FLOOD08469 - Laserfiche WebLink

Home Browse Search

r IV-3 I TABLEIV.l SEDIMENT YIELD - SOUTH PLATTE RIVER [ Annual Sediment Load River Location T(ms [ South Platte River Chatfield 33,000 Bear Creek Mouth 4n,OOQ [ Cherry Creek Mouth 300.000 Sand Creek Mouth 150,000 I Clear Creek Mouth 100,000 Other tributaries Mouth aO,MQ I South Platte River Henderson 1,000,000 Exposedutllitylines Bridge pier scour Caving river ~anks Eroded trees and resulting debris Lostayricultural1and Breached gravel pits Erosion downstream of dams and drop structures Headcutting on tributaries lowered groundwater tables Increased channel capacities Lost aquatic habitat Lost riparian habitat Changes ;n benthic invertebrate species I loIithin Denver, the se<jiment load has been reduced 95 oercent due to Tri_ lakes. At Hend€rson, theestimdtedsediment load has been reduced 80 per- cent, to 200,OO~ tons/year. Erosion The South Platte River is actively erOding its banks ~herever it is free to do so with the absence of controlled drops and adequate bank riprap. Effect of RecClrm1ended Plan The recOlll1lended plan will provide protection against erosion in Reach 1 prirnarlly through use of natural ve<Jetation in keeping ~ith the natural character of the river, In areas wh..re th.. river i~ in danger of ,;,rodinq berms protecting gravel lakes, riprap should be used. No measures to pre~ vent channel degradation are included in the plan. This plan recOllJllends managinqdowncuttingtoachievethegoalsofthedesiqnplan. I I I I [ I An inventory of condit ions and structure~ in the river channel is present€d in Table VllI-2 of the Phase A report. The inventory was based upon a field inspection of the entire forty rnl1e study reach. Estimates of bed erosion have been marle by Stevens (1983) by comparing historical 1963 data ~ith 1983 river bed conditions. In Reach 2, the Corps project will prevent erosion and degradation of the channel, Impacts of Erosion The erosion of the South Platte River has consequences. Damages experi- enced include th.. followIng: In Reaches 3 through 7 erosion will be controlled by using rockriprap in areas where d0?9rad~t ion is expected and in areas where there are ex i st i ng problems. Thi 5 protect ion ~i 11 be prov ided at the 2 to 5 year flood levels. Above that level natural vegetation and grass wnl provide needed protection except in a few problem areas and will stop the loss of riparian ha~itat occurring at thi s time. The exist ing tendency of the channel to degrade, except behind Check structures, will be utilized to deepen the Channel in a controlled fashion by r€<T1oving or lowering control structurt's.