North Lake Dam -- Internal Drainage SystemAs part of flattening the slope of the Main Dam, the downstream toe will
extend beyond the existing toe and cover a manhole associated with the
internal drainage system (Manhole #1 in the attached figure). At a
minimum, this manhole will be extended vertically (about 10 feet) to
account for the additional height of the new slope at this location.
Raising this manhole would satisfy any impacts caused by extending the
downstream toe, and the drainage system would effectively remain at
status quo.
However, there may be additional improvements that can be made to the
drainage system. Inspection reports from the last several years indicate
that Luminant has had issues at Manhole #3 and needed to pump water out
of it quite frequently because of backwater effects at the downstream
end of the drain outlet. A possible improvement to alleviate this issue
is abandoning the drain lines downstream of Manhole #2 and providing an
outlet at this location.
In order for this to be possible, we need to confirm a few elevations
around Manhole #2. As you can tell from the figure, the 2-foot LiDAR
contours indicate that there may be some issues with drain line
elevations. Knowing that LiDAR data in low-lying areas can often be
inaccurate and error-prone, we would like to take a few field
measurements to confirm whether these improvements might be possible or
not.
If these additional improvements are something the City would like to
consider, when can we schedule a time to make a quick visit to the site
to make these measurements? Let us know what additional guidance you may
have.
Please feel free to give me a call with any questions you may have.
Thanks.
Patrick Miles, P.E.
Water Resources
Freese and Nichols, Inc.
4055 International Plaza, Suite 200
Fort Worth, Texas 76109
817-735-7236
817-735-7483 fax
www.freese.com
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