ESTIMATING SURFACE-WATER RUNOFF TO NARRAGANSETT BAY, RHODE ISLAND AND MASSACHUSETTS By Kernell G. Ries III U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 89-4164 Prepared in cooperation with the RHODE ISLAND DEPARTMENT OF ENVIRONMENTAL MANAGEMENT Providence, Rhode Island 1990 U.S. DEPARTMENT OF THE INTERIOR MANUEL LUJAN JR., Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director For additional information, write to: Copies of this report can be purchased from: District Chief U.S. Geological Survey U.S. Geological Survey Books and Open-File Reports Section Water Resources Division Federal Center, Building 810 10 Causeway Street, Suite 926 Box 25425 Boston, Massachusetts 02222-1040 Denver, Colorado 80225 CONTENTS Page Abstract...................................................................................................................................... 1 Introduction ............................................................................................................................... 1 Purpose and scope ............................................................................................................. 2 Acknowledgments ............................................................................................................. 2 Study area .................................................................................................................................. 2 Location and physical setting ......................................................................................... 2 Surficial geology ............................................................................................................... 4 Land and water use ........................................................................................................... 4 Climate .............................................................................................................................. 4 Regulations and Diversions ............................................................................................. 5 Methods of estimating surface-water runoff ........................................................................ 6 Streamflow data base ....................................................................................................... 6 Estimating runoff during the study period .................................................................... 7 Estimating long-term runoff ............................................................................................ 16 Stepwise-regression analyses .................................................................................... 16 Quantification of variables for regression analyses .............................................. 18 Estimates of surface-water runoff to Narragansett Bay ..................................................... 22 Runoff during water year 1987 ....................................................................................... 22 Long-term runoff .............................................................................................................. 28 Accuracy of runoff estimates .......................................................................................... 35 Study period ................................................................................................................. 35 Long-term runoff estimates ....................................................................................... 39 Conclusions ............................................................................................................................... 40 Selected references .................................................................................................................. 41 ILLUSTRATIONS Page Figure 1. Map of location of study area......................................................................................................... 3 2. Graph showing high flow and low flow regression lines used to relate concurrent discharges at the Cole River partial-record site and the Segregansett River gaging station................................................................................................................. 13 3. Graphic representation of Conn's method of estimating monthly mean runoff at an ungaged site using February, 1987 as an example ................................................... 14 4. Map indicating distribution of urban-type land use within the Narragansett Bay basin ............ 21 5. Hydrograph showing daily mean and monthly mean runoff at U.S. Geological Survey gaging station 01109000, Wading River near Norton, Mass., for the 1987 water year with long-term statistics plotted for comparison ....................................................... 37 6. Graph showing accuracies of annual and monthly mean runoff estimates obtained using Cohn's, Riggs', and the drainage-area ratio methods, based on tests using data from gaging stations located within the Narragansett Bay basin ....................... 38 1U TABLES Page Table 1. Streamflow-gaging stations in the Narragansett Bay drainage basin ....................................... 8 2. Temporary gaging stations and partial-record stations in the Narragansett Bay drainage basin........................................................................................................................... 10 3. Study period weighted mean monthly and annual precipitation on Narragansett Bay, Rhode Island, and 1987 water year precipitation data for regional National Weather Service stations......................................................................................................... 17 4. U.S. Geological Survey land use and land cover classification system for use with remote sensor data........................................................................................................... 20 5. Long-term weighted mean monthly and annual precipitation on Narragansett Bay, Rhode Island, and 1951-1980 precipitation data for National Weather Service stations......................................................................................................................... 23 6. Annual and monthly mean runoff to the Narragansett Bay basin during water year 1987 ........................................................................................................................ 24 7. Long-term mean annual and monthly runoff to the Narragansett Bay basin........................... 30 8. Summary of regression equations used to estimate long-term mean monthly and mean annual runoff.................................................................................................................. 34 PLATES [Plate is in pocket at back.] Plate 1. Data collection network during water year 1987 and surficial features of the Narragansett Bay drainage basin (scale 1:125,000) IV CONVERSION FACTORS AND ABBREVIATIONS The following factors can be used to convert inch-pound units in this report to the International System of units (SI). Multiply inch-pound unit By To obtain SI unit Length inch (in.) 25.4 millimeter (mm) foot (ft) 0.3048 meter (m) mile (mi) 1.609 kilometer (km) Area acre 4,047 square meter (m2) 0.4047 hectare (ha) square mile (mi2) 259.0 hectare (ha) 2.590 square kilometer (km2) Volume cubic foot (ft3) 0.02832 cubic meter (m3) Flow cubic foot per second (ftVs) 0.02832 cubic meter per second (m3/s cubic foot per second 0.01093 cubic meter per second per square mile per square kilometer [(ftVs)/mi2] [(m3/s)/km2] Temperature Temperature in degrees Fahrenheit (°F) can be converted to degrees Celsius (°C) as follows: °C = 5/9 x (°F - 32). Estimating Surface-Water Runoff to Narragansett Bay, Rhode Island and Massachusetts By Kernell G. Ries III ABSTRACT The estimates of long-term runoff from ungaged areas of the basin were derived primarily by using multiple regression analyses. Long-term mean annual Monthly and annual estimates of mean fresh­ and mean monthly runoff data from 13 streamflow- water inflow to the 143 square mile Narragansett Bay gaging stations located within or near the basin were for water year 1987 (Oct. 1, 1986 through Sept. 30, 1987), and for long-term average conditions were re­ used as the dependent variables in the analyses, which quired for use by other investigators. Fresh-water produced separate predictive equations for each month and for the mean annual runoff. Various physi­ inflow consists of surface-water runoff from streams cal characteristics of the drainage basins for the draining into the bay, and precipitation on the bay streamflow-gaging stations were used as the inde­ itself. About 63 percent of the land area within the 1,820 square mile drainage basin was monitored by pendent variables. Lengths of continuous records for streamflow-gaging stations prior to commencement of the 13 stations ranged from 21 to 62 years, with a the study; the remainder was ungaged. mean record length of 38 years. Techniques used to estimate runoff from ungaged Mean runoff to the basin, which includes the bay, areas of the basin for the 1987 water year include a during water year 1987 was estimated to be 4,860 ft3Is previously unpublished method that uses linear (cubic feet per second), with estimates of monthly regression to relate discharge measurements obtained mean runoff ranging from a low of 1,060 ft3Is in monthly at an ungaged site to concurrent discharges at August, to a high of 14,400 ff Is in April. Long-term a nearby gaged site. Empirical tests of the method mean annual runoff