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Copperstone FS-CS 821108 FLOOD INSURANC STUDY CITY OF COPPELL, 1 TEXAS! DALLAS AND DENTON COUNTIESi PRELIMINARY MICHAEL BAKER, JR., I. NC. N OV 0 ~ 1982 FEBRUARY 1980 REVISED: Federal Emergency Management Agency COMMUNITY NUMBER . 480170 TABLE OF CONTENTS INTRODUCTION I.I Purpose of Study i.2 Authority and Acknowledgments 1.3 Coordination 2.0 AREA STUDIED 2. I Scope of Study 2.2 Community Description 2.3 Principal Flood Problems 2.4 Flood Protection Measures 3.0 ENGINEERING METHODS 3. I Hydrologic Analyses 3.2 Hydraulic Analyses 4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS 4.1 Flood Boundaries 4.2 Floodways 5.0 INSURANCE APPLICATION 5. I Reach Determinations 5.2 Flood Hazard Factors 5.3 Flood Insurance Zones 5.4 Flood Insurance Rate Map Description Page I I I I I0 I0 i0 15 15 16 REVISED: TABLE Of CONTENTS - continued 6.0 OTHER STUDIES Poge 1'8 7.0 LOCATION OF DATA 18' 8.0 BIBLIOGRAPHY AND REFERENCES 1'8 FIGURES Figure I- Figure 2- Figure 3- Vicinity Map Flood heights at Moore Road Floodway Schematic 3 II TABLES Table I- Table 2- Table 3- Summary of Discharges Floodway Data Flood Insurance Zone Data 8 12-I.Zt 1~7 EXHIBITS F10od Profi.les · Elm Fork of Trinity River Grapevine Creek Denton Creek Cottonwood Branch Flood Boundary and Floodway Map Panel s 01P-O3P Panel s 04P-O8P Panels ogP-13P Panels 14P-17P Panel 480170 0005C PUBLISHED SEPARATELY: Flood Insurance Rate Map Panel 480'170 0005C ii REVISED: FLOOD INSURANCE STUDY CITY OF COPPELL, TEXAS 1.0 INTRODUCTION 1.1 Purpose of Study Thi~ Flood Insurance Study investigates the existence and severity of flood hazards in the City of Coppell, Dallas and Denton Counties, Texas, and aids in the administration of the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973. This study will be used to convert the City of Coppell to the regular program of flood insurance by the Federal Emergency Management Agency (FEMA). Local and regional planners will use this study in their efforts to promotes sound flood plain management. In some states or communities, flood plain management criteria or regulations may exist that are more restrictive or comprehensive than these on which these Federally-supported s~udies are based. These criteria take precedence over the minimum Federal criteria for purposes of regulating development in the flood plain, as set forth in the Code of Federal Regulations at 24 CFR, 1910.1 (d). In such cases, however, it shall be understood that the state (or other jurisdictional agency) shall be able to explain these requirements and criteria. 1.2 Authority and Acknowledgments The source of authority for this Flood Insurance Study is the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973. The hydrologic and hydraulic analyses for this study were performed by the U.S. Army Corps of Engineers, (COE), Fort Worth district, for the Federal Insurance Administration,(FIA) under Interagency Agreement No. (IAA)-H-7-76, Project Order No. 21 and (IAA)-H-lO-77, Project Order No. 2. This study was completed in December 1978. Additional analy- sis for this study was performed by Carter and Burgess Inc. in NOvember 1981., anU reflects information on Denton Creek and Cottonwood Branch. Additional analysis was performed by Albert H. Halff Associates Inc. in November 1981. Levee improvements along the Elm Fork of Trinity River, below Ledbetter Road were incorporated in this study. 1.3 Coordination Community base map selection and the identification of streams requir- ing detailed study were done during the initial coordination meeting held on July 12, 1976, attended by the Community Executive Officer (CEO), the Community Coordination Office (CCO), a Texas Department of Water REVISED: Resources (TDWR) representative, and o COE representative. The Soil Conservation Service (SCS), the US Geological Survey (USGS), the State Department of Highways and Public Transportation, and the TDWR were contacted for information related to the study. A final coordination meeting was held on July 18, 1979, in Coppell; at which time the results of this study were reviewed with community officials. COE and FIA officials were repre- sented at this meeting. 2.0 AREA STUDIED 2. I Scope of Study This Flood Insurance covers the incorporated areas of the City of Coppell. The area of study is shown on the Vicinity Map (Figure I). Detailed hydrologic and hydraulic studies were made on four streams affect- lng the City of Coppeil. It was agreed between the COE, the F'IA CCO, ~ the city that the detailed studies, as shown in this report, cover the flood hazard areas needing analysis. All areas studied in detailed were chosen with consideration given to all forecasted development until December 1983. This study was prepared as part of a larger study entitled "Dallas County Metro Area, Texas," covering all of Dallas County and portions of Collin, Denton, Rockwall, and Tarrant Counties. In order to facilitate the manage- merit, filing, and retrieval of the large amount of data produced during the study and to insure compatibility of data provided to adjoining communi- ties, and to simplify future changes due to changes in city boundaries, the following plan of study was developed. USGS 7.5 minute quadrangle maps (Reference I) covering the entire area to be studied were enlarged to a scale of !" = 1,000'. The upper and lower halves of the enlarged maps were used to prepare master work maps for the entire metro area study. As the engineering data, developed on a stream or watershed basis, were completed, they were transferred to the appropri- ate work map. Floodway data and flood insurance zone data tables were. also prepared as the engineering on each stream was completed. When the master work maps contained all the data necessary for the completion of the Coppell flood inusrance study, copies were made and used to prepare the work maps for this report. The flood profiles were prepared in a similar manner. Data was extracted from the previously mentioned floodway data and flood insurance zone data tables to prepare similar tables for this report. 2 FIGURE I Although some data may be displayed on the work maps which are outside the corporate limits of the community, this should not present any problems in the preparation of the final insurance maps for public distribution. In.addition, as corporate boundaries change, the data will be readily available for making alterations in the final community maps. 2.2 Community Description The City of Coppell lies on the Dallas-Denton County line in north central Texas. The city is bounded on the north by unincorporated areas of Denton'County, on the east by. Carrollton, and unincorporated areas of Dallas County, on the south by Irving and Dalla% and' on the west by Grapevine. The chamber of commerce lists the 1980 population as 3,826. Coppell is a sparsely developed residential community of approximately 12 square miles. The city is drained by the Elm Fork of the Trinity River and its tributaries. The Elm Fork flows in a southerly direction, while the tributaries flow in an easterly direction. Figure 1, the vicinity map, shows the location of Coppell with respect to the streams which drain it. The Coppell area has terrain characteristic of the Blackland Prairie. The topography is gently rolling to almost level with narrow streams being well incised. The soils in the area are mainly of the Houston Black, Haiden, and Austin series. The native vegetation consists of bunch and short grasses with scattered mesquite trees on the uplands and hardwood, mainly elm, hackberry, and pecan occurring along the streams. Most of the existing development in Coppell lies in the southwestern part of the city. Little development exists on the flood plains in Coppell at this time. The climate of the study area is warm, temperate, and humid. Summers are hot, and winters are short and mild. Extremes of temperatures and Precipitation is about 35 inches. The mean relative humidity is 63 percent, and average temperature is 65.8 degrees F. The record temperature extremes range from a maximum of lll degrees F in July 1954 to a minimum of -3 degrees F in January 1930. 2.3 Principal Flood Problems Most of the flood producing storms that occur in the Coppell area are experienced in the spring and fall. Most of the higher floods that have occurred in the general geographical region have resulted from prolonged or successive storms that produce heavy rainfall during this period; however, severe flooding can be produced by intense local thunderstorms at any time. Coppell has experienced few flood problems in the past, due primarily to the fact that little development exists on the flood plains at this time. 4 REVISED: There are two US Geological S~lrvey stream gages in the study area. The gage on the Fire Fork of the Trinity River located at Sandy lake Road was established in November 1943. The gage on Denton Creek located at Highway 121 was established in October 1947 (Reference 2). Histori- cal data for ungaged watersheds are dependent on local resident obser- vations, news media records, published reports, and analysis of other near- by watersheds with gage data and similar characteristics. Significant flooding is known to have occurred within the vicinity in 1908, the early 1942, ~9~?, 1949, 1957, 1962, 1963, 1%4, 1965, ~%9, 1973, 1974, 1976, and 1977~ however, little specific data is available. Grapevine Creek and COttonwood Branch undoubtedly experienced flooding during the periods listed above, but no details are available. According to local resident interviews, historical data for Denton Creek begins in 1908 with a major flood which is the maximum known in the lower basin. However, no high water marks or related stage heights have been recorded. A flood in April 1942 reached 35.9 stage-feet (from high water marks) at the gage and is thought to be the second largest. Grapevine Dam, completed in 1952, regulates flows at the gage except those from a 10.3 square mile local area between the dam and the gage. The maximum flood of record on the Elm Fork near Coppell prior to con- struction of the upstream reservoirs occurred in May 1908. An estimated discharge of 145,000 cfs was experienced. The second largest discharge of record was 90,700 cfs which occurred in April 1942. The existing up- stream reservoirs would have reduced the 1908 and 1942 floods near Carroll- ton from 145,000 and 90,700 cfs to 26,000 and 24,100 cfs, respectively, b~ed upon reservoir regulation studies. In September 1%4 a flow of 33,000 cfs was experienced at the Carrollton gage. This flow was generated entirely from the uncontrolled area below the reservoirs and approaches the magnitude of the 100-year flood in the Coppell area (Reference 2). it should be noted that the frequencies assigned to the historical floods should be viewed with caution since the estimates are made by comparing high water marks or discharge estimates obtained from historical records with determinations made in connection with this or adjacent studies. It is seldom possible to determine the conditions that existed at the sites of the historical high water mark or discharge estimate. The hydrologic determinations for this study ore based on existing stream and watershed conditions that existed at the time of the historical flood. Additionally, the estimates may not be valid except in the immediate oreo of the esti- mate. Figure 2 shows the heights that could be reached by the respective future floods on Grapevine Creek at Moore Road. 2.4 Flood Protection Measures Crapevine Dam on Denton Creek and Lewisville Dam on the Elm Fork of the Trinity River are the only major flood control projects affecting the FIGURE 2: FLOOD HEIGH'I'~ This photograph shows future flood heights on Grapevine Creek at Moore Road. n 6 study area. These reservoirs, providing flood control, water supply, and recreation, were completed in 1952 and 1955, respectively. Additionally, several short reaches of stream straightening and/or enlarging have taken place in connection with road construction. The City of Coppeli regulates flood plain development through a zoning ordinance. 3.0 ENGINEERING METHODS For the flooding sources studied in detail in the community, standard hydrologic and hydraulic study methods were used to determine the flood hazard data required for this study. Flood events of a magnitude which are expected to be equalled or exceeded once on the average during any 10-, 50-, I00-, and 500-year period (recurrence interval~), have been selected ets having special significance for flood plain management and for flood insurance premium rates. These events, commonly termed the 10-, 50-, !00-, and 500-year floods, have a 10, 2, I, and 0.2 percent chance, respectively, of being equalled or exceeded during any year. Although the recurrence inter- val represents the long term, averac~e period between floods of a specific magnitude, rare floods could occur at short intervals or even within the same year. The risk of experiencing a rare flood increases when periods greater than one year are considered. For example, the risk of having a flood which equals or exceeds the 100-year flood (one percent chance of annual occurrence) in any 50 year period is about/~0 percent (four in 10), and for any 90 year period, the risk increases to about 60 percent (six in 10).--The analyses reported here reflect flooding potentials based on conditions existing in the community at the time of completion of this study. Maps and flood elevations will be amended periodically to reflect future changes. 3.1 Hydrologic Analyses Hydrologic analyses were carried out to establish the peak discharge-frequency relationships for floods of the selected recurrence intervals for each stream studied in detail affecting the community. The hydrologic procedures used in developing discharge-frequency curves for the East Fork of the Trinity River ore based on the method recommended in the Water Resources Council Bulletin No. 17, "Guidelines for Determining Flow Frequency" (Reference 3). Historical discharge-frequency curves were developed at six gages in the Trinity River bain near Dallas. The final discharge-frequency curve for each location is a composite curve using observed discharge data with consideration given to rare hypotheti- cal floods. The 100- and SOO-year events are based on the values reflected by the composite or final curves plotted on log probability paper. The only stream gage on the Elm Fork of the Trinity River is located at the Sandy Lake Road bridge just east of Coppell in Carrollton, Texas. Each 7 of the remaining streams were divided into subareas, and synthetic unit and flood hydrographs were developed at selected locations. National Weather Service Technical Paper Number/~0 (Reference/~) was used in developing the 10-, 50-, and 100-year storms. The 500-year storm was based on extrapolated data. Frequency peak discharges at selected loca- tions were computed. Additionally, numerous headwater areas of less than I square mile were modeled using the rational method, where Q = CIA. The variables in this method are defined as follows: Q is the peal< discharge in cfs, C is a runoff coefficient, I is the rainfall intensity in inches per hour for the watershed time of concentration, and A is the drainage area in acres. Drainage area peak discharge relationships for streams in the study area are shown in Table I, "Summary of Discharges." The decrease in peak discharge with an increase in drainage area for some streams is due to watershed shape and/or overbank storage effects. TABLE I - SUMMARY OF DISCHARGES FLOODING SOURCE AND LOCATION ELM FORK OF TRINITY RIVER USGS gage located at Sandy Lake Road GRAPEVINE CREEK Confluence with Elm Fork At South Fork At Moore Road Below Stream 7F1 Above Stream 7F1 At intersection with extension of Cotton Road At Radio Road DRAINAGE AREA (sq. miles) PEAK DISCHARGES (cfs) 'lO-YEAR 50-YEAR iO0-YEAR 500-YEAR 104 4__/ 16,400 30,200 37,400 65,000 DENTON CREEK Confluence with Elm Fork Below Cottonwood Branch Above Cottonwood Branch At Highway 121 11.48 3_/ 5,900 8,600 9,700 12,700 10.55 6,900 9,700 11,800 15,200 9.65 7,500 10,500 11,800 15,100 8.14 7,600 10,600 11,900 15,100 7.17 6,700 9,400 10,500 13,400 5.95 7,300 10,00 11,200 14,200 3.68 5,100 7,000 7,900 9,900 24.23 1/ 10,600 15,500 17,800 36,200 2/ 19.45 T/ 13,300 18,900 21,300 36,200~/ 12.52 T/ 9,400 13,200 14,900 36,200 2-'/ 10.30 ~/ 10,000 13,800 15,600 36,200~/ CO1-FONWOOD BRANCH Confluence with Denton Creek 6.93 4,500 6,400 7,300 9,400 At Sandy Lake Road 5.69 4,200 5,900 6,700 8,600 At State Road 4.69 3,600 5,100 5,700 7,300 At Bethel Road 3_/ 3.64 3,600 5,000 6,200 7,800 Drainage area below Grapevine Lake. 2_/ Discharge for Denton Creek below Grapevine dam controlled outflows from Grapevine Lake. 8 3_/ 4_/ Outside corporate limits. Drainage area below Grapevine Lake and Lewisville Lake. 3.2 Hydraulic Analyses Analyses of the hydraulic characteristics of the flooding sources studies in detail in the community were carried out to provide estimates of the elevations of floods of the selected recurrence intervals along each of these flood sources. Water-surface eleva- tions of floods of the selected recurrence intervals for each of the smaller streams were computed through use of the COE HEC-2 step-backwater computer program (Reference 5). Water-surface elevations for the Trinity River were computed using the LRD-I (Modified) water-surface profile computer program (Reference 6)~ Cross sections for the backwater analyses of the streams studied were filed surveyed and were located at close intervals above or below bridges and culverts in order to compute the significant backwater effects of these structures. Channel roughness factors (Manning's "n") for these computations were assigned on the basis of field inspections of flood plain areas and on previous studies by the COE. Following is a list of the "n" value ranges. Stream Name Channel Overbank Elm Fork of Trinity River Grapevine Creek Denton Creek Cottonwood Branch .030-.055 .035-.085 .045-.055 .060-.080 .045-.060 .050-.060 .050-.050 .060-.070 Flood profiles were drawn showing computed water-surface elevations to an accuracy, of O.1 foot for floods of the selected recurrence intervals. The computer backwater models for the Elm Fork of the Trinity River were compared to previous studies for verification of results. Starting water-surface elevations for the Elm Fork of the Trinity River and Denton Creek were based on coincident con- ditions. The remaining streams were based on slope-area determina- tions. All elevations are measured from National Geodetic Vertical Datum of 1929 (NGVD). Elevation reference marks used in the study are shown and described on the maps. For study purposes, it was assumed that no clogging would occur and that all bridge structures would stand intact. Significant changes in this premise, imposed by differing conditions of a future flood, could alter the estimated flood elevations and flood limits shown on profiles and maps. Locations of selected cross sections used in the hydraulic analyses are shown on the Flood Profiles. For stream segments for which a floodway is computed (Section 4.2), selected cross section locations are also shown on the Flood Boundary and Floodway Map. REVISED:-' 4.0 F LOODPLA_I_N__MANAGEMENT_A.P~L I CAT.I_O_NS The National Flood Insurance Prog~amencourages state and local governments to adopt sound flood plain management programs. Therefore, each Flood In'- surance Study includes a flood boundary map designed to assist conlnunities in developing sound flood plain management measures. 4.1 Flood Boundaries ! In order to provide a national standard without regional discrimina tion, the lO0-year flood has been adopted by FEMA as the base flood ~ for purposes of flood plain manageme6t measures. The 500-year flood is employed to indicate additional areas of flood risk in the con~nun- ity I ' For each stream studied in detail, the boundaries of the lO0-year and the 500-year flood have been delineated using the flood elevations determined at each cross section. Between cross sections, the boundaries were extrapolated 'using available topographic maps with a contour interval of 10 feet {Reference L1}. A topographic map, contour interval 2 feet, sunplied by Carter and Burgess Incorporated (Reference 7), was available for Denton Creek. In cases where the lO0-year and the 500-year flood boundaries are close together, only the lO0-year boundary has been shown. Small areas within the flood boundaries may lie above the iflood elevations and therefore not be subject to flooding owing to limitations of the map scale, such areas arL~-l~o-t--s)To~n. To assist users of the flood iinsurance report data in locating the actual boundaries of the base flood or for determining the elevatior~ of specific sites or structures in relation to the base flood, elev~- tion reference marks are shown on the maps. These reference marks include existing US Coast and Geodetic Survey bench marks, as well as bench marks established for the current study. Flood boundaries are indicated on the Flood Insurance Rate Map. On. this map, the lO0-year flood~boundary corresponds to the boundary of the areas of special flood hazards; and the 500-year flood boundary l corresponds to the boundary of areas of moderate flood hazards {Zon~ B). 4.2 Floodways I Encroachment on flood plainsj such as artificial fill, reduces the flood-carrying capacity, increases the flood heights of streams, and increases flood hazards in areas beyond the encroachment itself. One aspect of flood plain management involves balancing the economic gain from flood plain developmentlagainst the resulting increase in floo¢ hazard. For purposes of the'National Flood Insurance Program, the concept of a floodway is used as.a tool to assist local communities in this aspect of flood plain management. Under this concept, the area of the lO0-year flood is divided into a floodway and a floodway fringe. The-.fl oodway --is-the -channel-of-a-stream -pl us-any- adjacent.~ flood plain areas that must be kept free of encrachment in order that the lO0-year flood may be carried without substantial increases in flood heiohts. Minimum standards of FEMA limit such increases in flood heights to 1.0 foot, provided that hazardous velocities are not produced. 10 ? REVISED: A The floodway proposed for this study was computed on the basis of equal conveyance reduction from each side of the flood plain. The results of these computations are tabulated at selected field cross sections for each stream segment for which a floodway is computed (Table 24 As shown on the Flood Boundary and Floodway Map, the floodway' boundaries were determined at cross sections; between cross sections the boundaries were extrapolated. The floodways in this report are presented to local agencies as minimum standards that can be adopted or that can be used as a basis for additional studies. The area between the floodway and the boundary of the 100-year flood is termed the floodway fringe. The-floodway fringe thus encompasses the portion of the flood plain that could be completely obstructed without increasing the water-surface elevation of the 100-year flood more than !.0 foot at any point. Typical relationships between the floodway and the floodway fringe and their significance to flood plain development are shown in Figure 3. YEAR FLOOO PLAIN ! _ FLOODWAY _ I _ t FRINGE FLOOD ELEVATION WHEN CONFINED WITHIN FLOODWAY _1_ AREA Of FLOOO PLAIN THAT COULD M. U~ED FOR DEVELOPMENT BY RAISING GROUND FLOOOWAY FRINGE ~ FLO00 ELEVATION REFORE ENCROAClMEENT ON FLOOD PLAIN LINE A · B IS TIlE FLOOD ELEVATION BEFORE ENCROACHMENT LINE C -O IS THE FLOOD ELEVATION AFTER ENCROACHMENT e'S~RCHARGE NOT TO EXCEED 1.0 FOOT LESSER AMOUNT If SPECIFIED BY STATE FLOODWAY SCHEMATIC Figure 3 II TABLE 2 l? 13 TABLE 2 5.0 INSURANCE APPLICATION In order to establish actuarial insurance rates, .FEI~ has developed a process to transform the data from the engineering study into flood insurance criteria. This process includes the determination of reaches, Flood Hazard Factors (FI-IFs), and flood insurance zone designations for each significant flooding source affecting the City of Coppeii. 5. I Reach Determinations Reaches are defined as lengths of watercourses having relatively the same flood hazard, based on the average weighted difference in water- surface elevations between the 10- and 100-year floods. This difference does not have a variation greater than that indicated in the following table for more than 20 percent of the reach. Average Difference Between 10- and 100-Year Floods Variation Less than 2 feet 0.5 foot 2 to 7 feet 1.0 foot Eigh.treaches meeting the above criteria were required for the flooding sources affecting the City of Coppell. The location at reaches are shown on the Flood Profiles.. 5.2 Flood Hazard Factors (FHFs) The Flood Hazard Factor is used to correlate flood information with insurance rate tables. Correlations between property damage from floods and their assigned FHFs are used to set actuarial insurance premium rate tables based on FHFs from 005 to 200. The FHF for a reach is the average weighted difference between the 10- and 100-year flood water-surface elevations expressed to the nearest one-half foot, and shown as a three-digit code. For example, if the diff- erence between the water-surface elevations of the 10- and 10(L-year floods is 0.7 foot, the FHF is 005; if the difference is I./t feet, the FHF. is 015; if the difference is 5.0 feet, the FHF is 050. When the differ- ence between the 10- and 100-year flood water-surface elevations is greater than 10.0 feet, the accuracy for the FHF is to the nearest foot. 15 REVISED: $.3 Flood Insurance Zones After the determination of reaches and their respective FHFs, the entire incorporated area of Coppeli was divided into zones, each having a specific flood potential or hazard. Each zone was assigned one of the following flood insurance zone designations= Zone A: Special flood hazard areas inundated by the IO0-year flood, determined by approximate methods; no base flood elevations or FHF determined. Zone A2, A3, AA~, A5, Zone B: Special flood hazard areas inundated by the IO0-year flood, determined by detailed methods; base flood ele- vations are shown and zones subdivided according to FHF. Areas between the Special Flood Hazard Area and the limits of the 500-year flood; areas that are protected from the 100-year or 500-year flood by dike, levee, or other water control structure; areas subject to certain types of 100-year shallow flooding where depths are less than 1.0 foot; and areas subject to 100-year flooding from sources with drainage areas less than I square mile. Zone B is subdi- vided. Zone C: Areas of minimal flooding. Table 3, Flood Insurance Zone Data, summarizes the flood differences, FHF, flood insurance zones, and base flood for each flooding source in the community. 5./~ Flood Insurance Rate Map Description The Flood Insurance Rate Map for the City of Coppeil is, for insurance purposes, the principal result of the Flood Insurance Study. This map (published separately) contains the official delineation of flood insurance zones and base flood elevation lines. Base flood elevation lines show the locations of the expected whale-foot water-surface elevations of the base (100-year) flood. This map is developed in accordance with the latest flood insurance map preparation guidelines published by FEMA. 16 REVISED:: 6.0 OTHER STUDIES 7.0 A report entitled "Partial Hydrologic and Hydraulic Data foP'Flood Plain Delineation, Grapevine Creek, Cit~ of Coppell, Texas," was published in November 1976 (Reference 8). That~ report covers a reach of Grapevine Creek located between Moore Road ~nd Denton Tap Road. / The lO0-year frequency flood elevaltions and discharges developed in this report are based on a fully develdped watershed and as would be expected are higher than those developed fo'r the Coppell flood insurance study. / Flood insurance studies for the aJjacent 6on~nunities of Carroll ton, Grape~' vine, and Irving, Texas {References 9-11} were prepared concurrently with this study and are in total agreem~ent. Dallas County (Reference 12) wasI prepared before levee improvement idata along the Elm Fork of Trinity River was available and does not match this study. No published Flood Insur- ance Study has been prepared for the City of Dallas or Tarrant County. I This study is authorative for the !purposes of the Flood Insurance Program, and the data presented here eithe~ supersede or are compatible with previOus determi nations. LOcAT,IO____~N OF DATA Information concerning the pertin 'nt data used in preparation of this study can be obtained by contacti6g the Natural and Technological Hazards Division, Federal Emergency Management Agency, Federal Center, Denton, Texas 76201 8.0 BIBLIOGRAPHY AND REFERENCES Se US Geological Survey 7½ Minute Quadrangle Maps: Carollton, Texas, dated 1959 and photorevised in 1968 and 1973; Grapevine, Texas, dated 1959 and photorevised in 1968 and 1973. US Geolgoical Survey, Stream!Gaging Records. Water Resources Council Bull(~tin No. 17, Guidelines for Determining) Flow Frequency, March, 1976.. National Weather Service, Te(:hnical Paper Number 40, Rain~all Fre- quency Atlas of the United Sl:ates, May, 1961. COrps of Engineers, HEC-2, Water Surface Profiles, Hydrologic Engineer- ing Center, Davis California~ November, 1976 updated August, 1977. I Corps of Engineers, LRD-1 (Modified) Water Surface Profiles, Littler Rock District, Corps of Engineers, modified by the Fort Worth Dis- trict, Corps of Engineers. I Carter and Burgess Incorporated, topographic map, Univest, Coppell,I Texas, 2' contour interval, Scale 1:2400 July. lO, 1981. REVISED: Be ge 10. 11. 12. Albert H. Halff Associates, nc., Engineers, Partial Hydrologic and) odraulic Data for Flood Pla n Delineation, Grapevine Creek, City o~ Ppell, Texas, for North La~e Woodlands Addition, Furguson and Deeqe, Inc" N°vember 18' 1978'I ) Federal Emergency Management Agency,. Flood InsuranCee~Udy, Cit~ ofI ;ar__~rg~9~, Tex______as_, January, i980. {ReV, S,on ,n progr ) { ...' ....... Flood Insurance Study, City of GraPevine,'Texa~, May, 1982. .......... Flood insurance StUdy, City of Irvin9, Texas, May,. 1980. (ReVision in Progress) .... ...... Flood Insurance Study, Dallas Count , Texas, Unincorporated Areas, January, 1982. Albert H. Halff Associates, District--Section III, Irvin nc., Engineers, Irving Flood Control. , Texas. November, 1981.