Center for Research in Water Resources

Measurements of diffusion from slug releases of fluorescent dye performed in the bays of Texas are compiled along with attendant hydrographic and hydrometeorological data. These data sets are confined to conditions of low surface wave activity to better expose the effects of local currents on diffusion. Development of a dye patch is parameterized in terms of a lateral diffusivity, which measures "turbulent" diffusion, and a longitudinal dispersion, which measures the effect of vertical shear in the current. The former is found to follow a local 4/3-power dependence upon scale and has a noisy correlation with current speed. The latter is found to be consistent with a theoretical model predicting a variation with the square of current speed and inverse variation with the squared Ch•zy coefficient. These data are considered to be generally representative of the shallow lagoon environment typical of Gulf of Mexico bays.

The Nueces River is the primary source of freshwater inflow to Corpus Christi Bay and virtually the only source of freshwater inflow in the Nueces Delta. In association with reservoir development and operation within the Nueces Basin, the magnitude of freshwater inflow has been greatly reduced since 1958. Continually increasing salt concentrations in the soil and water have compromised the function of the delta as a viable component of the estuarine ecosystem. In 1993, the U.S. Bureau of Reclamation began a 5-yr diversion project to increase the opportunity for freshwater flow into the delta. With the excavation of two overflow channels, the minimum flooding threshold for the upper delta was significantly lowered, and more frequent diversions of freshwater from the Nuecess River were enabled. During the 50-mo diversion period, the amount of freshwater diverted into the upper Nueces Delta was increased sevenfold. The average salinity gradient in the upper delta reverted to a more natural pattern, with average salinity concentrations decreasing from the lower (bay) to upper (riverine) delta, and a corresponding improvement in abundance and diversity of both intertidal vegetation and benthic communities.

Engineered rivers in arid lands play an important role in feeding the world's growing population. Each continent has rivers that carry water from distant mountain sources to fertile soil downstream where rainfall is scarce. Over the course of the last century most rivers in arid lands have been equipped with large engineering structures that generate electric power and store water for agriculture and cities. This has changed the hydrology of the rivers. In this paper we discuss how climate variation, climate change, reservoir siltation, changes in land use and population growth will challenge the sustainability of engineered river systems over the course of the next few decades. We use the Rio Grande in North America, where we have worked with Mexican and American colleagues, to describe our methodology and results. Similar work is needed to study future water supply and demand in engineered rivers around the world.

In September 2006, the Texas Commission on Environmental Quality (TCEQ) and Texas ... State Soil and Water Conservation Board (TSSWCB) charged a seven-person Bacteria ... Total Maximum Daily Load (TMDL) Task Force with: ... • examining approaches that other states use to ...

Three independent studies were conducted to quantify ultimate biochemical oxygen demand (UBOD) and the corresponding decomposition rate constant for production pond (average 21.5 ha each) waters and effluents on six semi-intensively managed marine shrimp (Litopenaeus vannamei) farms in Honduras. Samples were collected during the rainy season in studies 1-3 and during the dry season only in Study 1. Pond water samples were collected during the culture period and/or at harvest. The dry season 30-d biochemical oxygen demand (BOD 30) of pond waters across all farms was 26% lower and UBOD was 54% lower, but the decomposition rate constant was more than twice as great as during the rainy season. During the dry season, biochemical oxygen demand was nearly completely expressed after 30 d of incubation whereas during the rainy season BOD was about 65% expressed after 31 d of incubation and the correlation between BOD 31 and UBOD was less strong compared to the dry season. Water quality variables were correlated with measures of BOD during rainy and dry seasons, but only the correlation between chlorophyll a and BOD measures was predictive. In studies 2 and 3, BOD after 88-94 d of incubation was expressed almost completely and corresponded closely with computed UBOD. No significant differences in UBOD were detected in pond samples taken after 30, 61, or 71 (harvest) d of grow out in study 3. Mean decomposition rate constant ranged from 0.054 to 0.071 d −1 in studies 1-3 (rainy season), compared to 0.123 d −1 in Study 1 (dry season).

Laguna Madre, Texas, is 3-7 km wide and more than 190 km long, making it one of the longest lagoons in the world. The lagoon encompasses diverse geologic and climatic regions and it is an efficient sediment trap that accumulates clastic sediments from upland, interior, and oceanic sources. The semi-arid climate and frequent tropical cyclones historically have been responsible for the greatest volume of sediment influx. On an average annual basis, eolian transport, tidal exchange, storm washover, mainland runoff, interior shore erosion, and authigenic mineral production introduce approximately one million m 3 of sediments into the lagoon. Analyses of these sediment transport mechanisms and associated line sources and point sources of sediment provide a basis for: (1) estimating the long-term average annual sediment supply to a large lagoon; (2) calculating the average net sedimentation rate; (3) comparing introduced sediment volumes and associated aggradation rates with observed relative sea-level change; and (4) predicting future conditions of the lagoon. This comparison indicates that the historical average annual accumulation rate in Laguna Madre (Ͻ1 mm/yr) is substantially less than the historical rate of relative sea-level rise (ϳ4 mm/yr). Lagoon submergence coupled with erosion of the western shore indicates that Laguna Madre is being submerged slowly and migrating westward rather than filling, as some have suggested.

A précis is presented of the status of the water resources of Texas at the turn of the century, both 1900 and 2000. The purpose is to assess the similarities maintained, and the changes wrought in water problems and their management over the intervening century. Then, as now, the state exhibits a wide range of hydroclimatology, the greatest of any of the contiguous states. Runoff derives mainly from deep convection, largely associated with equinoctial midlatitude storms and landfalling tropical depressions, so the resulting streamflow is flashy. There is a near balance between rainfall and evapotranspiration, making their difference—the water source for both runoff and recharge—susceptible to slight variations in either. These two facts, instability of and flashiness in runoff and recharge, together comprise the fundamental problem of Texas water supply. The close of both centuries showed Texans reeling from droughts and floods. Population growth in the state over the last decade of...

Intensive data collection and a modeling study have been underway for the past several years addressing two of the channel estuaries draining into the Gulf of Fonseca, Estero El Pedregal and Estero San Bernardo. Data have been compiled on the shrimp farm configurations, exchange rates, and effluent chemistry. Temperature, salinity, and dissolved oxygen profiles have been measured in the estuary channels during both rainy and dry seasons. Physiographic, hydrographic, and meteorological data have been obtained to supplement the estuary data. This report examines the assimilative capacity of these estuaries with respect to dissolved oxygen (DO). The oxygen demand of organics is measured by biochemical oxygen demand (BOD). Shrimp farm BOD loadings were estimated from effluent data and exchange. A transport model for salinity and DO in the estuaries was applied to predict the tidal-mean and section-mean concentrations of salinity and DO. The model predictions of DO—based on 1995 BOD load...

The Nueces River is the primary source of freshwater inflow to Corpus Christi Bay and virtually the only source of freshwater inflow to the Nueces Delta. In association with reservoir development and operation within the Nueces Basin, the magnitude of freshwater inflow has been greatly reduced since 1958. Continually increasing salt concentrations in the soil and water have compromised the function of the delta as a viable component of the estuarine ecosystem. In 1993, the U.S. Bureau of Reclamation began a 5-yr diversion project to increase the opportunity for freshwater flow into the delta. With the excavation of two overflow channels, the minimum flooding threshold for the upper delta was significantly lowered, and more frequent diversions of freshwater from the Nueces River were enabled. During the 50-mo diversion period, the amount of freshwater diverted into the upper Nueces Delta was increased sevenfold. The average salinity gradient in the upper delta reverted to a more natural pattern, with average salinity concentrations decreasing from the lower (bay) to upper (riverine) delta, and a corresponding improvement in abundance and diversity of both intertidal vegetation and benthic communities.

Water quality of highway runoff in the Austin, Texas, area was determined by monitoring runoff at three locations on the MoPac Expressway. Daily traffic volumes, surrounding land uses, and highway drainage system types were different at each site. The concentrations of ...

A literature review of the hydrography and biology of Matagorda Bay, Texas is presented. The goal was the identification, compilation, and synthesis of hydrographic and biological information in order to assess the fish and wildlife resources of the Matagorda Bay area and to delineate the dependency of these resources upon the hydrographic characteristics of the bay. The information is intended to be used to assess the probable effects of system perturbations. Twenty-five key species were selected and are described to represent major elements of the bay biological communities. (ACR)

For many years, data relating to the quality of water and sediment in the Galveston Bay system have been collected by a variety of organizations and individual researchers. The objectives of data collection have been equally varied, including the movement and properties of water, the biology of the bay, waste discharges and their impacts, navigation, geology and coastal processes, and fisheries. Some of this information dates back more than a century. While the specific purposes of the individual data collection projects have limited each Galveston Bay project in time and space, the data have great potential value to the Galveston Bay National Estuary Program (GBNEP) if they can be combined into comprehensive data bases yielding a historical depiction of the quality of the bay environment. As a part of the GBNEP, work is underway to compile and evaluate these data, and to employ these data in a quantitative assessment of alterations of bay quality and influences from point source loads.

The Texas Water Development Board collected suspended sediment samples across the state of Texas for approximately 60 years. Until this research, no comprehensive analysis of the data had been conducted. This study compiles the suspended sediment data along with corresponding streamflow and rainfall. GIS programs are developed which characterize watersheds corresponding to the sediment gauging stations. The watersheds are characterized according to topography, climate, soils, and land use. All of the data is combined to form several SAS data sets which can subsequently be analyzed using regression. Annual data for all of the stations across the state are classified temporally and spatially to determine trends in the sediment yield. In general, the suspended sediment load increases with increasing runoff but no correlation exists with rainfall. However, the annual average rainfall can be used to classify the watersheds according to climate, which improves the correlation between sedi...

Much of the existing information on Matagorda Bay is either a part of the " grey " literature or unpublished-and sometimes unreduced data holdings of various agencies and individual scientists. Thus, it is the generosity and cooperation of these people and agencies that have made this work possible in providing access to their information and taking time to share their experience and observations with us. The Texas Department of Water Resources has performed pioneering studies on the bays and estuaries of Texas, specifically the Matagorda Bay system , and the valuable work undertaken by this agency permeates this report. The U.S. Geological Survey maintains various monitoring programs (stream flow , riverine silt load, water quality) which comprise an invaluable data base characterizing the historical variations of the system. The U.S. Corps of Engineers (Galveston District) in its responsibilities for navigation , coastal protection and civil works has performed various studies of the Matagorda Bay system for the past century. The Texas Parks and Wildlife Department has collected the single most important series of historical data on the biological and ecological characteristics of the system. Other agencies which have provided important information on the system include the Lavaca-Navidad River Authority ,

A branching section-mean model has been developed for the simulation of the hydrodynamics and nutrient transport in estuarine deltaic systems, in which the momentum conservation, continuity and mass transfer equations are solved by the method of finite differences. Example executions of the hydrodynamic portion of the model are presented for the Lavaca, Guadalupe and Trinity deltaic systems. Computed water elevations and flows are compared to observations to evaluate model performance for a variety of conditions. The model is shown to obtain satisfactory results for conditions of variable freshwater inflow, such as associated with small-to-moderate floods, and meteorologically influenced tides, e.g., wind-induced setup or setdown, as well as low-flow, astronomical-tide regimes.