NORTH CAROLINA FLOODPLAIN MAPPING PROGRAM COOPERATING TECHNICAL STATE

Transcription

1 NORTH CAROLINA FLOODPLAIN MAPPING PROGRAM COOPERATING TECHNICAL STATE FINAL BASIN PLAN YADKIN RIVER BASIN Prepared by the: State of North Carolina and the Federal Emergency Management Agency Dated: November 8, 2007

2 TABLE OF CONTENTS PAGE Contact Information... iv Abbreviations and Acronyms... v I. Introduction...1 Why the State of North Carolina Created the Floodplain Mapping Program... 2 Components of the North Carolina Floodplain Mapping Program...2 Floodplain Mapping Program Funding and Work Plan...3 Program Benefits...4 II. Yadkin Basin Description...6 III. Scoping Phase for the Yadkin Basin Step 1 Initial Research and Coordination Step 2 Initial Scoping Meetings Step 3 Draft Basin Plan Step 4 Final Scoping Meetings Step 5 Final Basin Plan IV. Elevation and Flood Data Development and Digital FIRM Production for the Yadkin Basin Base Map Topographic Data Flood Hazard Data Detailed Study ine Limited Detailed Study Redelineation Use of Effective Information Variations from -Identified Needs and Priorities DFIRM V. Review and Due Process Final Basin Plan Yadkin Basin Date: November 8, 2007 Page i

3 TABLE OF CONTENTS PAGE List of Figures Figure 1. Total Policies in Force and Total Number Paid Losses...2 Figure 2. Three Phases of Development and Production...4 Figure 3. Phases of the North Carolina Statewide Floodplain Mapping Program... 4 Figure 4. Yadkin Basin Vicinity Map...6 Figure 5. Process for Scoping the Yadkin Basin Figure 6. Components of a Digital FIRM List of Tables Table 1. Information Table 2a. USGS Gage Information - Detailed Studied Flooding Sources Table 2b. USGS Gage Information - Approximate Zone A Flooding Sources Table 3. Initial Scoping Meetings for the Yadkin Basin Table 4. Summary of ine Flooding Sources to be Studied in Detail Table 5. Summary of Technical Methods for the Yadkin Basin Table 6. Summary of DFIRMs for the Yadkin Basin Appendices Appendix A. Attendance Sheets from Initial Scoping Meetings...A-1 Appendix B. Summaries of -Identified Flood Mapping Needs...B-1 Appendix C. Attendance Sheets from Final Scoping Meetings...C-1 Appendix D. Summary of Flooding Sources to be Studied by Limited Detailed Methods.D-1 Appendix E. Summary of Flooding Sources to be Redelineated.....E-1 Appendix F. Summary of Variations from -Identified Needs and Priorities to be added to the Final Basin Plan F-1 Final Basin Plan Yadkin Basin Date: November 8, 2007 Page ii

4 TABLE OF CONTENTS Attachments 1. Recommendations Yadkin Basin a. Alexander County, North Carolina b. Anson County, North Carolina c. Cabarrus County, North Carolina d. Caldwell County, North Carolina e. Davidson County, North Carolina f. Davie County, North Carolina g. Forsyth County, North Carolina h. Guilford County, North Carolina i. Iredell County, North Carolina j. Montgomery County, North Carolina k. Randolph County, North Carolina l. Richmond County, North Carolina m. Rowan County, North Carolina n. Stanley County, North Carolina o. Stokes County, North Carolina p. Surry County, North Carolina q. Union County, North Carolina r. Watauga County, North Carolina s. Wilkes County, North Carolina t. Yadkin County, North Carolina 2. Final Basin Plan Yadkin Basin a. Alexander County, North Carolina b. Anson County, North Carolina c. Cabarrus County, North Carolina d. Caldwell County, North Carolina e. Davidson County, North Carolina f. Davie County, North Carolina g. Forsyth County, North Carolina h. Guilford County, North Carolina i. Iredell County, North Carolina j. Montgomery County, North Carolina k. Randolph County, North Carolina l. Richmond County, North Carolina m. Rowan County, North Carolina n. Stanley County, North Carolina o. Stokes County, North Carolina p. Surry County, North Carolina q. Union County, North Carolina r. Watauga County, North Carolina s. Wilkes County, North Carolina t. Yadkin County, North Carolina Final Basin Plan Yadkin Basin Date: November 8, 2007 Page iii

5 CONTACT INFORMATION Questions or comments about this Basin Plan can be directed to: Randy Mundt, Development Planner North Carolina Floodplain Mapping Program (919) x119 or Questions about the National Flood Insurance Program (NFIP) and NFIP mapping can be directed to the Federal Emergency Management Agency s Map Assistance Center toll free information line at FEMA MAP ( ) or FEMAMapSpecialist@mapmodteam.com. Final Basin Plan Yadkin Basin Date: November 8, 2007 Page iv

6 ABBREVIATIONS AND ACRONYMS The following abbreviations and/or acronyms are used throughout this Basin Plan. Abbreviation/Acronym Description BFE Base Flood Elevation CGIA Center for Geographic Information and Analysis CTS DEMs Digital Elevation Models DFIRM Digital Flood Insurance Rate Map DOQs Digital Orthophoto Quadrangles FEMA Federal Emergency Management Agency FEMA-MCC FEMA s Mapping Coordination Contractor (Dewberry) FIS Flood Insurance Study FIRM Flood Insurance Rate Map FMIS Floodplain Mapping Information System GIS Geographic Information Systems LIDAR Light Detection and Ranging MENCA Mapping and Engineering Needs Assessment NAVD 88 North American Vertical Datum of 1988 NCEM North Carolina Division of Emergency Management NCDENR North Carolina Department of Environment and Natural Resources NCFMP North Carolina Floodplain Mapping Program NFIP National Flood Insurance Program NGVD 29 National Geodetic Vertical Datum of 1929 TIN Triangulated Irregular Network USGS U. S. Geological Survey Final Basin Plan Yadkin Basin Date: November 8, 2007 Page v

7 I. INTRODUCTION The State of North Carolina, through the Federal Emergency Management Agency s (FEMA s) Cooperating Technical partnership initiative, has been designated as the nation s first (CTS). As a CTS, the State has assumed primary ownership and responsibility of the National Flood Insurance Program s (NFIP) Flood Insurance Rate Maps (FIRMs) for all North Carolina communities. This role has traditionally been fulfilled by FEMA. North Carolina faces extreme hazard and consequence from hurricanes and flooding. Since 1989, there have been 21 federally declared disasters in North Carolina. Damages from Hurricane Floyd alone have reached $3.5 billion. As a result of Hurricane Floyd, 4,117 uninsured and under-insured homes were destroyed. Figure 1 below shows the number of flood policies in force and number of paid losses in the Yadkin Basin between the years of 1978 and The State s vulnerability to hurricanes and flooding make it crucial that communities and property owners have accurate, up-todate information about the flood risk. The updated DFIRMs produced through this Program will help to protect the lives and property, and contribute to the general well being, of North Carolina citizens. County No. of Policies/Claims since 1978 Repetitive Loss /Claims Alexander 39/0 0/0 Anson 1/0 0/0 Cabarrus 143/24 4/9 Caldwell 122/12 1/3 Davidson 253/10 2/4 Davie 45/4 0/0 Iredell 67/3 0/0 Montgomery 40/1 0/0 Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 1

8 Randolph 48/3 0/0 Richmond 8/0 0/0 Rowan 35/4 0/0 Stanly 39/3 0/0 Stokes 15/8 0/0 Surry 20/17 1/4 Union 146/18 1/2 Wilkes 5/0 0/0 Yadkin 2/0 0/0 Figure 1. Total Policies in Force and Total Number Paid Losses Why the State of North Carolina created the Floodplain Mapping Program There are several reasons why the State has initiated this Program; these include the following: Approximately 55% of North Carolina FIRMs were at least 10 years old. Approximately 75% of North Carolina FIRMs were at least 5 years old. FEMA s mapping budget is finite; on average, North Carolina received only one updated flood study for one county per year. Many counties and communities have indicated that they do not have the resources to take on this responsibility. Components of the North Carolina Floodplain Mapping Program The North Carolina Floodplain Mapping Program involves the following: Acquisition of high-resolution topographic data and development of accurate DEMs. Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 2

9 Development of up-to-date, accurate flood hazard data and floodplain mapping. Production of seamless digital FIRM coverage statewide: - DFIRMs will be produced on a statewide basis where all counties and incorporated communities are seamlessly shown across one set of state maps. - Digital Orthophoto Quadrangles (DOQs), produced in partnership by the State of North Carolina and the U.S. Geological Survey (USGS), will be used as the primary base map. In areas where there is a locally produced base map that is more current or accurate than the DOQs, the locally developed map may be used to supplement or in place of the DOQs as the base. - Flood Elevations on the DFIRMs will be converted to the North American Vertical Datum of 1988 (NAVD 88). - Unnumbered A Zones (where applicable) will be studied and be advanced to Limited Detailed Studies providing a Base Flood Elevation (BFE), where none currently exist. The North Carolina Floodplain Mapping Program, administratively located in the North Carolina Division of Emergency Management (NCEM), oversees and manages the Program. NCFMP will work closely with several other state agency partners such as North Carolina Geodetic Survey (NCGS), Center for Geographic Information and Analysis (CGIA), and the Floodplain Management Branch to ensure quality map production. In the production of the Basin Plan, NCFMP has worked in close cooperation with the Floodplain Management Branch of the NCEM to ensure that all flood hazards and NFIP issues are addressed. Additionally, after the updated flood data and maps are produced, NCFMP coordinates with Floodplain Management to conduct training and outreach to assist communities in utilizing the new data and maps to implement floodplain management and hazard mitigation activities. The North Carolina Floodplain Mapping Program has also implemented a state-of-theart, dynamic Floodplain Mapping Information System (FMIS) to analyze, maintain, and archive maps and associated flood hazard data. The FMIS also serves to present and distribute the mapping data and associated reports to the public via the Internet without the user needing to have sophisticated Geographic Information System (GIS) software. An additional component of the Program is a real-time flood forecasting and inundation mapping capability. The North Carolina Flood Warning System is currently being piloted in the Tar-Pamlico and Neuse Basins. The development of topographic and flood data and production of statewide digital FIRM panels will have three phases (Figure 2): (1) scoping, (2) flood map production, and (3) Review and Due Process (post-preliminary process). Scoping Flood Map Production Review and Due Process Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 3

10 Figure 2. Three Phases of Development and Production Flood Mapping Program Funding and Work Plan In August 2000, the North Carolina General Assembly allocated $42.8 million to the Floodplain Mapping Program. FEMA has contributed an additional $30.65 million toward the Program as well as in-kind contribution of engineering, mapping, and program management services. The State has also worked with other Federal partners to secure additional needed funding. Based on the General Assembly s directive, work began on the six eastern river basins as shown in Figure 3 (Phase I Cape Fear, Lumber, Neuse, Pasquotank, Tar-Pamlico, and White Oak). Work was initiated on six additional river basins in 2003 (Phase II Chowan, Roanoke, Yadkin, Catawba, Watauga, and New). Work on the remaining five basins (Phase III Broad, French Broad, Little Tennessee, Hiawassee, and Savannah) started in the summer of Figure 3. Phases of the North Carolina Floodplain Mapping Program Program Benefits The North Carolina Statewide Floodplain Mapping Program will provide many benefits to North Carolina communities, property owners, and citizens. These include: The updated flood hazard data will provide current, accurate information for North Carolina communities and property owners to make safe siting and design decisions when rebuilding from flooding disasters, building new structures and infrastructure, and retrofitting existing structures. Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 4

11 The use of the updated data by communities for floodplain management will dramatically reduce long-term flood losses to the State of North Carolina, its communities, and its citizens. Updated flood hazard data will alert those at risk of flooding of the need to purchase flood insurance protection. It will be faster and more cost effective to update DFIRMs. Current, updated base maps and the digital format of the FIRMs will allow users to make more efficient, precise flood risk determinations. The resultant DFIRMs will be the official NFIP maps; these DFIRMs will also be used by communities for floodplain management purposes. The digital format of the DFIRMs will allow use with GIS for analysis and planning. The digital Floodplain Mapping Information System will allow online access to all map users 24 hours a day without requiring sophisticated GIS software. The DEMs being developed will be useful for almost any engineering or planning application, such as site design, storm-water management, transportation planning and design, and spill response. This report summarizes and provides details about the scoping phase that was completed for the Yadkin Basin and how the results of this scoping effort were used to develop a plan for developing updated flood data and statewide DFIRMs for counties and communities located within the Yadkin Basin. This report also describes the process and schedule for completing the map production and community review phases. Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 5

12 II. YADKIN RIVER BASIN DESCRIPTION The Yadkin Basin drains from the Virginia border to South Carolina, cutting a swath through west central North Carolina. With 7,400 square miles, or 15.6% of the land area, this is the second largest drainage basin in the state. It also has the second largest number of stream miles - 5,855. The basin originates on the eastern slopes of the Blue Ridge Mountains in Caldwell, Wilkes, and Surry Counties (Figure 4). A small portion of the Yadkin headwaters originates in Virginia and flows northeasterly for about 100 miles, then flows to the southeast until it joins the Uwharrie to form the Pee Dee. The Pee Dee continues flowing southeasterly through South Carolina to the Atlantic Ocean. The North Carolina portion of the basin contains approximately 5,991 miles of freshwater streams and rivers. Figure 4. Yadkin Basin Vicinity Map Forest land covers approximately 50% of the basin and 95% of that forestry is privately owned. Agriculture (including cultivated and uncultivated cropland (15.6%) and pastureland (14.1%)) covers approximately 30% of the land area, while 13% of the land is developed. The urban and built-up category comprises roughly 11% and Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 6

13 exhibited the most dramatic change between 1982 and 1992 (38% increase). Other categories that showed substantial changes during this period were pasturelands (19% increase) and the "Other" category, which includes rural transportation (26% increase). Both cultivated and uncultivated cropland decreased by a total of 46% in the basin between 1982 and It is likely that some of this cropland was converted to pastureland and to urban and built-up areas. Major land use activities in the basin include agriculture (crops, swine, poultry, and cattle operations) and construction activities related to growth. Iredell County has the largest dairy cattle population in the state. The map below shows a general area of the Yadkin Basin, also known as the Yadkin-Pee Dee Basin. Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 7

14 There are 28 counties and over 93 municipalities in this large drainage area. The basin includes all or portions of the following counties: Alexander, Allegheny, Anson, Ashe, Cabarrus, Caldwell, Davidson, Davie, Forsyth, Guilford, Iredell, Mecklenburg, Montgomery, Randolph, Richmond, Rowan, Scotland, Stanly, Stokes, Surry, Union, Watauga, Wilkes, and Yadkin. (This Basin Plan does not include information for the following counties: Ashe, Alleghany, and Guilford. Ashe, Alleghany and Guilford are included in other Basin Plans.) This is the second most densely populated watershed, with 1,193,353 people or % of the state's total population. Based on 1990 census data, the population of the basin was 1.2 million people. Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 8

15 The most populated areas are in and near Winston-Salem and Charlotte. The overall population density is 163 persons per square mile versus a statewide average of 123 persons per square mile. While much of the basin contains rural areas surrounding small towns, many of the small to large cities have high density areas. The percent population growth over the ten year period between 1980 and 1990 was 10 percent. This region is characterized by rolling hills and geologic formations consisting of crystalline or sedimentary rocks. Because of the moderate topography, more streams drain a smaller amount of land, creating moderate drainage density. The Yadkin Basin serves as a corridor for plants and animals migrating from the mountains to the Coastal Plain, and vice-versa. This basin contains a variety of habitat types, as well as many rare plants and animals. Sportfishes in the Yadkin upstream of the Kerr Scott Reservoir include smallmouth bass, redbreast sunfish and bullhead catfishes. A considerable amount of white and striped bass fish exist below Idols Dam (west of Clemmons in Forsyth County) in the spring when the fish migrate from downstream reservoirs to spawn. In addition to being important natural resources, these reservoir fisheries also help make the basin a popular place for recreation, significantly boosting the local economy. Table 1 below summarizes the counties and communities located partially or entirely within the Yadkin Basin and their current NFIP participation and mapping status. Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 9

16 Name Table 1. Information County Participation Status Date of Current NFIP Map Alexander County Alexander Regular/Participating 7/20/1998 Town of Taylorsville Alexander Non-Participating Not Mapped Alleghany County Alleghany Regular/Participating 2/1/2004 Anson County Anson Regular/Participating 6/18/1990 Town of Ansonville Anson Emergency Not Mapped Town of Lilesville Anson Non-Participating Not Mapped Town of Morven Anson Non-Participating Not Mapped Town Of McFarlan Anson Non-Participating Not Mapped Town of Peachland Anson Regular/Participating 7/1/1987 Town of Polkton Anson Emergency 2/10/1978 Town of Wadesboro Anson Regular/Participating 8/19/1986 Ashe County Ashe Regular/Participating 10/20/1999 Cabarrus County Cabarrus Regular/Participating 11/2/1994 City of Concord, Cabarrus Regular/Participating 11/2/1994 Town of Harrisburg Cabarrus Regular/Participating 11/2/1994 City of Kannapolis Cabarrus Regular/Participating 11/2/1994 Town of Midland Cabarrus Non-Participating Not Mapped Town of Mount Pleasant Cabarrus Non-Participating 11/2/1994 Caldwell County Caldwell Regular/Participating 8/3/1998 Davidson County Davidson Regular/Participating 9/7/2000 Town of Davidson Davidson Regular/Participating 2/4/2004 Town of Denton Davidson Non-Participating 9/7/2000 City of Lexington Davidson Non-Participating 9/7/2000 City of Thomasville Davidson Non-Participating 9/7/2000 Town of Cooleemee Davie Non-Participating Not Mapped Davie County Davie Regular/Participating 12/17/1993 Town of Mocksville, Davie Emergency 6/27/2000 Town of Bethania, Forsyth Regular/Participating 4/24/2002 Village Of Clemmons, Forsyth Regular/Participating 10/20/1998 Forsyth County Forsyth Regular/Participating 10/20/1998 Town of Kernersville, Forsyth Regular/Participating 10/20/1998 Town of Lewisville, Forsyth Non-Participating Not Mapped Town of Rural Hall, Forsyth Regular/Participating 10/20/1998 Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 10

17 Table 1. Information (continued) Name County Participation Status Date of Current NFIP Map Village of Tobaccoville, Forsyth Regular/Participating 10/20/1998 Town of Walkertown, Forsyth Regular/Participating 10/20/1998 City of Winston-Salem Forsyth Regular/Participating 10/20/1998 Guilford County Guilford Regular/Participating 5/18/1998 City of High Point Guilford Regular/Participating 5/18/1998 Iredell County Iredell Regular/Participating 6/22/1998 Town of Harmony Iredell Non-Participating Not Mapped Town of Love Valley Iredell Non-Participating Not Mapped Town of Mooresville Iredell Regular/Participating 5/1/1980 City of Statesville Iredell Regular/Participating 9/28/1979 Town of Troutman Iredell Non-Participating Not Mapped City of Charlotte Mecklenburg Regular/Participating 2/4/2004 Town of Cornelius Mecklenburg Regular/Participating 2/4/2004 Town of Davidson Mecklenburg Regular/Participating 2/4/2004 Town of Huntersville Mecklenburg Regular/Participating 2/4/2004 Town of Matthews Mecklenburg Regular/Participating 2/4/2004 Mecklenburg County Mecklenburg Regular/Participating 2/4/2004 Town of Mint Hill Mecklenburg Non-Participating 2/4/2004 Town of Biscoe Montgomery Non-Participating Not Mapped Town of Candor Montgomery Non-Participating Not Mapped Montgomery County Montgomery Regular/Participating 6/1/1981 Town of Mount Gilead Montgomery Non-Participating Not Mapped Town of Star Montgomery Non-Participating Not Mapped Town of Troy Montgomery Emergency Not Mapped City of Archdale Randolph Regular/Participating 7/16/1981 City of Asheboro Randolph Regular/Participating 7/16/1981 City of Randleman Randolph Regular/Participating 7/1/1987 Randolph County Randolph Regular/Participating 7/16/1981 Town of Seagrove Randolph Non-Participating Not Mapped Town of Trinity Randolph Regular/Participating 7/16/1981 Town of Dobbins Heights Richmond Non-Participating Not Mapped Town of Ellerbe Richmond Non-Participating Not Mapped City of Hamlet Richmond Regular/Participating 9/6/1989 Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 11

18 Name Table 1. Information (continued) County Participation Status Date of Current NFIP Map Town of Hoffman Richmond Non-Participating Not Mapped Town of Norman Richmond Non-Participating Not Mapped Richmond County Richmond Regular/Participating 9/6/1989 City of Rockingham Richmond Regular/Participating 9/6/1989 Town of China Grove Rowan Regular/Participating 9/29/1978 Town of East Spencer Rowan Regular/Participating 12/11/1981 Town of Faith Rowan Regular/Participating 7/3/1978 Town of Granite Quarry Rowan Regular/Participating 9/15/1978 Town of Landis Rowan Regular/Participating 7/3/1978 Town of Rockwell Rowan Regular/Participating 5/15/1978 Rowan County Rowan Regular/Participating 11/1/1979 City of Salisbury Rowan Regular/Participating 5/15/1980 Town of Spencer Rowan Regular/Participating 9/29/1978 City of Albemarle Stanly Regular/Participating 9/21/2000 Town Of Badin Stanly Regular/Participating 9/21/2000 City of Locust, Stanly Regular/Participating 9/21/2000 Town of New London, Stanly Non-Participating 9/21/2000 Town of Norwood, Stanly Regular/Participating 9/21/2000 Town of Oakboro, Stanly Regular/Participating 9/21/2000 Town of Richfield, Stanly Non-Participating Sanctioned Town of Stanfield Stanly Non-Participating 9/21/2000 Stanly County Stanly Regular/Participating 9/21/2000 City of King, Stokes Regular/Participating 10/20/1998 Stokes County Stokes Regular/Participating 9/30/1988 Town of Dobson Surry Non-Participating Not Mapped Town of Elkin Surry/Wilkes Non-Participating Sanctioned Town of Mount Airy Surry Regular/Participating 2/19/1987 Town of Pilot Mountain Surry Non-Participating Not Mapped Surry County Surry Regular/Participating 9/15/1989 Town of Hemby Bridge Union Non-Participating Not Mapped Town of Indian Trail Union Regular/Participating 1/17/1997 Village of Lake Park Union Regular/Participating 1/17/1997 Town of Marshville Union Non-Participating 7/5/1994 Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 12

19 Name Table 1. Information (continued) County Participation Status Date of Current NFIP Map City of Monroe Union Regular/Participating 7/5/1994 Town of Stallings Union Regular/Participating 1/17/1997 Union County Union Regular/Participating 1/17/1997 Town of Wingate Union Regular/Participating 7/5/1994 Town of Blowing Rock Watauga Regular/Participating 1/17/1997 Watauga County Watauga Regular/Participating 9/21/1998 Town of North Wilkesboro Wilkes Regular/Participating 2/18/1998 Town of Ronda Wilkes Non-Participating Sanctioned Wilkes County Wilkes Regular/Participating 8/9/1999 Town of Wilkesboro Wilkes Regular/Participating 8/9/1999 Town of Arlington Yadkin Non-Participating Sanctioned Town of Boonville Yadkin Non-Participating Not Mapped Town of East Bend Yadkin Non-Participating Not Mapped Town of Jonesville Yadkin Regular/Participating 7/1/1987 Yadkin County Yadkin Regular/Participating 5/15/1991 Town of Yadkinville Yadkin Non-Participating Not Mapped NA Indicates that community did not participate in the Scoping Process. III. SCOPING PHASE FOR THE YADKIN RIVER BASIN The State worked closely with FEMA and Dewberry to complete the scoping phase for the Yadkin Basin counties and communities in late 2003 and early Stated simply, scoping is determining what areas are floodprone and need to have flood hazard data developed, what methods will be used to generate that hazard data, and how the data will be presented on the DFIRMs. For the Yadkin Basin, the comprehensive scoping phase entailed: Researching and inventorying available elevation, flood hazard, and digital base map data that may be useful for preparing updated DFIRMs; Assessing existing flood hazard data (for example: flood elevation profiles, floodplain boundaries, floodways, coastal hazard zones) on effective FIRMs for adequacy; Providing outreach to, and receiving input from, counties and communities regarding their needs for updated DFIRMs; Identifying data that needs to be developed or acquired, such as digital base maps, DEMs, or field surveys of stream channels, hydraulic structures, and coastal transects; Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 13

20 Determining the proposed scales and paneling scheme for statewide digital FIRM production; and Developing a schedule for completion of updated flood hazard data and digital FIRM production. For flooding sources within the basin, the flood hazard data from the effective FIRMs were assessed for adequacy in consultation with the impacted counties and communities. For areas where the existing flood hazard data was deemed to be inadequate or outdated, a priority level was established and the most appropriate method of developing updated data was selected based on the: Type and extent of manmade and natural changes within the floodplain and/or watershed; Quality of data available; and Existing and/or proposed levels of development affected by the flooding source. The process followed for completing the scoping is shown in Figure 5 and is described further below. Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 14

21 Scoping Flood Map Production Step 1 Step 2 Step 3 Step 4 Step 5 Initial Research & Coordination Initial Scoping Meeting Draft Basin Plan Final Scoping Meeting Revise Draft Basin Plan Technical & Cost Proposals for Contractors Finalize Basin Plan Figure 5. Process for Scoping the Yadkin Basin Distribute Final Basin Plan to Communities Analysis and Mapping Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 15

22 Step 1 Initial Research and Coordination The State held two central kickoff meetings in 2003 with county and community floodplain administrators, engineers, and planners on June 30, 2003 in Weldon and on July 8, 2003 in Statesville. The objectives of the meetings were to overview the State s CTS Agreement with FEMA and the North Carolina Floodplain Mapping Program, inform the floodplain administrators of the process that will be followed to develop updated mapping, and encourage them to be an active participant in the process. A questionnaire regarding the communities mapping needs was mailed prior to the meeting and distributed to those community representatives in attendance. This questionnaire contained pointed questions designed to help each community systematically ascertain its flood mapping needs. The county and community officials were encouraged to complete the questionnaire and submit it either digitally via or via hardcopy. Technical support was available for completion of the questionnaire through the State. Completed questionnaires were received by the State from the following counties and communities in the Yadkin Basin: Alexander County, Town of Rockwell (Alexander County), Town of Ansonville (Anson County), Town of Wadesboro (Anson County), City of Concord (Cabarrus County), City of Lenoir (Caldwell County), City of Thomasville (Davidson County), Town of Hoffman (Richmond County), Rowan County, Town of Granite Quarry (Rowan County), City of Salisbury (Rowan County), Stanly County, City of Albemarle (Stanly County), City of Mt. Airy (Surry County), Town of Elkin (Surry County), Town of Weddington (Union County), Wilkes County, Wilkesboro (Wilkes County). Additionally, the State completed research of community mapping needs as per its September 1999 Cooperating Technical agreement with FEMA, Assessment of Mapping Needs. Further, FEMA and Dewberry conducted research of effective Flood Insurance Study (FIS) and FIRM information and other relevant data available for each community in the FEMA Flood Mapping Archives and FEMA s Mapping Needs Update Support System database. This database contains information on community mapping needs collected over the past few years through community surveys. As part of the initial research, the State and Dewberry also evaluated post-hurricane Floyd data, such as gage information, high-water marks, and inundation mapping, obtained from FEMA, the U.S. Army Corps of Engineers, and the USGS. The purpose of this evaluation was to identify areas where actual flooding elevations and inundation limits experienced did not match the flood hazard data in the effective FIS and FIRM, thereby indicating a mapping need. Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 16

23 U.S. Geological Survey Gage Data Up-to-date analyses for 61 stream gages located in the Yadkin Basin were obtained from the USGS. The revised gage analyses were compared with effective FIRM information to determine the need for restudy of the flooding sources on which these gages are located. As part of this assessment, the 1% annual chance (100-year) discharge and 1% annual chance water-surface elevation were compared. Tables 2a and 2b outline this information for 40 stream gages in the Yadkin Basin. Table 2a. USGS Gage Information USGS Detailed Studied Flooding Sources 100-year Discharge (cfs) 100-year WSEL (ft) Gage Flooding Source Effective Gage Effective Gage Yadkin 11,900 13,210 1,218 1, Reddies 24,000 16, Yadkin 20,500 15, Elkin 11,000 9, N/A Harmon Mill 1,740 1, N/A Peters 6,175 3, N/A Salem 12,300 4, Muddy 20,500 18, South Fork M. C. 8,200 4, North Potts 3,000 2, Uwharrie 20,400 22, N/A not applicable because stream is currently not studied by detailed methods Table 2b. USGS Gage Information Approximate Zone A Flooding Sources 100-year Elevation Effective Zone 100-year Discharge (cfs) (NGVD) USGS Gage Flooding Source Effective Gage Zone A Elk 23, Zone A S. Prong Lewis Fork 3,005 N/A Zone A Roaring 33, Zone A Yadkin 39, Zone A Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 17

24 Mitchell 10, Zone A Fisher 5,490 N/A Zone A Fisher 12, Zone A Fisher 26, Zone A Yadkin 55, Zone A Ararat 33, Zone A Ararat 31, Zone A Little Yadkin 13, Zone A Yadkin 109, Zone A Forbush 3, Zone A Logan 830 N/A Zone A S. Deep 10,040 N/A Zone A Yadkin 91, Zone A Humpy Zone A McClelland 550 N/A Zone A Rocky 9, Zone A South Yadkin 16, Zone A Hunting 15, Zone A South Yadkin 24, Zone A Third Zone A Third 2, Zone A Second 10, Zone A Flat Swamp 1,600 N/A Zone A Yadkin 79, Zone A Cabin 1,260 N/A Zone A N/A not applicable because stream is currently not studied by detailed methods The results of the initial research and responses to the community questionnaires were entered into a GIS-enabled scoping database: Mapping and Engineering Needs Assessment (MENCA). This database was used to generate Initial Scoping Projects for each community; these projects were used to conduct the Initial Scoping Meetings (Step 2). Step 2 Initial Scoping Meetings The State held meetings in each county in the Yadkin Basin to present the results of the initial research to the county and its communities and to discuss their flood mapping needs. Elected officials, floodplain administrators, emergency managers, and Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 18

25 GIS staff were invited from the county and each incorporated community, including those communities that do not participate in the NFIP. The meetings were held at the County Seat or other readily accessible locations. FEMA and Dewberry staff attended to provide program and technical support during the meetings. NCEM Floodplain Management Branch staff attended the meetings to exchange contact information with community Floodplain Administrators, establish contact with non-participating communities, and distribute copies of the current North Carolina model Flood Damage Prevention Ordinance. Table 3 summarizes the initial scoping meeting dates with each community. Meeting attendance sheets are included as Appendix A. Please note that portions of some counties in the Yadkin Basin are contained in other river basins. The initial scoping meetings were conducted on a countywide basis and covered all areas of each county and community in the county irrespective of the basin. Table 3 contains a list of communities with the location and date of initial scoping meetings held for each community. Only those communities located entirely or partially within the Yadkin Basin are listed in Table 3. Table 3. Initial Scoping Meetings for the Yadkin Basin Meeting Location Meeting Date (s) Alexander County & Incorporated Communities Taylorsville October 6, 2003 Anson County & Incorporated Communities Wadesboro December 11, 2003 Cabarrus County & Incorporated Communities Concord January 7, 2004 Caldwell County & Incorporated Communities Lenoir November, 17, 2003 Davidson County & Incorporated Communities Lexington October 30, 2003 Davie County & Incorporated Communities Mocksville November 5, 2003 Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 19

26 Table 3. Initial Scoping Meetings for the Yadkin Basin (continued) Meeting Location Meeting Date (s) Iredell County & Incorporated Communities Statesville October 7, 2003 Montgomery County & Incorporated Communities Troy November 18, 2003 Randolph County & Incorporated Communities Asheboro November 17, 2003 Richmond County & Incorporated Communities Rockingham December 10, 2003 Rowan County & Incorporated Communities Salisbury January 8, 2004 Stanly County & Incorporated Communities Albemarle January 6, 2004 Stokes County & Incorporated Communities Danbury October 7, 2003 Surry County & Incorporated Communities Dobson November 6, 2003 Union County & Incorporated Communities Monroe October 8-9, 2003 Wilkes County & Incorporated Communities Wilkesboro November 18, 2003 Yadkin County Yadkinville November 6, 2003 At the initial scoping meetings, the State, NCEM Floodplain Management Branch, and Dewberry representatives met individually, or in groups, with the county and its incorporated communities representatives to: Provide a brief overview of the Floodplain Mapping Program purpose, objectives, and goals; Review the research results for each community using the Initial Scoping Package; Discuss the community s mapping needs and response to the questionnaire; and Identify available local data such as base maps, topographic data, ongoing studies, etc. In assessing the communities flood mapping needs, emphasis was placed on: Areas of future development; New or proposed crossings, encroachments, and flood controls; Historically flooded areas; Out-of-date or inadequate data on current FIRMs; Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 20

27 Existing data mismatches with contiguous communities; and Out-of-date FEMA analyses (detailed or approximate). For flooding sources identified in the meeting as having a flood mapping need, the community was asked to provide input on proposed study priorities and analysis methods. Appendix B contains tables summarizing the community-identified flood mapping needs, suggested type of study, and priorities for each community within the Yadkin Basin. Attachments 1A through 1T depict these community-identified needs and priorities. Also, as part of the initial scoping effort, CGIA met with county GIS staff to inventory the availability of local GIS data to identify potential base map data resources for the Floodplain Mapping Program. Information collected from the survey form was entered into MENCA for each Phase II county. Step 3 Draft Basin Plan Based on the results of the Initial Scoping Meetings, the State synthesized the research and the community input. These results were used to develop the Draft Basin Plan for developing updated flood hazard data for the basin and for producing statewide DFIRM panels for the affected counties and communities within the Yadkin Basin. Section IV of the Draft Basin Plan included a list of flooding sources to be updated within the basin, including the technical method of update (detailed, limited detailed, or redelineation) and reach limits and stream miles to be updated. Section IV also included a comprehensive list of counties for which statewide DFIRM panels will be produced including digital base map source to be used and proposed DFIRM paneling and tiling scheme. Lastly, Section IV also included a projected schedule for completing the basin studies and statewide preliminary DFIRMs. Step 4 Final Scoping Meetings The Draft Yadkin Basin Plan was sent to affected counties and communities and posted on the State s website in November Subsequently, the State held final scoping meetings for the Yadkin Basin counties and communities. These meetings were held on January 17 and 18, 2006 at the Stanly Agri-Civic Center, and on January 19 and 20, 2006 at the Yadkin Center of Surry College to review the information in the Draft Basin Plan within the Yadkin Basin communities. At the meetings, representatives from the NCFMP summarized the results of the Yadkin Basin scoping process as represented by the Draft Basin Plan. Meeting time was reserved for community and county representatives to meet individually with NCFMP representatives to discuss the studies proposed for flooding sources within their jurisdictions. Comments received at the meetings were reviewed, prioritized, and incorporated into the Final Basin Plan in accordance with the level of funding available. Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 21

28 The communities Chief Elected Officer, floodplain administrators, planners, Engineers, GIS staff, building and zoning officials were invited from each county and incorporated community in the basin to attend the Final Scoping Meetings. The objective of the final scoping meeting is for the State to overview the Draft Basin Plan, including the proposed scope, schedule for the project, and provide an opportunity for additional county and community input or suggested corrections and/or changes to the Draft Basin Plan. Individual meetings with each county were scheduled for community leaders to meet with representatives from the State and Dewberry. This Final Basin Plan summarizes the comments and/or feedback received during the Final Scoping Meetings and includes the Final Scoping Meeting Attendance Sheet(s) in Appendix C. Step 5 Final Basin Plan After the Final Scoping Meetings were held, the Draft Basin Plan was revised, as necessary, to produce a Final Basin Plan. This Final Basin Plan contains specific information regarding comments that were received and how the Draft Basin Plan was revised and why. The Final Basin Plan is posted on the State website, with a description and explanation of any changes made from the Draft Basin Plan. Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 22

29 IV. ELEVATION AND FLOOD DATA DEVELOPMENT AND DIGITAL FIRM PRODUCTION FOR THE YADKIN RIVER BASIN The State s flood mapping contractor will develop digital elevation data, conduct engineering flood hazard analyses, and prepare floodplain delineations for the flooding sources in the Yadkin Basin and produce statewide preliminary DFIRMs for the affected communities within the Yadkin Basin. Figure 6 shows how the base map, topographic data, and flood data will be used to build a DFIRM. Each component is discussed further in the following sections. + + Base Topography Flood Data = Digital FIRM Figure 6. Components of a Digital FIRM Base Map Locally produced digital orthophotography will be used as the base map for statewide DFIRM production, provided that it meets FEMA s base map standards. If local imagery is not available, the U.S. Geological Survey (USGS) Digital Orthophoto Quadrangles (DOQs), based on 1998 aerial photography, will be used. The base maps will be supplemented with stream and river centerlines, shoreline, political boundaries, and road name data from other sources; this may include locally available GIS data. The specific local GIS data to be used to supplement the DOQs will be determined on completion and assessment of the CGIA s GIS surveys as discussed in Section III of this Final Basin Plan. Topographic Data Watershed Concepts, under contract with the State, acquired digital topographic data of the Yadkin Basin using airborne Light Detection and Ranging (LIDAR). This LIDAR data was acquired during the Winter flying season. The topographic data satisfies a vertical root-mean-square error (RMSE) accuracy standard of ±25 cm (±0.8) feet accuracy at the 95% confidence limit (or roughly equivalent to a 2.2 foot contour interval map) in floodplain areas. All elevations are Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 23

30 referenced to the NAVD 88 and reflect orthometric heights. Variably spaced, bare-earth digital topographic data in ASCII point file format is combined with imagery (either flown concurrently with the LIDAR data or using existing digital orthophotos) to establish a Triangulated Irregular Network (TIN) to include selected breaklines used for hydraulic modeling. Furthermore, uniformly spaced Digital Elevation Models (DEMs), with 20 ft. x 20 ft. or 50 ft. x 50 ft. post spacing, are generated in multiple file formats. These topographic data will be primarily used for floodplain modeling and mapping for counties and communities in the Yadkin Basin (described below). However, the data will also be useful for other State and county engineering and planning applications using ARC/INFO and other GIS software and will be available through the State s online Information Management System described earlier in this plan. This data has been available online since the fall of Flood Hazard Data In developing flood hazard data for each of the flooding sources in the Yadkin Basin the State s Flood Mapping Contractor will utilize one of four options available. These are described below. All flood elevations will be referenced to the NAVD 88. All analyses and mapping will comply with FEMA s regulations, guidelines, and specifications for NFIP mapping. 1. Detailed Study ine This method entails using the TINs, supplements them with field surveys for channel bathymetry, bridge/culvert opening geometry, and channel and floodplain characteristics, to conduct fully detailed hydrologic and hydraulic analyses and floodplain mapping. This will include analyses of the 10%, 2%, 1%, and 0.2% annual chance flood peak discharges, water-surface elevations, profiles, and determination of a floodway. ine areas studied in detail will be designated as Zone AE on the updated DFIRMs. Flood profiles and base flood elevations will be referenced to NAVD 88. Table 4 summarizes the riverine flooding sources and reaches descriptions within the Yadkin Basin that will be studied using detailed methods. The estimated number of hydraulic structures is an approximation of the number of culverts, bridges, dams, and weirs along the reach to be studied in detail. These estimates were made based on the number of major road crossings using CGIA data and from the flood profiles in the current FIS report. Attachments 2A through 2T depict the specific reaches to be studied in detail. Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 24

31 Table 4. Summary of ine Flooding Sources to be Studied in Detail Flooding Source Downstream Limit Upstream Limit Anson County Brown At the confluence with Pinch Gut At the railroad Anson County Ledbetter Branch Approximately 1.85 miles At the confluence with upstream of the confluence Brown with Brown Anson County; Town of Polkton Anson and Richmond Counties Little Brown At the confluence with Brown At the confluence of Leggett Branch Pee Dee At the confluence with Pee At the confluence with Pee Dee Dee Trib 8 Trib At the confluence with Anson County Pinch Gut At the railroad Brown Anson and Stanly Counties Rocky At the confluence with Pee At the Anson / Union County Dee boundary Unnamed Approximately 0.62 mile At the confluence with Anson County Tributary to upstream of the confluence Rocky Rocky with Rocky Approximately 60 feet Cabarrus At the Cabarrus/Rowan/Iredell Coddle upstream of NC County County boundary (Davidson Highway) Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 25

32 Table 4. Summary of ine Flooding Sources to be Studied in Detail (continued) Cabarrus County; Town of Harrisburg Cabarrus County Cabarrus/ Stanly Counties Cabarrus County Town of Harrisburg Davidson County Davidson County Davidson County Flooding Source Downstream Limit Upstream Limit Mallard At the confluence with Rocky At the Cabarrus/Mecklenburg County boundary Reedy Tributary 1 Rocky (downstream) Rocky (upstream) At the confluence with Reedy At the Union/Cabarrus/Stanly County boundary Approximately miles downstream of East Rocky At the Cabarrus/Mecklenburg County boundary Approximately 160 feet downstream of SR 1114 (Garmon Mill ) At the Mecklenburg/Iredell County boundary Morris Branch Approximately 130 feet At the confluence with Rocky downstream of Patrician Avenue Fryes Approximately 400 feet At the confluence with upstream of Payne (SR Muddy 1505) Miller Approximately 200 feet At the confluence with upstream of SR 1510 (North Muddy Payne ) Hamby Trib 7 At the confluence of Hamby At East Holly Grove Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 26

33 Davidson County Davidson County; City of Thomasville Table 4. Summary of ine Flooding Sources to be Studied in Detail (continued) Flooding Source Downstream Limit Upstream Limit Hanks Branch At the confluence of At the upstream end of US Huntsfork 29/ Jimmys (Hambys Tributary) Approximately 1,000 feet downstream of Upper Lake At the confluence with Carter Just upstream of the railroad at Howard Street Davie County Smith Approximately 1,150 feet upstream of Interstate Davie and Forsyth Counties Forsyth County Forsyth County; Village of Clemmons; Town of Lewisville Forsyth County Forsyth County Yadkin Approximately 1,700 feet Approximately 560 feet upstream downstream of Railroad of Interstate Bashavia Just downstream of Just downstream of Balsom Kilmurry Hill Blanket At the confluence with Approximately 0.97 mile Yadkin upstream of Highway Fries Approximately 1.4 miles Just downstream of Reynolda upstream of the confluence with Yadkin Fries Trib 4 At the confluence with Fries Approximately 100 feet upstream of Waller Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 27

34 Table 4. Summary of ine Flooding Sources to be Studied in Detail (continued) Forsyth County Forsyth County; Village of Clemmons Forsyth County; Village of Tobaccoville Forsyth County; Village of Tobaccoville Forsyth County Forsyth County Forsyth County Flooding Source Downstream Limit Upstream Limit Approximately 1,130 feet Just downstream of Johnson upstream of Tanglebrook Middlebrook Drive Trail Johnson Trib 6 Mill Number 3 Mill Number 3 Trib 1 At the confluence with Johnson Approximately 0.9 mile upstream of Bowens Approximately 0.4 mile downstream of Tobaccoville Approximately 230 feet downstream of Clemmons Approximately 0.4 mile downstream of Tobaccoville Approximately 800 feet upstream of Tobaccoville Muddy At Interstate 40 crossing At Peace Haven Old Richmond Approximately 650 feet At Donnaha downstream of SR 1612 Approximately 1,480 feet Approximately 1.6 miles Reynolds upstream of Fairhaven upstream of Fairhaven Final Basin Plan Yadkin Basin Date: November 8, 2007 Page 28