Determining Your Stormwater Needs

How can I find out what my Stormwater Management needs are?

We have a seven step guide for how to prepare a stormwater management plan. The intent of these steps is to aid your planning effort; these steps are not required for design, potential permits, or potential construction approvals; they are simply meant to be useful to consider. While some of these steps may seem time consuming or complicated, doing these steps yourself can save money.

►Step 1 – Layout Proposed Footprint

Prepare a site plan with all existing development, proposed development, and grading details of the site.

►Step 2 – Identify Your Stormwater Management Needs

Where does water on your property go? Identify existing impervious surfaces, nearby discharge points for those impervious surfaces, and available existing stormwater systems.

Do you treat stormwater on your site? We recommend that all properties with over 1000 square feet of impervious surfaces treat water on site.

Do you live near a body of water? We recommend intervening with stormwater runoff, either by retaining or treating stormwater, prior to entering any body of water (stream, lake, rivers).

Source Controls: Does my property match any of the following site uses or characteristics: fuel dispensing, above ground storage of liquids, bulk storage, material transfer areas, loading docks solid waste storage, vehicle and equipment washing areas? If yes, then you may need to cover the pollutant, pave under the pollutant to protect the soil underneath, or implement an isolated drainage system.

Are you worried about pollutants on your property? Come talk to the Public Works and Development Office.

►Step 3 – Evaluate Your Development Site and Plan

This will tell you how much water is on your property.

First, identify types of soils and infiltration rates of soils. How to guide for performing your own infiltration test in supporting documents below.

►Step 4 – Identify Your Runoff Control Plan

If you have a low infiltration rate then the water from your property will potentially flood properties downstream. This step tells you how much water to keep on your property.

Identify where the stormwater runoff from new or replaced impervious surfaces area(s) will be discharged. Confirm that system has flood control capacity. A good indication of flood control capacity is if your property retains the same amount of stormwater postdevelopment as it did predevelopment.  

►Step 5 – Identify Your Stormwater Quality Plan

This step tells you what to do with the water left on your property. Select and design an approved stormwater facility from the BMP Matrix. Calculate the treatment facility size(s) and locate facilities on the site plan of the proposed development. If there is insufficient area for the treatment facilities, implement mechanical treatment. The BMP Matrix is in the supporting documents below.

►Step 6 – Develop an Operation and Maintenance Plan

Applicants are responsible for on-going operation and maintenance of stormwater facilities. Information on the operation and maintenance needs are specific to the individual BMPs and can be found in the supporting documents of the Choosing a BMP page.

►Step 7 – Technical Assistance

We want to be a resource for you! At any time during the planning, designing, or permitting process, you may contact the City of Cottage Grove for technical assistance.