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90,OOOcubicfeet.persecor.d. Flood Characteristics of the lnter- mediate Regional Flood for averaged ~xi~um conditions within the study reaches are shown on Table 1. llazardsofFloods The hazards to life and eKtent of danage caused by any flood depend on the topography of area flooded, depth and duration of flooding, velocity of flow, rate of rise, and developments On the !loodplio.ins. Velocities greater than three feet are generally con- sidered hazardous to life and property. Water flowing in e>:cess of four feet per second is capable of transporting sediment ar~ causing severe erosion of streambanks and fill around bridge abutments. ~~ere velocities drop below two feet per second, debris and silt deposits can build up, eKtending the flood da~ages and creating adverse health conditions. The saturation effects of prolonged flooding oan weaken bridge abu~ents, levees, and other structural works so they fail as the floodw~ters recede. Propcrtydamage from floods in developed areas can be overwhelminq. The entire community suffers when streets, bridqes, sewers, and other public utilities are damaged or destroyed. Add- ing to the physical haz~rds, ~ flood can unleash deadly epidemic di...."ses. Saniwrysewersbecomepressurelines,blowinq:nani'lole covers and sp~wing raw sewage into the floodwaters, sewage treatment plants and feede~ lines can be washed out, stockyard waste can acid to th~ rollu~ion a~d ha2ard of ,,~ cpidc~ic dice~~c. Ncwcp~pcr~ sometimes report a "lighter side of the news" in picturing children at play in the mud and water left by a receding flood. Unfortunately, the oontamination tl~eat to domestic water ~upplie~ cannot be illus- trated with similar ease. Standard proiect Flood The Standard Project Flood is defined as the flood that can be expected fromthernost Severe combination of ",eteorological and hydrological conditions--e>:cluding eKtremely rare oOmbinations-- considered Characteristic of the geographical reqion in which the drainage basin is located. The Standard Project Flood represents the reasonable upper limits of eKpected flooding. The S~ndard Project Flood, with a peak digcharge of 160,000 oubic feet per second will be about 80 percent as larqe as the June 1965 Arkansas River flood which had a peak discharge of 200,000 cubio feet per second. Flood characteristics of the Standard Project Flood for averaged maximu~ conditions within the study reaches a~e shown on Table 3. Frequency of rloods The rntermediate Regional Flood is defined as having an average occurrence fre'~ency of Onoe in 100 years at a desiqr~ted location. It is impracticaL however. to assign a fr"quency to t\"le greater Sta~dard Project Flood. Floods larger than the Standard Project Flood are possible, but the combination of factors necessary to produce s~ch large flown would rarely OCour. For purpo~cs of ha~ard evaluation, it is important to recogni~e that either of these major floods oan oocur in any year and possibly in successive years. Areas Subject to Flooding The study areas subject to possible future flooding, under existing and post-project conditions, by the Intermediate Regional and Standard Project Floods are shown On Plates 2 and 3. Depths of flow under existing and post-project conditions can ~ estimateJ fro~ the flood profiles shown on Plates 4, 5. a~d 6. App.4 n App.4 "