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| Publications—Open-File Report |
By Robert H. Flynn
U.S. Geological Survey Open-File Report 2006-1127
AVAILABLE ONLINE ONLY
The body of the report is available in PDF Format ( 4,8 MB)
This report was prepared by the U.S. Geological Survey (USGS) New Hampshire/VermontWater Science Center for scoping of flood-hazard mapping needs for Merrimack 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 floodplain 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 Merrimack 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 Merrimack County.
The average age of the FEMA floodplain maps in Merrimack County, New Hampshire is 18.5 years. Most of these studies were computed in the late 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 floodplains have changed as a result. In addition, as development has occurred, peak flooding has increased downstream of the development from increased flows across impervious surfaces. Therefore, many of the older studies may not depict current conditions nor accurately estimate risk in terms of flood heights.
Merrimack County gained 9,317 residents between 2000 and 2004. This represents a growth of 6.8 percent compared to 5.2 percent for the state as a whole. Merrimack County ranks third (from highest to lowest) out of New Hampshire’s 10 counties in terms of rate of population increase. Since 1990, Merrimack County has gained 25,537 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 Merrimack 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 Merrimack 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 Merrimack County.
Section 1. Introduction
Background
Scope of Work
Section 2. Data Collected from Merrimack 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 Merrimack County
Mapping Needs Update Support System
Mapping Needs in Merrimack County, New Hampshire
State and Community Meetings .
Meeting with New Hampshire Office of Emergency Management (NHOEM) and Scoping Team Members
Merrimack 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 Community - Dunbarton
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 Merrimack County
Appendix B. Mapping Needs Update Support System (MNUSS) Needs Assessment Reports
Appendix C. State and Community Meetings
Appendix D. Prioritized Flooding Sources
1. Merrimack County, New Hampshire, location map
2. Merrimack County, New Hampshire, hydrography and FEMA Digital Flood Insurance Rate Map (DFIRM) data
3. Letter of Map Change (LOMC) and community location map in Merrimack County, New Hampshire
4. Merrimack County, New Hampshire, stream final coverage
1. Merrimack County, New Hampshire, communities and populations
2. FIS and FIRM information for communities
3. Summary of specific mapping needs in Merrimack County, New Hampshire
4. FIRM horizontal accuracy
5. National standard for spatial data accuracy
6. Currently available high resolution orthophotography for Merrimack 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
(603) 226-7807
or visit our Web site at: http://nh.water.usgs.gov
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