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Tropical Storm Irene 10 years later

Date: September 02, 2021

Ten years ago, Tropical Storm Irene dropped five to seven inches of rain in parts of New Hampshire on August 28, 2011. Irene especially impacted New Hampshire’s mountainous terrain areas. It is time to look at the progress NHDES has made since 2011 in working to prepare for, and respond to, these types of events in the future, which is particulary relevant considering the recent near miss by Hurricane Henri. The rains from Irene overwhelmed the state’s rivers and streams, and the force of flows in the state’s steeper terrain led to miles of streambank erosion, clogged and washed out culverts, and in some cases, homes left on the verge of falling into rivers. The effects were made worse by already saturated ground from earlier rains in July and August. For many in the North Country, the images of Irene will remain etched in memory for years to come. The need to address the aftermath of Irene led to a series of long-term changes in the business processes of NHDES as to how we address major flood events, and to keep those processes alive.

In addition to damage to bridges and homes, the raw streambanks were ripe for further erosion in higher flows, increasing the risks from flooding. The scouring of streambeds created habitat impacts. All of this created a stream stabilization permitting and restoration workload that had to be closely coordinated across multiple state and federal programs to ensure that stream recovery protected property and the environment, while also minimizing future flood risks. To achieve this, in the weeks after Irene, NHDES created the Post-Irene River Response Team. This team, incorporating multiple state agencies, coordinated river recovery activities, rolling up its sleeves to help communities and citizens recover, while working together to reduce future risk and restore the environment. This team lives on today as the New Hampshire Silver Jackets, led by NHDES.

Buoyed by the lessons learned from Irene, plus smaller, but no less impactful flood events in the mid-2010s involving programs across NHDES, the agency improved in a variety of areas. All were designed to enhance NHDES’ service to New Hampshire during flooding. These have included:

  • Creation of an internal Emergency and Flood Response Group to coordinate mission-critical staff response during and after a major flood.
  • Increased emphasis on assessing road (i.e., culverts) and water (i.e., stormwater, drinking water facilities) infrastructure at greatest risk for impacts during future flooding, through increased partnerships with communities.
  • Conducting agency-wide exercises, facilitated in partnership with New Hampshire Homeland Security and Emergency Management, to improve staff response, recovery and integration – one has been completed, with future potential for a second.
  • Increased cross-agency communication and data sharing has supported greater knowledge of where highest flood risks are statewide.
  • Increased collaboration with state and federal agencies responsible for flood-related concerns, and with communities, which has been greatly expanded through the efforts of the Silver Jackets.

This year, New Hampshire was reminded once again that our state’s infrastructure remains vulnerable to the impacts from flood events. One example is road culverts. Areas of southwest New Hampshire received a staggering 19 inches of rain in total for the month of July. Instances where over seven inches occurred in a single evening washed away roads and caused numerous culverts to fail. Since 2009, multiple state agencies, led by NHDES, have been conducting culvert assessments in New Hampshire, with the goal to complete assessment of every culvert by 2026. The purpose of this work is to identify those culverts at risk for failure in the future to help prioritize replacing those that are at greatest risk for failure in a flood. Based on this work, of the 10,407 culverts that have been assessed to date, 23% are estimated to not be able to pass a two-year flow, while the same percentage are rated as either fully or mostly incompatible with stream processes; thus, posing failure risks. While NHDES has been working to adjust its practice to better accommodate flood mitigation, we strongly encourage communities to take a close look at their own infrastructure, such as culverts, to ensure they are as ready as can be to handle the next large storm that comes our way.

NHDES and New Hampshire itself have both come a long way in how we address flooding since Tropical Storm Irene. However, much work remains to be done. NHDES stands ready to continue to improve upon its work on flooding, and to work together with communities through continued provision of technical assistance to do so, and protect public safety and the environment.