20080820 Ver 1_Staff Comments_20080515

Faust Site Stream Enhanc3ment - Cabarrus Co. (20080820)
Subject: Faust Site Stream Enhanc3ment - Cabarrus Co. (20080820)
From: Eric Kulz <[e-mail]>
Date: Thu, 15 May 2008 10:42:29 -0400
To: Alan Johnson <[e-mail]>
Alan:
Not for mitigation, but was in my box so I reviewed.
Several comments that you can do what you want with:
1) On Table 1 (Geomorphic Characteristics), they list the existing bankfull discharge (Q) as ranging
from 10 - 20 cfs. The design range (whatever that means) is also listed as from 10 - 20 cfs. The
design for station 0+00 to 1+20 is 70 cfs. I have no idea what they are doing, but it was my
understanding from the classes we took that Q is a constant, and is dependant on the watershed size,
impervious surface, etc. It is not something that changes from the existing to the design.
2. Valley slope is also a constant. The channel slope can be expected to change between the existing
and the design, but not the valley slope. This was confirmed for me last year by Barbara Doll, when I
asked her about a different site. Here is what her response was:
"In my professional opinion, stream invert should not be used to calculate valley slope. For example, if
the stream is incised at the downstream end and there is a headcut working up the system, but it has
not made it's way up the entire valley, then you would report an artificially steep valley slope using the
stream invert. Rather, they should use the top of bank elevations out on the floodplain (or terrace as
the case may be) to calculate the valley slope. There are cases where you may need to report more than
one valley slope if the slope varies across the project length. But, you are correct in assessing that
valley slope should not change between existing condition and design. Well, unless they are planning
on clearing, grubbing and grading the entire floodplain to modify it's slope? I hope this makes sense.
Call me if not, 515-5287. I will be here until about 12:40 today if you want to talk more.
Barbara".
3. For their planting plan, they are proposing herbaceous planting only, to include riparian seed mis,
herbaceous plugs, and temporary seed mix for the stream banks, and riparian seed mis and temporary
mix for the floodplain benches. If they want this project to succeed and the stream to be stable from a
long-term perspective, they should be doing woody vegetation.
My $0.02.
Eric
Eric W. Kulz
Environmental Specialist
401 Oversight and Express Permitting Unit
2321 Crabtree Blvd., Suite 250
Raleigh, NC 27604
Phone: [phone]
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