Modeling is a way to simplify the processes of reality to better represent the state of current knowledge in
terms of inter-relationships across various variables. In the context of a watershed, modeling can be of many
types, including:
- Water Balance/Hydrologic Modeling: Accounting for what happens to the hydrologic cycle elements of a
watershed in terms of rainfall, evaporation, transpiration, surface flow, infiltration, outflow, etc. in both
a pristine watershed and as influenced by anthropogenic factors such as storage, pumping, use, discharge, etc.
- Hydraulic/Hydrodynamic Modeling: These tools explore flow in channels and flooding using tools of
varying
complexity.
- Water Quality Models: These models help explore pollution sources for various pollutants and explore
the
fate and transport of these pollutants and their implications on the water quality of the streams and further
downstream receiving bodies of water.
- Limnology Models: These explore the way lakes behave in more detail.
- Erosion Modeling: These generally use some version of a Universal Soil Loss Equation that models
potential
erosion based on information such as topography, soils, precipitation, landcover, and land management.
- Other Specialized Modeling: Watershed modeling can also include very specialized models related to
groundwaters/aquifers, energy systems, specialized economic modeling (e.g. game theory), etc.
- Water Systems Modeling: These usually use either simulation or optimization to look beyond single
“projects”
such as dams, irrigation command areas, hydropower plants, water supply, etc. and explore these in a larger
inter-related systems context (e.g. as a watershed, sub-basin, basin, etc.). Some of these model only
bio-physical aspects, but other extend this to include economic, environmental, and social aspects.
- Decision Support Systems: These are more integrated approaches to support water resources planning
(e.g.
watershed investment planning) or real-time systems operations (e.g. cascade of dams, flood management). It is
critical to note that these are not decision making systems but provide information to support decision making
where the appropriate stakeholders bring in the value judgements of the synergies and trade-offs involved with
various alternative decision paths.
The landscape for modeling is still not very satisfactory with often high costs of development or customization
of tools to model various aspects of watersheds. Recent trends to developing more easy-to-use free online tools
(some global) give some insight into what is possible in the near future.
