May / June, 2001

Developing Computer Modeling Tools
To Improve Water Quality in Agricultural Watersheds
By: William Northcott

Michigan has an abundant and diverse supply of freshwater due to its unique geographical location within the Great Lakes Region. These waters provide a wealth of resources for the diverse agricultural, industrial, and recreational activities of the state. However, continually growing human activities in watersheds add stress to this resource and often lead to degradation of both surface water and groundwater. The major source of this pollution is from non-point sources, and within Michigan, as in many states, one of the major contributors is agriculture. To protect the water quality of the Great Lakes Region and to maintain sustainable agriculture in this region, non-point source pollution must be kept at a minimum.

To address this problem, William Northcott, Geoffrey Habron, and Lois Wolfson, faculty members in the Departments of Agricultural Engineering, and Fisheries and Wildlife are conducting a USDA-CSREES sponsored research project to address water quality issues in agricultural watersheds in Michigan. They are working in cooperation with the Clinton County NRCS office who have received funding from the EPA to install vegetative buffer strips in the Stony Creek Watershed to help filter sediment and nutrients and reduce peak flow rates. As part of their project, the MSU team is intensively monitoring the hydrology and water quality of the Stony Creek Watershed and using that data to develop a computer model to target ideal buffer strip locations that can be used in agricultural watersheds across Michigan and the Midwest.

The Stony Creek Watershed is a local watershed that is experiencing a variety of water quality problems. High nutrient levels and sediment in the watershed are degrading aquatic habitats and recreational areas and polluting the Great Lake system. Stony Creek is located in south central Michigan and flows through parts of Clinton and Ionia Counties. The total watershed area of Stony Creek is 179 mi2 or 114,647 acres. The land use in the watershed is typical of agricultural watersheds in the state of Michigan, but is experiencing increased urbanization which is stressing the current drainage network.

The problem with the Stony Creek Watershed is that the upper portion of the watershed serves as an agricultural drain while the lower portion serves as a warm water fishery and recreational area. The agricultural and urban runoff occurring in the upper portion is depositing sediment and nutrients to the lower portion, causing eutrophic conditions downstream and disrupting aquatic habitat. As the creek continues downstream, eroded sediments and nutrients are eventually deposited into Lake Michigan. Due to the channelized agricultural drains and urban areas in the upper portion of the watershed, runoff flows more quickly throughout the watershed until it reaches the more natural, sinuous, slower running stream segments and results in downstream flooding. Figures 1 and 2 show the Stony Creek during normal flow and flood conditions.

The monitoring portion of the study includes measuring the stream flow and water quality at six locations within the watershed (Figure 3). At each location, flow rates are monitored and water quality samples are collected with automated samplers. The water samples are analyzed for sediment and nutrients (nitrate, ammonium, and phosphate). To determine the effectiveness of buffer strips on watershed water quality, a paired watershed study is being performed within Stony Creek. They are monitoring the hydrology and water quality between two smaller watersheds, the Trent and Bauer drains. Both watersheds are similar in size, (Trent 560 acres, Bauer 640 acres), have similar soils, topography, and land use. The primary difference between the watersheds is that the Trent drain has a 100 foot buffer strip planted along the entire length of the stream and the Bauer drain has no buffer strip. A comparison will be made on the sediment and nutrient load coming from each watershed and will be used to infer the benefit of buffer strips on watershed scale water quality.

Figure 3. Sampling locations within the Stony Creek Watershed.

The modeling portion of this study consists of developing a computer tool to analyze the watershed to determine where in the watershed installing buffer strips will get the most "bang for the buck" in improving water quality. For each stream segment in the watershed, the computer model will analyze the topography, land cover, and soil type and determine the reduction in peak flow rate, sediment, and nutrients that would be achieved by installing a buffer strip. The stream segments are ranked to help NRCS and stakeholders better target conservation practices. To handle all of the information used in the computer model, a geographic information system (GIS) is used to assemble data and present results. Some preliminary results of the computer model are shown in figure 4 for the Lost Creek watershed within Stony Creek. Developing, testing, and validating this computer and GIS tool in Stony Creek will allow it to be used to improve water quality in other agricultural watersheds in Michigan.

Figure 4. Erosion modeling results for Lost Creek Watershed.

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Agricultural Engineering
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June 5, 2001