HomeMy WebLinkAboutFDP201900004 Review Comments Floodplain Development Permit 2019-05-10 WOOLLEY ENGINEERING
May 10, 2019
MEMORANDUM
To: Mr. Frank Pohl, P.E.
County of Albemarle,Virginia
From: Mr. Eric Woolley,PE
Woolley Engineering
Regarding: Oakencroft Farm- FDP20190004
Responses to comments from County Staff
With this memo, I am responding to the comments that were directed to our office following the
review of our Floodplain Development Permit for the Oakencroft Farm located at 1455 Oakencroft
Circle. I have attached this response memorandum to one (1) revised copies of the floodplain
development plan. Our responses to the comments are as follows:
Engineering Review Comments
1. A copy of the current structural engineering drawings has been included with this
resubmission. The information requested is illustrated on these drawings.
2. A copy of the modeling data file for the stream has been emailed to your attention.
3. The modeling data shows the floodway for the study area.
4. Contour elevation annotation has been added to sheet C 1.0.
5. The County review signature block has been removed from the revised plan submission.
6. An engineering report has been attached to this memo to address this comment request.
I hope that these responses, in combination with the revised site plan have satisfied the deficiencies
as noted in your comment memorandum. Please do not hesitate to call with any questions or
concerns. Thank you for your time and consideration.
Sincerely,
Eric Woolley, PE
Attached: Floodplain Development Plan
Current Structural Engineering Documents
Engineering Report
WOOLLEY ENGINEERING 220 East High Street (434) 973-0045
Charlottesville,Virginia 22902
WOOLLEY ENGINEERING
May 10, 2019
Frank Pohl, P.E.
County of Albemarle
401 McIntire Road
Charlottesville, Virginia 22902
Re: Oakencroft Farm: Existing Stream Flow Report
Dear Mr. Pohl,
This report shall provide background and design calculation results for the stream flow rates that
pass through Oakencroft Farm. The drainage area was measured to be 3.57 square miles at the
furthest cross section downstream within our study. Due to the size of the drainage area,we
chose to calculate the flow rates for the stream utilizing the Anderson method. On the
subsequent pages of this report,we have provided a detailed summary of our equation results.
The results of the Anderson method calculations suggest the maximum rate of runoff for this
portion of the stream for the 10, 25, and 100-year flood events to be 942 cfs, 1,405 cfs, and 2,323
cfs,respectively. We modeled this data within our HEC RAS software and evaluated the results.
As a check against our calculated method of determining the flow data,we utilized the
proprietary flow information available from USGS government mapping and modeled the stream
with their projected flow rates. The calculated results from the USGS StreamStats data
suggested that the flood elevations are higher than the elevations we calculated utilizing the
Anderson method.
We visited the site with the results from both studies to evaluate the in-field conditions. After
walking the stream, we determined that the more conservative USGS StreamStats flow data
would be utilized with our design work. Our previous summary report we provided to you with
the initial Floodplain Development Permit application utilizes this data. We have attached
copies of these reports to this memo also. Please let us know if you have any questions or
require further support material.
TH of
Best regards, -
:aac" . WOO
Eric Woolley, P.E. LIC. NO. 37088
Attached: Exhibit E—Anderson method calculations SroNAL
USGS—StreamStats flow data
Cc: Oakencroft Holdings, LLC, Property Owner
WOOLLEY ENGINEERING 220 East High Street (434) 973-0045
Charlottesville,Virginia 22902