ST0301-CS040520From:
To:
Date:
Subject:
Page 1
"Loretta Mokry" <loretta@apaienv.com>
<CLM@freese.com>
5/20/2004 12:31:31 PM
Coppell Road Culvert
Chris,
After meeting with Jessica Napier (USACE project manager) at the site and reviewing the questions and
comments she wrote throughout our permit application for the proposed modifications for Tributary G-l, I
have several things that I need to bounce back to you for answers. I have already sent a list to Craig
Bond at TranSystems for him to address items pertaining to the Bethel Road crossing and the upstream
portion of the tributary, but need to try to cover the bases on the downstream portion and Coppell Road
crossing. Jessica has several issues regarding developing a more complex stream channel design based
on base flow, bank full discharge (calculated based on 1.5-2 year storm event) versus flood capacity for
25-year or 100-year storm event.
1. Area of gabion mattresses downstream of Coppell Road South? Am assuming that the area of 2"
select fill as bedding for the gabion mattresses will be the same as for the gabion mattresses. Will there
be filter fabric as well under the the select fill?
2. Area of four 10' x 8' box culverts at Coppell Road South?
3. Can the box culverts at Coppell Road South be designed so that one box is lower and the others higher
so that stream dynamics (i.e. base flow channel) are ma nta ned through the culverted area? (Call to
discuss or I can fax a sketch).
4. Change in elevation of the stream bed from existing to proposed (shown on profile views but after
talking with Suzan, know this may be changing again due to constraint of sanitary sewer at Bethel Rd.)
Aisc what is existing overall slope versus proposed slope? Jessica's concern is potential adverse effect to
water surface elevation (slope) resulting in change in water velocities downstream.
5. Size of base flow channel and relative size (or relationship) to bank-full channel flow. We have a 5'
width shown for the base flow channel but no depth shown yet. Channel depth was about 2' on April 29th
when I was at the site with Jessica. Do you think a 2' depth for the base flow channel would be adequate?
What would the channel forming flows (and velocities) be for a 1.5-2 year frequency storm?
6. Jessica requested specifics on velocities; existing flow volume and rates as well as projected with
proposed channel design. Jessica referred to channel design to get sediment balance (referenced "Lanes
Balance" pg. 2-19 of Stream Management by J. Craig Fischenich and Hollis Allen). Her specific concern
was related to change in sediment load resulting in adverse impacts to downstream reaches if the channel
is not designed correctly.
7. More detailed information (and drawings) regarding the transition downstream of Coppell Road South
back to the natural channel. What flow velocities are projected as the water reaches the natural channel?
Jessica handed me the Stream Management design manual developed from the USACE Waterways
Experiment Station in Vicksburg, MS. Below are the links to the manual and article Jessica handed me in
the field. I have also included the link to the USACE Fort Worth District Regulatory Branch web page
(which Jessica nows maintains). There are other links through their web page that may be of interest as
well, especially under the Stream Information Links
USACE web page
http:llwww.swf.usace.army.millpubdatalenviron/Regulatory/index.asp
"Technologies for urban stream restoration and watershed management" from Ecosystem Management
and Restoration.
http:~/www.swf.usace~army~mll/pubdata/envir~n~Regu~at~ry/~ther~~inks~stream~techurbanstreamrest.pdf
Stream Management by J. Craig Fischenich and Hollis Allen, Water Operations Technical Support
Program, March 2000
http://www~swf~usace~army~mi~~pubdata~envir~n~Regu~at~ry/~ther/~inks~stream~ERD~~treamManagement~
pdf
Please give me a call to discuss the information needed if you have any questions. You can reach me on
my cell phone at (817) 845-3280 or by calling our F.W. office and they will transfer you down.
Thanks,
Loretta
Loretta E. Mokry
Senior Environmental Scientist
Alan Plummet Associates, Inc.
1607 Todd Trail
College Station, Texas 77845
(979) 694-7619 home office
(817) 845-3280 cell
(979) 694-7619 fax (call first)
Through Fort Worth office
(817) 806-1700
(817) 589-0072 FAX
<loretta@apaienv.com>
www.apaienv.com
CC: <staylor@ci.coppell.tx.us>, <thh@freese.com>