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-IB-O1 10:33AM
TEL NUMBERI: [phone]
NAME :Colorado Division of Minerals 8 Geology
FILE NUMBER 185
DATE MAY-16 09:57AM
TO $3038410993
DOCUMENT PAGES 006
START TIME MAY-18 10:30AM
END TIME MAY-16 10:33AM
SENT PACES OOfi
STATUS OK
FILE NUMBER :195 *** SUCCESSFUL TX NOTICE ***
STATE OF COLORADO
UIV ISION OF MINERALS ANO OCOLOGY __ _ _ __
O.Partm.na o! Naoaral Rafourcaf ""' "' '~~"
1 ]l1 SM1..m.n e~.. Room Tl5 POel-Ili Fax NOl1 7871 d ..~ O 1 v , a , O N O r
Onnv.r, Cular.po eOTO3 i
scene: ISO91 esas9w to r.em MINERAL S
PA%: (:1UJ109T-OI Ob ~
eo.rp.m~ co. (, G E O LOG Y
MaY 17.3001 rTeMa _ _ w•c HA nr^i or
Rocky Hoffachneider ~ wa: o....n.
Plane Send ec Orayel LLC a...a.n..
P.O. SOX 1 BO e..e e. w.~en..
Lialeton, CO 60706 e..s oo%R,-•
.~ a.
oi~~een p,..r,e.
RE: RlverbrvlL sad Mt Slope Armoring Proposal, Techrlcal Rwiaiov
m BBrH M:re 9astlev 112 Rcclamattov permit Application, Plasb
Valley Snvd and Gravel. Flla No_ M-2000-138
Desr Mr. Hoff chnvidar,
Plane Smd g Orcvel LLC has provided s technical revision (TR) to further addteu concsrn• with oroalon
potentisl through the gravel pit mining calla during a large Ylood event. The TR Inoludas an illuctretlon of
locations shat she Applicmt has determined to by sanaldye areas with the potential for excessive erosion. Tho TR
Includes a proposal and designs to smbilize certain of xhese poteminlly 9ensit:ys areas by armoring through cha
placement of riprcp. The TR oleo includes tort vatimates for the plecsmant oP riprap and a dexrlption of rite
c:m:ng of riprap installation relative m the aegveace of excavation in the gravel pica. Tie Division's reYlaw of the
TR la broltsn out Into four sections in this mamormdum ns Tollow9:
The determination of locations that may be subjett to erosion during s large flood.
Thv spRiflcatlon sad drawings shat wall govern the slating and placement oTrlprap-
a The sstimated cost io purohue and take delivery o{riprap Nat mrtcs specifl¢at:on, aaad ro install dte riprap in
ordancv with dvaigna and drcw:njs approved by dte D:vlalon.
a The timernble i riprap Inainilndon. In pertlculss dos insmllae:on of the riyerbarda riprap.
As a reminder, rite purpoas of the Flood conaol/mitigation plan le io minimise Ne potential for ezwsslvs scouring
and erosion o£pit elopes mtl of berms promoting critical 9rr. such as gas pipvl/nas, and of oHllm ImpacL+
due co sedimvntadon or rcallgnment of the exirting raver channel
8fprop Leeoeioru
In oMer [o prevent exeefalYe ero9len~ areas Shat may be anbjatt so fcopr during a flood should ba armored. To
identify areas of scour, the depth and velociry oP floodwaters should be cstlntated and the gradation of the soil and
subao ll (9ma and gravel) may be warn fined along with veltetacfon aharacter:scies to deu:rtnine if the erosive power
of doe Aped wail out Sato the vv¢etacion and soil. Placement of larder and heaviee material Criprap). that c of be
IiRcd and moved by floodwater. will prevent erosion and down cutting in locadons idendflsd to be prone to scour.
There ate n number of published compptaiional mediod9 available m determ fine the sizing and gradation of riprap
required xo armor a~inst sroarvs flown of diffcront veloeitics.
Depth aatd velocity of floodwater :ncrcaxs exponentially in flood events of incrcaaingly lower probablliry of
The vn-percent annual chance flood [the ao-called ten-year flood) results in a subvurtdaliy Iowsr
flow, depth, and velocity <hatt a one-percent atmual thence flood (the 100-year return period event). Designs for
armorntg sgainar aroa:on during a 100-year Aeod would most likely Fa11 during a much lvgar, but longer return