FLOOD08996 - Laserfiche WebLink

Home Browse Search

South Platte River. Heavy rainfall occurred oVer portIons of the northern sectIons of the South Platte River basin on the 14th and 15th of June. As the storm system moved southward, torrential raln- hll centered principally over the Plum Creek watershed on liS June and on the Elljou Creek watershed on 17 Juna. Stonnr1l1nfallofthe period extended over some 3,000 square mIles of the South Platte River basin, IncludlngthePlumCreek,CherryCreek,andSandand Toll Gate Creek watershMs In the Denver region, and the Bijou Creek, Kiowa Creek, Commanche Creek, Badger Creek, and Beaver Creek water~ sheds to the east. Flooding occurred on the South Platte River fl"<)lO Plum Creek downstream to North Platte, Nebraska as a result of this rainfall. I I , j discharges were experienced along portions of the main stem of the South Platte River for most of the month of May and on into June, High water mark data from this flood In Morgan and Washington Coun- tIes is confalned In fable 5. The Flooded Areas, plates 3 through 19S, show the area flooded by this flood. 1969 _ Heavy rains during this perIod started on the after- noon of 4 May and contlnuM with only Intermittent breaks until 8 May. The storm covered an "rea along and near the eastern slopes of the mountains and extended Into portIons of fhe hIgh ptalns. The heaviest amounts were centered Z5milessou.thwestof Qenverand extended In a band along the foothi lis northward to neilr Esfes Park. The weather station at Morrison reported 11 total storm rainfall of 11.27 Inches and" maximum dai Iy amount of 5,77 Inches. General tlooding resulted along the South Platte River, 1973 . Snowmelt runoff from the lower mountain area of the South Platte River basin began about the middle ot April. Rainfall, amounting to as much as 6 Inches, which was the major causative factor of the floodln~ In the South Platt" RIver basin, b"g;}n on 5 May. $harp Increilses In flowilsa result of theralnfllll runoff wore recorded at all ~aglng stations along the South Platte River from Littleton to the Colorado-Nebraska State line. Theralnfalll"uooff was augmented by mountain snowmelt runoff which was also Increasing dUl"ln9thls!'>erlod. The result was generlll fioodlng throughout the South Platte River basin; flooding was characterIzed by high, ~harp hydrOgraphpellksfrO!'1theralnfal1 runoff followed bya slow reces. slon beclluse of the continuing mountain snc.wmelt runc.H, f\;!nkfull Future floods FlOOdS of the same or largor ma9nltude as thoso that have occurred could occur In the future. To determine the flood hazard posed by the South Platte River In Morgan "nd Weshlngton Counties, the IO-year, 50-yo"r, IOO-year, and 500-year floods were analyzod. The magnitudes of these future flOOdS are presented In this report In tabla 6 and in tho form of water surface profiles, stage~ dIscharge curves, flood width delineations, and the relationshIp of these future floods to the flood of May-June 1973. Frequency The 500-year flood is not the largest flOOd that can occur but the probabi I ity of larger floods Is remote. As can be seen from thegllging re<:ords for the South Platte River, discharges smaller than either the IOO-year or 500-year floods aro much more common. Large floods, ~wever, can happen; thIs W~5 Cle;}rly ne~n~traten by the Denver aroa floods of 1965, the Black Hills, South Dakoh area tloods of June 1972, and the July 1976 floods in the Big Thornpson Canyon noar Loveland, Colorodo. Hazards of Larqe floods Tho OKtOnt of damage caused by any flood depends on the topog- raphy of tho area flooded, depth and duration of flooding, velocity of flow, rate of rIse, developments on the flood plain, amount of debrIs in t~", tloodwater, and ice condi tlons, If Ice is a problem In that particular area. A loa-yoar flood or a 500-ye"r flood on " "