FLOOD09924 - Laserfiche WebLink

Home Browse Search

CURREt>;T FLOOD SITUATION the structure involved. A pronounced increase in flow velocities usually occurs downstream from obstructions, thus extending the flood damage potential. Natural obstructions to floodflows occur mostly in the upper reaches of the Purgatoire tributaries where trees, brush and Developments in the Flood Plains Plate 2 is an index map for Plates 3 through 15 which show the flooded areas along the Purgatoire River and tributaries considered in this report. The flood plains abound with co~,ercial, industrial, residential developments, and public utilities. Transportation facilities within the flood plains include portions of u.s. Highways 85-87 (Interstate 25), leO, 350, and State lIighways 12, 23Sand 239. along with numerous county roads and City streets. Rail lines crossing the flood plains include the Colorado and Wyoming (C&W) Railway, the Colorado and Southern (CSS) Railway, and the Atchi- son, Topeka, and Santa Fe (AT&SF) Railway. Starkville residents have abandoned many dwellings along the entrenched Raton Creek partly beeau~e of past destructive floods. No new developments were noted along this stream, Devel- opment along the other tributaries appears to be gaining momentum without considering the floodways amI drainage ways. Continuing economic development within the study .:Irea is expected and pressures leading to intensified flood plain use will undoubtedly accompany ~lIr.h d..velopl'l"nt. Futur.. d..v..lopm..nt. could ;ncl"d~ impr"p..r US" "f certain floodplain areas because of the "false sense of security" provided by the Trinidad Dam, other vegetation encroach into channel areas during periods of low flows. The denSity of such growth is especially pronounced at channel bends. Man-made obstructions include landfills, sometimes originating ~s random refuse dumps or often as levees constructed with the intent of protecting isolated properties. Flooding in the vicinity of well-intended levees may be ~re Severe than would have occurred under natural conditions. ShOuld a levee~-of random con- Obstructions to Floodflows Obstructions, natural and lIlan-made, within the flood- ways impede floodflows, cresting backwater and increased heights. Debris washing downstream during floods often collect against bridges or within restricted flow areas, redUCing the waterway openings and impeding the floodflow, This crellte. a damming effect a"d, depend- ing on the degree of clogging, causcs greater backwater depths with increased overbank floodin". water pressure on embankrnents and bridges can then result in stress damage or total destruction of struction--fail, large volumes of floodwater may be released unexpectedly into normally habitable areas. A major obstruction to floodflow on Fishers Peak Arroyo is the closed conduit running under the business district. It is rough and eroded, creating considerable turbulence within the conduit. Turbulence decreases the capacity for floodflow and causes further deterioration of the floor and walls. As erosion of the floor continues, the sidewalls will be endangered by undermining. Past experience indicates the conduit IldS serious cloggingprob~""'s, causing d=ging ov"..bank flow throughthebusi- ness district. Other man-made obstructions arc the approach ombank- mcnts for the various r<.lilroildilnd vehicular bridges distributed throughout the study reaches. Table 3 l{sts descriptive structural information for the bridge crossings, and representative photographs are shown in Figures 6 through 12. B "