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<br />utilities wexe heavily d~~ed as well as individual watex supply <br />and 5ewa~e disposal systems. A low levee to pxotect against ~inox <br />ovexflows on the Axkansas Rivex was lost and two bxidges were <br />damaged. National Guard assisted in the evacuation of 5DO~lOOO <br />people in Noxth La Junta. <br />About 300 residenoes were flooded in La Junta, 8 to 10 <br />blocks on the south side of town flooded. Damages were estimated <br />at $4oo,00Q. A county bridge west of town washed out. The Arkansas <br />River crest at La Junta was 14.2 feet (about 54,000 cubic feet pex <br />second) at 1:30 p.m. on May 20. <br /> <br />FLOOD SITUATION <br /> <br />Flood Season and Flood Characteristics <br />Storms ovex the up~r Axkansas Basin can be of the general <br />type charactexized by low~intensity, long-duxation rainfall over a <br />large area, and a shoxt duration rainfall and high intensity over <br />a small axea. The fc~er are most pxevalent during the aut~, wintex <br />and spring seasons. Thunderstorms are most active during July and <br />August, although the two laxgest and ~st destxuctive floods of <br />xecord occurred during the month of June when general storms concen~ <br />txated in a sexies of intense cloudbursts QVeX the foothills and <br /> <br />May1969 <br /> <br />Flood flows from Anderson Arroyo damaged about 35 re~l- <br />dences and businesses in La Junta. This floed also damaged a sani- <br />tary sewer line, city streets, farmsteads, cxoplands and fences. A <br />few livestock were lost and some hay was damaged or washed away. <br />The total estimated damages for this flood amounted to $144,000. <br />Some minox damage occurred to the Otero Canal. This canal crosses <br />Anderson Arroyo about five miles uPstream from the mouth. <br />Similar types of damage were expexienced in 1965 and 1972 <br />except to a lessex degxce. <br /> <br />plains axell... <br />Floods on the Arkansas Rivex are of two general types. <br />one type is represented by "spring flOOds" Which result frOM mel- <br />ting snow and ar'" often augmented by storm runoff. The other type <br />is repre8ented by "swnmer floods" which result entirely frOM stono. <br />runoff. The spring floods are characterized by comparatively modex~ <br />dte rates of flow of long duration with large volumcs of runoff. <br />The summex floods are characterized by high peak rates of discharge <br />with relatively smaller volumes of xunoff. <br /> <br />ractors Affectinq Flooding and Theix Impact <br />Obstructicns to Floodflow. Obstxuctions, natuxal and man- <br /> <br />ma.de, wiehin floodways impede floOOflow5, <.:r"..Lin'l w<.:kwater and <br />increased heights. Debris washing downstream during floods often <br />collects against bxidges or within restricted flow areas, xeducing <br />watexway openings and impeding the floodflow. This creates a dam- <br />mingeffectand,dependingonthedegreeofcl<>9ying,causesgreater <br />backwatex depths with incr.,...s..d overlMnk flooding. Also, a pxonounced <br />increas~ in flow velncities usually occurs downstream from an obstruc- <br />tion, thus extending the flood damage potential. Ma""'ad~ obstruc- <br />tions on or ovex the floodway such as da~s, levee$, bridge$ ~n~ <br />culvnrts can aha cr<>atc more exeensive floOdinq than w"uhi "Lh"'Wb~ <br /> <br />o~'cur. <br /> <br />H <br /> <br />l~ <br />