Addendum to Newsletter Issue 42: CMSCWD

Here are notes from discussion between Mike Blehert and Mike Isensee (CMSCWD - Carnelian Marine St. Croix Watershed District) in May, 2021 about watershed issues that impact BML.  These issues do not all relate to the BMLAAIS mission but are of interest. 

District Hydrologic and hydraulic model calibration:  

This study has been completed. Based on rain/snow, the existing BML drainage system is adequate for large storms (seven plus inches of rain for example) or record years like 2019 or 2020. The study conclusion does not consider possible  flooding of roads or homes. It also does not address lake shore erosion, meaning  a buffer program with deep rooted plants and beach reinforcement (rocks) is important. 

Does the CMSCWD plan to do more studies to determine what  can be done to limit BML  from rising far above the 941 ft overflow and staying there all summer?  If there had been a seven inch storm here (there were several in Southern MN in 2020), there would be significant erosion.   Yes, CMSCWD will determine the choke points and scope out possible changes in the system.  Several channel choke points (one was the narrow outlet creek from Big Carnelian) are of concern.  Culverts under County Rd 4 will also be reviewed.  However, the weather prediction based on the latest models was for a drier 2021, continuing into 2022 and 2023.  This forecast was proven out in 2021.

The last Watershed Update Newsletter reported an A+ rating for BML.   Our work has certainly contributed to this excellent water quality rating.   The WD Newsletter also mentions the native plants in the South Bay, clear water and reductions in algae caused by phosphorous and chlorophyll.   

It is fortunate that the great majority of the watershed surrounding BML slopes away or is wooded which limits farm and other nutrient rich runoff and high phosphorous levels.   BMLA work has limited the growth of EWM which crowds out native plants and can create excess decaying and smelly biomass.   The following quote from a paper published by the United States Geological Survey regarding EWM says it all.

From USGS:   The growth and senescence of thick vegetation degrades water quality and depletes dissolved oxygen levels (Honnell 1992; Engel 1995). Typical dense beds restrict swimming, fishing and boating, clog water intakes and result in decaying mats that foul lakeside beaches. 

Outlet Channel Maintenance:  

Maintenance is on-going under contract.  Lots of beaver dam material was pulled this season, and two culverts were replaced.   CMSCWD contracted last year at a cost of about $20K/year  to keep the drainage system clear and flowing.  

Big Marine Sub-watershed Analysis:   

This analysis will be used to guide projects to reduce phosphorus and sediment loading in BML from the entire watershed.   The report is scheduled to be completed in December,  2021, so new projects should be initiated in 2022.  

Examples projects are to reduce or eliminate:

a.  Bliss addition storm water drainage directly into the lake.

b.  East main lake public access runoff from the gravel road all the way down to the lake.

c.  In some wetlands, phosphorus in the sediment that can overflow into the lake or maybe leach into the lake through the ground.