FIRM-890207Kim/ey -Horn and Associates, Inc. 12660 Coit Road, Suite 200, Dallas, Texas 75251 . (214) 386 -7007
February 7, 1989 Raleigh, Charlotte, Nashville, Virginia Beach, Washington, Dallas, Phoenix,
West Palm Beach, Tampa, Orlando, Ft. Lauderdale, Vero Beach, Ft. Myers, Stuart
Ms. Shoree Danesmond
City of Coppell
732 Deforest Road
Coppell, Texas 75019
Re: Explanation of the FEMA restudy review of the City of Coppell. Job No. 9183.08
Dear Shoree:
As you know, the subject review was written for the benefit of FEMA, and as a result, is not
easily understood from a non - technical standpoint. Thus, we have written this letter to help
you better understand the contents of the report.
Definitions:
100 -year freauencv flood: the flood with a one percent chance of occurrence in any
given year.
500 -year frequency flood: the flood with a 0.2 percent chance of occurrence in any
given year.
Water surface profile: a plot of the flood level versus distance for a particular flood.
Floodwav encroachment: in order to determine the FEMA floodway for a stream
reach, it is necessary to mathematically encroach (or reduce) the 100 -year flood plain.
This encroachment causes the 100 -year flood level to rise. The floodway is
established by limiting this rise to a maximum of one foot. The floodway elevations
are thus up to one foot higher than the 100 -year floodplain.
The following are explanations of the computer printout results.
SECNO: Section Number, which corresponds to the section taken across the stream
C W SEL: Computed Water Surface Elevation at the section number where it was taken
Q: Total discharge over the entire cross section in cubic feet per second
DIFWKS: Difference in Water surface elevation between the first profile and the
profile in question
EG: Energy Grade line in feet
TOPWID: Computed Top Width of the flood plain. This may vary slightly from the
actual water surface delineation due to topography.
VCH: Channel velocity in feet per second
ELMIN: Minimum elevation of the cross section (�
XLCH: Distance from the last cross section measured along the �X—�-3 (]
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Ms. Shoree Danesmond
February 7, 1989
Page Two
Explanation of Attachments
Attachment 2: Denton Creek 100- and 500 -year frequency flood computer model.
The summary printout lists two profiles for each cross section. These represent first,
the 100 -year, then the 500 -year frequency data.
Attachment 3: Denton Creek encroachment model. The summary printout lists two
profiles for each cross section. The first is the 100 -year flood plain and the second
is the floodway 100 -year water surface elevation.
Attachment 4: Grapevine Creek 100- and 500 -year floodplain model. The summary
printout lists two profiles for each cross section. The first is the 100 -year condition
and the second is the 500 -year.
Attachment 5: Grapevine Creek encroachment model. The summary printout lists
two profiles for each cross section. The first is the 100 -year flood plain and the
second is the floodway 100 -year water surface elevation.
Attachment 6: Cottonwood Creek 100- and 500 -year floodplain model. The summary
printout lists two profiles for each cross section. The first is the 100 -year condition
and the second is the 500 -year.
Attachment 7: Cottonwood Creek encroachment model. The Summary printout lists
two profiles for each cross section. The first is the 100 -year flood plain and the
second is the floodway 100 -year water surface elevation.
Attachment 8: Elm Fork of the Trinity River 10 -, 50 -, 100- and 500 -year flood plain
model. The summary printout lists four profiles for each cross section. The first is
the 10 -year; the second, the 50 -year; the third, the 100 -year; and fourth is the 500 -
year flood plain elevation.
Attachment 9: Elm Fork of the Trinity River encroachment model. The summary
printout lists two profiles for each cross section. The first is the 100 -year flood plain,
and the second is the floodway 100 -year water surface elevation.
The last attachment is a 100 -year and a 500 -year fioodway delineation.
I hope this explains the report sufficiently. Call me if you need further information.
Very truly yours,
KIMLEY -HORN AND ASSOCIATES, INC.
i�
Ron W. Morrison, P.E.
Senior Hydrologist
RWM /pjw
Copy to: John Karlsruher
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