Iowa’s River Restoration Toolbox Level 1 / Base Training Module # 13 Understanding the Key Instability Drivers to Inform Design/Decision Matrix Iowa’s River Restoration Toolbox Level 1 / Base Training

Key Design Parameters

Key Drivers Floodplain Access Bank Height Ratio Entrenchment Bankfull Properties Area Discharge Width Depth Channel Evolution Stage Dominant BEHI Buffer Width

Bank Height Ratio (BHR) BHR= LBH/Dbkf Lowest Bank Height (LBH) Bankfull Depth (Dbkf)

Geomorphic Floodplain Entrenched Channel Bankfull Depth Geomorphic Floodplain Bankfull Width

Bankfull Geometry

Channel Evolution Models Simon’s Modification of Schumm’s Model

Shear Stresses in Streams  Discharge Return Interval Shear Stress Natural Stream Channelized Stream 2-Year Storm 100-Year Storm D100 D2 Channelized Stream 100-Year Storm D100 2-Year Storm D2 Natural Stream

BEHI Study Bank Height Bankfull Height Root Depth Bank Angle Surface Protection Bank Material Adjustment Stratification Adjustment Bank Length Reach Length

Heading for Text Over a Photo Riparian Buffer

Additional Key Drivers Pattern/Geometry Radius of Curvature Meander Width Ratio Pool to Pool Spacing Width to Depth Ratio Channel Length Channel Slope Stream Type Presence of Headcuts/Bed Stability Geomorphic Region/Geology Sediment Supply/Bed Materials Constraints

Pattern/Geometry Wbkf = Bankfull Width Lm = Meander Wavelength Wblt = Belt Width Am = Amplitude Lm = Meander Wavelength Rc = Radius of Curvature

Channel Slope

BKF Width / Mean BKF Depth Stream Type Classification A B C E DA D F G Entrenchment ratio* <1.4 1.4 -2.2 >2.2 >4.0 n/a FP width / BKF Width BKF Width / Mean BKF Depth W / D ratio* <12 >12 <40 >40 Typical sinuosity 1 -1.2 >1.2 >1.5 Not predictive Well-defined point bars Veg. islands Heavy veg. Both banks erode in wide dirt canyon Confined, u-shaped valley Often bedrock / log controlled Visual Cues Gully in soft materials Sed. islands Typical slope .04-.099 .02-.039 <.02 <.005 <.04 Typical stability Usually Stable Likely Unstable Classifications from Rosgen, 1996

Headcuts/Bed Stability Caused by Excess Shear Stress Often Triggered by Downstream Straightening of Channel Will Propagate Upstream Increases Channel Entrenchment

Sediment Supply/Bed Materials

Constraints

Key Design Parameters

Functional Status

The Assessment Process 8. Submit final analysis for review 7. Perform analysis of appropriate practices/techniques 6. Receive adjusted recommendations based on design intent 5. Update Key Drivers for design based on step 4 4. Make initial decisions that will affect the project design 3. Receive initial assessment based on site conditions 2. Fill out data collection Excel workbook 1. Assess project site conditions

Purpose of Decision Matrix Documentation of intuitive knowledge used in stream restoration design Establish logic used to determine appropriate practices & techniques Note that there are multiple “right answers”

Channel Evolution Models Simon’s Modification of Schumm’s Model

Decision Matrix – Channel Evolution

Bank Height Ratio (BHR) BHR= LBH/Dbkf Lowest Bank Height (LBH) Bankfull Depth (Dbkf)

Decision Matrix – Bank Height Ratio

Decision Matrix - Slope

Decision Matrix – Bankfull Width

Design Assessment Tab

Technique Ranking

Iowa’s River Restoration Toolbox Level 1 / Base Training Module # 13 Understanding the Key Instability Drivers to Inform Design/Decision Matrix Iowa’s River Restoration Toolbox Level 1 / Base Training