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FUTURE n.cons TABLE 2 Only in rare instances has a stream experienced the largest flood that is possible. Severe as the !O=iInum known flood may hav<' been on a given stream, it is generally accepted that a la~ge~ flood will occur. Larger floods have been experienced on streams with similar geographical and physiographical characteristics as those streams in the study area. Severe ~torms undoubtedly will occur in the study area to cause future floods thAt will equal or surpass known historic floods. Discussion of future floods in this report is limited primarily to those that have been designated as the 100- year flood and Standard Project Flood, however, 25-year and 50-year flood data are presented. Definition of these floods are found in the Glossary of Terms section. PEAK DISCHARGE~ ~RKANSAS RIVER AND TRIBUTARIES LA JUNTA, COLQRAOO Flood Frequencies/Peak Oischarges* Stream 2S-year 50-year laO-year SPFU - King Arroyo Anderson Arroyo 48,000 3,200 4,600 68,000 5,000 7,000 92,000 21~,0()O Arkansas River 7,500 10,500 Cubic feet per ~econd ** Standard Project Flood . Flood Magnitude and Their Frequencies Standard hydroloqic and hydraulic methods were us<>d to d"turmine the mIIgn:ltude of the diacharqe that. would occur during th" flood~ di9C"",,,ml in this TUl'Ort. Peak d:lschar'J"" of till' :!';-Y'..'T, 50-year, lOa-year, and Standard Project Floods are shown In Table 2. Floods larger than the Standard Froject are possible, but the com. binatlon of factors necessary to produce such large flows would be extremely rare. The Standard Project FLOOd for Anderson and King Arroyos were not computed for this report. The 10o-year flood is defined as having an average fre- quency of occurrtlnce of once in 100 years at a designated location, although it may occUr in any year and poSSibly even in successive years. It is repres<lntatlveof floods that have occurred in the past and those that !Oay be expected to r~cur in the future. The IOO-year frequency of occurrence can be expr~ssed in terms of per- ""ntag.. to avoid the posllibl<l inf"renc<l of roqular1ty of "ccurT"I\"". Thus. a flood ",lth a 100 year r"curr"nce interval ","",uld j",vc " "'''. pprcpnt ch"ncc of b"ing equated or exceeded in any year. P<1rhaps more significantly, it hil,~ about a 25 percent chance of oc<,urring during a 30~year mo~tgage period. , I I , I , I I I ! H"zarda of LarqeFloods The hazards to life and extent of damage cilused by any flood depend on the topography of the area flooded, depth "nd dur;>.- tion, velocity of flo"" rate of rise, and developtoents on the flood plains. VelOCities greater than three feet or more are generally considered hazardous to life as well ail. property. water flowinq in excess of four feet per ""cond is capable of transporting sedi- ,"ent and causing severe erosion of streambanks and fill around bridge abutments. Where velocities drop belo", t~ feet per SCCOI~j, debris and silt deposits can build up. Property damage from great floods in developed arcas Can be overwhelming. The entire community suffers ",hen streets, bridges. sewers and other pUbliC utilities a~e destroyed or otherwise toade inoperative. The delineation of what will occur during a flood cannot be totally measu~ed in dollars. The l~ssible loss of life, health and general well-being of a community are items that cannot be measured and must be considered. Adding to the physical haz.ards, a great flood can unleash illness and deadly epidemic disease. Dato- aged or destroynd sanitary s,,",,"gn faciltties can pollute the flood- ""ters and erellte ., health hazard. N",",spapers >lOmetimes H'port .' '" "