Laserfiche WebLink
<br />MEMORY TRANSMISSION REPORT <br /> <br />PAGE :001 <br />TIME W1Y-19-01 11:16AM <br />TEL NUMBERI: +13038663567 <br />NAME :Colorado Division at Minerals 8 Geology <br />FILE NUMBER 190 <br />DATE MAY-18 10:51AM <br />TO $3034237599 <br />DOCUIENT PAGES 006 <br />START TIME MAY-19 10:59AM <br />END 711E MAY-IB 11:16AM <br />SENT PAGES 006 <br />STATUS OK <br />FILE NUMBER :190 *** SUCCESSFUL TX NOTICE *** <br />STATE OF COLORADO <br />DIVISION OF MINFMLa ANO GEOLOGY <br />wn.nw..... ur N.,u,.l e•.ou.t.. ~~ <br />1f.3 al.w.m.n 5... Ream ]le <br />ounw.. ceior.mw eo]ot ° <br />iw n.: a]n]i wee-]set M 1 Ns E R A L 5 <br />Iso]I w] t-a 1 oe 6. <br />G E O L O G Y <br />May 17,200] I Q~wf.~.f y~('~ic°rd <br />Rocky Ho[Cachneider <br />Platte Sand 8c Gravel LLC <br />P.O. BOX 1 g0 c..s s. w.orclrr <br />Linleton, CO 80106 t~`.n~. ~~ <br />o' :Rea <br />oia:w. ~ <br />R8: Riverbank avd pit Slope Armoring Propwal, Tecbvlval Reylslav <br />to SdkB Mlva Sactlon 11~ Ramlamatlon Permit Applicatiovt Platte <br />Va/lay 9avd and Gravel. File Ho. M-2D00.13B <br />Dear lV1r. H°ffschneider, <br />Piave Smd $ Oravml LLC has provided n technical revision (TR) m further eddroas eoncmrna with erosion <br />potmtlel through the gravel pit mining cells during a large flood avrnt. Tha TR includss m 111usvstlon of <br />lorations that the Appllcmt has dewrmiaed to be s s:cive me with the powndal for azcaaslve sro The TR <br />inoludee a proposal and designs m awbilizs cerwin of these po[m<islly smnsitive areas by armorhtg through the <br />placement of riprap. T{te TR also includes cost estlma[es for the placsment o£riprop and a deacrlptlon of the <br />timing of riprap installation relativs m the sequence of exeav atlon :n the gravel plea. The Division's rov.ew of ehe <br />TR is brolcmn oux into { ur xmriona in this memotsndum as follows: <br />• The determination of lemaxlone that may be saltiaee to erosion during a largo flood. <br />• Ths spaciflcndon and drawings that will govern the sizing and placement of riprap. <br />• Tho matimawd moat m purchase and tska delivery of riprap that moats apeclficaxlon, and to Install the riprap k <br />ammordance with dcaigna and drawings approved by dte Division. <br />• The timetable for riprap insrdlatioa, in particular the :nawll lion of the riverbaNc riprap. <br />As a reminder, the purpox oP the flood convol/mitigation plm is to minimize the potenelal for aataess:ve scouring <br />and croa:on of pit aloyes and of berms proxeoting critical atrtacmros ouch ns gm p(pclines, and of otTiite lanpaccv <br />due to xdimentntion or realignmenS of the existing river channel. <br />R~rgp Zocpriorv <br />In ordsr m prwmx excessive erosion, areas that may be subject xo scow dur[ag a flood Ytould be ermorsd. To <br />identify oKV o£aeour, the depth and veloeiry of floodwaters should be metimatsd and the gradation of rho soil and <br />subsoil (sand and gravel) may be axarnlned along with vegetation characterlstica m detartnine if the erosive power <br />of the flood will mu[ into the vegetation and soil. Placemrnt of lsrger and haav:er material (riprap), ehae eannos bs <br />IiRed and moved by floodwnwr, will prevent a and down cursing in locations identified m be Drone m scour~ <br />Thera era a number of published mempuweional methods available to dataatn ine dte sizing and gradation oP riprap <br />required to armor against erosive flows of d:ffbrsne veloelties. <br />Depth and veloa(ry of floodwarnr incrcmea ezpoaentlally in flood NenL of Incrcaaingly lower probablliry of <br />Tfia wn-perount mravsl mhanoe flood (floe • called wet-yesr flood) results in a aubsv+atlnlly lower <br />flow, depth, and velomiry than cone-peroent m ua1 ehanme flood (thm 100-year rexurn period mvvnt). Dewlgna fbr <br />armoring against erosion during a 300-year flood would most likely fail during a much larger. but )ongar rvnam <br />