Fluvial Erosion Hazards and Geomorphic Assessments in New Hampshire - - PowerPoint PPT Presentation

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Fluvial Erosion Hazards and Geomorphic Assessments in New Hampshire - - PowerPoint PPT Presentation

Nov 18, 2022 683 likes •1.03k views

Fluvial Erosion Hazards and Geomorphic Assessments in New Hampshire 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

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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

  • logy = 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

  • f 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

Stressor Maps Departure Analysis FEH 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

  • utfall 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