GREENE COUNTY, ARKANSAS AND INCORPORATED AREAS

Transcription

1 GREENE COUNTY, ARKANSAS AND INCORPORATED AREAS Greene County Community Name Community Number DELAPLAINE, TOWN OF* GREENE COUNTY, UNINCORPORATED AREAS LAFE, TOWN OF MARMADUKE, CITY OF OAK GROVE HEIGHTS, CITY OF PARAGOULD, CITY OF SEDGWICK, TOWN OF *No Special Flood Hazard Areas Identified PRELIMINARY SEPTEMBER 22, 2011 EFFECTIVE DATE: Federal Emergency Management Agency FLOOD INSURANCE STUDY NUMBER 05055CV000B

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: June 16, 2009 First Revised FIS Revision Date: Map revised Month ##, #### to include the integration of the USACE, Memphis District Study of Eight Mile Creek and a New Limited Detailed Study of Loggy Creek Tributary 1.

3 TABLE OF CONTENTS Page 1.0 INTRODUCTION 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 i

4 TABLE OF CONTENTS (Cont'd) FIGURES Figure 1-Floodway Schematic TABLES Table 1 - Streams Studied by Detailed Methods: Detail... 4 Table 2 - Streams Studied by Detailed Methods: Limited Detail... 4 Table 3 - Streams Studied by Approximate Methods Table 4 - Summary of Discharges Table 5 Floodplain Roughness Coefficients Table 6 - Floodway Data Table 7 -Community Map History EXHIBITS Exhibit 1 Flood Profiles Eight Mile Creek Panel 01P Loggy Creek Panel 03P Loggy Creek Tributary 1 Panel 04P Reynolds Creek Panel 05P Tributary No. 1 Panel 06P Tributary No. 2 Panel 07P Tributary No. 3 Panel 08P ii

5 Exhibit 2- Flood Insurance Rate Map Index (published separately) Flood Insurance Rate Map (published separately) iii

6 1.0 INTRODUCTION FLOOD INSURANCE STUDY GREENE COUNTY, ARKANSAS AND INCORPORATED AREAS 1.1 Purpose of Study This Flood Insurance Study (FIS) revises and updates the current effective FIS from June 16, 2009 in the geographic area of Greene County, including the Cities of Marmaduke, Oak Grove Heights, and Paragould; the Towns of Delaplaine, Lafe, and Sedgwick; and the unincorporated areas of Greene County (referred to collectively herein as Greene County), which 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 Sedgwick is geographically located in Greene, and Lawrence Counties. Please note that the Town of Delaplaine 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 The hydrologic and hydraulic analyses for the original City of Paragould FIS were performed by the U.S. Army Corps of Engineers (USACE), Memphis District, for the Federal Emergency Management Agency (FEMA), under Inter-Agency Agreement No. IAA-H , Project Order No. 15, and Inter-Agency Agreement No. IAA -H -7-76, Project. Order No. 15. That work was completed in January For the May 4, 1992 revision of the City of Paragould FIS Report, updated hydrologic and hydraulic analyses for Eight Mile Creek, Tributary No.1, Tributary No.2, and Tributary No.3 were prepared by FTN Associates, Ltd., for FEMA, under Contract No. EMW-89-C This work was completed in March For the June 16, 2009 revision, a countywide FIS was compiled from all previous 1

7 studies and was prepared by CF3R JV under Contract No. EMT2002-CO-0049, Task Order No This work was completed in August This current revision of the FIS incorporated updated hydrologic and hydraulic analysis for Eight Mile Creek (as performed by the USACE Memphis District), and Loggy Creek Tributary 1. This work was performed by RAMPP under FEMA IDIQ Contract HSFEHQ-09-D-0369, Task Order HSFE06-09-J-0001, and completed in September Base map information shown on this Flood Insurance Rate Map (FIRM) was derived from multiple sources. Base map information for Greene County and all incorporated communities within Greene County was provided in digital format by the Arkansas Highway Transportation Department, United States Geological Survey, National Geodetic Survey, United States Census Bureau 2000 TIGER/Line Files and the Federal Emergency Management Agency. The digital FIRMs were produced in Arkansas State Plane North FIPS 0301 Feet coordinates referenced to the North American Datum of 1983 and the GRS 1980 spheroid. Differences in the datum and spheroid used in the production of the FIRMs for adjacent counties may result in slight positional differences in map features at the county boundaries. These differences do not affect the accuracy of information shown on the FIRM. 1.3 Coordination The initial Consultation Coordination Officer (CCO) meeting for the original City of Paragould FIS was held in October The results of the study were reviewed at the final CCO meeting held on March 16, Both meetings were attended by representatives of FEMA, the USACE, and the City of Paragould. All problems raised at that meeting were addressed in that study. For the May 1992 revision of the City of Paragould FIS, an initial CCO meeting was held on June 8, 1988 and was attended by representatives of FTN Associates, Ltd., the City of Paragould, and FEMA. A formal CCO meeting was not held. The May 1992 revision incorporated information from several sources. The following sources were contacted for information and/or coordination of results: the City of Paragould, the Natural Resources Conservation Service (formerly Soil Conservation Service), the USACE, and the U.S. Geological Survey (USGS). For the June 2009 Revision, the initial CCO meeting for this revision of the countywide FIS was held on December 4, 2007, and attended by representatives of FEMA and the local communities. All problems raised at that meeting have been addressed in this study. A final CCO meeting was not held. The initial CCO meeting for this revision of the countywide FIS was held on October 30, 2009 at 8:30 AM at the County Courthouse in Paragould, AR. The meeting was attended by local officials, as well as representatives from the US Army Corps of Engineers, FEMA Region VI, and RAMPP. A Kickoff Meeting 2

8 was held on April 21, AREA STUDIED 2.1 Scope of Study This FIS report covers the geographic area of Greene County, Arkansas including the incorporated communities listed in Section 1.1. This new Physical Map Revision (PMR) includes the integration of the USACE, Memphis District Study of Eight Mile Creek and a New Limited Detailed Study of Loggy Creek Tributary1. The non-revised areas on panels affected by the PMR were maintained as depicted on the previous effective FIRM panels dated June 16, In the original and the May 1992 revision City of Paragould FIS (Reference 1 and 2), Eight Mile Creek, Loggy Creek, Reynolds Creek, Tributary No.1, Tributary No. 2 and Tributary No. 3 were studied by detailed methods. In addition, depths and floodplain boundaries for areas of shallow flooding (Zone AO) were revised along Eight Mile Creek. These areas were located southeast of St. Louis Southwestern Railway. Limits of detailed study are indicated on the Flood Profiles (Exhibit 1) and on Exhibit 2, Flood Insurance Rate Map (FIRM). The areas studied by detailed methods were selected with priority given to all known flood hazards and areas of projected development or proposed construction. The following streams were studied by detailed methods in this FIS. 3

9 Table 1. Streams Studied by Detailed Methods Stream Study Type Study Area Eight Mile Creek Loggy Creek Reynolds Creek Tributary No. 1 Tributary No. 2 Tributary No. 3 Detailed Detailed Detailed Detailed Detailed Detailed From approximately 6,300 feet downstream of U.S. Highway 412 to a point approximately 400 feet upstream of Spring Grove Road. From its confluence with Eight Mile Creek to a point approximately 5,800 feet upstream of Reynolds Road. From its confluence with Loggy Creek to Reynolds Park Road. From its confluence with Eight Mile Creek to Honeysuckle Road. From its confluence with Eight Mile Creek to a point approximately 30 feet upstream of Maxwell Street. From its confluence with Eight Mile Creek to a point approximately 1.2 miles upstream of Bogil Road. Table 2. Streams Studied by Limited Detailed Methods Stream Study Type Study Area Loggy Creek Tributary 1 Limited Detailed From its confluence with Loggy Creek to 1.2 miles upstream of that confluence. Approximate analyses were used to study those areas having a low development potential or minimal flood hazards. All or portions of the streams listed in Table 3 were studied by approximate methods. For streams within the City of Paragould, the scope and methods of study were proposed to, and agreed upon by FEMA and the City of Paragould. 4

10 Table 3. Streams Studied by Approximate Methods Arkansas Ditch Henderson Creek Loggy Creek Beaver Dam Ditch Hurricane Creek Main Canal Beech Grove Lateral Hurricane Ditch Main Lateral Big Creek Hurricane/Henderson Ditch Mayo Ditch Big Creek North Jacks Creek Mill Creek Big Creek Site 1 Reservoir Johnson Creek Mud Creek Big Creek Site 3 Reservoir Johnson Creek Ditch Mud Slough Ditch Big Creek Site 15 Reservoir Jordan Creek Negro Head Slough Big Gum Lateral Jordan Creek Ditch Old Sugar Creek Big Slough Lake Ditch Petersburg Ditch Big Slough Ditch Lake Frierson Pigeon Roost Creek Bohanan Slough Ditch Lateral No. 1 Poplar Creek Buffalo Head Slough Lateral No. 2 Poplar Creek Ditch Cache River Lateral No. 3 Post Oak Ditch Caney Slough Lateral No. 5 Reynolds Creek Caney Slough Tributary Lateral No. 6 Reynolds Lake Conley Ditch Lateral No. 6B Saint Francis River Cottonwood Slough Lateral No. 9 Scatter Creek Culver Creek Lateral No. 12 Slavens Creek Ditch No.1 Lateral No. 13 Sugar Creek Main Eight Mile Creek Lateral No. 14 Swagger Slough Eight Mile Ditch Lateral No. 15 Swan Pond Ditch Fox Creek Lateral No. 16 Swan Pond Lateral Gate Ditch Lick Creek Tributary No. 3 Grassy Slough Locust Creek Village Creek Gum Slough Ditch Locust Creek Ditch Village Creek Ditch 2.2 Community Description Greene County encompasses an area of 579 square miles in northeastern Arkansas. It is bordered by the unincorporated areas of Clay County to the north, the unincorporated areas of Randolph County to the northwest, the unincorporated areas of Dunklin County, Missouri to the east, the unincorporated areas of Lawrence County to the southwest, and the unincorporated areas of Craighead County to the south. Greene County was formed on November 5, 1833 out of portions of Lawrence County. The county has rich, flat delta farmland in the eastern and western portions and rolling hills in the center that includes Crowley's Ridge. Crowley's Ridge rises above the flat delta and is comprised of ocean-bottom sand, gravel, 5

11 and clay. According to the 2007 Agriculture Statistics for Arkansas (Reference 3), about 267,000 acres, or 72 percent of the county, is in farms. The average size of a farm is 347 acres. The rest is woodland, cities and towns, federally-owned land, and transportation and utility facilities. The drainage in Greene County is generally south through a system of natural and improved drainage ways and connecting artificial channels (Reference 4). The eastern portion of the county is drained by Eight Mile Creek, Village Creek, Johnson Creek, Locust Creek, Slavens Creek, Hurricane Creek, Big Slough Ditch, Mayo Ditch, and the St. Francis River Floodway. The western part of the county is drained by Big Creek, Poplar Creek, Main Lateral, Sugar Creek, Swan Pond Ditch, Beach Grove Lateral, Beaver Dam Ditch, Post Oak Ditch, Cache River Main Ditch, Cache River Ditch No.1, and the Black River. Elevations in the county range from about 550 feet on Crowley's Ridge to about 250 feet above sea level where the Cache River leaves the county. The climate in the area of Greene County is characterized by hot, humid summers and cool, wet winters. According to the National Climatic Data Center's records from 1971 through 2000 (Reference 5), the mean annual temperature in the area is 60 degrees Fahrenheit (OF), with monthly averages ranging from 37 OF in January to 81 F in July. Precipitation averages about 48 inches per year, with monthly averages ranging from 3.2 inches in August to 4.9 inches in March. According to the U.S. Census Bureau 2009 census (Reference 6), Greene County has a population of 40,996. The City of Paragould, with a population of 25,027 in 2009, is the county seat and the largest community in Greene County. Other communities include the Cities of Marmaduke and Oak Grove Heights, and the Towns of Delaplaine, Lafe, and Sedgwick. Town of Delaplaine The Town of Delaplaine is located approximately 15 miles northwest of Paragould. Based on 2009 census data, the town encompasses a land area of 1.1 square miles and has a population of 130 (Reference 6). The town is drained by Post Oak Ditch and Lateral No.1 which flow into the Cache River. Delaplaine is considered non-flood prone since no floodplains are located within its corporate limits. Soils consist of Jacksonport silty clay loam with 1 to 2 percent slopes (Reference 4). Town of Lafe The Town of Lafe is an incorporated town that is located approximately 12 miles north of Paragould. According to the 2009 census, Lafe encompasses a 2.1 square mile area and has a population of 401 (Reference 6). The Town of Lafe is drained by Big Creek and its tributaries. Stream flow is generally from north to south along the tributaries and from east to west along Big Creek. The soils outside the 6

12 floodplains are primarily Loring silty loam. The soils within the floodplains consist of Falaya silty loam (Reference 4). City of Marmaduke The City of Marmaduke is located approximately 12 miles northeast of Paragould U.S. Census Bureau data indicate that Marmaduke has a land area of 1.3 square miles and a population of 1,175 (Reference 6). The city drains to Slavens Creek and an unnamed tributary of Hurricane Ditch. Soils consist primarily of Loring and Calhoun silt loarns. Soils within the floodplains consist of Oaklimeter silt loam (Reference 4). City of Oak Grove Heights The City of Oak Grove Heights is located approximately 5 miles north of Paragould. In 2009, the city had a land area of 3 square miles and a population of 406 (Reference 6). Stream flow in the community is from northwest to southeast along Locust and Jacks Creeks and their tributaries. The soils outside the floodplain consist of HilIemann-Lafe complex (0 to 3 percent slopes) and Loring silt loam (1 to 15 percent slope). Soils within the floodplain consist of Falaya silt loam, 0 to 1 percent slopes (Reference 4). City of Paragould The City of Paragould is located in central Greene County and is completely surrounded by unincorporated areas of the county. The City of Paragould experienced a 44 percent increase in population from 15,248 in 1985 to 22,017 in 2000 and a +13.7% increase in population to 25,027 since 2000 (Reference 6). This growth has brought about residential and commercial development within the floodplains, especially within the floodplain of Eight Mile Creek (Reference 2). Paragould's corporate limits encompass an area of 31 square miles with a population density of 812 people per square mile (Reference 6). The city is located along the eastern slope of Crowley's Ridge. The topography is gently sloping from west to east. The watershed of Eight Mile Creek and its tributaries contributing to flooding in the area is approximately 32.4 square miles. The soil outside the floodplains is primarily of the Loring-Memphis Association, a well-drained silty loam. The floodplain areas are composed of heavier, poorly drained silt loam of the Calhoun-Calloway Association (Reference 4). Town of Sedgwick A small portion of this town's corporate limits are located in the southwest comer of Greene County. According to the 2009 census, Sedgwick's land area comprised 0.1 square miles with a population of 106 (Reference 6). A portion of this town is also located in Lawrence County. 7

13 2.3 Principal Flood Problems The City of Paragould has a history of frequent damaging floods. In the past, floods have cost property owners millions of dollars in flood damages. The following tabulation details information on certain flood producing rainfalls, according to local accounts and related information: Date Rainfall (inches) Duration (hours) June 18, February 18, August 14, November 14, September 17, January 30, April 19, April 19, April 19, December 17, Paragould Daily Press 2 U.S. Weather Service maximum for 24 hours, duration determined from local interviews 3 Broadcast from Radio KHIG in the City of Paragould 4 Recorded at Cooperative Station Paragould 1S (Coop Id ) from 8:00 a.m. 12/16/2001 through 8:00 am 12/17/2001, NOAA-NCDC web site Based on the rainfall data tabulated above, the August 14, 1957 storm was in excess of a 0.5-percent-annual-chance rainfall. The April 19, 1973 flood was equivalent to the synthetic I-percent-annual-chance flood discussed in this report. No other storm events causing major flooding have occurred since There are no USGS continuous or real-time stream flow gages in Greene County. One USGS historic peak flow gage is located in Greene County. USGS Gage No is located on Sugar Creek Tributary near Walcott and recorded peak stream flow from 3/4/1963 through 11/27/1985. The National Weather Service 8

14 (NWS) has no recording gages in the County; however, cooperative rainfall stations are located in the City of Paragould and in unincorporated Beech Grove. The Cooperative Station (ID # ) in Beech Grove was maintained by the NWS from August 1, 1946 through May 14, 1975 and provides daily precipitation data. The Cooperative Stations in Paragould (Cooperative IDs # and ) have been in operation since August 1, 1946 and document daily precipitation and air temperature. Numerous factors contribute to flooding in the area. The steep slopes of Crowley's Ridge, many of which are seasonally cultivated, but barren during peak rainfall seasons, offer low retention rates and high degrees of rainfall runoff. The high velocity flows resulting from these conditions encourage erosion making ditch and channel maintenance difficult, especially where Eight Mile Creek's stream gradient flattens. Man-made structures such as roads, railroads, and bridges across the Eight Mile Creek floodplain restrict flood flows and raise flood levels. The high degree of development in the floodplain areas of the City of Paragould invites more flood damage in the future. Although the city's forefathers started the city on high ground, the growth process has gradually moved people and homes into low-lying areas. 2.4 Flood Protection Measures The only significant flood protection measures implemented on the streams studied in this report have been on Eight Mile Creek. The portion of Eight Mile Creek between stream miles 8 and 12 was restored by the USACE in 1957, under authority contained in Section 208 of the 1954 Flood Control Act. Also, in the latter part of 1957, the remainder of Eight Mile Creek through the city was improved. Following the April 19, 1973 flood, channel improvements on Eight Mile Creek was constructed by the city in the fall of This construction helped restore the flood flow carrying capacity of the channel, but did not eliminate the threat of future flooding. Also, a spoil bank levee downstream from mile 12.8 contains flood flows to a limited extent. The certification on this levee has since expired so therefore it is no longer a Provisional Accredited Levee. The most recent channel improvements were completed in Channel improvements from miles 12.0 to 15.9 were designed to improve a 100-year level of protection to the urban area resulting in a reduction of the 100-year floodplain. Channel improvement in the agriculture areas (mile 4 to 12) provided varying levels of improved protection. A recreational reservoir, Reynolds Lake, above Reynolds Creek, does provide some flood storage. It is not designed or used for flood control purposes; however, the City of Paragould is currently working with the Memphis District of the USACE to improve Eight Mile Creek so that it would have a 1-percentannual-chance flood channel capacity. The construction of these improvements was recently completed, and the revised floodplain will be described in a future Letter of Map Revision. 9

15 3.0 ENGINEERING METHODS For the flooding sources studied by detailed methods 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 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 community. Limited detailed hydrology was developed for the Study of Loggy Creek Tributary 1. The Discharges were developed using 1995 USGS Rural Regression Equations (reference 14). Arkansas is divided into 4 hydrologic regions based on physiographic province, elevation, and precipitation. Greene County falls within Regions C and D; however, the Loggy Creek Watershed falls entirely within Region C. The Region C regression equations have only one variable A (Drainage Area). Discharge point drainage areas were developed using the USGS National Elevation Dataset 10 meter DEM collected in Discharges developed for Loggy Creek Tributary 1 study are shown in Table 3. As part of this study, the USACE, Memphis District Study of Eight Mile Creek was integrated as a Physical Map Revision (PMR). They revised the effective HEC- 1 model and generated new discharges for their work. The HEC-1 model was extended downstream to develop discharge points from mile 4 to (original extent). Storage versus discharge curves were adjusted to reflect channel improvements and update the Modified Puls routings. In the 2009 study no useful stream flow records were available for the streams studied in detail. In the original City of Paragould FIS study, peak discharges for floods of the 10-,2-, 1-, and 0.2-percentannual-chance recurrence intervals were obtained by applying various rainfall-duration data from the National Weather Service Technical Paper No. 40 to unit hydrographs developed along the streams 10

16 (Reference 7). Unit hydrographs were developed using Snyder's method, with coefficients taken from the National Weather Service Technical Paper No. 40 to unit hydrographs developed along the streams (Reference 7). Unit hydrographs were developed using Snyder's method, with coefficients taken from previous studies of basins with similar characteristics (Reference 8). In the May 1992 City of Paragould FIS revision, peak discharges for floods of the 10-, 2-, land 0.2-percent-annual-chance recurrence intervals for Eight Mile Creek, and the 1-percent annual-chance recurrence interval for the tributaries studied in detail, were obtained by using rainfall-duration data from the National Weather Service Technical Paper No. 40, with the HEC-1 Flood Hydrograph Package computer program (References 7 and 9). Unit hydrographs were developed using Snyder's method, with coefficients taken from the General Design Memorandum for Eight Mile Creek (Reference 10). Minor modifications in the Eight Mile Creek HEC-1 model were required to model Tributary Nos. 1, 2, and 3. Since several sub-basins were further subdivided, the timing of the peak flows reaching Eight Mile Creek were slightly different, resulting in minor changes in the flow values developed for Eight Mile Creek. Peak discharge-drainage area relationships for the stream studied by detailed methods are shown on Table 5, Summary of Discharges. Flooding Source and Location Eight Mile Creek Table 4. Summary of Discharges Drainage Area 10% Annual Chance Discharge (CFS) 2% Annual Chance Discharge (CFS) 1% Annual Chance Discharge (CFS) 0.2% Annual Chance Discharge (CFS) At confluence of Lake Ditch Creek (Craighead County) Approximately 170 feet upstream of Village Creek Ditch Approximately 40 feet downstream of Highway Approximately 40 feet

17 Flooding Source and Location downstream of Highway 49 Table 4. Summary of Discharges Drainage Area 10% Annual Chance Discharge (CFS) 2% Annual Chance Discharge (CFS) 1% Annual Chance Discharge (CFS) 0.2% Annual Chance Discharge (CFS) Approximately 358 feet downstream of Carroll Blvd. Approximately 545 feet upstream of Rocking Chair Rd Approximately 300 feet downstream from Spring Grove Rd Loggy Creek At Cross section A At Reynolds Road At cross section E Loggy Creek Tributary 1 Approximately 600 feet upstream of Devon Road Approximately 470 feet upstream of Devon Road Approximately 350 feet upstream of Ranch Road Approximately 275 feet downstream of Ranch Road Approximately 1300 feet downstream of Country Club

18 Flooding Source and Location Road Table 4. Summary of Discharges Drainage Area 10% Annual Chance Discharge (CFS) 2% Annual Chance Discharge (CFS) 1% Annual Chance Discharge (CFS) 0.2% Annual Chance Discharge (CFS) At Mouth Reynolds Creek At confluence of Loggy Creek Tributary No. 1 At confluence with Eight Mile Creek Tributary No. 2 At confluence with Eight Mile Creek Tributary No. 3 At confluence with Eight Mile Creek Hydraulic Analysis Analyses of the hydraulic characteristics of floodplains in Greene County, Arkansas 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 DFIRM represent rounded whole-foot elevations and may not exactly reflect the elevations shown on the Flood Profiles, Floodway Data tables or Flood Hazard Data Table 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. Limited Detailed Hydraulic Study was performed on Loggy Creek Tributary 1 in April of Hydraulic Analysis was performed using HEC-RAS version

19 Geometry was developed using NED 10 Meter DEM, field investigation measurements of structures and measurement from 2006 Greene County, Digital Aerial photography. The starting water surface elevation was determined using the normal depth method in HEC-RAS. Floodplain roughness factors (Manning s n ) were chosen by engineering judgment and field inspection. The PMR update of Eight Mile Creek was performed in HEC-RAS The Effective HEC-2 model was converted to HEC-RAS and the geometry was updated with new channel and immediate overbank survey. The starting water surface elevation was determined using the normal depth method in HEC-RAS. Floodplain roughness factors (Manning s n ) were chosen by engineering judgment and field inspection. In the original City of Paragould FIS study, cross section data was obtained or extrapolated from field surveys. All of the cross sections on Eight Mile Creek were obtained from surveys conducted in July 1970 and updated to reflect current conditions. All spot elevations in the area were obtained in September 1975 and February In the May 1992 revision, cross sections for the backwater analyses of Eight Mile Creek and Tributary Nos. 1, 2, and 3 were field surveyed. Bridge data was obtained by field surveys and measurements. 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 DFIRM. Water-surface elevations of floods of the selected recurrence intervals were computed using the USACE HEC-2 step-backwater computer program (Reference 11). Flood profiles were drawn showing computed water-surface elevations for floods of the selected recurrence intervals. In the original City of Paragould FIS study, starting water-surface elevations were determined by the slope-area method. In the May 1992 revision, starting water-surface elevations for Eight Mile Creek were determined by slope-area method and starting watersurface elevations for Tributary Nos. 1, 2, and 3 were obtained from the 1- percent-annual-chance flood elevation on Eight Mile Creek from the HEC-2 analysis. In the original City of Paragould FIS study, shallow flooding areas were determined from topographic information, interviews with residents, and interpretation of aerial photographs of the January 1969 flood obtained from the Paragould Daily Press. The average depth of shallow flooding was estimated to be 2 feet. In the May 1992 revision, shallow flooding analyses were based on rating curves developed for the Eight Mile Creek General Design Memorandum and the amount of flow leaving the basin calculated by the split flow analysis. Channel roughness factors (Manning s n ) were chosen by engineering judgment and field inspection. For the streams studied by Detailed and Limited Detailed Methods in Greene County, Arkansas the floodplain n-values are listed in the table below. 14

20 Table 5. Floodplain Roughness Coefficients Stream Channel n Overbank n Eight Mile Creek to to 0.120* Tributary No to to Tributary No to to Tributary No to to Loggy Creek Loggy Creek Tributary Reynolds Creek * n-values of 500 used in lieu of ineffective. The hydraulic analyses for these 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. 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 Greene County is feet. For 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: 15

21 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-percentannual-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, Floodway Data tables, and Summary of Stillwater Elevation 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. 4.1 Floodplain Boundaries To provide a national standard without regional discrimination, the 1-percentannual-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 community. For each stream studied by detailed methods, the 1-and 0.2-percent-annual-chance floodplain boundaries have been delineated using the flood elevations determined at each cross section. In the original City of Paragould FIS, between cross sections, the boundaries were interpolated using topographic maps at a scale of 1:62,500, enlarged to 1:6,000, with contour intervals of 5 feet and 20 feet (Reference 12). In the May 1992 revision, the boundaries were interpolated using topographic maps at a scale of 1:24,000, enlarged to 1: 12,000, with contour intervals of 5 feet and 10 feet (Reference 13). The boundaries of the shallow flooding areas were determined 16

22 from topographic information, interview with residents, and interpretation of aerial photographs of the January 1969 flood, which were obtained from the Paragould Daily Press. For this study the boundaries were developed using computer automated GIS processes, the USGS National Elevation Dataset 10 meter DEM and survey provide as part of the USACE PMR. The 1-and 0.2-percent-annual-chance floodplain boundaries are shown on the FIRM (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, only the 1-percent-annualchance floodplain boundary is shown on the FIRM (Exhibit 2). The approximate floodplain boundaries for Johnson Creek were determined in a manner similar to that used for the streams studied in detail in the 1978 FIS. An approximate 1-percent-annual-chance flood profile was used to specify floodplain boundaries on the above referenced topographic maps. No field cross sections were taken in this area. In the May 1992 revision, the 1-percent-annual-chance floodplain boundaries for several flooding sources studied by approximate methods were delineated using topographic maps (Reference 13). 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 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 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 17

23 floodway boundaries were interpolated. The results of the floodway computations are tabulated for selected cross sections (see Table 5, Floodway Data). The computed floodways are shown on the FIRM (Exhibit 2). In cases where the floodway and 1-percent-annual-chance floodplain boundaries are either close together or collinear, only the floodway boundary is shown. No floodways were computed for Tributary Nos. 1, 2, and 3. Portions of the floodway widths for Eight Mile Creek extend beyond the corporate limits. Encroachment into areas subject to inundation by floodwater having hazardous velocities aggravates the risk of flood damage, and heightens potential flood hazards by further increasing velocities. A listing of stream velocities at selected cross sections is provided in Table 4, Floodway Data. In order to reduce the risk of property damage in areas where the stream velocities are high, the community may wish to restrict development in areas outside the floodway. 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 flood way and the floodway fringe and their significance to floodplain development are shown in Figure 1. 18

24 TABLE 6 FLOODING SOURCE CROSS SECTION DISTANCE (MILES) WIDTH (FEET) FLOODWAY SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) 1-PERCENT-ANNUAL-CHANCE FLOOD WATER- SURFACE ELEVATION (FEET NAVD) REGULATORY WITHOUT FLOODWAY WITH FLOODWAY INCREASE EIGHT MILE CREEK A ,900 3, B ,398 2, C , D , E F G LOGGY CREEK A , B , C , D , E , REYNOLDS CREEK A , B , River miles above confluence with St. Francis River 2 River miles above confluence with Eight Mile Creek 3 River miles above confluence with Loggy Creek FEDERAL EMERGENCY MANAGEMENT AGENCY GREENE COUNTY, AR AND INCORPORATED AREAS FLOODWAY DATA EIGHT MILE CREEK - LOGGY CREEK REYNOLDS CREEK

25 5.0 INSURANCE APPLICATIONS 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-annualchance) 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 AO Zone AO is the flood insurance rate zone that corresponds to areas of 1-percent-annualchance shallow flooding (usually sheet flow on sloping terrain) where average depths are between 1 and 3 feet. Average whole-foot depths derived from the detailed hydraulic analyses are shown within this zone. Zone X Zone X is the flood insurance rate zone that corresponds to areas outside the 0.2-percentannual-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. 6.0 FLOOD INSURANCE RATE MAP The FIRM is designed for flood insurance and floodplain management applications. For flood insurance applications, the map designates flood insurance rate zones as described in Section 5.0 and, in the 1-percent-annual-chance floodplains that were studied by detailed methods, shows selected whole-foot BFEs or average depths. Insurance agents use zones and BFEs in conjunction with information on structures and their contents to assign premium rates for flood insurance policies. For floodplain management applications, the map shows by tints, screens, and symbols, the 1- and 0.2-percent-annual-chance floodplains, floodways, and the locations of selected cross sections used in the hydraulic analyses and floodway computations. 20

26 The countywide FIRM presents flooding information for the entire geographic area of Greene County. Previously, FIRMs were prepared for each incorporated community and the unincorporated areas of the County identified as flood-prone. This countywide FIRM also includes flood-hazard information that was presented separately on Flood Boundary and Floodway Maps (FBFMs), where applicable. Historical data relating to the maps prepared for each community are presented in Table 6, "Community Map History." 21

27 COMMUNITY NAME INITIAL IDENTIFICATION FLOOD HAZARD BOUNDARY MAP REVISIONS DATE FLOOD INSURANCE RATE MAP EFFECTIVE DATE FLOOD INSURANCE RATE MAP REVISIONS DATE *Delaplaine, Town of None None None None Greene County (Unincorporated Areas) December 13, 1977 None June 16, 2009 TBD Lafe, Town of July 10, 1979 None June 16, 2009 None Marmaduke, City of April 11, 1975 June 1, 1987 June 16, 2009 None Oak Grove Heights, City of December 13, 1977 None June 16, 2009 TBD Paragould, City of September 7, 1973 June 15, 1978 May 4, 1992 June 16, 2009 TBD Sedgwick, Town of December 13, 1977 None June 16, 2009 None *No Special Flood Hazard Areas Identified TABLE 7 FEDERAL EMERGENCY MANAGEMENT AGENCY GREENE COUNTY, AR (AND INCORPORATED AREAS) COMMUNITY MAP HISTORY

28 7.0 OTHER STUDIES Because this study is based on more up-to-date analyses, it supersedes the previously printed FISs for the City of Paragould (References 1 and 2). Please note that this FIS also supersedes the Flood Hazard Boundary Map (FHBM) for the Town of Lafe and the City of Marmaduke. This FIS report either supersedes or is compatible with all previous studies published on streams studied in this report and should be considered authoritative for the purposes of the NFIP. 8.0 LOCATION OF DATA Information concerning the pertinent data used in the preparation of this study can be obtained by contacting FEMA Region VI, Federal Insurance and Mitigation Division, 800 North Loop 288, Denton, Texas BIBLIOGRAPHY AND REFERENCES 1. U.S. Department of Housing and Urban Development, Federal Insurance Administration, Flood Insurance Study. City of Paragould, Greene County, Arkansas, Washington, D.C., Flood Insurance Study report dated December 1977, Flood Insurance Rate Map dated June 15, Federal Emergency Management Agency, Flood Insurance Study, City of Paragould, Greene County, Arkansas, Washington, D.C., May 4, U.S. Department of Agriculture, Census of Agriculture, Volume 1 Chapter 2: Arkansas County Level Data, National Agricultural Statistics Service. 4. U.S. Department of Agriculture, Natural Resources Conservation Service, Soil Survey of Greene County, Arkansas. 5. NOAA, Divisional Normals and Standard Deviations of Temperature and Precipitation, and Heating and Cooling Degree Days National Oceanic and Atmospheric Administration, National Environmental Satellite, Data, and Information Service, National Climatic Data Center, Asheville, N.C. 6. U.S. Census Bureau. Census 2009 Summary File 1 Arkansas, prepared by the U.S. Census Bureau, U.S. Department of Commerce, Weather Bureau, Technical Paper No. 40, Rainfall Frequency Atlas of the United States, Washington, D.C., 1961 Revised U.S. Army Corps of Engineers, Memphis District Snyder's "t" vs. Weighted Stream Slope, unpublished. 9. U.S. Army Corps of Engineers, Hydrologic Engineering Center, HEC-1 Flood 23

29 Hydrograph Package, Davis, California, October U.S. Army Corps of Engineers, Memphis District, General Design Memorandum. Eight Mile Creek. Paragould. Arkansas. Vol. 1 and 2, August U.S. Army Corps of Engineers, Hydrologic Engineering Center HEC-2 Water Surface Profiles. Generalized Computer Programs, Davis, California, April U.S. Department of the Interior, Geological Survey, 15 Minute Series Topographic Maps, Scale 1:62,500, Contour Interval 5 Feet and 20 Feet: Gainesville, Arkansas, 1960; Marmaduke, Arkansas-Missouri, U.S. Department of the Interior, Geological Survey, 15 Minute Series Topographic Maps, Scale 1:24,000, Contour Interval 5 Feet and 10 Feet: Paragould East, Arkansas, Provisional Edition, 1983; Paragould West, Arkansas, Provisional Edition, Federal Emergency Management Agency, Flood Insurance Study, Greene County, Arkansas and Incorporated Areas, Washington, D.C., June 16,

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