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[ 11-1 [ I I I I I SECTlONlI STUDY AREA DESCRIPT!O~ Prior to the advent of irrigation. the ch~nnel width ranged from 1,500 to 2,500feet'..ithl1ultiplethalwegs. The raised water tableandcontinoous stream flow resulting from irrigation causel1 the river to change to a single thalweg channel and reduced channel width. GEOGRAPHIC LOCATION The South Platte River Master Drainage Plan includes the South Platte River frOOl Chatfield Resenoir in Jefferson County to Baseline Road in Brighton. The study area includes the D/>nverMetropolitan area. The South Phtte River flows in a valley cut into the landscape during Pleistocene or recent times. The valley floor is protohistoric and his_ tor i ~ all uv i urn. most 1 y reworked gravel over 1 a; n by a few feet of dark humus. I I HISTORICAL PERSPECTIVE In the 18!>0's the So~th Pl atte River served as a waterway and trai I route for traosportatioo of supplies aod ilTlllligrants to the west. It began to deteriorate io quality as the populatioo of Oeover increased. The profile of the river from Chatfield to Brighton is generally concave downward as expected with alluvial rivers. The dveraqe river bed slope from Chatfield Dam to the mo~th of Clear Creek is approximately 13 feet per mile. Thereafter, the average slope decreases to approximately 9 feet per mile to Brightoo. Where there are no major tributaries, the general river bed slnpeof the South Platte River rernains constant. Bed slopes of all l1ajor tributaries are"uchgreater thoo that at themainstem. I The history of the South Platte River began to change for tile better io 197~ when the Platte River Oevelo~€nt Committee initiated the task of restoring the river to its fonner importance to the city. ThiS qroup, using p'Jblic and private funds, started this task 'Nith thedevelojll1lentof Confluence P"rk at the confluence of Cherry Creek and the South Platte River. Later a system of trails andgreer.ways along tile river and J general cleaning uo of the river envirortment encouraged th~ recreaUoTldl use of the river corridor. In addition, boat ell utes were coostructed at several major dams to ellcourage boatinq on the river. I I I l I , GF.OLOGICSHTlNG The South Pl atte has b~en nU!11~rousl y d",scribed as "too thick to drink, too thin to Farm, too shallow to sail on, too broad to shoot a ri fl~ acros,." III Its prist ine state, the South Platte River adjusted its width, d~pth and sinuosity in re~ponse to thl' amo~nt and typ~ of ~ediml'ot ~nd ilIl1(1unt of water supplied to it by its tributaries. In the 1880'5 dgriculturebegan on the $o~t~ ~ I at te River and the character ot the r ;ver was forever altered. ~E~IOUS STUOIES rhere have been no prevfousmaster plan ,tudieson the South Platte Rj'ler t.hroughDenver. The U.S. An11yCorpsof Engineers completed stlldies of tile So~th Pl atte River and its tributaries through Metropol itan Denver in 1974 and 1977. These studies were floodplain information re!}Orts whiCh delin- f'atedthefloodplain and identified flood problems. Themainobjectiveof th(>~~ ~tudi~~ w~~ to nrllmotp non-structurdl floodplain management. In 1977, Gingery Associates, Inc. prepared a flood haurd delineation for th(> So~th Pl atte River through Adams County. Thi s ',;tiJdy used hydrology pre. pared My the U. S. Army Corp~ of Engineers. In 1'183, the Federal Insurance Administration prepdred d drdft flood insurance map for the City of Denver. This map al<;o WdS based on previous Corps of En'1ineersstudies. Numerous other flood insurance stiJdies have been prepare,j for stlortreachesofthe river for various municipdlities throuqh whiCh thp river flow~.