Erosion Vulnerability Assessment for Agricultural Lands (EVAAL)

The Wisconsin Department of Natural Resources Bureau of Water Quality has developed the Erosion Vulnerability Assessment for Agricultural Lands (EVAAL) toolset to assist watershed managers in prioritizing areas within a watershed that may be vulnerable to water erosion (and thus increased nutrient export), which may contribute to downstream surface water quality problems. It evaluates locations of relative vulnerability to sheet, rill and gully erosion using information about topography, soils, rainfall and land cover. This tool enables watershed managers to prioritize and focus field-scale data collection efforts, thus saving time and money while increasing the probability of locating fields with high sediment and nutrient export for implementation of best management practices (BMPs).

Erosion Vulnerability Index

EVAAL was designed to quickly identify areas vulnerable to erosion and thus more likely to export nutrients like phosphorus, using readily available data and a user-friendly interface. This tool estimates vulnerability by separately assessing the risk for sheet and rill erosion (using the Universal Soil Loss Equation, USLE), and gully erosion (using the Stream Power index, SPI), while de-prioritizing those areas that are not hydrologically connected to surface waters (also known as internally drained areas, IDA). These three pieces are combined to produce an erosion vulnerability index value that can be assessed at the grid scale or aggregated to areas, such as field boundaries.

EVAAL, Version 1.0.1 (December 2015)

(Although updates to the model files were made, documentation remains the same.)

• Fact Sheet [PDF]
• Tutorial [exit DNR]
  (Includes installation instructions to be read prior to downloading EVAAL model files)
• Methods Documentation [PDF]
• EVAAL Model Files [exit DNR]
• EVAAL Tutorial Data [ZIP file format] (includes 2014 gSSURGO geodatabase)

Model Training

• DNR Water Quality Modeling Tools

Using EVAAL?

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We would also like to know how and where you are using EVAAL. This information helps us support the maintenance and enhancement of this and other modeling tools. Contact: dnrwaterqualitymodeling@wisconsin.gov