A Stream-gaging Network Analysis for the 7-Day, 10-Year Annual     Low Flow in New Hampshire Streams
| **U.S. Geological         Survey         Water-Resources Investigations Report 03-4023****** | **ONLINE ONLY** |
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By Robert H. Flynn

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###  Abstract

 The 7-day, 10-year (7Q10) low-flow-frequency statistic       is a widely used measure of surface-water availability in New Hampshire.       Regression equations and basin-characteristic digital data sets were developed       to help water-resource managers determine surface-water resources during       periods of low flow in New Hampshire streams. These regression equations       and data sets were developed to estimate streamflow statistics for the annual       and seasonal low-flow-frequency, and period-of-record and seasonal period-of-record       flow durations. generalized-least-squares (GLS) regression methods were       used to develop the annual 7Q10 low-flow-frequency regression equation from       60 continuous-record stream-gaging stations in New Hampshire and in neighboring       States. In the regression equation, the dependent variables were the annual       7Q10 flows at the 60 stream-gaging stations. The independent (or predictor)       variables were objectively selected characteristics of the drainage basins       that contribute flow to those stations. In contrast to ordinary-least-squares       (OLS) regression analysis, GLS-developed estimating equations account for       differences in length of record and spatial correlations among the flow-frequency       statistics at the various stations. 

A total of 93 measurable drainage-basin characteristics       were candidate independent variables. On the basis of several statistical       parameters that were used to evaluate which combination of basin characteristics       contribute the most to the predictive power of the equations, three drainage-basin       characteristics were determined to be statistically significant predictors       of the annual 7Q10: (1) total drainage area, (2) mean summer stream-gaging       station precipitation from 1961 to 90, and (3) average mean annual basinwide       temperature from 1961 to 1990.

To evaluate the effectiveness of the stream-gaging       network in providing regional streamflow data for the annual 7Q10, the computer       program GLSNET (generalized-least-squares NETwork) was used to analyze the       network by application of GLS regression between streamflow and the climatic       and basin characteristics of the drainage basin upstream from each stream-gaging       station. Improvement to the predictive ability of the regression equations       developed for the network analyses is measured by the reduction in the average       sampling-error variance, and can be achieved by collecting additional streamflow       data at existing stations. The predictive ability of the regression equations       is enhanced even further with the addition of new stations to the network.       Continued data collection at unregulated stream-gaging stations with less       than 14 years of record resulted in the greatest cost-weighted reduction       to the average sampling-error variance of the annual 7Q10 regional regression       equation. The addition of new stations in basins with underrepresented values       for the independent variables of the total drainage area, average mean annual       basinwide temperature, or mean summer stream-gaging station precipitation       in the annual 7Q10 regression equation yielded a much greater cost-weighted       reduction to the average sampling-error variance than when more data were       collected at existing unregulated stations. To maximize the regional information       obtained from the stream-gaging network for the annual 7Q10, ranking of       the streamflow data can be used to determine whether an active station should       be continued or if a new or discontinued station should be activated for       streamflow data collection. Thus, this network analysis can help determine       the costs and benefits of continuing the operation of a particular station       or activating a new station at another location to predict the 7Q10 at ungaged       stream reaches. The decision to discontinue an existing station or activate       a new station, however, must also consider its contribution to other water-resource       analyses such as flood management, water quality, or trends in land use       or climatic change.

  

 TABLE OF CONTENTS

  

 Abstract

 Introduction

 Purpose and Scope

 Previous Studies

 Acknowledgments

 Method For Network Analysis of Annual 7-Day, 10-Year Low       Flow

 Description of Method

 Application of the Method to the New Hampshire Stream-gaging       Network

 Network Analysis Scenarios

 Scenario 1

 Scenario 2

 Scenario 3

 Results of the Stream-gaging Network Analysis

 Summary and Conclusions

 Selected References

 Appendix 1. Basin Characteristics Tested for Significance       in the Regression Analysis

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For additional information write to:

      District Chief      U.S. Geological Survey      New Hampshire/Vermont District      361 Commerce Way      Pembroke, NH 03275-3718      or through our Web site athttp://nh.water.usgs.gov

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