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Runoff Characteristics and the Influence of Land Cover In RUNOFF CHARACTERISTICS AND THE INFLUENCE OF LAND COVER IN DRYLANDS OF WESTERN TEXAS A Dissertation by YUN HUANG Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY August 2006 Major Subject: Water Management and Hydrological Science RUNOFF CHARACTERISTICS AND THE INFLUENCE OF LAND COVER IN DRYLANDS OF WESTERN TEXAS A Dissertation by YUN HUANG Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Approved by: Co-Chairs of Committee, Bradford P. Wilcox Clyde L. Munster Committee Members, Thomas W. Boutton Binayak P. Mohanty Chair of Water Management and Hydrological Science Faculty, Ronald A. Kaiser August 2006 Major Subject: Water Management and Hydrological Science iii ABSTRACT Runoff Characteristics and the Influence of Land Cover in Drylands of Western Texas. (August 2006) Yun Huang, B.S., Hefei University of Technology; M.S., Utah State University Co-Chairs of Advisory Committee: Dr. Bradford P. Wilcox Dr. Clyde L. Munster In dryland regions, where water is a limited resource, land use/land cover has undergone and continues to undergo significant change mainly due to human activities. The nature of runoff from dryland regions and the influence of land use/land cover change are largely not quantified. The objective of this study is to examine runoff dynamics and the influence of land cover in drylands of western Texas across multiple spatial and temporal scales. The study consists of four major components: (1) an experimental study at Honey Creek upland catchment (19 ha) to assess vegetation treatment effects on runoff by hydrometric and isotopic methods, (2) a hydrochemical evaluation of hydrologic linkage between the upland and bottomland at the second-order Honey Creek watershed, (3) a detailed precipitation-streamflow analysis at North Concho River basin to assess long-term and large-scale precipitation-streamflow- vegetation dynamics, and (4) a comparison of streamflow in North, Middle, and South Concho River basins and a regional streamflow trend analysis for the entire western Texas. The study indicates runoff in the drylands of western iv Texas is dominated by a few large runoff-producing events. The small catchment experiment indicated that runoff increased about 40 mm per year when 60% of woody plants were removed. This effect may relate to the presence of a baseflow component, but was not verified in regional trend analysis for the Edwards Plateau region where most rivers are spring-fed. The decrease in streamflow in North Concho River basin after 1950’s is in large part related to the enhanced infiltration capacity from reduced grazing pressure and improved vegetation cover. Regional streamflow trend analysis suggests some headwater areas outside the Edwards Plateau region experienced patterns of streamflow change similar to those in North Concho River basin, although artificial impoundments complicated the analysis. The study has broader application in ecohydrological research in evaluating the impact of ecosystem structure change on hydrology and water resources. v ACKNOWLEDGEMENT I would like to express my sincere gratitude to my dissertation committee members Drs. Bradford Wilcox, Clyde Munster, Thomas Boutton and Binayak Mohanty, for their time, feedback and advices during my graduate study at Texas A&M University. Special thanks go to Bradford Wilcox and Clyde Munster for their continued support and encouragement. I am deeply indebted to Bradford Wilcox for his guidance and insight throughout my dissertation research. I greatly appreciate the help and support from many faculty members, most notably, Drs. Ronald Kaiser, Robert Knight, and Keith Owens. They helped me in different ways. My efforts have been greatly enhanced by the members of hydrologic research group and graduate students in the Department of Biological and Agricultural Engineering and the Department of Rangeland Ecology and Management at Texas A&M University: Jason Afinowicz, Shane Porter, Joshua Sorenson, Lisa James, Lucas Gregory, Phillip Taucer, and Alyson McDonald, to name a few. I am also grateful to the College of Agriculture and Life Sciences of Texas A&M University for honoring me with a Tom Slick Graduate Research Fellowship which partially funded this study. Finally, I am grateful for the continued love and support from my family and friends, who always stand behind me during my time of need. vi TABLE OF CONTENTS Page ABSTRACT ......................................................................................... iii ACKNOWLEDGEMENTS.................................................................... v TABLE OF CONTENT ......................................................................... vi LIST OF FIGURES .............................................................................. viii LIST OF TABLES ................................................................................ x CHAPTER I INTRODUCTION............................................................ 1 Background............................................................... 1 Research Questions ................................................. 3 Organization of Study ............................................... 4 II EXPERIMENTAL STUDY OF RUNOFF AND VEGETATION INFLUENCE IN A SPRING-FED CATCHMENT ............ 5 Introduction ............................................................... 5 Study Area................................................................ 8 Methods .................................................................... 11 Runoff Dynamics....................................................... 17 Influences of Woody Plants ...................................... 23 Discussion ................................................................ 25 Conclusions .............................................................. 29 III HYDROCHEMICAL EVIDENCES OF STORAGE AND FLUX BETWEEN UPLAND AND BOTTOMLAND.................... 31 Introduction ............................................................... 31 Study Site................................................................. 33 Methods .................................................................... 35 Results...................................................................... 37 Discussion ................................................................ 41 Conclusions .............................................................. 45 vii CHAPTER Page IV TRENDS AND DRIVERS OF LONG-TERM STREAMFLOW CHANGE IN NORTH CONCHO RIVER BASIN ............. 46 Introduction ............................................................... 46 Study Site................................................................. 51 Data and Methodology.............................................. 55 Results...................................................................... 58 Discussion ................................................................ 68 Conclusions .............................................................. 71 V A REGIONAL ASSESSMENT OF STREAMFLOW CHANGE IN THE WAKE OF WOODY PLANT ENCROACHMENT.... 74 Introduction ............................................................... 74 Study Site................................................................. 77 Data and Methodology.............................................. 79 Results...................................................................... 81 Conclusions .............................................................. 87 VI SUMMARY..................................................................... 89 Major Findings .......................................................... 89 Suggestions for Future Research ............................. 92 REFERENCES .................................................................................. 94 APPENDIX A .................................................................................. 106 APPENDIX B .................................................................................. 113 VITA.. .......... .... .................................................................................. 115 viii LIST OF FIGURES FIGURE Page I Location of the Honey Creek catchment study area within the Honey Creek State Natural Area ................................... 10 2 Daily mean stream depths, as corrected, compared with depths of manual measurements done later in the study .............. 12 3 Hourly hydrograph of the largest precipitation event recorded during the 4-year study................................................... 19 4 Runoff events distribution during the study period ......... 20 5 Time series of the 18O isotopic compositions of baseflow and precipitation at the study area ........................................ 21 6 O-18 isotope hydrograph separation.............................. 23 7 Event-based regression plot of runoff amount versus rainfall amount ........................................................................... 25 8 Diagram of the sampling locations in Honey Creek watershed system............................................................................ 34 9 Average pH, electrical conductivity, temperature, and δ18O for all the sampling locations.................................................... 38 10 Hydrochemical parameters from springs along the bottomland creek and seeps from upland catchment........................ 40 11 Measured baseflow δ18O values vs time for
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