20130941 Ver 1_More Info Received_20131022

Confluence Engineering, PC
16 Broad Street
Asheville, NC 28801
828.255.5530
October 22, 2013
Ms. Karen Higgins
WBSCP Unit
1650 Mail Service Center
Raleigh, NC 27699 -1650
Subject: Additional Information
DWQ Project # 2013 -0941
Haw Branch Restoration
Buncombe County, North Carolina
Dear Ms. Higgins:
We received the Division of Water Resources October 10, 2013 letter requesting additional information
regarding the subject project and we offer the following responses.
Items 1 to 4 — Supporting Data and Calculations
Supporting data and calculations are attached to this letter. For the Haw Branch design, our reference
information consisted of a surveyed cross section located about 100 linear feet upstream of the impacted reach.
Because reach -wide pattern and profile changes are not proposed, a complete reference reach survey was
deemed unnecessary. Plots of the impacted and reference cross sections are included.
The UT to Haw Branch was dredged to the upstream property line, beyond which the stream lacks a well -
defined channel, vegetation is very dense and access for surveying is difficult. We did not locate a stable cross
section of the UT to survey, and as is the case on the main stem of Haw Branch, reach -wide changes to pattern
and profile are not proposed, so no reference data were collected. We did survey a cross section through the
impacted reach and a plot of this section is included.
For both streams, we measured the contributing drainage areas and developed predictions of bankfull
dimensions and discharge from regional hydraulic geometry relationships. Design dimensions were developed
based on a review of existing and reference data and regional relationships. The typical section design
summaries show channel dimensions, slopes and predicted discharges, along with regional curve predictions for
bankfull area and discharge. In both cases, the selected bankfull area is close to the regional curve predictions,
which in the case of Haw Branch is considerably larger than the reference section area. This difference is
mainly due to the flatter design bank slopes and increased design width -depth ratio. The expectation is that the
relatively wide and shallow design section will be more stable than a narrow and deep section in the short term,
before deep rooted vegetation is established on the banks.
In terms of sediment transport, our hydraulic and sediment transport analyses indicate .the design cross sections
will convey the bankfull discharge at bed shear stresses less than required to mobilize the largest particle size for
constructed riffles in the UT and the existing bed materials in the Haw Branch main stem. Constructed riffles in
the UT will be built with on -site cobble (approximate d100 of 300 mm) underlain by Class 1 riprap (dloo of 430
mm). No constructed riffles are proposed on Haw Branch main stem, where the existing bed is relatively stable.

Additional Information
Haw Branch Restoration
Page 2 of 2
Item 5 — Construction Observation
Mr. Mike Lovoy, PE will provide construction observation services and I will be available to assist as needed to
answer questions about the design intent.
Item 6 — Monitoring
The long -term stability of the restoration measures will be visually monitored for a period of three years after
construction. The monitoring plan will consist of approximately four reference photographs on each stream
reach. Annual photographs will be taken from the same locations each year and to allow for an evaluation of the
geomorpbic stability and planted vegetation survivability.
Closure
We trust that this information adequately addresses your comments, but feel free to contact me at 828.255.5530
if you have any additional questions or comments.
Sincerely,
Confluence Engineering, PC
Andrew Bick, PE
Principal
Attachments
Cc: Tim Fox, DWR Asheville
Mike Lovoy, PE