Scoping of flood hazard mapping needs for Carroll County, New Hampshire

This report was prepared by the U.S. Geological Survey (USGS) New Hampshire/Vermont Water Science Center for scoping of flood-hazard mapping needs for Carroll County, New Hampshire, under Federal Emergency Management Agency (FEMA) Inter-Agency agreement Number HSFE01-05X-0018. 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 Carroll 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 Carroll County. The average age of the FEMA flood plain maps in Carroll County, New Hampshire is 18 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 flood plains 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. Carroll County gained 3,773 residents between 2000 and 2005. This represents a growth of 8.6 percent compared to 6.0 percent for the state as a whole. Carroll County ranks second (from highest to lowest) out of New Hampshire's 10 counties in terms of rate of population increase. Since 1990, Carroll County has gained 12,029 residents (University of New Hampshire, 2006).