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Publications—Open-File Report

Prepared for the Federal Emergency Management Agency, Region 1

Scoping of Flood Hazard Mapping Needs for Coos County, New Hampshire

By Robert H. Flynn


U.S. Geological Survey Open-File Report 2006-1200


AVAILABLE ONLINE ONLY

The body of the report is available in PDF Format ( 4,805 KB)

Introduction

This report was prepared by the U.S. Geological Survey (USGS) New Hampshire/VermontWater Science Center for scoping of flood-hazard mapping needs for Coos County, New Hampshire, under Federal Emergency Management Agency (FEMA) Inter-Agency agreement Number HSFE01-05X-0018. This section of the report explains the objective of the task and the purpose of the reports.

Background

FEMA is embarking on a map modernization program nationwide to:

1. Gather and develop updated data for all flood prone areas in support of flood plain management.
2. Provide maps and data in a digital format for the improvement in the efficiency and precision of the mapping program.
3. Integrate FEMA’s community and state partners into the mapping process.

One of the priorities for FEMA, Region 1, is to develop updated Digital Flood Insurance Rate Maps (DFIRMs) and Flood Insurance Studies (FIS) for Coos County, New Hampshire. The information provided in this report will be used to develop the scope for the first phase of a multiyear project that will ultimately result in the production of new DFIRMs and FIS for the communities and flooding sources in Coos County.

The average age of the FEMA flood plain maps in Coos County, New Hampshire is 20 years. Most of these studies were computed in the mid 1970s to the mid 1980s. However, in the ensuing 20–30 years, development has occurred in many of the watersheds, and the rivers and streams and their flood plains have changed with time. In addition, as development has occurred, the peak flooding has increased downstream of the development due to increased flows from impervious surfaces. Therefore, many of the older studies may not depict current conditions nor accurately estimate risk in terms of flood heights.

Coos County gained 544 residents between 2000 and 2005. This represents a growth of 1.6 percent compared to 6.0 percent for the state as a whole. Coos County ranks tenth (from highest to lowest) out of New Hampshire’s 10 counties in terms of rate of population increase. Since 1990, Coos County has lost 1,173 residents (University of New Hampshire, 2005).

Scope of Work

The following is the scope of work as defined in the FEMA/USGS Statement of Work:

Task 1: Collect data from a variety of sources including community surveys, other Federal and State Agencies, National Flood Insurance Program (NFIP) State Coordinators, Community Assistance Visits (CAVs) and FEMA archives. Lists of mapping needs will be obtained from the Mapping Needs Update Support System (MNUSS) database, community surveys, and CAVs, if available. FEMA archives will be inventoried for effective Flood Insurance Rate Maps (FIRM) panels, FIS reports, and other flood hazard data or existing study data. Best available base map information, topographic data, flood hazard data, and hydrologic and hydraulic (H&H) data will be identified and obtained. FEMA Letters of Map Change (LOMC) areas will also be identified.

Task 2: Contact communities in Coos County to notify them that FEMA and the State have selected them for a map update, and that a project scope will be developed with their input. Topics to be reviewed with the communities include (1) Purpose of the Flood Map Project (for example, the update needs that have prompted the map update); (2) The community's mapping needs; (3) The community’s available mapping, hydrologic, hydraulic, and flooding information; (4) Target schedule for completing the project; and (5) The community’s engineering, planning, and geographic information system (GIS) capabilities. When requested by the community, or when needed to obtain information on mapping needs and available information, the USGS will schedule meetings with individual communities.

Based on the collected information from Task 1 and community contacts/meetings in Task 2, the USGS will develop a Draft Project Scope for the identified mapping needs of the communities in Coos County. The following items will be addressed in the Draft Project Scope: review of available information; determine if and how the currently effective FIS data can be used in new project; identify other data needed to complete the Project and its source; and the DFIRM format. The Draft Project Scope will establish priority levels for flooding sources to be analyzed and mapped, and estimate schedules for completion of the components of flood mapping.

The USGS is to supply the FEMA Contracting Officer’s Technical Representative (COTR) with a report summarizing the following:

1. Available data and collected information on mapping needs.

2. Documentation of meetings and contacts.

3. Suitability of existing data and options for future mapping.

4. Restudy needs and priorities.

5. Recommended project scope and influences on cost.

This report provides a summary of data-collection efforts conducted for this task, as well as information on available mapping/remote sensing data. The report includes recommendations for providing needed mapping/remote sensing data to accomplish the ultimate goal of producing new DFIRMs. It also provides options for accomplishing this goal within the context of FEMA’s Cooperating Technical Partner (CTP) Program. The report begins the process of establishing restudy priorities in Coos County.

TABLE OF CONTENTS

Section 1. Introduction

Background.

Scope of Work

Section 2. Data Collected from Coos County Communities

Community Flood Insurance Studies and Flood Insurance Rate Maps

Delineation of Detailed and Approximate Study Areas

Letters of Map Change

Letters of Map Change in Coos County

Mapping Needs Update Support System

Mapping Needs in Coos County, New Hampshire

State and Community Meetings

Meeting with New Hampshire Office of Emergency Management (NHOEM) and Scoping Team Members

Coos County Community Meetings

Available Digital Mapping and Remotely Sensed Data

Data-Collection Efforts

NH GRANIT Data Sources

Community Data Resources

Stream Final Coverage Output

Section 3. Options for Future Mapping and Digital Terrain Model Preparation

Mapping Requirements

Base Map

Digital Terrain Models

Flood Insurance Risk Zones

Suitability of the Available Data

USGS of GRANIT

Community Data Resources

County Data Resources

Base Map

Digital Terrain Model

Flood Insurance Risk Zones

Mapping Options

Base Map

Digital Terrain Model

Flood Insurance Risk Zones

Section 4. Hydrologic and Hydraulic Restudy Needs and Prioritization

Mapping Needs

Prioritization Process

Prioritization Results

Non-Participating Communities

Section 5. Recommendations and Schedule

Mapping Recommendations

Mapping Options

Project Alternatives

Schedule

Selected References

Appendixes:

Appendix A. Summary of Letters of Map Change (LOMC) Data in Coos County

Appendix B. Mapping Needs Update Support System (MNUSS) Needs Assessment Reports

Appendix C. State and Community Meetings

Appendix D. Prioritized Flooding Sources

 

Figures

 

1. Coos County, New Hampshire, location map.
2. Coos County, New Hampshire, hydrography and FEMA Digital Flood Insurance Rate Map (DFIRM) data.
3. Letter of Map Change (LOMC) and community location map in Coos County, New Hampshire.
4. Coos County, New Hampshire, stream final coverage.

 

Tables

 

1. Coos County, New Hampshire, communities and populations.
2. FIS and FIRM information for communities.
3. Summary of specific mapping needs in Coos County, New Hampshire.
4. FIRM horizontal accuracy.
5. National standard for spatial data accuracy.
6. Currently available high resolution orthophotography for Coos County.
7. Estimate of costs to obtain Digital Terrain Model data (2-ft contours).
8. Community flooding source prioritization.

 


If you have Adobe® Acrobat® or Adobe® Acrobat® Reader® installed on your computer, you may view and print the PDF version of this report. Acrobat Reader, is a free download from Adobe Systems, Inc. Users with disabilities can view information concerning accessibility at access.Adobe.com .


For further information, contact:

 

Keith W. Robinson, Director

U.S. Geological Survey

New Hampshire-Vermont Water Science Center

361 Commerce Way

Pembroke, NH 03275

 

dc_nh@usgs.gov

 

(603) 226-7807

 

or visit our Web site at: http://nh.water.usgs.gov


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