Creekview Add PD-CS 870908 PAWA-Winkelmann
& A~so~iates, Inc.
September 8, 1987
Mr. H. Wayne Ginn, PE -- ~ S~ =i'~-.
Ginn, Inc. - f~'
17103 Preston Road - Suite 100
Lock Box 118
Dailas, Texas 75248
re: Creek View Addition - Coppell, Texas
Review of Floodplain Reclamation Study
Dear Mr. Girm:
We have completed a preliminary review of the Floodplain Reclamation Study
submitted by Nathan D. Maier Consulting Engineers, Inc. (NDM) on the above
referenced project in Coppell. In addition to the August 18th report, Mr.
Dennis Johnson, PE, of NDM has submitted the computer models and floodplain
storage calculations required by the proposed Floodplain Management
Ordinance.
Based upon this review and as discussed with you at our meeting on Friday,
September 4th, we recommend that the approval of the floodplain fill be
delayed until NDM can show that the velocities in the channel can be
reduced to non-erosive in base flood conditions. As you pointed out, the
homeowners along the north side of Grapevine Creek are already concerned
about erosion. The project, as presently proposed, will increase
velocities now erosive at four locations of concern (see Table 3, page 12
of the NDM report). Locations of particular interest include the sections
at stream station 216+90 (12.2 fps will increase to 12.9 fps), NDM section
2.0 (increase from 10.0 fps to 10.3 fps), NDM section 4.0 (increase from
8.1 fps to 8.2 fps), and stream station 250+85 (increase from 14.1 fps to
14.5 fps).
In general, the project as proposed appears to be in compliance with the
other provisions of the proposed floodplain management ordinance with one
further exception; that of not increasing elevations of the regulatory
floodway. At stream station 257+85 both the energy grade line elevation
and the water surface elevation show increases of 0.01 ft. This variance
may or may not appear in a Summary Table 200 of the HEC-2 model output
12660 COlT ROAD, SUITE 200- DALLAS, TEXAS 75251 ' 214/661-9406
options (FIA Table 1), which rounds elevations to 0.1 ft increments. If
the increase is still present, additional channel controls must be added to
eliminate this increase caused by the proposed floodplain encroachments.
The necessary velocity controls noted earlier can accomplish both
objectives.
If you need further information or have questions on any of the foregoing,
please call.
Sincerely,
PAWA-Winkelmann & Associates, Inc.
Carl V. Anderson, PE
Vice President
cc: Dennis Johnson, Nathan D. Maier Consulting En[~ineers, Inc.
Shohre Daneshrnand, City of Coppell