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Mountain House Spedrfic Plan III - ........................................................................................................................................................................... 15.2.3 Implementation Measures b. Each segment of the storm drainage system shall be designed as needed to provide protection for each phase of development. c. The MHCSD shall coordinate with the agencies having jurisdiction over Mountain House off-site watersheds areas to ensure that any future development projects do not alter the existing volume, velocity and quality of storm water runoff discharged downstream to the Mountain House Project. d. All implementing projects shall comply with the applicable provisions of the MHCSD Storm Water — Master Plan Update and addenda and the Development Standards. 15.3 Primary Storm Drain Collection System 15.3.1 Master Plan Summary The primary storm drainage system at Mountain House provides for the conveyance of all off-site and on- site precipitation,plus any urban runoff,to the Old River as a terminal drain. The primary storm drain collection system includes trunk storm drain lines, secondary storm drain lines, major open-channels (Mountain House Creek) and water quality basins. The Master Plan requires that on-site and off-site drainage generated by precipitation and urban run-off be jointly considered and conveyed safely through the community. On-site drainage shall not impact — property owners adjacent or within the community, or downstream property owners. Discharge of sediments to creeks,ditches and Old River shall be minimized. _ Trunk line pipes, the water quality basin, and major open-channels within Neighborhood A shall he designed and constructed to transport the 100-year volumetric flow rate. Trunk pipe lines within Neighborhoods B and D shall be designed to transport the 10-year runoff flows, with the 100-year storm runoff to be conveyed within the street right-of-way(DeAnza Boulevard). Trunk line pipes shall be designed for gravity flow conditions. Should temporary open channels be required for construction phasing, erosion shall be minimized by designing and constructing open-channels to convey storm water runoff at or below the allowable _ maximum velocity,and by using appropriate streambed protection and/or energy dissipaters at transitions from supercritical to sub critical flow,at the confluence of channels,at the downstream location of culverts,and at channel transitions. Streambed protection shall include appropriate species of plants. The ultimate point of terminal discharge for all drainage shall be Old River. Terminal discharge will _ occur by gravity flow. 15-4 Draft 03114/05 ...........................................................................................................................................................................