Riverview Estates-CS 850731 INC.
CAFFEY AND MORRISON, INC.
ENGINEERS -- HYDROLOGISTS
PARKWAY CENTRAL PLAZA
611 RYAN PLAZA, SUITE 700
ARLINGTON, TEXAS 76011
METRO 1817) 261-0095
July 31, 1985
Mr. Jim LaGrote
Federal Emergency Management A~ency
Region 6
800 N. Loop 288
Denton, Texas 76201
Dear Jim,
I have attached a copy of a letter that I wrote to Mr. Tim
Tompkins of Tompkins Development Co. Would you please look it
over and let me know if I am on the right track.
Let me know if I can provide clarification.
Si nc er el y,
Vi c e-Pr esi dent
Caffey and Morrison, Inc.
-.-. ,, INC.
CAFFEY AND MORRISON, INC.
ENGINEERS -- HYDROLOGISTS
PARKWAY CENTRAL PLAZA
611 RYAN PLAZA, SUITE 700
ARLINGTON, TEXAS 76011
METRO (817) 261-0095
July 31, 1985
Mr. T~m Tompkins, President
Tompkins Development Company
Lo~ Colinas Business Park
3131 Premier Drive
Irving, Texas 75063
Dear Mr. Tompkins:
This letter is in regard to a 25 acre tract of land in the city
of Coppell, Texas. The location is generally south of Sandy Lake
Road and adjacent to the Elm Fork of the Trinity River. My
understanding is that you are considering purchasing the land
for future development and are naturally very interested in its
development potential. In this regard I have reviewed the
material available and talked to the parties involved and have
reached the following conclusions:
1. On July 12, 1976, the Federal Emergency Management
Agency (FEMA) contracted with the Fort Worth District Corps
of Engineers to produce a Flood Insurance Study (FIS). This
study used existing topographic information together with
some new surveys that the Corps performed to try to
mathematically "model" the Elm Fork of the Trinity River and
its overbanks. The purpose of this model was to determine
the flood plain, the floodway, and the lO0-year frequency
flood water surface elevations. This was a particularly
difficult task since the Trinity flood plain is sometimes
three and four miles wide. It is about 2 miles wide in the
area of the subject tract of land adjacent to Sandy Lake
Road. One can imagine the task of picking out and modeling
every spot of high ground in this wide flood plain for the
e~tire length of the Trinity. Needless to say, there are
many chances to miss portions of higher ground in this
pr oc ess.
The Corps study produced two maps, portions of which I have
attached. These maps are generally referred to as the F~RM
(Flood Insurance Rate Map) and the Floodway maps. The FIRM
shows the flood plain and the lO0-year flood elevations.
The Floodway shows an area inside the flood plain that is
very restrictive regarding development. In fact, in order
to build or fill or almost anything in the floodway the
developer must prove that the action has no adverse impact
on anyone outside his property. This means that the
development cannot increase flood elevations or cause
erosive velocity increases.
Generally, when someone wants to build in the floodway they
hire an engineer to do a flood study that prove~ that the
impact of the proposed development is offset by some other
work such as channelization or excavation. However, in some
cases it is possible to prove there is no adverse impact
simply by better defining the model, or by providing better
survey data, or both.
2. In April of 1983, a survey was performed on the subject
property by Mr. J. B. Pike, a registered public surveyor
(copy attached). Thi~ survey showed that most of the
subject property was elevated above the lO0-year frequency
flood. The sketch below (although not to scale)
illustrates this situation graphically.
The portion shown as cross hatched is above the flood levels
and therefore would not affect or be affected by the passage
of the lO0-year flood. Naturally, no one can exactly say
where the lO0-year elevation would occur because it depends
on rainfall patterns and watershed parameters and other
factors that are not easy to describe. However, this
elevation, along with the floodway have been accepted
administratively as exact; and they are very difficult to
change.
3. FEMA through the National Flood Insurance Program
regulates minimum standards for participating cities and
counties to follow in order to keep their Nationally backed
Flood Insurance and other related benefits. In many cases
the city may choose to enforce stricter standards and in
those cases FEMA backs them up. In fact FEMA encourages
adoption of more stringent standards. So meeting minimum
FEMA criteria does not always insure that development can
occur.
4. After my recent meeting with Coppell's City Engineering
Firm, Ginn Engineering, regarding this project, I concluded
that the city is unwilling to make any statement about the
potential for land development in Coppell. Mr. Ginn feels
that it might cause problems in the future. Also, they are
not sure about some of the survey work that has occurred £n
the past. Mr. Ginn was quick to point out that they are not
questioning the survey referrenced in this letter. However,
he would like to see more data on it, such as location of
benchmarks.
Mr. Ginn stated that the city would review a specific plat
correctly filed, but they would not make any statements
about potential development in the area.
In conclusion we have reviewed this entire process,
only state certainties in terms of "if".
and we can
1. If the 1983 Pike Survey is correct and represents
conditions that existed naturally at the time it was done
(and I have no reason to believe otherwise, at this time)
then any development on the areas shown outside the cross
hatched portion (attached survey) would not have an adverse
impact on flooding outside the property.
2. If the City of Coppell accepts FEMA minimum standards
for flood plain and floodway development, and the conditions
in the above statement No. I are true, then I can see no
reason why the city would not allow development on the
property. Assuming that the development meets with all
other city requirements.
3. I have contacted Mr. Jim LaGrote of-FEMA, Region 6 and
Mr. Matt Miller of FEMA National, and they both agree with
my conclusions. In fact, they have both stated that the
matter should not even involve FEM~ since no one would be
causing any adverse conditons to exist in the flood plain.
I have sent a copy of this letter to Mr. LaGrote at FEMA, Region
6 and asked him to provide some comment. If I can be of further
assistance in this matter please let me know.
Si nc er el y,
Ronald W. Morrison, P.E.
Vi ce-Pr esi dent
Caf fey and Morrison, Inc.
CC:
Mr. Jim LaGrote
FEMA, Region 6
Denton, Texas