Impacts of Tiling on Water Quality

The water quality of SMC Watershed has been affected by tiling and land use change, as well. The primary concern for water quality arises out of the implied reduction in residence time, the amount of time that it takes water to travel from cultivated fields into Seven Mile Creek itself. The purpose of tiling is to increase the speed of draining water, thereby reducing travel time from field to stream. However, residence time is directly proportional to the ability of natural processes to clean surface water. The introduction of tiling decreased residence time for agricultural runoff, which resulted in higher concentrations of agricultural pollutants making their way into the creek.

An example of wetlands, which once covered thousands of acres in SMC Watershed.

 

Regional Drainage

GIS images of SMC Watershed land cover, comparing presettlement to current conditions, illustrate the effects of significant drainage projects. Where wet prairie, wetlands, and lakes once comprised nearly 20% of land cover, today less than 3.5% of the watershed is wet. This reduction in surface water area and wetland acreage is of particular concern in an area that has seen a steady increase in application of phosphates, nitrates, and bacteria in the last century and a half. At the next stop on the tour, we will examine the role wetlands play in removing these contaminants from the water cycle.

 

Streams vs. Ditches

As addressed earlier, straight-line trapezoidal earthen drainage ditches support faster flow velocities than do natural meandering stream channels. This reduces residence time, which decreases biological consumption of pollutants. Faster flows also have the ability to carry a greater sediment load rather than promoting the settling out of particles.

Where does that leave us?

The reality of the current situation is that tiling is essential to the feasability of farming in SMC Watershed and the prosperity of its inhabitants. It is the mission of the Seven Mile Creek Watershed Project to develop a means for establishing a sustainable coexistence between agricultural practice and environmental health. To that end, we will proceed by considering a variety of practical agricultural practices that can lead to substantial improvements in water quality.