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FS8901-SY 890801FLOODPLAIN RECLAMATION STUDY HRWS TRACT Coppell, Texas AUGUST, 1989 NATHAN D. MAIER CONSULTING ENGINEERS, INC. Dallas, Texas (214) 739-4741 FLOODPLAIN RECLAMATION STUDY HRWS TRACT COPPELL, TEXAS INTRODUCTION This report summarizes the hydraulic evaluation conducted for a 4.50 acre tract of land known as the HRWS tract on the Elm Fork Trinity River in the City of Coppell, Texas. A specific site development plan for the tract is not currently available. Therefore, the purpose of the report Is to show that the subject tract is in the floodplain and not the floodway of the Elm Fork and that a portion of the site could be filled without increasing water surface elevations. SITE LOCATION The HRWS tract is located west of the Elm Fork, north of the St. Louis and Southwestern Railroad (ST.L&SWRR) and Belt Line Road; and immediately south of the golf course associated with the River- chase development in Coppell, Texas. Plate I provides a location map for the tract. The Flood Insurance Study (FIS) Floodway Map, revised February 1984, for the City of Coppell, showed the tract to be in the floodway of the Elm Fork. In late 1986, the U.S. Army Corps of Engineers (COE) developed a comprehensive HEC-2 hydraulic model of the Elm Fork which incorporated the modifica- tions to the Elm Fork and its floodplain since the initial FIS. In that model, the filled area downstream of Belt Line Road, which is adjacent to the HRWS tract was incorporated. In addition, at the first section (Section 89050) upstream of the ST.L&SWRR, a portion was blocked out to reflect a contraction to the opening in the ST.L&SWRR and Belt Line Road. Plate 2, which is a copy of the FIS work map for the study reach, shows this blocked out area in plan view. In 1987, the COE published the Final Re(~ional Environmental ImPact Statement (ELS) for the Trinity River and its major tributaries. The final ElS also incorporated the comprehensive HEC-2 model devel- oped by the COE for the revised FIS. In addition, the final ElS utilized discharges from an Existing Con- ditions and Future Conditions 100-Year and Standard Project Flood (SPF) based on the watershed hydrology for these conditions. HYDRAULIC I~VALUATION For purposes of this evaluation, a portion of the final ElS HEC-2 hydraulic models (GELMF-86 and GEL- 2040) for the Elm Fork were used. The portion used commences with Section 87530, downstream of Belt Une Road, and ends with Section 93670, the Carrollton weir at Sandy Lake Road. The starting water surface elevations were taken from the calculated final ElS models. Both the existing and future conditions models were run for the 100-year and SPF. The HEC-2 Input and output data for existing and future conditions are included in Appendix A. A review of the hydraulic model indicated that the blocked out area previously referred to did not truly reflect the effect of the high railroad embankment, the fill downstream of Bolt line Road, and the flow pattern into the main bridge and the trestle to the west, Therefore, the area to be blocked out was revised as shown on plan view on Plate 2 and in the cross section as shown on Plate 4, The model was rerun and resulted in no increase in water surface elevations, Table I provides a comparison of these elevations for sections 88050 to 90000, This model became the Interim Model and was used to com- pare the effect of the proposed fill project, The HEC-2 input and output data for the Interim Model is provided in Appendix B, The City of Coppell requested that a proposed grading plan be prepared for the site. This was done and was factored into Section 89050, as shown on Plate 4. Since the proposed fill on the tract is all con- tained within the blocked out area or ineffective flow area, no increase in water surface elevations will occur as a result of the flU. TABLE 1 COMPARISON OF WATER SURFACE ELEVATIONS ElS MODEL INTERIM MODEL CROSS SECTION 88050 88150 89050 90000 EXIST. 442.9 443.2 443.9 444.1 FUTURE EXIST. 4,!4.0 447.4 4~.4.2 447.9 ~.4~.8 448.6 445.0 448.7 FUTURE QSp= 448.0 448.6 449.3 449.5 EXIST. Q100 442.9 443.2 443.9 4~.4.1 FUTURE EXIST. Q~0o Qs~= ~44.0 447.4 444.2 447.9 ~.~. ~..8 448.6 ~5.0 ~8.7 FUTURE 448.0 448.6 449.3 449.5 The tract has been reviewed by the COE in accordance with Section 404 of the Clean Water Act and has determined that a permit from the Department of the Army will not be required to fill the reclaimable portion of the tract. A copy of the letter to that effect Is enclosed. CONCLUSION The portion of the tract to be filled lies within an existing ineffective flow area due to downstream condi- tions. As a result, no increase in water surface elevations occurs and once filled, can be removed from the floodplain and floodway. Therefore, a Conditional Letter of Map Revision (LOMR) is requested to remove the ineffective flow area from the floodway of the Elm Fork Trinity River. Since no change in water surface elevations occurs as a result of the proposed fill, revised water surface profiles are not included. DEPARTMENT OF THE Al FORT WORTH DISTRICT. CORPS OF P. O. BOX 17300 FORT WORTH. TEXAS 78102-0300 February 5, 1988 Operations Division Office Operations Branch SUBJECT: Project Number 8800132 ,.ERS Mr. Ervin A, Meyer Nathan D. Maier Consulting Engineers Three NorthPark 8800 N. Central Expressway, Sute 300 Dallas, Texas 75231 Dear Mr. Meyer: Thank you for your letter of February 3, 1988 requesting a jurisdictional determination for a fill project located north of Beltline Road and west of the Elm Fork of the Trinity River within Carrollton, Dallas County, Texas. Your project has been assigned Project Number 8800132; all further correspondence concerning the project should include this number. Your project has been reviewed in accordance with Section 404 of the Clean Water Act under which the U.S. Army Corps of Engineers regulates the discharge of dredged and fill material into waters of the United States Including adjacent wetlands. Based on your description of the proposed work and all information available to us, we have determined that your project will not involve such discharges and, therefore, will not require Department of the Army authorization. Thank you for your Interest in our nation's water resources. Please continue to check with us prior to Initiating construction in or affecting waters of the United States. If you have addi- tional questions concerning our regulatory program, please contact Mr. Victor Cole at the addrees above, telephone (817) 334-4623. Sincerely, Cht H§wkins, Jr ''ei, Office Operations 8ranch Dallas, Texas 75202 Mr. David Curtis U. S. Fish and Wildlife Se-~=rice Ecological Services 9A33 Fritz ~ Buil~{ng 819 Taylor Fort Worth, Te_~ 76102 Mr. Bol~n Mac.~ae Te~-~ Parks ar~ Wi/zi]~fe 4200 ~{th Sc.~ol Boad Austin, T~u~s 78744 "'1 3 A V CITY CITY BOUNDARY = ~TI'Y-- -~OU'~! ,/ ~4~ 0. O0 0 Po C~' 0 o O' 0 0 Oo i_~0' Oo 0 0 o Co o- 0 o o' 0 o o- o 420 · O0 430 · O0 440 · O0 450 · O0 ~ I ~410.00 420.00 430.00 440.00 450.00 0 0 0.00 420.00 I 430.00 440.00 450.00 I ACT_' t ! I'"~ WS TRACT I Z APPENDIX A FINAL ElS MODEL EXISTING AND FUTURE Q~oo & SPF o o o 0 ogo~o~oZ~g~Zgg gogg · . . gg ...... gg~ ' "gg~4g ' c~ c~,~ o o o o ~ -., o ooo o~-o ooooo ooo oooo oooooooooo ~oooooo~ oooooooooo o 0 0 0 0 0 0 O0 fl 0 0 O0 OC~ [DO O0 O0 0 ooo ooo~ooooooooooo~o~o© S44 ....... o gggggggo~oo ''jgggggj,~ ................... .~,o.~. o_;~ J~,~,~, g gggggggoJoo o O0 APPENDIX B INTERIM MODEL EXISTING AND FUTURE Q~oo & SPF x 0 ~oooo~o~oo ~o~o~J~ooo ~o o~o ooo~oooo~oo ooo~-,oooo~oo ~oooo~ · . .g · . .gg ................ oooo oooJJJJJ ~,~ o o o 0 ogoJJoooJoo 0 0 0 ? o o o (:3 ~ §o O0 O0 O0 O0 O0 O0 O0 O0 O0 O0 O0 0 0 0 o 0 ggg ......... oog~Joo ~S oooo (DO O0 O0 000 0o0 000 ooJoooJJJ ooo.oogJJ oooo~oJJJJ~ 0000 '' 'jjJ ..... ,4' ~ 'jjjjjjjj 00~00 000000000000 O0 o0o 00000 000 000 000 000 (DOC) 000 000 0 O0 ogggoo 0 0 o O0 0 0 C> 0 0 o O0 O0 O0 O0 O0 O0 O0 O0 O0 O0 oo ~o oo ~§ o~