AMHERST, Mass. – When planning responses to river floods, most risk managers in the United States focus on the effects of standing water, not the fast-moving torrents that can increasingly be expected to occur with climate change in regions with mountains, valleys and related land features. Now a group of geoscientists led by Christine Hatch at the University of Massachusetts Amherst report on their four-year project to update that approach by including fast-moving water in risk planning.
They write, “To our knowledge this represents the first assessment of its kind.”
With a focus on New England, but with the expectation that others across the nation will find theirs a useful model, Hatch and John Gartner at UMass Amherst, with first author Benjamin Warner of the University of New Mexico, point out that river flood management in the United States is focused on inundation – standing water – not geomorphic processes, because it has long been the primary flood risk management mechanism.
Hatch explains that inundation assumes no rapidly moving water. Fluvial geomorphic processes, on the other hand, involve both erosion due to the speed and force of moving water and sediment that the water leaves behind.
She says, “We need to set aside some space for rivers to be rivers, to let them move and meander, to let them flood and drain, to let them bring fertile soil to our floodplains and carry fresh water and aquatic life from headwaters to sea. But we also live and drive and work alongside rivers, and have developed our communities beside them.”
Further, “If we can bring awareness of river processes into our flood-risk management in a scientifically robust way, our rivers will be healthier and we can significantly reduce the cost of flood-associated damage. As changing climate brings us increasingly intense storms, we hope these tools will prepare us for healthy rivers and communities for generations.”
In the U.S., the authors say, just nine states have explored managing risks of fast-moving flood waters, and only Vermont and Washington have developed and now use legally binding geomorphic-based flood risk management based on mapping river corridors and assessing land forms. They add, “Massachusetts, having incurred substantial damages from landslides, bank failures, bed incision and sedimentation in recent years, has initiated a program to examine the inclusion of geomorphic processes into flood risk management.”
Over four years beginning in 2012, Hatch and colleagues held a series of workshops on the UMass Amherst campus with stakeholders, the Fluvial Geomorphology Task Force, which allowed them to produce a needs assessment identifying factors that should be included in developing a fluvial geomorphology assessment program for Massachusetts.
The task force’s steering committee analyzed data from such meeting products as transcripts, notes, pictures and breakout group summaries, and bundled information on similar topics together to meet goals in two broad areas: technical and policy.
Technical goals include such factors as river mapping, identifying areas adjacent to rivers where geomorphic processes such as sedimentation, bank erosion and landslides are likely to occur as a result of river flooding, identifying special hazard zones and identifying areas where erosion might take place, for example.
Policy goals, the authors say, should include geomorphic assessments that offer a process to help land use planners understand risks of development near rivers and the value of discouraging new development or providing incentives for land conservation and buy-outs in risk-prone riverfront areas, for example. These policy-oriented assessments “must incorporate multiple types and severities of geomorphic processes to accommodate existing and future conditions; within which proposed development may be subject to site-specific process modeling,” they note.
Overall, Hatch and task force members agreed that challenges include establishing a technically sound, science-based and transparent approach to identify the boundaries of river-driven or fluvial geomorphic processes, determining areas with different risk levels and different hazards, and developing protocols for documenting and mapping at three levels of detail from “relatively fast broad-scale GIS-based mapping over large areas (done from the desktop) to detailed, parcel-specific assessment (requiring measurements in the field).”
This work was supported by Massachusetts Fluvial Geomorphology Task Force members’ institutions and the USDA National Institute of Food and Agriculture’s Water Quality Grant Program.