ST. CLAIR COUNTY, ILLINOIS

Transcription

1 ST. CLAIR COUNTY, ILLINOIS AND INCORPORATED AREAS St. Clair County Community Community Community Community Name Number Name Number ALORTON, VILLAGE OF MARISSA, VILLAGE OF BELLEVILLE, CITY OF MASCOUTAH, CITY OF BROOKLYN, VILLAGE OF MILLSTADT, VILLAGE OF CAHOKIA, VILLAGE OF NEW ATHENS, VILLAGE OF CASEYVILLE, VILLAGE OF *NEW BADEN, VILLAGE OF CENTREVILLE, CITY OF O FALLON, CITY OF *COLUMBIA, CITY OF SAUGET, VILLAGE OF DUPO, VILLAGE OF SHILOH, VILLAGE OF EAST CARONDELET, SMITHTON, VILLAGE OF VILLAGE OF ST. CLAIR COUNTY EAST ST. LOUIS, (UNINCORPORATED AREAS) CITY OF ST. LIBORY, VILLAGE OF FAIRMONT CITY, VILLAGE OF SUMMERFIELD, VILLAGE OF FAIRVIEW HEIGHTS, CITY OF SWANSEA, VILLAGE OF FAYETTEVILLE, VILLAGE OF WASHINGTON PARK, FREEBURG, VILLAGE OF VILLAGE OF *HECKER, VILLAGE OF LEBANON, CITY OF LENZBURG, VILLAGE OF *No Flood Hazard Areas Identified Preliminary: FLOOD INSURANCE STUDY NUMBER 17163CV000B

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 (FIS) report may not contain all data available within the Community Map Repository. Please contact the Community Map Repository for any additional data. The Federal Emergency Management Agency (FEMA) may revise and republish part or all of this FIS report at any time. In addition, FEMA may revise part of this FIS report by the Letter of Map Revision process, which does not involve republication or redistribution of the FIS report. Therefore, users should consult with community officials and check the Community Map Repository to obtain the most current FIS report components. Initial Countywide FIS Effective Date: November 5, 2003 Revised Countywide FIS Effective Dates: (To Be Determined)

3 TABLE OF CONTENTS 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...60 i

4 TABLE OF CONTENTS (Continued) FIGURES Figure 1 - Floodway Schematic TABLES Table 1 - Detailed Study Streams... 8 Table 2 - Streams Restudied by Detailed Methods... 9 Table 3 - Summary of Discharges Table 4 - Summary of Stillwater Elevations Table 5 - Vertical Datum Conversvion Table 6 - Mississippi River Vertical Datum Conversion Table 7 - Floodway Data Table 8 - Community Map History Exhibit 1 - Flood Profiles EXHIBITS Ash Creek Canteen Creek Catawba Creek Douglas Creek Doza Creek Engle Creek Engle Creek Ditch Hog River Kaskaskia River Little Canteen Creek Little Silver Creek Loop Creek Mississippi River Northwest Tributary to Ogles Creek Ogles Creek Ogles Creek Tributary Prairie Du Pont Diversion Channel Richland Creek Schoenberger Creek No. 1 Schoenberger Creek No. 2 Silver Creek Unnamed Tributary to Doza Creek Unnamed Tributary to Loop Creek Panel 01P Panels 02P-03P Panel 04P Panels 05P-06P Panel 07P Panels 08P-09P Panel 10P Panel 11P Panels 12P-14P Panels 15P-16P Panel 17P Panels 18P-22P Panels 23P-24P Panel 25P Panels 26P-28P Panel 29P Panels 30P-31P Panels 32P-38P Panel 39P Panels 40P-41P Panels 42P-49P Panel 50P Panel 51P ii

5 TABLE OF CONTENTS (Continued) Exhibit 1 - Flood Profiles (Continued) Unnamed Tributary to Ogles Creek Unnamed Tributary to Richland Creek West Fork of Richland Creek Wolf Branch Panel 52P Panel 53P Panels 54P-56P Panels 57P-58P Exhibit 2 - Flood Insurance Rate Map Index Flood Insurance Rate Map iii

6 FLOOD INSURANCE STUDY ST. CLAIR COUNTY, ILLINOIS AND INCORPORATED AREAS 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 St. Clair County, including the Cities of Belleville, Centreville, Columbia, East St. Louis, Fairview Heights, Lebanon, Mascoutah, and O Fallon; the Villages of Alorton, Brooklyn, Cahokia, Caseyville, Dupo, East Carondelet, Fairmont City, Fayetteville, Freeburg, Hecker, Lenzburg, Marissa, Millstadt, New Athens, New Baden, Sauget, Shiloh, Smithton, St. Libory, Summerfield, Swansea, and Washington Park; and the unincorporated areas of St. Clair County (referred to collectively herein as St. Clair 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 Cities of Collinsville and Madison are geographically located in St. Clair and Madison Counties. Please see the separately printed FIS report and Flood Insurance Rate Map (FIRM) for flood hazard information for the Cities of Collinsville and Madison. The City of Columbia and the Village of Hecker are geographically located in St. Clair and Monroe Counties. Only the portions of the City of Columbia and the Village of Hecker that lie in St. Clair County are included in this FIS report. The Village of New Baden is geographically located in St. Clair and Clinton Counties. Only the portion of the Village of New Baden that is located in St. Clair County is shown in this countywide revision. See the separately published FIS report and FIRM for flood-hazard information in the area outside St. Clair County. The Village of Fairmont City is geographically located in St. Clair and Madison Counties. The Village of Fairmont City is included in its entirety in this FIS report and FIRM. Please note that the Villages of Hecker and New Baden and the City of Columbia have no mapped flood hazard areas within St. Clair County. 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

7 The Digital Flood Insurance Rate Map (DFIRM) and FIS report for this countywide study have been produced in digital format. Flood hazard information was converted to meet the Federal Emergency Management Agency (FEMA) DFIRM database specifications and Geographic Information System (GIS) format requirements. The flood hazard information was created and is provided in a digital format so that it can be incorporated into a local GIS and be accessed more easily by the community. 1.2 Authority and Acknowledgments The sources of authority for this FIS are the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of Precountywide FIS Report Information on the authority and acknowledgements for each jurisdiction included in this countywide FIS report, as compiled from their previously printed FIS reports, are shown below: Alorton, Village of: Belleville, City of: Brooklyn, Village of: The hydrologic and hydraulic analyses for the FIS report dated December 4, 1979, were prepared by the U.S. Army Corps of Engineers (USACE), St. Louis District, for the Federal Insurance Administration (FIA), under Inter- Agency Agreement No. IAA-H-7-76, Project Order No. 24. (FIA, 1979e). The work was completed in November The hydrologic and hydraulic analyses for the FIS report dated May 19, 1980 (FIA, 1980b), were prepared by the USACE, St. Louis District, for the FIA, under Inter-Agency Agreement No. IAA-H-10-77, Project Order No. 6. The work was completed in September The hydrologic and hydraulic analyses for the FIS report dated September 28, 1979 (FIA, 1979c), were prepared by the USACE, St. Louis District, for the FIA, under Inter- Agency Agreement No. IAA-H-10-77, Project Order No. 6. The work was completed in January

8 Cahokia, Village of: Caseyville, Village of: Centreville, City of: Dupo, Village of: East Carondelet, Village of: The hydrologic and hydraulic analyses for the FIS report dated April 17, 1978 (FIA, 1978a), were prepared by the USACE, St. Louis District, for the FIA, under Inter-Agency Agreement No. IAA-H-7-76, Project Order No. 24. The work was completed in March The hydrologic and hydraulic analyses for the FIS report dated September 16, 1980 (FIA, 1980e), were prepared by the USACE, St. Louis District, for the FIA, under Inter- Agency Agreement No. IAA-H-7-76, Project Order No. 7. The work was completed in June The hydrologic and hydraulic analyses for the FIS report dated September 4, 1979 (FIA, 1979b), were prepared by the USACE, St. Louis District, for the FIA, under Inter- Agency Agreement No. IAA-H-7-76, Project Order No. 7. The work was completed in December The hydrologic and hydraulic analyses for the FIS report dated August 4, 1980 (FIA, 1980c), were prepared by the USACE, St. Louis District, for the FIA, under Inter-Agency Agreement No. IAA-H-10-77, Project Order No. 16. The work was completed in January The hydrologic and hydraulic analyses for the FIS report dated September 2, 1980 (FIA, 1980d), were prepared by the USACE, St. Louis District, for the FIA, under Inter- Agency Agreement No. IAA-H-7-76, Project Order No. 16. The work was completed in February

9 East St. Louis, City of: Fairmont City, Village of: Fairview Heights, City of: Fayetteville, Village of: Lebanon, City of: Mascoutah, City of: The hydrologic and hydraulic analyses for the FIS report dated May 1, 1979 (FIA, 1979a), were prepared by the USACE, St. Louis District, for the FIA, under Inter-Agency Agreement No. IAA-H-7-76, Project Order No. 13. The work was completed in November The hydrologic and hydraulic analyses for the FIS report dated September 28, 1979 (FIA, 1979d), were prepared by the USACE, St. Louis District, for the FIA, under Inter- Agency Agreement No. IAA-H-10-77, Project Order No. 6. The work was completed in July The hydrologic and hydraulic analyses for the FIS report dated January 3, 1978 (FIA, 1978b), were prepared by Roy F. Weston, Inc., for the FIA, under Contract No. H The work was completed in March The hydrologic and hydraulic analyses for the FIS report dated December 15, 1980 (FIA, 1980g), were prepared by the USACE, St. Louis District, for the FIA, under Inter- Agency Agreement No. IAA-H-18-78, Project Order No. 14. The work was completed in November The hydrologic and hydraulic analyses for the FIS report dated January 2, 1981 (FIA, 1981a), were prepared by the USACE, St. Louis District, for the FIA, under Inter- Agency Agreement No. IAA-H-18-78, Project Order No. 14. That work was completed in December The hydrologic and hydraulic analyses for the FIS report dated December 15, 1980 (FIA, 1980f), were prepared by the USACE, St. Louis District, for the FIA, under Inter- Agency Agreement No. IAA-H-18-78, Project Order No. 14. The work was completed in October

10 O Fallon, City of: Sauget, Village of: St. Clair County (Unincorporated Areas): Swansea, Village of: Washington Park, Village of: The hydrologic and hydraulic analyses for the FIS report dated April 15, 1982 (FIA, 1982), were prepared by the USACE, St. Louis District, for the FIA, under Inter-Agency Agreement No. IAA-H-18-78, Project Order No. 14. The work was completed in October The hydrologic and hydraulic analyses for the FIS report dated February 1, 1980 (FIA, 1980a), were prepared by the USACE, St. Louis District, for the FIA, under Inter- Agency Agreement No. IAA-H-10-77, Project Order No. 6. The work was completed in January The hydrologic and hydraulic analyses for the FIS reports dated June 15, 1981 (FIA, 1981c) and August 5, 1985 (FEMA, 1985), were prepared by the USACE, St. Louis District, for the FIA, under Inter-Agency Agreement Nos. IAA-H-7-76 and IAA-H-10-77, Project Order Nos. 14 and 7, respectively. The work was completed in June The hydrologic and hydraulic analyses for the FIS report dated June 1, 1981 (FIA, 1981b), were prepared by the USACE, St. Louis District, for the FIA, under Inter-Agency Agreement No. IAA-H-18-78, Project Order No. 14. The work was completed in December The hydrologic and hydraulic analyses for the FIS report dated December 15, 1978 (FIA, 1978c), were prepared by the USACE, St. Louis District, for the FIA, under Inter- Agency Agreement No. IAA-H-7-76, Project Order No. 7. The work was completed in December The authority and acknowledgments for the City of Columbia and the Villages of Freeburg, Hecker, Lenzburg, Marissa, Millstadt, New Athens, New Baden, Shiloh, Smithton, St. Libory, and Summerfield are not included because there were no previously printed FIS reports for areas within St. Clair County for those communities. 5

11 November 5, 2003 Initial Countywide FIS Report The updated analyses for Schoenberger Creek No. 2 and Canteen Creek for the countywide FIS report dated November 5, 2003 (FEMA, 2003), were prepared by the USACE, St. Louis District, for FEMA, under Inter-Agency Agreement No. EMW-95-E The work was completed in April Hydrologic and hydraulic analyses for Wolf Branch were prepared by the USACE, St. Louis District. The work was completed May New hydrologic and hydraulic analyses of Silver Creek were prepared by the USACE, St. Louis District. The work was completed August This Countywide Revision The updated hydrologic and hydraulic analyses for Richland Creek were performed by the Illinois Department of Natural Resources (IDNR) for FEMA, under Contract No. HSFE-2004-D-0015, Project Order No. 04-C23. This work was completed in February The updated hydrologic and hydraulic analyses for the Mississippi River AR zones were taken from the report titled "Upper Mississippi River Floodway Computation, prepared by the USACE, St. Paul, Rock Island, and St. Louis Districts, (USACE, 2004b). Flood profiles and Base Flood Elevations (BFEs) for the Kaskaskia River and Silver Creek were revised to reflect updated backwater elevations from the Mississippi River. Base map information shown on the FIRM was derived from Sanborn Map Company, Inc., Digital Orthophoto Quadrangles produced at a scale of 1:1,200, from National Aerial Photography Program black and white photography dated 2005 or later. The projection used in the preparation of this map is Universal Transverse Mercator (UTM) Zone 15, and the horizontal datum used is NAD 83, GRS80 Spheroid. 1.3 Coordination An initial meeting is held with representatives from FEMA, the community, and the study contractor to explain the nature and purpose of a FIS, and to identify the streams to be studied or restudied. A final meeting is held with representatives from FEMA, the community, and the study contractor to review the results of the study. Precountywide Analyses The initial and final meeting dates for previous FIS reports for St. Clair County and its communities are listed in the following table: 6

12 Community Name Initial Meeting Date Final Meeting Date Alorton, Village of January 19, 1976 March 28, 1979 Belleville, City of January 19, 1976 August 30, 1979 Brooklyn, Village of August 26, 1976 October 18, 1978 Cahokia, Village of January 19, 1976 September 30, 1977 Caseyville, Village of March 31, 1975 May 1, 1980 Centreville, City of April 1975 October 17, 1978 Dupo, Village of August 26, 1976 January 29, 1980 East Carondelet, Village of August 26, 1976 December 27, 1979 East St. Louis, City of April 1975 October 18, 1978 Fairmont City, Village of August 27, 1976 March 28, 1979 Fairview Heights, City of March 1976 June 15, 1977 Fayetteville, Village of December 15, 1977 July 22, 1980 Lebanon, City of December 15, 1977 September 3, 1980 Madison, City of October 18, 1978 April 27, 1979 Mascoutah, City of December 15, 1977 June 16, 1980 O'Fallon, City of December 15, 1977 September 22, 1981 Sauget, Village of August 26, 1976 April 26, 1979 St. Clair County May 26, 1976 December 4, 1980 (Unincorporated Areas) Swansea, Village of December 15, 1977 * Washington Park, Village of April l, 1975 August 1, 1978 *Data Not Available November 5, 2003 Initial Countywide FIS Report For the November 5, 2003, countywide FIS, FEMA notified the county and incorporated communities with letters dated January 20, 1998, that a countywide FIS would be prepared. A final meeting was held on February 21, 2002, and was attended by representatives of the State, St. Clair County, and FEMA. This Countywide Revision For this countywide FIS the initial meeting was held on July 28, 2004, and attended by representatives of FEMA, State of Illinois, and St. Clair County. The results of the study were reviewed at the open house held on, and attended by representatives of. All problems raised at that meeting have been addressed in this study. 7

13 2.0 AREA STUDIED 2.1 Scope of Study This FIS covers the geographic area of St. Clair County, Illinois, 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. The streams studied by detailed methods in St. Clair County are listed in Table 1: Table 1 Detailed Study Streams Ash Creek Ogles Creek Canteen Creek Ogles Creek Tributary Catawba Creek Prairie Du Pont Diversion Channel Douglas Creek Richland Creek Doza Creek Schoenberger Creek No. 1 Engle Creek Schoenberger Creek No. 2 Engle Creek Ditch Silver Creek Hog River Unnamed Tributary to Doza Creek Kaskaskia River Unnamed Tributary to Loop Creek Little Canteen Creek Unnamed Tributary to Ogles Creek Little Silver Creek Unnamed Tributary to Richland Creek Loop Creek West Fork of Richland Creek Mississippi River Wolf Branch Northwest Tributary to Ogles Creek Limits of detailed study are indicated on the Flood Profiles (Exhibit 1) and on the FIRM (Exhibit 2). Many areas subject to shallow flooding and ponding areas in St. Clair County are also studied in detail. November 5, 2003 Initial Countywide FIS Report As part of the November 5, 2003, initial countywide FIS, portions of Harper Ditch and Canteen Creek were redelineated. High water marks and field reconnaissance determined where the water had spilled over spoil banks along each creek. Schoenberger Creek No. 2 was studied from just upstream of North 89 Street to a point approximately 1,500 feet upstream of Interstate Highway 161. Updated analyses were included for Silver Creek from the confluence with Kaskaskia River to a point approximately 1.25 miles upstream of Lebanon Loyett Road. Wolf Branch was restudied from the confluence with Richland Creek to a point approximately 900 8

14 feet upstream of Wabasha Avenue. Several ponding areas along Harding Ditch were also studied. Numerous flooding sources in the county were studied by approximate methods. 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 St. Clair County. This Countywide Revision The streams restudied by detailed methods in this revision are listed in Table 2. Table 2 - Streams Restudied by Detailed Methods Stream Mississippi River Richland Creek Reach From approximately 10,520 feet downstream of the downstream county boundary to approximately 4,710 feet upstream of the upstream county boundary, including the entire AR flooding zone within St. Clair County From approximately 5,200 feet upstream of Schiermeier Road to approximately 1,100 feet upstream of North Green Mount Road For this countywide revision, the FIS report and FIRM were converted to countywide format, and the flooding information for the entire county, including both incorporated and unincorporated areas, is shown. Also, the vertical datum was converted from the National Geodetic Vertical Datum of 1929 (NGVD) to the North American Vertical Datum of 1988 (NAVD). In addition, the Universal Transverse Mercator coordinates, previously referenced to the North American Datum of 1927, are now referenced to the North American Datum of The following tabulation presents Letters of Map Correction (LOMCs) incorporated into this countywide study: LOMC Case Number Date Issued Project Identifier LOMR P 03/01/2004 Unnamed Tributary to Kaskaskia River LOMR P 05/14/2004 Engle Creek and Unnamed Tributary to Engle Creek LOMR P 04/12/2004 Loop Creek LOMR B005P 03/08/2007 Orchards Subdivision; Unnamed Tributary to Loop Creek LOMR C230P 01/24/2008 Unnamed Tributary to Richland Creek 9

15 LOMC Case Number Date Issued Project Identifier LOMR P 09/28/2007 Unnamed / Northwest Tributary to Ogles Creek LOMR P 01/29/2008 Doza Creek and Unnamed Tributary to Doza Creek LOMR P 12/21/2007 Green Mount Station; Loop Creek 2.2 Community Description St. Clair County is located in southwestern Illinois, across the Mississippi River from St. Louis, Missouri. The county encompasses approximately 680 square miles. Elevations range from near 600 feet NAVD in the northern portion of the county to 400 feet NAVD along the Mississippi River. The population of St. Clair County was 261,316 in 2007 (U.S. Census Bureau, 2007). The county is bordered by Madison County to the north, Clinton County to the northeast, Washington County to the southeast, Randolph County to the south, Monroe County to the southwest, and St. Louis County, Missouri, to the west. The type of climate in south-central Illinois is characterized by warm to hot summers and cool to cold winters. Generally, more than 60 percent of the precipitation occurs in the warmer half of the year. The average annual rainfall is approximately 39 inches. Air temperature ranges from an average maximum of 90 degrees Fahrenheit ( o F) in July to an average minimum of 22 o F in January. Winter temperatures rarely go below 0 o F. Freezing temperatures normally occur between mid-october and mid-april (The Weather Channel, 2008). Vegetation includes mostly agricultural lands with some forests and residential lawns. The floodplain for all detailed studied streams is primarily agricultural and residential in nature. Topography consists of moderately rolling uplands with small streams. The Southern Metropolitan Area Planning Comission (SMAPC) reports that soils generally consists of silty sediments graded in five-foot thicknesses, which generally overlie stratified silty sediments (SMAPC, 1970). The American Bottoms area, the flat area adjacent to the Mississippi River in the vicinity of East St. Louis, is composed of recent alluvium and glacial valley-train materials. Its thickness ranges from 80 feet to 120 feet and is underlain by Mississippian limestone. Immediately above the bedrock surface is a stratum of glacial outwash overlain by coarse sands and gravels. Above this stratum is a layer of medium to fine sand. These deposits may also contain industrial wastes. Meandering loops of the Mississippi River and creeks have left complex and varied surface deposits. Approximately 20 percent of the county drains directly into the Mississippi River through the American Bottoms. The remaining portion of the county drains 10

16 through Richland Creek, Silver Creek or the Kaskaskia River. The general flow direction is southerly. 2.3 Principal Flood Problems Low-lying areas of St. Clair County are subject to periodic flooding by overflows from the streams studied in detail for this FIS. Notable floods have occurred on Richland Creek in 1908, 1912, 1915, 1916, 1919, 1927, 1942, 1946, and The flood of 1957 was the largest flood on record. The storm of 1957 was the result of a severe rainstorm of short duration. The storm was centered approximately 7 miles southwest of Belleville, where inches of rain fell in less than 12 hours causing $2.7 million in damage in the Belleville area. USGS streamflow gages exist on Richland Creek near Hecker and Silver Creek, near the Village of Freeburg. Based on the results of the hydrologic analysis for the unincorporated areas of St. Clair County FIS, dated August 5, 1985, the recurrence interval for Richland Creek at the streamflow gage near Hecker was approximately 20-percent-annual-chance for the November 1972 flood. The recurrence interval for the April 1975 flood of Silver Creek, at the streamflow gage near Freeburg, was 20-percent-annual-chance based on a limited period of record. Floods also occurred on Richland and Silver Creeks in 1943, 1946, 1957, 1969, 1972, 1979, 1986, 1990, 1993, 1995, 1996, and 2005 (USACE, 1974 and USGS, 2008a). A high recorded Mississippi River stage at St. Louis for the 117-year period of record occurred in April 1973 (USGS, 1977). This flood was determined to have a 2.9 percent-annual-chance recurrence interval. However, inundation of the Mississippi River floodplain did not occur within the urbanized areas of St. Clair County since they were protected by the extensive system of existing levees and related flood control structures. During the April 1973 flood, damage was experienced in the industrial and commercial areas within the American Bottoms. The Southwestern Illinois Metropolitan and Regional Planning Comission (SIMRPC) attributed the damage to ponding of interior runoff during high Mississippi River stages when backwater blocked the gravity drainage systems (SIMRPC, 1975). The highest recorded stage occurred in August 1993 (USGS, 2008b). The American Bottoms experienced extensive flood damages due to interior runoff in August 1915, July 1942, August 1946, July 1952, June 1957 and May 1961 (SIMRPC, 1975). The 1946 flood approximated a 1-percent-annualchance event, with an average depth of rainfall of 11.8 inches. 2.4 Flood Protection Measures Levees exist in the study area that provide the communities with some degree of protection against flooding. However, it has been ascertained that some of these 11

17 levees may not protect the communities from rare events such as the 1-percentannual-chance flood. The criteria used to evaluate protection against the 1- percent-annual-chance flood are 1) adequate design, including freeboard; 2) structural stability; and 3) proper operation and maintenance. Levees that do not protect against the 1-percent-annual-chance flood event are not considered in the hydraulic analysis of the 1-percent-annual-chance floodplain. The East St. Louis and Vicinity, Illinois, flood control project authorized by the Flood Control Act of 1936, provides urban design flood protection from the Mississippi River floods (U.S. House, 1936). Protection from the 1-percentannual-chance-flood is provided, primarily by levees located outside the local community boundaries, to all bottom lands between the bluffs on the east and the Mississippi River and Chain of Rocks Canal on the west, and extends from Prairie Du Pont Canal on the south side to Cahokia Creek diversion channel on the north. The project included raising and enlarging 16.7 miles of levee, 3.1 miles of concrete floodwall, gravity drainage structures, and alterations at bridge crossings. The levee and floodwall portion of the project was essentially completed by An extensive system of flood protection structures exists along the Mississippi River in St. Clair County. This system includes levees, stormwater pumping stations and gravity outlet structures. The levees offer protection against floods with recurrence intervals of equal or less than a 1-percent-annual-chance occurrence. The area of St. Clair County protected by these structures includes primarily the American Bottoms plus areas located along the major streams which outfall into the Mississippi River. The Eastside Levee and Sanitary District operates 13 stormwater pumping stations and maintains 52 miles of drainage ditches and stormwater sewer systems serving various cities and industries within the American Bottoms. Carlyle Reservoir is on the Kaskaskia River approximately 50 river miles upstream of the St. Clair County boundary. This reservoir, constructed by the USACE, was completed in 1967 and serves recreation, flood control, water supply and navigation needs. The Kaskaskia River channel, between its mouth and the City of Fayetteville, has been widened, straightened and deepened for navigational purposes. Flood protection structures along the Kaskaskia River within St. Clair County include a levee system and a stormwater pumping station, which protect the area surrounding the City of New Athens. The Kaskaskia River Levee systems provide protection from the 1% annual chance flood. The Blue Waters Ditch pump station reduces the 1-percent-annual-chance floodplain in the City of Cahokia. 12

18 FEMA specifies that all levees must have a minimum of 3 foot freeboard against the 1-percent-annual-chance flood to be considered a safe flood protection structure. South of Belleville, along Richland Creek, most of the levee stations are believed to represent agricultural levees, which may protect fields during smaller flood events. Most of these levees overtop during the 1-percent-annual-chance flood, or do not maintain adequate freeboard. North of State Highway 15 in Belleville, along Richland Creek, the levee stations represent the ring levees protecting the sewage treatment plant and sewage disposal ponds. On the landward side, the single levee feature was assumed to be ineffective, as the feature was not continuous in upstream or downstream cross sections. Several major levee systems in the American Bottoms Region provide protection from flooding of the main stem Mississippi River. While protection afforded by the these systems is significant, findings brought forward by the USACE in August 2007 show that certain systems do not meet the requirements set forth in the Code of Federal Regulations, Title 44, Section (44 CFR 65.10), entitled Mapping of Areas Protected by Levee Systems. Specific deficiencies were identified in the following five systems: Wood River Drainage & Levee District Chain of Rocks Levee Metro East Sanitary District Prairie Du Pont Levee & Sanitary District Fish Lake Drainage & Levee District 44 CFR establishes minimum design, operation, and maintenance standards for the accreditation of levee and levee systems in the NFIP. When FEMA learns that a flood control system no longer provides adequate protection in accordance with these standards, the affected FIRM panels are revised to show flood risk based on the system not providing that protection. Affected communities with established restoration plans for levees that are newly de-accredited may request a special flood control restoration zone (Zone AR) if the restoration can be accomplished within a specified length of time and the community can demonstrate conformance to all appropriate provisions contained in 44 CFR A community that does not receive Federal funds for the purpose of constructing the restoration project is given a maximum of 5 years for completion of restoration activities from the date of submittal of the community's application for the Zone AR designation. A community that receives Federal funds for the purpose of designing and/or constructing the restoration project is given a maximum of 10 years for completion of restoration activities (or meet the 13

19 requirements of 44 CFR 61.12) from the date of submittal of the community's application for the Zone AR designation. Upon completion of restoration activities, affected communities should provide written evidence to FEMA that the rehabilitated system(s) meets the requirements of 44 CFR Communities will often work through the levee owner for the submission of required documents. Communities that receive Federal funds for the purpose of design and/or construction of the restoration should provide evidence of support for this certification from the USACE or appropriate Federal agency involved in the design or construction. Meetings held on August 29, 2007, at the East West Gateway Council of Governments (St. Louis, Missouri) and September 29 at the Southwestern Illinois College (Belleville, Illinois), provided initial information to community officials and levee owners on the status of the levee evaluations and FEMA s deaccreditation process. FEMA and the USACE participated in presenting information at both meetings. Letters mailed in October 2007 to elected officials and levee owners provided notice of FEMA s intent to de-accredit the aforementioned flood protection systems for purposes of flood risk identification as shown on FIRMs projected for publication. The October 2007 letter also provided guidance for the submission of data used to support an application for Zone AR designation. On January 29, 2008, a consolidated application for Zone AR designation was submitted by the East West Gateway Council of Governments on behalf of the impacted communities in Monroe, St. Clair and Madison Counties. The application presents information on behalf of 25 incorporated communities and the three listed counties. FEMA responded to individual communities in letters dated, 2008, identifying application deficiencies and establishing submittal timeframes to allow finalization of Zone AR designations. The January 29, 2008, application establishes the start date for a maximum 10-year timeframe for completion of restoration plans if Federal funds are used, or a maximum 5-year timeframe if Federal funds are not used. 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 are 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 14

20 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 (100-year) 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. Precountywide Analyses The hydrologic analyses described in the previously printed FIS reports for communities within St. Clair County have been compiled from the FIS reports and are summarized below. The National Weather Service (NWS) has had a recording gage located at the Lambert St. Louis Airport since This station index number is Precipitation records are available for the St. Louis area for the period from 1871 to date. These records were used with the USACE HEC-1 computer program to determine the discharge frequency relationships for Schoenberger Creek No. 1 in the City of East St. Louis (HEC, 1973). Flood flow frequency data for Canteen Creek was derived from a log-pearson Type III statistical analysis. The gage and period of record was for the USGS gage on Canteen Creek near Caseyville (1939 to date, USGS ) (USGS, 1939 to date). Regionally optimized unit graph and loss rate parameters were used in the Canteen Creek basin HEC-1 (HEC, 1973) model with frequency rainfall amounts obtained from Technical Paper No. 40 (NWS, 1961). The 0.2- percent-annual-chance flood discharges were obtained with rainfall data extrapolated from that published in Technical Paper No. 40. The frequency curve derived from the HEC-1 model was then adjusted to closely match the computed frequency curve. Although the drainage area for Canteen Creek at State Highway 157 is greater than the drainage area at State Highway 159, peak discharges at State Highway 157 are less because a significant amount of water goes into storage. For Ash Creek, Catawba Creek, Douglas Creek, Engle Creek, Engle Creek Ditch, Hog River, Kaskaskia River, Little Canteen Creek, Little Silver Creek, Loop Creek, Ogles Creek, Ogles Creek Tributary, Prairie Du Pont Diversion Channel, Richland Creek from the downstream county boundary to approximately 5,200 15

21 feet upstream of Schiermeier Road, and West Fork Richland Creek, peak discharges for floods of 10-, 2-, and 1-percent-annual-chance recurrence intervals were developed by hydrologic basin modeling using the USACE HEC-1 program (HEC, 1973). The computer program utilizes frequency rainfall amounts obtained from Technical Papers No. 40 and 49, optimized unit hydrographs, and storage routing (NWS, 1961 and NWS, 1964). Discharges for the 0.2-percent-annualchance floods were extrapolated from rainfall data analyzed by the method published in Technical Paper No. 40 (NWS, 1961). All areas subject to shallow flooding had peak volume values for the 10- and 1-percent-annual-chance floods determined by these same methods. On upper Engle Creek, the rational method flows were adopted because it was judged that these flows were more reasonable than those of the regression equations. The divided flow for Engle Creek Ditch was determined by a trialand-error method which balanced the water surface elevation (WSEL) of the Ditch with that of Engle Creek. On the Kaskaskia River, discharges decrease between the confluence of Silver Creek and the upstream confluence of the Elkhorn River because of the effect of storage above the Silver Creek confluence. Discharges decrease along Silver Creek because of the storage effect of its floodplain. November 5, 2003 Initial Countywide Analyses For Schoenberger Creek No. 2, Harding Ditch, Canteen Creek, and various ponding areas, flood elevations experienced in May 1995 exceeded elevations published in previous FISs. Rainfall gage data published in Climatological Data, Illinois (NOAA, 1995) indicate that 96 hour rainfall totals at the Edwardsville, Cahokia, and Belleville gages are near those predicted for a 1-percent-annualchance storm event by Technical Paper No. 40. Therefore, this event was chosen as the basis for reevaluating flood hazards in these areas. The frequency-discharges for Silver Creek were based on the Regional Frequency Analysis for Streams in the St. Louis District. All peak discharges for Wolf Creek were estimated by applying synthetic unit hydrograph methodology to the HEC-1 rainfall-runoff mathematical model developed by the USACE (HEC, 1973). Parameters for Clark-unit hydrographs and exponential loss rate functions were determined from regional relationships developed from an optimization study of observed floods at 14 streamflow gages in the vicinity of St. Clair County. Rainfall data for Richland Creek, provided by the NWS (NWS, 1961 and 1964), were used to develop the 10-, 2-, 1-, and 0.2- percent-annual-chance synthetic storm events. Rainfall data for Wolf Branch were developed using Bulletin 70 (Huff and Angel, 1989) from the Illinois Department of Energy and Natural Resources. 16

22 This Countywide Revision The hydrologic analyses for the upstream portion of Richland Creek (from approximately 5,200 feet upstream of Schiermeier Road to approximately 1,100 feet upstream of North Green Mount Road) were performed from regression equations taken from SIR , Estimating Flood-Peak Magnitudes and Frequencies for Rural Streams in Illinois (Soong et. al, 2004). The results of these equations were adjusted for urbanization using WSP-2207, Flood Characteristics of Urban Watersheds in the United States (Sauer et. al, 1983). Mississippi River floodplain elevations were determined by the January 2004 Upper Mississippi River System Flow Frequency Study (UMRSFFS) (USACE, 2004a). The UMRSFFS was developed by five USACE Districts (St. Paul, Rock Island, Omaha, Kansas City, and St. Louis) and coordinated through representatives from seven federal agencies and seven states. The study addresses flooding of the Illinois River from Lockport to the mouth, the Missouri River below the Gavins Point Dam to the mouth, and the Mississippi River from St. Paul to the confluence with the Ohio River. Technical aspects of the study include impacts of levees, land use change, and climate variation. Hydrology was accomplished based on 100 years of record from 1898 to 1998 using a log-pearson Type III distribution for unregulated flows at gages. In situations where historic records were not adequate to develop discharge frequency relationships or to verify the results, hydrologic modeling was used to create synthetic flows based on rainfall. Peak discharge-drainage area relationships for St. Clair County, Illinois are shown in Table 3. Table 3 - Summary of Discharges Peak Discharges (cubic feet per second) Flooding Source and Location Drainage Area (square miles) 10-Percent- Annual- Chance 2-Percent- Annual-Chance 1-Percent- Annual-Chance 0.2-Percent- Annual-Chance ASH CREEK At confluence with Loop Creek CANTEEN CREEK At North Main Street /State Highway 57 At State Highway 159/North Illinois Street CATAWBA CREEK At confluence with Richland Creek DOUGLAS CREEK Just upstream of confluence with Richland Creek 4.1 1,490 2,750 3,490 4, ,300 7,000 8,400 11, ,500 7,100 8,600 11, ,040 2,800 3,130 3, ,200 9,300 10,600 12,800 17

23 Table 3 Summary of Discharges (Continued) Peak Discharges (cubic feet per second) Flooding Source and Location Drainage Area (square miles) 10-Percent- Annual- Chance 2-Percent- Annual-Chance 1-Percent- Annual-Chance 0.2-Percent- Annual-Chance DOZA CREEK Approximately 770 feet downstream of Winter Road Approximately 1,660 feet upstream of Winter Road * * 2,285 * * * 2,220 * ENGLE CREEK At Scott Troy Road ,200 1,500 2,000 Just downstream of Illinois ,200 1,600 Terminal Railroad Just upstream of convergence of Engle Creek Ditch ENGLE CREEK DITCH At confluence with Engle Creek HOG RIVER At confluence with Silver Creek KASKASKIA RIVER Just upstream of confluence of Richland Creek Just upstream of confluence of Silver Creek Just upstream of confluence of Elkhorn River LITTLE CANTEEN CREEK At North Main Street /State Highway 157 Approximately 3,350 feet upstream of North Main Street /State Highway 157 Approximately 1,500 feet upstream of Circle Drive ,190 1,360 1,680 5,210 47,500 69,800 80, ,600 4,702 41,000 59,900 68, ,100 4,410 42,400 62,100 70, , ,100 4,940 5,780 7, ,433 3,914 4,581 5, ,600 4,200 4,900 6,470 LITTLE SILVER CREEK At confluence with Silver ,050 10,380 12,760 16,790 Creek At CSX/Strack Lane ,840 9,060 10,700 13,750 At Midgely Neiss Road ,300 6,300 7,330 9,570 LOOP CREEK At confluence with Silver ,170 8,270 9,440 13,450 Creek MISSISSIPPI RIVER At St. Louis Gage 697, , , ,000 1,120,000 *Data Not Available 18

24 Table 3 Summary of Discharges (Continued) Peak Discharges (cubic feet per second) Flooding Source and Location Drainage Area (square miles) 10-Percent- Annual- Chance 2-Percent- Annual-Chance 1-Percent- Annual-Chance 0.2-Percent- Annual-Chance NORTHWEST TRIBUTARY TO OGLES CREEK At confluence with Unnamed Tributary to Ogles Creek 0.38 * * 155 * OGLES CREEK At confluence with Silver ,480 5,140 6,260 8,160 Creek At Illinois Terminal Railroad 8.5 2,230 3,290 3,860 4,820 At Interstate Highway ,400 1,750 2,300 OGLES CREEK TRIBUTARY At confluence with Ogles Creek PRAIRIE DU PONT DIVERSION CHANNEL At confluence with Mississippi River ,000 17,700 19,500 21,800 RICHLAND CREEK At State Highway 156 Just upstream of confluence of West Fork of Richland Creek Just upstream of confluence of Douglas Creek Just downstream of Strip Mine Road Just upstream of Schleutter- Germaine Road ,300 16,100 10,700 31,500 24,600 15,700 37,300 29,000 17,900 45,800 35,500 22, ,545 6,545 12,684 14, ,208 5,208 9,914 11,668 At West F Street ,384 4,761 5,669 7,742 Just downstream of the ,128 4,072 4,971 6,476 confluence of Wolf Branch Just upstream of the ,124 confluence of Wolf Branch Just downstream of Old ,057 4,132 5,145 6,479 Collinsville Road Approximately 2,000 feet downstream of Hartman 1Lane ,908 3,771 4,751 6,308 At North Green Mount Road ,210 1,607 SCHOENBERGER CREEK NO. 1 * * * * * SCHOENBERGER CREEK NO. 2 At State Highway ,610 7,430 8,860 11,860 SILVER CREEK At confluence with Kaskaskia River ,400 19,000 22,000 29,000 *Data Not Available 19

25 Table 3 Summary of Discharges (Continued) Peak Discharges (cubic feet per second) Flooding Source and Location Drainage Area (square miles) 10-Percent- Annual- Chance 2-Percent- Annual-Chance 1-Percent- Annual-Chance 0.2-Percent- Annual-Chance UNNAMED TRIBUTARY TO DOZA CREEK Approximately 1,070 feet downstream of Hillstown Road UNNAMED TRIBUTARY TO LOOP CREEK At confluence with Loop Creek 9.97 * * 3,915 * 1.85 * * 931 * UNNAMED TRIBUTARY TO OGLES CREEK At Pausch Road 1.23 * * 881 * At Merriam Parkway 0.46 * * 316 * At Longfellow Drive 0.77 * * 539 * UNNAMED TRIBUTARY TO RICHLAND CREEK At State Highway 15 1Westbound WEST FORK OF RICHLAND CREEK Just upstream of confluence with Richland Creek Just upstream of State Highway 159 WOLF BRANCH Just upstream of confluence with Richland Creek 3.79 * * 3,100 * ,100 8,300 10,100 1, ,000 7,900 9,600 12, ,300 1,545 1,750 2,215 *Data Not Available Stillwater elevations for ponding areas within St. Clair County are shown in Table 4. Flooding Source Table 4 - Summary of Stillwater Elevations 10-Percent- Annual-Chance Water Surface Elevations (Feet NAVD*) 2-Percent- Annual-Chance 1-Percent- Annual-Chance 0.2-Percent- Annual-Chance VILLAGE OF ALORTON Between Interstate Highway 255 and State ** ** 411 ** Highway 157 Approximately 600 feet southwest of the intersection of Pocket Road and State Highway 15 and Missouri Avenue ** ** 411 ** *National American Vertical Datum of 1988 **Data Not Available 20

26 Table 4 Summary of Stillwater Elevations (Continued) Water Surface Elevations (Feet NAVD*) Flooding Source 10-Percent- Annual-Chance 2-Percent- Annual-Chance 1-Percent- Annual-Chance 0.2-Percent- Annual-Chance VILLAGE OF CAHOKIA Areas east of Illinois Central Railroad ** ** 397 ** Areas between Falling Stream Road and ** ** 405 ** U.S. Highway 50 Areas south of Camp Jackson Road ** ** 406 ** Areas north and west of Jerome Lane ** ** 406 ** Areas between Range Lane and the Missouri ** ** 408 ** Pacific Railroad Area between Camp Jackson and Jerome ** ** 409 ** Lane Between Illinois Terminal Railroad and Camp ** ** 404 ** Jackson Road Approximately 20 feet south of the intersection of Fox Meadow Lane and Paris Avenue ** ** 404 ** VILLAGE OF CASEYVILLE At intersection of Sterling Place and ** ** 422 ** Bermuda Avenue At intersection of Countryside Drive and ** ** 422 ** Acorde Drive North of Harding Ditch, west of Black Lane ** ** 418 ** Approximately 1,000 feet northwest of intersection with Interstate Highway 64 and State Highway 157 ** ** 422 ** CITY OF CENTREVILLE At the intersection of Lake Drive and East ** ** 414 ** Side Levee and Sanitary Canal District At the intersection of Belleview Avenue and ** ** 414 ** North 80 th Street Approximately 1,000 feet west of the ** ** 411 ** intersection of State Highway 15 (New Missouri Avenue and Harding Ditch) Along Harding Drainage Ditch ** ** 411 ** Area bounded by 55 th Street and 51 st Street ** ** 411 ** and north of Lake Boulevard East Side Levee and Sanitary District Canal ** ** 411 ** CITY OF EAST ST. LOUIS Approximately 500 feet northwest of ** ** 414 ** intersection of Summit Avenue and Michigan Avenue Approximately 300 feet northeast of the ** ** 415 ** intersection of Louisville and Nashville Railroad and Kings Highway (State Highway 50) Approximately 400 feet east of intersection of ** ** 414 ** Ohio Avenue and North 62 nd Street Approximately 500 feet southwest of intersection of State Street and Terrace Drive ** ** 414 ** *National American Vertical Datum of 1988 **Data Not Available 21

27 Table 4 Summary of Stillwater Elevations (Continued) Water Surface Elevations (Feet NAVD*) Flooding Source 10-Percent- Annual-Chance 2-Percent- Annual-Chance 1-Percent- Annual-Chance 0.2-Percent- Annual-Chance CITY OF EAST ST. LOUIS (CONTINUED) Intersection of Marybelle Avenue and North 70 th Street Approximately 600 feet south of intersection of St. Clair Avenue and North 47 th Street ** ** 418 ** ** ** 414 ** VILLAGE OF FAIRMONT CITY Approximately 1,000 feet west of Collinsville ** ** 403 ** Road Southwest area of the Village of Fairmont 414 ** ** ** City Ponding North of Cahokia Canal, west of Madison ** ** 407 ** Road, and east of Industrial Avenue Approximately 1,000 feet west of the ** ** 403 ** intersection of Collinsville Road and Cookson Road At intersection of Site Road and Park Road ** ** 411 ** Approximately 400 feet east of intersection ** ** 411 ** of Pocket Road and Site Road At intersection of Park Drive and Major Street ** ** 418 ** Approximately 800 feet west of intersection ** ** 421 ** of Stowers Road and Bernia Street At intersection of Watts Street and Brinson ** ** 418 ** Drive Approximately 0.5 mile east of intersection ** ** 418 ** of Watts Street and Brinson Drive At intersection of Caseyville Road and ** ** 422 ** Bunkum Road At intersection of North 82 nd Street and ** ** 422 ** Bunkum Road At intersection of Rock Springs Road and ** ** 415 ** McKinley Avenue North of Old Cahokia Canal and south of ** ** 403 ** County Road boundary Approximately 1,000 feet northeast of the ** ** 418 ** intersection of Mullins Creek Road and Prairie Du Pont Creek South of Cahokia Canal, north of CSX ** ** 403 ** Transportation and southwest of Old Cahokia Canal Approximately 1,000 feet east of the ** ** 415 ** intersection of Rock Springs Road and St. Clair Avenue Approximately 750 feet west of the ** ** 414 ** intersection of Lake Drive and North 88 th Street Approximately 400 feet south of intersection of U.S. Highway 255 (County Highway 3) ** ** 404 ** *National American Vertical Datum of 1988 **Data Not Available 22