§ 6.06.11. Tailwater.

Determination of the hydraulic gradient and sizing of the stormwater system shall be based on the highest tailwater which can be reasonably expected to occur coincident with the applicable design storm event. Standard design tailwater conditions for the design of stormwater systems are as follows:

1.

Systems which discharge into ponds, lakes, and other wet facilities shall use the stage occurring at peak flow conditions for the design storm event used. Where no outlet exists, the seasonal high water elevation shall be used at the beginning of the storm event;

2.

Systems discharging into tidal areas shall use the mean high water elevation;

3.

Systems discharging into regulatory floodways shall use a tailwater design derived by use of the FEMA flood profile data contained in the FEMA Flood Insurance Rate Study or approved water surface profile study where available;

4.

Systems discharging into ditches shall use the normal depth flow in the ditch or if downstream control exists, the greater of the normal depth flow or the stage due to backwater from the downstream flow;

5.

Systems which connect to existing stormwater systems shall use the hydraulic grade line of the existing system at the point of connection.

(Ord. No. 11-01, § 2, 1-18-11)