GUADALUPE ESTUARY: An Analysis of Bay Segment Boundaries, Physical Characteristics, and Nutrient Processes TEXAS DEPARTMENT OF WATER RESOURCES LP-76 March 1981 GUADALUPE ESTUARY: AN ANALYSIS OF BAY SEGMENT BOUNDARIES, PHYSICAL CHARACTERISTICS, AND NUTRIENT PROCESSES Prepared by the Engineering and Environmental Systems Section of the Planning and Development Division The preparation of this report was financed through a planning grant from the United States Environmental Protection Agency under provisions of Section 208 of the Federal Water Pollution Control Act Amendments of 1972, as amended. Texas Department ofWater Resources LP-76 Printed March 1981 Report reflectswork completed in June 1979. TEXAS DEPARTMENT OF WATER RESOURCES Harvey Davis, Executive Director TEXAS WATER DEVELOPMENT BOARD Louis A. Beecherl Jr., Chairman John H. Garrett, Vice Chairman George W. McCleskey W. 0. Bankston Glen E. Roney Lonnie A. "Bo" Pilgrim TEXAS WATER COMMISSION Felix McDonald, Chairman Dorsey B. Hardeman, Commissioner Joe R. Carroll, Commissioner Authorization for use or reproduction of any original material contained in this publication, i.e., not obtained from other sources, is freely granted. The Department would appreciate acknowledgement Published and distributed by the Texas Department of Water Resources Post Office Box 13087 Austin, Texas 78711 TABLE OF CONTENTS Page PREFACE 1 SUMMARY 3 ANALYSIS OF BAY SEGMENT BOUNDARIES 4 PHYSICAL CHARACTERISTICS 6 Introduction 6 Sedimentation and Erosion 6 Mineral and Energy Resources 9 Groundwater Resources 15 Data Collection Program 15 Circulation and Salinity 16 Summary 16 Description of Estuarine MathematicalModels 16 Introduction 16 Description ofthe Modeling Process 21 MathematicalModelDevelopment 21 (1) Hydrodynamic Model 21 (2) Conservative Mass Transport Models 23 (3) DataSetsRequired 26 Application ofMathematical Models, Guadalupe Estuary 26 Simulated Flow Patterns 28 (1) Simulated Winter Circulation PatternsunderAverage Inflow Conditions . " •. 28 . (2) Simulated Non-Winter Circulation Patternsunder Average Inflow Conditions 28 in TABLE OF CONTENTS-Continued Page Simulated Salinity Patterns 36 (1) Simulated November, December, January and February Salinity Patterns under Average Inflow Conditions 36 (2) Simulated March andAugust Salinity Patterns under Average Inflow Conditions 36 (3) Simulated April, May, July,September andOctober Salinity Patternsunder Average InflowConditions 36 (4) SimulatedJune Salinity Patterns under Average Inflow Conditions 44 NUTRIENT PROCESSES 44 Summary 44 Nutrient Loading 44 MarshVegetative Production 58 MarshNutrient Cycling 59 ACKNOWLEDGEMENTS 70 BIBLIOGRAPHY 71 FIGURES 1. Locations ofthe Estuaries 5 2. Existing Bay Segment Boundaries 7 3. Proposed Bay Segment Boundaries 8 4. Geologic Map 11 5. Guadalupe Estuary,Shoreline Physical Processes 13 6. Oil and Gas Fields 14 7. Data CollectionSites in the GuadalupeEstuary 17 8. Locationsof Gaging Stations, GuadalupeEstuary 18 9. Relationship Between Tidal Hydrodynamic andSalinity Models .....' 22 10. ConceptualIllustration of Discretization of a Bay 24 11. Computational Grid, Guadalupe Estuary '. 25 IV TABLE OF CONTENTS-Continued Page 12. Monthly Distribution of Mean Annual Total Gaged and Ungaged Inflow, Guadalupe Estuary 27 13. Simulated Net Steady-State Flows in theGuadalupe Estuary under January Average Inflow 29 14. Simulated Net Steady-State Flows in theGuadalupe Estuary under February Average Inflow 30 15. Simulated Net Steady-State Flows in the Guadalupe Estuary under March Average Inflow . 31 16. Simulated Net Steady-State Flows in theGuadalupe Estuary under April Average Inflow 32 17. Simulated Net Steady-State Flows in the Guadalupe Estuary under May Average Inflow 33 18. Simulated Net Steady-State Flows in the Guadalupe Estuary under June Average Inflow 34 19. SimulatedNet Steady-State Flowsin the Guadalupe Estuaryunder July AverageInflow 35 20. Simulated Net Steady-State Flows in the Guadalupe Estuary under August Average Inflow 37 21. Simulated Net Steady-State Flows in the Guadalupe Estuary under September AverageInflow 38 22. Simulated Net Steady-State Flows in the Guadalupe Estuary under October Average Inflow 39 23. Simulated Net Steady-State Flows in the Guadalupe Estuary under November Average Inflow 40 24. Simulated Net Steady-State Flows in the Guadalupe Estuary under December Average Inflow 41 25. SimulatedSalinities in the Guadalupe Estuary underJanuary Average Inflow . 42 26. SimulatedSalinities in the Guadalupe Estuary under February Average Inflow 43 27. SimulatedSalinities in the Guadalupe Estuary under March Average Inflow 45 28. Simulated Salinities in the Guadalupe Estuary under April Average Inflow . 46 29. SimulatedSalinities in the Guadalupe EstuaryunderMayAverage Inflow . 47 30. SimulatedSalinities in the Guadalupe EstuaryunderJune Average Inflow . 48 31. Simulated Salinities in the Guadalupe Estuary underJuly Average Inflow . 49 TABLE OF CONTENTS-Continued Page 32. Simulated Salinities in the Guadalupe Estuary underAugust Average Inflow 50 33. Simulated Salinities in the Guadalupe Estuary underSeptember Average Inflow 51 34. Simulated Salinities in the Guadalupe Estuary underOctober Average Inflow 53 35. Simulated Salinities in theGuadalupe Estuary under November Average Inflow 54 36. Simulated Salinities in the Guadalupe Estuary underDecember Average Inflow 55 37. Exchange Rates forTotal Organic Carbon in Guadalupe Estuary 63 38. Exchange Rates for UnfUtered Total Kjeldahl Nitrogen in Guadalupe Estuary 64 39. Exchange Rates for Ammonia Nitrogenin Guadalupe Estuary 65 40. Exchange Rates for Nitrite Nitrogen in Guadalupe Estuary 66 41. Exchange Rates for Nitrate Nitrogenin Guadalupe Estuary 67 42. Exchange Rates for UnfilteredTotal Phosphorus in Guadalupe Estuary 68 43. Exchange Rates for Ortho-Phosphorus in Guadalupe Estuary 69 TABLES 1. USGS orCorps of Engineers (COE) Gages, Guadalupe Estuary 19 2. Mean Monthly Freshwater Inflows,Guadalupe Estuary 26 3. Carbon Levels in the San Antonio andGuadalupe Rivers at the Goliad and Victoria Gages 52 4. Inorganic Nitrogen Levels in the San Antonio and Guadalupe Rivers at the Goliad andVictoria Gages 56 5. Organic Nitrogen Levels in the San Antonio and Guadalupe Rivers at the Goliadand VictoriaGages 57 6. Total Phosphorus Levels in the San Antonioand Guadalupe Rivers at the Goliadand VictoriaGages 58 7. Discharge Data,Guadalupe River at Victoria 59 8. Discharge Data,San Antonio River at Goliad 60 9. Percent Total FlowContribution of the Guadalupe andSanAntonio Rivers 61. 10. Average Percent TotalContribution ofNutrients From theGuadalupe and San Antonio Rivers, 1974-76 61 11. 1974-76 Nutrient Contributions by the Guadalupe and San Antonio Rivers 62 vi GUADALUPE ESTUARY: AN ANALYSIS OF BAY SEGMENT BOUNDARIES, PHYSICAL CHARACTERISTICS, AND NUTRIENT PROCESSES PREFACE In 1976, the Section 208 Planning Program for 2. Analysis of the physical characteristics of nondesignated planning areas of Texas was initiated. the selected estuarine systems including Additional planning funds were subsequently made mixing, transport, current patterns, and available by EPA to expand the scope of this planning salinity patterns; and effort and to consider other issues not previously addressed. These planning monies, which were available 3. Definition of nutrient processes in Texas in early 1978 as a supplement to the EPA grant for estuarine systems, especially the effects Section 208 planning in nondesignated planning areas, of inflows on nutrient cycling and were earmarked for development of analyses which contributions from deltaic marsh areas. could be used in future planningefforts for evaluationof the appropriateness of existing water quality standards The above tasks are basic to any consideration in major Texas estuarine systems. Due to the short time of the adequacy of water quality standards for frame of the supplemental grant funds, only three tasks Texas estuarine systems. Future tasks, which are were selected. Later these can be expanded upon necessary to complete a comprehensive assessment throughout the continuing planning process. The three of coastal water quality standards, include selected tasks are the subject of this report on the definition of the water quality requirements to Guadalupe estuary: meet various water use criteria for estuarine/river systems, and an assessment of the costs and 1. Analysis of the appropriateness of existing benefits of various uses. bay segment boundaries; GUADALUPE ESTUARY: AN ANALYSIS OF BAY SEGMENT BOUNDARIES, PHYSICAL CHARACTERISTICS, AND NUTRIENT PROCESSES SUMMARY physical processes, including erosion, accretion and other changes in shorelineconfigurations. Because of the This report is one in a series of reports on major shallow depths throughout the estuary, wind can play a Texas estuaries. The objective is to analyze existing data major role in the generation of waves and longshore on the Guadalupe estuary for the purpose of water currents. The peak influx of freshwater to the system quality planning under Section 208 of P.L. 92-500.The normally corresponds with spring rains. Major impacts report has three sections. The first section, presents an from these inflows include overbank flooding of marsh analysis of the appropriateness of existing bay segment areas, extension and building of bay head and oceanic boundaries for water quality planning purposes, and deltas, and flushing of the bays, which reduces salinities. draws heavily upon the data analyses performed in the last two sections of the