Low-Flow, Base-Flow, and Mean-Flow Regression Equations for Pennsylvania Streams
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Low-Flow, Base-Flow, and Mean-Flow Regression Equations for Pennsylvania Streams By Marla H. Stuckey In cooperation with the Pennsylvania Department of Environmental Protection Scientific Investigations Report 2006-5130 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior DIRK KEMPTHORNE, Secretary U.S. Geological Survey P. Patrick Leahy, Acting Director U.S. Geological Survey, Reston, Virginia: 2006 For sale by U.S. Geological Survey, Information Services Box 25286, Denver Federal Center Denver, CO 80225 For more information about the USGS and its products: Telephone: 1-888-ASK-USGS World Wide Web: http://www.usgs.gov/ Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to repro- duce any copyrighted materials contained within this report. Suggested citation: Stuckey, M.H., 2006, Low-flow, base-flow, and mean-flow regression equations for Pennsylvania streams: U.S. Geo- logical Survey Scientific Investigations Report 2006-5130, 84 p. iii Contents Abstract. 1 Introduction . 1 Purpose and Scope . 2 Previous Investigations . 2 Physiography and Drainage. 2 Development of Regression Equations . 2 Streamflow-Gaging Stations . 2 Basin Characteristics . 5 Regression Techniques . 5 Low-Flow Regression Equations. 6 Base-Flow Regression Equations. 10 Mean-Flow Regression Equations. 13 Limitations of Regression Equations . 15 Summary . 15 Acknowledgments . 17 References Cited. 17 Appendixes . 19 1. Streamflow-gaging stations used in development of low-flow, base-flow, and mean-flow regression equations for Pennsylvania streams. 20 2. Partial-record streamflow-gaging-station measurements and correlation results. 29 3. Basin characteristics for streamflow-gaging stations used in the development of low-flow, base-flow, and mean-flow regression equations for Pennsylvania streams. 51 4. Low-flow characteristics computed from streamflow-gaging-station data and regression equations for stations used in analysis . 63 5. Base-flow and mean-flow characteristics computed from streamflow-gaging-station data and regression equations for stations used in analysis . 75 Figures 1. Map showing major physiographic provinces and major river basins of Pennsylvania . .3 2. Map showing streamflow-gaging stations used in development of low-flow, base-flow, and mean-flow regression equations for Pennsylvania streams . .4 3. Map showing low-flow regions in Pennsylvania. .6 4. Graph showing relation between observed 7-day, 10-year low flow computed from streamflow-gaging-station data and predicted 7-day, 10-year low flow computed from regression equations . .9 5. Graph showing relation between observed 10-year base flow computed from streamflow-gaging-station data and predicted 10-year base flow computed from regression equation. 11 6. Graph showing relation between observed mean annual flow computed from streamflow-gaging-station data and predicted mean annual flow computed from regression equation. 13 iv Tables 1. Number of streamflow-gaging stations and area in low-flow regions of Pennsylvania . 7 2. Regression coefficients for use with low-flow regression equations for Pennsylvania streams . 8 3. Regression coefficients for use with base-flow regression equations for Pennsylvania streams . 12 4. Regression coefficients for use with mean-flow regression equations for Pennsylvania streams . 14 5. Summary of basin characteristics used to develop low-flow, base-flow, and mean-flow regression equations for Pennsylvania streams . 16 Conversion Factors Multiply By To obtain Length inch (in.) 2.54 centimeter (cm) foot (ft) 0.3048 meter (m) mile (mi) 1.609 kilometer (km) Area square mile (mi2) 2.590 square kilometer (km2) Volume gallon (gal) 3.785 liter (L) gallon (gal) 0.003785 cubic meter (m3) million gallons (Mgal) 3,785 cubic meter (m3) Flow rate cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s) cubic foot per second per square mile cubic meter per second per square [(ft3/s)/mi2] 0.01093 kilometer [(m3/s)/km2] million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s) Low-Flow, Base-Flow, and Mean-Flow Regression Equations for Pennsylvania Streams By Marla H. Stuckey Abstract regulation, diversions, or mining activities. Watersheds with karst features need close examination as to the applicability of the regression-equation results. Low-flow, base-flow, and mean-flow characteristics are an important part of assessing water resources in a watershed. These streamflow characteristics can be used by watershed planners and regulators to determine water availability, water- Introduction use allocations, assimilative capacities of streams, and aquatic- habitat needs. Streamflow characteristics are commonly pre- Low-flow, base-flow, and mean-flow characteristics are dicted by use of regression equations when a nearby stream- an important part of assessing water resources in a watershed. flow-gaging station is not available. These streamflow characteristics can be used by watershed Regression equations for predicting low-flow, base-flow, planners and regulators to determine water availability, water- and mean-flow characteristics for Pennsylvania streams were use allocations, assimilative capacities of streams, and aquatic- developed from data collected at 293 continuous- and partial- habitat needs. It is essential that watershed planners and regula- record streamflow-gaging stations with flow unaffected by tors have access to accurate and easily obtainable low-flow and upstream regulation, diversion, or mining. Continuous-record base-flow characteristics to make informed decisions. Stream- stations used in the regression analysis had 9 years or more of flow characteristics commonly are predicted by use of regres- data, and partial-record stations used had seven or more mea- sion equations when a nearby streamflow-gaging station is not surements collected during base-flow conditions. The state was available. Low-flow regression equations for Pennsylvania divided into five low-flow regions and regional regression streams were last developed by the U.S. Geological Survey equations were developed for the 7-day, 10-year; 7-day, 2-year; (USGS) in 1982 (Flippo, 1982b), and statewide base-flow and 30-day, 10-year; 30-day, 2-year; and 90-day, 10-year low flows mean-flow regression equations have never been developed. using generalized least-squares regression. Statewide regres- Over 20 years of additional streamflow data have been collected sion equations were developed for the 10-year, 25-year, and 50- and new methods for obtaining basin characteristics have been year base flows using generalized least-squares regression. developed since the last low-flow regression equations were Statewide regression equations were developed for harmonic developed. The USGS and the Pennsylvania Department of mean and mean annual flow using weighted least-squares Environmental Protection (PaDEP) cooperated in a study to regression. develop new low-flow, base-flow, and mean-flow regression Basin characteristics found to be significant explanatory equations for Pennsylvania streams using streamflow-gaging 1 variables at the 95-percent confidence level for one or more stations with data through climatic year 2002 . Streamflow data regression equations were drainage area, basin slope, thickness from 293 stations and basin characteristics derived from Geo- of soil, stream density, mean annual precipitation, mean eleva- graphic Information System (GIS) methods were used to tion, and the percentage of glaciation, carbonate bedrock, for- develop these regression equations. ested area, and urban area within a basin. Standard errors of pre- Low flow typically occurs during the months of August diction ranged from 33 to 66 percent for the n-day, T-year low through October, when the streamflow is primarily sustained by flows; 21 to 23 percent for the base flows; and 12 to 38 percent ground-water discharge to the stream. Ground-water discharge for the mean annual flow and harmonic mean, respectively. The commonly contributes about 65 to 80 percent of streamflow regression equations are not valid in watersheds with upstream throughout the year. Low-flow characteristics can be described 1Climatic year is the 12-month period April 1 through March 31. The climatic year is designated by the calendar year in which it ends. Thus, the climatic year ending March 31, 2002, is the 2002 climatic year. 2 Low-Flow, Base-Flow, and Mean-Flow Regression Equations for Pennsylvania Streams as n-day, T-year events, which describe the average flow that miles of streams in the state. The major basins are the Delaware can be expected for n-consecutive days, every T-years. For River Basin, which makes up the boundary between New Jersey example, the 7-day, 10-year (Q7,10) low-flow characteristic is and Pennsylvania on the east and flows south into the Delaware the minimum average flow for 7 consecutive days, expected to Bay; the Susquehanna River Basin, which is in the central part occur once every 10 years, or has a 10-percent chance of occur- of the State and flows south into the Chesapeake Bay; the Poto- ring each year. Base flow is the part of streamflow attributed to mac River Basin, which is in the south-central part of the state ground-water discharge into a stream, without surface runoff, and also flows into the Chesapeake Bay; the Ohio River Basin, and is described in this report as the mean annual flow expected which drains the western part of the State,.