Stream channels in the Delaware Estuary Watershed
Past history, current status, and future challengesShandor J. Szalay
Natural Resources Scientist AKRF
• 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?
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
Deforestation
Increase in sediment supply Channel aggradation
Agriculture
Further Increase in sediment supply Channel aggradationFloodplain accretion
Mill dam construction
Beaver damremoval
Ditching and Straightening
Conservation practices Old field regeneration Channel cutting
Urbanization – construction phaseHigh sediment loading Channel aggradation
Urbanization – post constructionIncreased flows Decreased sediment loadsStream incision
Dredging
Channelization
Dams and impoundments
Riparian vegetation removal
Bridges and culverts
Piping and burial
Infrastructure DamageIncreased Sediment Loading
Aesthetics
In-stream Habitat
Flooding Water quality
• 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?
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
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
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
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
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
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
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
Thanks for listening.Questions? www.akrf.com