HomeMy WebLinkAbout100 yr ReportJohn W. Harris, P. E.
CONSULTING ENGINEER, INC. Telephone (919) 789-0744
5112 BUR OAK CIRCLE Fax (919) 789-0784
RALEIGH NC 27612 www.harriseng.net
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15, March 2013
Amanda Bader, P.E.
Harnett County
108 E. Front Street
Lillington, N.C. 27546
RE: Clear Letter of storm water run-off
Dear Ms. Bader;
Pursuant to our conversation of last week, I am hereby certifying, the following.
1) The anticipated, “developed” storm water run-off from the Fox Run site, via the pipe under Prairie
Lane is an increase of 10.7 cfs in the 10yr storm and an increase of 19.7 cfs in the 100 yr storm.
2) Due to there being no channel, and the width of the water flow, the calculated depth of flow is only
increased by +/- 0.08’ in the 10 yr storm and +/- 0.1’ in the 100 yr storm, both of which are
considered minor and insignificant.
3) The attached is a graphical representation of the anticipated 100 yr flow and how it affects the area
in Fox Run from the pipe at Prairie Lane to the property line adjoining Trotters Ridge. I have also
included computer generated crossections with flow, depth, and velocity indicated at each section.
It is my professional opinion that this flow represents an insignificant increase and that if the downstream
property (lots) is properly developed, there will be no adverse impact of this surface water run-off to the
Trotters Ridge building structures. (i.e.: if the builders of the lots do not build directly in the low point.)
The following plan view indicates that sufficient space is available on both Fox Run lots 49 and 50 for a 60’
X 40’ building pad and that the 100 yr flow does not come close to either building location.
I enjoyed meeting with you last week, it allowed me to better determine what information was needed. If
you should have any questions or need additional information, please let me know.
Sincerely;
John W, Harris, P.E.
Consulting Engineer, Inc.
These crossections correlate to the indicated crossections noted in the above Plan view and indicate
the minimum depth of flow and the low velocity being generated at each section.
This is the Pre-100 yr computation that indicates a depth of flow of 0.55’ which compares to the Post-
100 yr. computation above indicating a depth of flow of 0.65, thereby showing an increase of only 0.1
feet (1.2”).