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On the flood plain. Future floods of Intermediate Regional or Standard Project Flood magnitude on Sixmile Creek would inundate the roads and the few small buildings located in flood plain limits. velocities greater than three feet per second combined wIth depths of three feet or more are geno:.rally considered hazardous to life as well as to property. Water flowing in excess of f~ur feet pcr second is capable of transporting sediment and causing severe erosion of stream banks and embankment fill around bridge abutments. When velocities drop below two feet per second, debris and silt de- posits occur, extending the flood da~age and creating adverse health COnditions. 'I'hesaturationeffectsoffloodingoflongdurationcan effectively weaken bridge abutments, levees, earthen dams and other embankment works so that they fail. Proper~y damage from great floods in developed areas can be overwhelming. The entire community suffcrs whcn streets, bridges, sewers and other public utilities are destroyed or otherwise made inoperative. In addition to the pl'lysical hazards, a great flood may contribute to illness and eV~n d~adly epidemic dis- eaSe. The waste from sanitary sewers and stockyards can become mixed with surface flood waters. Treatment plants and sewage lines may be washed out. The threat to the health of inhabitants is always a major concern during floods. Flooded Areas and Flood Damage Plate 2 is an index map for the succeeding Plates 3 through 6 Which show the areas that would be flooded by the Standard Project Flood and the Intermediate Regional Flood on Sixmile Creek. Depths of flow for any given river location in the study reach can be estimated from high water prOfiles shown on Plates 7 through 11. Plate 12 shows selected cross sections of the river that are typical of the local reach of the river from Which they were taken. All crOSg section locations are sho~~ on the flooded areas and profile " . plates. Stream characteristics determined chiefly from channel cross sections, topographic maps and aerial photographs were used to com- pute and define the flood situation. Floodwater elevations determined at any particular crOSS section are not always indicative of the heights actually attained. Often, floodwaters become isolated end entrapped in overbank areas resulting in flood elevations higher than those shown on the high W>lterprofiles. It can be Seen from Plates 3 through 6 that the most severe accumulations of flood waters occur at the roadway embankments and bridges where culverts of inadequate capacity or constrictions due to bridge abutments allow only limited flood flows to be passed without causing overtopping of the structures. All five bridges or roadways crossing Sixmile Creek will be inundated by both the Inter- mediate Regional Flood and the Standard Project Flood. The few houses and farm buildings located within the flooded area limits of Plates 3 througl'l 6, especially those struc- tures at Mile 3.5, will probably be damaged extensively by the Inter- nediate Regional and Standard Project Floods. rtshouldoonotedthatinthecilseofhighsimultan- coue flood flow3 o~ t~a Arkan~a~ Ri7c~ ~~cl'l more 3a7are floo~i~~ will occur at the mouth of Sixrnile Creek than under flood situationn . . limited tc only the Si~ile Creek Basie. Tr.e severity cf th~ situ~- tion in the case of simultaneous flooding would depend On such factors as the frequency of flood occurring on both streams and tl'le time relationship of the peak flow periods on both streams. For the purposes of this report the most severe conditions were ass~.ed; thus for the Standard Project Flood On Sixmilc Creek the s~~e frequency with simultaneous peak flows was assumed on the Arkansas River. The same also applied for the Intermediate Regional Flood. . "