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~o~d~ AcrQS5 the Stre~m Lena Gulch has 26 roadway crossings which cange from dirt trailstosJperh''lhwdY5. Maj0r' highways 'nclude Ic,tecstat", 111'lhway 70, U.S. Hish'~ay 6 On '1\'. 6th I\ve.. and S'jclte ~'rrl"."y 391 on Kip I in~ Street. T'o'{) of tho rO<lCWilY STructur-"5 ,Kross the e,tr'lam ,~rl) hr,rl'les aM till' r-e~ini"15tr-ucturesdn,..II c"'lverTS. The I ntermnd i;;rte Regional Flood will overtop the 10wapPcOiJChestonostcrossings. The lowest portion of thO roadways is olten s~e distance fr-~ tho cr-eek. cl major- flood The roadway at th!! cr-ook Cr-DSS i t"I<J Is h iOh ~nd drv the appr-Odches are "ndor wator. During whll" 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 sizoofthowaterwayopeningoverthec:reek. The effect of the rOild- way obstructIon 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 reducIng peak flows. Tho IntermedIate Regional Flood is reduced from 5,200 c.f.s. TO 3,800 c.t.s. and the $tand.~rd Proj<><::t Flood Is r"dueoo fr~ 15,'JOOc.f.s.to 13,200c.f.s. If the resarvoir isfullatthastart <..>f .. i ther of tn..se lloods, .. portion of t~lO flood f lows will ov"rtop the ""'bankment. It, 5 flOt known whothor Or not the ove~f low IoIOU Id cause dam failure. HO'.vEVER,INVIEWOFTHECONSEOUENCESWHICHCOULO OCCUR FRC>>-! DA~1 FA I LURE THE RESERVQ I R L~VELS SIIDJLO BE CLOSEL" WITCHED SO TIlE VALLE'!" COULD IlE E~ACUATED IF HlfJAW('-1ENT OVERFlO'A' IS IMNINENT. Table B - page 31 - presonts a SU"mdry of the Maple Grove Reservoir Routlngs. , , ! I , I SANDU<SON GULCH & NORTH SANDERSON GIJLCH. GRQUo 3 Strearnand'lailey:::haracterlstlcs S"nJerson Gu Icr, I S a ""Id I i ~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 ~bout 1.5 miles south of the Denver Federal Center. From its source the stream flows eastward near Jewel Ave. and joIns tne South Platte River neClr west Florida Ave. North Sanderson Gulch Is a princIpal tributary to Sanderson Gu I ch and joi ns The me i n stem 0.7'; ml Ie upst~eam of Sher i dan 81 vd. Sanderson GulCh was stUdied from WadsworTh to Sharld~n Bivd.,adtstenceof 1.6mllas. North Sanderson Guich was studied from Wadsworth Blvd. to its mouth. Sanderson Gulch draIns a 3.4_square mile area above Sheridan Blvd. AnumberofS/llaildilmsClre locClTed on the creek within the study raach. A small lOw flo...chennel....hichvaries from I to 5 feet deep, pClsses through a flood plain whIch is about 200 feeT wide. The North Sanderson GulCh Channel has oeen improved in the urbanized eree 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 platn whiCh Is several hundred feet wide. Development on the Flood Plain The Green 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 flood plil'lnwithinthe studyreech. AfcwOOmosarelocatedbeside the small reservojr bUT the flood plain is otherwise undeveloped. The reach of North Sanderson Gulch between Wadsworth Blvd. and Pierce Street I. devoted to residential deveiopment. The area between PIerce STreet and the mouth, Which amounts to about one-half of the studyr<>ach, Isundaveloped. "