Assessing TMDL Implementation in the Macatawa
Watershed,
Michigan, using SWAT
Laurence Picq
Geography Dept., Western Michigan University
Lake Macatawa, a small coastal lake on the eastern shore of Lake Michigan,
has been impaired by nonpoint source pollution from agriculture. In
1997, a Total Maximum Daily Load (TMDL) established a 60% reduction goal
in phosphorus load by 2009. While agricultural best management practices
have been implemented in the past three years, the local watershed organization
has not had the means to evaluate the effectiveness of these practices, and
to assess progress made towards the phosphorus reduction goal.
The Soil and Water Assessment Tool (SWAT), available through the Environmental
Protection Agency’s modeling framework, Better Assessment Science Integrating
point and Nonpoint Source (BASINS), was chosen to estimate phosphorus load,
and quantify the long-term effects of different management practices and
land use changes on water quality. A detailed land use/land cover map, produced
from a 2002 Landsat ETM+ image to input into SWAT, confirmed the rapid urbanization
of the watershed. The model was calibrated for streamflow. Several land use
scenarios, including wetland restoration, implementation of agricultural
BMPs, filter strips and urbanization, will be simulated to assess long-term
impacts on phosphorus load.
The results will provide essential information to support informed decision-making
by the Macatawa Watershed Council. The approach and methods could be replicated
in other watersheds.