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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
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Module # 13Understanding the Key Instability Drivers to Inform Design/Decision Matrix Iowa’s River Restoration Toolbox Level 1 / Base Training
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 Bankfull Width Bankfull Depth Entrenched Channel
Channel Evolution Models Simon’s Modification of Schumm’s Model
100-Year Storm D100 Shear Stress = R S 2-Year Storm D2 Shear Stresses in Streams Channelized Stream Shear Stress Natural Stream Channelized Stream Discharge Return Interval 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 Wblt = Belt Width Am = Amplitude Lm = Meander Wavelength Rc = Radius of Curvature
Stream Type FP width / BKF Width BKF Width / Mean BKF Depth Well-defined point bars Veg. islands Heavy veg. Both banks erode in wide dirt canyon Confined, u-shaped valley VisualCues Gully in soft materials Often bedrock / log controlled Sed. islands 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
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
Bank Height Ratio (BHR) BHR= LBH/Dbkf Lowest Bank Height (LBH) Bankfull Depth (Dbkf)
Module # 13Understanding the Key Instability Drivers to Inform Design/Decision Matrix Iowa’s River Restoration Toolbox Level 1 / Base Training