C. For undivided major and secondary highways, one twelve (12) foot lane in the center will be clear of water for a 10-year storm peak runoff. For divided highways, one ten (10) foot lane in each direction will be clear of water for the peak runoff from a 10-year storm at ultimate development conditions (see Figure V-3). Subdivisions adjacent to highways with pre-existing flooding will be considered on a case-by-case basis.

If a storm drain is required to meet any of the three conditions listed above, it shall be designed for a minimum capacity of the peak flow from a 10-year storm. If a master planned storm drainage facility is proposed through the project which would mitigate the flooding, the developer may be required to construct the facility.

B. HYDROLOGIC DESIGN STANDARDS AND PROCEDURES

The design of all master and local facilities will be in accordance with the following standards and procedures:

  1. Hydrologic calculations will be performed in accordance with the Los Angeles County Department of Public Works Hydrology Manual except the initial time of concentration will be determined from Figure V-4 and used in the subsequent calculations. Figure V-4 may be used, subject to the limitations of length and area.
  2. Design frequencies will be as described under "Hydrologic Protection Levels".
  3. Where applicable, the design shall include provisions for future extension of the drainage system to serve the entire drainage basin.
  4. Required submittals - Improvement Plan Stage
  5. Hydrology map on a scale of 1:500 or larger (e.g. 1:200) showing the entire drainage area tributary to a master plan drainage facility or a regional drainage facility. It will show the entire tributary area with contours/elevations, drainage area sizes, catch basins, connector pipes, mainline pipes, and the pertinent discharge data. Appropriate soil classifications and land use information will also be submitted.

V-3