Loading...
ST9301A-SY 931130 DRAFT ELM FORK OF THE TRINITY RIVER -- SANDY LAKE ROAD BRIDGE HYDRAULIC STUDY PREPARED FOR: CHARLES GOJER AND ASSOCIATES, INC. THE COUNTY OF DALLAS, TEXAS COUNTY PROJECT NO. 91-838 PRELIMINARY - FOR INTERIM REVmW ONLY THESE DOCUMENTS ARE FOR INTERIM REVmW AND ARE NOT -- INTENDED FOR FINAL PLANNING OR PERM1T PURPOSES. THEY WERE PREPARED BY, OR UNDER THE SUPERVISION OF: -- C. JEAN HANSEN 69365 NOVEMBER, 1993 PEg DATE NOVEMBER 1993 AVO 12687 ALBERT H. HALFF ASSOCIATES, INC. 8616 NORTHWEST PLAZA DroVE DALLAS, TEXAS 75225 - ALBERT H. HALFF ASSOCIATES, INC. ENGINEERS · SCIENTISTS · SURVEYORS · PLANNERS · LANDSCAPE ARCHITECTS ALBERT H. HALFF ASSOCIATES, INC. Engineers s Scientists · Architects · Planners 8616 NoAhwest Plaza Drive DALES, TEXAS 75225 214-7a9-0094 · FAX 739-0095 > WE ARE SENDING YOU,,~ Attached [] Under separate cover via the following items: [] Shop drawings [] Prints [] Plans [] Samples [] Specifications [] Copy of letter [] Change order (~ COPIES DATE NO. DESCRIPTION l THESE ARE TRANSMITTED as checked below: [] For approval [] Approved as submitted [] Resubmit__copies for approval [] For your use [] Approved as noted [] Submit copies for distribution l"~As requested [] Returned for corrections [] Return__corrected prints [] For review and comment [] [] FOR BIDS DUE 19__ [] PRINTS RETURNED AFTER LOAN TO US REMARKS ~ 40%Pre-ConsumerConten,-lO%Post-Cor,,sumerContent SIGNED:~'"--'-~' _ PR0OUCT240 ~ I<, er,ton, ~ 014ri If enclosures ere not as noted, kindly notify us . ELM FORK OF THE TRINITY RIVER SANDY LAKE ROAD BRIDGE HYDRAULIC STUDY NOVEMBER 1993 AVO 12687 Sandy Lake Road Improvements within the cities of Carrollton and Coppell, Texas are a part of the 1992 Dallas County Bond Program. Albert H. Halff Associates, Inc. has been retained for hydraulic design of the proposed bridge crossing over the Elm Fork of the Trinity River. This report describes the existing and proposed condition hydraulic modelling for the Elm - Fork of the Trinity River, upstream of Belt Line Road through the Sandy Lake Road crossing. I. EXISTING CONDITIONS During the late 1970's and early 1980's numerous reclamation projects were constructed in the Trinity River flood plain including several projects along the Elm Fork. Hydraulic - modelling was prepared for each individual project, however an analysis of the cumulative effects of the many reclamation projects was needed throughout the watershed. In 1984 the Fort Worth District, U.S. Army Corps of Engineers (COE) began preparation of a Regional Environmental - Impact Statement (REIS) to address the cumulative impacts of development within the Trinity River flood plains in the Dallas - Fort Worth metroplex. This study utilized existing hydraulic models, looking at existing fidis/encroachments and future development scenarios within the - watershed. One of the conclusions was that intense flood plain development upslxeam could imperil the Dallas levees. Recognizing the need for a comprehensive plan the Senate Committee on Environment and Public Works authorized an 18 - month Reconnaissance Study on the Upper Trinity River corridor. This study has been completed and the COE has now preceded to the Feasibility Study phase which includes the preparation of new hydrologic and hydraulic _ modelling based on updated topography for the entire Trinity River corridor within the Dallas - Ft. Worth metroplex. _ The Upper Trinity River Feasibility Study is a projected five-year study. Aerial Mapping was performed in February 1991 and preliminary versions of these maps are currently available. However, updated hydrologic and hydraulic modelling for the Elm Fork will not be completed - by the COE until 1994. Since the Feasibility Study is ongoing and the new topography is available, Halff Associates has prepared an updated existing condition model in the Sandy Lake Road area. This new hydraulic model is based on the best currendy available data (1991 aerial -- topography). This section describes the procedures, calibration and results of the new hydraulic modelling on the Elm Fork of the Trinity River from upstream of Belt Line Road through Sandy Lake Road. A. Data Collection The current hydraulic model (EF-CDC) for the Elm Fork was obtained from the U.S. Army Corps of Engineers Ft. Worth District (COE) in April, 1993. This model is utilized Albert H. Halff Associates, Inc. Page 1 November 1993 for base conditions and starting water surface elevations immediately upstream of Belt Line Road. In addition new topographic data (1991) was also obtained from the COE for the study reach from Belt Line Road to north of Sandy Lake Road. This is the topography generated for the Upper Trinity River Feasibility Study. Digital Photogrametric cross section data was also provided along with the "in-house" COE computer program "FINTER", which reduces the _ number of ground points in each cross section to 100 or less. B. Procedures The US Army Corps of Engineers computer program, HEC-2 is utilized to compute water surface elevations on the Elm Fork of the Trinity River. This stream hydraulics - program is used to establish the relationship between discharge and water surface elevation for each cross section along the river. The digital cross-section data provided by the COE was reduced in steps by cross section to develop hydraulic model cross sections with less than 100 - ground points as required by HEC-2. Sandy Lake Road bridge sections and existing "n" values were inserted from the Corps of Engineers CDC model for the Upper Trinity River Reconnaissance Study. Reach lengths and bank stations were input utilizing the digital files '- containing section locations as provided by the COE. The revised base hydraulic model was then calibrated to high water marks from the 1989 and 1990 floods. Other engineering studies were also reviewed for applicable modelling notes or corrections. Discharges from the COE Reconnaissance Study are utilized for this Design Study. These discharges were developed by the Corps of Engineers and are based on fully developed land use - throughout the watershed. An analysis utilizing existing land use discharges from the current Flood Insurance Study will be prepared after review and approval of the recommended bridge alternative. A comparison of these discharges is shown in Table 1. TABLE 1 - DISCHARGE COMPARISON ELM FORK - TRINITY RIVER SANDY LAKE ROAD Existing Fully Developed Conditions (cfs) (cfs) 100-year Lewisville FIS 44350 - Coppell FIS - Morrison 48600 (COE Reconn) COE w/CDC 55000 Reconn Study SPF COE w/CCD 100000 - Reconn Study Albert H. Halff Associates, Inc. Page 2 November 1993 The Elm Fork flood plain is partially urbanized through this reach restricting flows through four main passages: two routes within the east overbank, the main channel and the west overbank. Noneffective flow areas were modelled by establishing encroachment limits in a revised base model based on a delineation of the 100-year water surface elevation from the EF- CDC model and the standard practice of 4:1 expansion downstream and 1:1 contraction upstream - of an obstruction. The "ET" option was utilized to model different encroachments for high and low flows. "GR" points were modified, where necessary, to model encroachments and non- effective flow areas withha the flood plain. C. Calibration Severe flooding occurred in the Dallas/Ft. Worth area in the spring of 1989 and 1990. High water marks at the existing USGS Gage No. 08055500, immediately downstream of Sandy Lake Road and along Sandy Lake Road in Carrollton were utilized as a comparison for - calibration to the revised base hydraulic model. Table 2 shows a list of the high water elevations and recorded discharges for these floods. TABLE 2 HIGH WATER DATA 1989 A~',q) 1990 FLOODS ELM FORK OF TttE TRINITY RIVER -- DATE AGENCY ELEVATION DISCHARGE NOTES (MSL) (C~'S) 05-17-89 USGS - gage 441.13 8,720 05-05-90 USGS - gage 444.88 27,600 Discharge measured at Belt Line Rd: 2605 cfs right bridge, 18916 cfs main bridge, 4097 cfs left bridge. 05~08-90 COE - City 444.82 Road sign on Sandy Lake Rd. west of of IH 35, east of Nursery; 2.6' from _ Carrollton bottom of sign. - In addition water surface elevations and flow distributions were compared to: · C.O.E. model EF-CDC - · "Alignment Study of Belt Line Road from Coppell City Limits to IH-35E Project No. 490-402" prepared for the County of Dallas, January 1986. · "Proposed Sandy Lake Road Improvements at Elm Fork Trinity River" prepared - for the City of Carrollton, March 1993. This comparison is discussed in Section D. The fully developed watershed discharges developed by the Corps of Engineers for the Reconnaissance Study were utilized for this hydraulic study. The recorded discharge at Bek Line Albert H. Halff Associates, Inc. Page 3 November 1993 Road, May 1990 (Q=27600 cfs, Table 2) is within one percent of the 10-year discharge used in the CDC HEC 2 model, therefore the 10-year profile was utilized for calibration to this high water mark. A low flow of 8720 cfs was inserted into the model for calibration to the May 1989 high water mark. Mannings 'n' values (roughness coefficients) and effective flow areas were utilized to calibrate to the high water marks and balance the flows through the obstructed flood plain areas. It was determined that the two recorded floods (1989 and 1990) were not large enough to cause the entire overbank area downstream of Sandy Lake Road to be effective. In fact, for the low flow (1989, Q=8720 cfs) conveyance is confined to the main channel throughout the model. The effective flow limits utilized for calibration to the 1990 flood are shown on the attached map. - Table 3 shows a comparison of the high water marks and the computed (EFEXRV) water surface elevations at Sandy Lake Road. TABLE 3 COMPARISON OF RECORDED VS COMPUTED WATER SURFACE ELEVATIONS ELM FORK OF TIrlE TRINITY RIVER DISCHARGE RECORDED EFEXIST RECORDED RECORDED COMPUTED DATE -- WSEL Sandy Lake Road 8,720 441.13 441.70 05-89 -- Sandy Lake Road 27,600 444.88 444.12 05-90 D. Profile Concurrence In addition to the calibration, flows in the two left bank paths are balanced utilizing the results of the split flow analysis prepared for Dallas County in January 1986 for the Belt Line Road Improvements. A 100 year flood discharge of 55,800 cfs based on a fully _ developed watershed was utilized for that study with a flow of 9500 cfs through the east (left) Belt Line Road Bridge. Flows are balanced within 10% through existing Sandy Lake Road as shown in Table 4. Albert H. Halff Associates, Inc. Page 4 November 1993 TABLE 4 FLOW DISTRIBUTION - 100 YEAR FLOOD ELM FORK - TR_rNYrY RIVER BELT LINE THROUGH SANDY LAKE ROAD SECTION LEF~ OVER BANK MAIN CHANNEL NOTES & ROB CFS 88140 9295 45705 Immediately upstream, Belt Line Road 89210 9130 45870 90160 9218 45782 91020 9152 45848 92040 9323 45677 92850 8459 46541 93660 9241 45760 93670 9130 45870 93730 8635 46365 Sandy Lake Road 93760 8982 46019 Sandy Lake Road 93880 8800 46200 Average 9050 45950 _ Adjustments to Manning's "n" values, along with varying effective flow areas are utilized to balance these flows. Generally a 0.20 "n" value is utilized in the left bank flat area with a 0.18 in the small channel bordering the east City of Dallas property line. Flows are allowed to _ cross the levee along this channel downstream of Section 92850. The 'n' values transition to 0.10 in the left overbank downstream of Sandy Lake Road. Low areas such as the Dallas Water Utilities (DWU) sludge lagoons are mod/fled with GR points to reflect non-effective flow below - the top of the levees. GR points are also mod/fled within the cross sections for non-effective flow areas such as the City of Carrollton Landf'rll area. - The existing dam and Sandy Lake Road cross sections are from the COE Reconnaissance Study hydraulic model, EF-CDC. The overbank areas are modified using the new topography. Sandy Lake Road sections are also modified to reflect the top of the road shown on the new - maps. As with previous models, the culverts under Sandy Lake Road at the DWU channel (east + 6000') are assumed to be non-effective for the 100-year flow. Three comparison sections are attached to this report which show the differences between EF-CDC and the updated hydraulic - model EFEXRV. A diskette containing the revised existing condition HEC-2 f'fle is enclosed at the back of the report. Mapping is also included. Albert H. Halff Associates, Inc. Page 5 November 1993 E. Conclusions In general, the revised existing conditions model reflects higher computed water surface elevations for the 100 year flood, as compared to the COE model EF-CDC (see Table _ 5). This appears to be primarily the result of the more detailed modelling with all f'flls and encroachments included in the topography. The revised modelling was submitted to the Fort Worth District Corps of Engineers (COE) in the report entitled "Sandy Lake Road Design Study, - Hydraulic Analysis - Existing Conditions", August 1993. The COE has reviewed the HEC-2 model, but has made no comments. The updated modelling is utilized as the base hydraulic conditions for the proposed Sandy Lake Road improvements discussed in the following section. Albert H. Halff Associates, Inc. Page 6 November 1993 TABL~ 5 SANDY LAKE ROAD - COMPARISON OF EXISTING CONDITION WATER SURFACE ELEVATIONS L~E 1 = RECORD FLOOO 5~0 EF-CDC MODEL BY CC6 EFEXRV 1993 MCOEL BY AHH LINE 2 = 10(~YR FLOOO COMPARED TO EF~DC LINE 3 = SPF FLCOO LOCATION CDC~J3 XSEC WSEL WSEL DIFFERENCE NOTES/HIGH WATER MARKS IMMEDIATELY UPSTREAM 88150/88140 43824 4,38 P4 0.00 - OF BELT LINE ROAD 8815~88140 441.80 441.80 0.00 TRANSITION FROM BELT LINE 88150/88140 448.71 448.71 0.00 ROAD BRIDGES {3) 89050/89230 439.70 440.76 1.06 89050/89230 443.07 444.07 1.00 - 89050/89230 449.34 45022 0.88 90000/90210 440.47 441.43 0.96 93(X)0~:30210 443.49 444.35 0.86 90000/90210 449.5O 450"34 0.84 90880/91050 441.51 441.92 0.41 90880/91050 44428 444.62 0,34 90880/91050 449.81 450.45 0.84 92090/92050 442_05 442.86 0.81 92090/92050 444.74 445.18 0.44 92O90~2050 450.05 450.68 0.63 923O0/ 442-15 92300/ 450.09 /92880 443.36 192880 445.53 /9288O 45O.89 93620/93660 442_97 444.04 1.07 9362G93660 445.60 446.10 0.50 93620~J3O60 450.49 451 24 0.75 93670/93710 443.16 443.90 0.74 DAM 93670/93710 445.70 448.08 0,38 93670~3710 450.51 451 24 0.73 SANDY LAKE RD BRIDGE 93730~3750 441.70 RECORD MAY 1989 = 441.13 FOR AND GAGE Q=- 872O CFS 93730/93750 44322 444.12 0.90 RECORD MAY 199(~ = 444~8 93730/93750 445.78 446.19 0.41 93750~93750 450.54 451.39 0.85 SANDY I.A~E RD BRIDGE 93760/93780 443.49 444.39 0.93 93750~3780 445.89 448.59 0.70 93760/93780 450~55 451.43 0.881 60" WATER LINE /93840 445.86 60" WATER LINE /93840 447.18 SECTION ADDED /93840 451.54 93810~3890 443.86 445.87 2.01 93810~3890 446.02 44720 1.18 93810~3890 450;59 451.55 0.96 97570/ 440.78 97570/ 450.94 /97710 445&1 /97710 447.57 /97710 451.76 ~0 444.94 448.76 1.82 98450/98460 446.97 447.79 0.82 984.50/98460 451.05 451~8 0.63 9928G~9420 44525 447.03 1.78 99280/99420 44723 44821 0.98 99280/99420 451.19 452.13 0.94 100040 445.56 447.12 1.58 100040 447~2 448.37 0.85 100040 451 "35 45225 0.90i TABLE 8 SANDY LAKE ROAD - COMPARISON OF EXISTING CONDITION WATER SURFACE ELEVATIONS LINE 1 = RECORD FLOOD 590 EF~;DC MODEL BY COE EFEXRV 1993 MODEL BY AHH LINE 2 = 10~YR FLOOO COMPARED TO EF~3DC LINE 3 = SPF FLOOD LOCATION CDC/93 XSEC WSEL WSEL D~FF~HENCE NOTESA-IIGI-I WATER MAP, S 103060 447.24 447.7g 0.55 103060 448.87 449271 0.40 103060 452.08 452.78 0.70 106080 45023 450.14 -0,09 1060801 451.47 451.47 0,00 106080 ~ 453.67 454.00 0.33 110580 451.36 451.32 -0.04 110580 452.81 452.80 -0.01 110580 455.09 455.27 0.18 110720 451.38 451.34 -0.04 110720 452.84 452.83 -0.01 110720 455.12 455.30 0.18 110750 451,39 451.35 -0.04 110750 452.85 452.84 -0.01 110750 455,13 455.32 0.19 110790 451.36 451.32 -0.04 IH-35E 110790 452.77 452,76 -0.01 110790 454.94 455.14 0.20 110910 451.48 451.42 -0.04 110910 452.94 452.94 0.03 110910 45524 455.53 0~9 110930 451,56 451,51 -0.05 110930 453.19 453.18 -0.01 110930 455.79 455.99 0 20 110980 451.62 451.58 -0.04 110980 45324 453.24 0.00 110980 455.82 456.02 0.20 113000 451.83 451.80 -0.03 113000 453.481 453.48 0.00 I 113000 455.08 455~6 0.18 113090 451.71 451.88 -0.03 MKT RAILROAD 113090 453.41 453.41 0.03 113090 455.09 456.27 0.18 113110 451.73 45 1.70 -0.03 113110 453.47 453.46 -0.01 113110 456.13 456.31 0.18 113180 452.00 451.97 -0.03 113180 453.68 453.88 0.03 113180 45522 456.39 0.17 118580 452.51 452.48 -0.03 118580 454.19 454.19 0.08 118580 455.85 456.98 0.13 119960 452.67 452_65 -0.02 HEBRON PARKWAY LEVEE 119960 454,36 454.35 -0.01 (TOP OF LEVEE 464.46) 119960 457.12 457241 0.12 123260 453.11 453.10 -0.01 1 23260, 454.88 454.87 -0.01 12326O ! 453.05 458.14 0 125570 453.36 4,53,35 -0.01 125570 455.24 45523 -0.01 125570 458.72 458.80 0.08 126550 453.36 453.36 0.03 126550 458.24 455.24 0.00 126550 458.72 458.72 0.00 13O5OO 453.56 453.56 0.00 130500 455.69 455.69 0.03 130500 459.73 459.73 0.00 470 .200 . 0 .20 035 .0 .04 · 080 ' LEFT MEN]-' 460 ENCROAC~ MENT LINE I"i~'E'-~"O 0"' ENCROAC -IMENT LINE 450 z o ~: 440 uJ 430 " NON EFF ;TIVE FLOW ARE .420 EF-CD£' ENCROACHMENT 410 ... EF-CDC SECTION 434. !0 LEFT ~ I 441.00 RIGHT 410. 50 ELNIN 400 0 2000 4000 6000 8000 10000 12000 14000 16000 1800( 11-~5-93 EFEXRV.DAT SECT I ON 90210 470 · 200 .200 . 120 . 150 .040 .045 · 045 /,'LEFT /- LEFT ENCROACHIV ENT' 460 ./ ENCR~DACHMENT/ LINE C~\LIBRATION · ' ~,.-~RI(~HT ENCROACHMENT LINE 450 /\ . 440 SANDY LAKE RD. SE(;TION 420 FROM F'.F - CDC ..... EF-CD(; SECTION 410 .... 447. 43 LEFT 447. 85 RI6HT 414.50 ELMIN 40O O 2000 4000 6000 8000 lOOOO 12000 14000 18000 1800E 11- f5-93 SECT T ON 93750 EFEXRV.DAT t I I t i t I i t i I l ..... I i-- I i ......I I I ~ 070061)0g0 ~~LIiF ENCROACHMENT ~ LINE 470 ~' ....... i RIGHT EN,DROACHME ,,IT LINE 4150,, . I x I x 450 ~ , 440 L-J \ I II 430 "~' EF-ODC ....... ENCROI~CHMENT. EF-CDC SECTION 42O 44-3.90 LEFT 4.4.5., O0 RIGHT 426.00 ELMIN 410 - -2000 0 . 2000 4000 6000 8000 10000 12000 14000 i~rOE 11-15-~3 SEC T I ON EFEXRV.DAT II. PROPOSED CONDITIONS Several alternative bridge and compensating excavation alternatives were tested for this proposed crossing of the Elm Fork at Sandy Lake Road. Each alternative was evaluated based on current design criteria (no rise in 100-year water surface elevation for fully developed landuse) - for the cities of Carrollton, Coppell, and Dallas. Proposed water surface elevations are compared to the existing conditions modelling as submitted to the Fort Worth District Corps of Engineers (COE) in the report entitled "Sandy Lake Road Design Study, Hydraulic Analysis - Existing - Conditions", August 1993. Cross Sections for this modelling were taken from the aerial mapping flown February 1991, produced for the COE Upper Trinity River Feasibility Study. The following is a brief recap of the alternatives evaluated: Alternate 1. The fkst alternative tested is as shown on the preliminary schematic profile provided to - Halff Associates by Charles Gojer and Associates (CGA). This profile showed a 640-ft main bridge and a 160-ft relief bridge immediately adjacent to the main bridge. A modification of this alternative was evaluated, combining the two bridges into one 800 foot long opening. The near left overbank area underneath the proposed bridge was lowered to elevation 439.0, approximately matching the existing parking area by the Carrollton Dam. This 439.0 elevation remains unchanged in all subsequent proposed condition models. The existing interior drainage channel on the east bank is relocated to match the bridge layout. This alternative causes approximately a 1 ft rise in the 100-yr _ flood water surface elevation and a 2 ft rise in the SPF water surface elevation. Alternate 2. _ This alternate, in addition to the 800-ft proposed main channel bridge described above includes a relief swale in the left overbank within Mclnnish Park. This swale replaces the interior drainage channel in Alternate 1. This alternative produces approximately a 0.3 - ft rise in the 100-yr flood water surface elevation. Alternate 3. -- This option includes the Alternate 2 swale and extends it both upstream and downstream. The swale flow line slope is 0.5 percent. This alternate produces a 0.22 ft rise in the 100- yr flood water surface elevation and a 0.44 ft rise in the SPF water surface elevation (see - Tables 6 and 7). Alternate 4. - In addition to the revised swale in the left overbank described in Alternate 3, this alternate uses the series of ponds on the Riverchase property as a second relief channel. The normal pool elevation of the ponds is maintained. However, the hydraulic connection with the main channel is modified by lowering the Elm Fork right bank downstream of the Carrollton Dam to form a weir at elevation 434.0. This weir is located approximately 600 ft downstream of the dam. This alternative produces approximately a 0.1 ft rise in the 100-yr flood water surface elevation. Albert H. Halff Associates, Inc. Page 12 November1993 Alternate 5. _ Alternate 5 includes the 800-ft main channel bridge proposed in Alternate 1 with a 200-ft relief bridge in the left (east) overbank and improvements to an existing channel downstream of the proposed relief bridge. The existing channel is situated on Dallas - Water Utilities property approximately 6000 ft east of the Elm Fork. The channel would be upgraded to a 200 ft wide swale discharging into existing ponds. A swale within Mclnnish Park is not included. This alternate produces a 0.5 ft rise in the 100-yr flood - water surface elevation. Alternate 6. - Alternate 6 includes both the far left bank improved channel introduced in Alternate 5 and the extended version of the swale through Mclnnish Park modeled in Alternate 3. A 260 foot relief bridge is included, approximately 6000 feet east of the main channel. This - alternative maintains both the 100-year water surface elevation (within 0.01 ft) and the SPF water surface elevation (see Tables 6 and 7). - Alternate 7. Alternate 7 includes all the proposed improvement in Alternate 3, including the extended version of the swale, with the addition of a 260 ft relief bridge and channel on the right overbank within the City of Coppell. This channel would be excavated on property that belongs to the Carrollton-Farmers Branch ISD, upstream and James Hardngton, downstream. The bridge is located approximately 500 ft west of the Elm Fork. Flow from this channel would discharge into the series of small ponds located on the Riverchase Golf Course. This alternate causes a 0.03 ft rise in the 100-yr flood water _ surface elevation and a 0.25-ft rise in the SPF water surface elevation (see Tables 6 and 7). _ Other Alternatives Both "No Action" and a "Maximum Bridge" alternatives were considered. Under "No Action", Sandy Lake Road would continue to flood during events such as the May 90 - storm and would constitute a continued hazard to the public. The "Maximum Bridge" alternative would consist of 3000 to 4000 foot of bridge in the areas that are currently effective for 100-year flood flows. This alternative would maintain existing flood flow - depths and distribution throughout the area. However, because of the great expense associated with this lengthy bridge and its associated limitations on access along Sandy Lake Road, this alternative was not developed in detail. Other alternatives which - incorporate different flood control channels or swales upstream or downstream of Sandy Lake Road are probably feasible from a hydraulic standpoint. However, such alternatives are impossible to incorporate into a Bridge Plan for Sandy Lake Road without an overall - flood control plan acceptable to the many cities and districts located in the area. Ali the above alternates assume flow over Sandy Lake Road for the SPF. Albert H. Halff Associates, Inc. Page 13 November 1993 121I. PRELIMINARY RECOMMENDATIONS Halff Associates recommends Alternate 6, with improvements to a far left bank channel on Dallas Water Utilities property and an extended swale on the near left bank. This option -- involves the construction of two bridges, a 260-ft relief bridge and an 800-ft main channel bridge. The configuration of the swale requires the relocation of the Mclnnish Park access road, one small parking lot and at least one ball field. All alternatives assume that SPF flows overtop - Sandy Lake Road in the left (east) overbank. This alternate was selected because it causes only a 0.01 ft rise in the 100-yr flood water -- surface elevation and no rise in the SPF water surface elevation. In addition, flow paths similar to existing conditions are maintained for the 100-year flood because the far left overbank remains effective. A schematic plan of this alternative is shown on Figure 1. A viable alternative to this option would be the relief bridge and swale in the west bank (Alternative 7) within the City of Coppell. Flows would still overtop Sandy Lake Road in the - east bank area for the SPF but would be conf'med at the crossing for the 100-year flood. High ground (land above the 100-year flood elevation) in the west overbank area would have to be purchased for the proposed swale downstream of Sandy Lake Road. The large relief swale - through Mclnnish Park is also required for this alternative. A schematic plan of this alternative is shown on Figure 2. Water surface elevation comparisons for the two viable alternatives are shown on Tables 6 and 7. Alternate 3 with the Mclnnish Park swale and no relief bridge is also shown on the tables for comparison purposes. This alternative would cause additional flooding as shown in the table and would have the highest velocities in and around Carrollton Dam. ' _ It is recommended that these alternatives be reviewed by the cities of Carrollton, Coppell and Dallas, and the Dallas County Public Works Department prior to f'malization of the recommended plan. In addition, the £mal plan should be tested in the existing condition - (discharges based on existing land use) hydraulic model prior to f'mal design. This project will require submission to the Federal Emergency Management Agency (FEMA) for a Conditional Letter of Map Revision and the Corps of Engineers for a 404 (Wetlands) permit. Albert H. Halff Associates, Inc. Page 14 November1993 TABLE 6 SANDY LAKE RD - COMPARISON Of EXISTING AND PROPOSED CONDITION WATER SURFACE ELEVATIONS - 100-YR FLOOD. 800' MAIN BRIDGE 800' MAIN BRIDGE SINGLE 800'BRIDGE 260'RELIEF LOB 260'RELIEF ROB W/SWALE LOB W/ LOCATION II EFEXRV 1993 MODEL '~L~r'l~l~ (*) ~'E~:~-~E-I~D~ED (*) ' ALTI~RNATE'~ (*) SECTION WSEL WSEL DIFF, WSEL DIFF, WSEL DIFF, 88140 441.80 441.80 0.00 441.80 0.00 441.80 0.00 89230 444.07 444.01 -0.06 443.89 -0.18 d~.~,.01 -0.06 90210 444.35 444.37 0.02 ~,~.~,. 11 -0,24 4~, ~..37 0.02 91050 444.62 444.50 ~.12 ~,~,~,.23 ~).39 d~.~..50 ~.12 92050 445.18 444.72 -0.46 d~,~,.39 -0.79 4~,~,.72 ~.46 92880 445.53 444.85 -0.68 ~,~.~,.47 -1.06 ~,~?,.87 -0.66 93660 446.10 444.89 -1.21 ~.4~..56 -1.54 d~,d.92 -1.18 CARROLLTON DAM 93710 446.08 444.70 -1.38 d ~?..44 -1.64 d~,d.77 -1.31 D/S PROPOSED SANDY LAKE RD 93750 446.19 445.41 -0.78 ~,dd.86 -1.33 445.11 -1.08 U/S PROPOSED SANDY LAKE RD 93780 446.59 445.51 -1.08 ~.~.d.90 -1.69 445.16 -1.43 93840 447.18 446.11 -1.07 445.39 -1.79 446.00 -1.18 93890 447.20 446.40 -0.80 445.44 -1.76 446.05 -1.15 DENTON CREEK CONFLUENCE 97710 447.57 447.72 0.15 446.85 -0.72 447.41 ~.16 98460 447.79 447.98 0.19 447.20 ~.59 447.73 -0.06 99420 448.21 448.43 0.22 447.76 -0.45 448.22 0.01 100040 448.37 448.59 0.22 447.96 -0.41 448.40 0.03 1 03060'1 449.27 449.40 0.13 449.05 ~.22 449.28 0.01 1060801 451.47 451.47 0.00 451.46 ~.01 451.47 0.00 110580 452.80 452.81 0.01 452.81 0,01 452.80 0.00 110720 452.83 452.83 0.00 452.83 0.00 452.83 0.00 110750 452.84 452.84 0.00 452.84 0.00 452.84 0.00 IH-35E 110790 452.76 452.77 0.01 452.76 0.00 452.76 0.00 110910 452.94 452.94 0.00 452.94' 0.00 452.94 0.00 110930 453.18 453.19 0.01 453.18 0.00 453.18 0.00 110980 453.24 453.24 0.00 453.24 0.00 453.24 0.00 113000 453.48 453.48 0.00 453.48 0.00 453.48 0.00 MKT RAILROAD 113090 453.41 453.41 0.00 453.41 0.00 453.41 0.00 113110 453.46 453.47 0.01 453.47 0.01 453.46 0.00 113180 453.68 453.68 0.00 453.68 0.00 ! 453.68 0.00 118580 454.19 454.19 0.00! 454.19 0.00~ 454.19 0.00 HEBRON PARKWAY LEVEE 119960 454.35 454.35 0.00 454.35 0.00 454.35 0.00 (TOP OF LEVEE - 464.46) 123260 454.87 454.87 0.00 454.87 0.00 454.87 0.00 125570 455.23 455.23 0.00 455.23 0.00 455.23 0.00 126550 455.24 455.24 0.00 455.24 0.00 455.24 0.00 130500 455.69 455.69 i 0.00 455.69 0.00 455.69 0.00 MAXIM'UM RISE: 0.22 0.01 0.03 NOTE: ALL PROPOSED CONDITION MODELS COMPARED TO THE REVISED EXISTING CONDmONS MODEL (EFEXRV.DAT) (*) SANDY LAKE ROAD EAST OVERBANK - ROAD LOWERED TO ALLOW SPF FLOW OVER ROAD TABLE 7 SANDY LAKE RD - COMPARISON OF EXISTING AND PROPOSED CONDITION WATER SURFACE ELEVATIONS - SPF FLOOD. 800' MAIN BRIDGE 800' MAIN BRIDGE SINGLE 800'BRIDGE 260'RELIEF LOB 260'RELIEF ROB W/,~ W/SWALE LOB LOCATION X EFEXRV 1993 MODEL '~LT'ER'NATE~ (*) 'RECOMMENDED (*) ~J~'TERN'ATE'7 (*) SECTION WSEL 'WSEL DIFF, WSEL DIFF, WSEL DIFF, 88140 448.71 448.71 0.00 448.71 0.00 448.71 0.00 89230 450.22 450.22 0.00 450.16 -0.06 450.22 0.00 90210 450.34 450.37 0.03 450.26 -0.08 450.37 0.03 91050 450.45 450.47 0.02 450.32 -0.13 450.47 0.02 92050 450.68 450.61 -0.07 450.41 -0.27 450.61 -0.07 92880 450.89 450.71 -0.18 450.47 -0.42 450.72 -0.17 93660 451.24 450.84 -0.40 450.58 -0.66 450.84 -0.40 CARROLLTON DAM 93710 451.24 450.79 -0.45 450.52 -0.72 450.78 -0.46 D/S PROPOSED SANDY LAKE RD 93750 451.39 451.14 -0.25 450.77 -0.62 451.04 -0.35 U/S PROPOSED SANDY LAKE RD 93780 451.43 451.32 -0.11 450.89 -0.54 451.16 -0.27 93840 451.54 451.78 0.24 451.25 -0.29 451.60 0.06 93890 451.55 451.83 0.28 451.29 -0.26 451.64 0.09 DENTON CREEK CONFLUENCE 97710 451.76 452.20 0.44 451.69 -0.07 452.00 0.24 98460 451.88 452.32 0.44 451.82 -0.06 452.13 0.25 99420 452.13 452.54 0.41 452.08 -0.05 452.36 0.23 100040 452.25 452.64 0.39 452.20 -0.05 452.47 0.22 1 03060 452.78 453.11 0.33 452.74 -0.04 452.97 0.19 106080 454.00 454.19 0.19 453.98 -0.02 454.10 0.10 110580 455.27 455.39 0.12 455.26 -0.01 455.33 0.06 110720 455.30 455.42 0.12 455.29 -0.01 455.37 0.07 110750 455.32 455.43 0.11 455.30 -0.02 455.38 0.06 IH-35E 110790 455.14 455.25 0.11 455.12 -0.02 455.20 0.06 110910 455.53 455.63 0.10 455.52 -0.01 455.58 0.05 110930 455.99 456.09 0.10 455.98 -0.01 456.05 0.06 110980 456.02 456.11 0.09 456.01 -0.01 456.07 0.05 113000 456.26 456.35 0.09 456.25 -0.01 456.31 0.05 MKT RAILROAD 113090 456.27 456.36 0.09 456.26 -0.01 456.32 0.05 113110 456.31 456.39 0.08 456.30 -0.01 456.35 0.04 113180 456.39 456.47 0.08 456.38 -0.01 456.43 0.04 118580 456.98 457.05 0.07 456.97 -0.01 457.02 0.04 HEBRON PARKWAY LEVEE 119960 457.24 457.30 0.06 457.24 0.00 457.27 0.03 (TOP OF LEVEE = 464.46) 123260! 458.14 458.19 0.05 458.14 0.00 458.16 0.02 125570 458.80 458.83 0.03 458.79 -0.01 458.82 0.02 126550 458.72 i 458.72 0.00 458.72 0.00 458.72 0.00 130500 459.73; 459.73 0.00 459.73 0.00 459.73 0.00 MAXIMUM RISE: 0.44 0.00 0.25 NOTE: ALL PROPOSED CONDITION MODELS COMPARED TO THE REVISED EXISTING CONDITIONS MODEL (EFEXRV. DAT) (*) SANDY LAKE ROAD EASTOVERBANK - ROAD LOWERED TO ALLOW SPF FLOW OVER ROAD ~.,.,?::;::?L,.. *:~ ~ ~::-:,? S LAKE ROAD ...... ::..'" ...... · . ............ :' :I:L..~:~: _AKE" :::::::::::=::::::::::4::::::;::::: , ~:: ~: ............ : ............. ~ED B~~ .:.::.:.:~.: .... ?: ;.~" "~>. ~...~:~.._~ ...~ ~ ) .............. .~. .:-.:- :::'" ~: -------~>,:.:~:~:.... :.~., :~' :.::.' .............. , ...... ::: .....::. ::: ., ....... ..;.- ......... {"-.:; ~; .:.": ............ .,? ;;'~ ..: ::~?;? ,? ';~ . ,~:?:~::~ ::~: ..~ .:: ~ ,..~ ...... :~ ':... :?.::~?. ::~:::.* ...... ::...% .. ....... . ........ .~ ::~:.::~.;:::~ :~ .................................... ::.:,:~ ::. /)~ .? ::.'--.-::. ,:~ ...... ....:.. ....... .... ........ ~ ~,. .......... . ....................... / .:...:~'::::~':;..---;;';:.' ..... :.:::-: , ~ ................... ~. ............. ~ :'"'"~ (' . ..... ..... ~:.::.~ ~: .~..-...;~ :~. ~ ~ ./.~ .................. .. ............ .~.-:;..'.--:-~ ~ ; ~( :': .: ~ ....... i:--' ~.:."~ ~. ................................. . .- ............... .... , &., ~ ~ .... ,., ............. ~.~,~ )' ? ~ /' i <: ~ ¢ L~ ~~._ ' ............. '"'""~ r:: ~ ......... " : ..... =::,. ::: SANDY LAKE ROAD HYDRAULIC DESIGN STUDY "'"2' 7 ,:. ~ F~N o¢ the Trinity River "~ ~ ,'" ¢' (;4 t ~ ~% ,,. --..-..,." E..-~ ,,-, ,.,..,¢ ?% !~..-% ..¢.? ~' "'~' ....'- <'x .... ' ~' , , .:¥ ~ .......... "~ : :' ~, '¥... ' ,.,/'>L...-f ......... . ....:..-:.. ~ ........ ' ......... : ~ ........ ~ ~.~...~.::'::: ':....- .., . ..?. .... .: . / -- . ' .......>.:,.:':'~:'" ~- - ./::?: ..- .-' ::~::.:....+..:::::?.. ~ .: : ::: ~ .. ................. . ~ . . ................. ... ,...~/ ..: ~ . ........... :::.:.:., L.,: ' I .: :<..':':..:.... .... :- -.~<.