Keeping Waterways Healthy
Local Precipitation Patterns
The current lack of snow this winter makes it easier to understand that weather patterns are changing. As mentioned in the February newsletter, recent precipitation patterns reveal more localized, intense rainstorms of shorter duration in Coon Creek Watershed District (CCWD). Dr. Mark Seeley of the University of MN notes the same pattern for the state.
The CCWD has been tracking precipitation amounts to not only record what is happening locally, but also to aid in monitoring storm events, flood possibilities, soil moisture and wetland hydrology. For example, here in the flat landscape of the Anoka Sandplain, a storm event could cause a backup of water upstream and downstream in a creek or drainage ditch.
Minimizing Flood Risk
To minimize flood damage potential, the CCWD and the city review building plans to ensure foundations are planned above the 100-year flood elevation. What is that? It is the flood elevation having a 1% chance of being equaled or exceeded each year from a 24-hour rainfall of 6.2 inches or more.
More water falling in a short time can also result in more water force and therefore more erosion potential. The sandy soils of this area are especially erosion prone. The eroded material (sediment) can obstruct culverts and ditches downstream and cloud the water (which blocks sunlight to plants and other organisms needed for good water quality).
To help manage these issues, the CCWD periodically cleans drainage ditches of deposited sediment and obstructions, and has a Bank Stabilization program for badly eroded creek and ditch banks.
Heavy, short bursts of rain can also rapidly change water levels in creeks, ditches, ponds and lakes. Some wetlands function as sponges for such fluctuations. Engineers use the 100-year storm event (6.2" of rainfall in 24 hours) standard for designing detention and retention stormwater ponds that capture runoff, functioning as rate-control tools to minimize flooding. The CCWD and the City of Blaine review building plans for correctly designed ponds.
With less time for the rain to soak into the ground, it can instead run off lawns, streets, driveways and rooftops. And that runoff can carry pollutants from your roof, vehicle or yard to the nearest waterway. Thus, the runoff is best treated before it enters public waters. Some wetlands serve this function. Stormwater ponds are also commonly designed to collect and detain runoff to allow time for pollutants to settle out or be taken up by aquatic vegetation. The CCWD and the city review building plans for these ponds as well.
These are a few of the issues and programs at CCWD. Managing water resources requires a complex balance of education, planning, review, design and implementation. Best Management Practices such as stormwater ponds and vegetated riprap are used, and others like previous paving stones and rain gardens are being researched. For more information, contact CCWD at 763-755-0975 or email the District.
Avoid cabin fever and occupy some of time in the next few months planning for the yard and gathering the materials to be ready for springtime. Your lawn and gardens will thank you.