UNC-WRRI-94-284 EFFECTS OF URBAN IZATION AND LAND-USE CHANGES ON LOW STREAMFLOW by Jack B. Evett with Contributions from Margaret A. Love and James M. Gordon Department of Civi 1 Engineering College of ~ngineering The University of North Carolina at Char1 otte Charlotte, North Carolina 28233 The research on which this report is based was financed in part by the Department of the Interior, U.S. Geological Survey, through the Water Resources Research Institute of The University of North Carol ina. The contents of this publication do not necessarily reflect the views and policies of the Department of the Interior, nor does mention of trade names or commercial products constitute their endorsement by the United States government. Agreement No. 14-08-0001 -G2O37 USGS Project No. 14 (FY93) WRRI Project No. 70122 .One hundred fifty copies of this report were printed at a cost of $1,981 -50 or $13.21 per copy. ACKNOWLEDGEMENT The research on which this report is based was financed in part by the United States Department of the Interior, Geological Survey, through the N.C. Water Resources Research Institute. Margaret A. Love, a graduate student in civil engineering supported financially by the project, contributed significantly to all phases of the study. James M. Gordon, also a graduate student in civil engineering, was instrumental in developing, as part of his master's thesis, some of the statistical methodology used herein. Ms. Love contributed to the writing of the "Introduction" section; Mr. Gordon contributed to the writing of both the "Introduction" and the "Procedures" sections. Civil engineering graduate students William L. Saunders, Jr. and Scott A. Robidoux also provided assistance in conducting the project. Specid. thanks go to Robert Mason of the Water Resources Division of the U.S.Geological Survey in Raleigh, NC, for providing streamflow data and helpful comments, and also to the government documents library staff of Atkins Library at The University of North Carolina at Charlotte for their generous efforts in assisting the project. College of Engineering Dean R. D. Snydex and Civil Engineering Department Chairman L. Ellis King of The University of North Carolina at Charlotte provided personal as well as facilities support. ABSTRACT Historical low-streamflow data were analyzed for a number of gaging stations on streams in and around various urban areas in North Carolina in an attempt to find and document effects of urbanization and land-use changes on low streamflows. Records for streams within each urban area were compared with streams outside (but nearby) the urban area by two statistical methods. It was concluded from the study that there is some support for the premise that urbanization causes a decrease in low streamflows over time, but statistically the results are inconclusive. It appears more likely that most small streams--both urban and rural--are experiencing decreasing low flows over time. (Key words: low streamflows, urbanization, land-use change, urban hydrology) TABLE OF CONTENTS Page Acknowledgement Abstract List of Figures v1 .. List of Tables Vlll Summary and Conclusions ix Recommendations Introduction Purpose and Objectives Procedures One Sample Run Test for Randomness Test for Equality of Slopes Applications to Various Urban Areas Asheville Greensboro Raleigh Charlotte Goldsboro-kin ston Rocky Mount-Tarboro Other Attempts Results and Discussion References Glossary Appendix A 7Q Flows (annual and five-year mean values), precipitation. and population data for stations in the Asheville area Appcfidix B 74Rows (annual and five-year mean values), precipitation, and population data for stations in the Greensboro area 85 Appendix C 74mows (annual and five-year mean values), precipitation, and population data for stations in the Raleigh area 96 Appendix D 7Q Rows (annual and five-year mean values), precipitation, and population data for stations in the Charlotte area 105 Appendix E 74Flows (annual and five-year mean values), precipitation, and population data for stations in the Goldsboro-Kinston area 116 Appendix F 7Q Flows (annual and five-year mean values), precipitation, and population data for stations in the Rocky Mount-Tarboro area 123 Appendix G Equality of slopes test applied to Swannanoa River at Biltmore and Mills River near Mills River 130 LIST OF FIGURES Page Location Map of Stations in the Asheville Area 9 5-Year Averaged 7-Day Low Flows for Study Stations in the Asheville Area 11 Annual Precipitation for Study Stations in the Asheville Area 12 Area Population for Study Stations in the Asheville Area 13 Low-Flow Trends for Swannanoa River at Biltmore 14 Low-Flow Trends for Mills Fbver near Mills River 15 Location Map of Stations in the Greensboro Area 18 5-Year Averaged 7-Day Low Flows for Study Stations in the Greensboro Area 20 Annual Precipitation for Study Stations in the Greensboro Area 2 1 Area Population for Study Stations in the Greensboro Area 22 Low-Flow Trends for North Buffalo Creek near Greensboro 23 Low-Flow Trends for East Fork Deep River near High Point 24 Low-Flow Trends for Reedy Fork near Oak Ridge 25 Low-Flow Trends for Little Yadkin River at Dalton 26 Low-Flow Trends for Deep River at Ramseur 27 Low-Flow Trends for Hunting Creek near Harmony 28 Location Map of Stations in the Raleigh Area 30 5-Year Averaged 7-Day Low Flows for Study Stations in the Raleigh Area 32 Annual Precipitation for Study Stations in the Raleigh Area 33 Area Population for Study Stations in the Raleigh Area 34 Low-Flow Trends for Middle Creek near Clayton 35 L,ow-Flow Trends for Little Fishing Creek near White Oak 36 Low-Flow Trends for Flat River at Bahama 37 Low-Flow Trends for Little River near Pnnceton 38 Low-Flow Trends for Deep River at Moncure Location Map of Stations in the Charlotte Area 5-Year Averaged 7-Day Low Flows for Study Stations in the Charlotte Area Annual Precipitation for Study Stations in the Charlotte Area Area Population for Study Stations in the Charlotte Area Low-Row Trends for Indian Creek near Laboratory Low-Flow Trends for Long Creek near Bessemer City Low-Flow Trends for Big Rear Creek near Richfield Low-Flow Trends for Irwin Creek near Charlotte Low-Flow Trends for McAlpine Creek at Sardis Road near Charlotte Low-Flow Trends for Twelve Mile Creek near Waxhaw Low-Row Trends for Long Creek near Paw Creek Low-Flow Trends for McMullen Creek at Sharon View Road near Charlotte Location Map of Stations in the Goldsboro-Kinston Area 5-Year Averaged 7-Day Low Flows for Study Stations in the GoIdsboro-Kinston Area Annual Precipitation for Study Stations in the Goldsboro-Kinston Area Area Population for Study Stations in the Goldsboro-Kinston Area Low-Row Trends for Nahunta Swamp near Shine Low-Flow Trends for Contentnea Creek near Lucama Location Map of Stations in the Rocky Mount-Tarboro Area 5-Year Averaged 7-Day Low Flows for Study Stations in the Rocky Mount-Tarboro Area Annual Precipitation for Study Stations in the Rocky Mount-Tarboro Area Area Population for Study Stations in the Rocky Mount-Tarboro Area vii LIST OF TABLES Page Stations in the Asheville Area 8 Results of One Sample Run Test for Stations in the Asheville Area 16 Stations in the Greensboro Area 19 Results of One Sample Run Test for Stations in the Greensboro Area 29 Stations in the Raleigh Area 29 Results of One Sample Run Test for Stations in the Raleigh Area 3 1 Stations in the Charlotte Area 40 Results of One Sample Run Test for Stations in the Charlotte Area 53 Stations in the Goldsboro-Kinston Area 54 Results of One Sample Run Test for Stations in the Goldsboro-Kinston Area 01 Stations in the Rocky Mount-Tarboro Area 61 Summary of Results of the Equality of Slopes Test 67 SUMMARY AND CONCLUSIONS Historical low-streamflow data were analyzed for a number of gaging stations on streams in and around various urban areas in North Carolina in an attempt to find and document effects of urbanization and land-use changes on low streamflows. The urban areas included Asheville, Greensboro, Raleigh, Charlotte, Goldsboro-Kinston, and Rocky Mount-Tarboro. Records for streams within each urban area were compared with streams outside (but nearby) the urban area by two statistical methods--the One Sample Run Test and the Equality of Slopes Test. The former test checked on the randomness of data; the latter compared slopes of low-flow trends for various pairs of urban versus rural stations. The hypothesis was that low streamflows in North Carolina would exhibit a decreasing trend as urbanization progressed, with the proviso that a similar decreasing trend would not be present for nearby nonurban (rural) areas. In the Asheville area, two rivers were considered--one urban, the other rural. Both exhibited a negative (downward) trend in low flow over time with the urban station's slope being more negative, but statistically they did not differ significantly. In the Greensboro area, two of the three urban areas had positive trends; the third was slightly negative. All of the rural stations exhibited negative trends. This outcome in itself is contrary to the project's hypothesis (that rural slopes should be greater than urban ones). The statistical analyses were, however, inconclusive. In the Raleigh area, trends of all stations were negative, but the lone urban station did have the greatest negative slope; and the statistical analyses did tend to uphold the project's hypothesis. In the Charlotte area, trends for all stations except one--a rural one--were negative. The statistical analyses were not entirely favorable to the project's hypothesis, but the overall results did tend to uphold the hypothesis.