Click on “Download PDF” for the PDF version or on the title for the HTML version.

If you are not an ASABE member or if your employer has not arranged for access to the full-text, Click here for options.

The Soil and Water Assessment Tool (SWAT) model is a river basin scale hydrologic and water quality model that is currently being used for national conservation and environmental assessments in the U.S. and for watershed planning around the world. Current developments include submodels for landscape routing, plant competition, metal fate and transport, and improved sediment routing. Another recent development is a new algorithm to schedule management operations throughout the simulation. Currently, management scheduling such as fertilizer, irrigation and tillage, is based on cropping rotations making it difficult to schedule operations that occur independently, potentially only once in a long-term simulation. To solve this problem, a new operations input file was added that allows users to schedule management by Julian day and calendar year without considering cropping rotations and without using heat unit scheduling. Operations have been added for contouring, terracing, subsurface drains, filter strips, fire, grass waterways, and filter strips. This paper describes the new operation scheduling procedure and testing of the algorithms for an Iowa watershed, as well as improved approaches for simulating grassed waterways and filter strips. A brief summary of other new enhancements will also be provided.