Nawa Raj Pradhan

Improvement of hydrologic model soil moisture predictions using SEBAL evapotranspiration estimates

Soil moisture conditions influence practically all aspects of Army activities and are increasingly affecting its systems and operations. Regional distributions of high resolution soil moisture data will provide critical information on operational mobility, penetration, and performance of landmine and UXO sensors. The US Army Corps of Engineers (USACE) developed the Gridded Surface/Subsurface Hydrologic Analysis (GSSHA), which is a grid-based two-dimensional hydrologic model that has been effectively applied to predict soil moisture conditions. GSSHA computes evapotranspiration (ET) using the Penman-Monteith equation. However, lack of reliable spatially-distributed meteorological data, particularly in denied areas, makes it difficult to reliably predict regional ET and soil moisture distributions. SEBAL is a remote sensing algorithm that computes spatio-temporal patterns of ET using a surface energy balance approach. SEBAL has been widely accepted and tested throughout the world against lysimeter, eddy-covariance and other field measurements. SEBAL estimated ET has shown good consistency and agreement for irrigated fields, rangelands and arid riparian areas. The main objective of this research is to demonstrate improved GSSHA soil moisture and hydrological predictions using SEBAL estimates of ET. Initial results show that the use of SEBAL ET and soil moisture estimates improves the ability of GSSHA to predict regional soil moisture distributions, and reduces uncertainty in runoff predictions.

Benchmarking Optical/Thermal Satellite Imagery for Estimating Evapotranspiration and Soil Moisture in Decision Support Tools†

Generally, one expects evapotranspiration (ET) maps derived from optical/thermal Landsat and MODIS satellite imagery to improve decision support tools and lead to superior decisions regarding water resources management. However, there is lack of supportive evidence to accept or reject this expectation. We “benchmark” three existing hydrologic decision support tools with the following benchmarks: annual ET for the ET Toolbox developed by the United States Bureau of Reclamation, predicted rainfall-runoff hydrographs for the Gridded Surface/Subsurface Hydrologic Analysis model developed by the U.S. Army Corps of Engineers, and the average annual groundwater recharge for the Distributed Parameter Watershed Model used by Daniel B. Stephens & Associates. The conclusion of this benchmark study is that the use of NASA/USGS optical/thermal satellite imagery can considerably improve hydrologic decision support tools compared to their traditional implementations. The benefits of improved decision making, resulting from more accurate results of hydrologic support systems using optical/thermal satellite imagery, should substantially exceed the costs for acquiring such imagery and implementing the remote sensing algorithms. In fact, the value of reduced error in estimating average annual groundwater recharge in the San Gabriel Mountains, California alone, in terms of value of water, may be as large as

A Physics Based Hydrologic Modeling Approach to Simulate Non-point Source Pollution for the Purposes of Calculating TMDLs and Designing Abatement Measures

1 billion, more than sufficient to pay for one new Landsat satellite.

Gridded Surface Subsurface Hydrologic Analysis Modeling for Analysis of Flood Design Features at the Picayune Strand Restoration Project

Non-point source pollution has become the major source of surface water impairment in the United States. The transport of suspended sediments and nutrients from watersheds to aquatic resources directly influences their environmental quality and ecosystem. The Environmental Protection Agency calculates maximum daily loads from watersheds that allow receiving water bodies to meet water quality standards and mandates load reductions on suspended sediments, nutrients, and other pollutants through the implementation of best management practices. Calculation of these loads and assessment of best management practices is often done with simplified methods, such as spreadsheets and lumped, empirical models that do not account for the spatial heterogeneity or the physical processes occurring in the watershed. The physically based, distributed watershed hydrologic, sediment, constituent transport and fate model Gridded Surface Subsurface Hydrologic Analysis (GSSHA) represents another approach where the spatial heterogeneity, physical and chemical processes in the watershed are explicitly included in the simulation. In this study, GSSHA is used to simulate sediment, nitrogen and phosphorous in Eight-Mile Run, a 264-ha watershed located in the Upper Eau Galle River Basin, west-central Wisconsin. The quality of the GSSHA simulation results demonstrates that the model is capable of quantifying and predicting flow and the transport of sediment and nutrients, nitrogen and phosphorous, in the watershed.

Testing the Effects of Detachment Limits and Transport Capacity Formulation on Sediment Runoff Predictions Using the U.S. Army Corps of Engineers GSSHA Model

Abstract : The Picayune Strand Restoration Project is one of many components of the Comprehensive Everglades Restoration Project (CERP) intended to restorenearly 700 hectares of a failed residential development in southwestern Collier County, FL, to its predevelopment wetland conditions. A detailed analysis was performed to derive a restoration plan that will achieve this goal. As required by the Water Resources Development Act (WRDA) 2000,the U.S. Army Corps of Engineers (USACE) is required to ensure that no component of CERP results in an effective taking of land by adversely impacting the level of flood protection of adjacent landowners. To ensure the current level of flood protection is maintained, a hydrologic model was developed to assess the potential for flooding and to refine the proposed flood mitigation features. The USACE physically based Gridded Surface Subsurface Hydrologic Analysis (GSSHA) model was selected for this effort. The GSSHA model simulates fully coupled rainfall distribution, extraction, retention, overland flow, and one-dimensional channel flow. Models of varying resolution were developed from existing and proposed design data and were initially populated with parameter values from a previous hydrodynamic modeling effort. Parameters were then tuned to observed stage and flow data using the Secant Levenberg-Marquardt method, a nonlinear least squares minimization computer-based local search method. The calibrated model is capable of reproducing canal flows, canal stages, and overland stages with very high Nash Sutcliffe Forecast Efficiencies, generally 0.9 or higher. Subsequent uncertainty analysis allowed water stages to be estimated with 95% certainty. Modeling and uncertainty analysis results allowed for refinement of the proposed flood mitigation features.

Laboratory Investigation of Sedimentation Effects on V-Notch Weirs

AbstractThe physics-based Gridded Surface Subsurface Hydrologic Analysis (GSSHA) model was developed by the U.S. Army Corps of Engineers for hydrologic, sediment transport, and water quality analyses. GSSHA simulates erosion and transport of sediments on the overland flow plain based on rainfall intensity and overland flow depth and velocity. The original sediment transport capabilities in GSSHA were taken from the GSSHA predecessor, CASC2D-SED. Independent testing of the sediment transport methods in CASC2D-SED by researchers identified several deficiencies in the formulation that caused significant overestimation of sediment yield during hydrologic events that were much larger than a calibration event. Sediment detachment limits and a variety of overland sediment transport equations were incorporated into the GSSHA model to address these deficiencies. This paper presents an evaluation of these modifications in terms of GSSHA sediment yield predictions of both single-event and summer growing season sedim...

Relative Importance of Impervious Area, Drainage Density, width Function, and Subsurface Storm Drainage on Flood Runoff from an Urbanized Catchment

Weirs are widely used to measure discharges. In excellent installations they provide accurate measurements of discharge over a wide range of flows with a constant discharge coefficient. However, many weirs around the globe are filled with sediment and require manual rating curve adjustments or dredging. In this study we used a scale model to identify discharge coefficients with quantified uncertainty to identify the effect of sedimentation on the performance of a 140-degree sharp-edged V-notch weir. Variables changed included the discharge, channel slope, and degree of sedimentation. The experiments were performed in the University of Wyoming water resources lab, which is equipped with highly accurate weight-based flow measurement capability up to 0.1 m 3 s –1 (3.5 ft 3 s –1 ). Ultrasonic distance sensors were mounted on a computer-controlled traverse to make measurements of the water surface profile along the channel centerline, and at one transect off the channel centerline a specified distance. Data collected included discharge, and 100 water surface heights at each measurement point. Repeat measurements of water surface elevation allow statistical inference of the effect of turbulent unsteadiness on discharge measurements. Results indicate that sedimentation increases the discharge coefficient for a given channel slope, and that the discharge coefficient is not constant over the range of depths from 20% to 100% of the design depth.