2013-04-08_PERMIT FILE - C1981019A ‎(2)‎

• Permit No: C1981019A
• IBM Index Class Name: Permit File
• Doc Date: 4/8/2013
• Doc Name: East Pit Recl Sequencing & Ditch Designs for Prospect Ditch, N Tribut E Pit Ditch & Final E Pit Ditc
• Section_Exhibit Name: Exhibit 07 Item 14 Appendix Exh7-14R
• Media Type: D
• Archive: Yes

Ditch Design, overview
As the reclamation advances to the west, the three permanent ditches will be constructed
to convey runoff from the disturbed and reclaimed lands southeasterly toward the
Prospect sedimentation pond. From north to south these ditches are Prospect Ditch,
North Tributary East Pit Ditch (NTEP), and Final East Pit Ditch. Although the total
drainage area tributary to Prospect Pond is 711.1 acres, including significant undisturbed
lands, the largest watershed for any single ditch is 153.3 acres, that being Prospect Ditch
just before it releases into undisturbed lands. The ditches are therefore all designed for
the 10 year -24 hour storm in accordance with Rule 4.05.3.
The two southern ditches (NTEP and Final East Pit Ditch) are rip -rap lined for most of
their entire length. The only exception is the lower segment of NTEP Ditch inunediately
before it joins the Final East Pit Ditch (SEDCAD Str. No. 8) which is grass lined. In the
Prospect Ditch to the north, all three reaches are grass lined. The lowermost reach in
Prospect Ditch (Reach 1) has a distinct flattening of gradient below Sta 1 +50 where a
large reclaimed watershed from the north enters. This sub -reach is also grass lined.
Alignment and slopes in the ditches are presented on Maps 41 and 33 respectively. The
man -made segments of all three ditches are trapezoidal sections, with 12 foot bottom
width and 2H:1 V side slopes.
The peak 10 -year design flow for each ditch is presented below:
• Prospect Ditch, maximum peak flow 10.0 cfs in the lowermost reach
• N. Tributary, East Pit, maximum peak flow 11.9 cfs into Pond NTEP -1
• Final East Pit Ditch, maximum peak flow 23.7 cfs in the lowermost reach
After NTEP and Final East Pit Ditch have joined, the combined peak flow is 35.4 cfs.
Selection of rip -rap size has been done as described in Exh. 7 -14, and in general is based
on SEDCAD's OSM- Simons method. Rip -rap is used for erosion protection in about half
of the reaches of described in this section. Minimum stone size (D50) for each ditch was
determined in SEDCAD using the Simons /OSM model as described in Exh. 7 -14. The
required stone size for the rip -rap lined ditches in this section varies from as small as 6-
inches in some reaches to 12- inches in others. All ditches are nevertheless designed with
a minimum D50 of 12 inches.
For grass lined channels, SEDCAD generally recommends keeping velocities less than 7
fps for flat channels and no higher than 5 fps for steeper channels. For Prospect Ditch's
grass lined channels, the maximum peak flow velocity for the design storm is 3.1 fps,
occurring in the lowermost sub -reach of Reach 1, immediately before release to the
natural channels. The majority of the flows in Prospect Ditch segments run closer to 2.1
fps. In the lowermost reach of NTEP Ditch, the velocity in the vegetative lined channel
Exh. 7 -14R -2 Revision Date: 3/27/13
Revision No. TR -97