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<br /> <br />. <br /> <br />agri~ultural purposes. Most of the new construction--primarily <br />residantial__i~ located in the vicinity of ford Lana, U.S. Hign- <br />~ay 50, Or 27th Lare. This development trend no~ appears to be <br />gai~ing momentum, but agrIculture and ~tock-gra~i~g Betlvitle, <br />remain dominant. <br /> <br />. <br /> <br />Trensportetion facilities in the flood plain include <br />portions of U.S. Highway 50, 85-87 (Interstate 25), various couo_ <br />ty roads, and rei 1 lines of the Denver and Rio Granda Western <br />Railroad Company (O&RGW) and the Colorado and Southern Railway <br />Company (C&5) Five vehicular bridges and ona railroad bridge <br />span the river channel and ~rOaS the flood plain. The railroad <br />bridg~ i8 used jointly by the twe r~ilroad companies mentioned. <br /> <br />TABLE: 1 <br /> <br />ORAINACE AREAS IN WAT(RS~EO Of ST. C~ARLES RIVER <br /> <br /> Mile <br /> Abave Drainage <br />Loclltion ~ Area <br /> 'q. miles <br />" rivermauth 0.00 '" <br />Below Creenhorn River cO'1flue'1c" 18.45 m <br />Above Cree'1horn River co"fluence 18.80 189 <br />Below Sti'1ki"9Hrroyo confluence 27.07 in <br /> <br />. <br /> <br />Bridoe,; across theStrearn <br />Three vehicular bridges cross the St. Charles River <br />at paints within the 10w8r 10 miles of the 27.6 mile study reach. <br />The other two vehicular bridges and single railrOlld bridge are <br />located within the upper 10 mile segment. Photographs of these <br />bridges appear i'1 figures 1 through 3. Desoriptive struotural <br />informatio'1 and pertinent elevotio'1s are listed in Table~ 2 <br />a'1d3. <br /> <br />. <br /> <br />" <br /> <br /> <br />During the Intermediate Regional flOOd and Standard <br />Projeot flood, the U.S. High~~y 50 bridge would not be overtopped, <br />although floadflaws would top the high~~y as it crasess the flood <br />plain. The South Road and Interstate 25 bridges would be Over_ <br />topped by ons or both flood eve'1ts, while the 27th Lane bridge <br />wauld be overtopped by the Standard Praject fload o'1ly. In CO'1_ <br />trast, the tops af raile on the railraad bridge would be 22.2 feet <br />and 42 feet ebove the respective flood ~rests. [~oess1ve head <br />losses would cause increased depths of flow immediately upstream, <br />from e~~h af the bridges. <br />Depths of flow at bridges wauld be effected by the de_ <br />gree of etruotural obstruction and clogging of waterway openings <br />that occurs during flaods. for etudy purposes hersin, it has bee'1 <br />assumed that limited clogging Can be e~pected end ell bridge struc- <br />tures would stand intact. Sig'1ificant changss in this premise, <br />imposed by difforing cO'1ditio'1s of a future flood, cauld alter the <br />estimated flood crests and related fload limite shawn. <br /> <br />Dbstructior,stoFloodflow <br />Thseffe<:t ofobstructio'1e dCJe to bridges "ndtheir <br />approach fille has bee'1 described in previnu$ paragraphs. New <br />development and futCJre lS'1d-filling i'1 or near the river Channel <br />oould obstruct floodflowe ~nd c~use increasnd depths. These con- <br />ditions af greater hazard Oan also occur where trees and under_ <br />brush are allowed to grow without reetraint within the flowage <br /> <br />arca. <br /> <br />FlaodRecords <br />Stream stags and discharge recards which derive fram <br />stream gagin9 stations on the study reach are fragmentary or other_ <br />wise inadequate for accurate determinations as to the characteris- <br />tics of past floods. These records include limited flow dat~ ob- <br />tained from a gaging station maintained '1e~r the mauth of the <br /> <br />13 <br />