HomeMy WebLinkAboutWPO201300032 Correspondence 2021-08-11John Anderson
From: Dustin Greene <DGreene@roudabush.com>
Sent: Wednesday, August 11, 2021 BAB AM
To: John Anderson; Frank Pohl
Cc: Charlie A. Hurt; Jim Taggart
Subject: RE: WPO201300032, Cascadia - Amendment #2
Attachments: SW01.pdf; SW14.pdf
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John,
Please see the updated pdfs for WPO201300032 Amendment #2. Let me know if you have any further
questions or concerns. Note that the elevation of the channel section A -A of the emergency spillway (348.95'-348.0' _
0.95' depth) coincides with the (Pond #2 Emergency Spillway Channel Minimum Slope 5%.pdf) sent to you on 8/2/2021.
Best Regards,
Dustin Greene, PE
Roudabush, Gale & Associates, Inc
(o) 434-977-0205 ex - 724
(Direct) 434-328-1069
(m)415-420-8238
dgreene@roudabush.com
Physical Address:
999 Second Street SE
Suite 201
Charlottesville, VA 22902
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Mailing Address:
435 Merchant Square
Suite 300-159
Charlottesville, VA 22902
From: John Anderson <janderson2@albemarle.org>
Sent: Tuesday, August 10, 20214:16 PM
To: Dustin Greene <DGreene@roudabush.com>; Frank Pohl <fpohl@albemarle.org>
Cc: Charlie A. Hurt <Charlie@VirginiaLandCompany.com>; Jim Taggart <JTaggart@roudabush.com>
Subject: RE: WPO201300032, Cascadia -Amendment#2
Dustin, last: Please ensure plan revision date is 8/10/21, that PE seal is signed -dated; thanks, best, JA
From: John Anderson
Sent: Tuesday, August 10, 20214:14 PM
To: Dustin Greene <DGreene@roudabush.com>; Frank Pohl <fpohl@albemarle.org>
Cc: Charlie A. Hurt <Charlie@Virginia LandCompany.com>; Jim Taggart <JTaggart@roudabush.com>
Subject: RE: WP0201300032, Cascadia -Amendment #2
Dustin,
Formal memo is nearly finished —Amendment #2 is at point of approval, but Engineering needs a revised .PDF showing that the
`emergencysspillway control section is a cut section, as opposed to a diversion on top of the downhill side of the
embankment.' Also, Aug-2 email below indicates As -built channel = 14', 1.5' deep. Please ensure rev. WPO Amendment #2
presents this information, and with that, Amendment #2 can be approved. Please send .PDF of WPO Amendment #2 showing
cut, rather than berm, and showing As -built channel dimensions, then we can digitally approve. I work till 6pm, and hope to do
this, today, depending when we receive a revised .PDF. Thanks for your patience.
[ Most recent .PDF of WPO Plan Amendment #2 appears to be attachment to email, 7/1/2021 8:25 AM, which is likely identical
with print items delivered 18-Jun; this is the plan to revise. ]
best, J. Anderson
From: John Anderson
Sent: Friday, August 6, 20218:58 AM
To: Dustin Greene <DGreene@roudabush.com>; Frank Pohl <fpohl@albemarle.org>
Cc: Charlie A. Hurt <Charlie@VirginiaLandCompany.com>; Jim Taggart <JTaggart@roudabush.com>
Subject: RE: WP0201300032, Cascadia -Amendment #2
Frank, thoughts?
Dustin,
I have a meeting at 9, then hope to turn to this —at first glance, reading all the way through, your email /analysis appears to
address remaining comments. Let me wrap this meeting, and at the same time, offer the county engineer a chance to respond, at
his discretion. At this point, from my vantage, without pulling most recent WPO Amendment #2 review comments, you are
likely there. Thanks for time spent on this, and for your patience. -best, J. Anderson
From: Dustin Greene <DGreene@roudabush.com>
Sent: Monday, August 2, 2021 1:50 PM
To: John Anderson <landerson2@albemarle.org>; Frank Pohl <fpohl@albemarle.org>
Cc: Charlie A. Hurt <Charlie@Virginia LandCompany.com>; Jim Taggart <JTaggart@roudabush.com>
Subject: WPC201300032, Cascadia - Amendment #2
John,
Thanks for your review of the amendment for Cascadia Pond #2.
1s` comment: 10-year capacity for the Broadus Memorial Baptist Church culvert.
The original reduction of the 10-yr storm event from the pre to post developed condition reduced the flow from
27.83 cfs to 8.77 cfs. This is a reduction of almost 70% of the original 10 year flow to the culvert underneath the church
access.
Pre -developed = 27.83 cfs
Post -developed = 8.77 cfs
The capacity of the 30" RCP culvert is 39 cfs. The headwater to depth ratio exceeds 1.50 at 40 cfs (See attached
pdfs). The reduction and the capacity show that this culvert will be able to handle the 10-year flow. There does not
appear to be any erosion around the culvert area further showing that it has not eroded since being built for the church
access in 1994.
2"" comment: The emergency spillway channel should have the some cross-section as the control section.
I have provided the County an equivalent cross section for the 40' control section and the 16' wide emergency
spillway channel to the toe of the slope for the dam. There are an infinite amount of cross sections that could be used
to convey the 100-yr storm from the control section of the emergency spillway to the toe of slope for the dam. The 100-
year storm conveys 147.43 cfs through the emergency spillway at 356.99' (WSE). The emergency spillway uses the weir
equation for cross sectional area of 44.20 square feet. The emergency spillway channel uses Manning's equation to
determine the required depth to convey the 100-yr storm in the rip rap channel. The slope of the channel reduces the
required cross sectional area required to safely convey the storm, that is why I am calling it an equivalent cross section
as opposed to the same cross section.
Maximum slope of 20% requires a depth of 0.64' or equivalent area of 9.78 square feet for the emergency
spillway channel.
Minimum slope of 5% at the toe of the slope requires a depth of 0.95' or equivalent area of 15.10 square feet
for the emergency spillway channel.
As -built channel = 14', 1.5' deep, OK.
The existing channel is at least 1.5' deep so the existing channel will be able to safely convey the 100-yr storm to the toe
of slope without erosion. The contractor has been instructed to remove all woody plan materials from the emergency
spillway channel and embankment. The contractor has also been instructed to cut the emergency spillway control
section as opposed to providing a diversion on top of the downhill side of the embankment Please let me know if you
have further questions or concerns.
Best Regards,
Dustin Greene, PE
Roudabush, Gale & Associates, Inc
(o) 434-977-0205 ex - 724
(Direct) 434-328-1069
(m)415-420-8238
dareene@roudabush.com
Physical Address: Mailing Address:
999 Second Street SE 435 Merchant Square
Suite 201 Suite 300-159
Charlottesville, VA 22902 Charlottesville, VA 22902
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