Impervious Surface Permits
Impervious surfaces are surfaces that are compacted or covered with a layer of material that is highly resistant to the infiltration of water through the soil. This includes, but not limited to gravel, rock, asphalt, concrete and non-pervious paver systems. District rules are aimed at minimizing the effects of impervious surfaces, particularly in shoreland areas. Projects meeting District Rule threshold will require a Stormwater Management Plan
Stormwater Management Plans
The goal of a stormwater management plan is to minimize long-term erosion and manage storm water runoff discharging from a project's impervious surface after construction is complete.
The link below is a Technical Memo from the District Engineer that should be used to properly design a stormwater management plan.
Best Practices for Design of Stormwater Management Systems
Some of the items that need to be included in the stormwater management plan.
- Description of the proposed land use and a description of all adjacent lands
- Location/dimensions of property lines, existing roads, buildings, other structures, paved or surfaced areas, utilities (e.g., water, sewer, gas, electric) and easements
- Detailed site topographic plan showing:existing grades (minimum of 2-foot contours recommended) and all hydrological features such as ditches, grass channels, swales, perennial/ intermittent streams, wetlands, lakes, ponds, floodplains, culverts, and storm sewers
- Tributary subwatersheds and on-site drainage paths
- Mapping/description of predominant soils from most current version of USDA's “Soil Survey for Becker County, MN” or “Soil Survey for Otter Tail County, MN”
- Boundaries of existing predominant vegetation and proposed limits of clearing
- Detailed site topographic plan for the proposed project conditions which clearly indicate alterations to existing grades and topographic features. The plan should outline changes in subwatershed divides, emergency overflows, and drainageways. Proposed location of new roads, buildings, and other structures should be noted
- Show any items to be removed
- Calculations demonstrating that post-development, peak discharges rates are not increased over existing conditions for the 5-, 25-, and 100-year storm events
- Calculations demonstrating that detention facilities have been designed with permanent pool volume sufficient to retain the runoff from a 5-year, 24-hour rain event. An alternative standard would be to show a minimum of 90% removal of total suspended solids and a 50% or higher total phosphorus removal for a 5-year-24-hour rainfall event using Walker’s Pond Net model.
- Preliminary landscaping plans for stormwater treatment practices and any site revegetation or reforestation.
- Maintenance plan for on-site treatment measures
- Name, address, telephone number, license number of appropriate professional preparing the plan