Ehab A. Meselhe

Analysis of radar-rainfall error characteristics and implications for streamflow simulation uncertainty

Abstract Due to the inherent indirect nature of radar-rainfall measurements, hydrologists have been interested in understanding the characteristics of radar-rainfall estimation errors and how they propagate through hydrological simulations. This study implements an observation-based empirical approach to analyse different characteristics of the total radar-rainfall estimation error such as overall and conditional bias, random error and spatio-temporal dependence. The implications of the radar error characteristics for streamflow simulations and the estimation of their uncertainty are examined using a physically-based distributed rainfall—runoff model. An empirical error model is used to generate several realizations of probable surface rainfall fields that reflect the identified characteristics of the radar error. These realizations are used to generate ensemble of streamflow predictions. The main conclusions are that: (a) radar errors have complex spatio-temporal characteristics that exhibit significant sampling and natural variations; (b) adjustment of overall and conditional radar biases results in the most significant improvements in runoff predictions; (c) radar random errors have non-negligible correlations both in time and space; and (d) the simulated runoff hydrographs are sensitive to the assumed degree of correlation in the radar errors fields. This study is an initial step toward developing more rigorous approaches for accounting for the effects of radar error on hydrological predictions.

The Role of the Everglades Mangrove Ecotone Region (EMER) in Regulating Nutrient Cycling and Wetland Productivity in South Florida

The authors summarize the main findings of the Florida Coastal Everglades Long-Term Ecological Research (FCE-LTER) program in the EMER, within the context of the Comprehensive Everglades Restoration Plan (CERP), to understand how regional processes, mediated by water flow, control population and ecosystem dynamics across the EMER landscape. Tree canopies with maximum height <3 m cover 49% of the EMER, particularly in the SE region. These scrub/dwarf mangroves are the result of a combination of low soil phosphorus (P < 59 μg P g dw−1) in the calcareous marl substrate and long hydroperiod. Phosphorus limits the EMER and its freshwater watersheds due to the lack of terrigenous sediment input and the phosphorus-limited nature of the freshwater Everglades. Reduced freshwater delivery over the past 50 years, combined with Everglades compartmentalization and a 10 cm rise in coastal sea level, has led to the landward transgression (∼1.5 km in 54 years) of the mangrove ecotone. Seasonal variation in freshwater input strongly controls the temporal variation of nitrogen and P exports (99%) from the Everglades to Florida Bay. Rapid changes in nutrient availability and vegetation distribution during the last 50 years show that future ecosystem restoration actions and land use decisions can exert a major influence, similar to sea level rise over the short term, on nutrient cycling and wetland productivity in the EMER.

Three-dimensional numerical model for open-ehannels with free-surfaee variations

A numerical model to calculate three-dimensional turbulent flew In open channels ef arbitrary cress-section is developed and validated: The model selves the incompressible, Reynolds-averaged Navier-Stekes (RANS) equations, formulated in generalised curvilinear coordinates, in conjunction with the fcg turbulence closure. The free-surface elevation is determined by allowing the gomputatienal mesh to deform during the iterative solution procedure so that the proper kinematic and dynamic conditions are satisfied at convergence- The numerical model is validated by application to simulate the flow through meandering open channels for which detailed experimental measurements are available. Comparisons of the computed solutions with experimental data reveal that the model predicts the details of the velocity field, including changes in secondary motion, the distribution ef bed shear, and variations of flow depth in both the transverse and longitudinal directions.

Ecohydrology Component of Louisiana's 2012 Coastal Master Plan: Mass-Balance Compartment Model

ABSTRACT Meselhe, E.; McCorquodale, J.A.; Shelden, J.; Dortch, M.; Brown, T.S.; Elkan, P.; Rodrigue, M.D.; Schindler, J.K., and Wang, Z., 2013. Ecohydrology component of Louisianas 2012 Coastal Master Plan: mass-balance compartment model. Coastal Louisiana is a complex system that encompasses large expanses of wetlands interspersed with shallow bays and estuaries of varying sizes and degrees of connectivity to the Gulf of Mexico, numerous water control structures, large riverine systems, and an intricate system of natural and manmade channels. This complex system is experiencing devastating rates of land loss that have been exacerbated by subsidence and sea level rise. As part of Louisianas 2012 Coastal Master Plan, this modeling effort utilizes an efficient mass-balance approach to provide coastwide (∼100,000 km2), long-term (∼50 y) performance projections for proposed restoration and protection measures. The model presented here provided detailed information about the spatial and temporal variability of water depth, salinity, accretion rates, deposition, and other water quality parameters across the Louisiana coastal zone. Furthermore, the model provided this information to subsequent modules in the master plan suite of models, namely, wetland morphology, vegetation, ecosystem services, and barrier shoreline morphology. Collectively, this suite of models served as an effective approach to provide valuable comparative assessments for the various proposed restoration and protection scenarios and alternatives.

Surface water sulfate dynamics in the northern Florida Everglades.

Sulfate contamination has been identified as a serious environmental issue in the Everglades ecosystem. However, it has received less attention compared to P enrichment. Sulfate enters the Arthur R. Marshall Loxahatchee National Wildlife Refuge (Refuge), a remnant of the historic Everglades, in pumped stormwater discharges with a mean concentration of approximately 50 mg L(-1), and marsh interior concentrations at times fall below a detection limit of 0.1 mg L(-1). In this research, we developed a sulfate mass balance model to examine the response of surface water sulfate in the Refuge to changes in sulfate loading and hydrological processes. Meanwhile, sulfate removal resulting from microbial sulfate reduction in the underlying sediments of the marsh was estimated from the apparent settling coefficients incorporated in the model. The model has been calibrated and validated using long-term monitoring data (1995-2006). Statistical analysis indicated that our model is capable of capturing the spatial and temporal variations in surface water sulfate concentrations across the Refuge. This modeling work emphasizes the fact that sulfate from canal discharge is impacting even the interior portions of the Refuge, supporting work by other researchers. In addition, model simulations suggest a condition of sulfate in excess of requirement for microbial sulfate reduction in the Refuge.

Assessing Effects of Data Limitations on Salinity Forecasting in Barataria Basin, Louisiana, with a Bayesian Analysis

Abstract Reliable forecasts of salinity changes are essential for restoring and sustaining natural resources of estuaries and coastal ecosystems. Because of the physical complexity of such ecosystems, information on uncertainty associated with salinity forecasts should be assessed and incorporated into management and restoration decisions. The objective of this study was to investigate uncertainty in salinity forecasts imposed by limitations on data available to calibrate and apply a mass balance salinity model in the Barataria basin, Louisiana. The basin is an estuarine wetland-dominated ecosystem located directly west of the Mississippi Delta complex. The basin has been experiencing significant losses of wetland at a rate of nearly 23 km2/y. A Bayesian-based methodology was applied to study the effect of data-related uncertainty on both the retrieval of model parameters and the subsequent model predictions. We focused on uncertainty caused by limited sampling and coverage of salinity calibration data and by sparse rain gauge data within the basin. The results indicated that data limitations lead to significant uncertainty in the identification of model parameters, causing moderate to large systematic and random errors in model results. The most significant effect was related to lack of accurate information on rainfall, a major source of fresh water in the basin. The approach and results of this study can be used to identify necessary improvements in monitoring of complex estuarine systems that can decrease forecast uncertainty and allow managers greater accuracy in planning restoration of coastal resources.

Landscape-Level Estimation of Nitrogen Removal in Coastal Louisiana Wetlands: Potential Sinks under Different Restoration Scenarios

ABSTRACT Rivera-Monroy, V.H.; Branoff, B.; Meselhe, E.; McCorquodale, A.; Dortch, M.; Steyer, G.D.; Visser, J., and Wang, H., 2013. Landscape-level estimation of nitrogen removal in coastal Louisiana wetlands: potential sinks under different restoration scenarios. Coastal eutrophication in the northern Gulf of Mexico (GOM) is the primary anthropogenic contributor to the largest zone of hypoxic bottom waters in North America. Although biologically mediated processes such as denitrification (Dn) are known to act as sinks for inorganic nitrogen, it is unknown what contribution denitrification makes to landscape-scale nitrogen budgets along the coast. As the State of Louisiana plans the implementation of a 2012 Coastal Master Plan (MP) to help restore its wetlands and protect its coast, it is critical to understand what effect potential restoration projects may have in altering nutrient budgets. As part of the MP, a spatial statistical approach was developed to estimate nitrogen removal under varying scenarios of future conditions and coastal restoration project implementation. In every scenario of future conditions under which MP implementation was modeled, more nitrogen () was removed from coastal waters when compared with conditions under which no action is taken. Overall, the MP increased coast-wide average nitrogen removal capacity (NRC) rates by up to 0.55 g N m−2 y−1 compared with the “future without action” (FWOA) scenario, resulting in a conservative estimate of up to 25% removal of the annual + load of the Mississippi-Atchafalaya rivers (956,480 t y−1). These results are spatially correlated, with the lower Mississippi River and Chenier Plain exhibiting the greatest change in NRC. Since the implementation of the MP can maintain, and in some regions increase the NRC, our results show the need to preserve the functionality of wetland habitats and use this ecosystem service (i.e. Dn) to decrease eutrophication of the GOM.

Numerical Modeling of the Mississippi-Atchafalaya Rivers' Sediment Transport and Fate: Considerations for Diversion Scenarios

Abstract The hydrodynamics, salinity circulation, and transport of suspended fine sediment from major rivers on the northern Gulf of Mexico (GOM) were simulated with the numerical model H3D. Tides, river inflow, wind, and heat exchanges were used to drive the three-dimensional baroclinic model. Tide propagation in the northern Gulf and seasonality in the sediment plume advection from the Mississippi and Atchafalaya rivers into the GOM were well represented in the model. The similarity between the models results and the sediment plume as seen in MODIS satellite images and the salinity structure as observed in previous studies is demonstrated. This qualitatively valid model is used for initial guidance in design of new Mississippi River (MR) diversions by studying the effects of five conceptual MR diversions on the fate of its suspended fine material. The diversions were positioned halfway between Port Sulphur and Venice, southeast Louisiana. The scenario transporting 70% of the MR to the west and 30% to the east of the delta presents the best configuration in terms of retention of sediment within the continental shelf. This configuration redirects the main sediment and freshwater flow from the river to the nearshore and the upper continental shelf with the least losses to deeper GOM waters. Given the local dominant westward wind regime, increased discharges diverted to the east will increase the amount of sediment that travels west around the MR birdfoot delta and over the Mississippi Canyon, with a higher chance of being lost to deeper waters.

Coupled physical-numerical analysis of flows in natural waterways

The recent digital-electronic revolution has helped experimental hydraulics benefit from a new generation of acoustic-, laser-, and imaging-based instrumentation. These newly developed techniques are not only of superior accuracy, but they have also expedited data collection. Powerful visualization software has been used increasingly to present and interpret experimental results. In addition, numerical models have become increasingly available in some cases providing turnkey solutions to complex flows. The outcome of this intensive development is powerful computer-based research tools that allow an unprecedented interaction between physical and numerical experiments. This integrated approach is considerably improving our understanding of numerous aspects and practical consequences of flow mechanics and allows a comprehensive treatment of space-time processes in fluid flows which is difficult to obtain using alternative means. This holistic experimental-numerical approach is readily available for integration as expertsystems or decision-making programs in hydroinformatics systems. The present paper discusses the beneficial synergy between laboratory measurements and computational models of different levels of complexity. A study, conducted at the Iowa Institute of Hydraulic Research (IIHR) is presented herein as an example to demonstrate the interaction among the three investigation components, namely, laboratory measurements, the kinematic model, and the hydrodynamic model, as well as the benefits and limitations of each of them. The laboratory velocity measurements were made using three-component Acoustic-Doppler Velocimeters. A simple numerical model based exclusively on flow kinematics was used to empower results visualization and to provide insight in several flow features. The kinematic model feedback was used to optimize the data acquisition scheme for the ensuing measurements. The detailed hydrodynamic flow analysis for regions with complex three-dimensional flows was obtained by a numerical model that solves the Reynolds Averaged Navier-Stokes (RANS) equations in general curvilinear coordinates.

Water budget model for a remnant northern Everglades wetland

The Arthur R. Marshall Loxahatchee National Wildlife Refuge overlays Water Conservation Area 1, a 580 km2 freshwater wetland remnant of the northern Everglades in Palm Beach County, Florida, USA. Changes in water quantity and quality have impacted the Refuge ecosystem. Ensuring appropriate management to maximize benefits for wildlife while meeting flood control and water supply needs is a refuge priority. The Simple Refuge Stage Model described herein supports these management decisions. The two-compartment model with a daily time step predicts temporal variations of water level in the refuge rim canal and interior marsh, based on observed inflows, outflows, precipitation and evapotranspiration. The model was used to evaluate various water management scenarios. The modelling approach applied herein may have utility in managing other wetland systems where over-bank flooding is a dominant mechanism, affecting hydrology and water quality.