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

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MEMORY TRANSMISSION REPORT
• ~II ~I~~I~~I~~~~~'I~
999
PAGE :001
TIME :MAY-I6-O1 10:00AM
TEL NUhOERI: [phone]
NAME :Colorado Dlvlslon of Minerals i GeololsY
FILE NUI~ER 176
DATE MAY-IB 09:49AM
TO : 83032744464
DOCUMENT PAGES 006
START TIME MAY-16 09:49AM
END TIME MAY-18 IO:OOAM
SENT PACES 006
STATUS OK
FILE NUMBER :176 *** SUCCESSFUL TX NOTICE ***
STATE OF COLORADO
Of VfSfON OF MINERALS ANO GEOLOGY __ _ _ ___ _______
1-J.f,. r.m.nl of N.aueol Res, o,:,ev. '-' _ "' '
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Mny 17, 2001
PeetJY Fax Note 'rO7l pea
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MI Nr~RALSi1
G E O LOGY'
n PNI"`^-S Fe~rtl
Ronlry HoT£echnerder I:I res...
Plane Ssnd R Oaevel LLC c...°'^°'•
P.O. HOX 180 ,~, ,,,~,
Igo ^sa
Littleton, CO 80106
oil:i°^ nl::..,.
RE. Rlverbaglc and Ple Slope Armoring ProPOSaI, Tecbn/cal IieMalon
to SB<H Miae Section 112 liaclamatioa Permit Appl/eaelon, Platte
Valley Sand and Gravel, File No_ M-2000-156
Dear Mr. Hoffschnvider,
Plane Snnd dt Orvvel LLC leas provided a tscbnical r n (TR) to furdter eddrcsa concerns with erosion
pmvntlal through Na grevei pit mining cells during a large flood wens. Ths TA Includes an illusvation of
locations that the Applicant has determined to be sensitive area with the potential Eor exceaaiva erosion. The TR
clvdes a proposal nod deaigva to stabilize watain of Lteae potentially sensitive axes by srrtroring through she
ylecement of riprap. Tha TR also includes cost cstimetes Eor the placemsnt of riprap and a description of Lae
timing of riprap insullation relative to Ne sequences of excavation in she gravel piss. 'ihv Dlylalon'a review of doe
TR is broken out inm four sections in this memorandum as £ollows_
The de<mtrrination o£ locations Nat may be subJect ro erosion during a large Tood_
Th¢ speeiRontion and drawings [hat wall govern Ne a ng end placement of riprap.
The estlmnted coot to purohnee sad take delivery of riprap these mess,, apecifleatlon, and to install Nv rlprap in
ordsnce w1N designs and drawings approved by Oav Dlylslon.
• Tha tlmeuble for riprap installation, in perticuler Ns installaton o£dae riverbank riprap.
Ae a reminder, Ne purpose oP the flood convoVmltlga[ion plan is w m:nimirs Ne poxmtial for excessive scouring
and erosion of pit slopes and of berms protecting critical structures ouch ao gas pipelines, and of ofShise lmpavta
dues co sedimsnution or realignment of Ne exlating Ayer charcoal.
AI(prop Locorlorrr
In order to pretrant excessive erosion, areas that may be subject [o scour during a flood altould be armored_ To
identify nrees of scour, the depth and velocity o£floodwnters should be estimstad and Nv gradation of the Boll and
subso/1 (sand and gravel) may be examined along wiN vegetaslon characteristics to detcrm:ne if the erosive power
of the flood wail nut ln[o th¢ vegeret:on and soii_ Placsmeni of larger end hoavlter material (riprap). that ewrtnnt be
lifted sad anoved by floodwamr, will prnvnnt ero and down cueing in locations Idenslflad to be prone to scour.
There are a number of publiMed compuutional medtode available to determine the sizing end gradation of rlprap
required to armor egainsc moslve Howe o£dlfF rent velocisi¢e.
DepN and velociry offloodwstcr increases exponentially in flood wcnts oEinereasingly lower probebiliry of
oveurrence. The tan-portent annual chance flood (Na so-aW1W [en-year flood) results in a subasantislly fewer
flo -depth- sad veloei[y than none-percen[ n al chance flood ([ha 100-year renrrn period a en[). Deelgns Pot
armoring nga:nse croaion during a ] 00-year flood would mast likely fail daaring a much larger, but longer return