Latest revision as of 20:08, 17 April 2008

Preface

PREFACE

The work described in this report was authorized by Headquarters, U. S. Army Corps of Engineers (USACE). Funding for this report was provided by the Hydrologic Systems Branch, Coastal and Hydraulics Laboratory (CHL), Engineer Research and Development Center (ERDC) and the System Wide Water Resources Program (SWWRP). At the time of preparation, Mr. Earl Edris was the chief, Hydrologic Systems Branch, CHL, ERDC.

This report was prepared by Dr. Charles W. Downer, Coastal and Hydraulics Laboratory (CHL) Engineer Research and Development Center (ERDC), Dr. Fred L. Ogden, Department of Civil and Environmental Engineering, University of Connecticut, and Mr. Aaron Byrd USACE-ERDC-CHL.

This report was prepared under the general supervision of Mr. Earl Edris, Chief, Hydrologic Systems Branch, CHL, ERDC. Mr. Tom Richardson was Director of CHL. Dr. Steve Ashby (EL) was the SWWRP program manager. The report was reviewed by Dr Mark Jourdan, CH-HW and Dr Jeffery D. Jorgeson, CH-HW.

At the time of publication Dr. Jim Houston was ERDC Director.

This document and the software GSSHA are products of the Watershed Systems Group, Hydrologic Systems Branch, Coastal and Hydraulics Laboratory, Engineer Research Development Center. For more information about GSSHA, contact:

Barbara Parsons

Hydrologic Systems Branch

Coastal and Hydraulics Laboratory

Engineer Research Development Center

3909 Halls Ferry Road

Vicksburg, MS 39180

http://chl.wes.army.mil/software

This report should be cited as follows:

Downer, C. W., Ogden, F. L., and Byrd, A.R. 2008, GSSHAWIKI User’s Manual, Gridded Surface Subsurface Hydrologic Analysis Version 4.0 for WMS 8.1, ERDC Technical Report, Engineer Research and Development Center, Vicksburg, Mississippi.

The Watershed Systems Group (WSG) within the Coastal and Hydraulics Laboratory of the US Army Engineer Research and Development Center (ERDC) supports the US Army and the US Army Corps of Engineers (USACE) in both military and civil operations through the development, modification and application of surface and sub-surface hydrologic models. The Department of Defense (DoD) is also charged with managing approximately 200,000 km² of land within the United States on military installations and flood control and river improvement projects. The WSG provides the Army with predictions of stream flow and stage, inundated areas, saturated areas, soil moistures, groundwater levels, and contaminant fate and transport. Predictions are provided for anticipated changes in weather conditions, project alternatives and land-use changes. The WSG uses a variety of models that are supported by the DoD graphical user interfaces (GUI) Watershed Modeling System (WMS) (Nelson, 2001), Groundwater Modeling System (GMS) (Jones, 2001), and Surfacewater Modeling System (SMS) (Zundel, 2001). These GUIs are commonly referred to the XMS system. The XMS interfaces support a variety of model classes, from simple lumped-parameter runoff models, to 2-D overland, and 3-D unsaturated groundwater models.

For many problems the distributed modeling approach may offer substantial potential improvement in capability compared with traditional lumped-parameter hydrologic models such as the USACE surface hydrologic model HEC-1 (USACE, 1985). The US Army, with additional support from the US Environmental Protection Agency (EPA), funded the development of the physically-based, distributed parameter, Hortonian runoff model CASC2D (Ogden and Julien, 2002; Downer et al., 2002a). Past experience with CASC2D has been favorable when the model has been properly applied, i.e. when Hortonian flow is the dominant process (Doe and Saghafian, 1992; Doe et al. 1996; Ogden et al., 2000; Senarath et al., 2000; Downer et al., 2002a). CASC2D Version 1.18b is linked with WMS Version 5.1 (BYU, 1997a; 1997b), which greatly simplifies model setup, results analysis and visualization. The WSG and the US Army no longer support the development or application of the CASC2D model. CASC2D development continues at Colorado State Univerity.

While Army experience with CASC2D has generally been favorable, there are many instances where the assumptions inherent in the CASC2D model limit its applicability (Senarath et al., 2000; Downer et al., 2002a). Figure 1 illustrates hillslope hydrology with an emphasis on the different runoff and streamflow generating processes. When saturation excess runoff, groundwater discharge to stream, exfiltration, etc., contribute significantly to the stream flow, the application of Hortonian runoff models is ill advised and can lead to erroneous results (Loague and Freeze, 1985; Loague, 1990; Grayson et al., 1992; Smith et al., 1994; Loague and Kyriakidis, 1997; Downer et al., 2002a).

1.1 History

The GSSHA model is a significant reformulation and enhancement of the CASC2D model. The CASC2D runoff model began with a two-dimensional overland flow routing algorithm developed and written in APL (A Programming Language) by Professor P.Y. Julien at Colorado State University. The overland flow routing module was converted from APL to FORTRAN by Dr. Bahram Saghafian, then at Colorado State University, with the addition of Green & Ampt infiltration and explicit diffusive-wave channel routing (Julien and Saghafian, 1991; Julien et al., 1995). The FORTRAN code was reformulated, significantly enhanced, and re-written in the C programming language by Dr. Bahram Saghafian at the U.S. Army Construction Engineering Research Laboratory (CERL). Implicit channel routing was added to CASC2D by Fred L. Ogden (Ogden, 1994), formerly at Colorado State University, then Associate Professor, Department of Civil and Environmental Engineering, University of Connecticut, Storrs, Connecticut, now Cline Distinguished Chair of Engineering, Environment and Natural Resources, Department of Civil & Architectural Engineering and Haub School of Environment and Natural Resources, University of Wyoming. This version, named r.hydro.casc2d, was part of the GRASS GIS for hydrologic simulations (Saghafian, 1993). Work began in 1995 to re-formulate CASC2D with the addition of continuous simulation capabilities, including an interface with the Watershed Modeling System (WMS) interface developed by Brigham Young University (BYU). This version, known as CASC2D for WMS, is distinguished from its predecessors by the addition of a number of new capabilities, numerous improvements and bug fixes, and a more stringent copyright. Johnson et al. (2000) added overland and channel transport to the CASC2D model.

The GSSHA model is a direct result of the dissertation work of Charles W. Downer, USACE-ERDC-CHL (Downer, 2002), and was developed from a need to simulate watersheds with runoff producing processes other than Hortonian flow. While the capability of the CASC2D model was included in GSSHA (many of the processes were taken directly from CASC2D) the continuous nature of the GSSHA model resulting in a need to develop an entirely new model. The first release of the model respresents a fully coupled surface water/groundwater simulator with sediment transport capability (Downer and Ogden, 2006). Since the original development of GSSHA, a myriad of improvements and capabilities have been added to model: coupling of the Green and Ampt with redistribution (GAR) model to the saturated groundwater (Downer et al, 2002), improved channel routing including non-orthogonal stream networks, reservoirs, detention basins and hydraulic structures (Downer et al., 2008), improved soil mositure accounting for use with GAR (Downer, 2008), constituent transport (Downer and Byrd, 2007), and coupling of constituent transport with the Nutrient Simulation Model (NSM) (Johnson and Gerald, 2007). The new features have been tested in a variety of watersheds (Downer et al., 2002, Downer 2008a, Downer 2008b, and others).

1.2 Purpose

GSSHA is intended to be a complete physics based wateshed analysis model and includes important processes related to the generation of runoff, stream routing, overland and stream sediment processes, and constituent transport. The primary purpose for the original version of GSSHA model is to correctly identify and realistically simulate the important hydrologic processes in watersheds. The model is intended to simulate different types of runoff production and determine the controlling physical processes in watersheds, i.e. infiltration excess, saturated source areas, and groundwater discharge. In addition, the model is to physically simulate soil erosion, transport and deposition, as well as constituent transport. Development of the model has been directed by the following requirements:

• model must be capable of explicitly calculating flows, stream depths, and soil moistures in a variety of hydrologic regimes and conditions including non-Hortonian watersheds;
• formulation must account for sub-surface effects on stream flow;
• numerical algorithms must be robust;
• model must conserve mass;
• model simulates soil erosion, transport, and deposition;
• model simulates contaminant transport problems;
• simulation times must be short enough to allow real-time predictions for use at DoD training facilities;
• model must be supported by the standard DoD graphical user interface (GUI) WMS;
• source code must be available to the U.S. Army without restrictions or limitations on modification or publication of results.

1.3 Differences Between GSSHA and CASC2D

Introduction:Differences Between GSSHA and CASC2D