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DR9502-CS 960611lll · ,, Halff Associates ill ENGINEERS · ARCHITECTS · SCIENTISTS PLANNERS · SURVEYORS 8616 NORTHWEST PLAZA DRIVE DALLAS, TEXAS 75225 (214) 739-0094 FAX (214) 739-0095 June 11, 1996 AVO 15254 Mr. Kenneth M. Griffin, P.E. Assistant City Manager/Director of Public Works City of Coppell 255 Parkway Blvd. Coppell, Texas 75019 q 6-D2 Re: Flood Plain Map Revisions at Andrew Brown Park West Hydraulic Analysis for a Future Swimming Pool Site Dear Mr. Griffin: Included in this letter report you will find the results of a hydraulic analysis requested during our May 14, 1996 meeting conceming the potential reclamation of part of Andrew Brown Park West for a future swimming pool. This hydraulic study consisted of revising part of cross-sections 32725, 33145 and 33470 along Denton Creek, first in a revised existing condition model, then in different versions of a proposed condition model. This letter describes the results of the two best alternatives, Reclamation Alternate A and Reclamation Alternate B. In this package you will find documents illustrating each alternative such as a table of water surface elevation comparison, a set of cross-section plots, a 1 lx17 site map and a summary of hydraulic data. Revisions to the existing condition model included updating the ground data to reflect the City of Coppell's latest topographic mapping for all 3 cross-sections. In addition, the effective flow was widened at cross-section 33470 to provide a more realistic flow transition between cross-sections 33145 and 34260. The Manning n-value was increased at that location in order to better balance Q's (discharges) throughout the park. No revisions were made to the cross-sections downstream of the site in neither the existing nor any of the proposed models. These changes result in a revised existing conditions model. Reclamation Altemate A involves reclaiming an area along Denton Creek that stretches across cross- sections 32725 and 33145 as shown in red on the attached map A. Because the ~park is in a non- effective flow area of cross-section 32305 upstream of Denton Tap Road, the shape of the fill in that area has no effect on hydraulics. A smaller fill that would not involve destruction of part of the recently refinished parking lot would be modeled in the same manner as a larger one. This alternative causes a negligible 0.01 foot rise in water surface elevation at 2 locations upstream of the site (see' attached table A). Any attempt to fill or excavate section 33470 resulted in water surface elevation rises that could not be resolved. Please note that the attached map A shows the extent of the existing 100-year flood plain but not yet that of the proposed flood plain. DALLAS · FORT WORTH · HOUSTON · ARLINGTON · McALLEN · CHICAGO TRANSPORTATION ° WATER RESOURCES · LAND DEVELOPMENT · MUNICIPAL · ENVIRONMENTAL ° STRUCTURAL MECHANICAL ° ELECTRICAL ° SURVEYING · GEOGRAPHIC INFORMATION SYSTEMS ARCHITECTURE ° LANDSCAPE ARCHITECTURE · PLANNING ' -rr- I T il l,, Halff Associates Ill ENGINEERS · ARCHITECTS ° SCIENTISTS PLANNERS ° SURVEYORS Reclamation Alternate B involves removing most of the park area from the Denton Creek effective flood plain to allow additional future improvements to the park. As shown on map B, a berm would be constructed upstream of the site that would prevent any flow from Denton Creek across the park. Only the south end of the park would remain in the Cottonwood Creek effective flow area. In essence, from a hydraulic standpoint, this approach involves moving the confluence of the two streams upstream of cross-section 32305 (moving the discharge change in the hydraulic models). If this option were to be further considered, the Cottonwood Creek model would have to be revised as well to include the area between cross-sections 32305 and 33145 (the extent of the reclamation to the south as shown in red on map B is approximate). Without some sort of channelization, this option is unacceptable as it causes rises in Denton Creek flood levels of as much as 0.15 foot upstream of the site (see attached table B). Encroachments effects on Cottonwood Creek were not tested. Please note that map B shows the extent of the existing 100-year flood plain but not yet that of the proposed flood plain. Please review these documents and call either Walter E. Skipwith or myself at 214-739-0094 should you have any questions. Sincerely, HALFF ASSOCIATES, INC. Sabine Borgnet-Harris Enclosures. File: lt~06-06.doc Table A - Andrew Brown Park West Comparison Table of 100-year Water Surface Elevations FIS Duplicate FIS Duplicate Effective Revised Existing Conditions Proposed Conditions Location DCMODZ.hc2 DCMODZ.dat RVEXDC3.dat PROPDC3.dat Section WSEL Section WSEL Difference Section WSEL Difference Section WSEL Difference 30027 456.38 30027 456.38 0 30027 456.38 0 30027 456.38 0 30384 456.74 30384 456.74 0 30384 456.74 0 30384 456.74 0 30604 457.42 30604 457.42 0 30604 457.42 0 30604 457.42 0 30958 457.93 30958 457.93 0 30958 457.93 0 30958 457.93 0 ~ 31335 457.83 31335 457.83 0 31335 457.83 0 31335 457.83 0 32150 457.91 32150 457.91 0 32150 457.91 0 32150 457.91 0 Denton Tap Rd Bridge 32200 457.71 32200 457.71 0 32200 457.71 0 32200 457.71 0 DenOn Tap Rd Bridge 32230 457.91 32230 457.91 0 32230 457.91 0 32230 457.91 0 32250 460.31 32250 460.31 0 32250 460.31 0 32250 460.31 0 U/S Den~nTap Road 32305 460.15 32305 460.15 0 32305 460.15 0 32305 460.15 0 32725 461.24 32725 461.24 0 32725 461.22 -0.02 32725 461.18 -0.04 33145 461.44 33145 461.44 0 33145 461.54 0.10 33145 461.51 -0.03 33470 461.72 33470 461.72 0 33470 461.70 -0.02 33470 461.71 0.01 34260 462.54 34260 462.54 0 34260 462.27 -0.27 34260 462.27 0 34850 462.56 34850 462.56 0 34850 462.31 -0.25 34850 462.31 0 34950 463.65 34950 463.65 0 34950 463.41 -0.24 34950 463.42 0.01 36970 465.99 36970 465.99 0 36970 465.99 0 36970 465.99 0 38200 466.71 38200 466.71 0 38200 466.70 -0.01 38200 466.70 0 39290 466.99 39290 466.99 0 39290 466.99 0 39290 466.99 0 39440 466.72 39440 466.72 0 39440 466.71 -0.01 39440 466.71 0 ~ 39490 467.15 39490 467.15 0 39490 467.15 0 39490 467.15 0 39540 467.06 39540 467.06 0 39540 467.05 -0.01 39540 467.05 0 40650 468.20 40650 468.20 0 40650 468.20 0 40650 468.20 0 48000 470.69 48000 470.69 0 48000 470.69 0 48000 470.69 0 51350 472.00 51350 472.00 0 51350 472.00 0 51350 472.00 0 53350 472.57 53350 472.57 0 53350 472.57 0 53350 472.57 0 55590 473.25 55590 473.25 0 55590 473.25 0 55590 473.25 0 56940 474.50 56940 474.50 0 56940 474.50 0 56940 474.50 0 File: i:\avo\15254\h&h\clomr~rv-fis-3.xls 10:13:15 6/11/96 z cz) 490 IIII IIII IIII IIII IIII IIII IIII IIII III1__ -.050 .(55 .08I) .045 .05~ .050 480 470 440 - 465. OD LEFT tl t~ - 480.00 RIGHT - _437.70 ELMIN - 420 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 0 500 1000 1500 2000 2500 3000 oqnn Annn ~500 6- 5-1gg6 SECTION 32305 propdc3, dot Al&~ 49O 480 470 460 450 44O I I I I · 060 · O~ I I I I 430 I I I I 7050 t489.00 482. I0 4~8.20 420 ~ ~ ~ I 0 6- 5-1gg6 propdcB, dot I I I I LEFT RIGHT ELMIN I I I I · 05." I I I I ,5 I I I I · 040 I I I I · 055 I I I I I I I I 500 1000 1500 2000 2500 BO00 32725 SECTION 3500 4000 4500 Z 0 W ._~ W 350 .055 .045 .055 - .060 45O 440 49O -460.64 LEFT 460.00 RIGHT _ _438.40 ELMIN - 420 IIII IIII III IIII IIII IIII IIII IIII __1111.__ 0 500 1000 i500 2000 6- 5-ig96 SECT I ON pnopdc3, dot 2500 3000 3500 4000 ~3145 4500 : ] ,,. Z O 490 480 470 460 45O 440 43O - .055 .0§0 . lO0 - .04~5 - -460.20 LEFT i~ ~ 462.00 RIGHT _ _439.00 ELMIN - 42O -500 6- 5-1996 propdc3, dot 0 500 1000 1500 2000 2500 BO00 3500 4000 SECT I ON 33470 ~ ~ ~, z 0 490 48O 470 46O 450 440 43O 42O -1000 6- 5-1996 - 055 .060 055 - .045 .050 -461.20 LEFT 464.00 R!GHT _ _438.80 ELMIN - propdc3, dot -500 0 500 1000 1500 2000 2500 3000 350C SECTION 34260 ~ Z (] 47O 485 460 455 450 445 44O - · 355 .060 . I45 .055 - -464.30 LEFT 464.00 RIGHT _ _439.30 ELMIN - 435 I I I I I I I I I I I I I I I I I I I I I I I I I I I O 200 400 600 800 1000 1200 1400 1600 180C 6- 5-1996 SECTION 34850 pnopdc3, dot SUM P 0 Interactive Summary Printout for MS/PC-DOS micro computers May 1991 NOTE - Asterisk (*) at left of profile number indicates message in summary of errors list DENTON CREEK, TEXAS Summary Printout SECNO CWSEL TOPWID VOL 25530.00 25770 00 26830 00 26880 00 27165 00 27449 00 27748 00 27992.00 28168 00 28492 00 28720 00 28890 00 29124 00 29651 00 29831 00 30027 00 30384 00 30604 00 30958 00 31335 00 32150 00 32200 00 32230 00 32250 00 32305 00 32725 00 33145 00 33470 00 34260 00 34850 00 34950 00 36970 00 38200 00 39290 00 39440 00 39490 00 39540 00 453 52 453 97 454 69 454 71 455 24 455 35 455 42 455 48 455 53 455 57 455 62 455 65 455 70 456 24 456 33 456 38 456 74 457 42 457 93 457 83 457 91 457 71 457 91 460 31 460 15 461 18 461 51 461 71 462 27 462 31 463 42 465 99 466 70 466 99 466 71 467 15 467 05 235 67 272 69 1199 25 1173 21 1418 55 1551 59 1445 81 1344 42 1313 08 1220 21 1095 73 1077 65 984 06 1020 00 857 57 680 98 429 26 825 02 1140 63 1022 21 375 99 165 96 168 00 1263 17 506 02 1616 42 1722 23 1465 82 588 49 168 68 1658 80 1085 02 1222 53 1026 91 848 15 551 15 872 92 .00 18.58 124.23 143.17 178 62 233 09 296 21 363 27 413 14 488 38 554 71 589 31 630 58 696 13 726 11 759 58 795 94 818 92 864 28 911 11 923 18 925.47 927.44 927 51 931 78 969 71 1016 92 1055 81 1133 51 1175 73 1182 80 1392 22 1549 64 1737 30 1763 12 1767 37 1771 78 VCH 6 86 5 50 5 48 5 53 3 07 1 99 2 13 2 32 1 88 1 98 2 40 3 26 5 05 3 48 3.11 4 50 6 22 5 35 2 39 8 02 10 78 13 44 13 20 5 45 7 36 4 48 3 39 4 09 3 29 8 72 5 72 5 12 2 88 3 34 7 22 4.60 6.54 "4o o oo 48000 O0 51350 O0 * 53350 O0 * 55590 O0 5694O O0 468 20 470 69 472 O0 472 57 473 25 474 50 826 54 1538 61 1438 65 2182 61 1412 63 1465 27 1863.96 2453.93 2908.32 3120.97 3322.91 3418.95 4 57 3 37 2 63 3 30 5 83 5 06 ? r I I // :- '~ I I . J ~ _-:~ 6.1,8 ,~ - _~ .~ ~ ~ ~ __ / / ' / ~1~ ~ /1 I 45~2 II N 7044000 // I / ~ / 455.8 ~ / %'---~?: :_ / / /'~ ~.~.~.~/ I I / / __1 / Z - / - -Z _- ~f f t / // WIS 456,2 I fI I t I i / I / I I x I 5 ,~ x I I ~ I t 462,3 xx ~x, I E~T x 704300D / \ WIS z152,3 bid %,N% "x ,xx %x\\ X x ~59.5 :\ I X I 0.4 k / / \ ELDS !//i/I/ APPI~)XlMA TI LC I co'rToNwo00 cF .× 4 5 (,0 Table lB - Andrew Brown Park West Comparison Table of 100-year Water Surface Elevations FIS Duplicate FIS Duplicate Effective Revised Existing Conditions Proposed Conditions Location DCMODZ.hc2 DCMODZ.dat RVEXDC3.dat PROPDC4.dat Section WSEL Section WSEL Difference Section WSEL Difference Section WSEL Difference 30027 456.38 30027 456.38 0 30027 456.38 0 30027 456.38 0 30384 456.74 30384 456.74 0 30384 456.74 0 30384 456.74 0 30604 457.42 30604 457.42 0 30604 457.42 0 30604 457.42 0 30958 457.93 30958 457.93 0 30958 457.93 0 30958 457.93 0 31335 457.83 31335 457.83 0 31335 457.83 0 31335 457.83 0 32150 457.91 32150 457.91 0 32150 457.91 0 32150 457.91 0 Denton Tap Rd Bridge 32200 457.71 32200 457.71 0 32200 457.71 0 32200 457.71 0 Den~nTap Rd Bridge 32230 457.91 32230 457.91 0 32230 457.91 0 32230 457.91 0 32250 460.31 32250 460.31 0 32250 460.31 0 32250 460.31 0 U/S Denton Tap Road 32305 460.15 32305 460.15 0 32305 460.15 0 32305 460.15 0 32725 461.24 32725 461.24 0 32725 461.22 -0.02 32725 461.17 -0.05 33145 461.44 33145 461.44 0 33145 461.54 0.10 33145 461.56 0.02 33470 461.72 33470 461.72 0 33470 461.70 -0.02 33470 461.81 0.11 34260 462.54 34260 462.54 0 34260 462.27 -0.27 34260 462.42 0.15 34850 462.56 34850 462.56 0 34850 462.31 -0.25 34850 462.45 0.14 34950 463.65 34950 463.65 0 34950 463.41 -0.24 34950 463.54 0.13 36970 465.99 36970 465.99 0 36970 465.99 0 36970 465.99 0 38200 466.71 38200 466.71 0 38200 466.70 -0.01 38200 466.70 0 39290 466.99 39290 466.99 0 39290 466.99 0 39290 466.99 0 39440 466.72 39440 466.72 0 39440 466.71 -0.01 39440 466.72 0.01 39490 467.15 39490 467.15 0 39490 467.15 0 39490 467.15 0 39540 467.06 39540 467.06 0 39540 467.05 -0.01 39540 467.05 0 40650 468.20 40650 468.20 0 40650 468.20 0 40650 468.20 0 48000 470.69 48000 470.69 0 48000 470.69 0 48000 470.69 0 51350 472.00 51350 472.00 0 51350 472.00 0 51350 472.00 0 53350 472.57 53350 472.57 0 53350 472.57 0 53350 472.57 0 55590 473.25 55590 473.25 0 55590 473.25 0 55590 473.25 0 56940 474.50 56940 474.50 0 56940 474.50 0 56940 474.50 0 File: i:\avo\15254\h&h\clomr~rv-fis-4.xls 10:09:26 6/11/96 SUM P 0 Interactive Summary Printout for MS/PC-DOS micro computers May 1991 NOTE - Asterisk (*) at left of profile number indicates message in summary of errors list DENTON CREEK, TEXAS Summary Printout SECNO CWSEL TOPWID VOL 25530.00 25770.00 26830.00 26880.00 27165.00 27449.00 27748 00 27992 00 28168 00 28492 00 28720 00 28890 00 29124 00 29651 00 29831 00 30027 00 30384 00 30604 00 30958 00 31335 00 32150 00 32200 00 32230 00 32250 00 32305 00 32725 00 33145 00 33470 00 34260 00 34850 00 34950 00 36970 00 38200 00 39290 00 39440 00 39490.00 39540.00 453 52 453 97 454 69 454 71 455 24 455 35 455 42 455 48 455 53 455 57 455 62 455 65 455 70 456 24 456 33 456 38 456 74 457 42 457 93 457 83 457 91 457 71 457 91 460 31 460 15 461 17 461 56 461 81 462.42 462.45 463 54 465 99 466 70 466 99 466 72 467 15 467 05 235 67 272 69 1199 25 1173 21 1418 55 1551 59 1445 81 1344 42 1313 08 1220 21 1095 73 1077 65 984 06 1020 00 857 57 680 98 429 26 825 02 1140 63 1022 21 375 99 165 96 168 00 1263 17 506 02 749 65 525 46 832 81 593 04 172 88 1691 80 1085 56 1222 67 1026 99 848 31 551 21 873 05 00 18 58 124 23 143 17 178 62 233 09 296 21 363 27 413 14 488 38 554 71 589 31 630 58 696 13 726 11 759 58 795 94 818 92 864 28 911 11 923 18 925 47 927 44 927 51 931 78 963 30 1002 32 1034 46 1110 72 1153 69 1161 06 1375 65 1533 14 1720 85 1746 68 1750 93 1755 35 VCH 6 86 5 50 5 48 5 53 3 07 1 99 2 13 2 32 1 88 1 98 2 40 3 26 5 05 3 48 3 11 4 50 6 22 5 35 2 39 8 O2 10 78 13 44 13.20 5.45 7.36 4.87 3 69 4 21 3 23_~ 8 6O 5 49 5 12 2 88 3 34 7 22 4 59 6 53 40650 O0 48000 O0 51350 O0 * 53350 O0 * 55590 O0 56940 O0 468 20 470 69 472 00 472 57 473 25 474 50 826 60 1538 63 1438 66 2182 69 1412 63 1465 34 1847 55 2437 58 2891 98 3104 64 3306 58 3402 63 4.57 3.37 2.63 3.30 5.83 5.06 Z 0 490 - 050 .(m55 .061 .045 .055 .050 480 47O 450 440 430 -465.00 LEFT ~ / 460.00 RIGHT - _437.70 ELNIN - 420 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I _ 0 500 1000 1500 2000 2500 3000 3500 Annn 6- 5-1996 SECTION B2305 PROPOC4.0AT .> z cD 490 IIII IIII IIII IIII IIII IIII IIII IIII III1__ 7050 .05~i .060 .040 .055 __ 480 470 ~ __ 460 , ~ ~ 4~ 440 - j 430 -463.00 LEFT ~ ~, - / 462.10 RIGHT - _435.20 ELNIN - 420 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 0 5oo iooo i500 2000 2500 3000 35® Annn ~sl 6- 5-i996 SECTION 32725 PROPOC4. DAT ~1+~ 460 450 III1 350 440 490 420 I I I I I I I · 055 IIII .045 O6O 460. O0 RIGHT 438· 40 ELMIN 500 lO00 1500 PROPDC4. OAT I I I I I I I · 055 2000 2500 BO00 3500 4000 4500 SECT I ON B3145 a ~+r~ Z W _1 49O 48O 470 460 450 440 430 42O -500 6- 5-1996 - .055 .060 . ,00 - .045 - ~ - -460.20 LEFT ~ I 462.00 R'[GHT _ _439,00 ELMfN - PROPBC4. D^T 0 500 1000 1500 2000 2500 SECTION 33470 3000 3500 400C Z o 490 48O - 055 .060 055 - · 045 .050 - -461.20 LEFT 464.00 RIGHT _435.80 ELHIN _ I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 470 460 45O 440 43O 420 -1000 6- 5-1996 PROPDC4. DAT -500 0 500 1000 1500 2000 2500 3000 3500 SECTION 34260 z o w _J W 470 465 460 455 450 445 440 435 6- - .055 .060 .045 .055 - / _-464'30 LEFT {~ _ _464-00 RIGHT _ _439,30 ELNIN - I I I I t I I I I I I I I I I I I I I I I I I 0 200 400 600 800 lDO0 1200 1400 1600 1800 5-1996 SECTION 34850 PROPDC4. 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