and the boundary of K-Zone, J-Zone and I-Zone are shown on Figure V-10.

Proper nonerosive emergency spillways directing flow away from private properties shall be provided.

Nuisance water flow shall not be allowed into the retention basins.

2. Detention and Retarding Basins'

• a.Detention basins will be allowed only if they are appurtenant to an approved storm drainage facility or approved blue line creek. They will be designed such that no more than 85% of the predeveloped peak flow rates for the 2, 10, and 25 year storm will discharge downstream.
• b.Retarding basins will route the entire storm runoff for 2, 10 and 25-year storms through the basin and provide outlets which will maintain the downstream flow at no more than 85 percent of respective peak predevelopment flows.

The minimum required flood storage volume for retarding basins is that volume described by the area between the 25-year storm runoff hydrographs for the post-development condition and predevelopment conditions on the rising limb up to 85 percent of the peak predevelopment flow plus the difference between the post-development hydrograph and 85 percent of the predevelopment condition peak flow as shown on Figure V-11. Hydrographs will be developed using the Los Angeles Department of Public Works Hydrology Manual.

Using this design procedure, the flow through retarding basin may be divided into two regions; the detention region and the retention region. The detention region shall be designed with adequate volume to assure that postdevelopment flows, for the 2, 10, and 25-year storm conditions, do not exceed 85% of respective predevelopment peak flows. The retention region volume, as a minimum, shall be the difference between the required flood storage volume and the detention volume, subject to other Conditions necessitated by basin design requirements. The retention volume shall be located such that it will not discharge downstream. The retention volume will not be considered as a credit in the detention region volume calculation.

V-11