20181502 Ver 1_More Info Received_20181203

Johnson, Alan
From:Aliisa Harjuniemi <[e-mail]>
Sent:Monday, December 03, 2018 3:12 PM
To:Johnson, Alan; Shaeffer, David L SAW
Subject:\[External\] Response to NCDEQ Comments - Cheyney (SAW-2006-41171, 20181502,
Version 1)
Attachments:Cheyney Stream Restoration_Dam Removal Plan (1).pdf; CheyneyPondRemoval-
Stream Rest_FigureD_rev11-30-18.pdf
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Alan,

Find our responses to your comments (in red) and changes to the Cheyney Site - Pond Removal and Stream Restoration
Plan.

1. Something I run into is that the fabric punctures at the juncture of the two logs. I suggest dropping the fabric deeper
and allow some slack in the fabric to eddy into log void (shown in red). Not sure of the rock size, should be consistent
with the stream. A good soil/sand/stone/gravel medium.
Attached is the revised Figure D - Proposed Profile and Cross-sections. The Typical Log Grade Control Structure was
revised per your recommendations. Now the typical instructs and depicts the filter fabric to follow the logs contours,
eliminating voids between the logs. The upstream end of the fabric is buried beneath the streambed. The originally
portrayed rock clusters at each log structure have been changed to rock footers that will be placed beneath the stream
bed. Stream medium matching the stream bedload material upstream of the project reach will be placed over-top the
rock footers. The rock footers are being placed below the stream bed elevation to prevent headcutting or scouring
around the log structures.

2. The stream bank on the plans with the log sills, indicates riprap. If so, this should be clarified. We would expect
matting, except maybe for some minor toe slope reinforcement. The attached revised Figure D now depicts matting and
livestakes at each log grade control structure (see Typical Log Grade Control Structure, on sheet). Figure C - Stabilization
Plan indicates matting and livestake planting along the restored stream reach, and it provides planting and installation
instructions.

3. The plan indicates a two percent slope. I know typically 1 to 1.5% is the goal.
The upstream reference reaches were classified as Rosgen B channels with valley slopes averaging 2% and bankfull
slopes averaging 1.5%. Rosgen B streams typically average 2-9% slopes. The valley slope through the pond removal area
and stream restoration, measured from the upstream back water edge to the outfall pipe outlet invert, was estimated to
be 2%, as well. On Figure A, in the Channel Morphology Table, the proposed bankfull slope is shown as 1.5%. Based on
the current design, the restored stream channel will be constructed between 1.5-2.0% slope, matching upstream
reference conditions.

4. Finally, there is always the concern of headcutting up channel where the old pond (point of dam removal) ties back
into the channel.
Agreed, and this why rock footers have been designed to be installed upstream/downstream of the log grade control
structures. The lowest log structure on the restoration reach at the tie-in location (St: 6+40) will be built with added
footer rocks, larger in size, placed deeper below the stream bed, and with increased lengths. If you need a call-out on
the current figures in the Cheyney Stream Restoration and Dam Removal Plan (attached with revised Figure D), along
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with a detail for this grade control structure, it can be provided and added to the Plans. However, CWS will be
completing construction of the stream restoration and will ensure the tie-in grade control structure is built to prevent
headcutting. If you recommend a rock grade control measure instead of a log structure at this location, one can be
placed into the design.

Let me know if you need anything else.

Thanks,
Aliisa

--
Aliisa Harjuniemi, PWS
Project Manager
Carolina Wetland Services, Inc.
550 E. Westinghouse Boulevard
Charlotte, NC 28273
Direct: 980-259-1222
Office: 704-527-1177
www.cws-inc.net
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