§ 13.36.130. Stormwater site plans

The detailed form and contents of a stormwater site plan shall be as follows:

Guidance on the approach to preparing a stormwater site plan is contained in the public works standard plans and the ecology manual, Vol. 1, Chapter 3 (2005).

A. Plans shall be prepared and certified by a professional civil engineer registered in the state.

B. The contents of a stormwater site plan shall include the following:

1. Project Description.

a. A legal description of the property;

b. The name(s), address(es) and telephone number(s) of the owner(s) and person(s) ordering the work to be performed;

c. To the extent necessary to adequately evaluate the accuracy of computations, the project description will include:

i. The location of any existing or proposed buildings, structures and utilities on the property where the work is to be performed; and

ii. The location of any existing building or structure on the adjacent property which is within fifteen feet of where the work is to be performed;

d. Elevations, dimensions, location, extent, and the slopes of all work proposed to be done, shown on a contour map. Such contour map shall show existing and proposed contours. A minimum of a two-foot contour interval or otherwise as approved shall be used to adequately show drainage courses through the property and shall relate to the grade changes on the property. The datum used to depict information related to elevations will be as approved;

e. The soils types and existing and proposed vegetative cover, including trees, shrubs and grasses, shall be depicted on a map of the site;

f. Location of existing and proposed drainage features which transport water onto, across, or from the site including natural creeks, swales, artificial channels, drains or culverts. Also locations of springs, or other subsurface water outlets as well as ponds, lakes, swamps, wetlands, wet ponds, critical areas or potholes shall be shown on the contour map;

2. Background Computations for Sizing Drainage Facilities.

a. Topographical map of approved scale and contour interval showing:

i. Existing and proposed drainage basins;

ii. Acreage of existing and proposed pervious and impervious areas; and

iii. Slopes/grades and lengths of the existing and proposed time-of-concentration (Tc) lines;

b. Indication of the peak discharge and volume of surface water, assuming current conditions, entering and leaving the subject property due to the design storm;

c. Indication of the peak discharge and volume of runoff which will be generated due to the design storms, assuming developed conditions, within the subject property;

d. Determination of the peak discharge and volume of water that will be generated by the design storm, assuming undeveloped and developed conditions, at critical points on the subject property and at all naturally occurring discharge points off the property;

3. Proposed measures for handling the computed runoff in accordance with the requirements in this chapter;

4. Proposed measures for controlling runoff and erosion/sedimentation during clearing, grading and construction; and proposed staging and schedule of all building, clearing and grading activities in accordance with this chapter and the Department of Ecology and King County manuals;

5. Proposed schedule for maintenance of all applicable storm drainage-related facilities. The maintenance schedule shall extend for the life of the facility;

6. Detailed information regarding surface and pertinent subsurface water flows entering, flowing within, and leaving the subject site, both during and after construction;

7. Compliance with the provisions for large parcel stormwater plan requirements Nos. 2 through 11;

8. Provisions set forth in Section 13.36.080, General design and construction standards, Section 13.36.090, General water quantity standards, and Section 13.36.100, General water quality standards. (Ord. 2441 § 12, 1997)

(Ord. No. 2827, § 1(Exh. A), 6-21-2010)