How the USGS Tracks Floods, Droughts, Erosion and Landslides in New England

The U.S. Geological Survey runs many water-related natural hazard programmes in New England, with other agencies, to help lessen the harm floods, droughts, erosion and landslides do.

Damage along U.S. Route 4 in Mendon, Vermont, from Mendon Brook's floodwaters during Tropical Storm Irene, August 2011. Photograph by the USGS.

Erosion and landslides

• River erosion. Erosion and sediment carried by rivers can damage buildings, bridges, dams and roads, degrade habitats, threaten water supplies and carry chemicals. Storm runoff moves large amounts of suspended and bed sediment, by scouring streambeds and banks and around structures, and by washing in from the land. With the Federal Emergency Management Agency (FEMA) and New Hampshire's Department of Environmental Services, the USGS studied sediment moved by the Suncook River at Epsom, New Hampshire, after the river broke through its banks in a 2006 flood.
• Channel size. The USGS has developed equations to estimate the bankfull width, mean depth, cross-sectional area and discharge of streams in Massachusetts and Maine.
• Landslides occur in all 50 states, causing on average $1 to 2 billion in damage and more than 25 deaths a year. Tropical Storm Irene set off several in Massachusetts, New Hampshire and Vermont on August 28, 2011. The USGS Landslide Hazards Program works to understand landslide hazards and reduce repeated losses, and the National Cooperative Geologic Mapping Program maps past and recent slides.

Floods

Flooding is New England's most frequent and costly natural disaster. After FEMA disaster declarations the USGS has recorded flood heights with high-water marks, modelled streamflows and recurrence intervals, mapped the extent of flooding, and given communities information for rebuilding, publishing flood reports across New England after record rain from storms in 2005, 2006 and 2010 and Tropical Storm Irene in 2011.

A flooded bridge on the St. John River in Maine. The 2008 flood was the highest flow measured at the USGS gauge at Fort Kent, in a record going back to the 1920s. Photograph by the USGS.

Flood inundation maps overlay current and forecast flooding on detailed aerial photographs, giving emergency managers what they need to order evacuations and road closures, declare disasters and plan recovery. They can be made for any stretch of river with a National Weather Service forecast gauge, lidar and a hydraulic model, and about 55 percent of USGS streamgauges nationwide are also forecast gauges. In 2015 the USGS and FEMA mapped parts of the Hoosic, Deerfield, North and Green Rivers in northwestern Massachusetts and the Winooski River in central Vermont. All USGS inundation maps are gathered in the online Flood Inundation Mapper.

Droughts

Floods are brief; droughts can last months or years. In New England they can dry up private wells, limit withdrawals of surface and ground water for towns and businesses, harm aquatic habitat, and cause severe water-quality problems below pollution sources. The USGS analyses streamgauge and well data for statistics on low flows and groundwater levels in drought, which states use to issue drought warnings, plan and share water, and protect fish and wildlife.

Monitoring networks

• Streamflow: more than 400 streamgauges, reporting in real time by mobile phone and satellite so emergency agencies can watch flows, dams and flood-control systems and forecast flood levels and timing.
• Groundwater: 57 wells reporting hourly in near real time, and 180 measured monthly, on the New England groundwater network.
• Tides and storm surge: 10 permanent tide gauges, plus 245 mounts for temporary storm-surge sensors and 17 rapid-deployment gauges along the coast, installed in the hours and days before a storm. The Hurricane Storm Tide Sensor Map shows data collected since 2005; in 2015 the USGS reported on the surge from a major nor'easter.
• Snow and ice: in late winter and early spring, when snowmelt flooding is most likely, the USGS and partners measure snow depth and water content, which go to the National Weather Service for flood outlooks and forecast models. The USGS also watches for dangerous river ice in northern New England with live cameras at vulnerable sites, such as the Kennebec River at Augusta, Maine, which the Army Corps of Engineers and the Weather Service use to judge the risk of ice jams.

Tools

• Lidar, through the 3D Elevation Program, provides elevation detailed enough for 2- to 4-foot contours, available through The National Map; agencies can arrange new lidar flights with the USGS where existing data fall short.
• StreamStats, built on equations developed with many agencies, lets anyone outline a basin online and estimate flow statistics at ungauged sites across New England: peak flows for 2- to 500-year recurrence intervals, low flows, monthly and annual flows, the chance a stream flows year-round, and bankfull discharge.

Sources

• Pamela J. Lombard, Flood- and Drought-Related Natural Hazards Activities of the U.S. Geological Survey in New England, USGS Fact Sheet 2016–3008, March 2016. https://doi.org/10.3133/fs20163008
• The photographs are taken from the fact sheet's PDF.