevation for a did not produce the extreme rainfall intensities that can variety of reasons. For example, wave action can cause be associated with thunderstorms and hurricanes. As marks to be higher than peak water-surface elevations discussed in the Rainfall Amounts section, most of the and settling of flood debris can cause marks to be lower rain from this storm fell at a relatively constant rate for than the peak water-surface elevations. Any other about 26 hours (at the Portland International Jetport). available information, such as observations by local residents, was also used in the process of evaluating the DESCRIPTION OF FLOOD high water marks. The rain that fell in southern Maine on October 20-22, Flood peak elevation data should be used with an 1996, caused record-breaking streamflows and understanding of the methods used to obtain them and consequent flooding. On October 24, 1996, President their relation to the river profile. For example, flood Clinton declared an emergency in the State of Maine, elevations may be affected by pileup on the upstream and on October 28 a major disaster declaration was side of hydraulic structures (bridges, culverts, etc.) and issued for York and Cumberland Counties (Federal by drawdown on the downstream side of these Emergency Management Agency, 1996). The structures (Fontaine and Nielsen, 1994). Interpolation following sections describe the flood and its effects. of peak water-surface elevations between the sites The photographs included as figures 4 through 8 listed in table 1 should not be done without further illustrate the severity of the flooding. investigation.
Peak Water-Surface Elevations The time of the peak elevation or the peak flow from Peak water-surface elevations were determined for 74 the October 1996 southern Maine flood is not known sites in southern Maine following the October 1996 for most sites. The peak elevation on the Presumpscot flood (table 1, page 11). The site locations and the total River at S. D. Warren Co. in Westbrook was on rainfall isolines from the October 20-22, 1996 storm October 22 at about 2:00 a.m. (Tom Howard, S. D. are shown in figure 9 (page 10). Most of the sites are at Warren Co., oral commun., 1997). bridges or culverts, which typically have a large influence on peak water-surface elevations. For Peak Flows example, bridges and culverts often cause constrictions The peak streamflows determined for the October 1996 in a stream during flood flows that result in higher peak southern Maine flood and their associated recurrence water-surface elevations on the upstream side of the intervals and exceedance probabilities are listed in structure than on the downstream side. Because of this, table 2 (page 18). Also included in the table are the both upstream and downstream peak water-surface highest peak flows previously known at these sites, the elevations were measured and reported, when possible. periods for which peak flow data are available (periods
6 Flood of October 1996 in Southern Maine USGS WRIR 97-4189 Figure 4. Aerial view of the Presumpscot River at Route 302 in Westbrook, Maine (site 11) on October 22, 1996 (Photograph by John Patriquin / The Port land Newspapers).
Figure 5. Presumpscot River at Route 302 in Westbrook, Maine (site 11) on Octo ber 22, 1996. Note the high-water mark on Route 302 and the debris on the upstream guardrail of the bridge (Photograph by David A. Ftodgers / The Portland Newspapers).
Flood of October 1996 in Southern Maine USGS WRIR 97-4189 Figure 6. Flooding at Winona Avenue in the Ocean Park area of Old Orchard Beach, Maine (site 54) on October 22, 1996 (Photograph by David A. Rodgers / The Portland Newspapers).
Figure 7. Stroudwater River at Saco Street in Westbrook, Maine (site 26) on Octo ber 22, 1996 (Photograph by Doug Jones / The Portland Newspapers).
8 Flood of October 1996 in Southern Maine USGS WRIR 97-4189 Figure 8. Cascade Brook (Stuart Brook) at Old Blue Point Road in Scarborough, Maine (site 34) on October 22, 1996 (Photograph by David A. Rodgers/ The Portland Newspapers).
of known peak flows), and the drainage areas of the between site 14 and site 10. The peak flows at sites. The location of the sites with peak-flow Stroudwater River in Portland (site 28) and at Capisic determinations and their associated recurrence intervals Brook in Portland (site 55) were computed by using a are shown in figure 10 (page 19). Recurrence intervals culvert flow computation technique (Bodhaine, 1967). are discussed in the Peak-Flow Frequency section of The peak flow at Cascade Brook in Saco (site 33) was this report. Total rainfall isolines for the October 20-22, calculated by using the Water-Surface Profile 1996 storm are also included in this figure. Computation (WSPRO) step-backwater computer model (Shearman, 1990) using critical depth The flows in table 2 were determined by several assumptions (Chow, 1959) and was verified by use of a different methods. The Presumpscot River peak flow in slope-area peak-flow computation (Dalrymple and Falmouth (site 14) was computed by using a contracted Benson, 1968). The contracted opening, culvert, opening computation technique (Matthai, 1967). The critical depth, and slope-area methods all use hydraulic Presumpscot River in Westbrook (site 10) is at a principles to compute peak flows from peak water- discontinued USGS streamflow gaging station. surface elevations and channel geometry data. However, an accurate peak flow determination at this site for the October 1996 flood was not possible. For Crooked River in Casco/Naples (site 41), Stony Brook this reason, the peak flow was calculated by applying a in Sebago (site 62), and Royal River in Yarmouth (site drainage area correction (Morrill, 1975) to the 74) are active (1997) USGS stream gaging stations. calculated flow at site 14. Flows released from Sebago The peak flows for these sites were computed from the Lake were insignificant compared to the peak flows on relation between water-surface elevation and flow, the lower Presumpscot River for the October 1996 using standard USGS techniques (Rantz, 1982). Pease flood (as shown in the Reservoir Storage section of this Brook in Cornish (site 42), Collyer Brook in Gray (site report). Because of this, only drainage areas for the part 49). Little Ossipee River in Limington (site 50), of the drainage basin downstream of the outlet of Mousam River in Sanford (site 59), and Branch Brook Sebago Lake were used for the drainage area correction in Wells (site 68) are former USGS gaging stations.
Flood of October 1996 in Southern Maine USGS WRIR 97-4189 70 "SO1 70° 15'
u iuu r\i EXPLANATION Line of equal precipitation, in inches -
Base from U.S. Geological Survey SCALE Portland, and Kittery quadrangles SMILES 1:100,000,1985 ______I 0 5 KILOMETERS Figure 9. Total rainfall isolines andI location of sites where pipeak water-surface elevations were determined for... October_ Jtober 1996 southern Maine flood. [Rainfall iisolines provided by National Weather Service.] 10 Flood off October 1996 In Southern Maine USGS WRIR 97-4189 Table 1. Peak water-surface elevations for October 1996 southern Maine flood [na indicates not applicable]
Latitude Longitude Upstream Downstream Site (degrees, (degrees, Elevationb Location elevation3 elevation3 number minutes, minutes, (feet) (feet) (feet) seconds) seconds)
Presumpscot River 1 Hurricane Rd. Bridge, 43 45 58 70 26 55 138.3 None found. na Windham/Gorham (50ft) 2 Gambo Rd. Bridge (discon 434451 70 26 21 137.2 118.0 na tinued)0, Windham/Gorham ' (20ft) (500 ft) 3 Route 202 Bridged, 43 44 02 70 25 35 115.7 97.6 na Windham/Gorham (600 ft) (300 ft) 4 Mallison St. Bridge6, 43 43 40 702515 None found. 95.5 (75 ft) na Windham/Gorham 87.5 (900 ft) 5 7 Rousseau Road, 43 41 55 7023 11 na na 80.9 Windham 6 40 Lincoln Streetf, 43 40 52 702219 na na 76.8 Westbrook 7 Bridge St. Bridge, 43 40 39 70 22 03 58.8 55.5 na Westbrook (130 ft) (75 ft) 8 20 Water St., 43 40 50 70 21 29 na na 54.5 Westbrook 9 Cumberland St. Bridges8, 43 40 59 70 21 08 52.5 51.6 na Westbrook (10ft) (30 ft) 10 S. D. Warren Bridge, 4341 11 70 20 55 47.5 None found. na Westbrook (5ft) 11 Route 302 Bridge, 434211 70 19 32 43.8 None found. na Westbrook/Portland (50 ft) 12 Blackstrap Rd. Bridge, 43 43 28 7018 11 41.0 40.0 na Falmouth (50ft) (200 ft) 13 Route 26/100 Bridge, 43 43 42 70 17 45 38.8 None found. na Falmouth (100ft) 14 1-95 Bridges, 43 43 40 70 17 10 37.2 36.4 na Falmouth (200 ft)h (150ft)1 15 Smelt Hill Dam, 43 43 06 701611 26.5 14.4 na Falmouth (350 ft) (170ft)
Flood of October 1996 in Southern Maine USGS WRIR 97-4189 11 Table 1. Peak water-surface elevations for October 1996 southern Maine flood--Continued [na indicates not applicable]
Latitude Longitude Upstream Downstream Site (degrees, (degrees, Elevation Location elevation3 elevation3 number minutes, minutes, (feet) (feet) (feet) seconds) seconds)
Nonesuch River
16 Watson Mill Rd. Culvert, 43 35 10 70 27 59 89.8 80.2 na Saco (50 ft) (100ft) 17 Broadturn Rd. Culvert, 43 36 13 70 26 48 50.0 49.2 na Scarborough (5ft) (5ft) 18 Mitchell Hill Rd. Culverts, 43 37 16 70 25 41 41.8 41.5 na Scarborough/Gorham (25 ft) (20 ft)
19 Beech Ridge Rd. Culvert, 43 37 39 70 24 33 37.9 37.5 na Scarborough (20 ft) (30ft) 20 Payne Rd. Culvert, 43 36 58 702120 25.3 None found. na Scarborough (30ft) 21 Route 114 (GorhamRd.) 433651 70 20 30 24.6 None found. na Culvert, Scarborough (70ft)
22 Route 1/9 Bridge, 43 36 33 701851 17.4 15.0 na Scarborough (5ft) (200 ft)
23 Route 207 (Black Point Rd.) 43 34 47 70 19 36 9.2 7.8 na Bridge, Scarborough (5ft) (5ft)
Stroudwater River
24 Route 114 Bridge, 43 38 36 70 25 20 91.5 91.0 na Gorham (50ft) (160ft)
25 Brackett St. Culverts, 43 39 23 70 24 04 None found. 80.4 na Gorham (15 ft) 26 Saco St. Culvert, 43 40 03 70 22 28 74.8 71.2 na Westbrook (15ft) (40 ft) 27 Spring St. Culvert, 43 39 38 702143 59.3 50.6 na Westbrook (10ft) (50ft)
28 Congress St. Bridge, 43 39 26 701851 33.8J (right 29.4 na Portland bank) (25 ft) (60 ft) 34.7J (left bank) (20 ft) 29 Westbrook St. Bridgek, 43 39 22 701838 26.0 None found. na Portland (100ft)
12 Flood of October 1996 in Southern Maine USGS WRIR 97-4189 Table 1. Peak water-surface elevations for October 1996 southern Maine Rood Continued [na indicates not applicable]
Latitude Longitude Upstream Downstream Site (degrees, (degrees, Elevationb Location elevation3 elevation3 number minutes, minutes, (feet) (feet) (feet) seconds) seconds)
Cascade Brook
30 Jenkins Rd. Bridge, 43 33 03 70 26 17 125.9 121.5 na Saco (20 ft) (80 ft)
31 Route 1 Culvert, 43 32 38 70 24 54 88.0 None found. na Saco (50ft) 32 Route 98 Culvert, 43 32 37 70 24 33 85.4 76.0 na Saco (60 ft) (60 ft) 33 Cascade Falls, 43 32 34 70 24 23 66.0 None found. na Saco (300 ft)
34 Old Blue Point Rd. Culvert, 43 33 27 70 22 54 20.3 15.9 na Scarborough1 (20 ft) (100 ft)
35 136 Pine Point Rd., 43 33 56 70 22 30 10.4 8.6 na Scarborough1 (10ft)m (25 ft)n
OTHER SITES BY TOWN
Biddeford
36 Moors Brook Culvert, 43 28 16 70 24 48 16.1 None found. na Route 208 (25 ft) 37 Thatcher Brook Culvert, 43 29 41 70 28 46 61.9 59.0 na South St. (40 ft) (30 ft) 38 West Brook Culvert, 43 28 19 70 27 23 124.5 None found. na West St. (130 ft)
Cape Elizabeth
39 Spurwink River Culvert, 43 35 24 70 14 44 8.8 7.0 na Spurwink Ave. (10ft) (30 ft) 40 Willow Brook Culverts, 43 35 41 701431 19.5 17.0 na Scott Dyer Rd. (5ft) (10ft)
Flood of October 1996 in Southern Maine USGS WRIR 97-4189 13 Table 1. Peak water-surface elevations for October 1996 southern Maine Rood Continued [na indicates not applicable]
Latitude Longitude ,, ,, Upstream Downstream Site (degrees, (degrees, , . a Elevationb Location . . elevationa elevationa number minutes, minutes, ._ . (feet) (feet) seconds)A \ seconds)A \ (feCt)
Casco/Naples 41 Crooked River Bridge, 43 58 45 70 33 51 None found. 280.8 na Route 11 (5ft)
Cornish 42 Pease Brook Culvert, 434715 704557 326.4 323.7 na Route 25/1 17 (30 ft) (30 ft)
Cumberland 43 East Branch Piscataqua 434627 701509 44.5 44.1 na River Culvert, Route 9 (55 ft) (105 ft)
Falmouth
44 Piscataqua River Culverts, 43 44 15 70 17 40 38.2 38.1 na Leighton Rd. (20 ft) (85 ft)
Gorham 45 Little River Bridge, 434315 702528 92.5 92.3 na Route 202 (60 ft) (50 ft) 46 Little River Bridge, 43 42 48 70 24 52 88.6 87.3 na Route 237 (120ft) (100ft)
47 South Branch Stroudwater 43 37 42 70 26 55 None found. 103.9 na River Culvert, Hodgdon Rd. (100 ft) 48 Tannery Brook Culverts, 434111 702651 147.1 140.8 na Route 114 (160ft) (50 ft)
Gray
49 Collyer Brook Bridges, 43 55 05 70 19 02 None found. 182.9 na Route 202/1 00/4 (50 ft)0
14 Flood of October 1996 in Southern Maine USGS WRIR 97-4189 Table 1. Peak water-surface elevations for October 1996 southern Maine Hood--Continued [na indicates not applicable]
Latitude Longitude Upstream Downstream Site T . (degrees, (degrees, Elevation13 Location . . elevation3 elevation3 number minutes, minutes, (feet) (feet) (feet) seconds) seconds)
Limington 50 Little Ossipee River Bridge, 43 41 21 70 40 15 280.9 None found. na Nason's Mills Rd. (35 ft)
Old Orchard Beach 51 42 Walnut St. 43 3 1 22 70 22 28 na na 10.3
52 15 Casco Ave. 43 30 06 70 23 07 na na 9.6
53 18 Roanoke Ave. 43 30 09 70 23 05 na na 9.5
54 1 8 Winona Ave. 43 30 12 70 23 03 na na 9.6
Portland 55 Capisic Brook Culvert, 43 39 52 70 1 8 27 36.3 34.0 na Capisic St. (65 ft) (5ft) 56 Fall Brook Culvert, 43 41 18 70 16 26 50.0 47.6 na Washington Ave. (120ft) (10ft)
Saco 57 Goosefare Brook Culvert, 43 3 1 06 70 25 1 1 33.4 30.0 na Ross Rd. (40 ft) (20 ft) 58 Sawyer Brook Culvert, 43 30 18 70 26 53 66.1 66. 1? na Sawyer St. (50ft) (30ft)
Sanford 59 Mousam River Bridge, 43 25 05 70 39 30 171.1 None found. na Wieners Mill Rd. (120ft)
Flood of October 1996 in Southern Maine USGS WRIR 97-4189 15 Table 1. Peak water-surface elevations for October 1996 southern Maine flood Continued [na indicates not applicable]
Latitude Longitude ., ,-. Upstream Downstream Site (degrees, (degrees, , . fl Elevationb Location . 5 . 5 elevation3 elevation3 number minutes, minutes, .,. (feet) (feet) seconds)A \ seconds)A\ ( feCt)
Scarborough 60 521 Route 1 43 34 37 70 22 40 na na 9.7
61 Stuart Brook Culvert, 43 33 40 70 23 58 77.4 69.6 na Route 1 (10ft) (25 ft)
Sebago
62 Stony Brook Culvert, 435120 703825 282.7 None found. na Route 114 (5ft)
South Portland 63 Kimball Brook Culverts, 433801 701501 12.4 12.2 na Highland Ave. (40 ft) (20 ft)
64 Long Creek Culverts, 43 38 30 70 20 02 52.5 52.5 na Maine Mall Rd. (20 ft) (20 ft)
65 Long Creek Culverts, 433810 701946 50.9 43.9 na Foden Rd. (5ft) (70ft) 66 Long Creek Culvertq, 433758 701850 26.9 8.4 na Route 9 (20 ft) (400 ft)
Wells
67 Blacksmith Brook Culvert, 431959 703417 47.4 42.1 na Route 1 (75 ft) (20 ft) 68 Branch Brook Culvert, 43 22 45 70 35 02 50.6 50.0 na Route 9A (50ft) (30 ft)
Westbrook
69 39 Eisenhower Drive 43 39 35 70 22 03 na na 59.5
70 29 Eisenhower Drive 43 39 34 70 21 59 na na 59.6
16 Flood of October 1996 in Southern Maine USGS WRIR 97-4189 Table 1. Peak water-surface elevations for October 1996 southern Maine Rood Continued [na indicates not applicable]
Latitude Longitude Upstream Downstream Site (degrees, (degrees, Elevationb Location elevation3 elevation3 number minutes, minutes, (feet) (feet) (feet) seconds) seconds)
Windham 71 Colley Wright Brook 43 44 38 70 23 55 None found. 119.6 na Bridge, Montgomery Rd. (50ft)
72 Colley Wright Brook 43 43 35 70 24 24 96.3 96.2 na Bridge, River Rd. (70ft) (100ft)
73 Pleasant River Bridge, 4347 11 7025 18 167.0 161.9 na Pope Rd. (70ft) (60 ft)
Yarmouth 74 Royal River Bridge, 43 47 56 70 10 45 15.1 None found. na East Main St. (150ft) a The location of the upstream and downstream flood elevations in relation to the hydraulic structure are referenced from the upstream or downstream side of the structure, respectively. All distances are approximate and are shown in parenthesis under the flood mark elevations. b This column is used for flood elevations that are not associated with hydraulic structures. c Newhall Dam is located about 150 feet downstream of discontinued bridge. d Little Falls Dam is located about 200 feet downstream of bridge. e South Windham Dam is located about 150 feet downstream of bridge. f Saccarappa Dam is located about 1000 feet downstream of this site. g Cumberland Mills Dam is located about 200 feet downstream of bridges. h Upstream of the upstream bridge. 1 Downstream of the downstream bridge. J The difference in elevations was probably caused by superelevation of the water around a bend. k Dam is located about 50 feet upstream of bridge. 1 Cascade Brook is also known as Stuart Brook at this location. m Upstream of the road at 136 Pine Point Rd. n Downstream of the road at 136 Pine Point Rd. 0 Downstream of discontinued Route 202/100/4 Bridge. p At normal flows, Sawyer Brook flows underground, starting at Sawyer Street. q Clark Pond Dam is located about 40 feet upstream of culvert.
Peak flows were determined at these sites by using the "Water Resources Data - Maine". A significant amount most recent elevation-flow relation at each site with the of historical information for the Presumpscot River in peak water-surface elevation from the October 1996 Westbrook near site 10 (explained further in the flood. Historical Perspective on Flood section) was obtained from S. D. Warren Co. The highest peak flows previously known for the sites in table 2 were taken from USGS records, which are published by the USGS in the annual report series titled
Flood of October 1996 in Southern Maine USGS WRIR 97-4189 17 Table 2. Peak-flow data for October 1996 flood and previous floods in southern Maine o [dash indicates not available, none indicates not a current or former U.S. Geological Survey stream gaging station, cubic feet per second abbreviated as ft /s, 00 square miles abbreviated as mi , > indicates greater than, < indicates less than]
Peak flow during October 1996 flood Highest peak flow previously known OctoberFloodof1996in USGS Drainage Site gaging Flow Recurrence Exceedance Flow Period of known Stream and location area number3 station (ft3/s) interval probability (ft3/s) peak flows (mi2) number
10 01064118 Presumpscot River at S. D. Warren 23,300b 250 years0 0.004 1991 13,900 1895-present 577d 0 Bridge, Westbrook
00 42 01066100 Pease Brook at Route 25/117, Cornish 352 1 0 years 0.100 1969 486 1964-1974 4.80 49 01059800 Collyer Brook at Route 202/100/4, 1,150 15 years 0.067 1969 1,220 1964-1982 13.8 Gray 50 01066500 Little Ossipee River, at Nason's Mills 5,800 30 years 0.033 1936 8,530 1936, 1940-1982 168 Rd., Limington 55 None Capisic Brook at Capisic St., Portland 865 >500 years0 <0.002 - 2.63 59 01069500 Mousam River at Wichers Mill Rd., 3,600 50 years 0.020 1983 4,020 1939-1984 99.0 Sanford 62 01063310 Stony Brook at Route 114, Sebago 106 7 years 0.143 1996 63 1995-present 1.50 68 01069700 Branch Brook at Route 9A, Wells 1,020 40 years 0.025 1972 723 1964-1974 10.3 74 01060000 Royal River at East Main St., 4,410 3 years 0.330 1977 11,500 1949-present 141 Yarmouth a The site number refers to the site numbers from Table 1. b Based on a drainage area correction from site 14. c Recurrence intervals greater than 100 years have a large uncertainty associated with them. The drainage area is 136 mi2 below the outlet of Sebago Lake. e The drainage area is 199 mi2 below the outlet of Sebago Lake. 70 45' 70° 15'
44'00'
43° 45'
43 "30'
Site where peak flow was determined. Top number is site number, bottom number is recurrence interval of peak flow in years (asterisk indicates not determined).
Base from U.S. Geological Survey SCALE Portland, and Kittery quadrangles 0 SMILES 1:100,000,1985 ~ 5 KILOMETERS Figure 10. Total rainfall isolines and location of sites where peak flows and recurrence intervals were determined for October 1996 southern Maine flood. [Rainfall isolines provided by National Weather Service.]
Flood of October 1996 in Southern Maine USGS WRIR 97-4189 19 Peak-Flow Frequency estimate of the recurrence interval of the 1650 ft3/s The recurrence interval is the average period of time October 1996 peak flow at site 33 is not possible. In between peak flows that are greater than, or equal to, a general, because of the extreme uncertainties in peak- specified magnitude. For example, the 50-year peak flow recurrence intervals greater than 500 years, flow is the flow that would be exceeded or equaled, on applicable peak-flow recurrence intervals from the long-term average, once in 50 years. This does not October 1996 flood are reported as >500 years (in table imply that flooding will happen at regular intervals. 2), instead of their calculated recurrence intervals. Two 50-year peak flows could be experienced in 2 consecutive years. Conversely, a 50-year peak flow The 500-, 100-, 50-, 25-, 10-, 5-, and 2-year peak flows might not be experienced for 100 years or longer. The for the Presumpscot River in Westbrook (site 10) were reciprocal of the recurrence interval is called the calculated using the guidelines (Bulletin 17B) of the annual exceedance probability; that is, the probability Interagency Advisory Committee on Water Data that a given peak flow will be exceeded or equaled in (1982). The calculations involve fitting the log-Pearson any given year. For example, the annual exceedance Type III probability distribution to the observed annual probability of the 50-year peak flow would be 0.02. In peaks at a site. Bulletin 17B provides a procedure for other words, there is a 2 percent chance that the 50- incorporating historical peak flow information into the year peak flow will be exceeded or equaled in any recurrence interval calculations. The historical peak given year. flow information provided by S. D. Warren Co. (explained further in the Historical Perspective on The 500-, 100-, 50-, 25-, 10-, 5-, and 2-year Flood section) was used in the Bulletin 17B analysis. recurrence-interval peak flows for sites in table 2 were determined as explained below. The peak flows from Table 3. Recurrence intervals, exceedance probabili the October 1996 flood were then compared to these ties, and peak flows for the Presumpscot River at the recurrence-interval peak flows to determine the S.D. Warren Bridge in Westbrook, Maine (site 10) recurrence intervals of the October 1996 peak flows. [cubic feet per second abbreviated as ft /s] All recurrence interval estimates have an uncertainty associated with them. The uncertainty generally Recurrence Exceedance Peak flow increases as the recurrence interval increases. interval probability (ft3/s) Recurrence intervals that are greater than 100 years have a large amount of uncertainty associated with 2 years 0.500 5,310 them. For example, the calculated 500-year peak flow 5 years 0.200 7,830 for Cascade Brook in Saco (site 33) is 650 ft3/s, but the one-standard-error-of-estimate range of the 500-year 10 years 0.100 9,890 peak flow extends from about 200 ft3/s to about 1200 25 years 0.040 13,000 ft3/s. This means that the actual 500-year peak flow 50 years 0.020 15,700 will be between 200 ft3/s and 1200 ft3/s for about two- thirds of sites with the same drainage basin 100 years 0.010 18,900 characteristics (drainage area, stream slope, etc.) as site 200 years3 0.005 22,400 33. This corresponds to a flow uncertainty factor of about 2 to 3. The recurrence interval uncertainty is 500 years3 0.002 28,000 greater than the flow uncertainty. The recurrence a Recurrence intervals greater than 100 years interval for a given flow of 650 ft3/s at site 33 is have a large uncertainty associated with them. estimated to be 500 years with a recurrence interval uncertainty factor of about 9 (William H. Kirby, U.S. Geological Survey, written commun., 1997). That is, at two-thirds of sites similar to site 33, the actual recurrence interval is estimated to be in the range of 60 to 4500 years. Given these uncertainties, a reasonable
20 Flood of October 1996 in Southern Maine USGS WRIR 97-4189 The calculated peak flow from the October 1996 flood A strong positive relation was found between was also used in the calculations. The recurrence recurrence interval of peak flows and basin-average intervals, exceedance probabilities, and peak flows for rainfall for the October 1996 southern Maine flood (fig. site 10 are shown in table 3. 11). The 12 data points in figure 11 represent the peak- flow recurrence interval and the basin-average rainfall The peak flows for the 500-, 100-, 50-, 25-, 10-, 5-, and of the sites in table 2. The greater-than-500-year 2-year recurrence intervals for Pease Brook in Cornish recurrence intervals for sites 28, 33, and 55 were (site 42), Collyer Brook in Gray (site 49), Little plotted at the 500-year level. The basin-average rainfall Ossipee River in Limington (site 50), Mousam River in is an estimate of the total rainfall that fell in a given Sanford (site 59), Branch Brook in Wells (site 68), and basin during the October 20-22, 1996 storm. To Royal River in Yarmouth (site 74) were all calculated compute basin-average rainfall, approximate drainage using the guidelines in Bulletin 17B. basin boundaries were drawn on an enlarged version of figure 10. The drainage basin for each site was divided The peak flows for the 100-, 50-, 25-, 10-, 5-, and 2- into subareas based on the rainfall isolines. The areal year recurrence intervals for Stroudwater River in average of the rainfall for all of the subareas was then Portland (site 28), Cascade Brook in Saco (site 33), computed to give the basin-average rainfall. Crooked River in Casco/Naples (site 41), Capisic Brook in Portland (site 55), and Stony Brook in Sebago It is probable that unmeasured streamflows from the (site 62) were calculated using the procedures of October 1996 flood fall in the gray range shown in Morrill (1975). These procedures involve computing figure 11. Given this conclusion, additional drainage basin characteristics (such as drainage area conclusions can be made, all of which apply only to the and stream slope) and inputting these values into October 1996 flood in the area covered in this study. regression equations to compute the peak flows for Also, the following conclusions may not apply to specified recurrence intervals. The 500-year flood basins with drainage areas smaller than 1.5 square flows for these 5 sites were computed by the miles because no peak flow data was collected on extrapolation method of Thomas and Kirby (1994). For basins of this size. Any drainage basin with an basin- Capisic Brook, an urban adjustment to the peak flows average rainfall of more than 15 inches probably was applied using the nationwide 7-parameter urban experienced a peak flow (at the drainage basin outlet) regression equations (Sauer and others, 1983). with a recurrence interval of greater than 100 years. Drainage basins with average rainfalls of less than The extreme rains of October 20-22, 1996, in southern 11 inches probably had peak flows with recurrence Maine did not cause extreme flows on the lower Saco intervals of less than 100 years. Those with less than River. The Saco River at Skelton Dam in Dayton 10 inches of rain likely had peak flows with recurrence } peaked at 17,200 cubic feet per second (ft /s) on intervals of less than 50 years. October 22, 1996 (Francis R. (Mike) Towns, Jr., Central Maine Power Co., written commun., 1997). A range of likely recurrence intervals for peak The 10-year peak flow at this location is 25,800 ft3/s streamflows at any location (for basins in the area (Federal Emergency Management Agency, 1980). covered by this study, with drainage areas greater than 1.5 square miles) could be calculated by computing a basin-average rainfall for the stream's drainage basin. This basin-average rainfall would then be entered into Extrapolation of Peak-Flow Frequency figure 11 to estimate a range of recurrence intervals for It is not feasible to determine at-site flows and their the October 1996 flood. For example, for the October associated recurrence intervals for all streams in a 1996 flood, a drainage basin with an average total flood-affected area. It is sometimes possible, however, rainfall of 10 inches probably experienced a peak flow to draw general conclusions based on the streams with a recurrence interval of 12 to 50 years. A basin where peak-flow recurrence intervals have been with an average total rainfall of 13 inches likely had a determined. peak flow with a recurrence interval of 40 to 250 years, while one with an average total rainfall of 16 inches
Flood of October 1996 in Southern Maine USGS WRIR 97-4189 21 probably had a peak flow with a recurrence interval of 1996, 165 ft3/s on October 21, 1996, and 75 ft3/s from 160 to greater than 500 years. It must be remembered October 22 to 31, 1996. that peak-flow recurrence intervals greater than 100 years have a large uncertainty associated with them Lake elevation and usable storage data for Sebago (as discussed in the Peak-Flow Frequency section). Lake are shown in table 4. Usable storage is the Estimates of peak-flow recurrence intervals greater volume of water normally available for release from a than 500 years have extreme uncertainty associated reservoir, between the minimum and maximum with them. This is why recurrence intervals greater than controllable elevations. The usable storage statistics 500 years are not reported exactly. were obtained from the monthly report, Current Water Resources Conditions in Maine (U.S. Geological Reservoir Storage Survey, 1996). From October 16 to October 23, 1996; 2,238 million cubic feet of water were stored in Sebago Flow records for the Presumpscot River at the outlet of Lake. Sebago Lake and storage data for Sebago Lake (Tom Howard, written commun., 1996) indicate that most The peak flow for the October 1996 flood on the precipitation that fell on October 20-22, 1996, on the Presumpscot River at 1-95 in Falmouth (site 14) was Sebago Lake drainage area, was stored in Sebago Lake. o The daily mean flow at the outlet of the lake was 31,500 ft /s. The outflow from Sebago Lake during the o October 1996 flood was less than one percent of this 257 cubic feet per second (ft /s) from October 16 to 20, peak flow. Therefore, the drainage area above the outlet
500 33 400 300 EXPLANATION C/5 200 Site number
LU 100
70 DC 50 40 LLJ 30 Oz LLJ 20 DC DC 12 O LU 10 DC 7 "62 5 4 41 3
8 10 12 14 16 18 2C
BASIN-AVERAGE RAINFALL, OCTOBER 1996 STORM (INCHES)
Figure 11. Relation between recurrence interval of peak flows and basin-average rainfall for October 1996 southern Maine flood.
22 Flood of October 1996 in Southern Maine USGS WRIR 97-4189 Table 4. Elevation and usable storagea data for Sebago Lake. The Small Business Administration estimated that 45 [dash indicates not available]______homes and 27 businesses had major damage from the , . Volume _ Long-term flood and 2,002 homes and 110 businesses had minor Elevation . .,,. Percent Date ._ . (million _ average damage. (feet) , . _ . full cubic feet) percent full Damage to large water mains left the City of Portland Sept. 30, 1996 263.19 5,301 55 46 without water for several hours. A boil order was Oct. 16, 1996 262.76 4,754 49 - issued because of contaminated water, forcing most businesses in Portland to close from October 21, 1996 Oct. 23, 1996 264.52 6,992 72 - to October 25, 1996. Sewer treatment plants in Oct. 30, 1996 265.72 8,517 88 57 Berwick, Old Orchard Beach, and Saco suffered significant damage. Clam flats from Kittery to a Usable storage for Sebago Lake is the 9700 million cubic feet of Rockland were closed due to pollution. water between the elevations of 259.0 feet and 266.6 feet. Many state and local roads were washed away when their drainage structures failed. Bridges were destroyed of Sebago Lake did not contribute a significant amount in Cape Elizabeth, Falmouth, Old Orchard Beach, of water to the flooding, at site 14, in October 1996. Scarborough, Wells, Westbrook, and Windham. The The drainage area of the Presumpscot River at the Maine Turnpike was closed for many hours at several outlet of Sebago Lake is 441 square miles (mi 0 ). The locations. drainage area of the Presumpscot River at site 14 is ^ 640 mi . Therefore, the October 1996 flooding at site Highland Lake Dam in Westbrook, Milliken Mills /-\ Dam in Old Orchard Beach, Rocky Gorge Lower Dam 14 was caused by rain falling on the 199 mi of in South Berwick, and 2 dams owned by the State drainage area below the outlet of Sebago Lake. The Inland Fisheries and Wildlife in Scarborough were contribution of Sebago Lake outflows to October 1996 destroyed in the flood. The Balch Pond Outlet in peak flows and elevations in the entire lower Shapleigh was damaged and the Rod and Gun Club Presumpscot River (defined for this report as Dam in the Lower Falls area of Gorham failed. downstream from the confluence with the Little River Concern over possible loss of structural integrity has in Gorham) was very likely insignificant. If the large provoked an inspection and assessment of major dams amount of rain that fell in the Sebago Lake drainage in southern Maine. basin in October 1996 had not been stored in Sebago Lake, peak flows and peak water-surface elevations on the lower Presumpscot River would have been even higher than they were. HISTORICAL PERSPECTIVE ON FLOOD
Flood Damages Peak flows and peak water-surface elevations from the The October 1996 flood in southern Maine affected the southern Maine flood of 1996 are compared to lives of many area residents by destroying homes and historical data in this section. Based on the recurrence businesses, contaminating water, and washing out intervals listed in table 2 (page 18), the 4 measured roads, bridges, and dams. The following damage streams with the most extreme flooding in the October information was taken from the Federal Emergency 1996 flood were the Presumpscot River (site 10, 250- Management Agency's Interagency Hazard Mitigation year recurrence interval), the Stroudwater River (site Team Report (1996). 28, >500-year recurrence interval), Cascade Brook (site 33, >500-year recurrence interval), and Capisic A motorist drowned after driving into floodwaters in Brook (site 55, >500-year recurrence interval). Scarborough. There were fifteen reported injuries due to the flood.
Flood of October 1996 in Southern Maine USGS WRIR 97-4189 23 Historical Peak Flows Table 5. Significant historical peak flows on the Presumpscot River in Westbrook, Maine Measured peak flows from the October 1996 flood are compared to the highest peak flows previously known, Flow (cubic in table 2 (page 18). All previously known flows are Date feet per from the USGS annual report series "Water Resources second) Data - Maine" with the exception of many flows on the April 15, 1895 Presumpscot River in Westbrook. The flows at the 13,000a USGS gaging stations were calculated by standard March 1, 1896 13,800a USGS methods (Rantz and others, 1982). February 13, 1900 ll,300a Historical peak flows for the Presumpscot River at the Saccarappa Dam in Westbrook (which is about March 2, 1900 9,720a 1000 feet downstream from Site 6, see figure 9 for site May 17, 1916 locations) were supplied by S.D. Warren Co. (Tom 12,400a Howard, written commun., 1996). The flows were June 17, 1917 9,7 10a calculated using weir computations. Some historical flows on the Presumpscot River are also available from March 12, 1936 ll,200a the USGS at stream gaging stations in Westbrook (site 10, USGS station 01064118) and Falmouth (site 12, September 11, 1954 12,400a USGS station 01064140). The October 1996 peak flow March 14, 1977 for the Presumpscot River at 1-95 in Falmouth (site 14) ll,200b was determined by using a contracted opening indirect May 12, 1989 9,200C measurement (Matthai, 1967). The difference in drainage area between Saccarappa Dam and the USGS August 20, 1991 13,900C gaging station at Westbrook (site 10) is less than 2%, making the flows at the two sites comparable. Flows October 22, 1996 23,300d from the USGS Falmouth gaging station and from the 1-95 bridge were adjusted by drainage area corrections a Flow computed by S.D. Warren Co. using weir (Morrill, 1975) to make them comparable to the flows equations at Saccarappa Dam in Westbrook. at the USGS gaging station in Westbrook. All known Flow computed by U.S. Geological Survey at significant historical peak flows on the Presumpscot streamflow gaging station in Falmouth and adjusted River are listed in table 5. The October 1996 peak flow to Westbrook using a drainage area correction. of 23,300 cubic feet per second was 68 percent larger c Flow computed by U.S. Geological Survey at streamflow gaging station in Westbrook. than any other flow in the last 102 years. Flow computed by U.S. Geological Survey by con tracted opening measurement at 1-95 bridge in Fal Because no significant historical flows have been mouth and adjusted to Westbrook using a drainage recorded for the Stroudwater River (site 28), Cascade area correction. Brook (site 33), or Capisic Brook (site 55), a site- specific historical perspective of the October 1996 flood at these sites is not possible. A general into 17 different regions in the Crippen and Bue report. comparison, however, is possible. Crippen and Bue Maine is in region 1 (region 1 covers Maine, Vermont, (1977) determined envelope curves for peak flow most of New Hampshire, most of Connecticut, western versus drainage area. These envelope curves were Massachusetts, and a small part of Rhode Island) and developed to provide a guide for estimating potential this envelope curve is shown in figure 12. The points maximum flood flows. The curves were developed by that were used to define the Crippen and Bue envelope analyzing thousands of sites with recorded flood flows, curve for region 1 are listed in table 6. A general and using the sites with the most extreme flows to draw historical flood comparison is made by plotting the the envelope curves. The United States was divided Presumpscot River (site 14), Stroudwater River (site
24 Flood of October 1996 in Southern Maine USGS WRIR 97-4189 1,000,000
500,000 EXPLANATION MA17 Historical Flows Q Site 55 1996 Flows Z »NH7 o o 100,000 LJJ C/) 50,000 CT7 DC LJJ CT6 Q_ VT12 ASite14 LJJ LJJ LJ_ ASite 28 O 10,000 CD 13 5,000 MA17 O
Q ^ Site 33 1,000 Site 55 500
100 0.1 1 10 100 1,000 10,000
DRAINAGE AREA (SQUARE MILES)
Figure 12. Crippen and Bue (1977) region 1 envelope curve with data from October 1996 southern Maine Flood.
28), Cascade Brook (site 33), and Capisic Brook (site Table 6. Flood flows that defined Crippen and Bue 55) peak flows from October 1996 on the Crippen and (1977) region 1 envelope curve Bue envelope curve for region 1. Site 14 is plotted using the drainage area below the Sebago Lake outlet Peak flow Drainage (cubic feet area (for reasons discussed in the Reservoir Storage Point Site name Date section). Flows in figure 12 that plot closest to the per (square envelope curve are more extreme flows than those that second) miles) plot further away. On this basis, the most extreme MA17 Powdermilk 5,740 2.50 8-19-1955 measured flow from the October 1996 southern Maine Brook near flood was the Stroudwater River in Portland (site 28). Westfield, MA The measured flows from this flood that are not plotted VT12 Rock River at 27,200 42.6 9-21-1938 in Figure 12 are less extreme than the 4 sites that are Williamsville, plotted. VT CT6 Salmon Brook 40,000 66.8 8-19-1955 near Granby, CT Historical Peak Water-Surface CT7 Naugatuck 53,400 101 8-19-1955 Elevations River at Tho- maston, CT Comparisons of historical flood elevations can be CT4 Farmington 140,000 360 8-19-1955 made, but changes that occur over time, such as River at Collins- physical changes in structures (for example, dams and ville, CT bridges) and changes in land uses can make such NH7 Merrimack River 150,000 3,092 3-20-1936 comparisons difficult and unreliable. The only known below Manches significant historical peak water-surface elevations (in ter, NH
Flood of October 1996 in Southern Maine USGS WRIR 97-4189 25 the area severely affected by the October 1996 flood) drainage basin characteristics and other factors. The are located on the Presumpscot River and are listed in cause of the southern Maine flood of October 1996, table 7. The peak elevations for 1896, 1916, and 1954 however, was not complex. Up to 19.19 inches of rain were provided by S. D. Warren Co. (Tom Howard, were recorded in southern Maine from October 20-22, written commun., 1996). The elevations for 1977, 1996. The maximum 24-hour rainfall total of 1991, and 1996 are from USGS records. The peak 13.32 inches at the Portland International Jetport elevations in table 7 were associated with the peak exceeded the previous record (records have been kept flows that are listed in table 5. The peak elevations since 1871) by 5.49 inches. Most of the rain from this from the October 1996 flood exceeded all previously storm fell in about 26 hours at a relatively constant rate recorded peak elevations on the lower Presumpscot (at the Jetport). None of the available data regarding River. hydrologic conditions prior to the October 20-22 storm were abnormally high or low. These facts and the SUMMARY AND CONCLUSIONS strong relation (for this flood) between basin-average rainfall and the recurrence interval of peak flows indicate that the extreme rainfall totals from the Flood flows are typically caused by a complex October 1996 storm were the cause of the extreme interrelationship of rainfall, rainfall intensity, peak streamflows experienced in southern Maine. antecedent drainage basin conditions, physical
Table 7. Historical peak water-surface elevations on the Presumpscot River in Maine [feet abbreviated as ft, na indicates not applicable, dash indicates not available]
Year Site Location 1896 1916 1954 1977 1991 1996
na Upstream of Saccarappa Dam, 73.8 ft 73.7 ft 76.8a ft Westbrook
9 Upstream of Cumberland Mills 46.0 ft 45.8 ft 51.6b ft Dam, Westbrook
10 Upstream of S. D. Warren 38.9 ft 47.5 ft Bridge, Westbrook 11 Upstream of Route 302 Bridge, 36.6ft 34.1ft 36.5ft 43.8 ft Westbrook 11 Downstream of Route 302 33.9ft 35.5ft Bridge, Westbrook
12 Upstream of Blackstrap Rd. 35.8ft 32.0ft 33.5ft 32.3ft 41.0ft Bridge, Falmouth
13 Upstream of Route 267100 35.1ft 31.7ft 31.8ft 38.8 ft Bridge, Falmouth 15 Upstream of Smelt Hill Dam, 22.5ft 25.2ft 23.4ft 26.5 ft Falmouth a About 1000 feet upstream of Saccarappa Dam at Site 6. This peak water-surface elevation on the upstream side of Cumberland Mills Dam is the downstream elevation of the Cumberland Street bridge (see table 1).
26 Flood of October 1996 in Southern Maine USGS WRIR 97-4189 Peak water-surface elevations from the October 1996 REFERENCES CITED flood were determined at 74 locations. Peak flows were calculated at 13 sites and recurrence intervals were Benson, M. A., and Dalrymple, Tate, 1967, General calculated at 12 of these 13 sites. Three of these flows field and office procedures for indirect discharge had recurrence intervals of greater than 500 years. The measurements: U.S. Geological Survey peak flow on the Presumpscot River in Westbrook, Techniques of Water-Resources Investigations, Maine had a recurrence interval of 250 years. Peak- Book3, Chapter A 1,30 p. flow recurrence intervals greater than 100 years have a large amount of uncertainty associated with them. Bodhaine, G. L., 1967, Measurement of peak discharge Based on historical data gathered for this report, the at culverts by indirect methods: U.S. Geological October 1996 peak flow on the Presumpscot River in Survey Techniques of Water-Resources Westbrook was 68 percent larger than any other flow at Investigations, Book 3, Chapter A3, 60 p. this location in the last 102 years. All known significant historical peak flows and peak elevations (in the area Chow, V. T., 1959, Open-channel Hydraulics: New covered by this report) have been presented. York, McGraw-Hill, 680 p.
A strong positive relation was found between basin- Crippen, J. R., and Bue, C. D., 1977, Maximum average rainfalls and the recurrence intervals of peak floodflows in the conterminous United States: flows from the October 1996 flood (in the area covered U.S. Geological Survey Water-Supply Paper by this study). Based on this relation, it is probable that 1887, 52 p. any drainage basin with an basin-average rainfall of more than 15 inches experienced a peak flow (at the Dalrymple, Tate, and Benson, M. A., 1968, drainage basin outlet) with a recurrence interval of Measurement of peak discharge by the slope area greater than 100 years. Drainage basins with average method: U.S. Geological Survey Techniques of rainfalls of less than 11 inches probably had peak flows Water-Resources Investigations, Book 3, Chapter with less than 100-year recurrence intervals. Those A2, 12 p. with less than 10 inches of rain likely had peak flows with less than 50-year recurrence intervals. Because of Federal Emergency Management Agency, 1980, Flood the strong relation between basin-average rainfall and Insurance Study, Town of Dayton, Maine, York peak-flow recurrence interval, peak-flow recurrence County: December 1, 1980, 19 p. intervals for the October 1996 flood can be estimated for sites where peak flows were not determined (for Federal Emergency Management Agency, 1996, basins in the area covered by this study with drainage Interagency Hazard Mitigation Team Report: areas greater than 1.5 square miles). FEMA-DR-1143-ME, 37 p.
The October 1996 flood devastated parts of southern Fontaine, R. A., and Nielsen, J. P., 1994, Flood of Maine. One person drowned after driving into April 1987 in Maine: U.S. Geological Survey floodwaters. More than 2,100 homes and businesses Water-Supply Paper 2424, 50 p. were damaged in the flood. Bridges, dams, or both were destroyed in Cape Elizabeth, Falmouth, Old Hershfield, D. M., 1961, Rainfall Frequency Atlas of Orchard Beach, Scarborough, Wells, South Berwick, the United States: U.S. Department of Commerce, Westbrook, and Windham. Clam flats from Kittery to Weather Bureau Technical Paper 40, 115 p. Rockland were closed due to pollution. Huff, F. A., and Angel, J. R., 1992, Rainfall Frequency Sebago Lake stored most of the rain that fell on the Atlas of the Midwest: Illinois State Water Survey, 441 square miles of the Presumpscot River drainage Champaign IL, Bulletin 71, 141 p. basin that is above the outlet of the lake. If this water had not been stored, peak flows and peak water-surface elevations on the lower Presumpscot River would have been even higher than they were in October 1996.
Flood of October 1996 in Southern Maine USGS WRIR 97-4189 27 Interagency Advisory Committee on Water Data, 1982, Thomas W. O., Jr., and Kirby, W. H., 1994, Estimation Guidelines for determining flood flow frequency: of extreme floods, in Nationwide summary of Water Resources Council Bulletin 17B, 28 p. U.S. Geological Survey regional regression equations for estimating magnitude and frequency Matthai, H. F., 1967, Measurement of peak discharge of floods for ungaged sites, 1993: U. S. at width contractions by indirect methods: U.S. Geological Survey Water-Resources Geological Survey Techniques of Water- Investigations Report 94-4002, p. 13-16. Resources Investigations, Book 3, Chapter A4, 44 p. U.S. Geological Survey, 1996, Current water resources conditions in Maine: Augusta, Maine (published Morrill, R. A., 1975, A technique for estimating the monthly). magnitude and frequency of floods in Maine: U. S. Geological Survey Open File Report 75-292,44 Wilks, D. S., and Cember, R. P., 1993, Atlas of P- Precipitation Extremes for the Northeastern United States and Southeastern Canada: Cornell National Oceanic and Atmospheric Administration, University, Northeast Regional Climate Center, 1990, Daily Normals of Temperature, 40 p. Precipitation and Heating and Cooling Degree Days, 1961-1990, Maine, Portland WSMO AP: National Climatic Data Center, Climatography of the United States No. 84.
National Oceanic and Atmospheric Administration, 1996a, Climatological Data, New England, September 1996-October 1996: National Climatic Data Center, v. 108, nos. 9-10.
National Oceanic and Atmospheric Administration, 1996b, Local Climatological Data, Portland, ME, October 1996 (revised): National Climatic Data Center.
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Flood of October 1996 in Southern Maine USGS WRIR 97-4189 28