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CHAPTER 2 <br />HISTORY OF FLOODING AND FLOOD PR.OTECTI~N <br />INTRODUCTIO~N <br />Storms over the upper Arkansas River Basin can be chazacterized as low-intensity, long duration <br />rainfall over a large area, or short duration thunderstorms of high inter~sity rainfall over a small <br />azea. The former is most prevalent during the autumn, winter and spring seasons. <br />Thunderstorms aze most active during July and August, although the two lazgest and most <br />destructive floods of record occurred during the month of June when ~eneral storms concentrated <br />a series of intense cloudbursts over the foothills and plains areas. ' <br />Floods on the Arkansas River are of two general types. "Spring floods" resulting from melting <br />snow are often augmented by rainfall runoff. "Summer floods" result entirely from rainfall <br />runoff. The spring floods are characterized by comparatively moderate rates of flc~w of long <br />duration with large volumes of runoff. The summer floods aze chazacterized by high peak rates <br />of dischazge with relatively smaller volumes of runoff. During the swnmer months, the entire <br />state is subject to convective thunderstorms that aze capable of producing lazge amounts of <br />rainfall over a very short time if humidity is present in the atmosphere. In eastern Colorado, <br />these storms are typically supplied with moisture drifting in from the Gulf of Mexico and the <br />central plains states. In midsummer and later, monsoonal wind patterns also bring moisture from <br />either Baja California, the Gulf of Mexico, or both. This moisture moves into Colorado after <br />coming northward across Mexico and the southwestem United States, and is the source of many <br />late summer storms in Colorado. <br />~ARI~Y FLOOD HISTORY <br />Historical accounts of early travelers and trappers includ~ references t~~ many major floods in the <br />Arkansas River subbasin in Colorado prior to the period of reliable records. The eazliest known <br />flood on the Arkansas River occurred in 1826, long before permanent settlement of the valley, <br />and was reported to have inundated the bottomlands near the present location of Las Animas to a <br />depth of 15 feet. In 1859 a wagon train reported that the Arkansas River flooded to a width of 2 <br />or 3 miles in the vicinity of present day Lamar downstream of John Martin Dam. The June 1864 <br />flood on Monument Creek north of Colorado Springs caused the loss of 13 lives. During May- <br />June 1867, flooding was so extensive in the Arkansas River valley that Fort Lyon rvas forced to <br />relocate 17 miles farther west to a site on the north side of the river just downstream of Las <br />Animas. Large magnitude floods also were reported in July 1885, Jul,y 1886, and May 1894. In <br />August 1904 the runoff from a local cloudburst over Hogan's Gulch, a. small tributary of the <br />Fountain River located about 8 miles north of Pueblo, washed out a railway bridge over the <br />normally dry arroyo causing a major train wreck which resulted in the loss of 100 lives. Property <br />Chapter 2- History of Floodin~ and Flood Protection <br />Post Flood Assessment Report~ 5 Draft Revised 09/09/99 <br />