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

PACE :001
TIME :MAY-16-O1 10:36AM
TEL NUMfiERi: +1303666?567
NAME :Colorado Division of Minerals 6 Geology
FILE NUMBER 186
DATE W1Y-16 09:56AM
TO : 83032836705
DOCUMENT PAGES 006
START TIME MAY-16 10:36AM
END TIME MAY-16 10:36AM
SENT PAGES 006
STATUS ON
FILE NUMBER I66 *** SUCCESSFUL TX NOTICE ***
STATE OF COLORADO
OIV ISION OP MINERALS ANO GEQy~ --. _ .. __ -- .
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G E O^ O G Y
May 1 7, 2001 Pbn. A Pw ikI s - iw is4r a

Rpcky Hoffachneidsr
Plante Sand 6L Gravel LLC
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P.O. HOX 1 60 ems„!
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L/vleron. CO BO106
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RS: Rlverbanic
avd Pit 8tope Armorlvg Propose[. Tacbvtul Rwislon ~
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to Sdkli Miva Saetiop 112 Raclamatiov permit App1[eatloa• Pietta
Vattry Saad sad Gravel, Fira No. M-3000-138
Desr Mr. Holr ehnslder,
Plassa Sand 8c Gravel LLC has provided a technical tavlelon (TR) to further address ooneema with erosion
potential through the gravel pit mining calls during a large flood w nt_ The TR includes an Illusmtivn oY
locations that the Applicant has dstentllnad so by senaisiva nrcsa with the potential for exceaa(ve aroaion_ The TR
includes a proposal avd designs so stnbilize certain of shaae potentially sensitive erou by armoring drrouglr rire
plat snt of.iprsp_ Tha TR also includes tour astimssas Yor the piacament of rlprap and a daacriprion of the
timing of ripmp /natellaeion relative so the sequence of excavarion in lha gravel pits. The Dlvieion's rwlew of she
TR is broken out into £our sections in this msmorandum Y follows:
The determination of locations that may be eubjner ro erosion during a large flood.
The specification and drawlrags the[ will govam <he li ng and plneament of ripmp.
e The ast(maxad coat to purchase snd take delivery o£riprap that masts apeci£cati®, and W (nssall she riprsp In
ordanca with designs and drawings apprwad by lhs Division.
a The timeuble Tor riprsp ivatallativv, in particular the inssallasion oT the riverbank rlprap.
As s rsrraindsr, the purpose of the flood con[ro Vmisigstion plan (s to minim/ze [hs pognc:al for exnesalve scouring
end erosion oT pis elopes and o£bertps protecting critical svuesuree such as gas Dlpalines. and of ofTalse impaco
due to sedlmentarion or rcalignmrns oS She exiaring river channel.
Riprgp Locorler•r
In order to pravenr vacess(ve erosion, aromas that may be su4lect to scour during a [food should be ermorod. To
identify areas of scour. the depth and velocity of floodwatma should be estimated snd she gradation of she soil and
subsoil (nand and gravel) mny ba etrarrllnad along wish vegetation e1]sraervrlrties to deRarmine If rise arpsive power
of the flood will cut (stn the vegeution end se:l_ Placorl¢nx of larger end heavier maeeriei (riprsp), these o nos be
liftsd snd m vsd by floodwemr, will provent erosion end down cueing in locations (drntiflcd ao bo promo m scour.
There ma s number oC published eomputeslooal methods avnilnbls to determine ehs eizing and gradation of riprsp
xqu(rcd to armor against erosive flows of dill rant veloc(tlee.
Daprh and velocity of floodwater iareransas axponentislly in flood events of in mlltgly lower probnblllry of
oeeurranee. Tha ran-peresnr annual chmca flood (the so-called een-year flood) rcaulsa In n subatanslnlly lower
flow, depth, end velocity Lhan none-percent annual chance flood (the 100-ymr ratum period wmrt). Designs { r
armoring againa[ erosion during s 100-year flood would mom likely fail during a much larger, but longer retvm