DWU-CS121026 ••• HALFF
October 26, 2012
AVO 21721
Mr. Kenneth M. Griffin, P.E.
Director of Engineering and Public Works
City of Coppell
255 Parkway Boulevard
P.O. Box 9478
Coppell,TX 75019
RE: Proposed Bridge Crossing of Denton Creek
Dear Mr. Griffin,
At the request of the City of Coppell, Halff Associates, Inc. has prepared the following letter
report to summarize the hydraulic study results for a proposed bridge crossing of Denton Creek
(see Exhibit 1: General Location Map). This crossing will be utilized by Dallas Water Utilities for
access to the proposed pre-sedimentation basins constructed along the Elm Fork of the Trinity
River. A Corridor Development Certificate (CDC) application for the pre-sedimentation basin
project was submitted on April 22, 2009. Halff was informed by the North Central Texas Council
of Governments that all municipalities affected by the CDC were notified on June 30, 2009 by
the City of Carrollton (refer to the attached email). The CDC for the project was approved in
February 2010.
The hydraulic model used for this analysis is based on the most up to date model from the
United States Army Corp of Engineers (USACE), received in June 2008.
The USACE model was updated by adding three (3) cross sections in the proposed bridge area
and 17 lateral weirs to create a revised existing model. A proposed conditions model, analyzing
the hydraulic impacts of the proposed crossing, was developed by modifying the USACE model
with the proposed crossing. The proposed crossing was inserted into the model (see Figure 1)
based on preliminary design plans.
The analysis found that the proposed crossing will result in water surface elevation rises along
the creek when compared to results from the Denton Creek revised existing conditions model.
However, all but one of these rises occurs at cross sections in an area where the Elm Fork of the
Trinity River controls regulatory flood levels. At cross section 15899.2 a rise of 0.01 feet occurs
in the Denton Creek flood profile. Upstream of this section water surface elevations either
match or are slightly less than existing conditions (see attached tables in Appendix A). Velocity
changes due to the project are minor. The amount of freeboard provided by the proposed
bridge crossing is approximately 7.7 ft. above the Denton Creek 100-year water surface
HALFF ASSOCIATES.INC.
12(2 r;OR7H BOWSER ROAD EL (2:4)346 6200 1.,/WW.HALF(CO,
.,.(HA4D)ONI TX 75051.2275 CAX (2t4)739-0095
EE HALFF
elevation profile and approximately 3.9 ft. compared to the Elm Fork 100-year (CDC) water
surface elevation profile. This freeboard should be more than adequate to prevent debris build
up at the proposed bridge for this and lesser storm magnitudes. Appendix A contains water
surface elevation and velocity comparison tables for the analysis.
In my opinion, the impact is insignificant. The 0.01 ft. rise is within the tolerance of 0.04 ft.
allowed in the current CDC guidelines (Section 2.1.1.1, page 2-1, Fourth Edition Corridor
Development Certificate Manual,July 2009).
Please contact us if you have any questions or comments about this analysis.
Sincerely,
HALFF ASSOCIATES, INC. , -le OF,T k
F4
•,s
TBPE Firm No. F-312 ,�s••' .c'
.. .............ER E. SKIPtiNITH
48752 14;
Walter Skipwith, P.E., D.WRE 41°A,'4$0/sTPK.s4,1
it
Chairman *.,../0 A N/
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cc. Dallas Water Utilities I' /4'I
HALFF ASSOCIATES,INC.
120`.NORTH LIOWSER ROAD DEL (214)546-6200 WWWHAI.1
RICHARDSON TX 75081-7275 ,AX (2V:) 739-OO95
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KEY TO FEATURES Scale in Feet 1
-Stream Centerline Q General Location Exhibit 1 ■■■ HALF F`
;r Cross Section General Location Map NNE
;;; HALFF!
Figure 1
Denton Creek Plan 1)RAWrevex_Final 10/24/2012 2)HiBridge_Final 10/24/2012
y RS•4563 BR
�--.075 T .035 �- .05
455-
Legend
4'.'S 100-year-Proposed
•
Ground
450 ..___.nef1._ .........
•
Bank Sta
445-
440'
Existing Conditions
435• Proposed Conditions
430-
425• -
100 200 300 400 500 600 700
Station(n
Figure 2 — Upstream Bounding Cross Section
Denton Creek Plan 1)RAWrevex_Final 10/24/2012 2)HiBridge_Final 10/24/2012
RS•4594
.075 111 .04 � .05
450'
Legend
4 A 4
WS 100-year-Proposed
WS 100-year-Revised Existing
•
Ground
445 a
• bett
•
Bank Ste
•
440'
.5
16 •
W '
435'
•
430-
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0 100 200 300 400 500 600 700
Station(11)
HALFF ASSOCIATES,INC.
1201 NORTH BOWSER ROAD TEL (214)346-6200 WWWHALFF.COM
RICHARDSON.TX 75081-2275 FAX(214)739-0095
HALFF=
Figure 3 —Downstream Bounding Cross Section
Denton Creek Plan- 1)RAWrevex_Finai 10/24/2012 2)HiBridge_Final 10/24/2012
RS=4526
450' .075 r� .04 r' 65
'--4 Lege�
INS 100-year-Proposed
• WS 100-year-Revised Existing
■
Ground
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heft
•
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440-
1'0
a
w
435-
430-
42`
0 100 200 300 400 500 600
Station(11) ,
HALFF ASSOCIATES,INC.
1201 NORTH BOWSER ROAD TEL (214)346-6200 WWWHALFF COM
RICHARDSON,TX 75081-2275 FAX(214)739-0095
I! HALFF
Appendix A
HALFF ASSOCIATES,INC.
1201 NORT H BOWS-R ROAD , (2■4)346 6200 VW/M41AL)I COw
111K 1A1 VSON. IX 7S0E1-2275 1 AX 12/4)739-0091,
Table 1-100 Year Water Surface Elevation Comparison
.. c . .',... £-, t a,w s
TJ- 4 � S f �'+W�. '' ' ( fi ' d f 1,,,,,,,,-.;,y
g, k - A 5 Fp �;' zF, . ,1 if t � , _� a y
.o '/ ' ^ r ,,L4 F $'� (i * - � 444424441
' C. 0 b L } } '1 ,,,,..,$t, Y � Vi � ,-ss � ' . 4 ' ,,�.xy ,>. , , .: -4, , s , :a� -,. - -- m .
238.8046 97178 437.6 437.62 447.97 0.02 -10.35
682.9643 * 438.22 438.25 448.13 0.03 -9.88
1193.827 * 438.79 438.82 448.09 0.03 -9.27
1622.861 97178 439.29 439.31 447.97 0.02 -8.66
2111.729 * 439.87 439.9 446.98 0.03 -7.08
2572.454 * 440.11 440.13 446.78 0.02 -6.65
3196.112 93940 440.17 440.19 445.81 0.02 -5.62
3883.857 93940 440.88 440.92 445.81 0.04 -4.89
4162.358 93940 441.08 441.11 445.81 0.03 -4.7
4444.47 93940 441.37 441.4 445.81 0.03 -4.41
Proposed 4526 93940 441.42 441.44 445.81 0.02 -4.37
Bridge Area 4594 93940 441.53 441.55 445.81 0.02 -4.26
4684 93940 441.57 441.59 445.81 0.02 -4.22
4946.34 93359 441.71 441.73 444.77 0.02 -3.04
5627.715 * 442.11 442.13 446.19 0.02 -4.06 Elm Fork
6610.648 * 442.63 442.65 446.9 0.02 -4.25 Controls
7314.804 * 443 443.02 448 0.02 -4.98
8225.475 * 443.46 443.48 448.04 0.02 -4.56
8809.744 * 443.89 443.91 448.13 0.02 -4.22
9415.459 * 444.19 444.21 448.31 0.02 -4.1
9967.479 * 444.46 444.48 448.41 0.02 -3.93
10496.35 * 444.86 444.89 448.51 0.03 -3.62
11174.68 * 445.51 445.53 448.56 0.02 -3.03
11776.66 * 446.3 446.31 448.64 0.01 -2.33
12550.71 * 447.26 447.26 448.63 0 -1.37
13143.72 * 447.58 447.59 448.62 0.01 -1.03
13768.48 * 447.89 447.89 448.66 0 -0.77
14425.32 * 448.33 448.33 448.74 0 -0.41
14819.43 * 448.71 448.72 448.76 0.01 -0.04
15238.36 102686 449.22 449.22 448.8 0 0.42
15899.2 * 450.07 450.08 448.86 0.01 1.22
16286.33 • 450.89 450.89 448.91 0 1.98 Denton Creek
16726.37 * 451.35 451.34 448.99 -0.01 2.35 Controls
17232.21 * 451.25 451.25 449.14 0 2.11
17623.43 * 452.61 452.61 449.24 0 3.37
17892.44 105936 452.9 452.9 449.34 0 3.56
Table 2-2 Year Water Surface Elevation Comparison
ey. "�. pf-tt*ttON "<2r4-Wx
a KA i' ,t,t46 ''-,'13AV ¢ le ee : ' X �'a `t-,
' E o ,, '-z :,,,,:,,,,1„ :.
` ` � �' i,k ? "S.' e s_s a ® t y "3 - Yt r { .
5 .�,, ti��`'' .� sx�� ate � � 1 � � �t z� � fi � 'a ��'
w {H-, Z -ti, W� ,hC k ,4�� `hJ '` „$1 1 5 ,�y
b P+^p'3-.9 @ Psr�+av `"U' \ }. r`. i' F '4.'t, `y
����e�'�"�.,•'p¢�ms.-c' .,,F �ai �;.., ',, �zs�� a:h;����5`?s'�-,‘.nst,
238.8046 437.2 437.21 0.01
682.9643 437.82 437.83 0.01
1193.827 438.38 438.39 0.01
1622.861 438.88 438.88 0
2111.729 439.45 439.46 0.01
2572.454 439.68 439.69 0.01
3196.112 439.73 439.74 0.01
3883.857 440.42 440.43 0.01
4162.358 440.62 440.63 0.01
4444.47 440.91 440.92 0.01
Proposed 4526 440.96 440.96 0
Bridge Area 4594 441.07 441.07 0
4684 441.12 441.11 -0.01
4946.34 441.26 441.25 -0.01 Elm Fork
5627.715 441.66 441.65 -0.01 Controls
6610.648 442.17 442.17 0
7314.804 442.54 442.54 0
8225.475 442.99 442.99 0
8809.744 443.43 443.43 0
9415.459 443.72 443.72 0
9967.479 443.99 443.99 0
10496.35 444.42 444.42 0
11174.68 444.95 444.95 0
11776.66 445.43 445.43 0
12550.71 446.05 446.04 -0.01
13143.72 446.36 446.36 0
13768.48 446.71 446.71 0
14425.32 447.17 447.17 0
14819.43 447.51 447.51 0
15238.36 448.04 448.04 0
15899.2 448.91 448.91 0
16286.33 449.5 449.5 0 Denton Creek
16726.37 449.91 449.91 0 Controls
17232.21 449.85 449.85 0
17623.43 450.53 450.53 0
17892.44 450.64 450.64 0
Table 3- 100 Year Velocity Comparison
,.,,,.', ,- -+i ''nrN £ ,,,-...4x. 4„x3 4:4 �e a C' *AG `,...
1-n-.`,'Z'/C,.‘',;-.. -`4. ;;;'-',-;:5--n--4. 4 ,y '". 1 3'3� Cc ,.tB ,� �7 :
238.8046 3.12 3.12 0
682.9643 3.12 3.12 0
1193.827 2.92 2.93 0.01
1622.861 3.15 3.16 0.01
2111.729 2.99 3 0.01
2572.454 1.42 1.42 0
3196.112 3.5 3.5 0
3883.857 3.11 3.11 0
4162.358 3.56 3.56 0
4444.47 3.05 3.06 0.01
Proposed 4526 3.23 3.23 0
Bridge Area 4594 2.65 2.66 0.01
4684 2.63 2.64 0.01
4946.34 2.67 2.68 0.01
5627.715 2.19 2.2 0.01
6610.648 2.68 2.69 0.01
7314.804 2.38 2.38 0
8225.475 2.95 2.96 0.01
8809.744 2.39 2.39 0
9415.459 2.1 2.1 0
9967.479 2.62 2.61 -0.01
10496.35 2.78 2.79 0.01
11174.68 3.32 3.3 -0.02
11776.66 5.12 5.12 0
12550.71 3.34 3.34 0
13143.72 2.98 2.98 0
13768.48 3.21 3.21 0
14425.32 3.23 3.23 0
14819.43 4.05 4.04 -0.01
15238.36 4.6 4.6 0
15899.2 4.5 4.5 0
16286.33 5.5 5.5 0
16726.37 1.3 1.3 0
17232.21 6.78 6.78 0
17623.43 4.72 4.72 0
17892.44 3.41 3.41 0
Table 4-2 Year Velocity Comparison
s ._ E Ei ' `9[ Q �f `1.m.jP+ �G zr.K `0. C:
238.8046 3.08 3.08 0
682.9643 3.04 3.04 0
1193.827 2.86 2.86 0
1622.861 3.1 3.1 0
2111.729 2.93 2.93 0
2572.454 1.37 1.37 0
3196.112 3.47 3.47 0
3883.857 3.07 3.07 0
4162.358 3.52 3.52 0
4444.47 3.01 3.01 0
Proposed 4526 3.23 3.23 0
Bridge Area 4594 2.62 2.63 0.01
4684 2.59 2.6 0.01
4946.34 2.63 2.63 0
5627.715 2.15 2.16 0.01
6610.648 2.63 2.63 0
7314.804 2.32 2.32 0
8225.475 2.9 2.9 0
8809.744 2.35 2.35 0
9415.459 2.07 2.07 0
9967.479 2.67 2.67 0
10496.35 2.69 2.69 0
11174.68 2.61 2.6 -0.01
11776.66 3.5 3.5 0
12550.71 2.96 2.96 0
13143.72 2.84 2.84 0
13768.48 3.07 3.07 0
14425.32 2.96 2.96 0
14819.43 4.14 4.14 0
15238.36 4.43 4.43 0
15899.2 3.92 3.92 0
16286.33 4.91 4.91 0
16726.37 0.96 0.96 0
17232.21 4.67 4.67 0
17623.43 2.82 2.82 0
17892.44 1.48 1.48 0 I
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