A Survey of Major Watershed (Rainfall-Runoff) Models. Knowing what is out there in the Workplace Capabilities of each model Requirements of each model What is the best model? Examples Ungaged area needing WRE management (expansion) Balancing $$, needs and requirements (Consulting)
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What kind of Water Resources Management Strategy/Measures would be needed to ensure long-term water needs?
1. A major expansion of urbanization is planned in forested land – malls, apts, parks, industry
2. How will the planned urbanization change the response of the land to rainfall? Increase chances of floods? Flashier? Bring down GWT?
Watershed Models are used to answer such questions
All watershed Models (or Rainfall-Runoff) attempt to model the Hydrologic Cycle at the watershed scale.
Unsaturated Zone flow
Rainfall is usually the major input in Hydrologic Models – it is not modeled!
Based on mathematical representation of processes
Based spatial nature of input/output of models
Conceptual Models – Idealization of processes as stores, buckets, parameterizations – simplified equations representing mass, momentum, energy.
Physically-based Models – “rigorous numerical solution of partial differential equations governing flow through porous media, overland and channel flows. “
Lumped - The spatial and temporal variation of meteorological, hydrological, geological and hydrogeological data across the model area is described as one aggregated value for input and output
!All models are lumped at the finest scale!
Distributed - The spatial and temporal variation of meteorological, hydrological, geological and hydrogeological data across the model area is described in gridded form for the input as well as the output from the model
More Physically-based means more data requirement
More Conceptual requires less data!
Data acquisition is an investment that needs to be commensurate with the model
The multiple needs of the TVA river reservoir system
For a comprehensive guide refer to: VP Singh – Computer Models for Watersheds
This is situational – It All Depends!
Level of Tolerable Accuracy/precision
Complexity and uniqueness of the problem
Time frame for delivery
It’s a highly complex question whose answer is sensitive to a multiplicity of factors