2011-06-29_PERMIT FILE - C1981019A ‎(29)‎

• Permit No: C1981019A
• IBM Index Class Name: Permit File
• Doc Date: 6/29/2011
• Doc Name: East Taylor Ditch July 2006
• Section_Exhibit Name: Exhibit 07 Item 14 Appendix Exh7-14I
• Media Type: D
• Archive: Yes

• Appendix Exh7 -14I - East Taylor Ditch
The East Taylor Ditch is located in Sections 4 and 9 of T3N, R93W. Although the
upstream end of the ditch is in Section 9, the watershed that it drains extends about a half
mile southward to the watershed divide near the center of Section 16. The alignment of
the East Taylor Ditch is shown on Map 41 and on Figures 14C -1 and 14C -2 in the
discussion of the Taylor Tributary Ditch in Appendix 14C of this Item 14. The design
profile of the East Taylor Ditch is provided on Map 33A. The entire channel was
redesigned following a revision to the post- mining topography submitted under TR -81.
The total drainage area reporting to the ditch is 399.2 acres. The ditch is designed to
meet the requirements of Rule 4.05.3 for permanent drainages less than one square mile.
This requires that the channel be capable of handling flows from a 10 year, 24 hour event.
As shown on the profile, the steepest portion of the channel, which is the lower portion,
has a slope of about 22 percent. There is also a relatively flat section, about 2,000 feet in
length. This section has a slope of 1.5 percent. The overall length of the channel is
about 8,185 feet.
The assumed hydrologic condition is the post- mining condition wherein the entire
watershed is reporting to the lowest portion of the ditch, and for which the density of
vegetation will vary depending on the time since the particular area has been mined. As
shown on the attached SEDCAD printout, the design storm produces a peak discharge of
• about 53.0 cfs and a total runoff volume of about 8 acre -feet. This design event is based
on a Curve Numbers of 74 for the lower (northern) portions of the watershed that will
have 3 or more years of revegetation growth, and 77 for the upper portion of the
watershed which are assumed to have only 1 to 2 years of revegetation growth, as
adopted pursuant to TR -73. That upper portion of the watershed comprises about 56% of
the total watershed.
•
For ease of construction, a trapezoidal channel cross - section 12 feet in width will be
employed for the rip -rap lined portions of the ditch. Channel side slopes will be 3H:1 V
slopes and a minimum depth of 4.0 feet will be used for all sections. Riprap size has
been selected based on the SEDCAD modeling as described in the Introductory Text in
this Exhibit 7 Item 14, pages Exh. 7 -14 -1 through 4. For this ditch a minimum riprap size
of 18- inches has been selected which exceeds the minimum size of 12- inches calculated
in SEDCAD. For the flat portion of the channel, the ditch bottom is widened to 20 feet,
and a vegetative liner is adequate for the design velocities, as presented in the attached
SEDCAD printout.
The following pages present the SEDCAD analysis for this ditch. The ditch design
parameters are also presented in Table 1 of Exhibit 7, Item 14.
Exh.7 -14I -2 Revision Date: 12/31/10
Revision No.: TR -81