Module 16 Restoring Functions to Streams Through Design

Module # 16 Restoring Functions to Streams Through Design Iowa’s River Restoration Toolbox Level 1 / Base Training

Indicators of Geomorphic Instability • Incision/Bedcutting • Channel Filling • Entrenchment/High Streambanks • Lateral Migration • Over Widening • Lack of Habitat • Eroded Banks • Slope Instability

Incision/Bedcutting • Caused by Excess Shear Stress • Often Triggered by Downstream Straightening of Channel • Will Propagate Upstream • Increases Channel Entrenchment

Grade Control - Constructed Riffle

Grade Control – Vane Structures

Grade Control – Rock & Log Riffle

Channel Filling/Aggradation • Caused by: • Excess Sediment Supply • Low Shear Stress • High Width/Depth Ratio • Can Lead to Lateral Migration • Reduces Capacity of Culverts

Geomorphic Channel Design Multi -Stage Channel

Entrenchment/High Streambanks • Very Significant Indicator of Instability • Results in High Shear Stress • Often Early Stage of Channel Evolution • Results in Excess Sediment Supply

Bankfull Bench

Toe Wood Protection

Fabric Encapsulated Soil Lifts

Lateral Migration • Often Due to: • Slope Adjustment • High Sediment Supply • Downstream Channel Straightening • Often Triggers Bank Erosion • Belt Width Considerations

Geomorphic Channel Design

Over-Widened Streams • Cannot Effectively Transport Sediment • Can be High Maintenance Areas • Poor Water Quality/Habitat • Elevated Water Temperatures • Bedrock Bottom Streams Often Overwidened

Geomorphic Channel Design

J-Hook/Straight Vane

Module # 16 Restoring Functions to Streams Through Design Iowa’s River Restoration Toolbox Level 1 / Base Training