Getchel, Unnamed, Stoney (GUS) - Turbidity: TMDL Project

Minnesota's Impaired Waters and TMDLs

Background

This report includes a turbidity TMDL for Un-named, Stony and Getchell Creek, three stream tributaries in the Sauk River Watershed River in Central Minnesota. The Sauk River Watershed lies in the heart of the North Central Hardwood Forest Ecoregion and discharges to the Upper Mississippi River. Land use in the watershed is primarily agriculture with the majority of land in corn/soybean rotations and pasture land. Un-named Creek was included on Minnesota’s 2008 303(d) Total Maximum Daily Load (TMDL) list for excess turbidity. Neither Stony nor Getchell Creeks are currently on this list but were included in this document for turbidity assessment due to the significant proportion of loading into the Sauk River from these two watersheds. However, the furthest downstream reach of Stony will be added to the 2020 Impaired Waters list for Total Suspended Solids, as Turbidity is no longer used as the standard.
 
Turbidity is a measure of the cloudiness or haziness of water caused by suspended and dissolved substances in the water column. Turbidity can be caused by increased suspended soil or sediment particles, phytoplankton growth, and dissolved substances in the water column. Since turbidity is a measure of light scatter and adsorption, loads need to be developed for a surrogate parameter. Total suspended solids (TSS) is a measurement of the amount of sediment and organic matter suspended in water and is often used as a turbidity surrogate to define allocations and capacities in terms of daily mass loads.

Map and location

GUS is located in the south central portion of the Upper Mississippi Basin, within the Sauk River watershed.

TMDL report and implementation plan

Total Maximum Daily Loads were established for Un-named, Stony and Getchell Creek using the load duration curve approach (Cleland 2002). It was estimated that a 35% to 95% reduction in total suspended solids is required for Un-named and Stony Creek during the higher flows and 7% to 66% reduction during the lower flows to meet current state standards. The only load reduction required for Getchell Creek is during the high flow category, where a 26% reduction is needed to comply with state standards.
 
A source assessment was conducted for each basin to qualitatively assess potential sediment sources to the channel. The potential contribution of sediment to the stream channel from field erosion out-weighed estimated in-channel sediment delivery by almost 10 to 1 suggesting that field erosion is likely a more important source of sediment in the Stony, Un-named and Getchell Creek watersheds. However, serious signs of bank failure and erosion suggest that active bank erosion is occurring in all three stream systems. Both of these potential sources should be addressed however, field erosion warrants greater attention because of the magnitude of sediment potentially delivered to the stream. Neither point sources nor stormwater are important contributors of suspended particles to either stream. No data are available to assess algal productivity in the stream systems, but this source was assumed to be not as significant since the majority of violations occur during high flow which is associated with erosion.

Links

Information contact

Anna Bosch
Watershed Project Manager
MPCA Brainerd Regional Office
7678 College Rd, Suite 105, Baxter, MN 56425
218-316-3929
anna.bosch@state.mn.us