Maintenance is necessary for a stormwater pond to operate as designed on a long-term basis. The pollutant removal, channel protection, and flood control capabilities of ponds will decrease if:
Pond maintenance activities range in terms of the level of effort and expertise required to perform them. Routine pond and wetland maintenance, such as mowing and removing debris or trash, is needed multiple times each year. Owners may consider an “adopt-a-pond” program in which properly trained citizen volunteers perform basic landscape maintenance activities (the City of Plymouth, for example, has instituted such a program). More significant maintenance such as removing accumulated sediment is needed less frequently, but requires more skilled labor and special equipment. Inspection and repair of critical structural features such as embankments and risers, needs to be performed by a qualified professional (e.g., structural engineer) that has experience in the construction, inspection, and repair of these features.
The following terminology is used throughout this section:
HIGHLY RECOMMENDED - Indicates design guidance that is extremely beneficial or necessary for proper functioning of the bioretention practice, but not specifically required by the MPCA CGP.
RECOMMENDED - Indicates design guidance that is helpful for bioretention practice performance but not critical to the design.
Implicit in the design guidance in the previous sections, many design elements of pond systems can minimize the maintenance burden and maintain pollutant removal efficiency. Key maintenance considerations are providing access for inspection and maintenance, and designing all outlets and the principal spillway to minimize clogging.
Stormwater ponds can be designed, constructed and maintained to minimize the likelihood of being desirable habitat for mosquito populations. Designs that incorporate constant inflows and outflows, habitat for natural predators, and constant permanent pool elevations limit the conditions typical of mosquito breeding habitat (see section on mosquito control).
The construction phase is another critical step where O&M issues can be minimized or avoided.
Inspections during construction are needed to ensure that the practice is built in accordance with the approved design standards and specifications. Detailed inspection checklists should be used that include sign-offs by qualified individuals at critical stages of construction, to ensure that the contractor’s interpretation of the plan is acceptable to the professional designer. An example construction phase inspection checklist is provided at this link.
Some important post construction maintenance considerations are provided below. More detailed maintenance guidance can be found in the Pond and Wetland Maintenance Guidebook (CWP, 2004).
Example operation and maintenance checklist here.
It is Highly Recommended that the Operation and Maintenance plan include a provision to lower the level of the permanent pool in the late fall, to provide additional retention storage for snowmelt runoff and ensure that some permanent pool storage is available above the ice (the permanent pool should not be completely eliminated nor allowed to freeze through completely).