GSSHA (Gridded Surface/Subsurface Hydrologic Analysis) is a two-dimensional, physically based watershed model developed by the

Engineer Research and Development Center The Engineer Research and Development Center (ERDC) is a US Army Corps of Engineers (USACE) research and laboratory organization. The headquarters is located in Vicksburg, Mississippi, on the site of an antecedent organization, the Waterways Exper ...

of the

United States Army Corps of Engineers , colors = , anniversaries = 16 June (Organization Day) , battles = , battles_label = Wars , website = , commander1 = ...

. It simulates

surface water Surface water is water located on top of land forming terrestrial (inland) waterbodies, and may also be referred to as ''blue water'', opposed to the seawater and waterbodies like the ocean. The vast majority of surface water is produced by prec ...

and

groundwater Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...

hydrology Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and environmental watershed sustainability. A practitioner of hydrology is calle ...

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...

and

sediment transport Sediment transport is the movement of solid particles (sediment), typically due to a combination of gravity acting on the sediment, and/or the movement of the fluid in which the sediment is entrained. Sediment transport occurs in natural system ...

. The GSSHA model is used for

hydraulic engineering Hydraulic engineering as a sub-discipline of civil engineering is concerned with the flow and conveyance of fluids, principally water and sewage. One feature of these systems is the extensive use of gravity as the motive force to cause the mov ...

and research, and is on the

Federal Emergency Management Agency The Federal Emergency Management Agency (FEMA) is an agency of the United States Department of Homeland Security (DHS), initially created under President Jimmy Carter by Presidential Reorganization Plan No. 3 of 1978 and implemented by two Exec ...

(FEMA) list of hydrologic models accepted for use in the national flood insurance program for flood hydrograph estimation. Input is best prepared by the

Watershed Modeling System WMS (Watershed Modeling System) is a watershed computer simulation and modeling software application from Aquaveo. It was originally created in the early 1990s at the Engineering Computer Graphics Laboratory at Brigham Young University. The softw ...

interface, which effectively links the model with

geographic information system A geographic information system (GIS) is a type of database containing Geographic data and information, geographic data (that is, descriptions of phenomena for which location is relevant), combined with Geographic information system software, sof ...

s (GIS). GSSHA uses a square-grid, constant grid-size representation of watershed topography and characteristics, similar to a

digital elevation model A digital elevation model (DEM) or digital surface model (DSM) is a 3D computer graphics representation of elevation data to represent terrain or overlaying objects, commonly of a planet, moon, or asteroid. A "global DEM" refers to a discrete gl ...

representation. Relevant model parameters are assigned to the model grids using index maps. Index maps are often derived from soils, landuse/land cover, vegetation, or other physiographic maps.

History

The GSSHA model was derived from the CASC2D hydrologic model. GSSHA represents a significant improvement on CASC2D in terms of capabilities, options, and numerical procedures. GSSHA includes dynamic time-stepping depending on stability criteria, different time steps for different numerical processes, and the ability to run on multi-processor computers. Processes included in GSSHA include surface and ground water flow, channel hydraulics,

evapotranspiration Evapotranspiration (ET) is the combined processes by which water moves from the earth’s surface into the atmosphere. It covers both water evaporation (movement of water to the air directly from soil, canopies, and water bodies) and transpi ...

, erosion and sedimentation, storm drainage networks, tile drains, a variety of hydraulic structures, and contaminant/nutrient fate and transport.

Formulation

GSSHA uses a regular square grid computational discretization of the watershed. Elevation data are taken from a

. GSSHA uses a vector channel representation. This allows feature allows channels to flow in any direction and meander, independent from the grid resolution; this feature accurately preserves channel length and slope. The GSSHA model was developed from the outset to be capable of 'long term' simulations consisting of multiple events. As such, required inputs include meteorological variables, and surface energy-balance parameters. Seasonality in

parameters is included in the model. Overland and channel flow hydraulics are based on explicit, finite-volume, diffusive wave schemes. The overland and channel flow routines use dynamic time stepping to improve model stability and decrease simulation times. Surface and subsurface stores are linked though the

vadose zone The vadose zone, also termed the unsaturated zone, is the part of Earth between the land surface and the top of the phreatic zone, the position at which the groundwater (the water in the soil's pores) is at atmospheric pressure ("vadose" is fr ...

using a number of different optional numerical methods. A two-dimensional finite-difference groundwater solver is coupled to streams through a stream bed conductance layer. There are a number of optional methods to calculate erosion and sediment transport. The model can be used to simulate transport of sediments with specific gravity different from sand.

Specific process simulation options

* Rainfall input ** rain gages, inverse-distance squared or nearest neighbor interpolation ** radar-rainfall * Evapotranspiration using the

Penman–Monteith equation The Penman–Monteith equation approximates net evapotranspiration (ET) from meteorological data, as a replacement for direct measurement of evapotranspiration. The equation is widely used, and was derived by the United Nations Food and Agriculture ...

Infiltration Infiltration may refer to: Science, medicine, and engineering *Infiltration (hydrology), downward movement of water into soil *Infiltration (HVAC), a heating, ventilation, and air conditioning term for air leakage into buildings *Infiltration (me ...

** Green-Ampt ** Multi-layer Green-Ampt ** Green-Ampt with redistribution **

Richards equation The Richards equation represents the movement of water in unsaturated soils, and is attributed to Lorenzo A. Richards who published the equation in 1931. It is a quasilinear partial differential equation; its analytical solution is often limited to ...

Overland flow Surface runoff (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when the s ...

** Explicit finite-volume diffusive wave ** Explicit finite-volume alternating-direction predictor-corrector diffusive wave ** Overland flow dikes, such as roadway embankments * Channel flow using explicit finite-volume diffusive-wave *

Hydraulic structures A hydraulic structure is a structure submerged or partially submerged in any body of water, which disrupts the natural flow of water. They can be used to divert, disrupt or completely stop the flow. An example of a hydraulic structure would be a da ...

Weir A weir or low head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the river level. Weirs are also used to control the flow of water for outlets of l ...

s **

Culvert A culvert is a structure that channels water past an obstacle or to a subterranean waterway. Typically embedded so as to be surrounded by soil, a culvert may be made from a pipe, reinforced concrete or other material. In the United Kingdom ...

s **

Detention basin A detention basin or retarding basin is an excavated area installed on, or adjacent to, tributaries of rivers, streams, lakes or bays to protect against flooding and, in some cases, downstream erosion by storing water for a limited period of time ...

s **

Lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...

s **

Wetland A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The ...

s ** Rating curves ** Rule curves ** Scheduled releases * Overland

and

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...

transport ** Detachment limits ** Raindrop impact ** Deposition ** Arbitrary sediment size classes ** Arbitrary sediment specific gravity ** Sediment transport using three different optional equations *** Kilinc and Richardson *** Englund Hanson Englund, F., and E. Hansen, A Monograph on Sediment Transport in Alluvial Streams, 62 pp., Teknisk Vorleg, Copenhagen, Denmark, 1967. ***

Stream power Stream power originally derived by R. A. Bagnold in the 1960s is the amount of energy the water in a river or stream is exerting on the sides and bottom of the river. Stream power is the result of multiplying the density of the water, the acceler ...

* Channel sediment transport ** Sand routing using stream power ** Fines routing using advection-diffusion * Two-dimensional

** Two-dimensional finite-difference scheme ** Wells ** Constant head and constant flux boundary conditions ** Stream/aquifer interaction Current additions to the GSSHA model include source/sink/transport of nutrients and contaminants.

Computational specifics

GSSHA is programmed in C++, and runs on Windows or Linux computers. The model is command line driven and can be used in a batch mode.

Parallel computing Parallel computing is a type of computation in which many calculations or processes are carried out simultaneously. Large problems can often be divided into smaller ones, which can then be solved at the same time. There are several different fo ...

is enabled at present using the MPI or the OpenMP approach. Work is underway to port the code to run on

massively parallel Massively parallel is the term for using a large number of computer processors (or separate computers) to simultaneously perform a set of coordinated computations in parallel. GPUs are massively parallel architecture with tens of thousands of t ...

distributed memory In computer science, distributed memory refers to a multiprocessor computer system in which each processor has its own private memory. Computational tasks can only operate on local data, and if remote data are required, the computational task mu ...

architecture machines.

Applications to date

Flash flood A flash flood is a rapid flooding of low-lying areas: washes, rivers, dry lakes and depressions. It may be caused by heavy rain associated with a severe thunderstorm, hurricane, or tropical storm, or by meltwater from ice or snow flowing o ...

modeling * Soil moisture predictions * Sediment loading to receiving water bodies * Tidal and hurricane

storm surge A storm surge, storm flood, tidal surge, or storm tide is a coastal flood or tsunami-like phenomenon of rising water commonly associated with low-pressure weather systems, such as cyclones. It is measured as the rise in water level above the n ...

coastal

flood forecasting Flood forecasting is the use of forecasted precipitation and streamflow data in rainfall-runoff and streamflow routing models to forecast flow rates and water levels for periods ranging from a few hours to days ahead, depending on the size of the ...

* Engineering design * Hydrology education * Hydrologic research

References

External links

GSSHA WIKIDepartment of Defense Watershed Modeling SystemWMSFEMA List of Hydrologic Models Meeting the Minimum Requirement of National Flood Insurance Program
{{DEFAULTSORT:Gssha Integrated hydrologic modelling Hydrology models Public-domain software Hydrology software