ST9301A-CS 950103 HALFF ASSOCIATES, INC.
ENGINEERS · SCIENTISTS · SURVEYORS
DALLAS · FORT WORTH · ARLINGTON · CHICAGO
8616 NORTHWEST PLAZA DRIVE · DALLAS, TEXAS 75225
214/739-0094 · FAX 214/739-0095
January 3, 1995
AVO 12687
Mr. Ken Griffin, P.E.
City of Coppell
P.O. Box 478
Coppell, Texas 75019
Re: Sandy Lake Road/Elm Fork Hydraulic Study,
Cities of Carrollton, Coppell and Dallas
Dear Ken:
As discussed in our December 21st meeting the attached tables compare the 100-year and
Standard Project Flood discharges and water surface elevations as computed by Halff Associates
for the referenced study and by the COE for the preliminary Upper Trinity River Feasibility
Study. The Halff Associates revised base model uses the same topographic data (1991
Greenhorne-O'mara) as the Feasibility Study with minor differences in modelling techniques.
The 100-year water surface elevations (Table 2) converge for the Feasibility Study versus the
Revised Base at Section 92050 approximately half way between Belt Line and Sandy Lake
Roads. The SPF water surface elevations are 1.0 to 1.5 foot lower in the Feasibility Study
preliminary hydraulic model due to the lower discharges computed by the COE for their latest
study. Please note that the Corps is currently revising the hydrology and hydraulics for the entire
Trinity River Feasibility Study.
Please feel free to call if you have any questions. Thank you again for taking the time to
expedite the FEMA submittal prior to the first of the year.
Sincerely,
HALFF ASSOCIATES, INC.
ansen, P.E.
cc: Lloyd James, P.E., Gojer and Associates, Inc.
TRANSPORTATION · WATER RESOURCES · LAND DEVELOPMENT · MUNICIPAL · ENVIRONMENTAL · STRUCTURAL
SURVEYING · GLOBAL POSITIONING SYSTEM (G.P.S.) · REMOTE SENSING AND MAPPING
LANDSCAPE ARCHITECTURE · PLANNING
Table 1
Elm Fork - Trinity River
Discharge Comparison
Model/Frequency EF-CDC Reconn~ I Feasibility Study2
At Belt Line Road
100-Year 55000 cfs 51800 cfs
SPF 100000 cfs 85200 cfs
At Sandy Lake Road
100-Year 55000 cfs 55200 cfs
SPF 100000 cfs 93200 cfs
Discharges utilized in the Sandy Lake Road/Elm Fork Hydraulic Study
Preliminary (1994) COE Feasibility Study Hydrology
Table 2
Elm Fork - Trinity River
100-Year Water Surface Elevation Comparisons
Fully Developed Landuse
Location Section~ EF-CDC2 Section Feasibility Section~ Halff Assoc. Proposed Sandy
Study 19943 Revised Base4 Lake Rd~
immediately u/s 88150 441.80 88150 441.80 441.80
of Belt Line Rd
87645 442.86 88160 441.71 441.71
(EF111) (EFlll)
88450 443.12 443.15
89050 443.07 88712 444.62 89230 444.09 443.98
(EF112) (EF112)
90000 443.49 89694 445.02 90210 444.39 444.39
(EF113) (EF113)
90880 444.28 90532 445.19 91050 444.73 444.66
(EF114) (EF114)
92090 444.74 91530 445.36 92050 (EF115) 445.35 445.06
(EF115)
92351 445.51 92880 (EF116) 445.71 445.19
(EF116)
93620 445.60 93141 446.02 93660 (EFII7) 446.30 445.52
(EF117)
Carroliton Dam 93670 445.70 93196 446.04 93710 446.29 445.49
Sandy Lake 93730 445.78 93232 445.16 93750/93735 446.69 445.77
Road
Sandy Lake 93760 445.89 93262 447.01 93780/93815 446.87 445.88
Road
60" Waterline 93840 447.17 446.00
93810 446.02 93359 447.27 93890 (EFI20) 447.20 446.04
(EF120)
Denton Creek 97570 446.78 97178 448.07 97710 (EF121) 447.80 447.32
Confluence (EFl 21 )
98450 446.97 97919 448.31 98460 (EFI22) 447.99 447.63
(EF122)
99280 447.23 98884 448.48 99420 (EF123) 448.35 448.13
(EF123)
Sections labelled as shown on Figures 3 and 4 "The Elm Fork of the Trinity - Sandy Lake Road Bridge Hydraulic Study". Digital Section number
from Greenhorne and O'Mam shown in ().
The Fort Worth District COE Reconnaissance Study hydraulic model - utilized as the base model for the Sandy Lake Road hydraulic study.
The preliminary (May 1994) COE Feasibility Study hydraulic model utilizing 1991 topographic data. (Note: Feasibility Study SPF discharges are lower -
see Table 1).
Halff Associates revised base hydraulic modelutilizing EF-CDC(2) as a base model with cross sections from the 1991 Feasibility Study topographic
mapping.
Halff Associates revised base model with proposed Sandy Lake Road and downstream swale/pond.
Table 3
Elm Fork - Trinity River
SPF Water Surface Elevation Comparison
Location Section~ EF-CDC2 Section Feasibility Section~ Halff Assoc Proposed Sandy
Study COE Revised Base4 Lake Rds
19943
Immediately n/s of Belt 88150 448.71 88150 448.71 448.71
Line Road
87645 448.54 88160 448.60 448.60
(EFlll) (EFlll)
88450 449.67 449.70
89050 449.34 88712 449.13 89230 450.19 450.09
(EF112) (EF112)
90000 449.50 89694 449.23 90210 450.32 450.22
(EF113) (EF113)
90880 449.81 90532 449.34 91050 450.49 450.34
(EF114) (EF114)
92090 450.05 91530 449.44 92050 450.81 450.53
(EF115) (EF115)
92351 449.52 92880 451.04 450.61
(EF116) (EF116)
93620 450.49 93141 449.70 93660 451.41 450.90
(EF117) (EF117)
Carrollton Dam 93670 450.51 93196 449.71 93710 451.41 450.89
Sandy Lake Rd 93730 450.54 93232 449.81 93750/93735 451.55 450.84
Sandy Lake Rd 93760 450.55 93262 449.81 93780/93815 451.58 451.15
60" Waterline 93840 451.66 451.48
93810 450.59 93359 449.87 93890 451.68 451.56
(EFI20) (EF120)
Detuon Creek Confluence 97570 450.94 97178 450.43 97710 451.95 452.01
(EF121) (EF121)
98450 451.05 97919 450.60 98460 452.06 452.12
(EP122) (EF122)
99280 451.19 98884 450.73 99420 452.29 452.35
(EF123) (EF123)
Sections labelled as shown on Figures 3 and 4 "The Elm Fork of the Trinity - Sandy Lake Road Bridge Hydraulic Study". Digital Section number
from Greenhorne and O'Mara shown in ().
The Fort Worth District COE Reconnaissance Study hydraulic model - utilized as the base model for the Sandy Lake Road hydraulic study.
The preliminary (May 1994) COE Feasibility Study hydraulic model utilizing 1991 topographic data. (Note: Feasibility Study SPF discharges are lower -
see Table 1).
Halff Associates revised base hydraulic model utilizing EF-CDC(2) as a base model with cross sections from the 1991 Feasibility Study topographic
mapping.
Halff Associates revised base model with proposed Sandy Lake Road and downstream swale/pond.