Flood Hazard Areas

Floodplains are areas adjacent to streams, lakes, and ponds that become inundated during heavy precipitation or snowmelt.  Floodplains perform a role similar to wetlands in that they trap sediment; promote groundwater infiltration; and reduce downstream flooding, erosion, and property damage.  Unlike wetlands they are often suitable for farming since flooding leaves behind nutrient rich soil, but is not inundated as frequently as wetlands.  Left in their natural state floodplains help prevent erosion and can serve as travel corridors for wildlife.  As climate changes preserving floodplains is of critical importance to protect this wildlife habitat and reduce flooding further downstream.

The area most prone to flooding in Eaton is the girl’s camp just north of Crystal Lake and nearby portions of Route 153 and the Brownfield Road.  Further east the Brownfield Road follows Snow Brook in several places that create the potential for flooding during extreme storm events. Route 153 south of Eaton Center also has several places with the potential for flooding. Low lying areas around Conway Lake are also susceptible.

Flood hazard areas on the map below have a 1% annual chance of flooding based on data from the Federal Emergency Management Agency (FEMA).  FEMA classifies these as special flood hazard areas that require the mandatory purchase of flood insurance.  It is worth noting that these maps may understate which areas are in danger of flooding given that “100-year” floods are happening more and more frequently due to the effects of climate change.

Lakes, ponds, and major streams are also included on the map.  Clicking on the lakes or ponds will provide information about their area, depth, and volume.  For streams the information is about average water flow over the course of a year.  Flooding will occur when flow is greater than the normal capacity of the water body.  Wetlands can help reduce water flow and flooding.

Culverts play a big role in helping to reduce the possibility of damage due to flooding. The New Hampshire Stream Crossing Initiative is a multi-agency group that collaboratively works to align resources and improve management of stream crossing infrastructure across the state. The collaborative was formed by several New Hampshire Departments including Environmental Services, Transportation, Fish and Game, and the Department of Safety’s Emergency Management group.

The Stream Crossing Initiative has studied culverts in Eaton and rated them for geomorphic compatibility and their ability to handle large storm events. Geomorphic compatibility is a measure of how well a culvert is sized and aligned with a stream to effectively transport water and sediment downstream without altering the velocity of stream flow. Poor compatibility can lead to culvert failure and road damage.

The map below shows culverts that were studied by the initiative. Surveyed culverts are shown as small colored circles. Ones ranging from yellow to red are vulnerable to flooding. Red indicates vulnerability to flooding in even a 2-year storm. Yellow indicates flooding for a 100-year storm. Shades of orange represent possible flooding for 10-year, 25-year, or 50-year storms. Green circles are for culverts that seem adequate for even a 100-year storm. Black ones are for culverts that were not rated. Clicking on a culvert will provide information about its location, the date it was evaluated, the road it is on, the type of crossing it is, its suitability for aquatic organisms, its vulnerability for various levels of storm, and its geomorphic compatibility.

Lakes, ponds, perennial and intermittent streams, and marshes in Eaton are also shown. The Town boundary is in red.  Surface waters are in various shades of blue.  Clicking on a surface water will display its type and name if it is known.  If it is a lake, pond, or marsh its acreage will be displayed.  Flow data will be displayed for streams, lakes, and ponds if it is known.