stream channels in the delaware estuary watershed · natural resources scientist akrf • how have...

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