CRAIGHEAD COUNTY, ARKANSAS AND INCORPORATED AREAS

Transcription

1 CRAIGHEAD COUNTY, ARKANSAS AND INCORPORATED AREAS COMMUNITY NAME COMMUNITY NUMBER BAY, CITY OF * BLACK OAK, TOWN OF BONO, CITY OF BROOKLAND, TOWN OF CARAWAY, CITY OF CASH, TOWN OF CRAIGHEAD COUNTY, UNINCORPORATED AREAS EGYPT, TOWN OF JONESBORO, CITY OF LAKE CITY, TOWN OF MONETTE, CITY OF *NON-FLOODPRONE COMMUNITIES Revised: Federal Emergency Management Agency Flood Insurance Study Number 05031CV000A

2 NOTICE TO FLOOD INSURANCE STUDY USERS Communities participating in the National Flood Insurance Program have established repositories of flood hazard data for floodplain management and flood insurance purposes. This Flood Insurance Study may not contain all data available within the repository. It is advisable to contact the community repository for any additional data. Part or all of this Flood Insurance Study may be revised and republished at any time. In addition, part of this Flood Insurance Study may be revised by the Letter of Map Revision process, which does not involve republication or redistribution of the Flood Insurance Study. It is, therefore, the responsibility of the user to consult with community officials and to check the community repository to obtain the most current Flood Insurance Study components. A listing of the Community Map Repositories can be found on the Index Map. Initial Countywide FIS Effective Date: September 27, 1991 First Revised Countywide FIS Revision Date:, 20 i

3 TABLE OF CONTENTS 1.0 INTRODUCTION... 1 Page 1.1 Purpose of Study Authority and Acknowledgments Coordination AREA STUDIED Scope of Study Community Description Principal Flood Problems Flood Protection Measures ENGINEERING METHODS Hydrologic Analyses Hydraulic Analyses Vertical Datum FLOODPLAIN MANAGEMENT APPLICATIONS Floodplain Boundaries Floodways INSURANCE APPLICATIONS FLOOD INSURANCE RATE MAP OTHER STUDIES LOCATION OF DATA BIBLIOGRAPHY AND REFERENCES ii

4 TABLE OF CONTENTS (Cont d) FIGURES Figure 1 Floodway Schematic TABLES Table 1 Streams Studied by Detailed Methods... 4 Table 2 Streams Studied by Approximate Methods...5 Table 3 Stream Name Changes...6 Table 4 Summary of Discharges Table 5 Summary of Roughness Coefficients Table 6 Floodway Data Table 7 Community Map History EXHIBITS Exhibit 1 Flood Profiles Asher Ditch Panel 01P Butlers Ditch Panel 02P Christian Creek Panels 03P - 05P Christian Creek Lateral Panel 06P Gum Slough Panel 07P Higginbottom Creek Panels 08P - 10P Honey Cypress Ditch Panel 11P Lateral No. 3 Panels 12P - 13P Lateral No. 5 Panel 14P Little Bay Ditch Panels 15P - 17P Lost Creek Panels 18P - 20P Maple Slough Ditch Panel 21P Middle Drain Panel 22P Moore's Ditch Lateral Panel 23P Tributary to Maple Slough Ditch Panel 24P Turtle Creek Panels 25P - 26P Turtle Creek Lateral Panel 27P Viney Slough Panels 28P - 29P Whaley Slough Ditch Panel 30P Whiteman's Creek Panels 31P - 33P Exhibit 2 Flood Insurance Rate Map Index Flood Insurance Rate Maps Page iii

5 FLOOD INSURANCE STUDY CRAIGHEAD COUNTY AND INCORPORATED AREAS, ARKANSAS 1.0 INTRODUCTION 1.1 Purpose of Study This Flood Insurance Study (FIS) revises and updates information on the existence and severity of flood hazards in the geographic area of Craighead County, including the Cities of Bay, Bono, Caraway, Jonesboro and Monette; and the Towns of Black Oak, Brookland, Cash, Egypt, and Lake City; and the unincorporated areas of Craighead County (referred to collectively herein as Craighead County), and aids in the administration of the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of This study has developed flood-risk data for various areas of the community that will be used to establish actuarial flood insurance rates and to assist the community in its efforts to promote sound floodplain management. Minimum floodplain management requirements for participation in the National Flood Insurance Program (NFIP) are set forth in the Code of Federal Regulations at 44 CFR, Please note that the Town of Black Oak is non-floodprone. In some States or communities, floodplain management criteria or regulations may exist that are more restrictive or comprehensive than the minimum Federal requirements. In such cases, the more restrictive criteria take precedence, and the State (or other jurisdictional agency) will be able to explain them. 1.2 Authority and Acknowledgments The sources of authority for this FIS report are the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of This study was prepared to include incorporated areas within Craighead County in a countywide FIS. This information was previously published in separate FIS documents for these communities. Information on the authority and acknowledgments for each of the previously printed FIS documents and Flood Insurance Rate Maps (FIRMs), compiled from their effective FIS reports, is shown below. City of Bono: Town of Brookland: The hydrologic and hydraulic analyses for the study effective December 4, 1985 were prepared by the Arkansas Soil and Water Conservation Commission and the Soil Conservation Service (SCS) during the preparation of the Flood Plain Management Study for the City of Bono. This work was completed in December The hydrologic and hydraulic analyses for the FIS dated October 15, 1979 (FIRM dated April 15, 1980) were prepared by Carver & Carver, Inc., for FEMA, under Contract No This work was completed in July

6 City of Caraway: City of Jonesboro: The hydrologic and hydraulic analyses for the FIS dated December 1979 (FIRM dated June 18, 1980) were prepared by Carver & Carver, Inc., for FEMA, under Contract No This work was completed in July The hydrologic and hydraulic analyses for the FIS dated December 5, 1980 (FIRM dated June 15, 1981) were prepared by the U.S. Army Corps of Engineers (USACE) Memphis District for FEMA, under Inter Agency Agreement No. IAA Il 7 76, Project Order No. 19. This work was completed in July Authority and acknowledgements for the Cities of Bay and Monette and the Towns of Cash and Lake City are not available because no FIS reports were ever published for these communities. In the original countywide study, the hydrologic and hydraulic analyses of flooding sources within the unincorporated areas of Craighead County were prepared by the Memphis District of the USACE for the Federal Emergency Management Agency (FEMA), under Inter Agency Agreement No. EMW 87 E This work was completed in July The initial countywide study also incorporated an updated hydraulic analysis for Lateral No. 3, within the City of Jonesboro. This work, prepared by Miller Newell Engineering, Ltd., was completed in August In this revision of the Craighead County FIS, analysis of flooding sources within the corporate limits of the City of Jonesboro were prepared by the City of Jonesboro for FEMA under Inter Agency Agreement No. EMT-2004-CA-0123r (Reference 1). This work was completed in May The Comprehensive Flood Risk Resources and Response (CF3R) Joint Venture completed the updates for the remainder of the county under contract EMT CO Coordination The dates of the initial and final Consultation Coordination Officer s (CCO) meetings for the first countywide FIS for Craighead County and the incorporated areas within its boundaries are shown in the following tabulation. Community Name Initial CCO Date Final CCO Date City of Bono * January 17, 1985 Town of Brookland June 23, 1977 February 28, 1979 City of Caraway June 23, 1977 February 28, 1979 City of Jonesboro December 16, 1975 February 11, 1980 Craighead County January 8, 1987 September 26, 1990 Unincorporated Areas * Data not available Both the initial and final CCO meetings for the first countywide FIS were attended by representatives of FEMA, the communities, and the study contractors. The final CCO meeting for the unincorporated areas of Craighead County also served as the final CCO meeting for the initial countywide study and was open to representatives from all 2

7 2.0 AREA STUDIED communities within the county that were covered by the countywide study. All problems raised at that meeting were addressed in the study. The initial CCO meeting for this revision of the countywide FIS was held on September 24, 2004, and attended by representatives of FEMA, CF3R, Arkansas Geographic Information Office, Craighead County, City of Bay, City of Bono, Town of Brookland, City of Jonesboro, and Town of Lake City. The results of the study were reviewed at the final CCO meeting held on, and attended by representatives of. All problems raised at that meeting have been addressed in this study. 2.1 Scope of Study This FIS report covers the geographic area of Craighead County, Arkansas including the incorporated communities listed in Section 1.1. The areas studied by detailed methods were selected with priority given to all known flood hazards and areas of projected development or proposed construction through December 16, Table 1, Streams Studied by Detailed Methods, lists the limits of study for the streams studied by detailed methods. Under Inter-Agency Agreement No. EMT-2004-CA-0123r (Reference 1), the City of Jonesboro redelineated Butlers Ditch, Christian Creek, Christian Creek Lateral, Higginbottom Creek, Lateral No. 3, Lateral No. 5, a portion of Little Bay Ditch, Lost Creek, Moore s Ditch Lateral, Turtle Creek, Turtle Creek Lateral, a portion of Viney Slough, and a portion of Whiteman s Creek. The mapping extents for several of the re-delineated areas within the City of Jonesboro changed from the effective mapping extents. The differences can be attributed to three main factors; (1) new topographic data, (2) change in the vertical datum, and (3) channel centerline adjustments. Several mapping areas decreased in size while others increased slightly. There were a few instances on Christian Creek Lateral, Turtle Creek, and Lateral No. 5 where the channel centerlines were shifted to reflect their current locations. Turtle Creek and Lateral No. 5 shifted at the upper end of their reaches while Christian Creek Lateral was shifted along its entirety. All other changes to mapping extents were minor in comparison to the effective study information (Reference 1). The remaining streams in Craighead County were redelineated by CF3R, including Asher Ditch, Gum Slough, Honey Cypress Ditch, a portion of Little Bay Ditch, Maple Slough Ditch, Middle Drain, Tributary to Maple Slough Ditch, a portion of Viney Slough, Whaley Slough Ditch and a portion of Whiteman s Creek. 3

8 Stream Asher Ditch TABLE 1 STREAM STUDIED BY DETAILED METHODS Limits of Detailed Study From State Highway 158 to a point approximately 449 feet upstream of Missouri Street Butlers Ditch From its confluence with Little Bay Ditch to County Road 910 Christian Creek From its confluence with Lost Creek to Neely Road Christian Creek Lateral From its confluence with Christian Creek to Culberhouse Street Gum Slough From its confluence with Big Bay Ditch to County Road 673 Higginbottom Creek From its confluence with Viney Slough at Ingels Road to the downstream side of Parkview Street Honey Cypress Ditch From the St. Louis Southwestern Railway to a point approximately 475 feet upstream of State Highway 158 Lateral No. 3 From its confluence with Little Bay Ditch to the Union Pacific Railroad Lateral No. 5 From its confluence with Turtle Creek to a point approximately 158 feet upstream of the most upstream Burlington Northern Railroad crossing Little Bay Ditch From the county boundary to County Road 910 Lost Creek From a point approximately 0.22 mile downstream of U.S. Highway 63 to Peachtree Avenue Maple Slough Ditch From its confluence with Gum Slough to a point approximately 2 miles upstream of State Highway 18 Middle Drain From its confluence with Whaley Slough Ditch to a point approximately 2,750 feet upstream of Main Street Moore s Ditch Lateral From its confluence with Moore s Ditch to a point approximately 0.23 mile upstream of the Union Pacific Railroad Tributary to Maple Slough Ditch Turtle Creek Turtle Creek Lateral Viney Slough Whaley Slough Ditch Whiteman s Creek From a point approximately 53 feet downstream of Rural Road to a point approximately 0.4 mile upstream of Stevens Street From its confluence with Whiteman s Creek to the downstream site of U.S. Highway 49 at State Highway 1 From its confluence with Turtle Creek to Aggie Road From the county boundary to the confluence of Higginbottom Creek From a point approximately 1,300 feet downstream of State Highway 230 to the confluence of Middle Drain From its confluence with Little Bay Ditch to Caraway Road 4

9 The following flooding sources were studied by approximate methods (Table 2). TABLE 2 STREAM STUDIED BY APPROXIMATE METHODS Angle Ditch Emerson Ditch Lateral Ark Slough Ditch Gum Slough Asher Ditch Gum Slough Ditch Big Bay Ditch Gunner Slough Big Creek Honey Cypress Ditch Big Creek Lateral No. 1 Johnson Ditch Big Slough Ditch Lateral No. 3 Black Fork Creek Little Bay Ditch Bohanan Slough Ditch Little Slough Ditch Bridger Creek Lost Creek Cache River Maple Slough Ditch Cache River Tributary 25 Moore s Ditch Lateral. Cane Island Slough Ditch Mud Creek Caney Ditch Mud Slough Ditch Cockle Burr Slough Ditch Podo Creek Deep Slough Purcell Slough Ditch Ditch No. 1 Rogers Bayou Ditch No. 2 Saint Francis River Ditch No. 3 Thompson Creek Ditch No. 4 Tributary to Maple Slough Ditch Ditch No. 5 Tupelo Slough Ditch No. 7 Whaley Slough Ditch Ditch No. 8 Whistle Ditch Ditch No. 10 Whiteman s Creek Ditch No. 32 Willow Ditch East Cache River Approximate analyses were used to study those areas having a low development potential or minimal flood hazards. The scope and methods of study were proposed to, and agreed upon, by FEMA and Craighead County. Table 3, Stream Name Changes lists those streams whose name has changed or differs from that published in the previous FIS or published Flood Insurance Rate Maps (FIRMs) for Craighead County. 5

10 TABLE 3 - STREAM NAME CHANGES Community Old Name New Name Bay, City of Ditch No. 6 Ditch No. 3 Bay, City of Gum Slough Ditch Gum Slough Jonesboro, City of Big Creek Ditch Big Creek Jonesboro, City of Davis Branch Rogers Bayou Jonesboro, City of Viney Slough Ditch Viney Slough Lake City, Town of Purcell Slough Ditch No. 6 Purcell Slough Ditch Lake City, Town of Ditch No. 7 Ditch No. 9 Lake City, Town of Thompson Creek Ditch Thompson Creek Unincorporated areas of Johnson Ditch Lateral No. 3 Johnson Ditch Craighead County Unincorporated areas of Craighead County West Cache River Cache River Tributary Community Description Craighead County encompasses an area of 713 square miles in northeastern Arkansas. It is bordered by the unincorporated areas of Greene County to the north, the unincorporated areas of Lawrence County to the northwest, the unincorporated areas of Jackson County to the west, the unincorporated areas of Poinsett County the south, the unincorporated areas of Mississippi County to the east, and the unincorporated areas of Dunklin County, Missouri, to the northeast. Crowley's Ridge, extends from Greene County to the north and crosses the west central portion of Craighead County in a southerly direction. The lands on the ridge are gently rolling, and gradually slope down to bottom-lands on either side. The bottom-lands are rich delta land, used mainly for agricultural purposes. The portion of Craighead County lying east of Crowley's Ridge is drained by the St. Francis River and its numerous tributaries. Cache River enters from the north and flows in a southerly and southwesterly direction. Cache River and its tributaries drain all that territory lying west of Crowley's Ridge. The climate in the area of Craighead County is humid subtropical, with a mean annual temperature of 61 degrees Fahrenheit ( F). Temperature extremes range from 18 F to 116 F. The average annual precipitation is 48 inches (Reference 2). According to the U.S. Census Bureau 2000 census, Craighead County has a population of 82,148. The 2008 Census estimate shows the county increased in population to 92,640 people. The county has two county seats located in the City of Jonesboro and the Town of Lake City (Reference 3). The City of Jonesboro is the largest city in northeast Arkansas and is the fifth most populous city in the state. According to the 2008 U.S. Census Bureau estimates, Jonesboro s population is 63,960 with an area of 80 square miles. Over 75 percent of the county s residents live in Jonesboro. Nine smaller communities with populations ranging from 106 to 2,130 are located throughout the county (References 3 and 4). The Town of Lake City is located about 10 miles east of Jonesboro. Lake City, the second 6

11 county seat, is the second most populous city in Craighead County with a 2008 population estimate of 2,130 people and an aerial extent of 2.2 square miles (References 3 and 4). The City of Bay comprises 3.4 square miles located south east of Jonesboro. The U.S. Census Bureau estimates the 2008 population at 2,030 residents (References 3 and 4). The Town of Black Oak has a 2008 population estimate of 300 within a 0.4 square mile area. The Town is located approximately 15 miles east of Jonesboro (References 3 and 4). The City of Bono has a 2008 population estimate of 1,599 within 1.4 square miles in the north west portion of the County. Bono is located approximately 5 miles north west of Jonesboro (References 3 and 4). The Town of Brookland s 2008 estimated population was 1,670 people. The Town has an area of 1.4 square miles located approximately 5 miles north east of Jonesboro (References 3 and 4). The City of Caraway is located in south east Craighead County. The City s corporate boundary encompasses 2.3 square miles and extends to the Craighead-Mississippi County boundary. According to the U.S. Census Bureau, Caraway had an estimated 1,393 residents in 2008 (References 3 and 4). The Town of Cash is located about 10 miles west of Jonesboro. Cash s corporate limits extend 0.4 square miles. The 2008 population estimate is 318 (References 3 and 4). The Town of Egypt is located in the western portion of the County, approximately 15 miles west of Jonesboro. The Town has an aerial extent of 0.4 square miles and a population estimate of 106 (References 3 and 4). The City of Monette is located about 20 miles east of Jonesboro. The City has an area of 1.6 square miles and a 2008 population estimate of 1,229 (References 3 and 4). 2.3 Principal Flood Problems The majority of floods in the Craighead County occur in the winter and spring. The flooding is aggravated by roads and bridges in the floodplains that restrict flows and by urbanization of the watersheds. In the City of Bono, flooding is from manmade ditches that provide drainage from urban areas and upstream runoff from Crowley s Ridge. Flood problems in the City of Bono are aggravated by undersized road openings and excavated soil piled along North Drain. In March 1997, excessive rainfall combined with high water levels on the Mississippi River caused flooding in portions of eastern Arkansas including Craighead County. Flooding caused 18 bridges to be washed out in Poinsett County to the south of Craighead County. Approximately 100 homes were flooded in the area. Property damage of $1.8 million dollars was estimated for this flood event (Reference 5). 7

12 On October 5, 1998, flash flooding was reported in the eastern part of Craighead County where over 3 inches of rain fell in a short period of time. Streets were flooded in the Towns of Bay and Monette with two cars under water in Monette. The flash flooding forced people to use sandbags in Bay (Reference 5). On February 14, 2001, 4 inches of rain fell in a short period of time and caused flood waters to reach many houses in the City of Jonesboro where about 100 residents were forced to evacuate (Reference 5). On August 13, 2002, 20 homes and several businesses flooded in Jonesboro (Reference 5). A cold front moved into Arkansas during the afternoon and evening hours of September 26th, Showers and thunderstorms that developed ahead of the front dumped four to five inches of rain south of Brookland and produced flash flooding on Bridger Creek. The flood waters moved into the Windsor Landing and Sage Meadow Subdivisions in the Farrville area. At least twenty-five homes were flooded. Two of the home's garages exploded due to fumes from gasoline containers interacting with water heater pilot lights. A few automobiles were also flooded (Reference 5). Above normal rainfall across Northeast Arkansas brought the Black River to record-setting levels in March The record setting levels put pressure on many levees in the area causing a few breaks. Numerous roads were closed due to the flooding and many homes were inundated. Heavy rain caused flooding along the Cache River and Big Creek Ditch. The Windsor Landing Subdivision on U.S. Highway 49 at Farville was flooded as well as the Cottonwood Subdivision near Jonesboro. Many streets in the City of Jonesboro were flooded (Reference 5). A semi-tropical low pressure system that tracked across the Mid-South during the late afternoon and evening of May 24, 2009 produced heavy rainfall and flash flooding in the northern parts of Jonesboro. Several homes were flooded along Burke Avenue and North Patrick Street. Three fatalities were reported for this storm. A child was swept into a drainage ditch near Burke Avenue and Vine Street in Jonesboro. In the Greensboro area, a sport utility vehicle was pulling into a flooded driveway off County Road 785 and was swept 100 yards downstream, killing both passengers. At least 2 feet of water covered the bridge. A portion of the bridge was washed out (Reference 5). Four United States Geological Survey (USGS) stream flow gages are located in Craighead County. The gages are located on the St. Francis River (Gage ) in the Town of Lake City, on the Cache River (Gage ) in the Town of Egypt and on Lost Creek (Gage ) and Whiteman s Creek (Gage ) in the City of Jonesboro. The two gages located in the City of Jonesboro are operated by the USGS in cooperation with the City. These gages are real-time data sites that record gage height only. Data for these gages are available on-line for only the past 60 days (Reference 6). The gages located on St. Francis River and Cache River are operated by the USGS and record daily gage height and stream flow along with peak observations. Peak stream flows recorded for these gauging stations are listed below. The period of record for the gage on St. Francis River extends from 1931 to present. The period of record for the gage on Cache River extends from 1938 to present (Reference 6). 8

13 Peak Peak River Gage Date Gage Height(ft) Stream Flow (cfs) St. Francis April 2-3, ,700 Cache January 6, , Flood Protection Measures The Natural Resources Conservation Service (NRCS), formerly the Soil Conservation Service (SCS) has constructed three flood control reservoirs in the upper reaches of the Lost Creek watershed. The effects of these reservoirs were considered in the hydraulic analysis of Lost Creek (Reference 7). Several PL-566 flood retarding structures are located in the Big Creek watershed. Many of the older PL-566 dams are nearing the end of their 50 year life span and have significant rehabilitation needs. In fiscal year 2007, the NRCS developed rehabilitation plans for PL- 566 reservoir, Big Creek Site 6 in Craighead County (Reference 8). Several levees are located along the St. Francis River in the eastern portion of the county. The St. Francis West Levee, St. Francis East Levee and Thompson Creek Levee were constructed by the USACE and operated by the Bay and St. Francis Drainage District No. 29. The St. Francis River Left Bank Levee, Cockle Burr Slough Levee and the Right Hand Chute of the Little River Levee were constructed by the USACE and operated by the Buffalo Island Drainage District No. 9. FEMA specifies that all levees must meet and continue to meet, minimum design, operation, and maintenance standards consistent with the level of protection sought through the comprehensive flood plain management criteria established by 44CFR The St. Francis East and West Levees and the Thompson Creek Levee were certified by USACE and meet the requirement of 44CFR Although a Provisionally Accredited Levee agreement was signed on March 14, 2007 for the St. Francis River Left Bank Levee, Cockle Burr Slough Levee and the Right Hand Chute of the Little River Levee, FEMA did not receive the documentation necessary to demonstrate compliance with 44CFR65.10 within the 24-month period, so these levees are not shown as providing protection from the 1-percent-annual-chance flood. Several man-made channels have been constructed within the County to convey floodwaters including Big Slough Ditch, Ditch No. 2, and Main Ditch. In 2004, the NRCS initiated an improvement project for Segment No. 7 of the Main Ditch to provide flood prevention benefits. The project included four miles of channel improvement for Segment No. 7 of Main Ditch in the Poinsett watershed south of Jonesboro (Reference 9). In the City of Bono, two man made channels Whaley Slough Ditch and Middle Drain convey floodwaters through the area (Reference 7). In 1999, the Memphis District USACE initiated a channel maintenance project for Ditch No. 9 in the St. Francis River Basin (Reference 10). The Memphis District USACE also initiated channel improvements for several streams in Craighead County in The improvements consisted of 6.1 miles within the City of Jonesboro including channel enlargement of 2.95 miles of Higginbottom Creek, 0.72 miles of Moore s Ditch, 0.92 miles of Turtle Creek and 9

14 1.5 miles of Whiteman s Creek (Reference 11). Most of the flood protection measures on the remaining streams in the county are limited to cleaning and excavating the channels to promote drainage through the study area. 3.0 ENGINEERING METHODS For the flooding sources studied by detailed methods in the communities, standard hydrologic and hydraulic study methods were used to determine the flood-hazard data required for this study. Flood events of a magnitude that is expected to be equaled or exceeded once on the average during any 10, 50, 100, or 500 year period (recurrence interval) have been selected as having special significance for floodplain management and for flood insurance rates. These events, commonly termed the 10, 50, 100, and 500 year floods, have a 10, 2, 1, and 0.2 percent chance, respectively, of being equaled 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 same year. The risk of experiencing a rare flood increases when periods greater than 1 year are considered. For example, the risk of having a flood that equals or exceeds the 1-percent-annual-chance flood in any 50 year period is approximately 40 percent (4 in 10); for any 90 year period, the risk increases to approximately 60 percent (6 in 10). The analyses reported herein 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 peak discharge-frequency relationships for each flooding source studied by detailed methods affecting the communities. Peak discharge frequency relationships for Little Bay Ditch, Viney Slough, and Whiteman s Creek (from its confluence with Little Bay Ditch to a point approximately 0.5 mile upstream of the Union Pacific Railroad), were determined using USACE HEC 1 hydrographs (Reference 12). Peak discharges for Butlers Ditch were based on the HEC 1 analysis of Little Bay Ditch, because Butlers Ditch is a sub basin area of Little Bay Ditch. Peak discharges for Gum Slough and Maple Slough Ditch were determined from drainage area discharge relationships. Information on the methods used to determine peak discharge frequency relationships for the streams studied by detailed methods is shown below. The incorporated communities are listed in alphabetical order; methodologies are described for each community. For streams that flow through two or more communities, each methodology described applies only to that portion of the stream studied by detailed methods within that particular community. The original FIS for the City of Bono considered Whaley Slough Ditch and Middle Drain (Reference 13). In that study, peak discharges were determined using the SCS Technical Release 20 computer program (Reference 14). Variables included factors such as soil moisture condition, watershed land use, precipitation amount and time distribution, and channel characteristics that influence water flow. 10

15 The original FIS for the Town of Brookland considered Tributary to Maple Slough Ditch (Reference 15). In that study, synthetic storms were computed to define the discharge frequency data. Rainfall distribution for the 10, 2, and 1 percent-annual-chance frequencies were computed from rainfall frequency data contained in the National Weather Service Technical Paper No. 40 (Reference 16). Unit hydrographs were computed for the stream using Snyder s coefficients. The hydrographs and rainfall distributions were used to compute synthetic storms of the desired frequencies from which the peak discharges were obtained. A log probability relationship of the lower frequency peak discharges was used to compute each of the 0.2-percent-annual-chance peak discharges. The original FIS for the City of Caraway considered Honey Cypress Ditch and Asher Ditch (Reference 17). In that study, synthetic storms were computed to define the discharge frequency data. Rainfall distribution for the 10, 2, and 1-percent-annual-chance frequencies were computed from rainfall frequency data contained in the National Weather Service Technical Paper No. 40 (Reference 16). Unit hydrographs were computed for the stream using Snyder s coefficients. The hydrographs and rainfall distributions were used to compute synthetic storms of the desired frequencies from which the peak discharges were obtained. A log probability relationship of the lower frequency peak discharges was used to compute each of the 0.2-percent-annual-chance peak discharge. The original FIS for the City of Jonesboro considered the following streams: Christian Creek, Christian Creek Lateral, Lateral No. 3, Lost Creek, Moore s Ditch Lateral, Higginbottom Creek, Whiteman s Creek (from a point approximately 1.2 miles downstream of U.S. Highway 63 to the downstream side of Highland Drive), Turtle Creek, Turtle Creek Lateral, and Lateral No. 5 (Reference 18). In that study, because there are no stream flow records for these streams, peak discharges were obtained by applying various rainfall duration amounts to unit hydrographs developed along the streams. Rainfall frequency values were determined from Technical Paper No. 40 (Reference 16). Unit hydrographs were developed using Snyder s method with coefficients taken from regional curves developed by the Memphis District USACE from previous studies of basins with similar characteristics. Storage routing models were developed for all streams using standard procedures. A summary of the drainage area peak discharge relationships for the streams studied by detailed methods is shown in Table 4, Summary of Discharges. 11

16 TABLE 4 SUMMARY OF DISCHARGES DRAINAGE AREA (sq. miles) 10% Annual Chance PEAK DISCHARGES (cfs) 2% 1% Annual Annual Chance Chance 0.2% Annual Chance FLOODING SOURCE AND LOCATION Asher Ditch At State Highway ,148 1,270 1,580 Butlers Ditch At confluence with Little Bay Ditch 6.00 * * 1,016 * Christian Creek At County Road ,485 4,385 4,790 5,725 At Matthew's Avenue ,170 4,120 4,540 5,490 At West Nettleton Avenue ,465 3,375 3,750 4,580 At Woodsprings Road ,100 1,335 1,455 1,735 At U.S. Route 63 Bypass ,100 1,360 1,470 1,720 Christian Creek Lateral At confluence with Christian Creek Gum Slough At confluence with Big Bay Ditch * * 8,100 * Higginbottom Creek At Caraway Road ,400 4,615 5,210 6,600 At State Highway 1 Bypass ,835 3,910 4,375 5,655 At Stroud Street ,725 2,410 2,710 3,370 At Parkview Street ,085 1,360 Honey Cypress Ditch Approximately 0.2 mile above the mouth ,230 Lateral No. 3 At confluence with Moore's Ditch ,155 1,580 1,890 2,555 At Burlington Northern Railroad Lateral No. 5 ** At Burlington Northern Railroad ,145 1,675 1,905 2,395 At mile ,555 2,180 2,455 3,070 Little Bay Ditch At mouth * * 10,025 * Lost Creek Approximately 1,125 feet downstream of U.S. Highway ,360 9,560 10,515 12,765 At Burlington Northern Railroad ,310 5,790 6,450 7,995 At Culberhouse Street ,250 5,715 6,330 7,650 At cross section L ,140 4,050 4,445 5,435 At Peachtree Avenue (cross section M) ,220 3,105 3,500 4,375 Maple Slough Ditch At confluence with Gum Slough Ditch * * 6,375 * * Data not computed **Discharges decrease downstream in some cases because of valley storage effects 12

17 TABLE 4 SUMMARY OF DISCHARGES (continued) DRAINAGE AREA (sq. miles) 10% Annual Chance PEAK DISCHARGES (cfs) 2% 1% Annual Annual Chance Chance 0.2% Annual Chance FLOODING SOURCE AND LOCATION Middle Drain At Burlington Northern Railroad * 1,026 * Moore's Ditch Lateral At North Kathleen Street ,025 1,125 1,340 Tributary to Maple Slough Ditch At St. Louis Southwestern Railway Bridge ,060 2,650 2,930 3,530 At Stevens Street ,000 2,590 2,870 3,440 Turtle Creek ** At Union Pacific Railroad ,475 4,050 4,270 5,120 At Nettleton Avenue ,328 4,080 4,360 5,295 At confluence of Lateral No ,015 3,930 4,350 5,360 At confluence of Turtle Creek Lateral ,540 3,315 3,670 4,505 At State Highway ,025 1,155 1,445 Turtle Creek Lateral At Aggie Road Viney Slough Upstream of County Road * * 4,080 * Whaley Slough Ditch Approximately 1,300 feet downstream of State Highway ,265 * 1,888 * Whiteman's Creek At confluence with Little Bay Ditch * * 5,001 * At County Road 604 (mile 2.42) ,685 4,845 5,360 6,600 At Ingels Road (mile 3.5) ,680 4,675 5,120 6,330 At Highway 63 Bypass ,450 4,370 4,800 5,955 At confluence of Turtle Creek ,280 4,370 4,865 5,900 At Mo-Pac Railroad ,045 1,150 1,365 At Highway No. 1 Bypass ,155 1,295 1,590 At Highland Drive * Data not computed **Discharges decrease downstream in some cases because of valley storage effects 13

18 3.2 Hydraulic Analyses Analyses of the hydraulic characteristics of flooding from the sources studied were carried out to provide estimates of the elevations of floods of the selected recurrence intervals. Users should be aware that flood elevations shown on the FIRM represent rounded whole-foot elevations and may not exactly reflect the elevations shown on the Flood Profiles or in the Floodway Data tables in the FIS report. Flood elevations shown on the FIRM are primarily intended for flood insurance rating purposes. For construction and/or floodplain management purposes, users are cautioned to use the flood elevation data presented in this FIS in conjunction with the data shown on the FIRM. Cross section data for the streams studied by detailed methods were obtained by field inspection. All bridges and culverts were field surveyed to obtain elevation data and structural geometry. Cross sections were located at close intervals above and below bridges and culverts in order to compute the significant backwater effects of these structures. Locations of selected cross sections used in the hydraulic analyses are shown on the Flood Profiles (Exhibit 1). For stream segments for which a floodway was computed (Section 4.2), selected cross-section locations are also shown on the FIRM (Exhibit 2). The hydraulic analyses for the FIS studies were based on unobstructed flow. The flood elevations shown on the Flood Profiles (Exhibit 1) are thus considered valid only if hydraulic structures remain unobstructed, operate properly, and do not fail. Water surface elevations for floods of the selected recurrence intervals on Little Bay Ditch, Whiteman s Creek, Gum Slough, Maple Slough Ditch, and Viney Slough were determined using the USACE HEC 2 step backwater computer program (Reference 19). Information on the methods used to determine the water surface elevations for floods of the selected recurrence intervals on the streams studied by detailed methods within the incorporated areas of the county, compiled from the previously printed narratives for those communities, is shown below. The listing of streams considered in each FIS includes only those streams or portions of streams whose hydraulic analyses were taken from that particular study. The original FIS for the City of Bono considered Whaley Slough Ditch and Middle Drain (Reference 13). In that study, water surface elevations were computed using the SCS WSP 2 computer program (Reference 20). Starting water surface elevations were taken at critical depth. The original FIS for the Town of Brookland considered Tributary to Maple Slough Ditch (Reference 15). In that study, water surface elevations were computed using the USACE HEC 2 step backwater computer program (Reference 19). Starting water surface elevations were determined using the conveyance water surface elevation curves constructed for the downstream sections of the streams. The original FIS for the City of Caraway considered Honey Cypress Ditch and Asher Ditch (Reference 17). In that study, water surface elevations were computed using the USACE HEC 2 step backwater computer program (Reference 19). Starting water surface elevations 14

19 were determined using the conveyance water surface elevation curves constructed for the downstream sections of the streams. The original FIS for the City of Jonesboro considered the following streams: Christian Creek, Christian Creek Lateral, Higginbottom Creek, Lateral No. 3, Lateral No. 5, Lost Creek, Moore s Ditch Lateral, Turtle Creek, Turtle Creek Lateral and Whiteman s Creek (Reference 18). In that study, water surface elevations were computed using the USACE HEC 2 step backwater computer program (Reference 19). Starting water surface elevations were obtained by the slope/area method and from previous studies performed by the USACE. Letter of Map Revisions (LOMRs) that affect the studied stream reaches were evaluated and incorporated, as necessary. Flood profiles were drawn showing computed water surface elevations for floods of the selected recurrence intervals. Channel roughness factors (Manning s n ) used in the hydraulic computations were assigned on the basis of field inspections. Table 5, Summary of Roughness Coefficients, shows the ranges of channel and overbank n values for the streams studied by detailed methods. TABLE 5 SUMMARY OF ROUGHNESS COEFFICIENTS Stream Channel n Overbank "n" Asher Ditch Butler's Ditch Christian Creek Christian Creek Lateral Gum Slough Higginbottom Creek Honey Cypress Ditch Lateral No Lateral No Little Bay Ditch Lost Creek Maple Slough Ditch Middle Drain Moore's Ditch Lateral Tributary to Maple Slough Ditch Turtle Creek Turtle Creek Lateral Viney Slough Whaley Slough Ditch Whiteman's Creek Data not available Average value 15

20 3.3 Vertical Datum All FIS reports and FIRMs are referenced to a specific vertical datum. The vertical datum provides a starting point against which flood, ground, and structure elevations can be referenced and compared. Until recently, the standard vertical datum used for newly created or revised FIS reports and FIRMs was the National Geodetic Vertical Datum of 1929 (NGVD). With the completion of the North American Vertical Datum of 1988 (NAVD), many FIS reports and FIRMs are now prepared using NAVD as the referenced vertical datum. Flood elevations shown in this FIS report and on the FIRM are referenced to the NAVD. These flood elevations must be compared to structure and ground elevations referenced to the same vertical datum. Some of the data used in this revision were taken from the prior effective FIS reports and FIRMs and adjusted to NAVD88. The datum conversion factor from NGVD29 to NAVD88 in Craighead County is feet. For additional information regarding conversion between the NGVD and NAVD, visit the National Geodetic Survey website at or contact the National Geodetic Survey at the following address: Vertical Network Branch, N/CG13 National Geodetic Survey, NOAA Silver Spring Metro Center East-West Highway Silver Spring, Maryland (301) Temporary vertical monuments are often established during the preparation of a flood hazard analysis for the purpose of establishing local vertical control. Although these monuments are not shown on the FIRM, they may be found in the Technical Support Data Notebook associated with the FIS report and FIRM for this community. Interested individuals may contact FEMA to access these data. To obtain current elevation, description, and/or location information for benchmarks shown on this map, please contact the Information Services Branch of the NGS at (301) , or visit their website at FLOODPLAIN MANAGEMENT APPLICATIONS The NFIP encourages State and local governments to adopt sound floodplain management programs. To assist in this endeavor, each FIS report provides 1-percent-annual-chance floodplain data, which may include a combination of the following: 10-, 2-, 1-, and 0.2-percent-annual-chance flood elevations; delineations of the 1- and 0.2-percent-annual-chance floodplains; and a 1-percent-annual-chance floodway. This information is presented on the FIRM and in many components of the FIS report, including Flood Profiles and Floodway Data tables. Users should reference the data presented in the FIS report as well as additional information that may be available at the local community map repository before making flood elevation and/or floodplain boundary determinations. 16

21 4.1 Floodplain Boundaries To provide a national standard without regional discrimination, the 1-percent-annual-chance flood has been adopted by FEMA as the base flood for floodplain management purposes. The 0.2-percent-annual-chance flood is employed to indicate additional areas of flood risk in the county. Within the City of Jonesboro, the 1- and 2- percent annual chance flood hazard boundaries were digitally mapped using the flooding sources listed in the 1991 FIS for Craighead County within the City of Jonesboro using water surface elevations, lettered cross-sections, and floodway information included in the effective study data, including LOMRs. This data was geo-referenced, the datum shifted from NGVD 29 to NAVD 88, and the Base Flood Elevations (BFEs) re-delineated using 2005 LlDAR 2-foot contours (Reference 1). All floodway data was reproduced from the existing 1991 FIS and adjusted slightly for smoothing purposes. The effective delineations were used at any location where the new redelineation boundaries extended beyond the effective delineations. In areas where the floodplains fell within the effective boundaries, the redelineated boundaries were used. Zone A hazard areas were reproduced from the effective data and adjusted to fit revised channel locations and new topographic information (Reference 1). For detail study streams outside of Jonesboro, the 1- and 0.2-percent-annual-chance floodplain boundaries have been redelineated using the flood elevations determined at each cross section. Between cross sections, the boundaries were interpolated using topographic maps at a scale of 1:24,000 with a contour interval of 5 feet (Reference 21). The 1-and 0.2-percent-annual-chance floodplain boundaries are shown on the Flood Insurance Rate Map (Exhibit 2). On this map, the 1 percent-annual-chance floodplain boundary corresponds to the boundary of the areas of special flood hazards (Zones A and AE), and the 0.2-percent-annual-chance floodplain boundary corresponds to the boundary of areas of moderate flood hazards. In cases where the 1-and 0.2-percent-annual-chance floodplain boundaries are close together, only the 1 percent-annual-chance floodplain boundary has been shown. Small areas within the floodplain boundaries may lie above the flood elevations but cannot be shown due to limitations of the map scale and/or lack of detailed topographic data. For the streams studied by approximate methods, the 1 percent-annual-chance floodplains were delineated using the Flood Hazard Boundary Map for the unincorporated areas of Craighead County (References 7 and 22). 4.2 Floodways Encroachment on floodplains, such as structures and fill, reduces flood-carrying capacity, increases flood heights and velocities, and increases flood hazards in areas beyond the encroachment itself. One aspect of floodplain management involves balancing the economic gain from floodplain development against the resulting increase in flood hazard. For purposes of the NFIP, a floodway is used as a tool to assist local communities in this aspect of floodplain management. Under this concept, the area of the 1-percent-annual-chance floodplain is divided into a floodway and a floodway fringe. The floodway is the channel of a stream, plus any adjacent floodplain areas, that must be kept free of encroachment so that 17

22 the base flood can be carried without substantial increases in flood heights. Minimum Federal standards limit such increases to 1 foot, provided that hazardous velocities are not produced. The floodways in this study are presented to local agencies as minimum standards that can be adopted directly or that can be used as a basis for additional floodway studies. The floodways presented in this study for Christian Creek, Christian Creek Lateral, Lateral No. 3, Lateral No. 5, Lost Creek, Moore s Ditch Lateral, Higginbottom Creek, Turtle Creek, Turtle Creek Lateral, and Whiteman s Creek were taken from the FIS for the City of Jonesboro (Reference 18). The floodway for Tributary to Maple Slough Ditch was taken from the FIS for the Town of Brookland (Reference 15). The floodways presented in this study were computed for certain stream segments on the basis of equal-conveyance reduction from each side of the floodplain. Floodway widths were computed at cross sections. Between cross sections, the floodway boundaries were interpolated. The results of the floodway computations are tabulated for selected cross sections (see Table 6, Floodway Data). In cases where the floodway and 1-percent-annual-chance floodplain boundaries are either close together or collinear, only the floodway boundary is shown. The area between the floodway and 1-percent-annual-chance floodplain boundaries is termed the floodway fringe. The floodway fringe encompasses the portion of the floodplain that could be completely obstructed without increasing the water-surface elevation (WSEL) of the base flood more than 1 foot at any point. Typical relationships between the floodway and the floodway fringe and their significance to floodplain development are shown in Figure 1. Figure 1 - Floodway Schematic 18

23 Near the mouths of streams studied in detail, floodway computations are made without regard to flood elevations on the receiving water body. Therefore, Without Floodway elevations presented in Table 6 for certain downstream cross sections of Christian Creek Lateral, Turtle Creek Lateral, Lateral No. 3, and Lateral No. 5 are lower than the regulatory flood elevations in that area, which must take into account the 1 percent-annual-chance flooding due to backwater from other sources. Because of the scope of this study, floodways were not calculated for Asher Ditch, Gum Slough, Honey Cypress Ditch, Little Bay Ditch, Maple Slough Ditch, Middle Drain, Viney Slough, and Whaley Slough Ditch. Although floodways were not calculated for the streams within the City of Caraway, sufficient right of way should be provided for maintenance of the channels. 5.0 INSURANCE APPLICATION For flood insurance rating purposes, flood insurance zone designations are assigned to a community based on the results of the engineering analyses. These zones are as follows: Zone A Zone A is the flood insurance rate zone that corresponds to the 1-percent-annual-chance floodplains that are determined in the FIS report by approximate methods. Because detailed hydraulic analyses are not performed for such areas, no base (1-percent-annual-chance) flood elevations (BFEs) or depths are shown within this zone. Zone AE Zone AE is the flood insurance rate zone that corresponds to the 1-percent-annual-chance floodplains that are determined in the FIS report by detailed methods. Whole-foot BFEs derived from the detailed hydraulic analyses are shown at selected intervals within this zone. Zone X Zone X is the flood insurance rate zone that corresponds to areas outside the 0.2-percent-annual-chance floodplain, areas within the 0.2-percent-annual-chance floodplain, areas of 1-percent-annual-chance flooding where average depths are less than 1 foot, areas of 1-percent-annual-chance flooding where the contributing drainage area is less than 1 square mile (sq. mi.), and areas protected from the base flood by levees. No BFEs or depths are shown within this zone. 19