Alexander Ct-SY070610N D NATHAN D. MAIER
CONSULTING ENGINEERS, INC.
June 10, 2007
Mr. Brad W. Pickering, EIT (IN), CFM
Kimley -Horn and Associates, Inc.
12700 Park Central Drive, Suite 1800
Dallas, TX 75251
Re: Letter of Map Revision (LOMR)
Grapevine Creek/Alexander Court
NDMCE Project No. 07 -03 -026
KHA No.: 0613124008
Dear Mr. Pickering:
This is in response to your letter dated May 23, 2007 regarding the above referenced LOMR request. We
have addressed each of the items requested in that letter and have made revisions to the submittal
accordingly. Here are provided your comments in bold with our responses following.
Item 1: The MT -2 Form 2, page 1 of 2, states that the upstream tie -in of the study is at cross
section 27620. Cross section 27900 has been added to the revised existing conditions model and
is not included in the effective model. Revise the forms to reflect an effective tie -in upstream of
the model modifications.
The MT -2 Form 2 has been modified to reflect the effective cross - section 30130 as the tie-in cross
section.
Item 2: Revise the Floodplain Work Map to include the benchmarks and vertical datum used for
the on- ground survey.
An updated copy of the Floodplain Work Map with benchmarks and vertical datum used for the on- ground
survey is included as part of this package.
Item 3: The water surface elevations table in the report text is not consistent with the modeling
output for the effective foodway HEC -RAS model. Revise the report to be consistent with the
modeling output.
The water surface elevation table in the report has been modified to be consistent with the Effective
Floodway HEC -RAS modeling output.
Item 4: Revise the Location Map to reflect the boundaries of the LOMR submittal.
The Location Map has been reviewed to include the boundaries of the LOMR submittal. An updated copy
is included in this package.
Item 5: Cross section 22600, the location of the downstream effective tie -in, is not shown on the
Floodplain Work Map. Revise the Work Map to show this cross - section.
The Work Map has been revised to include cross - section 22600
Two Park Lane Place / 8080 Park Lane / Suite 600 / Dallas, Texas 75231 / (214) 739 -4741
Item 6: The sum of reach lengths for the HEC -RAS revised conditions model does not match the
sum of reach lengths in the FEMA effective model. Revise the reach lengths in the revised
conditions model or explain the discrepancy.
Channel lengths vary slightly due to the more detailed topographic information in the area. The sum of
channel reach lengths in the revised conditions model is a total of 11.0 -ft larger than the sum of the
channel reach lengths in the effective model. Such a small difference should not significantly impact the
results obtained.
Item 7: The report text states that Manning's 'n' values were taken from the effective model, but
they vary from the effective model at multiple locations. Revise the model to be consistent with
the effective modeling or justify the proposed Manning's 'n' values.
The revised conditions model Manning's 'n' values have been modified to be consistent with the effective
model. This change affected the resulting water surface elevations. An updated water surface elevation
summary table and a copy of the modified computer run are also included in this revision.
Item 8: Property owner notification is required by NFIP regulation 65.7(b)(1) due to the floodway
revision. The notices must include the extent of revision, the changes to the floodway, and
contact information for any interested parties.
Property owner notifications will be sent once the City approves the results obtained by this study, and a
final submittal to FEMA is done.
Item 9: Revise the legend on the Floodplain Work Map to reflect revised existing conditions and
not proposed conditions.
The Floodplain Work Map legend has been modified and an updated copy has been included in this
package.
Item 10: Future development adjacent to the subject reach shall respect both the 100 -year fully
developed and FEMA effective Foodplain boundaries.
The plat being approved has set the minimum finished floor elevations to be the higher of 2 -ft above
FEMA, or 1 -ft above the fully developed.
Don't hesitate to contact me at (214) if you have any questions regarding the information listed above.
Thank you for your assistance.
Sincerely,
NATHAN D. MAIER
CO TING ENGINEERS, INC.
Od
Y
Design eer
P: (214) 739 -4741
F: (214) 739 -5961
E: oiohnson(cbndmce.com
Cc: Ken Griffin, P.E.