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Summary Statistics and Graphical Comparisons of Historical Hydrologic and Water-Quality Data, Seco Creek Watershed, South-Central Texas

By David S. Brown, Richard N. Slattery, and Jon R. Gilhousen

U.S. Geological Survey
Open-File Report 98–627

In cooperation with the U.S. Department of Agriculture and
Texas State Soil and Water Conservation Board


Abstract

The U.S. Geological Survey collected hydrologic (rainfall, streamflow, and reservoir content) and water-quality data in the Seco Creek watershed, south-central Texas. Most of the data from 15 sites were collected as part of a study in cooperation with the U.S. Department of Agriculture and the Texas State Soil and Water Conservation Board to evaluate the effects of agricultural best-management practices on surface- and ground-water quantity and quality in the 255-square-mile watershed. Nearly 400 best-management practices at 58 sites were implemented by landowners in the watershed during March 1990–September 1995.

Most of the data are from the early 1990s, the period during and after implementation of best-management practices. Data from five sites include water quality and are summarized in tables and graphics in the text; and data from all 15 sites are summarized on a diskette.

Maximum annual rainfall among the sites for which data are presented in the text (excluding one site) for the during-and-after-implementation period (March 1990–September 1995) was 53.27 inches in water year 1992. Maximum annual total streamflow among the sites for the period was 63,400 acre-feet, also in water year 1992. At the one site with water-quality data (under base-flow conditions) for both the before-implementation period and the during-and-after implementation period of best-management practices, percentiles (5, 25, 50, 75, 95) for specific conductance, nitrate concentration, and fecal coliform density were less for the during-and-after-implementation period than for the before-implementation period.

Table of Contents

Abstract

Introduction

Summary Statistics and Graphical Comparisons

Rainfall and Streamflow

Water Quality

References Cited

Appendix—“Readme” File

Data Diskette

Figures

1–2.   Maps showing:
  1.   Location of the Seco Creek watershed, south-central Texas
  2.   Location of data-collection sites in the Seco Creek watershed, south-central Texas
3–4.   Hydrographs showing:
  3.   Daily rainfall at selected stations, Seco Creek watershed, south-central Texas, during-and-after implementation period of best-management practices
  4.   Daily mean streamflow at selected stations, Seco Creek watershed, south-central Texas, during-and-after implementation period of best-management practices
5–9.   Scatterplots showing:
  5.   Specific conductance and pH data aggregated by stream-stage condition at selected stations, Seco Creek watershed, south-central Texas, during-and-after implementation period of best-management practices
  6.   Dissolved oxygen and biochemical oxygen demand data aggregated by stream-stage condition at selected stations, Seco Creek watershed, south-central Texas, during-and-after implementation period of best-management practices
  7.   Fecal coliform and fecal streptococcus data aggregated by stream-stage condition at selected stations, Seco Creek watershed, south-central Texas, during-and-after implementation period of best-management practices
  8.   Hardness and potassium data aggregated by stream-stage condition at selected stations, Seco Creek watershed, south-central Texas, during-and-after implementation period of best-management practices
  9.   Dissolved solids and nitrate data aggregated by stream-stage condition at selected stations, Seco Creek watershed, south-central Texas, during-and-after implementation period of best-management practices

Tables

1.   Rainfall, streamflow, reservoir-content, and water-quality stations in the Seco Creek watershed, south-central Texas
2–6.   Summary statistics for monthly rainfall and streamflow at:
  2.   Site 4, Seco Creek at Miller Ranch near Utopia, Texas (08201500), during-and-after implementation period of best-management practices
  3.   Site 6, Seco Creek Reservoir Inflow near Utopia, Texas (08202450), during-and-after implementation period of best-management practices
  4.   Site 12, Parkers Creek Reservoir Inflow near D’Hanis, Texas (08202790), during-and-after implementation period of best-management practices
  5.   Site 16, Seco Creek at Rowe Ranch near D’Hanis, Texas (08202700), during-and-after implementation period of best-management practices
  6.   Site 18, Seco Creek near Yancey, Texas (08202900), during-and-after implementation period of best-management practices
7–11.   Summary statistics for selected physical properties and water-quality constituents at:
  7.   Site 4, Seco Creek at Miller Ranch near Utopia, Texas (08201500), before-implementation and during-and-after implementation periods of best-management practices
  8.   Site 6, Seco Creek Reservoir Inflow near Utopia, Texas (08202450), during-and-after implementation period of best-management practices
  9.   Site 12, Parkers Creek Reservoir Inflow near D’Hanis, Texas (08202790), during-and-after implementation period of best-management practices
  10.   Site 16, Seco Creek at Rowe Ranch near D’Hanis, Texas (08202700), during-and-after implementation period of best-management practices
  11.   Site 18, Seco Creek near Yancey, Texas (08202900), during-and-after implementation period of best-management practices

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