Knowledge Base by Barry Evans, Ph.D., Senior Research Associate, Penn State University
Barry M. Evans, Ph.D.
Penn State Institutes of Energy and the Environment
Pennsylvania State University
Stroud Water Research Center (Adjunct)
Watershed (Landscape) Models
Generally used to estimate flows and pollutant loads
produced by a given geographic area
SWAT, GWLF, AGNPS, HSPF, PLOAD, WAM, SWMM
Receiving Water (Waterbody) Models
Used to estimate environmental impact of flows and loads
to a given waterbody (lake, river, estuary, etc.)
LAKE2K, QUAL2K, Bathtub, SWAT, HSPF
Vary in Complexity
Pollution potential indices (GIS-based)
Unit area loading models (STEPL)
Statistical models (SPARROW)
Simulation models (SWAT, GWLF)
Watershed Models: Pollutants and Pathways
Nutrients (nitrogen and phosphorus)
Organic matter (e.g., BOD)
Exotics (pesticides) and heavy metals
Primary transport pathways
Dissolved or washed off solids in surface runoff
Attached to eroded soil in surface runoff
Leached and transported via subsurface flow
Direct disposal in surface water (e.g., WWTPs, cows)
Water Quality Models: Calibration
• GIS “pre-processor” used to overlay and manipulate
GIS layers, statewide weather files, and other data for
purpose of creating input file for the core watershed
simulation model (GWLF-E)
•GWLF-E model is then used to run input files to
estimate nutrient (N and P), sediment, and pathogen
loads for a given watershed
•Various ancillary tools can be used to visualize and
analyze model output, and to evaluate BMP effects
Some Key Questions
Planning or regulatory?
Need to compare results against observed data?
Focus on urban, agriculture or mixed land use?
How large is the area/watershed?
What pollutants/processes are to be modeled?
Level of detail for model processes?
How readily available are data?
Can “what-if” scenarios be analyzed?
How important is acceptance by state agency?
How user-friendly is it?
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