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~o~d~ AcrQS5 the Stre~m Lena Gulch has 26 roadway crossings which cange from dirt tra1istosJperh''lhwdY5. Major-highways 'nclude Ic,tecstat", 111'lhway 70, U,S. H1sh'~ay 6 On '1\', 6th I\ve., and S'jclte ~'rrl;",,,y 391 on K;p I in~ Street. T'o'O of tho rO<lCWilY STructur-"5 ,Kross the e,tr'lam ,~rl) hr,rl'l('s aM till' r-('-"'dln;"'] str-uctures dn, ..II cc'lverTS. The Intermndi<rte Regional Flood will overtop the 10wapPcOiJChestonostcrossings. The lowest portion of thO roadways 1s olten s~e distance fr-~ tho cr-eek. cl major- flood -the roadway at th!! cr-ook Cr-DSS i ng 15 h ioh ~nd drv the appr-Odches are "ndor wator. During "hll" Obstructions to Flood Flows Tho roads across th" flood plain oller varying dcqr-ees of obstruction, dep~nalng upon the height o' the roadway emban~nt and si to 0/ thO) waterw~y openi ~g Over the c:reek. The effect of the rOild- way obstructlon On flooding is shown in the Relerence Point taoul~tion. table9d-p"ges53_58, Maple Grove reservoir also r"tards flood flows producing beneficl~1 effects by storing Sane 01 the floodwater and reduclng peak flows. Tho Intermedlate Regional Flood is reduced from 5,200 c, f. s. TO 3.800 c. t. s. and the $tend.~rd Proj<><::t F load Is r"dueoo IrCllO' 15,'JOOc.f.s.to 13,200e.f.s. If the rcsarvoir isfullatthastart <.if .. i ther of tn..se lloods, .. portion of t~lO flood f lows will ov('rtop the ""'bankment. It '5 not knownwhothorornot the overflow loIOuld cause dam failure. HO'.vEVER,INVIEWOFTHECONSEOUENCESWHICHCOULO OCCUR FRC>>-I DA~1 FA I LURE THE RESERVQ I R L~VELS Si-!OlJLO BE CLOSEL v WITCHED SO TIlE VALLE'!" COULD IlE E~ACUATED IF H\fJAf~K'1ENT OVERFlO'A' IS IMNINENT. Table B - page 31 - presonts a SU"mdry of the Maplc Grove ReservoIr RoutlO<;]s. , , ! I , I SANDU<SON GULCH & NORTH SANDERSON GIJLCH. GRQUo 3 Strearnand'lalley:::horacteristlcs S"nJerson Gu Icr, 1 S a '""Id II ~I ,-""" drilln i no e Sma II ~r,," 'e in the southwestern metropolltCln area. The source of the stream Is In the vicinIty of Green Mountain Village about 1.5 miles south of th~ Danvar Faderal Cantar. From its sourca the stream flows eastward near Je"el Ave. and joins tne South Platte River near west Florida Ava, North Sanderson Gulch 15 a princIpal tributary to Sanderson Gulchandjo;ns-themainstemO.7'jmlleupstraamofSheridenBlvd. Sanderson GulCh was stUdied from Wadswor-th to Sheridan Bivd.,adlstenceof 1,6mlles. North Sanderson Gulch was studiad from Wadsworth Blvd, to its mouth. Sanderson Gulch dralnsa 3,4_squara mile area above Sheridan Blvd. AnumberofS/llalldilmsClre loca-ted on the creek within the study raach. A small lOw flowchennel,whichvaries from I to 5 feet deep, pClsses through a flood plain whiCh is about 200 fee-twlde, The North Sanderson GulCh Channel has oeen Improved in the urbanized erea between Wadsworth Blvd. and Pierce Street. The channel averages 4 feet deep with a 35 foot top width. Between Pierce Street and the mouth the channel ilverages 3.5 feet deep with a 14 foot top width and meanders through a flood plaIn whiCh Is several hundredfectwide. Development on the Flood Pla,n The Grecn G"bles Golf Course occupies O.6mlleof the Sanderson Gulch flood plain downstream of Wadsworth Blvd. This golf course and the reservoirs occupy all but a 2,000 foot length of the fload plil'lnwithlnthe study reach. AfcwOOmosarelocatedhes;de the small reservojr bu-t the flood plain is otherwise undeveloped. The reach of North Sanderson Gulch between Wadsworth Blvd. and PierCe Street Is devoted to residential development. The area between Plerce STreet and the mouth, Which emounts to about ona-half of the studyr<>ach, lsundaveloped. "