TRINITY-SAN JACINTO ESTUARY: An Analysis of Bay Segment Boundaries, Physical Characteristics, and Nutrient Processes ^'tyMffi-'*-'',!\ ••*'•: ^'-:''"''' '.'.'.' "I~t~" .. TEXAS DEPARTMENT OF WATER RESOURCES LP-86 March 1982 TRINITY - SAN JACINTO ESTUARY: AN ANALYSIS OF BAY SEGMENT BOUNDARIES, PHYSICAL CHARACTERISTICS, AND NUTRIENT PROCESSES Prepared by the Engineering and Environmental Systems Section ofthe 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 ActAmendmentsof1972,as amended. Texas Department ofWater Resources LP-86 Printed in March 1982 Report reflects work completed in June 1979. TEXAS DEPARTMENT OF WATER RESOURCES Harvey Davis, Executive Director TEXAS WATER DEVELOPMENT BOARD Louis A. Beecherl Jr., Chairman George W. McCleskey, Vice Chairman Glen E. Roney Lonnie A. "Bo" Pilgrim W. O. Bankston Louie Welch TEXAS, WATER COMMISSION Lee B. M. Biggart, Chairman Felix McDonald, Commissioner John D. Stover, 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 7 Introduction 7 Sedimentation and Erosion 7 Mineral and Energy Resources 12 Groundwater Resources 14 Data Collection Program 14 Circulation and Salinity 21 Summary 21 Description of Estuarine Mathematical Models 21 Introduction 21 Description of the Modeling Process 21 Mathematical Model Development 22 (1) Hydrodynamic Model 22 (2) Conservative Mass Transport Model 25 (3) Data Sets Required 25 Application of Mathematical Models, Trinity-San Jacinto 25 Estuary Simulated Flow Patterns 27 (1) Simulated March, August, and October 27 Circulation Patterns Under Average Inflow Conditions (2) Simulated January, February, July, 30 September, November and December Circulation Patterns Under Average Inflow Conditions (3) Simulated April, May and June Circu- 30 lation Patterns Under Average Inflow Conditions Simulated Salinity Patterns 30 (1) Simulated Spring and Early Summer Salinity 55 Patterns Under Average Historical Freshwater Inflow Conditions in TABLE OF CONTENTS-Continued Page (2) Simulated Fall, Winter and Late Summer 55 Salinity Patterns Under Average Historical Freshwater Inflow Conditions NUTRIENT PROCESSES 55 Summary 55 Nutrient Loading 56 Marsh Vegetative Production 64 Marsh Nutrient Cycling 66 ACKNOWLEDGEMENTS 69 BIBLIOGRAPHY 70 FIGURES 1. Location of Estuaries 5 2-3. Existing Bay Segment Boundaries, Trinity-San Jacinto Estuary 6 4-5. Proposed Bay Segment Boundaries, Trinity-San Jacinto Estuary 8 6. Geologic Map 9 7-8. Shoreline Physical Processes, Trinity-San Jacinto Estuary 11 9-10. Oil and Gas Fields, Trinity-San Jacinto Estuary 13 11-12. Land-Surface Subsidence in the Houston Area (1964-1973) 15 13. Data Collection Sites in Trinity-San Jacinto Estuary 16 14. Location of Gaging Stations, Trinity-San Jacinto Estuary 17 15. Relationships Between Tidal Hydrodynamic and Salinity Models 23 16. Conceptual Illustration of Discretization of a Bay 24 17. Computational Grid, Trinity-San Jacinto Estuary 26 18. Total Mean Monthly Inflow Distribution, Trinity-San Jacinto Estuary, Gaged, Ungaged, and Return Flows Excluding San Jacinto River 29 19. Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary under January Average Inflow (1941-1976) 31 20. Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary under February Average Inflow (1941-1976) 32 21. Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary under March Average Inflow (1941-1976) 33 IV TABLE OF CONTENTS—Continued Page 22. Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary under April Average Inflow (1941-1976) 34 23. Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary under May Average Inflow (1941-1976) 35 24. Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary under June Average Inflow (1941-1976) 36 25. Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary under July Average Inflow (1941-1976) 37 26. Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary under August Average Inflow (1941-1976) 38 27. Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary under September Average Inflow (1941-1976) 39 28. Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary under October Average Inflow (1941-1976) 40 29. Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary under November Average Inflow (1941-1976) 41 30. Simulated Net Steady-State Flows in the Trinity-San , Jacinto Estuary under December Average Inflow (1941-1976) 42 31. Simulated Salinities in the Trinity-San Jacinto Estuary under January Average Inflows 43 32. Simulated Salinities in the Trinity-San Jacinto Estuary under February Average Inflows 44 33. Simulated Salinities in the Trinity-San Jacinto Estuary under March Average Inflows 45 34. Simulated Salinities in the Trinity-San Jacinto Estuary under April Average Inflows 46 35. Simulated Salinities in the Trinity-San Jacinto Estuary under May Average Inflows 47 36. Simulated Salinities in the Trinity-San Jacinto Estuary under June Average Inflows 48 37. Simulated Salinities in the Trinity-San Jacinto Estuary under July Average Inflows 49 38. Simulated Salinities in the Trinity-San Jacinto Estuary under August Average Inflows 50 39. Simulated Salinities in the Trinity-San Jacinto Estuary under September Average Inflows 51 40. Simulated Salinities in the Trinity-San Jacinto Estuary under October Average Inflows 52 41. Simulated Salinities in the Trinity-San Jacinto Estuary under November Average Inflows 53 42. Simulated Salinities in the Trinity-San Jacinto Estuary under December Average Inflows 54 TABLE OF CONTENTS-Continued Page 43. Mean Monthly Organic Nitrogen Concentrations of Streams Contributing to the Trinity-San Jacinto Estuary 57 44. Mean Monthly Inorganic Nitrogen Concentrations of Streams Contributing to the Trinity-San Jacinto Estuary 58 45. Mean Monthly Total Phosphorus Concentrations of Streams Contributing to the Trinity-San Jacinto Estuary 59 46. Mean Monthly Total Organic Carbon Concentrations of Streams Contributing to the Trinity-San Jacinto Estuary 60 TABLES 1. USGS or Corps of Engineers Gages, Trinity-San Jacinto Estuary 18 2. Mean Monthly Freshwater Inflows, Trinity-San Jacinto Estuary, 1941-1976 28 3. Range of Expected Inorganic Nitrogen Loading to the Trinity-San Jacinto Estuary Based on Mean Monthly Gaged Discharge 61 4. Range of Expected Organic Nitrogen to the Trinity-San Jacinto Estuary Based on Mean Monthly Gaged Discharge 61 5. Range of Expected Total Phosphorus Loading to the Trinity-San Jacinto Estuary Based on Mean Monthly Gaged Discharge 62 6. Range of Expected Total Organic Carbon Loading to the Trinity-San Jacinto Estuary Based on Mean Monthly Gaged Discharge 62 7. Scientific and Common Names of Important Plant Species Occurring in the Trinity River Delta 65 8. Summary of Nutrient Exchange Rates 67 9. Summary of Nutrient Exchange Rates for Plant Types from the Lower Trinity River Delta Marshes Corrected for Wall Effects 68 10. Exchange Rates of Carbon, Nitrogen, and Phosphorus in the Linear Marsh from the Trinity River Delta 68 vi TRINITY-SAN JACINTO 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 the nondesignated planning areas of Texas was selected estuarine systems including mixing, initiated. Additional planning funds were subse transport, current patterns, and salinity pat quently made available by EPA to expand the scope terns; and of this planning effort and to consider other issues 3. Definition of nutrient processes in Texasestua not previously addressed. These planning monies rine systems, especially theeffects ofinflowson were available in early 1978 as a supplement to the nutrient cycling and contributions from deltaic EPA grant for Section 208 planning in nondesig nated planning areas. A part of the funds were ear marsh areas. marked for development of analyses which could be The above tasks are basic to any considerationof used in future planning efforts for evaluation of the the adequacy of water quality standards for Texas appropriateness of existing water quality standards estuarine systems. Future tasks, which are necessary in major Texas estuarine systems. Due to the short to complete a comprehensive assessment of coastal time frame of the supplemental grant funds, only water quality standards, include definition of the three tasks were selected. Later these can be waterquality requirements to meet various wateruse expanded upon throughout the continuing planning criteria for estuarine/river systems, and an assess process. The three selected tasks are the subject of ment of the costs and benefits of various uses. this report on the Trinity-San Jacinto estuary: 1. Analysis of the appropriateness of existingbay segment boundaries; TRINITY-SAN JACINTO ESTUARY: AN ANALYSIS OF BAY SEGMENT BOUNDARIES, PHYSICAL CHARACTERISTICS, AND NUTRIENT PROCESSES SUMMARY The Trinity-San Jacinto estuary can be