PERMFILE104930

• Permit No: M2000113
• IBM Index Class Name: Permit File
• Doc Date: 8/17/2001
• Doc Name: DRAINAGE STUDY ROARING FORK RESOURCES INC MAMM CREEK SAND & GRAVEL PIT
• Media Type: D
• Archive: No

' the slough, existing irrigation ditches which create a barrier to flow or the natural grade of the
ground. (See attached Exhibits DS-1 and DS-2)
' The section of the I-70 corridor that provides runoff to the Dry Creek mining azea was divided
into 10 subareas to estimate the amount of runoff that could potentially enter the Dry Creek
mining area. This study assumes that the diversion ditch will be sized based on the cumulative
' flows from the drainage subareas so that it can contain the 100 yeaz storm event with an adequate
factor of safety. The time of concentration path and drainage subareas are shown on Exhibits
DS-1 and DS ?.
' The drainage areas for the mining areas are:
Mining Area Acres
West End 30.69
' Dry Creek 22.32
Slough to East Property Line 47.03
West Property Line to Horse Fence 57.51
The TR-5~ and Rational Method methods are used to estimate the runoff for the Mamm Creek
Gravel Pit site. The Rational Method was used for areas less than 10 acres while the TR-55
Method was used for areas in excess of 20 acres. The capacity of the existing culverts was
estimated using Manning's equation and Haestad Methods FlowMaster software. The surface
facility diversion ditch and the road borrow ditches were sized using Manning's equation. The
diversion ditch for the Dry Creek mining area has been divided into two sections for design
purposes. The first section is relatively flat and extends from the inlet to the culvert which
' discharges into the field in the Dry Creek mining area to the bank of the slough and the second is
from the top of the slough bank down to the water surface.
' The runoff from the surface facility azea prior to the pit being established in the Dry Creek
mining area will be collected by the road borrow ditches and directed to a detention pond on the
' east end of the surface facilities. (See Exhibit SF-1) The borrow ditch on the south side of the
road will be used to collect the runoff from the surface facility azea. The ditch on the north side
of the road will be sized to collect water from the north half of the road. The detention pond was
' sized using the TR-55 method, Chapter 6. The design assumes that the dischazge is limited to the
historic flows from the site. Sediment storage has been included in the detention pond volume.
Only the detention pond for the surface facility area with no pit has been sized since the pits are
' both incised and large enough to provide sufficient storage for storm water runoff.
The topographic mapping and the property boundary survey is based on data provided by K. S.
Professional Surveying, Inc. The rainfall precipitation is based on data from the NOAH maps.
The design events aze:
' Culvert Sizing - 25 yeaz
• Detention Pond Capacity - 25 year
' Spillway Capacity Detention Pond - 100 yeaz
• Diversion Ditches - 100 year