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 10:01 AM
TEL NUMBERI: [phone]
NAME :Colorado Division of Minerals Z Geology
FILE NUMBER 177
DATE MAY-19 09:49AM
TO : 83034237297
DOCUMENT PAGES 006
START TIM: MAY-18 09:49AM
END TI1~ MAY-18 10:01AM
SENT PAGES 000
STATUS NC BO
FILE NUMOER :177 *** TX FAILURE NOTICE ***
STATE OF COLORADO
DIVISION OP MtNEMLS ANO GEOLOGY
OaPar[mcn[ o! Navral Rttaurctt / '- "' '
1313 51[wrmwn St.. Room 31.
rJnnvwc ColorwPa OP303 a ~
FA
n~. uo31 eeeaam M 1 N E RA L 5
Y
1]031 eJl-e106 6
G E O L O G Y

Rocky Hoffschneider
Plane Smd do Gravel LLC
P.O. HOX 1 g0
Lfdle[on, CO gOl Ofi
pat-K~ F« Nob 7e'11 ~°
P
r.em Cori as

ATc Rlverbanlt sad pit Slope Armorfvg Proposal. To¢hp/cal Rwieioo
to 96rH Mlve Sccdov 112 Rsolamatioo Permit Appllutfoa, Platte
Valley Saari sad Gravel, FLC No_ M-2000.158
Dear Mr- Hoffachneider,
e..t[ m~w.mer.
c. .~ vu.r er
.~Itnw a te..v
ova.:en nw...r.
plane Sand A Gravel LLC has provided n cechnlcal roviaion (TR) to further address concerns with erosion
potcnxlal through the gravel pi[ mining cells during a large flood went. The TR includaa nn illustration of
locations that Ne ADplicmt has dv[ermfned to b¢ senaixive areas with the potential for «eeealye erosion. The TR
elude a proposal and designs to smbilize certain of xheso potentially a aitfve nrons by armoring dtrough the
plae¢menc of riprap. The TR elw includaa cost es[imaxes for xha plwoment of riprap and a description of dse
timing of riprap installndon rclacfva co she sequence of «cavadon In the gravel pie. The Divfaion•a review of the
TR is broken out inm £our smxions in this memorandum ea follows:
e Thc dcterminadon of locatioaa Shat may be subject ro erosion during a large flood.
e The apeciflenxion and drawings iha[ will govern the sizing and plmement of riprap.
e The estimated cos[ to purchase and take delivery of riprap that meers specification, and eo Install the riprap in
nccordancs with dsafgns and drawings approved by ihv Division.
The timetable for riprap iaatillndov, in particular the instillation of the rivvrbatlk riprep-
As areminder, xhe purpose of xhe flood eontroVmicigstion plan is to minim zc the poundal for «ceaslve scouring
and erosion of pit slopes and of berms protecting critfcsl atructurcs such as gas pipelines, and of offs its fmpneta
due xo aedimvntation or roWlgnment of Ne axtsdng river chavnel.
Aipwp LocaHertJ
In order to prcvenx ex¢esaivs eroalort, arcu drat may b¢ aubjsct m x r during a flood should by armored- To
identify arena of aeour, she depth and velocity of floodwaters should be estimaxcd and the gradation of the sail and
subaoll (asnd and gravel) may b¢ examined along wixh vegetit:on charaetnriacics to demrm lap If the erosive power
of the flood will c ro the vegsbtion and soil. Placemerat o£ larger and hsavier manurial (riprepj, drat cannot bo
lifted end moved by floodwaxer, will prevent moalon and down ousting in locations Idenrifled so bs prone to aeour.
There tiro a number of published computational methods oval labia to daxarm ins the afzfnII and gradation of riprap
required to armor agafnat erosive flows of d:IF¢rcnt vslocltlss.
Depth end velocity of tloodwatar fnexseses exponcnxial ly in flood events of increasingly lower probability o£
The ten-percent a ua1 chance !'laud (the s eallsd ran-year flood) rsau to In a aubaantially lpwei
flow, depth, and velocity thm a c-percent mausl ohance flood (xhe 100-year rextlr++ period event). Dsaigns for
armoring agalnat eroalon during a 100-year flood would most likely fail during a much larger, bet longer re[um