PERMFILE60699

• Permit No: M2000158
• IBM Index Class Name: Permit File
• Doc Date: 5/18/2001
• Doc Name: Riverbank Faxes
• From: DMG
• To: PLATTE SAND GRAVEL LLC
• Media Type: D
• Archive: No

MEMORY TRANSMISSION REPORT
l~
PAGE :001
TIME :MAY-19-O1 10:43AM
TEL NUMBERI: [phone]
NAME :Colorado Divlslan of Minerals l Gealoay
FILE NUMBER 197
DATE MAY-19 09:59AM
TO : 819703566496
DOCUMENT PAGES 006
START TIRE MAY-19 10:39AM
END TIME MAY-18 10:43AM
SENT PAGES 006
STATUS OK
FILE NUMBER :197 *** SUCCESSFUL TX NOTICE ***
STATE OF COLORADO
OIV ISION OF MaNIRALa ANO GEOLOGY __
LIaP.~rm.n, OI Nalutal Rewurcar
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May 3 7, 2001 G E O L O G Y
n°I+ICV Ct-'pi's°rv
Roeky Hoffscltneider
Plate Savd ec Gravel LLC
P-O. HOX ] BO
Littleton, CO 80106
Pet-1t~ Pnx Nota '10'rl aT B
Ca ee.
PFOn• 1[ Pnm.
-~
ELT,.a lilysrbanl[ apd Pic Slops Armoring Proposal, TecbnlcPl iievlalov
to SdkH M1ae Semtloa 113 Raelamatlon Parmlc ApptutloPa Platte
valley 9nad and Grayel. Flla No. M-3000.138
Dear Mr. HofAchnslder,
ce..° e:
..1 n. `r.r:s,
Plnte Swad do Grat.el I-LC has provided a technical revision (TR) to fwtlasr address concerns with erosion
potential through she gravel pit mining calls during s large Hoed evsn[. The TR includes an 111vrtraUOn of
locations that the Applicant has dmisrmined xo be aencicive areas with the potential for exeessive erosion. Thm TA
ncludsa n proposal and deslgtls tm ernbllize cer[ain of Uteae potsnsially aenaitive eroY by armoring through the
placemen[ of rlprap. The TR also ipcludea core eacimewa for Ne placsmens of riprsp and n dsseriprion of the
timing of riprsp insrallacion telmiys ro the eequsnce of excavae:on In the gravel piv. The Divislon•a review oCrhe
TR is brokso our into four aaoUons in Chia memorandum as follows:
The demrm lnetion of locations that may ba subjeet co erosion during n large flood.
The speciFcation and drawings that will govern the sizing end placement of riprsp.
• The animated soar to purohase and tales dslivaty of tiptop that meera apeeifleasion. and to Install the riprsp in
accordance wiUt designs and drawings approved by the Division.
• The Umamble for riprsp installation, in pvtieuler the Inrtallacion of the rlverbardc riprsp.
Aa a rasrainder, the purpoas of the flood controLmitlgncion plan fa co minimise the potential Tor sxceaslve acouring
and sroslon of pit slopes and of bsrms protecting critical strummava such as gas pipelines, and of otFSita Irnpacu
due to aedimsnratlon or realignment of the exJsting raver ehannel.
R(P/'eP LocnNoar
In order m proven[ axcecsivs sroslon, area Nat may be aubjeec to ac au during s flood should by armored. To
identity arm_ of scour, the dsptb and velocity oPfloodwatmrs should be sarimatsd and the gradation of [he soil and
subsoil (sand sad gravel) may be axamitted along wilt vegesation charvcreriecics to dererm ins if the eroeivs power
of the flood wil I mat into the vegeuc:on and soil. Placement of larger and heavimr material (riprsp), these eannox be
IiRed and moved by floodwamr, will prsvent erosion and down cursing in Iocaciona identified m be prone m scour.
There are a number of published compura[ional msrhoda available [o detvrm ins the sizing and gredaUon of rlprap
rcqulaed to armor against erosivo tlowa of different vslocitiea.
Depth and velocity of floodwater Increases exponentially in flood evsnrs o{ increasingly iowar probablllry of
ocmuateace. The tea.-pea,=ant a ual mhaame flood (rho so-called tm-year flood) R ulia In o subatantelly lower
flow, depN, and vsloolry Nan a ono-psroenr annual chancm flood (Use ] 00-year return period evanq. Designs for
armoring agalnrt eroalon during e 1 OD-year flood would Mort likely fail during a much larger, but longer return