MASON COUNTY, MICHIGAN

Transcription

1 MASON COUNTY, MICHIGAN (ALL JURISDICTIONS) MASON COUNTY Community Community Community Community Name Number Name Number AMBER, TOWNSHIP OF LOGAN, TOWNSHIP OF BRANCH, TOWNSHIP OF LUDINGTON, CITY OF CUSTER, TOWNSHIP OF *MEADE, TOWNSHIP OF *CUSTER, VILLAGE OF PERE MARQUETTE, CHARTER TOWNSHIP OF EDEN, TOWNSHIP OF RIVERTON, TOWNSHIP OF *FOUNTAIN, VILLAGE OF *SCOTTVILLE, CITY OF *FREE SOIL, TOWNSHIP OF *SHERIDAN, TOWNSHIP OF *FREE SOIL, VILLAGE OF *SHERMAN, TOWNSHIP OF GRANT, TOWNSHIP OF SUMMIT, TOWNSHIP OF HAMLIN, TOWNSHIP OF *VICTORY, TOWNSHIP OF *NO SPECIAL FLOOD HAZARD AREAS IDENTIFIED Preliminary: July 29, 2011 FLOOD INSURANCE STUDY NUMBER 26105CV000A

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. Selected Flood Insurance Rate Map panels for this community contain information that was previously shown separately on the corresponding Flood Boundary and Floodway Map panels (e.g., floodways, cross sections). In addition, former flood hazard zone designations have been changed as follows: Old Zone(s) Al through A30 B C New Zone AE X X Initial Countywide FIS Effective Date: 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 i

4 TABLE OF CONTENTS (Continued) FIGURES Figure 1 - Floodway Schematic TABLES Table 1 - Summary of Discharges... 8 Table 2 - Summary of Stillwater Elevations... 9 Table 3 - Vertical Datum Conversion Table 4 - Community Map History EXHIBITS Exhibit 1 - Flood Insurance Rate Map Index Flood Insurance Rate Map ii

5 FLOOD INSURANCE STUDY MASON COUNTY, MICHIGAN (ALL JURISDICTIONS) 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 Mason County, including the Charter Township of Pere Marquette; the Cities of Ludington and Scottville; the Townships of Amber, Branch, Custer, Eden, Free Soil, Grant, Hamlin, Logan, Meade, Riverton, Sheridan, Sherman, Summit and Victory, and the Villages of Custer, Fountain, and Free Soil (referred to collectively herein as Mason 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 City of Scottville; the Townships of Free Soil, Meade, Sheridan, Sherman, and Victory; and the Villages of Custer, Fountain, and Free Soil have no mapped special flood hazard areas. 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. 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

6 Precountywide Analyses Information on the authority and acknowledgements for each jurisdiction included in this countywide FIS report, as compiled from their previously printed FIS reports, is shown below: Hamlin, Township of: Summit, Township of: The hydrologic and hydraulic analyses for Big Sable River, Hamlin Lake, and Lake Michigan for the December 17, 1987, FIS report (FEMA. 1987a) were performed by the U.S. Army Corps of Engineers (USACE), Detroit District, for FEMA, under Inter- Agency Agreement No. EMW-84-E-1506, Project Order No. 1. The study was completed in December The hydrologic and hydraulic analyses for Bass Lake, Kibby Creek, Lake Michigan, and Quinn Creek for the December 17, 1987, FIS report (FEMA, 1987b) were performed by the USACE, Detroit District, for FEMA, under Inter-Agency Agreement No. EMW-84-E-1506, Project Order No. 1. The study was completed in December The Charter Township of Pere Marquette; the Cities of Ludington and Scottville; the Townships of Amber, Branch, Custer, Eden, Free Soil, Grant, Logan, Meade, Riverton, Sheridan, Sherman, and Victory; and the Villages of Custer, Fountain, and Free Soil have no previously printed FIS reports. This Countywide FIS Report The hydrologic and hydraulic analyses for all areas studied by approximate analyses were performed by Atkins North America, Inc. (Atkins) for FEMA, under HSFE05-05-D-0023, Task Order 29. Flooding effects from Lake Michigan were redelineated by Atkins, using the USACE revised report on Great Lakes open-coast flood levels (USACE, 1988). The work was completed in March Base map information shown on the FIRM was derived from U.S. Geological Survey (USGS) Digital Orthophoto Quadrangles produced at a scale of 1:12,000, from National Aerial Photography Program black and white photography dated 2001 or later. The projection used in the preparation of this map in Universal Transverse Mercator (UTM), Zone 16, and the horizontal datum used is North 2

7 American Datum 1983 (NAD83), Geodetic Reference System 1980 (GRS80) Spheroid. 1.3 Coordination 2.0 AREA STUDIED 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 Mason County and all its jurisdictions are listed in the following table: Community FIS Date Initial Meeting Final Meeting Hamlin, Township of December 17, 1987 March 9, 1984 January 6, 1987 Summit, Township of December 17, 1987 March 9, 1984 February 6, 1987 This Countywide FIS Report The initial meeting was held on May 23, 2007, and attended by representatives of FEMA, Mason County, and Atkins. The results of the study were reviewed at the final meeting held on, and attended by representatives of. All issues and/or concerns raised at that meeting have been addressed. 2.1 Scope of Study This FIS covers the geographic area of Mason County, Michigan, including the cities, townships, and villages listed in section 1.1. The areas studied by detailed methods were selected with priority given to all known flood hazards and areas of projected development or proposed construction through the time of the study. The following lakes are studied by detailed methods in this FIS report: Bass Lake Hamlin Lake Lake Michigan 3

8 The limits of detailed study are indicated on the FIRM (Exhibit 1). This Countywide FIS Report For this countywide study, all areas studied by approximate methods were either newly studided or revised based on updated hydrologic and hydraulic models. Lake Michigan was delineated using the stillwater elevation of feet, North American Vertical Datum of 1988 (NAVD), from the USACE report on opencoast flood levels of the Great Lakes (USACE, 1988) Also for this countywide FIS, 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 NAVD. In addition, the UTM coordinates, previously referenced to the North American Datum of 1927 (NAD27), are now referenced to the NAD83. Approximate analyses were used to study those areas having low development potential or minimal flood hazards. The scope and methods of study were proposed to and agreed upon by FEMA and Mason County. 2.2 Community Description Mason County is located approximately 65 miles northwest of the City of Grand Rapids and is bounded on the north by Manistee County, on the east and southeast by Lake and Newaygo Counties, on the south by Oceana County and on the west by Lake Michigan. The county seat is the City of Ludington. The population of the county and all its jurisdictions at the time of the 2010 Census was 28,705 (U.S. Census Bureau, 2011). The area of the county is approximately 1,242 square miles. The region can be characterized into two different areas, gently rolling to hilly on the eastern side of the county to dunes and beaches that border Lake Michigan on the west. Mason County has many lakes and poorly drained land. The climate classification in Mason County varies from quasi-marine to continental, modified by winds across Lake Michigan. Seasonal temperatures range from an average of 25 degrees Fahrenheit ( F) in the winter to an average of 67 F in the summer. The warmest month of the year is July with an average maximum temperature of 81 F, while the coldest month of the year is January with an average minimum temperature of 16 F (The Weather Channel, 2011). The annual average precipitation is inches. Rainfall is evenly distributed throughout the year. The wettest month of the year is August with an average rainfall of 4.13 inches (The Weather Channel, 2011). 4

9 2.3 Principal Flood Problems No major flood problems are known to have occurred in Mason County; however there is a problem of shore erosion on some portions of Lake Michigan. It was indicated that Bass Lake has no past flooding history. However, based on the Lake Michigan levels presented in the USACE report on Great Lakes opencoast flood levels (USACE, 1988) and the detailed hydraulic analysis performed for this study, flooding would be expected in a limited area in the eastern portion of the community of Bass Lake as well as the undeveloped low-lying areas north and west of the lake. Limited flooding could also be expected in the eastern portion of Hamlin Lake as well as the undeveloped low-lying areas east and south of the lake. Shoreline erosion is due primarily to high-water and seiche effects in Lake Michigan. A seiche is the term describing the piling up of water on one end or side of the lake due to wind blowing in one direction for a considerable duration. The water subsequently returns in a fairly violent manner, and on occasion, may be great enough to be quite dangerous. High-water effects are caused by the seasonal and long-term variations in lake levels. Generally, there is approximately a 1-foot seasonal change from a low in winter to a high in early summer which is superimposed upon long-term variations. Precipitation in the Lake Michigan watershed, combined with evaporation, diversion, and the connecting navigational channels, is mainly responsible for determining the lake level. 2.4 Flood Protection Measures The Hamlin Lake Dam located along the Big Sable River provides the Township of Hamlin with some degree of protection against flooding, however may not protect the Townships of Hamlin from rare events such as the 1-percent-annualchance flood. 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 same year. The risk of experiencing a rare 5

10 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 An analysis was performed to establish lake stage-frequency relationships for Bass Lake. Basic data used in the construction of the stage-frequency curve consist of recorded lake stages for the years 1947 through The frequency curve was computed using Weibull plotting positions. Hamlin Lake is formed by the Hamlin Lake Dam along the Big Sable River. The dam is sufficiently high so that no influence from backwater conditions of Lake Michigan is felt by Hamlin Lake. Lake stages are the result of the interaction of dam outlet control structures discharge relationships, the Big Sable River inflows, and the lakes stage-storage characteristics. An annual frequency analysis of peak discharge flow records was performed on the Big Sable River at the Freesoil gage, using Weibull plotting positions and the log-pearson Type III distribution recommended by the Water Resources Council (WRC, 1976). A generalized skew coefficient of was used at suggestion of the Michigan Department of Environmental Quality (MDEQ). The annual frequency analysis was adjusted to the Hamlin Lake Dam based on the following drainage area relationship provided by the MDNR. Qadj = D1 (0.947) Qgage D2 Where D1 = drainage area at the dam = 206 square miles D2 = drainage area at the gage = 127 square miles Qadj = flow adjusted to the Hamlin Lake Dam Qgage = flow at gage 6

11 In order to establish the peak lake stages, it was necessary to do a routing through Hamlin Lake. Because of the storage capacity of the lake, the volume of runoff is as important as peak inflow. To convert the above discharges into flood hydrographs, several observed flood hydrographs were investigated to be used as a model. The April 27, 1951, flood was selected to produce the ice-free hyrdrograph, because flood records show that most floods during ice-free conditions were in late April and May and mean annual flood occurred prior to the flood peak to produce wet antecedent conditions. Any flow of 251 cubic feet per second (cfs) or below was considered a base flow. The flood hydrographs for the 10-, 2-, 1-, and 0.2-percent-annual-chance events were computed by multiplying the ordinates of the ice-free hydrograph by a factor necessary to produce the calculated flood peak. This factor as presented is a ratio of peak flows adjusted to the Hamlin Lake Dam to the peak flow of the April 1951 flood. Since 251 cfs is assumed as a level of base flow, any flows of 251 cfs or below were not multiplied by the factor to obtain the 10-, 2-, 1-, and 0.2-percent-annual-chance hydrographs. Using the Dam Safety Inspection Report, the lake stage vs. storage vs. dam spillway rating curve was obtained. Then, using the USACE, Hydrologic Engineering Center (HEC) Computer Program, HEC-1, the floods were routed through the reservoir and the peak reservoir elevations were determined (HEC, 1982). The following two basic conditions were considered in the reservoir routing analysis: winter lake levels and summer lake levels. During winter, the spillway crest of the dam is lowered by removal of stoplogs; however, peak inflows are larger. In the summer, peak inflows are less, but the spillway crest is higher. Therefore, both conditions were checked to see which one would produce the highest level. By examining the rating cure for the winter stoplogs settings, which is based on the information contained in the Dam Safety Inspections Report, it was determined that the.02-percent-annucal chance flood peak (1,030 cfs) could pass over the principle spillway without attenuation and the lake would not reach the normal summer pool elevation which is feet NAVD. Therefore, summer lake levels will produce the highest lake stages. According to the State Park personnel, the stop logs on the Hamlin Lake Dam are put in place after there is no ice on the lake. In 1983 and 1984, the stoplogs were put in place on April 1 and April 6, respectively. It was indicated that these were fairly typical dates. Based on this information, it is assumed that stoplogs are placed in very early April. From April 1-14, the reservoir is considered to be filling. 7

12 An ice-free frequency of peak annual discharges was also performed on the Big Sable River at the Freesoil gage using the log-pearson Type III distribution. Starting April 15 through November 15, the highest yearly discharge is used. Using the previously mentioned drainage area relationship, the frequency analysis was adjusted to the Hamlin Lake Dam. The flood elevations for Lake Michigan at the townships of Hamlin and Summit were taken from the USACE report on Great Lakes open-coast flood levels (USACE, 1977), which includes a frequency analysis from lake level gage records, an analysis of wind record, and an evaluation of wind setup calculations. This Countywide Analysis Peak discharges for the approximate study streams in Mason County were derived using either the published USGS regional regression equations, or the MDEQ Soil Conservation Service procedures. For the majority of the approximate analyses, peak discharges were estimated using the published USGS regional regression equations (USGS, 1984). Regression equations estimate peak discharges for ungaged streams based on characteristics of nearby gaged streams. For streams with a drainage area of less than 1 square mile, the peak discharges were determined based on guidelines from the Michigan Department of Environmental Quality (Sorrell, 2008) Flood elevations for Lake Michigan along Mason County were obtained from the USACE report on Great Lakes open-coast flood levels (USACE, 1988). Peak discharge-drainage area relationships for each flooding source studied in detail are shown in Table 1. Table 1 - 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 BIG SABLE RIVER (HAMLIN LAKE) At Hamlin Lake Dam ,030 Ice-free at Hamlin Lake Dam At Freesoil gage Ice-free at Freesoil gage

13 The stillwater elevations for Mason County are shown in Table 2. Table 2 - Summary of Stillwater Elevations Water Surface Elevations (feet NAVD) Flooding Source 10-Percent- Annual-Chance 2-Percent- Annual-Chance 1-Percent- Annual-Chance 0.2-Percent- Annual-Chance BASS LAKE HAMLIN LAKE LAKE MICHIGAN Hydraulic Analyses Analyses of the hydraulic characteristics of flooding from the sources studied were carried out to provide estimates of the elevations of floods of the selected recurrence intervals. Users should be aware that flood elevations shown on the FIRM represent rounded whole-foot elevations and may not exactly reflect the elevations shown on the Flood Profiles or in the Floodway Data 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 report in conjunction with the data shown on the FIRM. Precountywide Analysis Analyses of the hydraulic characteristics of flooding from the sources studied were carried out to provide estimates of the elevations of floods of the selected recurrence intervals. This Countywide Analysis For the approximately studied streams, cross section data was obtained from the topography. Roads were modeled with available bridge and culvert inventory data or as weirs, using elevations from topography. The studied streams were modeled using the USACE, HEC computer program HEC-RAS, version (HEC, 2005). The hydraulic analyses for this study were based on unobstructed flow and are thus considered valid only if hydraulic structures remain unobstructed, operate properly, and do not fail. 9

14 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 in use for newly created or revised FIS reports and FIRMs was NGVD. With the finalization of NAVD, many FIS reports and FIRMs are being prepared using NAVD as the referenced vertical datum. All flood elevations shown in this FIS report and on the FIRM are referenced to NAVD. Structure and ground elevations in the community must, therefore, be referenced to NAVD. It is important to note that adjacent communities may be referenced to NGVD. This may result in differences in Base Flood Elevations (BFEs) across the corporate limits between the communities. Some of the data used in this study were taken from the prior effective FIS reports and adjusted to NAVD. The average conversion factor that was used to convert the data in this FIS report to NAVD was calculated using the National Geodetic Survey s (NGS) VERTCON online utility (NGS, 2009). The data points used to determine the conversion are listed in Table 3. Table 3 - Vertical Datum Conversion Quad Name Corner Latitude Longitude Conversion from NGVD29 to NAVD88 Custer SE Free Soil SE Hamlin Lake SE Hamlin Lake OEW SE Kings Corners SE Ludington SE Manistee SE Manistee NW SE Millerton SE Scottville SE Star Corners SE Tallman SE Udell SE Average:

15 For additional information regarding conversion between NGVD and NAVD, visit the National Geodetic Survey website at or contact the National Geodetic Survey at the following address: Vertical Network Branch, N/CG13 National Geodetic Survey, NOAA Silver Spring Metro Center East-West Highway Silver Spring, Maryland (301) Temporary vertical monuments are often established during the preparation of a flood hazard analysis for the purpose of establishing local vertical control. Although these monuments are not shown on the FIRM, they may be found in the Technical Support Data Notebook associated with the FIS report and FIRM for this community. Interested individuals may contact FEMA to access these data. To obtain current elevation, description, and/or location information for benchmarks shown on this map, pleases 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. Therefore, each FIS provides 1-percent-annual-chance (100- year) flood elevations and delineations of the 1- and 0.2-percent-annual-chance (500- year) floodplain boundaries and 1-percent-annual-chance floodway to assist communities in developing floodplain management measures. This information is presented on the FIRM and in many components of the FIS report, including Flood Profiles, Floodway Data Table, and Summary of Stillwater Elevations Table. Users should reference the data presented in the FIS report as well as additional information that may be available at the local 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. 11

16 For the streams studied by approximate methods, between cross sections, the boundaries were interpolated using topographic maps at a scale of 1:24,000, with a contour interval of 10 feet (USGS, 2004). For Hamlin Lake, the floodplain boundaries were interpreted using topographic maps at a scale of 1:2400 with a contour interval of 2 feet (Abrams Aerial Survey Corporation, 1984). For Bass Lake, the floodplain boundaries were delineated using the Flood Hazard Boundary Map for the Township of Summit (Federal Insurance Administration (FIA), 1975) and modified by using quadrangle maps at scale of 1:25,000 with a contour interval of 3 meters (USGS, 1983). For the Lake Michigan coastline, the floodplain boundaries were delineated using coastal Light Detection and Ranging (LiDAR) data. The coastal LiDAR was developed and managed by the Joint Airborne LiDAR Bathymetry Technical Center of Expertise (JALBTCX, 2009), and the data had a horizontal accuracy of +/ meters and a vertical accuracy of +/ meters. The 1- and 0.2-percent-annual-chance floodplain boundaries are shown on the FIRM (Exhibit 1). 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 1). 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 1-percent-annual-chance flood can be carried without substantial increases in flood heights. Minimum Federal standards limit such increases to 1 foot, 12

17 provided that hazardous velocities are not produced. In Michigan, however, under Michigan Act 245, Public Acts of 1929, as amended by Act 167, Public Acts of 1968 (State of Michigan, 1968), encroachment in the floodplain is limited to that which will cause only an insignificant increase in flood heights. Thus, at the recommendation of the Bureau of the Water Management, a floodway having no more than a 0.1 foot surcharge has been delineated for this study. 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 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 1-percent-annual-chance flood more than 1 foot at any point. Typical relationships between the floodway and the floodway fringe and their significance to floodplain development are shown in Figure 1. Figure 1 Floodway Schematic No floodways have been mapped for Mason County. 13

18 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 risk zone that corresponds to the 1-percent-annual-chance floodplains that are determined in the FIS by approximate methods. Because detailed hydraulic analyses are not performed for such areas, no BFEs or base flood depths are shown within this zone. Zone AE Zone AE is the flood insurance risk zone that corresponds to the 1-percent-annual-chance floodplains that are determined in the FIS by detailed methods. In most instances, wholefoot BFEs derived from the detailed hydraulic analyses are shown at selected intervals within this zone. Zone X Zone X is the flood insurance risk 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, and areas protected from the 1-percent-annual-chance flood by levees. No BFEs or base flood 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 risk 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 the 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. 14

19 The countywide FIRM presents flooding information for the entire geographic area of Mason County. Previously, FIRMs were prepared for each incorporated community and remaining jurisdictions 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, where applicable. Historical data relating to the maps prepared for each community are presented in Table OTHER STUDIES This report either supersedes or is compatible with all previous studies on streams studied in this report and should be considered authoritative for 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, Federal Insurance and Mitigation Division, 536 South Clark Street, Sixth Floor, Chicago, Illinois

20 COMMUNITY NAME INITIAL IDENTIFICATION FLOOD HAZARD BOUNDAY MAP REVISION DATE FIRM EFFECTIVE DATE FIRM REVISION DATE Amber, Township of To Be Determined None To Be Determined None Branch, Township of To Be Determined None To Be Determined None Custer, Township of To Be Determined None To Be Determined None *Custer, Village of N/A None N/A None Eden, Township of To Be Determined None To Be Determined None *Fountain, Village of N/A None N/A None *Free Soil, Township of N/A None N/A None *Free Soil, Village of N/A None N/A None Grant, Township of To Be Determined None To Be Determined None Hamlin, Township of August 23, 1974 December 12, 1975 December 17, 1987 None *No Special Flood Hazard Areas Identified TABLE 4 FEDERAL EMERGENCY MANAGEMENT AGENCY MASON COUNTY, MI (ALL JURISDICTIONS) COMMUNITY MAP HISTORY

21 COMMUNITY NAME INITIAL IDENTIFICATION FLOOD HAZARD BOUNDAY MAP REVISION DATE FIRM EFFECTIVE DATE FIRM REVISION DATE Logan, Township of September 7, 1998 None September 7, 1998 None Ludington, City of To Be Determined None To Be Determined None *Meade, Township of N/A None N/A None Pere Marquette, Charter Township of January 30, 1976 None July 3, 1985 None Riverton, Township of To Be Determined None To Be Determined None *Scottville, City of N/A None N/A None *Sheridan, Township of N/A None N/A None Sherman, Township of N/A None N/A None Summit, Township of January 31, 1975 None December 17, 1987 None Victory, Township of N/A None N/A None *No Special Flood Hazard Areas Identified TABLE 4 FEDERAL EMERGENCY MANAGEMENT AGENCY MASON COUNTY, MI (ALL JURISDICTIONS) COMMUNITY MAP HISTORY 17

22 9.0 BIBLIOGRAPHY AND REFERENCES Abrams Aerial Survey Corporation, Topographic Maps of Hamlin Lake, prepared from Aerial Survey, Scale 1:2400, Contour Interval 2 feet, November Federal Insurance Administration, Flood Hazard Boundary Map, Township of Summit, Mason County, Michigan, U.S. Department of Housing and Urban Development, January Federal Emergency Management Agency, Flood Insurance Study, Township of Hamlin, Mason County, Michigan, Decmeber 17, 1987a. Federal Emergency Management Agency, Flood Insurance Study, Township of Summit, Mason County, Michigan, December 17, 1987b. Hydrologic Engineering Center, HEC-1 Flood Hydrograph Package, U.S. Army Corps of Engineers, Davis, California, June Hydrologic Engineering Center, HEC-RAS River Analysis System, Version 3.1.3, U.S. Army Corps of Engineers, Davis, California, May Joint Airborne LiDAR Bathymetry Technical Center of Expertise, CHARTs Program LiDAR, Contour Interval 2 feet, Mason County, Michigan, National Geodetic Survey, VERTCON-North American Vertical Datum Conversion Utility. Retrieved January 7, 2009, from The Weather Channel, Monthly Averages for Mason County Fairgrounds, MI. Retrieved May 26, 2011, from Sorrell, Richard C., Computing Flood Discharges For Small Ungaged Watersheds, Michigan Department of Environmental Quality, Land and Water Management Division, June State of Michigan, Act 25, Public Acts of 1929, as amended by Act 167, Public Acts of U.S. Army Corps of Engineers, Detroit District, Revised Report of Great Lakes Open-Coast Flood Levels, for the Federal Insurance Administration, Department of Housing and Urban Development, April U.S. Geological Survey, 7.5 Minute Series, Topographic Maps, Scale 1:25,000, Contour Interval 3 meters: Township of Summit, Michigan,

23 U.S. Geological Survey, 7.5 Minute Series, Topographic Maps, Scale 1:24000, Contour Interval 10 feet: Custer NE, Michigan, 2004; Custer NW, Michigan, 2004; Custer SE, Michigan, 2004; Custer SW, Michigan, 2004; Hamlin Lake, Michigan, 2004; Ludington NE, Michigan, 2004; Ludington NW, Michigan, 2004; Pentwater, Michigan, 2004; Wiley, Michigan, U.S. Geological Survey, Statistical Models for Estimating Flow Characteristics of Michigan Streams, Water-Resources Investigations Report , U.S. Department of the Interior, U.S. Census Bureau, Mason County, Michigan, U.S. Department of Commerce, Retrieved on May 2011, from Water Resources Council, Hydrology Committee, Guidelines for Determining Flood Flow Frequency, Bulletin 15, December