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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 />B. H~GHWAY 159 CROSSING OF RITa SECO <br /> <br />1. Hi story <br /> <br />In 1985, the Colorado Department of Hi ghways repl aced a dangerous <br />b ri dge at the 1 ocati on of the State Hi ghway 159 crossi ng over the <br />Rito Seco. The old highway bridge at this location was estimated to <br />be a 20 foot span with a 4 foot vert i ca 1 openi ng 0 r 80 square foot <br />of conveyance area. The Highway Department replaced the bridge with <br />two 24 inch corrugated metal pipe culverts with a conveyance area of <br />6.3 square feet. The Highway Department believed that only the flow <br />from the Rito Seco Basi n whi ch woul d be rel eased by the 24 inch <br />culvert through the levee crossing location would enter the two 24 <br />inch CMP's at the highway location. However, during heavy rains and <br />flooding conditions, the flow from the North and East Drainage <br />Ba,s ins is choked off by the cul verts. The stormwater runoff wi 11 <br />overflow the hi ghway cul verts and run southerly down Main Street. <br />The North Drainage Basin of 4.5 squareomiles should have been <br />i ncl uded in the si zi ng of the new cul verts at the Rito Seco and <br />Highway 159 location. In addition, the Corps' Emergency Levee <br />System does not meet FEMA Levee standards. <br /> <br />2. Investigation <br /> <br />WRC performed an inventory of the hydraul ic structures along the <br />Rito Seco to determine the hydraulic capacity of the existing <br />st ructures. Based on thi s inventory, channel cross secti ons <br />surveyed by Rincon, and the 100 year storm flow hydrology developed <br />by SCS, WRC was able to explore alternate structures capable of <br />passing the 100 year flow beneath Highway 159. <br /> <br />3. Alternative Solutions <br /> <br />Based on the fact that the Corps of Engi neers' Emergency Levee has <br />restricted the flow into the Rito Seco from the East Drainage Basin <br />and that the SCS hydrology indicates that the 100 year flow from the <br />North Drainage Basin is approximately 180 cfs, the proposed crossing <br /> <br />-17- <br />