5.8.1 Minnehaha Creek Diagnostic Study/TMDL

ProjectMinnehaha Creek Diagnostic Study and Biotic Integrity TMDL
DescriptionA study to identify in-stream processes that might be contributing to phosphorus concentrations in the creek and in Lake Hiawatha as well as stressors that might be contributing to impaired biological integrity in Minnehaha Creek.

This study is part of the effort to prepare and/or implement two Total Maximum Daily Load (TMDL) studies for water resources in the Minnehaha Creek subwatershed. Lake Hiawatha, which is in-line to Minnehaha Creek, has been designated by the MPCA and EPA as an Impaired Water for excess nutrient concentrations that lead to excessive algae blooms and poor water clarity. Phosphorus transported by Minnehaha Creek is the primary source of those excess nutrients. To help achieve Lake Hiawatha water quality goals, the Hiawatha TMDL study estimated that the total phosphorus load from nonpoint sources in the watershed must be reduced by at least eight percent and the load contributed from near- and in-stream processes to be reduced by an additional eight percent. This Diagnostic Study would identify in-stream processes that might be contributing to phosphorus concentrations in the creek and in Lake Hiawatha, including streambank erosion, internal loading in the impoundment areas, and contributions from riparian wetlands. This study would also identify potential reductions from internal and streambank improvements as a means of determining what part of the eight percent load reduction allocated to near- and in-stream improvements can actually be achieved, and whether additional watershed load reductions would be necessary to meet overall phosphorus reduction goals.

Minnehaha Creek itself has been designated an Impaired Water because of its impaired biologic community. Many of the processes that the Diagnostic Study will evaluate are also likely stressors to the biotic community. Combining the Diagnostic Study and Biotic Integrity TMDL would be efficient and would provide for the coordination of implementation efforts. For example, streambank erosion is often a contributor of sediment and phosphorus loading downstream. Biostabilization with native vegetation reduces that pollutant source while improving fish and macroinvertebrate habitat.

OutcomeAn implementation plan identifying the most effective suite of projects to reduce phosphorus and sediment loading and to restore ecological integrity
Estimated Cost and FundingDiagnostic and TMDL study. The District has received a grant from the MPCA to complete this study in 2006-2007.$150,000