The Little Rock Creek Watershed is 67,650 acres and is nearly evenly split between Benton (36,030 acres) and Morrison (31,620 acres) counties and is made up predominately of fine sandy soils. Little Rock Creek flows south through Little Rock Lake and ultimately discharges to the Mississippi River via the Harris Channel. The main stream of Little Rock Creek is perennial (flow year round), whereas, a majority of the tributaries are intermittent or have been converted to drainage ditches.
Little Rock Creek is a DNR designated trout stream (Class 2A Brook and Brown Trout). Since 1907, portions of Little Rock Creek have had a self-sustaining population of Brown Trout, but in the early 1990s DNR Fisheries surveys noted a decline in trout populations. Little Rock Creek has been determined as impaired for lack of coldwater fish assemblage and was included on the Minnesota Pollution Control Agency (MPCA) 303(d) list of Impaired Waters in 2002.
Little Rock Creek TMDL
Benton SWCD has conducted the Total Maximum Daily Load (TMDL) study in three phases. The first phase included the collection of historical data; phase two wrapped up at the end of 2009 with stream monitoring and data collection resulting in the completion of a Stressor Identification Report. This report identifies any type of stressor or combination of stressors that cause biological impairment. A stressor is any physical, biological, or chemical entity that can induce an adverse response. Stressors identified for Little Rock Creek include:
- Dissolved oxygen
Phase three began in late 2010, with Benton SWCD contracting with Barr Engineering to complete the modeling required for the TMDL report. The TMDL report was developed for the stressors identified (Sediment, Temperature, Nitrates, and Dissolved Oxygen). This was accomplished by calculating the total pollutant load with reference to flow as the source of impairment.
Overall, a 52% reduction in total oxygen demand is necessary to ensure that the DO (dissolved oxygen) standard is met throughout Little Rock Creek under the critical flow conditions. Reductions in nitrate load of 47% and 29% are necessary to ensure that the standard is met in Little Rock Creek under the dry and low flow conditions, respectively. Reductions in nitrate load of 33% and 19% are necessary to ensure that the standard is met in Bunker Hill Creek under the moist and mid-range flow conditions, respectively.
Little Rock Lake & Creek Watershed TMDL Implementation Plan
The TMDL indicates that the ideal combination of implementation strategies would combine restoration of groundwater flow, reductions in nutrient and organic contributions to the stream and a free-flowing system at the Sartell Wildlife Management Area (WMA) impoundment to minimize thermal impacts. More specifically, these implementation strategies, or combinations of BMPs, would provide some or all of the following:
- Reductions in groundwater use will be necessary to improve conditions in the stream.
- A variety of potential options to reduce groundwater use should be explored, including: limits on total appropriations, improved irrigation efficiency, scheduling and technologies, identifying alternative sources, timing, proximity to the stream and other options not yet identified
- Nutrient and organic constituent reductions
- Creating more of a free flowing system, while incorporating current WMA management strategies, to improve connectivity and temperature issues during the critical condition
Benton and Morrison SWCDs have a history of successfully installing Best Management Practices in the Little Rock Watersheds. Both districts have taken a leadership role in the coordination and implementation of BMPs, water quality and quantity projects, and programs. Since the development of the TMDL, a significant effort has been put forth to address external phosphorus sources, and over 70 BMPs have been installed in the watershed
Water Quality Monitoring
Benton SWCD is currently in year two of a three year monitoring plan for Little Rock Creek and other tributaries to Little Rock Lake including; Bunker Hill Creek and Sucker Creek to evaluate our progress towards meeting watershed load reduction goals. This monitoring plan consists of bi-weekly chlorophylla, total phosphorus (TP), total suspended solids (TSS), BOD5, and nitrate nitrogen, and total Kjeldahl nitrogen (TNK) samples as well as stream flow, pH, stream temperature, and dissolved oxygen measurements. A consultant was hired to evaluate the monitoring data each year to develop water quality progress reports. We will use these reports to evaluate the effects of watershed BMPs and other variables, and apply the adaptive management concepts in the implementation plan by adjusting implementation activities in future years.