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COMMENTARY Station 240+00 to Station 300+00 800-fp.et downstrean of Federal Bl vd. to 1000-feet upstream of Lowell Blvd. Portions of Reach IIA and Rp.ach lIB The Colorado State Division of Highways (CSDH) has proposed a Nature Pre- serve and Wildlife Area for the area between the 1-76 embankment and Clear Creek from Tennyson Street to Lowell Blvd. The floodplain will be preserved through the upper limits of this segment to Lowell Blvd. The CSDH's plan proposes an extension of their hiker/biker trail, with no associated channel improvffilents, through thi s reach. As part of the Major Drainageway Pl an, improvffilents have been recommended at Lowell Blvd, Denver and Rio Grande Western Railroad and Federal Blvd. The proposed CSDH channel improvements upstreiJ11 of Tennyson increase the 100-year flood discharge along the main channel south of 1-76 at the Lowell Blvd. bridge. Unli'ss improvffilents are made at Lowell Blvd. the increase in flood discl1arge will ralse the 100-year water surface elevation above the existing 100-year flood level by approximately 3 feet immp.diately upstrecJl1 of the bridge. The improvements at Lowell Blvd. include a 100-feet bridge span extension to the existing structure, a grass-lined transition to improve the bridge en- trance condltions, 500-feet of rock-lined channel downstreiJ11 of the bridge and the extension of the existing drop structure for the Fi sher Ditch in- take. Minor flooding may still occur along the Fi sher Ditch after these im- provffilents are constructed. Due to the location and extent of the concrete drop structure, it wi 11 be necessary to provide a trail/maintenance road crossing and access point at the ditch below the headgate. The channel improvffilents at Federal and at the Denver and Rio Grande Rail- road will tie to the proposed CSDH improvements at Station 272+30. The Ma~or Drainageway Pl an improvements at the railroad crossina include a rock-llned channel and the removal of approximati'ly 40-feet of fhe existing rail road trestle with the add it i on of a 200-feet span from the 1 eft centp.r pier. The r811ainder of the trestle will be left intact. Due to the bridge expansion, the 3g-inch Denver Metro sanitary sewer will be relocated. The final design of the proposed Hidden Lake drainage outfall should be made compatible with the proposed rock-lined channel downstream of the railroad. A grass-l ined channel upstream of the rail road crossing has been designatp.d to capture the overland floodwaters north of the 1-76 embankment. This drainage collection swale has not been included in the costs of Major Drain- aqeway Improvements as it has been assumed that future developllp.nt will bear tne expense needed for flood mitigation in this area. Improvffilents at Federal Boulevard include the construction of a rock-lined channp.l to the Brannan Sand and Gravel property. The exact improv811ent plans for the Brannan Sand and Gravel property have not been completed and, therefore, were unavail able at the time of this study. It is rp.commended, however, that any channel improv811ents be designed for compatabil ity with thp. other pl anned flood control structures and strategies. A 12-inch water line will be required to be relocated at Federal due to the excavation of the channel invert in this segment. The improvffilents confine the IOO-year floodpl ain to the proposed channel. Shallow flooding, however, may still occur downstreiJ11 of Federal where the channel transitlOns to the Brannan Sand and Gravel property. The exact nature of the floodpl ain and water surface elevations on the Brannan pro- perty will depend upon the final accepted and approvp.d plans. COST ESTI MATE Station 240+00 to Station 300+00 CONSTRUCTION Channel Improvement Costs Channe l-Cross ing Costs Ut il ity Relocation Costs TOTAL CONSTRUCTION COSTS ENGINEERING AND CONTINGENCIES (30% of Construction Costs) FISCAL, LEGAL AND ADMINISTRATIVE (10% of Above Total) PROPERTY ACQUISITION COSTS MAINTENANCE TOTAL IMPROVEMENT COSTS (1981 Dollars) Annual Operation/Maintenance Cost $2,687,600 I I I I I I I I I I I I I I I I I I I $ 673,000 $ 110,000 $3,470,600 $1,041,200 $ 451,200 $ 459,100 $5,422,100 $ 18,200