FLOOD06593 - Laserfiche WebLink

Home Browse Search

;\ tributaries. The Standard Project Flood for the Big Thompson River at Loveland is 44,000 c.f.s. Hazards of Great Floods The effects of the Intermediate Regional and Standard Project Floods were analyzed to determine the flood potential for the Big Thompson River at Loveland. The analysis was made using bridge and val ley cross sections which were surveyed in February 1970. The water surface profiles were determined using backwater computations employing the Standard Step Method. The head losses at the bridges were computed us I ng data In "Hydrau I ics of Br i dge Waterways" pub I i shed by the U. S. Department of Commerce. WeTr and submerged weir fiow formulas were used with the above whenever water overtopped any por- tion of the roadway. The extent of flooding is shown on the "Flooded Areas" plates. Flood out lines were produced by match i ng flood he i ghts with corresponding elevations at the surveyed cross sections and on U. S. Geological Survey 7 1/2 minute quadrangle maps. These outlines are reasonable rather than precise. For any specific situation, where accuracy is needed, it will be necessary to take the appropriate flood elevations from the profiles or reference date and locate by survey its corresponding elevation.on the flood plain. The Intermediate Regional and Standard Project Flood water surface profi les are shown on the "Prof i Ie" plates which follow the "Flooded Areas" plates. The prof i les show the depths of flooding in the channel, and the water surface elevations to relate the floods to features on the flood plain. The "Cross Section" plaTes follow the "Prof i Ie" plates. The cross seCTions show the nature of flooding across. the valleys. Reference points are listed in Table 2 to pinpoint flood elevations aT intervals along the stream, The reference points are shown on the plan and profile plates and coincide with the location of the cross sections which were used to make the study. The tables include data for reference points - the stream bed belevation,the elevations of the Standard Project and Intermediate Regional Floods, the bearing of the cross sections and special identification info~a- tion where needed. This study shows that broad areas of the Big Thompson plain would be InundaTed by a large flood. During an Reg i ana I Flood depths of 3 feet w j II be common on The Overbank velocities wi I I typically range from 1.5 to second. Overbank velocities around localized obstruc- River flood Greater Floods .F1oods even larger than The STandard Project Flood are possible, but The combination of factors to produce such floods would be eXTremely rare. Such floods are not further discussed in this reporT, although they should not be overlooked where absolUTe safety from flooding is a requirement. I ntermed I ate flood plain, 3.5 feet per ~ i ! tions such as buildings or over roadways wi I I often exceed 6 feet per second. Erosion wil I continue to be a major source of future flood damage. The flood potent I a I descr i bed i n th I s report wi I I be only a reminder TO the people who wiTnessed the 1951 flood. To tho many people who did not experience the 1951 flood, this.report should create a respeCT for the awesome power of the flooding river, [ f ,. L I I I' 15 16