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

PAGE :001
TIME :MAY-18-O1 10:11AM
TEL NUMBERI: [phone]
NAME :Colorado Division of Minerals i Geology
FILE NUMBER 161
DATE MAY-18 09:54AM
TO : 83039931379
DOCUIi~NT PAGES 006
START TIME MAY-IB lO:OBAM
END TIME MAY-IB 10:11AM
SENT PAGES 006
STATUS OK
FILE NUMBER :181 *** SUCCESSFUL TX NOTICE ***
STATE OF COLORADO
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May 17, 3001
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L:t[leton, CO 801 Od "~ o~~ ~••
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BTi.r RlvarbePlc end PI< 61o1r Armoring Propwel, ToehWeal Rev:e[on
to Sdk13 Mine BacHOe 112 Ssc]emetfon Permit AppllcnHoa, Plate
Yaliry seed nod Gravel, File No. M-2000-158
Dcsr Mr. HofTechneider.
Platte Sand dt Ormve1 LLC has prow:dad a [sclanicsl rev on (TR) ro Purther addrcvv concerns with aroafon
pot<n<isl shrough the gravel pix mining calls during a largo flood c cnr_ The TR includes nn illuvtra[:on oT
locations xhnx the Applicant has determined to be eenalxlve Braes with the potcntiel Por excessive erosion. The TR
cluds a propowl and devigna xo avb:lizc cerWn of them porenxially sensitive areas by efia ng through the
pleeemon[ of riprap. The TR also ioeludea Dour cs<:mama {or the placement of r:prmp and a deseriprion oTthe
aiming of riprmp invmllaxion rclaxive xo iha sequence of ezeevs[ion :n the gravel pits- The Divia:on'e review of xhe
TR is broRm out Into four sections in [his memorandum u fbllowc:
• The determination of locations that may bs subjecx xp crosion during a large flood.
• The vpecifaoa[:on and drawings shat will govern dae v ng and placement o£r:prep.
• The estimates covx xo puroheve and tale delivery of riprmp that masts spsciflcation, and t0 instill the riprmp in
ordance wi[b deelgnv and drawings approved by xhe D:v iaion.
• The simerable for riprmp Installetlon, in particular the installaxipn of cho rivarbnnlc riprmp.
Aa a reminder, the purpove of the flood control/mitiga[lon plan ie [o m:nimiu the po[ent:al for exceviva scouring
and erosion oT pit slopes and o£ berms protecting eri[:eal vtr<acxurca such sa gas pipelines, and of oRVita impacts
doe w sedvnenmxion or realignment of the existing raver channel.
R/prop Loersr/ons
In order to prevent ezcessivc crosion, areas that may be subject to scour during a Hoed should be armored. To
fdenufy areas of scour, the depth end velocity of floodwaters should be estimated amd the gradaxion of the soil and
subsoil (send end gravel] may be examined along with vegetaxion chnrscterlexice w determine :f the erosive power
of the flood w:11 cut inrn the vegetation end soil. Placement of larger and heavier maxerlal (rlprmp), xlra[ canno[ be
lifted and moved by floodwater, will present crosion and down cuxxing in loratlona identified to be prone to scour.
Thorn ern a number of published c mputac:onal maLaoda ava:leble to determ ins rhs sizing and grmdat:on of riprap
rmquired so armor egWnat erosive flows of dlffermt velocities.
Depth and vcloclry of floodwater increen<s exponentially in flood evenxv of incraacingly Iowar probsblliry of
The son-perosnt an val charace flood (the so-called [en-year flood) rc tilt In a substantially IOWer
slow, depth. and veloeiry thaw a ono-peroant annual chance flood (Han ] 00-year raxurn per'od come). Designv for
armoring agaana[ crosion during n 300-ye.r flood would most likely fall during a much larger, bux longer rsmm