Appendix 204. Drainage Plans.

The drainage plan shall include at a minimum:

A.

A Topographic Survey. Existing conditions of the site and areas upstream and downstream necessary to determine the offsite impacts of the drainage plan.

B.

The Drainage System. Mapping and descriptions, where relevant, of the site and watershed features, the existing and proposed drainage system features of the property and vicinity, and a delineation of site and offsite drainage features that might be affected by the development.

C.

Environmental Features. A depiction of environmental features of the property and vicinity including:

1.

The limits of mapped wetlands;

2.

The limits of regulated flood zones;

3.

Any designated natural areas or greenways.

D.

Proposed Drainage System Design. A proposed condition grading plan and the basis for design for the final network components including:

1.

Supporting calculations for the detention requirements and an application for fee in lieu of detention, if applicable;

2.

Supporting calculations for the stormwater conveyance system;

3.

Design and identification of site overland flow paths;

4.

Flow rates and velocities at representative points in the system;

5.

Basis for any variances requested and mitigation plans for any adverse impacts that may follow were the variance granted;

6.

Evidence of how the system will handle storm events greater than the one hundred-year event, including a statement of how the overflow system will access a suitable emergency flood path;

7.

Evidence that immediate downstream properties are not adversely affected.

E.

Environmental Mitigation Measures. A plan detailing and discussing the use of environmental mitigation measures and BMP such as:

1.

Greenways and vegetated buffer zones;

2.

Site infiltration practices;

3.

Erosion and sediment control plans.