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 :NAY-18-O1 10:30AM
TEL NUM3ER1: [phone]
NAME :Colorado Division of Minerals l Geology
FILE NUMBER 184
DATE MAY-18 09:57AM
TO : 819705359654
DOCUl4=NT PAGES 006
START TIME MAY-18 10:25AM
END TIME MAY-18 10:30AM
SENT PAGES 006
STATUS OK
FILE NUMBER :184 *** SUCCESSFUL TX NOTICE ***
STATE OF COLORADO
OIV ISION OP MINEMLS ANO GEOLOGY
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May l7, 2001
Rooky Hoftbchneider
Platte Smd 8c Gravel L.LC
P.O. HOX 180
Llttleson. CO 60106
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REl liivarbank and Pit Siope Armoring proposal, Technical AeYLlon
b 9dr8 Mloa 6ectlon 112 Aeclamatlon Psrmit Appllentlon, Pinety
Valley Band and Gravel, Silc No. M-2000.158
Dsar Mr. Hoffachneider,
Platte Sand ~ Oraval LLC hoc provided a taohnlcnl revision (TRj to iwtl]cr addross concerns with eroalon
potrntial through the grovcl pit mining tolls during a large flood went. Ths TR i cludsa an Illustration of
locations that rile Applicmt has determined to bo smsirivv areas with the potential for excessive erosion. The TR
:ncludea a proposal and deaigru to atabilire cervin oT these potmrially aensiciva nraaa by armoring through the
pleeeman[ of riprop. The TR also includes core esclmetes for the plmemmt of riprop and a deseriprioa of dte
riming of riprep installation rotative m the sequence of excavation in the grovel pies. The DlYlalon•• review of the
TR is broken out Into Lour smtiona in this melnarondum es follows:
Ths dc[vrm inaxion of locarions that may be aubjsct to erosion during a large Hood.
The epeclficarion and drowings chat will govern rho sizing attd plmement oP riprop.
The eetimatsd cone to purchase and Llce delivery of riprep fhn[ 1 eels cpeci£acatim, and [o install the riprep in
cordmce with designs and drawings approved by the Div/sion.
s The timetable for riprep (vatallsrlov, iv perrieular the installation o£ehe riverbmlc riprep.
As s reminder, ihs purpose of the flood oontroVmirigerion plm is to minimize the potential for mccesslYe eoouring
and eroalon of pit slopes and of berms protecring arl[Ieel structures such as gas pipelines. end of off im impecv
due to acdlmenration or renligrtrrtent of the existing river channsl.
R/prop Lpeor/ons
In order to prvYmt o[cessive erosion, assns that may be aubjec[ m scour during a flood should ba armorod. To
identity trees of scour, dre depth and velocity of floodwaters should be esrimated and the grmdsrion o£thv soil end
subsoil (nand and gravrlj mny be examined along with vegstation characteristics to detatrnins if the erosive power
of the tlootl will cut into the yvgetarion m0 soil. Placement of iargQ and heavier mabrlal (riprep), that Donner be
IiRad and moved by floodwater, will provent erosion and down cutting In locations idmtiflnd to bs prone to scour.
Thva are a number of publlehed eomputarlonsl methods avnilable to determine the elzblg and grodatier of tiptop
required to ertrtor against eroaiYe flows of dill rent Yclooltles.
Depth and velocity of noodwecer lneroeses exponmtlnlly in flood events of inctvnsingly Tower probability of
ocourtenws. The trn-parvant a ual whence flood (rhos walled ten-year noodj rcaulb in a substantially lower
flow. depth, and velocity then as ono-perccot amual chanty flood (ths 100-year rotum paried evrnt). Dealgna for
armoring ngainst erosion during a 100-year flood would most lil[sly tlil during a much larger, but longer rKUm