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Estimation of low-flow statistics at ungaged sites on streams in the Lower Hudson River Basin, New York, from data in geographic information systems

Scientific Investigations Report 2017-5019
By:  and 
https://doi.org/10.3133/sir20175019

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Abstract

A variety of watershed properties available in 2015 from geographic information systems were tested in regression equations to estimate two commonly used statistical indices of the low flow of streams, namely the lowest flows averaged over 7 consecutive days that have a 1 in 10 and a 1 in 2 chance of not being exceeded in any given year (7-day, 10-year and 7-day, 2-year low flows). The equations were based on streamflow measurements in 51 watersheds in the Lower Hudson River Basin of New York during the years 1958–1978, when the number of streamflow measurement sites on unregulated streams was substantially greater than in subsequent years. These low-flow indices are chiefly a function of the area of surficial sand and gravel in the watershed; more precisely, 7-day, 10-year and 7-day, 2-year low flows both increase in proportion to the area of sand and gravel deposited by glacial meltwater, whereas 7-day, 2-year low flows also increase in proportion to the area of postglacial alluvium. Both low-flow statistics are also functions of mean annual runoff (a measure of net water input to the watershed from precipitation) and area of swamps and poorly drained soils in or adjacent to surficial sand and gravel (where groundwater recharge is unlikely and riparian water loss to evapotranspiration is substantial). Small but significant refinements in estimation accuracy resulted from the inclusion of two indices of stream geometry, channel slope and length, in the regression equations. Most of the regression analysis was undertaken with the ordinary least squares method, but four equations were replicated by using weighted least squares to provide a more realistic appraisal of the precision of low-flow estimates. The most accurate estimation equations tested in this study explain nearly 84 and 87 percent of the variation in 7-day, 10-year and 7-day, 2-year low flows, respectively, with standard errors of 0.032 and 0.050 cubic feet per second per square mile. The equations use natural values of streamflow and watershed properties; logarithmic transformations yielded less accurate equations inconsistent with some conceptualized relationships.

Suggested Citation

Randall, A.D., and Freehafer, D.A., 2017, Estimation of low-flow statistics at ungaged sites on streams in the Lower Hudson River Basin, New York, from data in geographic information systems: U.S. Geological Survey Scientific Investigations Report 2017–5019, 42 p., https://doi.org/10.3133/sir20175019.

ISSN: 2328-0328 (online)

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Table of Contents

  • Abstract 
  • Introduction
  • Calculation of Low-Flow Indices 
  • Compilation of Watershed Properties 
  • Regression Analysis Using Ordinary Least Squares 
  • Regression Analysis Using Weighted Least Squares 
  • Suggested Methods for Estimating Statistical Indices of Low Flow at Ungaged Sites in the Lower Hudson River Basin 
  • Summary
  • References Cited
  • Appendix 1. Aggregation of Soil Series Into Surficial Geology Units and Sources of Abundant Evapotranspiration for Use in Regression Analysis 
Publication type Report
Publication Subtype USGS Numbered Series
Title Estimation of low-flow statistics at ungaged sites on streams in the Lower Hudson River Basin, New York, from data in geographic information systems
Series title Scientific Investigations Report
Series number 2017-5019
DOI 10.3133/sir20175019
Year Published 2017
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) New York Water Science Center
Description v, 42 p.
Country United States
State New York
Other Geospatial Lower Hudson River Basin
Online Only (Y/N) Y
Additional Online Files (Y/N) N
Additional publication details