HomeMy WebLinkAboutWPO201400075 Review Comments WPO VSMP 2014-11-17John Anderson
From:
John Anderson
Sent:
Monday, November 17, 2014 5:45 PM
To:
'Morgan Bell'
Cc:
'Justin Shimp, P.E.'; Glenn Brooks
Subject:
RE: WP0201400075 -Rocky Hollow
Morgan,
I would suggest that plans include: detail from Virginia Erosion and Sediment Control Handbook (VESCH) Std. 3.21
(Plate 3.21 -1); symbol /abbreviation for level spreader (LS, etc /sheet C4), and LS label at the 3 pipe outfalls furthest from
the stream. At the 4th pipe nearest the stream/box culvert, I suggest extending riprap all the way to the receiving steam.
DA at box culvert =594.5 Ac, which marks endpoint of analysis for energy balance. I apologize for not grasping design
implications of 9VAC25- 870 -66 earlier, which exist even at high -DA receiving streams. Although the increase in runoff
and flow appear relatively minor, both increase with conversion of forest to asphalt. Using TR -55 graphical method, I
estimate 1 -year (24 -hr event) pre - developed flow to be 0.186cfs, vol. = 1,270.5cf, post - developed uncontrolled flow /vol. to
be 0.414cfs /1,924cf. Given constraining relationship between Vol. /Q, and assuming DA =1 Ac (not 1.9 Ac), it appears
Energy balance limits Q post/]-year to 0.123cfs, or else it imposes volume reduction.
Level spreaders do not lower Q -post, but attenuate velocity. There is no evading 9VAC25- 870- 66.b.3
(hgp:Hlis.vir ig nia.gov/c ig b�gp6O4.exe ?000 +re,g +9VAC25- 870 -66 ), but to require detention higher on the hillside to
lower Q -post or Vol. -post would require loss of forest, the best available cover. The only impervious areas are a paved
entrance, and single- residence walks /roof /patio, etc. Concentrated flows are at driveway ditches and gutter lines. At 3
points, it appears ditch flow passes under the drive into the woods some distance from property lines or stream. At these
locations, level spreaders (with outlet protection) would limit velocity and erosion. At the 4th pipe, riprap (manmade
conveyance) "shall convey the post - development peak flow rate from the two -year, 24 -hour storm event without causing
erosion of the system" (riprap).
If design extends riprap at the one pipe and includes level spreaders at the remaining three (1, sheet C4; 2, sheet C3), it
meets intent of 9VAC25- 870 -66, in my view. You do not need to accept these suggestions, and are free to consider
meeting requirements of 9VAC25- 870 -66 any way that you wish.
Thanks for your patience, for speaking with me earlier today. Please let me know if you have any questions.
John E. Anderson, PE I Civil Engineer II
Department of Community Development I County of Albemarle, Virginia
401 McIntire Road I Charlottesville, VA 22902
434.296.5832 ext. 3069
From: Morgan Bell [mailto :morgan @shimp - engineering.com]
Sent: Monday, November 17, 2014 9:38 AM
To: John Anderson
Subject: RE: WP0201400075 -Rocky Hollow
Good morning, John.
I forgot to submit the revised spreadsheet. My apologies. I have attached it. Have a good one.
- Morgan
From: John Anderson [ mailto :janderson2Cclalbemarle.org]
Sent: Monday, November 17, 2014 9:17 AM
To: Morgan Bell
Subject: RE: WP0201400075 -Rocky Hollow
Morgan, have I overlooked VRRM spreadsheet? —1 think you planned to send revised .xIs as an e-mail attachment.
Thank you-
From: Morgan Bell [mailto:morgan @ shimp- engineering.com]
Sent: Tuesday, November 11, 2014 1:59 PM
To: John Anderson
Subject: RE: WP0201400075 -Rocky Hollow
Thanks so much for all of your assistance with this project, John.
- Morgan
From: John Anderson [ma i Ito: Janderson2@albemarle.org]
Sent: Tuesday, November 11, 2014 1:25 PM
To: Justin Shimp, P.E.; Morgan Bell
Subject: RE: WP0201400075 -Rocky Hollow
Morgan, last note misdirected —take care, John
From: John Anderson
Sent: Tuesday, November 11, 2014 1:24 PM
To: 'Justin Shimp, P.E.'; 'Michael Ball'
Subject: WP0201400075 -Rocky Hollow
Morgan, Justin,
I received revised plans today, but will be away Wed -Th. The rest of today is taken. I work half day Friday. I'll try to
review /comment Fri. Otherwise, it will be Monday —sorry for the delay.
Thank you-
John E. Anderson, PE I Civil Engineer II
Department of Community Development I County of Albemarle, Virginia
401 McIntire Road I Charlottesville, VA 22902
434.296.5832 ext. 3069