Stream Channels in the Delaware Estuary Watershed · Natural Resources Scientist AKRF • How have...
Transcript of Stream Channels in the Delaware Estuary Watershed · Natural Resources Scientist AKRF • How have...
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Stream channels in the Delaware Estuary Watershed
Past history, current status, and future challengesShandor J. Szalay
Natural Resources Scientist AKRF
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• How have human activities changed river channels in the Delaware Estuary?
• What are the costs and consequences of human-caused river change?
• How can we better protect river channels?
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Channel Constraints Watershed Hydrology Sediment Loading
Adjustments over time
Stable Channel Form
Channel Evolution
WatershedDisturbance
Local Disturbance
Changes to Sediment LoadingChanges to Hydrology
Changes to Channel Constraints
Unstable Channel Form
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Deforestation
Increase in sediment supply Channel aggradation
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Agriculture
Further Increase in sediment supply Channel aggradationFloodplain accretion
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Mill dam construction
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Beaver damremoval
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Ditching and Straightening
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Conservation practices Old field regeneration Channel cutting
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Urbanization – construction phaseHigh sediment loading Channel aggradation
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Urbanization – post constructionIncreased flows Decreased sediment loadsStream incision
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Dredging
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Channelization
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Dams and impoundments
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Riparian vegetation removal
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Bridges and culverts
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Piping and burial
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Infrastructure DamageIncreased Sediment Loading
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Aesthetics
In-stream Habitat
Flooding Water quality
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• What is the extent and severity of channel instability?
• What are the cumulative economic, social, and ecological costs associated with unstable stream channels?
• What are the costs of restoration? • Are restoration efforts successful? • How do we manage explicitly for stable
streams?
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Managing for Stable Streams• Landscape management
– Land consumption and conservation patterns– Stormwater management
• Channel corridor management – Bridge and culvert design – Riparian buffer requirements – Large wood management
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Sensitivity as a Management Paradigm
• Sensitivity– Vulnerability – the tendency for the fluvial
system to change form as a result of a change to boundary conditions or driving variables
– Susceptibility – the ease with which a river is able to adjust within its natural capacity for adjustment
• Resiliency – The tendency for the fluvial system to resist changes in form as a result of a change to boundary conditions or driving variables
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Geomorphic Sensitivity
• Ratio of stream power (ability to do work) to resistance (ability to resist work) defines sensitivity – Streams with immobile boundaries (bedrock, boulder
bed) are intrinsically resilient to change– Streams with high stream power are inherently more
sensitive to change all other variables equal • Streams with high sediment loading are
inherently more sensitive to change than low supply streams
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Stressor/Response RelationsLandscape Change
Watershed ResponseChange in Sediment Yield
Change in Hydrology
Soils VegetationSlope
-Type - Density - Location- Pattern
SW Management
Channel Response
Bed materialBank material Depositional historyGeologic controls VegetationSlope
Sensitivity
Planform, X Section, ProfileReaction timeRelaxation timeThreshold vs. equilibriumResponse shapeRate
Corridor ChangeVegetation removalBridges ChannelizationRevetments
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Regional Scale Understanding • Can we map/predict steam channel sensitivity
based on predictor variables?– Historical aerial photo/map series
• Planform adjustments – Depositional history reconstruction
• Location of mill deposits • Stratigraphic analysis• Tree ring analysis
– Present day channel measurements • Infer adjustments from present condition • Existing data sets • Field and remotely sensed measurements – LIDAR
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Decision Tools
• How can we build decision tools that can incorporate stream channel sensitivity into decision making? – Conceptual models– Classification systems – Predictive models (empirical, mechanistic,
ANNs) – Written guidance – GIS data products
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Policy Implications • How can the concept of sensitivity be incorporated into
policies that regulate urbanization? – Development patterns
• Limit stream crossings, valley encroachment near sensitive channels
– Zoning ordinances• Impervious cover thresholds
– Stormwater ordinances• Infiltration + peak flow requirements
– Bridge design criteria • Designs to maintain hydraulics and sediment transport• Span active adjustment zone
– Land conservation • Acquire lands within sensitive subwatersheds
– Riparian buffers • Scale width with sensitivity ratings and capacity for adjustment