Review Storm water Pond Maintenance and Aquatic Vegetation Conditions

The purpose of this case is to highlight the City's existing maintenance practices associated with storm water ponds, and also discuss the periodic concerns by residents that these ponds do not meet their aesthetical expectations.  

There are many physical aspects to the storm water system, including pavement, curb and gutter, ditches, streams, swales, upland vegetation, catch basins, storm-cepters, culverts and pipe, as well as sedimentation ponds, and wetlands (natural or created).

 In the matter of  practices associated with sediment ponds or wetlands, maintenance is generally limited to removal of sediment and solids at the outlets to these holding areas or water bodies, so as to retain their capacity or ability to convey water.  Another maintenance activity is the removal of woody vegetation so as not to impede the flow of water - or, to ensure trees to do grow up in these outlet areas to prevent maintenance equipment from physically removing the aforementioned sediment that accumulates in the outlet areas.

Wetlands and shallow lakes naturally 'fill in' with aquatic vegetation, which decays, and becomes nutrient-rich sediment, and overtime becomes slowly shallower, and with more vegetation.  This process is accelerated when phosphorus and other 'pollutants' such as warm storm water or other nutrients are introduced to water bodies.  The attached content from an interpretive sign at Sunfish Lake Park discusses eutrophication in more detail - as does the Minnesota Pollution Control Agency report on existing conditions at the lake.

As it relates to residents expectations on the aesthetical appearance for ponds, or created wetlands areas, it is speculated that often the dissatisfaction with increasing amounts of 'weeds' or algae may be in part, attributable to persons moving to a home site when sedimentation or storm ponds are newly created, and largely free of aquatic vegetation.  Then, as aquatic vegetation increases, it may be perceived as some failure in storm water maintenance.

A resident in the vicinity of Emerald Pond Park may be in attendance to discuss with the committee, dissatisfaction with the amount of plants and algae in the pond at the park.  The area of concern is circled in a white dotted line on the attached exhibit entitled 'complaint area'.  Within this exhibit is National Wetland Inventory, and the arrows depict the flow of storm water, all of which connects to various wetlands and much of which flows to the Rum River.

 

10 minutes: Present background and exhibits depicting aquatic vegetation conditions within storm water/wetland ponds. (Riverblood)
10 minutes(?): Dialog/discussion with resident and Committee on options, costs and Staff direction.  (Riemer, Riverblood, and Westby)

Complaints about aquatic vegetation in suburban and urban environments are common, with the City of Champlin's Mill Pond being a good example.  In this case, the concern went beyond just the appearance of the surface water, as the vegetation inhibits swimming and fishing, and causes other problems.  Attached is the City of Champlin's FAQ which provides background on some of their attempts at addressing the situation.

Often due to frustration, residents and officials will try any means to reduce the amount of aquatic vegetation in wetlands and sediment ponds, including aeration - usually with little effect.  In the instance of the Mill Pond, three very large aerators have been installed, again with no apparent improvement on the amount of aquatic vegetation in the pond - despite the fact the Elm Creek flows 'new' water through the pond at a present rate of about 3 million gallons per day.  Attached is a photo of the Mill Pond at the point where Elm Creek flows past one of the aerators.

This case does not discuss or request funding.

Staff recommends no change in storm water pond maintenance practices at this time.

Based upon committee discussion.