Watershed models are mathematical representations with the aid of computer. It consists of computing the stream flow, sediments and all other associated parameters of the watershed. In the watershed model, the main input is the precipitation and the model simulates the flood flow, sediments, erosion, vegetation cover, crop growth, chemicals, nutrients and the impact of human activities on the watershed. The model helps to develop design flood hydrograph which is essential to construct and design hydraulic structures such as dams, reservoirs, weirs, spillways, embankments, flood walls, channel improvement works, bridges and culverts and these designed structures help in floodplain management programmes. The new generation of watershed model is quite diverse and varies significantly in input data and computational and simulated data requirements.
Various Watershed Models :
1. Stanford Watershed Model (SWM)
SWM was instrumental in civil engineering profession to the concept of continuous hydrologic modelling.
The most effective way of developing this medal was to establish continuous mathematical relationships between the elements of the hydrologic cycle .
2. Hydrocomp Simulation Program (HSP)
SWM expanded and refined it to create the Hydrocomp Simulation Irogram (HSP), which also included general nonpoint source loadings and water quality simulation capabilities.
3. Storm Water Management Model (SWMM)
SWMM is a hydrologic, hydraulic and water quality simulation model Applications of this model include planning and design of urtun drainage, storm water management and studies related to nonpoint pollution SWMM is a complex software package capable of simulating the move movement of It can compute run off volume, flow hydrograph and pollutant loads.
4. Storage, treatment, overflow, runoff model (STORM)
Storage, treatment, overflow, runoff model (STORM) in Hydrologic Engineering Centre (HEC) was developed by US. Army Corps of Engineers.
5. HEC – HMS
Hydrologic Engineering Centre (HEC) – Hydrologic Modelling System (HMS) is a hydrologic model which can be used for estimate water discharge in a specific catchment area with the input data are rainfall, landuse, etc.
HEC-HMS of 2001 the is perhaps most extensively used watershed computer model. This model can be used from urtun small watershed of 1 km² to the river basin of a few thousand km².
HEC-1, developed by U.S. Army Corps of Engineers, is used for design of dams, spillways, flood control improvement works and some other hydraulic structures in the United States and abroad. This model is also used in flood plain management works, economic evaluation of flood mitigation, dam safety and flood forecasting.
7. Soil And Water Assessment Tool (SWAT)
SWAT is a well-known and popular watershed model which is used by many universities and government agencies around the world. SWAT is a daily time step continuous model to predict the impact of land management activities on water and sediment. SWAT can simulate crop growth and crop yield based on climatic variables. It can also determine the nutrition loading along with water and sediments. SWAT can also simulate the amount of nitrogen and pesticide transport along with run-off.
8. Agricultural Runoff Management (ARM)
It was developed at EPA by Donigian and Davis. Agricultural Runoff Management (ARM) model worked on modelling pesticides and nutrients on agricultural lands (MPNAL).
9. Water Erosion Prediction Project (WEPP)
Watershed model was calibrated and validated for a small hilly watershed named Karso in India. The analysis shows that the sediment yield is highly sensitive to interrill erodibility.
Hydrologic Engineering Center (HEC) River Analysis System (RAS)
HEC-RAS is a computer program for modeling water flowing through systems of open channels and computing water surface profiles. HEC-RAS finds particular commercial application in floodplain management and [flood insurance] studies to evaluate floodway encroachments. Some of the additional uses are: bridge and culvert design and analysis, levee studies, and channel modification studies. It can be used for dam breach analysis, though other modeling methods are presently more widely accepted for this purpose.
Watershed model is the major tool for predicting the solution of varieties of environmental and water resources problems, including water resources planning, management, design, development and operation.
Moreover, floods, droughts, stream bank erosion, upland erosion, gully erosion, coastal erosion, sedimentation in reservoir, river, lake and low lying areas, water pollution from industrial, domestic, agricultural and industrial sources, soil salinity and alkalinity, degradation of hill, cropland, decay of rivers, irrigation of agricultural lands, consumptive use of surface and groundwater, a reliable design of hydraulic structures and controlling river meandering, predicting zones of river training works like spurs, flood plain zoning, flood forecasting are some of the critical environmental problems which are solved using watershed models.
Watershed models are also employed in military operations.