HomeMy WebLinkAboutWPO200900020 Review Comments Erosion Control Plan 2009-09-04� OF AL
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COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road
Charlottesville, Virginia 22902 -4596
Phone (434) 296 -5832 Fax (434) 972 -4126
Project: University Village, Phase 1; SDP - 2009 - 00033, WPO- 2009 -00020
Plan preparer: Mr. Scott Collins; Collins Engineering
Owner or rep.: Next Generation, LLC
Plan received date: 6 Aug 2009 (activated 19 Aug with the ZMA variation approval)
Date of comments: 3 Sep 2009
Reviewer: Glenn Brooks
The erosion control plan and stormwater management plan for Phase 1 of the University Village
Retirement Community project have received engineering review.
A. Erosion and Sediment Control Plan
1. Site plan approval is required.
2. Revise the plan to place sediment collection facilities downhill of major fill sections, and in the
low points of the topography.
3. "Clean water" diversions are not an approved variation. Basins should be sized for the
contributing drainage areas.
4. Regarding the MS -19 analysis;
a. Location 3 does not appear to be a channel. This outfall and basin should be moved to
discharge to a channel. See comments below.
b. Location 1 and 2 need to go further downstream and look at the pond.
c. Locations 2 and 3 appear to be have been impacted some time in the past, and are deeply
entrenched. They appear inadequate for the flows to them. Calculations should use
varying, lower n- values and have higher velocities, instead of one n -value and an
oversimplified, average velocity for the section.
5. Detailed review will be conducted when concepts are revised as above.
B. Stormwater Management Plan
1. The layout does not appear to address the overall plan. Areas of future development will need to
be captured.
2. The embankments must be wide enough to drive in order to reach the forebays, and there are too
many 2:1 slopes. See VSMH 3.01.
3. Both biofilters are short- circuited.
4. The computations and drainage areas appear to be over - manipulated. There must be some attempt
to honor existing drainage divides. The change to the basin two area, and its placement, are an
extreme example. Removal rates must be computed by drainage area. There is not enough control
of depth in a weir built with class I1 rip -rap to obtain the results as shown. Why is a fudge factor
used in the 100 year routing? 24hr storm distributions should be used, and routed above the WQV
volume. Some of the drainage areas are in error.
5. The 5% sizing guideline falls short of providing the volume of 1" of runoff over impervious
surfaces to achieve a 65% removal rate. For example, basin 1 provides a capture volume of
2071cf as designed. The required volume is about 189000sf(1 "/12)= 15750cf.
6. Detailed review will be conducted when concepts are revised as above.
File: E1_ ecp, swm_ GEB_ WP0200900020 _UniversityVillage29.doc
Be
Current Development
Engineering Review Comments
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