Conference on Lake Pepin TMDL

Lake Pepin Watershed TMDL
What is a tmdl? The acronym stands for total maximum daily load. And it refers to the total amount of a pollutant that a water body can carry without violating water quality standards. I recently attended a conference on the Lake Pepin tmdl and appeared on a panel representing counties and the Minnesota River Board. In accordance with the Clean Water Act, states are required to submit a list of impaired waters to the U.S. Environmental Protection Agency every two years. More than that, the states must evaluate the waters to determine the pollutant sources and make progress toward cleaning up or restoring the listed waters. The Lake Pepin project is a big one because the area that drains into Lake Pepin involves more than half of the state of Minnesota.
The researchers say that sediment is being deposited in Lake Pepin at a rate of one million metric tons of sediment per year. To visualize this amount of dirt, just visualize the size of a city block in a cube form. A city block – cubed would hold one million metric tons. The scientists at the conference indicated that the present rate of the sediment deposit is a bit higher than it was in the 1990’s. Furthermore, a majority of that sediment is coming from the Minnesota River and hence the Minnesota River watershed.
The next question posed was, if the sediment is coming from the Minnesota River watershed, where in the watershed does it originate? Does it come from stream banks or from fields? Through use of geochemical finger printing they can determine where the sediment comes from. They have been tracking this for many years and in the past 30 years they are seeing an increase in streambank erosion. They estimate that today 50% of the sediment is coming from streambank erosion whereas in 1967 about 29% was from that source. At the conference, several speakers were challenged because it appeared they were not including increased development, increased population, and the increase in the amount of impervious surfaces in their calculations. This writer is of the opinion that a study without these issues considered is flawed-to say the least. Several speakers alluded to the climatic events we have experienced in the last 50 years. The intensity of our rain events certainly has a lot to do with increase erosion from fields, ravines, streets, and residential areas. When water starts to move and when it picks up momentum, the force it exerts is great. It is logical to expect more erosion under this scenario. End.