UDO FEM (122091480014 i 1/ > FLOOD INSURANCE’ j STUDY Libra Texas AMA ll . erslty out 2 e zoos g“ DOCUMENTS E“ Library Texas ASLM University ATASCOSA coumv, *iiR@2'98 1 TEXAS EDEPOSITQRY UNINCORPORATED AREAS DECEMBER 15, 1980 O federal emergency management agency federal insurance administration COMMUNITY NUMBER -480014 2.0 3.0 LLO » 5.0 TABLE OF CONTENTS INTRODUCTION |.| Purpose of Study I.2 Authority and Acknowledgments I .3 Coordination AREA STUDIED 2.l Scope of Study 2.2 Community Description 2.3 Principal Flood Problems 2.4 Flood Protection Measures ENGINEERING METHODS 3.I Hydrologic Analyses 3.2 Hydraulic Analyses FLOOD PLAIN MANAGEMENT APPLICATIONS 4.I Flood Boundaries ll.2 Floodways INSURANCE APPLICATION 5.I Reach Determinations 5.2 Flood Hazard Factors 5.3 Flood Insurance Zones 5.4 "Flood Insurance Rate Map Description J-‘J-‘NDNJNJ IO I3 I3 I3 I3 m TABLE OF CONTENTS - continued 6.0 OTHER STUDIES 7.0 LOCATION OF DATA 8.0 BIBLIOGRAPHY AND REFERENCES FIGURES ‘ ' Figure I - Vicinity Map Figures 2-5 - Historical Flood Scenes Figure 6 - Floodway Schematic TABLES Table I - Summary of Discharges Table 2 - Floodway Data Table 3 - Flood Insurance Zone Data EXHIBITS Exhibit I - Flood Profiles Atascosa River Bonita Creek Exhibit 2 — Flood Boundary and Floodway Map Index Exhibit 3 - Flood Boundary and Floodway Map PUBLISHED SEPARATELY: Flood Insurance Rate Map Index Flood Insurance Rate Map 5,6 I2 I5 Panels OI P-O2P Panels O3P-OZIP FLOOD INSURANCE STUDY ATASCOSA COUNTY, TEXAS (UNINCORPORATED AREAS) l.O INTRODUCTION Purpose of Study This Flood Insurance Study investigates the existence and severity of flood hazards in Atascosa County, Texas, and aids in the administration of the National Flood Insurance Act of I968 and the Flood Disaster Protection Act of I973. This study will be used to convert Atascosa County to the regular program of flood insurance by the Federal Insurance Administration (FIA). Local and regional planners will use this study in their efforts to promote sound flood plain management. In some states or communities, flood plain management criteria or regula- tions may exist that are more restrictive or comprehensive than those on which these Federally-supported studies 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 Regula- tions at 2i» CFR, I9I0.l (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. ' Authority and Acknowledgments The source of authority for this Flood Insurance Study is the National Flood Insurance Act of I968 and the Flood Disaster Protection Act of I973. The hydrologic and hydraulic analyses for this study were performed by URS/Forrest and Cotton, lnc., Consulting Engineers, Austin, Texas, for the Federal Insurance Administration, under Contract No. H4643. This study was completed in August, I979. Coordination An initial coordination meeting, attended by representatives of Atascosa County, the FIA, and representatives of URS/Forrest and Cotton, lnc., was held on March 9, I978 to explain the nature and purpose of the study and to establish the geographic limits of the study. A legal notice announcing the beginning of the study and stating its objectives was placed in the local newspaper. During the course of the study, preliminary results of the hydrologic analyses were submitted to the Soil Conservation Service and the U.S. Army Corps of Engineers for their review. In addition, officials of Atascosa County were periodically advised of the progress of the study. The preliminary results of the study were presented at an intermediate coordination meeting attended by Atascosa County officials, representatives of FIA and URS/Forrest and Cotton, Inc. Following review by the county, and incorporation of necessary changes, a final meeting was held on July 9, I980, and the final results were presented to the county. 2.0 AREA STUDIED 2.l 2.2 Scope of Study This Flood Insurance Study has been prepared for Atascosa County, Texas. The Atascosa River and Bonita Creek comprise the major sources of flooding within the study area. These waterways and their associated drainage basins were selected for study by detailed methods. Other areas of the county will utilize Flood Hazard Boundary Maps (FHBM) to identify areas subject to flooding (Reference I). Selection of areas for detailed study was based upon known flood problems, or upon suspected flood hazards for areas where development was projected to occur over the next five years, through March, I983. That portion of the Atascosa River studied‘ in detail is from I, I60 feet downstream of the east city limits of Pleasanton to the north city limits of Pleasanton. Bonita Creek was studied in detail from 5,500 feet above its confluence with Atascosa River, which is the south city limits of Pleasanton, to the east city I imits of Pleasanton. A part of the Atascosa River and of Bonita Creek meanders inside the corporate limits and is discussed in a separate report for the City of Pleasanton. The area of study is shown on the vicinity map (Figure I). Community Description Atascosa County is located in south-central Texas approximately 35 miles south of San Antonio, Texas. Jourdanton is the county seat while Pleasanton is the largest commercial and trading center serving the 20,300 population (Reference 2) in the surrounding area. U.S. Highway 28I, State Highway 97 and a branch line of the Missouri-Pacific Railroad are the major transportation arteries. The area is an agricultural and ranching center with some crude oil production and related oil field services. Livestock, peanuts, grain, hay and strawberries are the main forms of agribusiness. Topography of the area is nearly level to gently sloping with deep, fine sandy loams or loamy fine sand that have moderately or moderately slowly permeable subsoils (Reference 3). Elevations range from 330 feet to 425 feet based on the National Geodetic Vertical Datum of I929 (NGVD). .2: :=_a_> Qua-Egg. .2 i=3“. 3825 co=~._§:_Eu< 3c~._:»c_ Ghana“. >uzwo< hzwzmouzmwmm2w imwawm m... UJQOw mhki-XOCQI? .3 y». W. v \ J‘ w,‘ I, .1 zwficmm A xww , / éé. caqfi Tehua \h 2.3 2.4 Atascosa County has 0 subtropical climate characterized by hot, low humidity summers and mild winters. The annual precipitation is 27.9 inches, occurring mostly in the spring and fall months. The hot summers bring heavy evaporation so that cultivation without irrigation is limited. Temperature extremes have ranged from I3 to I08 degrees F (Reference 2). Prinicipal Flood Problems The areas studied experience flooding from two main sources, the Atascosa River and Bonita Creek. The drainage area of the Atascosa River watershed at Pleasanton is about 356 square miles which includes l2 square miles drained by Bonita Creek. The Atascosa River has a narrow, shallow and fairly straight low-water channel which is lined with large trees and brush. The capacity of the shallow channel is small and most of the flood flow is carried in the overbanks. ~ The stream flow discharge of the Atascosa River and Bonita Creek at Pleasanton has not been measured on a continuous basis. However, there is a collection of data at Whitsett, Texas, 43 miles downstream on the Atascosa River. The recorded maximum peak flow at Whitsett is l2l , 000 cubic feet per second (cfs), which was a result of hurricane Beulah in September I967. The estimated peak flow at Pleasanton as a result of this storm was 36,300 cfs. Based on the hydrologic analysis performed for this detailed study the estimated peak discharge of 36,300 cfs has a recurrence interval of l l0 years. Shown in Figures 2 through 5 are some photographs obtained from the local newspaper (Reference Li) which show flooding as a result of hurricane Beulah. Flood Protection Measures Several flood protection measures have been undertaken on the Atascosa River and Bonita Creek as recommended by the Corps of Engineers (Reference 5). These include channel enlargement and clearing of brush along the Atascosa River and the building of an earth levee along the left bank of Bonita Creek. The Missouri-Pacific Railroad branch line embankment, which is along the east bank of the Atascosa River, acts as a levee and prevents northeast Pleasanton from flooding. Atascosa County has an established emergency operations plan that involves the Atascosa County Sheriff's Office, volunteer fire department, police department and all city officials. Communications and severe weather warnings are disseminated by telephone, siren, radio and short wave radio. FIGURE 2: September 1967, looking south at the Atascosa River in Pleasanton near Adams Street. FIGURE 3: September 1967, looking southwest at Atascosa River and State Highway 97. '—fl', " __ ~.- - ‘QQQ-p Jafl‘ y‘ FIGURE 4: September 1967, looking west across River Street in Pleasanton between White and Goodwin Streets. .w&i"~....~ 1i _.,, . l- (¢¢_ w _ d’ l p. . ‘L.’ ...».< w-xh c»... a l FIGURE 5: September 1967, intersection of Chapman and Good- win Streets looking east along Goodwin Street in Pleasanton. 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 lO-, 50-, lOO-, and SOO-year period (recurrence intervals), have been selected as having special significance for flood plain management and for flood insurance premium rates. These events, commonly termed the lO-, 50-, lOO-, and SOO-year floods, havea IO, Z, I, and 0.2 percent chance, respectively, of being equalled or exceeded during any year. Although the recurrence interval represents the long term, average period between floods of a specific magnitude, rare floods could occur at short intervals or even within the some 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 IOO-year flood (one percent chance of annual occurrence) in any 50 year period is about 40 percent (four in IO), and for any 90 year period, the risk increases to about 6O percent (six in l0). 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. I Hydrologic Analyses Hydrologic analyses were carried out to establish peak discharge-frequency relationships for floods of the selected recurrence intervals for each flooding source studied in detail in the community. The procedures used by the SCS were adopted as the preferred method to compute peak discharges (Q) for the selected drainage area associated with Bonita Creek in Atascosa County. The Soil Conservation method (SCS method of estimating direct runoff from storm rainfall) (Reference 6) is based on procedures developed by SCS hydro- logists over the last three decades. Rainfall and watershed data including soil properties are included as hydrologic parameters in calculating peak flows. Soils are divided into four groups based on the minimum rate of in- filtration obtained for a soil after prolonged wetting. Surface conditions are evaluated by land use and treatment classifications. Time of travel, peak flows, and accumulated runoff ratios from SCS dimensionless hydrographs are used to tabulate the design flood hydrographs and peak discharges for the lO-, 50-, and IOO-year storms. The 500-year discharge can then be determined by a log-normal extrapolation of the lO-, 50-, and IOO-year flows. _ FLOODING SOURCE AND LOCATION The physical parameters of soil type and group classification were determined following a field reconnaissance of the watershed and the use of the General Soil Map of Atascosa County, published by the SCS (Reference 3). Each watershed was divided into the percentage of contributing soil group classifi- cation and land use cover; and a calculated composite curve number which describes the physical parameters was used to modify the unit hydrograph tabulations. A curve number of 8O was used in this study. The additional parameters of drainage area and stream length were determined from topographic maps of the drainage basin. Rainfall data was obtained from the U.S. Weather Bureau Technical Paper No. 40 (Reference 7). The SCS method is not adequate for determining flows of the Atascosa River because of its size and lack of soils information. Therefore, the log-Pearson Type lll method, which is recommended by Water Resources Council (WRC) (Reference 8), was selected as the preferred method for estimating flows of the desired frequencies. Annual maximum flow data for the period I932 to I977 for the USGS stream gauge station at Whitsett was used in the frequency analysis. The lO-, 50-, l00-, and 500-year frequency peak flow data at Whitsett (drainage area of l,l7l square miles) were reduced by the drainage area ratio to obtian the desired frequency flood flows at the City of Pleasanton (Drainage area of 356 square miles). Thepeak discharge-drainage area relationships for the selected recurrence intervals are presented in Table l, "Summary of Discharges." TABLE 1 — SUMMARY OF DISCHARGES PEAK DISCHARGES (cfsl - EAR 50-YEAR 00- EAR 500-‘ EAR DRAINAGE AR EA (sg. miles) ATASCOSA RIVER Pleasanton East City Limit 356 7,150 21,730 33,150 49,100 BONITA CREEK Pleasanton South City Limit 10.4 5,400 7,900 9,200 11,500 3.2 Hydraulic Analyses Analyses of the hydraulic characteristics of the flooding sources studied in detail in the county were carried out to provide estimates of the elevations of floods of the selected recurrence intervals along each of the flood sources. These elevations were computed thorugh use of the Corps - of Engineers (COE) HEC-2 step-backwater computer program (Reference 9). i Cross sections for the backwater analyses of the Atascosa River and Bonita Creek were obtained from aerial photographs provided by International Aerial Mapping Company and flown in November I978, at a scale of l.0 inch equals 500 feet (Reference l0). Horizontal and vertical ground control was established by field surveying using 3rd-order accuracy. The stream bed elevations below the water-surface were obtained by field measurement. All bridges and culverts were field checked to obtain elevation data and structural geometry. Locations of selected cross sections used in the hydraulic analyses are shown on the Flood Profiles (Exhibit I). Selected cross section locations are also shown on the Flood Boundary and Floodway Map (Exhibit 3). Channel roughness factors (Manning's "n") used in the hydraulic computations were chosen by engineering judgement based on field observations of the streams and flood plain areas. Roughness values for the main channel and overbanks ofithe Atascosa River range from 0.030 to 0.070. Roughness values for the main channel of Bonita Creek range from 0.030 to 0.060 with flood plain roughness values ranging from 0.030 to 0.070 for all frequency floods. As mentioned previously, water-surface elevations of floods of the selected recurrence intervals were computed through use of the Corps of Engineers HEC-2 step-backwater computer program. Flood profiles were drawn showing computed water-surface elevations for floods of the selected recurrence intervals. Starting water-surface elevations for Atascosa River and Bonita Creek were calculated using the slope-area method. All elevations are referenced from the National Geodetic Vertical Datum of I929 (NGVD), formerly referred to as Mean Sea Level Datum of I929. Elevation reference marks used in this study are shown and described on the maps. The hydraulic analyses for this study were based on unobstructed flow. The flood elevations shown on the profiles are thus considered valid only if hydraulic structures remain unobstructed, operate properly, and do not fail. 4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS The National Flood Insurance Program encourages state and local governments to adopt sound flood Plain management programs. Therefore, each Flood Insur- ance Study includes a flood boundary map designed to assist communities in developing sound flood plain management measures. ll.l 4.2 Flood Boundaries ln order to provide a national standard without regional discrimination, the IOO-year flood has been adopted by the FlA as the base flood for pur- poses of flood plain management measures. The 500-year flood is employed to indicate additional areas of flood risk in the community. For each stream studied in detail, the boundaries of the l00- and the 500-year floods have been delineated using the flood elevations determined at each cross sec- tion; between cross sections, the boundaries were interpolated using the aid of existing topographic maps. ln cases where the IOO- and the 500- year flood boundaries are close together, only the l00-year boundary has been shown. The boundaries of the l00- and 500-year floods are shown on the Flood Boundary and Floodway Map (Exhibit 3). Small areas within the flood boundaries may lie above the flood elevations and, therefore, not be subject to flooding; owing to limitations of the map scale, such areas are not shown. To assist users of the Flood Insurance Study to locate, in the field, the actual boundaries of the base flood or to assist users in determining the elevations of specific sites or structures in relation to the base flood, elevation reference marks have been established and are shown and des- cribed on the maps. These reference marks include previously existing Coastal and Geodetic Survey Bench Marks as well as reference marks established during the current study by URS/ Forrest and Cotton, lnc. Floodways Encroachment on flood plains, 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 development against the resulting increase in flood hazard. For purposes of the 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 IOO-year flood is divided into a f loodway and a floodway fringe. The floodway is the channel of a stream, plus any adjacent flood plain areas that must be kept free of encroachment in order that the IOO-year flood may be carried without substantial increases in flood heights. Minimum standards of the FlA limit such increases in flood heights to |.O foot, provided that hazardous velocities are not produced. 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 floodway presented in 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 cross sections and are shown in the Floodway Data Table (Table 2). As shown on the FBFM (Exhibit 3), the floodway widths were determined at cross sections; between cross sections the boundaries were interpolated. ln cases where the boundaries of the floodway and the I00-year flood plain are either close together or collinear, only the floodway boundary has been shown. The area between the floodway and the boundary of the lOO-year flood is termed the floodway fringe. The floodway fringe thus encompasses the portion of the flood plain that could be completely obstructed with- out increasing the water-surface elevation of the I00-year flood more than l.O foot at any point. Typical relationships between the floodway and the floodway fringe and their significance to flood plain development are shown in Figure 6. T? IN YEAH FLOOD PLAIN nooowav nooownv ___ _r - rams: FLOODW" T rnmac smum ' CHANNEL noon ELEVATION WHEN courmeo wmuu FLOODWAY _ e~cno5cgusur smcngqguutut l I \ l c _—'1-KQ4 . Vsuacnmncc- l ii m GUI?‘ I . AK t‘ “flask-P AREA or noon rfATn nun couu) as useo won oevnomeut av ruusma cnouuo FLOOD ELEVATION - BEFORE ENCROACHMENT ON FLOOD PLAIN LINE A ~ B IS THE FLOOD ELEVATION BEFORE ENCROACHMENT LINE C - DIS THE FLOOD ELEVATION AFTER ENCROACHMENT ‘SURCHARGE NOT TO EXCEED 1.0 FOOT (FIA REOUIREMENTI OH LESSEH AMOUNT IF SPECIFIED BY STATE. F LOODWAY SCH EMATIC Figure 6 0E5 <55» 52¢ $03.13 02g =fi<5§05=a0 0: .259. 05035, =2=a§=_=i< 02552.. 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A . . _ . . . ww@wm~_m0_z_ ><>bm_m>0d >¥$flwwnm Ewfiwowkmwm >»>__m,0..mm__%w> _.,_.,.m%w»%0,m._m% 10km“? m0z<55 20.5mm wwomo 20.553 004055 mESs ><>>DOO.I womnow 02.0001 000.; mw232 5835i! >255 is» ._< OwhIm¥w>>~ 62,3 n-(S- m5: wuz<¢:mz_ D004“? “P2; ~< QHO 36+ fid- 8.7 E8 H 53¢ xwwgu ~p@=om mmT3> 3< o8 mo . ~+ 3 . ~.. mm . m: E 8 GENO H zummm V »w>@¢ ~mouw~»< fCe> ©Ofiv _.¢e> Om~ ¢¢> O: muwfiwwwww ~23 “in. .3 a fi i: .325. muzaom wzEooi D24 DOOII 2436c: $9. w zmwihmm “muzwzmkzo ZO_.-.<>m._m 7.0 LOCATION OF DATA 8.0 Survey, hydrologic, hydraulic, and other pertinent data used in this study can be obtained by contacting the Insurance and Mitigation Division, Federal Emer- gency Management Agency, Federal Center, Denton, Texas 7620i. BIBLIOGRAPHY AND REFERENCES U.S. Department of Housing and Urban Development, Federal Insurance Administration, Flood Hazard Boundar Ma Atascosa County, Texas, Community No. 4800M, November 29, I97 Texas Almanac and State Industrial Guide, Published by Dallas Morning News, Dallas, Texas, I978-79. U.S. Department of Agriculture, Soil Conservation Service General Soil Map, Atascosa County, Texas, June I972. Pleasanton Express, Photograph Files of Past Floods. U.S. Army Corps of Engineers, Fort Worth, Texas, Project Report on Flood Protection at Pleasanton, Texas, September I950. T U.S. Department of Agriculture, Soil Conservation Service, SCS National Engineering Handbook Section 4, Hydrology, January l97l. U.S. Department of Commerce, Weather Bureau, "Rainfall Frequency Atlas of the United States", Technical Paper No. 40 May I96 I. United States Water Resources Council, Guidelines for Determining Flood Flow Freguencl, June I977. U.S. Army Corps of Engineers, Hydrologic Engineering Center, Computer Program 723-X6-L202A HEC-2 Water-Surface Profiles, Davis, California, November I976, with updates. International Aerial Mapping Co., San Antonio,'Texas, Aerial Photogrpahy of Atascosa County, Texas, November I978. Chow, Ven T., Open-Channel Hydraulics, McGraw-Hill Book Company, I969. Viessman, Jr., Warren; Knapp, John W.; Lewis, Gary L.; Harbaugh, Terrence E.; Introduction to Hydrology, IEP-A Dun-Donnelley Publisher, I977. ELEVATION (FEET NGVD) 360 355 350 345 340 335 330 325 320 400 800 1 200 1 600 2000 2400 2800 3200 STREAM DISTANCE IN FEET ABOVE DOWNSTREAM LIMIT OF DETAILED STUDY H.000 PIIDFILES ATASCOSA RIVER I LEGEND ——*—-—i SOD-YEAR FLOOD -————-— IOO-YEAR FLOOD 50—YEAR FLOOD 10—YEAR FLOOD STREAM BED CROSS SECTION LOCATION 3600 4000 FEDERAL EMERGENCY MANAGEMENT AGENCY ATASCDSA COUNTIIY, TX [UNINCORPORATED AREAS] ' 01 T ELEVATION (FEET NGVD) 360 355 350 345 340 335 330 ' 325 4000 370 365 360 355 350 345 340 4800 5200 1 2800 1 3200 1 3600 14000 14400 STREAM DISTANCE IN FEET ABOVE DOWNSTREAM LIMIT OF DETAILED STUDY LEGEND 500—YEAR FLOOD 100—YEAR FLOOD 50—YEAR FLOOD 10—YEAR FLOOD STREAM BED CROSS SECTION LOCATION 1 4800 1 5200 if) - 5 =' z H- Q n: == a “' o = a 9 < = n- -: < Lb >< E '4"- §s>TE iffiPm :fi=»< gI§== géQfi r55’: {£68 i232 {i125 ... |- g <1: _ _ . l.» ~ .:"'=', . 13w?‘ w '~ ' w " ' " -' ' ‘ s '- ' ‘ >1. ,\ < - '1 ' . I .- < a. M , I 1a b’; . . - ‘~ ' z ’“ . ~ =, . w‘ w‘ . \ . 1' -- . . L‘! ' I -' ._. . . ‘ -- ‘ g ‘ -_ . a. __ . ,_ .' L . . ' ‘ l ' .1 - ;- \, ' 3' ‘ \ ‘.- >- _¢ i .. ‘I . " .‘- _,¢._ . - . . - 1__ " g}. m» ','-"“5' ,_ - flyh- n 1 4}’- .\-', ' a. _,..v, f,‘ ‘ ATw rm .-u_|-::",: .»;~"~¢.a.£ ni-‘Vflfi '.§-. .. .3’ l ELEVATION (FEET NGVD) 365 360 355 350 345 I 34o 3200 4000 4800 5600 STREAM DISTANCE IN FEET ABOVE MOUTH _ I — 6000 6400 noon Pnorucs BONITA CREEK LEGEND SOD-YEAR FLOOD IOO-YEAR FLOOD ‘SO-YEAR FLOOD IO-YEAR FLOOD STREAM BED CROSS SECTION LOCATION 6800 4 rsnzm zmenszucv ununecmcur AGENCY ATAFEFEYSSsUZEEFIIEaTtiIF, TX [UNINCORPORATED AREAS] b) ‘U -| iu..\\l)..\.o||\|l|||\I.\|I'\§)|v P .. , 411.1115 I I .. ‘ 1 .I. ‘ .\|(k: 1|‘ l; |.1.| |i..\.J. . :11.‘ ‘ l | .! \vl \ lxl\rl\l4ll|itzlll\.t\.iltly!al \ i‘ l“\l .. \. ‘. . ., \ I? 1 i ..1-( .. . 5M5 <==8 n._===_._ =25 .22”: .E<.a._._=u.__z=_ , E. .358 052 5323522 >emwzuzu .3225» 04P 5 0 6 6 3 3 AQ>0Z Em“: z0;<>w._w 370 LEGEND 500—YEAR FLOOD -— - - -- 100—YEAR FLOOD ——- — —- 50—YEAR FLOOD ———--— mwmFmm g cnoss SECTION LOQNHON 355 350 8400 8000 7600 7200 ssoo STREAM DISTANCE IN FEET ABOVE MOUTH |umgflwiigfigiigingfiflimfljimiwmum -a-.<-‘.., _