Temporal variability of freshwater and pore water recirculation components of submarine groundwater discharges at Baffin Bay,Texas   总被引：1，自引：1，他引：0  

Venkatesh Uddameri  Sreeram Singaraju  E. Annette Hernandez 《Environmental Earth Sciences》2014,71(6):2517-2533

Submarine groundwater discharges (SGDs) are an important source of freshwater as well as nutrients and other chemicals to bays and estuaries. SGDs are particularly important for coastal bodies in arid and semi-arid regions that are not fed by perennial streams. The Baffin Bay, TX is a shallow coastal water body that is weakly connected to the Gulf of Mexico and has no major rivers or streams draining into it. A year-long submarine groundwater discharge measurement study was carried out at the Loyola Beach of the Baffin Bay during the months of July 2005–June 2006. A total of 23 synoptic SGD sampling events were carried out with most events collecting SGD data continuously over a period of 24 h at a 1-min temporal resolution using an ultrasonic seepage meter. The median SGD was noted to be 3.83 cm/d with an inter-quartile range (IQR) of 11.36 cm/d. Four sampling events had anomalously high SGD values (~27–48 cm/d) which are hypothesized to be due to the geologic heterogeneity of the sea bed and meteorological effects. Eight of the 23 sampling events had a negative average SGD flux indicating landward flow. The short-term diurnal variability of SGD was comparable or sometimes higher than the longer-term and between-events variability. No long-term trend could be inferred. In the short-term, SGD measurements showed considerable persistence and the effective sample size analysis indicated each sampling event (consisting of over 1,000 samples) yielded only a handful of statistically independent measurements of SGD. The measured SGD values exhibited both negative (hydraulically controlled) and positive (wave set-up controlled) correlations with the bay water levels. Marine controls appeared to be the most significant SGD drivers and are in turn controlled by prevailing aeolian forcings. The salinity of the SGDs were estimated from measured sonic velocities and used in conjunction with the end-member mixing models to estimate fresh (meteoric) and re-circulated pore-water fractions. The freshwater fraction of the SGD was estimated to vary between nearly 4 and 89 % with a median value of 9.96 % and an IQR of 7.16 %. Three events were noted to have abnormally high freshwater fractions (~28, 50 and 84 %) which are likely artifacts caused by bay water freshening from rainfall and plausible thermal expansion. The meteoric and pore-water partitioning was sensitive to the assumed end-member concentrations. This study provides preliminary estimates for SGDs along the South Texas coast line and is useful for calibrating groundwater flow models and understanding the relative importance of terrestrial and marine controls on SGD. However, the heterogeneous nature of the sedimentary geology of the Texas Gulf Coast implies the SGD fluxes are likely to exhibit considerable spatial variation that has not been characterized yet. Therefore, the study provides useful insights for such future data collection and monitoring activities. The measured SGD values at Baffin Bay, TX are comparable to those reported at other parts of the Gulf of Mexico.  相似文献   

A fuzzy simulation–optimization approach for optimal estimation of groundwater availability under decision maker uncertainty     

Venkatesh Uddameri  E. Annette Hernandez  Felipe Estrada 《Environmental Earth Sciences》2014,71(6):2559-2572

As groundwater is a slowly replenishing resource that can be depleted relatively easily, there is a growing interest in actively managing aquifer resources. Participatory, multi-stakeholder driven approaches are increasingly being adopted to plan groundwater use such that the resource is available for present as well as future needs. The state of Texas requires neighboring GCDs (local regulatory bodies) within a groundwater management area (GMA) to engage in joint planning activities and define desired future conditions (DFCs) for the aquifers they regulate. The DFCs are then used to estimate modeled available groundwater which defines how much water is available within an aquifer in a given region. The groundwater joint planning process was modeled using a combined simulation–optimization modeling scheme in this study. The response surface methodology was used to establish regional-scale aquifer stress-response relationships. In addition to average county-wide drawdown, other aquifer responses including stream-aquifer exchanges, coastal-aquifer exchanges and GMA-wide drawdown were considered to define the DFCs. A constrained linear regression was used in conjunction with a regional groundwater flow model to obtain the necessary response functions which formed the basis for a crisp optimization model whose objective was maximizing groundwater production while ensuring that the prescribed DFCs are not violated (constraints). This model was transformed into a fuzzy linear programming model to account for the fact that groundwater planners find it difficult to specify DFCs with a high degree of precision. Using linear membership functions, the decision makers’ preferences were captured using two values––a minimum preferred cut-off and the maximum allowable value for the metric. For estimating groundwater availability, the fuzzy optimization model reconciles production and maximizes the goal and the constraints representing the DFCs. The developed framework was illustrated by applying it to joint planning in Groundwater Management Area 15 in South Texas. The optimization models were highly sensitive to acceptable average drawdowns, while the coastal-aquifer interactions had secondary impacts. The fuzzy optimization model yielded lower estimates of groundwater availability in comparison to the crisp optimization scheme. The fuzzy optimization model is therefore consistent with the precautionary principle and recommended for use in the early stages of groundwater planning where incomplete understanding of the aquifer dynamics precludes specification of precise limits for the DFCs.  相似文献   

A multi-media planning model for assessing co-located energy and desalination plants     

E. Annette Hernandez  Venkatesh Uddameri  Marcelo A. Arreola Jr. 《Environmental Earth Sciences》2014,71(6):2673-2686

The co-location of desalination plants with existing or proposed power plants can bring forth economic and ecological advantages in terms of reducing the costs of water intake and reducing fish impingement. However, fossil fuel-based power plants are a source of ozone precursors and the added strain of power needed for the energy intensive desalination process increases these pollutants into the atmosphere. Furthermore, withdrawal from brackish water sources puts a stress on slowly replenishing aquifers. Additionally, the resulting concentrate is highly saline and disposal into ecologically sensitive bays and estuaries may be problematic. Balancing these limitations with the need for freshwater is of great importance for sustainability of water scarce arid and semi-arid regions and also requires a holistic multimedia impact evaluation. Therefore, an integrated system of systems approach is adopted in this study and a decision support system that integrates the flow of water, concentrate and resulting pollutants through two engineered (power plant and desalination plant) as well as three natural systems (coastal bay, aquifer and the atmosphere) is developed to study the co-location of a power plant and a desalination plant near the City of Corpus Christi in South Texas. The objective of the model is to minimize the amount of groundwater extraction and minimize the amount of water extracted from the bay to emphasize water and ecosystem conservation, respectively. These objectives, in turn, are subject to various other constraints including (1) conservation of mass; (2) air quality regulations; (3) salinity regulation policies; (4) groundwater management constraints; (5) water demand requirements; and (6) energy demand constraints. The results indicate that when conservation of the aquifer is weighted more, less water is pulled from the aquifer until later time periods. The salinity of the bay increases and creates a need for a greater amount of power necessary to process the saline water which, in turn, enhances the atmospheric loading of ozone precursors. Therefore, the conservation of groundwater scenario is limited by the air quality standards. Alternatively, when the goal is to conserve the ecological integrity of the bay while meeting freshwater demands, the model is bound by the prescribed drawdown constraint that limits the amount of water that can be extracted from the aquifer. The results from the study indicate that blending saline bay water with brackish groundwater and using cleaner burning fossil fuels that have limited air quality impacts will enhance the performance of the co-located power and desalination operations. The results of the study highlight the need for an integrated multimedia evaluation in assessing the feasibility of desalination in areas with marginal air quality.  相似文献   

High resolution climate simulations over the Arctic   总被引：1，自引：0，他引：1  

Annette Rinke  Klaus Dethloff  Arne Spekat  Wolfgang Enke  Jens Hesselbjerg Christensen 《Polar research》1999,18(2):143-150

The regional atmospheric climate model HIRHAM has been applied to the Arctic. Simulations for the whole year 1990 and for an ensemble of winter months (January of 1985-1995) have been performed. The comparison of the simulations with observational data analyses shows that the general spatial patterns are in good agreement with the data, in both the vertical structure and the annual cycle. For an additional validation of the model results, a multivariate classification of large-scale circulation patterns has been applied to the January ensemble model simulations.  相似文献