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HomeMy WebLinkAboutNew Business#2 4-6-87 Flood ConDATE: NARCH 25, 1987 NEW BUSINESS NO. 2 4-6-87 Inter- Com TO: FROM: SUBJECT: WILLI~ HUSTO#, CITY MANAGER PUBLIC WOR~S DEPARll~ENT/ENGINEERING DIVISION SA~ DIE60 CREEK REGIONAL FLOOD CONTROL 'MASTER PLAN RECOMMENDATION: For the City Council meeting of April 6, 1987. 1. Approve the attached "San Diego Creek Flood Control Master Plan" (Exhibit 1} as the conceptual regional flood control plan for the San Diego Creek Watershed. 2. Authorize staff to initiate a cooperative process with the sponsoring parties and Orange County Environmental Management Agency for the preparation of the required environmental documents. BACKGROUND: In June, 1986, the cities of Irvine and Tustin and The Irvine Company entered into an agreement to fund the engineering services for the preparation of a master plan for the San Diego Creek Watershed upstream of the Interstate 405 freeway. This study is currently being finalized by the consultant, John Tettemer and Associates, and is being funded as follows: The I rvine Company ........ 50% City of Irvine ............ 41.67% City of Tustin 8.33% The Orange County Environmental Management Agency (OCEMA) has participated in the study as a responsible Agency governing the regional flood control facilities. DISCUSSION: The regional drainage channels wi thin the San Diego Creek Watershed area (Tustin-Irvine) were originally established as agricultural drainage facilities. These channels do not have adequate capacity to carry the lO0-year flood. Flood waters originating in the foothills flow across the plain toward San Diego creek. Because of these inadequate drainage channels and the inadequate culverts beneath the Interstate 5 freeway, flooding occurs approximately as indicated on Exhibit 2. As development in the area occurs, the flood hazard must he eliminated by construction of lO0-year capacity flood control facilities. MARCH 25, 1987 PAGE~ TWO In order to develop .the most economical flood facilities on a community-wide basis, the cities of Tustin and Irvine and The Irvine Company have developed a conceptual Regional Flood Control Master Plan per the above mentioned agreement. This plan includes the proposed construction of several detention basins and channels. OCEMA staff has reviewed the Master Plan and Concurs with the concept. The communi'ty will benefit from implementation of the Flood Control Master Plan through lower overall flood control costs. This Master Plan concept is also being utilized in discussions with Caltrans to determine ultimate sizing of freeway drainage facilities required as a part of the Interstate 5 Widening Project. It is anticipated that the Master Plan will significantly reduce the cost of the freeway drainage facilities allowing Caltrans to contribute to construction of portions of the Master Plan facilities. Since the detention features of the Master Plan reduce flows downstream, there will be a savings to OCEMA should' it become necessary for the County to improve or enlarge any of its channels downstream from the detention facilities. The budget impact to the City of Tustin is limited to financing its share ($10,000.00) of the Master Plan preparation costs. These funds have been previously funded and expended per the above mentioned agreement. Approval of the Regional Flood Control Master Plan concept will demonstrate the City's commitment to the conceptual plan which is essential for continued discussion with Caltrans regarding required freeway drainage facilities as they pertain to the upcoming .Interstate 5 Freeway Widening Project. Exhibit I is the conceptual Master Plan document which is recommended for approval. Lower Peter's Canyon detention basin is the only basin planned within the Tustin City limits. This basin is proposed to be constructed within the limits of the proposed Peter's Canyon Regional Park. In order to for~lly adopt a Master Plan of Drainage for the San Diego Creek Watershed it will be necessary to prepare a detailed.envirOnmental document. The cost for this study has not yet been established, but it is assumed that Tustin's share would still be approximately 8.33% and would be in the range of $10,000-$12,000. Bob .Ledendecker Director of Public Works/City Engineer BL:jm Attachments Exhibit i - San Diego Creek Flood Control Master Plan Exhibit 2 - Existing lO0-year flood zones impacting I-5 freeway / t ! j.