U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 02-4298
Regression equations and basin-characteristic digital datasets were developed to help water-resource managers estimate surface-water resources during periods of low flow in New Hampshire. The regression equations were developed to estimate statistics for the seasonal and annual low-flow-frequency and seasonal period-of-record and period-of-record flow durations. Because streamflow is maintained by ground-water discharge during periods of low flow, these equations also will aid in the assessment of ground-water availability. Ultimately, the equations and datasets developed herein can be combined with data on water withdrawals, discharges, and interbasin transfers in a geographic information system (GIS) to allow assessments of water use and water availability in any drainage basin in the State of New Hampshire.
Regression equations developed in this study provide estimates of the seasonal (spring, summer, fall, and winter) and annual 7-day 2-year (7Q2) and 7-day 10-year (7Q10) low-flow-frequency values, as well as seasonal period-of-record and period-of-record flow durations (60-, 70-, 80-, 90-, 95-, and 98-percent exceedences) for ungaged reaches of unregulated New Hampshire streams. Regression equations were developed using seasonal and annual low-flow statistics from 58 to 60 continuous-record stream-gaging stations in New Hampshire and nearby areas in neighboring states, and measurements of various characteristics of the drainage basins that contribute flow to those stations.
The estimating equations for the seasonal and annual 7Q2 and 7Q10 values were developed using generalized-least-squares (GLS) regression analyses. T he GLS equations developed for these flow statistics gave average prediction errors that ranged from 11 to 61 percent.
The estimating equations for flow-duration exceedence frequency values were developed using ordinary-least-squares (OLS) regression analysis. The OLS equations developed for these flow statistics gave average prediction errors ranging from 14 to 79 percent.
A total of 93 measurable drainage-basin characteristics were selected as possible predictor variables. Of these 93 variables, the following 10 were determined to be statistically significant predictors for at least one of the dependent variables: drainage area, average basin slope, maximum basin elevation, average summer gage precipitation for 1961-90, average spring gage precipitation for 1961-90, average mean annual basin temperature for 1961-90, average mean summer basin temperature for 1961-90, average winter basin-centroid precipitation for 1961-90, percent of the basin that is coniferous, and percent of the basin that is mixed coniferous and deciduous. These 10 basin characteristics were selected because they were statistically significant based on several statistical parameters that evaluated which combination of characteristics contributed the most to the predictive accuracy of the regression-equation models. A GIS is required to measure the values of the predictor variables for the equations developed in this study.
Purpose and scope
Description of Study Area
Low-Flow Frequency and Flow-Duration Estimating Methods at Stream-Gaging Stations
Low-Flow-Frequency and Flow-Duration Estimating Methods at Ungaged Stream Sites
Drainage-Area Ratio Approach
Development of Regression Model for Estimation of Low-Flow-Frequency and Flow-Duration Statistics
Physical Basis for Regression Relations
Limitations on the Use of Regression Equations
Summary and Conclusions
Appendix 1. Basin Characteristics Tested for Significance in the Regression Analysis
Appendix 2. Flow-Duration Statistics Estimated Using Available Data and Regression Equation Predicted Values for the Period-of-Record
Appendix 3. Flow-Duration Statistics Estimated Using Available Data and Regression Equation Predicted Values for the Winter Season, January 1 to March 15
Appendix 4. Flow-Duration Statistics Estimated Using Available Data and Regression Equation Predicted Values for the Spring Season, March 16 to May 31
Appendix 5. Flow-Duration Statistics Estimated Using Available Data and Regression Equation Predicted Values for the Summer Season, June 1 to October 31
Appendix 6. Flow-Duration Statistics Estimated Using Available Data and Regression Equation Predicted Values for the Fall Season, November 1 to December 31
Appendix 7. Low-Flow Statistics Estimated Using Available Data and Regression Equation Predicted Values for Annual and Seasonal Periods
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For further information contact
Keith Robinson, Director
New Hampshire-Vermont Water Science Center
361 Commerce Way
Pembroke, NH 03275
or visit the Water Science Center home page at
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Last modified: Wednesday, February 22 2006, 01:36:57 PM