fluvial erosion hazards and geomorphic assessments in new
TRANSCRIPT
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Fluvial Erosion Hazards and Geomorphic Assessments in
New Hampshire
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What is fluvial geomorphology? Fluvial = action of running water Geomorphology
Geo = Earth morph = form ology = study of
The study of how running water shapes the landforms on the Earth’s surface.
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Connecticut River – northern NH/VT line Lamprey River – southeast New Hampshire
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Fluvial erosion = the wearing away of river channel bed and banks by the action of water
Is a natural process
Typically seen at high flows (bankfull flows) or during flood events, and particularly in reaches that have been altered by human activity or recent natural events.
Fluvial Erosion
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Erosion on the ground
November 2009
March 2010
June 2010
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1979 1998
Photos courtesy of Dan Cemerelli, USFS
•Stream narrowed by culvert
•Velocity increased → erosion downstream of culvert
Erosion on the ground
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Fluvial erosion ... and its effects
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Piscataquog River Watershed
•Major flood events in New
Hampshire (20052007)
•$75.6 million total inundation
and erosion damage
•Heavy rains and repetitive rains
•New Hampshire’s highest recurring natural hazard risk
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New Hampshire Flood Damage $$$$
Since 1978
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Can we determine areas that are most susceptible to these kinds of events?
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Fluvial Erosion Hazard (FEH) and River Geomorphic Assessments
(RGA) Program
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New Hampshire’s FEH/RGA Program 2008 Upper and Lower Exeter River
Watersheds – Bear Creek Environmental
2009 Ammonoosuc – Field Geology Services Isinglass – New Hampshire Geological
Survey Middle Exeter – Bear Creek
Environmental
Late 2010 2011 Cocheco/Lamprey watersheds, southeast
New Hampshire
Beyond Piscataquog Souhegan ????
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Methods
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How can this information be used?
• Hazard mitigation plans • The geomorphic condition data will be available in a database for stream restoration activities
• Stream restoration and alteration of terrain activities • Prioritization of problematic culverts for rehabilitation or replacement
• Watershed management plans • Fluvial Erosion Hazard zoning
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Stream restoration activities • Ensure that fluvial
geomorphic processes are adequately considered in assessing the longterm sustainability of project benefits.
• Essentially, we want to make sure a proposed project or modification to a river doesn’t cause more problems down the road.
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We want to work with the river as a system!
• With some understanding of how rivers naturally work, we can try to minimize future infrastructure effects by reducing constrictions and disruptions to river process.
• Put another way – managing toward rivers that are in balance
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2008 & 2009 2009 & 2010
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Methods • Phase 1 Stream Geomorphic Assessment • Phase 2 Stream Geomorphic Assessment • Bridge and Culvert Assessment • River Corridor Plan ØStressor Maps ØDeparture Analysis ØFEH zones • Project Identification
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Major Stressors: Exeter River
• Stormwater inputs from suburban areas • Impacts to riparian buffer • Floodplain encroachment • Undersized & poorly aligned stream crossings • Relict structures • Impoundments (dams) • Agricultural impacts
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Localized stormwater outfall erosion
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Relic stream ford
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Bank failure & buffer encroachment
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Dam Impoundments ME07: Phillips Mill Dam ME07: Scribner Road Dam
Flooding & erosion problems
Altered flow regime
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Retrofit Culvert & Plant Trees
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Little River, Exeter: Land protection
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Projects to Address Stressors
• Stormwater management • Conservation and corridor easements • Remove relic structures • Replace/retrofit undersized bridges and culverts
• Streambank restoration • Streamside planting • Riparian buffer restoration and protection • Further protect floodplain and floodplain access