20170752 Ver 1_More Info Received_20171107

Johnson, Alan
From:Shanaberger, Erin <[e-mail]>
Sent:Tuesday, November 07, 2017 11:52 AM
To:Amschler, Crystal C CIV USARMY CESAW (US)
Cc:Johnson, Alan
Subject:\[External\] RE: Lyon Ct
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Alan and Crystal,

I followed up with the design engineer to clarify some of the comments I made on their latest set of plans and I wanted
to clarify some things for you guys. Referencing Crystals comment in #2 below, some of the channel widths up and
downstream of the culverts are wider than the proposed baseflow width through the culverts. Originally this project was
much more comprehensive, covering far longer lengths of channel improvements; however, after initial agency reviews
and multiple agency field reviews, we were directed to minimize channel disturbances because the channels appeared
to be stable. In an effort to address that comment and minimize channel disturbance, we shortened up enhancement
lengths. In order to bring the grade of the stream to meet the new culvert, we had to accommodate changes in grade
over shorter lengths. In areas like upstream of Chesnut St and Kensington Avenue, the addition of the grade control
structures and the shorted length, made the engineer have to widen out the channel to accommodate the same flows
and meet City design standards. In areas where stilling basins are proposed at culvert outlets, there will be no floodplain
benches at the culvert outlets; in locations where benches are shown on the plans, benches will start at the end of the
stilling basins. In order to accommodate the large flows at these outlets and dissipate velocities, they employed stilling
basins in the design because a traditional rip rap apron, or a plunge pool only in the baseflow channel would have
required a much longer impact length than the stilling basin. This was unclear on the plans that were sent to you for
review on 8/9/17. The culvert cross-section sheets showed a “proposed finished grade line” that was meant to represent
only the grade at the face of the culverts and not the grade immediately downstream, which is what myself and the PM
were originally thinking.

As you both know, this project has gone through extensive avoidance and minimization efforts over the course of the
previous 5 years. There is a trade-off of potentially over-widening the stream immediately up and downstream of some
of the culverts in Phase 2, and a larger number permanent loss impacts that would have resulted from more preferable
energy dissipaters. The designer agreed that they could narrow the baffles and has done so; however, in locations where
there are stilling basins, I anticipate that the stream will remain wider than the low-flow channel cross section. In the
interest of addressing the primary concern with over-widening (aquatic life passage), we have altered the design of the
stilling basins to include smaller sizes of rock to fill the voids such that water will maintain on top of the rock as it flows
through these sections of stream. The basins will also be lined with geotextile fabric. The aprons at the tails of the stilling
basins will be “notched” to facilitate a quick return to baseflow channel dimensions. Notes have been added to the
construction plans to ensure this is understood and constructed correctly. The design is to have the stilling basins filled
with water, so baseflow and aquatic life passage will be maintained in spite of a wider channel.

Please let me know if you all would like to discuss this further while we are waiting for SHPO to sign off on the project.
Thanks,

Erin Shanaberger
Water Quality Program Specialist
City of Charlotte | Engineering & Property Management | Storm Water Services
mobile: [phone] | [e-mail]
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From: Shanaberger, Erin
Sent: Thursday, September 14, 2017 3:04 PM
To: 'Amschler, Crystal C CIV USARMY CESAW (US)'
Cc: Johnson, Alan ([e-mail])
Subject: RE: Lyon Ct

Crystal,

See responses to your concerns below in red. I will be working with the project manager and design consultant to
address concerns. Please let me know if you have anything to add!

Thanks,
Erin

-----Original Message-----
From: Amschler, Crystal C CIV USARMY CESAW (US) \[mailto:[e-mail]\]
Sent: Wednesday, September 13, 2017 3:33 PM
To: Shanaberger, Erin
Cc: Johnson, Alan ([e-mail])
Subject: Lyon Ct

Erin,

I've finally been through all the plans for this project and have completed my review. I have the following comments:

1) I know we've been on site and may have discussed this, but I can't find it anywhere in my notes. Can you tell me why
the culvert at Central Drive (single 9x7 culvert) overall has a smaller capacity than the culverts upstream at Randal
(double culverts: 8x6 and 8x4)? Just concerned that it is undersized since the culvert just upstream is bigger. Since the
area upstream of Central Avenue has large floodplain benches that provide attenuation/storage for flood waters, a
larger culvert or set of culverts wasn’t necessary in this location. Additionally, there were significant utility conflicts and
performing a larger jack and bore operation to install multiple barrels would have been cost prohibitive.

2) I saw that all the culverts have baffles to reduce the base flow widths, but I didn't see any benches on the plans and
the stream widths appear to be the widths of the culverts which would result in over widened streams and render the
baffles useless. I'm concerned that although the culverts allow for base flow, the stream reaches above and below the
culverts don't. Please address this issue. The culvert packages that I uploaded to supplement the PCN included typical
stream cross sections with a table that listed baseflow riffle dimensions for each stream segment in the plans. See table
below for info. The floodplain culvert benches are also shown in red in the same packages. One of my comments on the
most recent set of plans was to add a note to “appropriately taper floodplain bench from edge of baffle back to existing
channel”. I have asked if they can show this on the cross sections of the culvert like below to make it more clear.
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3) based on the SAM forms and the overall enhancements that will result from this project, I think your mitigation ratios
are appropriate with just 2 exceptions.
a. During previous site visits we discussed that the replacement of concrete flumes with culverts would not be a
loss used in determining if the project would exceed the IP thresholds, based on the fact that the flumes currently are a
complete fill of the stream beds. However, mitigation wasn't discussed, and although we would not consider the
replacement of the flumes with culverts a loss as it relates to IP thresholds, there will be loss function that results from
taking day lighted streams and placing them in culverts. Therefor I recommend mitigation at a 0.25:1 ratio (123 lf of
streams currently have concrete flumes and are proposed to be piped resulting in 30.75 of mitigation credits required to
offset those impacts). Agreed.
b. Site 32 was discussed during our 8/31/2016 field visit. You explained that based on the downstream
replacements of culverts at lowered elevations, the entire length of this stream would need to be graded down to a new
lower elevation to match the downstream elevations. My notes indicate that this stream is currently stable with some
bed form. During the site visit we discussed the possible use of in stream structures to ensure stream stability and
replace bed form and/or the use of natural channel design to ensure the stream doesn't lose function and become a
straight line ditch subsequent to construction. The plan doesn't seem to show any of these things we discussed. Please
indicate if the plan will be revised to include these recommendations. When we discussed this section of stream, we
were planning to permit the channel improvements on this project under NWP #27; which you explained that you were
not in agreement with, without additional improvements beyond the planting proposed. When the RGP was approved, it
allowed for the grading to accommodate “increased storm water flows and flood reduction measures which include
minor instream grading, etc.” Since the intent of the channel grading is to accommodate the pipes and not improvement
for improvement’s sake we did not change the plans. We felt like grading stable banks and planting them with the
appropriate native seed and woody species was sufficient.

4) During our 8/31/2016 site visit and in a subsequent email summary (attached) we discussed concerns that the box
culverts at Tippah Ave driveways and Randall St would need to maintain low flow channel of 3-4 foot through the cross
sections. The currently designed base flow widths created by baffles is 5-6.' Can you clarify why the current design
allows for 5-6' base flow if the stream is 3-4' wide? Alan made the same comment. I have included this comment in the
latest round of design comments for the engineer to address. We will re-evaluate with them and see how long it will
take if we can revise the plans as requested.

5) lastly, you sent an email 8/9/17 that was supposed to have the signed PJD and PCN forms attached but they
weren't? not sure if you sent them in another email but I don't have them. Can you resend and also include the
completed PJD table that should be attached to the PJD form. See attached as JPEG since PDF never works…

Thanks,

Crystal C. Amschler
Project Manager
Asheville Regulatory Field Office
3

151 Patton Avenue, Room 208
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