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I V-I SECTJONV FLOOOPROOLEM5 Erosion is the most significant potential cause ofddITlage in this reach. The USACE has one drop structure for this reach. I I REAC~ 1; CHATFIELD TO COLUMBINE DAM This reach, immediately below Chatfield Dam, is characterized by active and inactivegr;lvel pits and a regional floodplain park. Thechdnnel in this reach is relatively undisturbed !lyman. flood diJ/llages that occur are to utility crossings, bridges, gravel pit lakes, and include extensive erosion to the river banks. Damages could be significant to active and inactive gravel mines due to herm erosion and potential failure. REACH 4: BATES AVENUE TO COLFAX AVENUE Evans Avenue The 100-year flood is contained within the channel from Bat..s to Evans Ave~ue. The Evans Ave~ue bridge ,dll pass the lOO-ye~r flood l<Iithout overtopping. It does, hol<lever, cause a backup of about 2 feet as the result of inefficient piers and a 101<1 Chord elevation 4 feet below the lOO-year flood. This 2 foot rise, cOlllbi~ed with the low banks upstream of the bridge on the left bank, results in flooding on the left bank which includes retail stores, warehouses, offices, a~d small manufacturing facilities. The Reach 1 floodpl ain under e~isti~g conditions shown on Sheets 4 to 7, is based on Federal Emergency Management Agency floodplain mapping. I The major flood problem is erosion which >lQuld c<J.use a breach in the berms protecting and sep<J.rating the gravel mining lakesresu1tinq in the release of water ~ich could increase peak flow, in the ;outh Platte River. On the right bank '~ater leaves the channel, crosses Evans Avenue, and either flol<ls dOl<ln South Huron Street into the Overland Golf Cour,e, or returns to the channel immediately dOl<ln,tream. No structures would be damaged by this flooding. REACfl2: COLUMBINE DAM TO OXFORD AVENUE - - The U. S. Army Corps of Eng ineers has des i gned ~ Channel improvement project for this reach of the river. Constructlon was begun in 1984 on the channel improvement project which is desi9~ed to prevent flood damages outs ide the channel for the lOO-year event. The propOser! Channel ~l ignment for th<< CorpsprojectisshownonSheets8toll. REACH 3; OXFORD AVENUE TO 8ATES AVENUE In this reach the lOO-ye~r flood would be confined to the ch<J.nnel except for a small portiM of floodplain ~t the mouth of Bear Creek. Because this area is c urreflt 1 y in ~ natural state and i, expected to remain so, the damages from flooding are expected to remai~ minimal. ValiejotoColfax From the Evans Avenue bridge to the 3rd AyenueOam the 100-year flOOd is contained within the channel. The 6th Avenuebridqe lsovertopoedby the lOO.year flood, resulting in almost a 2 foot rise in the lOO-year flood eleyation. '~hen combined with the low left h~nk upstream of the bridge, extensive flooding occurs on the left bank from Vallejo Street to the 6th Avenue bridge. The dredflooded includes l<Iarehouses, retail stores, and small fabricating stJops. Depth of flooding is generally less than 2 feet. The South Platte River channel is narrowfrorn about 10th i\venueto 13th Avenue, in some places only 150 feet wide and 13 feet deep. As a result, flooding alsooccur<;on about 50 acres on the left bank betl<lf'en 6th Avenue and Colfax. The structures loc~ted in this floodplain include a Publ ic Service Power plant, publ\chousing structur<,s, fOOd industries, and w~rehouses.