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Hydrologic Conditions and Quality of Rainfall and Storm Runoff in Agricultural and Rangeland Areas in San Patricio County, Texas, 2000-2001

U.S. Geological Survey
Open-File Report 02-291

In cooperation with the U.S. Department of Agriculture,
Natural Resources Conservation Service;
San Patricio Soil and Water Conservation District; and
The Welder Wildlife Foundation

By Darwin J. Ockerman


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CONTENTS

Abstract

Introduction

        Purpose and Scope

        Description of Study Area

        Texas Water-Quality Standards

        Acknowledgments

Data-Collection Methods

        Runoff Monitoring

        Water Quality

        Rainfall Sampling

        Runoff Sampling

Hydrologic Conditions

        Rainfall

        Runoff

Water Quality

        Rainfall

                Nutrients

                Rainfall Deposition of Nitrogen

        Runoff

                Nutrients, Major Inorganic Ions, and Trace Elements

                Pesticide

                Bacteria

                Loads and Yields

Summary

References

 

PLATE

    1. Map showing aerial photograph of agricultural and rangeland watersheds (11" X 17")

 

FIGURES

    1. Map showing Coastal Bend area of South Texas and study area

    2. Hydrograph showing rainfall, discharge, and subsample-collection timing at watershed site 2 during
        storm event, August 30, 2001

    3-5. Graphs showing:

        3. Mean monthly rainfall at National Oceanic and Atmospheric Administration (NOAA) weather
   
         station, 1965-2001, and monthly study area rainfall, 2000-2001

        4. Comparison of computed and estimated (from regression) total nitrogen deposition for sampled
            rainfall events, June 2000-August 2001

        5. Comparison of runoff concentrations for selected constituents between mixed agricultural
            watershed (Moody Creek watershed) and rangeland watersheds (watersheds 1 and 2),
            2000-2001

TABLES

    1. Rainfall, runoff volumes, and runoff coefficients for runoff events, 2000-2001

    2. Concentrations of nutrients in rainfall samples, 2000-2001

    3. Summary statistics of selected nutrient concentrations in rainfall samples, 2000-2001

    4. Event-mean concentrations for selected properties and constituents in runoff samples, 2000-2001

    5. Summary statistics of event-mean concentrations for selected constituents in runoff samples,
        2000-2001

    6. Densities of bacteria in runoff samples, 2000-2001

    7. Summary statistics of bacteria densities in combined runoff samples, 2000-2001

    8. Monthly and annual loads of selected constituents in runoff, 2000-2001


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