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`' MOUNTAIN HousE PRoPosED MAcHAoo TENTATIVE MAP 4. ENVIRONMENTAL CHECKLIST <br /> 4.8 HYDRoLoGY AND WATER QUALITY <br /> low <br /> Less Than <br /> rte, Potential SPIIIEIR Significant <br /> Significant Requires Impact Due New New <br /> Impact Additional to Mitigation Additional Additional <br /> Less Than Adequately Review:No Measures In Impact Not Mitigation <br /> Significant Addressed in Significant Project Addressed in Measures <br /> '%W Issue or Nolmpact SPIIIEIR Impact Description SPIIIEIR Required <br /> i) Expose people or structures to a ■ ❑ n ❑ <br /> significant risk of loss,injury or <br /> death involving flooding,including <br /> flooding of as a result of the failure <br /> of a levee or dam? <br /> `r j) Inundation by seiche,tsunami,or ■ ❑ ❑ ❑ ❑ <br /> rnudflow? <br /> V <br /> %r SETTING <br /> `n Climate and Topography <br /> star <br /> Average annual rainfall in the vicinity of the Machado property is 12 inches with most rainfall <br /> %W occurring from November to April. Average temperatures range from 38 degrees Fahrenheit <br /> •. in winter months to 93 degrees Fahrenheit in summer months(Western Regional Climate <br /> Center, 2002). The project site is relatively flat,sloping gently at approximately one percent <br /> to the northeast. Current drainage at the project site is generally in a northeasterly direction <br /> via overland sheet flow,small surface swales,ditches and pipelines that convey runoff and <br /> `,r excess irrigation water into larger collectors. <br /> %. <br /> Surface Hydrology <br /> %kw <br /> 11110, The project site is located in the 15-square mile Mountain House Creek watershed.The <br /> headwaters of the creek are in the Altamont Hills approximately 6.5 miles southwest of the <br /> ty Mountain House Community. The creek enters the Mountain House Community at the <br /> western boundary of Neighborhood E and flows in a northeast direction to its discharge to <br /> Old River. The creek is approximately 8,000 feet northwest of the center of the Machado <br /> property. Runoff generated on and flowing through the project site would drain through a <br /> storm drain system to Mountain House Creek. <br /> 1ti <br /> Master Drainage Plan <br /> Drainage improvements for the Mountain House Community are described in the Mountain <br /> House Master Drainage Plan(PACE, 2002)that was updated in the Storm Water Master Plan <br /> Update,Addendum I(PACE,2004). Drainage infrastructure includes primary and secondary <br /> %W storm drain systems,improvements to Water Quality Basin(WQB)No. 1, and improvements <br /> to Mountain House Creek. New drainage infrastructure would be constructed to convey <br /> runoff from the Specific Plan III area,in which the project site is located. Discussion of <br /> %' storm drainage facilities for the proposed project is included in Section 4.16: Utilities and <br /> �. Service Systems. <br /> �.r <br /> a. <br /> 4-43 <br /> rr.. <br /> v <br />