SW4070701_Add Info_20200226

Farkas, Jim J
From:Farkas, Jim J
Sent:Wednesday, February 26, 2020 9:16 AM
To:Chris Brown
Cc:[e-mail]
Subject:Echota IV SW4070701
Chris,

I was looking over the additional information you provided on 2/17/2020. Everything looks good except for a few small
issues:

Please correct the following:
1) Clearly indicate on the plans which typical section applies to each swale. For example, swale 3, is shown to use
the typical section for the v-ditch and also the drainage swale w/ 6” riprap while others, such as swale 12, do not
have a listed typical section associated with them.
2) Please show or clarify in the calculations why certain swales use a Manning’s roughness coefficient of 0.035 and
others use 0.104. Please provide a reference of some sort if using the 0.104 roughness coefficient.
3) Since the proposed side slopes of the vegetated conveyances are 2:1, please provide calculations showing
stability of the channels during a 10-year storm. Please also indicate the method used to calculate the actual
shear stress and provide a reference for the maximum allowable shear stress used.
4) Please sign & seal the calculations.
5) Please review the calculations for accuracy. For example, swale 9 appears to receive flow from swales 6, 7, & 8
(flow rates of 1.4 cfs, 0.7 cfs, & 0.8 cfs respectively). The flow reported for swale 9 (1.1 cfs) is less than the sum
of the flow of the contributing swales. Please clearly indicate in the calculations which swales flow into each
other and ensure that the calculations are correct.

While not required, it is recommended that, where possible, riprap lined swales be avoided as they are not considered
vegetated conveyances.

Please provide the following:
- 2x hard copies and 1 x electronic copy uploaded to Laserfiche of the applicable updated plan sheets.
- 2x hard copies and 1 x electronic copy uploaded to Laserfiche of the title sheet indicating the revisions to the
plan set.
- 1x hard copy of the corrected swale calculations or 1x response to comments explanation for using the different
Manning’s n values.
- 1x hard copy of the swale shear calculations for the 10-year storm.
- 1x original, signed hard copy of the calculation coversheet.
- 1x electronic copy uploaded to Laserfiche of the full, corrected calculations.

Since these are really minor things, once I get the hard copies, anything else that may have changed from addressing
these issues, and the documents are uploaded to Laserfiche (Provided everything is still in order), we can issue the
permit without doing a formal 30-45 day review.

Let me know if you have any questions.

Jim Farkas
Environmental Engineer
North Carolina Department of Environmental Quality
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Division of Energy, Mineral, & Land Resources – Stormwater Program

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