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I I \ [a~ard. of Large Flooos The hazards to life and extent of damage cause~ by any flood depend on the topography of the area flooded, depth and dura- tion of flooding, velooity of flow. rate of rise, and developments on the flood plains. future iloods of Intermediate Regional or Standard Project magnitude On Fountain Creek and tributaries would inundate residential. commeroial, and industrial developments in P~nitou Springs and west Colorado Springs. Velocities greater than three feet per second combined with depths of three rcet Or more are generally considered hazardous to life and property. Water flowing in excesS of four fect per second is capable of transportinu sediment and causing severe ero- sion of str~ambanks and fill around bridge abutments. ~~ere veloci- ties drop below t~~ feet per second, debris and silt deposits can b~ild up, extending tte flood cla~gee ana creating adverse heal~t conditions. The saturation effect~ of prolongecl flooding Can weaken bridge ab~trnents, lev",,,,", aI'.d other ,,;e.bank"'cnt works sO they fail as the floodwaters recede. flooded Areas and rlood Damage Plate 2 is an index ~ap for Plates 3 through 8 which show the areas along Fountain Creek that will be flooded by the Intermediate Regional Flood and the Standard Project Flood. Depths of flow for any location on the streams can be estimated fron the high water prOfiles shown On Plate$ 9 through 14. Floodwater ele- vations determined in any particular arca are not always indicative of the depths actually Attained. Often floodwatees become isolated and entrapped in overbank areas resulting in depths greater than those ShoWIlon thc high "ster profiles. Plates 15 and 16 show selected cross sections that are typical of the sections surveyed in the study reaChes, all ceoss section locations are Sho~l On the pro- file platea. StreAm characteristics determined from topographic maps, aerial photographs, and valley cross sections were ~sed to compute and define the flood situation. ?ro?erty dama7e from floods in developed areas Can he ovcrwhel"ing. ':'he entire cown~nity suffers when streets, bridg€s, sewers, and other public utilities are damaged or de$troy~. Adding to the phy..ical M=r<i~, a flooo ",a" unl..,,~h d.."oly epiuemh' d.is,,".~"s. S~nitary sewers becom~ pressure lines, blowing manhole covers and spew-ing raw aewage iI'.to the floodwaters: sew"g" treatOlent plants a~d feeder lines can be washed out: stockyard waste can add to the pollution and ha~ard of an epidemic disease. ~ewspapers sometime repOt"t a "ligl-.ter side of the r.c",s" in picturing childr"" atphy in the mud 11nd water left by a receding flood. IJnfort\.mately, tl:c Velociti~s, Rates of Rise, and Duration rhe o~currence of the Intermediat~ RGgional ar Standard Pr"ject Flood would result ir. t!1e flood characteri~tic~ shown ia Table 4. this data reflects the averaged maxi:m.u\\ conditions .lith heights of rise, rates of ri~e, and durations of flooding meAsured above bankf~ll stage. Floodflow velocities depend upon the general waterway configuration, and the size, shape, and slope of streambed and over- bank flow arcas. Velocities may range from the maximums appearinq in Table 4 to less than 50 percent of the~e values. Obstructions " Of major cOncern is maintenance of channel and overbank capaCity of a stream to convey floodwater~ without causing serious flood damage. Reducing waterway openings by approach embankments at bridges and changing channel and overbank capacities will impede flood flows and cause greater backwater clepths with consequent increase in flooded areas. c"ntamination t!-,r~l\t to d","~sti" ",,_er s"I'rli~s ~~.~T\"t. ,,,, .il1u~~ trated with similar ea~e. "