Trend analysis and selected summary statistics of annual mean streamflow for 38 selected long-term U.S. Geological Survey streamgages in Texas, water years 1916-2012

Scientific Investigations Report 2013-5230
Prepared in cooperation with the Texas Water Development Board
By:  and 

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Abstract

In 2013, the U.S. Geological Survey (USGS) operated more than 500 continuous streamgages (streamflow-gaging stations) in Texas. In cooperation with the Texas Water Development Board, the USGS evaluated mean annual streamflow data for 38 selected streamgages that were active as of water year 2012. The 38 streamgages have annual mean streamflow data considered natural and unregulated. Collected annual mean streamflow data for a single streamgage ranged from 49 to 97 cumulative years. The nonparametric Kendall’s tau statistical test was used to detect monotonic trends in annual mean streamflow over time. The monotonic trend analysis detected 2 statistically significant upward trends (0.01 one-tail significance), 1 statistically significant downward trend (0.01 one-tail significance level), and 35 instances of no statistically significant trend (0.02 two-tailed significance level). The Theil slope estimate of a regression slope of annual mean streamflow with time was computed for the three stations where trends in streamflow were detected: 2 increasing Theil slopes were measured (+0.40 and +2.72 cubic feet per second per year, respectively), and 1 decreasing Theil slope (–0.24 cubic feet per second per year) was measured.

Selected summary statistics (L-moments) and estimates of respective sampling variances were computed for the 35 streamgages lacking statistically significant trends. From the L-moments and estimated sampling variances, weighted means or regional values were computed for each L-moment. An example application is included demonstrating how the L-moments could be used to evaluate the magnitude and frequency of annual mean streamflow.

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Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title Trend analysis and selected summary statistics of annual mean streamflow for 38 selected long-term U.S. Geological Survey streamgages in Texas, water years 1916-2012
Series title Scientific Investigations Report
Series number 2013-5230
DOI 10.3133/sir20135230
Edition First posted 2/10/2014; Version 1.1 revised 8/1/2014
Year Published 2014
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Texas Water Science Center
Description iv, 16 p.
Time Range Start 1915-10-01
Time Range End 2012-09-30
Country United States
State Texas
Datum North American Datum of 1983
Projection Lambert Conformal Conic Projection
Scale 25000
Online Only (Y/N) N
Additional Online Files (Y/N) N