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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />, I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />structure at Hi ghway 159 wi 11 not requi re the capacity of the <br />bridges upstream and downstream (approximately 300 cfs). Therefore, <br />the need for a larger single or double span bridge was eliminated. <br />The alternatives considered were single or multiple culvert <br />installations. Due to the limited amount of depth available between <br />the crown of the hi9hway and the channel bottom, selections were <br />further limited to multiple culvert installation, specifically a <br />double 6' x 3' reinforced concrete box culvert and double 57" x 38" <br />corrugated steel pipe and with concrete headwalls. <br /> <br />4. Recommendations <br /> <br />WRC recommends that a double 6 I X 3' rei nforced concrete box cul vert <br />with headwall and wingwalls be installed in the Rito Seco beneath <br />Highway 159. In addition, the downstream channel from Highway 159 <br />to Highway 142, including the portion under the Highway 142 bridge <br />will need to be graded to provide positive slope and reduce the <br />backwater downstream from Highway. 159. The concrete structure will <br />provide approximately 2.0 feet of freeboard during the 100 year <br />storm as opposed to approximately 0.5' for the corrugated steel <br />structure. The concrete structure would provide the business area <br />with additional flood and drainage protection. <br /> <br />See Sheet 2 of 4 of Drawings. <br /> <br />-18- <br />