20230527 Ver 1_More Info Received_20230608

Chandler, Rebecca D
From: Rav Bissram <[e-mail]>
Sent: Thursday, June 8, 2023 10:32 PM
To: Chandler, Rebecca D
Cc: Michael Brame
Subject: [External] Middleton Phase 2 Response to comments
Attachments: 2023-06-08 Pipe Crossing Exhibit -Stream Crossing 36.pdf
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Rebecca:
It was good talking with you on Wednesday. Attached is the exhibit that shows the actual centerline of stream that we
located. The field points are small (if you zoom in you can see the elevations) so I added leader captions for ease. Below
is the response to your question:
1. Exhibit 3 of the plans indicate that 48 LF of 36" metal culvert will be installed at a grade of 10.89%, followed by
an additional segment at a grade of 3%. Please note that the GC states "Culverts should be designed and
installed in such a manner that the original stream patterns and profiles are not altered and allow for aquatic life
movement during low flows. The dimension, pattern, and profile of the stream above and below a pipe or
culvert shall not be modified by widening the stream channel or by reducing the depth of the stream in
connection with the construction activity. The width, height, and gradient of a proposed culvert shall be such as
to pass the average historical low flow and spring flow without adversely altering flow velocity. If the width of
the culvert is wider than the stream channel, the culvert shall include multiple boxes/pipes, baffles, benches
and/or sills to maintain the natural width of the stream channel. If multiple culverts/pipes/barrels are used, low
flows shall be accommodated in one culvert/pipe and additional culverts/pipes shall be installed such that they
receive only flows above bankfull. For structures less than 72" in diameter/width, and topographic constraints
indicate culvert slopes of greater than 2.5% culvert burial is not required, provided that all alternative options
for flattening the slope have been investigated and aquatic life movement/connectivity has been provided when
possible (e.g. rock ladders, cross -vanes, sills, baffles etc.). Notification, including supporting documentation to
include a location map of the culvert, culvert profile drawings, and slope calculations, shall be provided to DWR
30 calendar days prior to the installation of the culvert."
As discussed, the steep slope of pipe represents the actual grade of the channel. The upstream end is around 690+/-
and the discharge end is approximately 684+/-. The proposed pipe grade (from end to end) is approximately the same
grade of the existing channel as indicated by the survey points. The lower pipe segment was flattened out to reduce
downstream velocity; thus, lessening the impacts of the proposed culvert. In terms of aquatic life movement, the post
condition is really not much different from the pre-existing condition due to the natural topography at this crossing
location.
Please feel free to contact me if you have any questions or need additional information.
Thanks,
Rav

Ravindra Bissram, PE
Senior Project Manager
IFEI
Civil Engineers and Land Surveyors
8518 Triad Drive
Colfax, NC 27235
Phone:[phone]
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