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2011-03-21_GENERAL DOCUMENTS - C1982057
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2011-03-21_GENERAL DOCUMENTS - C1982057
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Last modified
8/24/2016 4:31:53 PM
Creation date
3/22/2011 2:48:55 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1982057
IBM Index Class Name
General Documents
Doc Date
3/21/2011
Doc Name
Proposed Decision & Findings of Compliance for SL3
From
Phase I
Permit Index Doc Type
Findings
Email Name
SLB
SB1
Media Type
D
Archive
No
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erosion, although there was some rilling going into the channel and areas on the north side of the <br />channel with minor side-cutting. There was also some under-cutting of the TRM in places. <br />There was some erosion and down cutting at the inlet of the surge pond while the outfall of the <br />surge pond exhibited little to no erosion. <br />PM-3A: The as-built channel location for PM-3A is shifted approximately 40 feet to the south, <br />due to the change in alignment of channel PM-3 in that area. The lower 659 feet of the as-built <br />channel generally follows the designed flow path. The length of the as-built channel is <br />approximately 790 feet shorter than the designed length. The as-built channel PM-3A basically <br />stops at the shrub enclosure while the designed channel goes up the slope almost to the east edge <br />of the disturbance boundary. Although the as-built channel was shorter than the designed <br />channel, the area above the as-built channel was well vegetated and stable, with no erosional <br />problems noted. The as-built profile for channel PM-3A was between 3 and 9 feet higher than <br />the design profile. Despite these elevation changes, the grades of the as-built profile generally <br />matched the grades of the designed channel and were functioning well. There was moderate <br />erosion in the entire length of channel PM-3A. There was also under-cutting of the TRM in <br />places. All of the flow from precipitation and runoff was contained in the channel. <br />PM-6: The upper half of the as-built channel is approximately 30 feet farther south than the <br />designed location. The as-built location for the lower portion of the channel PM-6 intercepts <br />channel PM-2A approximately 500 feet farther up the slope than the designed channel (and <br />enters at a right-angle as opposed to flowing into channel PM-2A at a more acute angle). Based <br />on these location changes, the as-built channel profile differs from the designed channel profile. <br />The as-built elevations are between 14 and 50 feet higher than the design elevations. The as- <br />built channel does not appear to be steeper than the designed profile, although the location of the <br />steep grades has changed. Although channel PM-6 has been changed significantly, including the <br />location where it intercepts channel PM-2B, it is stable and well vegetated. The entire length of <br />the channel had riprap and vegetation and no erosion was noted. All of the flow from <br />precipitation and runoff was contained in channel PM-6. <br />PM-4: The channel is designed as a trapezoidal ditch, with a bottom width of 3 feet and an <br />overall depth of 0.6 feet and a lining of vegetation. The as-built channel has a bottom width of 6 <br />feet, an overall depth of approximately 2 feet and is lined with riprap (with grass growing up into <br />the riprap). The channel flows at an approximate slope of 27%, as compared to an average <br />design slope of 22%. Although the average grade of the as-built channel is steeper than the <br />design, it did not appear to be a problem. There was minor scouring in the lower section of the <br />channel, which will need some maintenance work. This lower portion of the channel may be a <br />good place for TRM. <br />PM-4A: The channel is designed as a trapezoidal ditch with a bottom width of 3 feet, an overall <br />flow depth of 0.65 feet and a lining of vegetation. The as-built channel is a "V" ditch with a top <br />width of 12 feet an overall depth of 12-18 inches and a lining of riprap. The V ditch has a cross- <br />sectional area of 9 square feet while the designed trapezoidal ditch has a cross-sectional area of <br />3.2 square feet, so the as-built ditch has a larger capacity for the designed flow. The ditch flows <br />at an approximate slope of 25%, as compared to an average design slope of 18%. Despite the <br />Page 14 of 22
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