ST0502A-CS161019 (2)
October 19, 2016
Mr. Michael Garza, P.E.
Assistant Director of Public Works
City of Coppell
255 Parkway
Coppell, TX 75019
RE:Comments for LOMR for Sandy Lake Road and Freeport Parkway at Cottonwood Branch
Dear Mr. Garza:
Kimley-Horn and Associates, Inc. (Kimley-Horn) is in receipt of the Letter of Map Revision (LOMR)
submittal for Sandy Lake Road and Freeport Parkway, prepared by Teague Nall and Perkins, Inc.
(Engineer) dated August 2016 and received by Kimley-Horn on October 6, 2016. Kimley-Horn has
reviewed the documents for adherence to the City of Coppell Floodplain Management Ordinance and
National Flood Insurance Program regulations. Kimley-Horn offers the following comments based on a
review of the above documents:
Comment 1:Water surface elevations shown in Tables 3 and 4 are inconsistent with hydraulic
modeling output. Revise the tables to remove this discrepancy.
Comment 2:Mapping should not be based on the preliminary maps for Dallas County. FEMA will only
accept topographic information, mapping, and hydraulic modeling that is based on current FEMA
effective information. Revise the regulatory floodplain and floodway delineations to tie-in to FEMA
effective floodplain and floodway delineations. Update MT-2 Form 1, the topographic workmaps and
Annotated FIRM accordingly to be based on current FEMA effective information.
Comment 3:Per the topographic workmaps, this LOMR application is proposing to revise the effective
floodway, 100-year floodplain, and 500-year floodplain delineations. However, the Annotated FIRM
only maps the revised floodway and 100-year floodplain. Revise the Annotated FIRM to include the
revised 500-year floodplain delineation.
Comment 4:It is unclear how the Engineer determined the boundary condition for the floodway HEC-
RAS models. Typically, 1 foot above the Base Flood Elevation (BFE) is a standard assumption as the
boundary condition for a floodway profile. Revise the modeling accordingly or provide justification of
the boundary condition water surface elevation values.
Comment 5:Provide a discussion in the report that summarizes the source of the reach boundary
conditions used in the ultimate condition hydraulic modeling.
Comment 6:Due to the LOMR application being prepared for recently constructed improvements, it is
recommended to revise the nomenclature to be “Pre-Project” (before construction) as opposed to
“Revised Existing”.
kimley-horn.com12750 Merit Drive, Suite 1000, Dallas, TX 75251972 770 1300
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Comment 7:The Engineer noted on page 3 of the report that the cross sections at the bridge face
were assigned contraction and expansion coefficients of 0.1/0.3; however, the values of 0.3/0.5 were
assigned at the bridges per the Engineer’s hydraulic modeling. It is our opinion that 0.3/0.5 values are
appropriate for the bridges. Revise the report to be consistent with the modeling. Also, revise the typo
in the Contraction/Expansion column of Table 2 at cross section 9494.
Comment 8:Floodway encroachments in the provided hydraulic models should be revised such that
they are not located inside of the channel bank stations.
Comment 9:Discrepancies were found when comparing the mapped floodplain and floodway widths
to the hydraulic modeling output widths. Revise the modeling and/or mapping to remove this
inconsistency.
Comment 10:Mapped floodplains on the topographic workmaps are not consistent with topography in
some locations; especially near the Sandy Lake Road crossing. For example, a portion of the Sandy
Lake bridge is mapped as being overtopped in the 100-year event per both floodplain workmaps.
Additionally, mapped floodplain elevations are not consistent with the elevations shown in the hydraulic
modeling output at some locations. Revise the mapping to remove these inconsistencies.
Comment 11:Per the Engineer’s hydraulic modeling, flowlines of the channel were modified in post-
project conditions from pre-project conditions. More specifically, flowlines were relocated, elevated, or
lowered at cross sections 9590, 9475, 12539, 12567, and 12707; however, topographic workmaps do
not indicate re-grading within the channel at these locations. Modify the topographic workmap and/or
modeling to remove this inconsistency.
Comment 12:Cross section 12420 geometry is the same when comparing pre- and post-project
condition hydraulic modeling; however proposed contours are shown in the left overbank of the cross
section. Similar case for 12868 cross section. Revise the modeling to remove these errors.
Comment 13:Per the Engineer’s provided hydraulic modeling, the post-project condition proposed an
approximate 3.5-foot flowline drop from 12567 to 12539, and then an approximate 1.5-foot rise in
flowline from 12539 to 12420. Confirm this is correct and that positive drainage will occur in this portion
of the channel.
Comment 14:Per FEMA’s NFIP Regulations 44 CFR Section 60.3(d)(3), encroachments within the
floodway are prohibited unless the proposed encroachment doesn’t cause an increase in Base Flood
Elevations. The Engineer is not following this criterion per the post-project hydraulic modeling output at
cross section 12539.
Comment 15:The water surface elevation summary tables provided in the report are inconsistent with
the workmaps. Revise the report accordingly to remove this inconsistency.
Comment 16:There are no cross section labels on the “Topographic Workmap – Freeport Existing/FIS
discharges”. Revise the workmap to include cross section labeling. Additionally, the North Arrow is
incorrect on the Freeport Parkway topographic workmaps. Revise the workmaps to remove this error.
kimley-horn.com12750 Merit Drive, Suite 1000, Dallas, TX 75251972 770 1300
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Comment 17:Geometry shown in the post-project hydraulic model cross section 9590 is not consistent
with the topographic workmap. Revise the modeling accordingly.
Comment 18:Gabion wall and proposed grading contour information shown on the “Topographic
Workmap – Freeport Existing/FIS Discharges” and the “Topographic Workmap – Freeport Ultimate
Conditions Discharges” at cross sections 12868, 12707, 12567, 12539 and 12420 do not match the
information shown on the provided channel grading plan sheets from the “Reconstruction Plans for
Freeport Parkway” (Teague, Nall & Perkins, September 2015). Provide as-built information for the
channel improvements near Freeport Parkway that matches the as-built hydraulic modeling and
floodplain workmaps. Revise the modeling and workmaps as necessary.
Comment 19:The Engineer indicated the LOMR does not involve the placement of fill per MT-2 Form
2; however, the provided workmaps and modeling indicate there are several locations of fill in the
regulatory floodplain. Revise the forms accordingly.
Comment 20:Provide the effective water surface elevation values in MT-2 Form 2, Section B.1.
Comment 21:The proposed/revised water surface elevation at cross section 12957 in MT-2 Form 2,
Section B.1 does not match hydraulic modeling output. Revise the form accordingly.
Comment 22:Update the MT-2 Forms with the Licensed Engineer’s new expiration date.
Comment 23:Per FEMA criteria, “channelization” sections of the MT-2 Forms shall be filled out when
any portion of the stream channel is altered or relocated; however, the Engineer did not fill out any
information under these sections in the provided FEMA forms. Revise the forms to include the
channelization information.
Further modifications to the modeling and the report as a result of addressing these comments may
result in additional comments not noted in this letter. The City should reserve the right to make
additional comments to subsequent submittals. Should you have any questions regarding these
comments, please do not hesitate to contact me at (972) 770-1300 orkate.ploetzner@kimley-horn.com.
Sincerely,
Kate E. Ploetzner, P.E., CFM
Engineer
kimley-horn.com12750 Merit Drive, Suite 1000, Dallas, TX 75251972 770 1300