Module # 17 Overview of Geomorphic Channel Design Practice Iowa’s River Restoration Toolbox Level 1 / Base Training

Geomorphic Channel Design Process by which new or re-constructed stream channels and their associated floodplain riparian systems are designed to be naturally functional, stable, healthy, productive, and sustainable.

Soil Bioengineering The use of living and non-living materials to provide soil reinforcement and prevent erosion

Comparison of Geomorphic Channel Design and Soil Bioengineering Bankfull Discharge Bankfull Depth Channel Design Design of Channel Form Channel Form Not Altered Stream System and Processes Disturbed Section Channel Dimensions Critical Vegetation Critical Design Parameters Vary Typically Constant In-Stream Construction Streambank Construction Sediment Transport Slope Stability Bioengineering

Geomorphic Channel Design Components Analog Empirical Analytical

Form Vs Process Not Mutually Exclusive Process Drives Form Must Consider Time Scale as Part of Design Process Ultimately Must Design and Build a Stream Form Can Create Backlash Towards the Profession

National Engineering Handbook Primary Reference Stream Restoration Design National Engineering Handbook Part 654 Released, August 2007 (vs. 031908) Chapter 11: Geomorphic Approach for Natural Channel Design USDA NRCS, Stream Restoration Design Handbook, 2007. U.S. Department of Agriculture Natural Resources Conservation Service

Phases of Geomorphic Channel Design (NCD Approach) Define Restoration Objectives Develop Regional & Localized Specific Geomorphic and Hydraulic Data Conduct Watershed/River Assessment Assess Potential for Passive Restoration (i.e. Land Use Changes) Initiate Geomorphic Channel Design w/ Analytical Testing of Hydraulics & Sediment Transport Design Stabilization/Enhancement Measures Implement Proposed Design Design & Implement Monitoring & Maintenance Plan

Define Restoration Objectives Flooding Issues Streambank Stability Reduction in Sediment Supply Improved Fish Habitat & Biological Diversity Self Maintenance /Natural System Aesthetics Mitigation Needs

Develop Regional & Localized Specific Geomorphic and Hydraulic Data Identify Valley Type & Stream Type Obtain Reference Reach Data for Intended Stream Type Compare Impacted Reach and Reference Reach Data to Regional Curves Convert Reference Reach Data to Dimensionless Ratios Calculate Bankfull Discharge & Velocity

Locating Reference Reaches Same Stream as Impacted Reach Same General Watershed Review Gazetteer Maps for Similar Pattern Streams as Intended Design Be Prepared to Drive to Numerous Sites Reference Reaches are Typically not Found at Bridges and Culverts!! Look upstream and downstream of impacted reach for possible references. Look at best “spots” of degraded reach to evaluate natural tendencies of the reach and have some ballpark for where you should be landing your design.

Reference Reach Criteria Stable Reference Stream in Same Hydro-Physiographic Region Same Stream Type as Intended Design Stable for Two Meander Wavelengths (20 Bankfull Widths) Best if Similar Valley Slope and Sediment Regime as Impacted/Design Reach Coastal Plains or Piedmont, etc. Design valley slope and width may be different than overall valley.

Dimensionless Ratios Key Element in the Geomorphic Approach to Natural Channel Design Used to “Size” a Reference Stream to a Designed Stream Requires Numerous Geomorphic Measurements Make “Dimensionless” Geomorphic Measurements by Dividing by a Bankfull Parameter In Order to Capture Stream’s Natural Variability, Need a Range of Dimensionless Ratios Used to Design Pool/Riffle/Glide/Run Habitat Obtain all ratios on reference reach Obtain only some of the “useful” ratios on degraded reach if you don’t need them for comparison or to show divergence.

Dimensionless Ratios Wbkf = 20 Lm = 200 Feet

Dimensionless Ratios Lm/Wbkf = 200/20=10 Wbkf = 20 Lm = 200 Feet

Dimensionless Ratios Reference Reach Designed Reach Wbkf = 10 Lm = 100 Feet Wbkf = 20 Lm = 200 Feet

Primary Dimensionless Ratios – Cross Sectional Dimensions Pool, Run, or Glide Feature Area/Riffle Bankfull Area Max. Feature Depth/Mean Riffle Bankfull Depth Mean Feature Depth/Mean Riffle Bankfull Depth Feature Width/Riffle Bankfull Width

Primary Dimensionless Ratios – Pattern Meander Wavelength (Lm)/Riffle Bankfull Width (Wbkf) Radius of Curvature (Rc)/Riffle Bankfull Width (Wbkf) Beltwidth (Wblt)/Riffle Bankfull Width (Wbkf) = MWR MWR = Meander Width Ratio

Primary Dimensionless Ratios – Profile Slope Riffle Slope/Bankfull Slope Pool Slope/Bankfull Slope Run Slope/Bankfull Slope Glide Slope/Bankfull Slope Pool Spacing Pool to Pool Spacing/Riffle Bankfull Width Pool Length/Riffle Bankfull Width Maximum Depths Max. Riffle Depth/Mean Riffle Bankfull Depth Max. Pool Depth/Mean Riffle Bankfull Depth Max. Run Depth/Mean Riffle Bankfull Depth Max. Glide Depth/Mean Riffle Bankfull Depth

Geomorphic Data Collection Site Review/Toothpick Survey Cross Sections Longitudinal Profiles Pebble Counts/Sediment Samples Stream Assessments

Profile Analysis Bankfull Slope Facet Slopes – Always Measure Water Surface Pool to Pool Spacing Pool Lengths Facet Maximum Depths – Channel Bottom to Bankfull Elevation Low Bank Height or Valley Bottom

Cross Sections Bankfull Call/Elevation Inner Berm Features Floodprone Width Bankfull Area Bankfull Width and Depth

Pebble Counts & Bar Samples 3. Obtain Sieve Analysis at the location of the largest particle on lower 1/3 of point bar or other depositional feature 1. Obtain a 100-particle pebble count on 10 transects from bankfull to bankfull throughout the reach (Classification) 2. Obtain a 100-particle pebble count in the riffle bed (Sediment Transport)

Design Reach Data Collection Dependant Upon Purpose of Project Impacted Reach (Minimum Data per Stream Type) Planform Measurements Riffle Cross Section Reach Average Pebble Count Riffle Bed Material Pebble Count Bar Sample Sieve Analysis Longitudinal Profile If you are looking at a long tributary that changes from 5% slope at the top down to 1% slope at the bottom, you will need data for more than one reach.

Reference Reach Data Collection Planform Measurements Facet Cross Sections (Riffle, Run, Pool & Glide) Longitudinal Profile through 2 Meander Wavelengths (Minimum) or 20 to 30 Bankfull Widths Reach Average Pebble Count Riffle Bed Material Pebble Count Bar Sample Sieve Analysis Pfankuch Channel Stability Assessment Site Controls (Bedrock, Wood) Multiple Cross sections preferred Understand what type of material is moving through the site and what type of material is armoring Are site controls holding the stream in place (such as large bolders) or is the stress very low…

Compare Impacted & Reference Reach Data to Regional Curves Make Comparison to Help Validate Data Need to Use Regional Curves from Same Hydro-physiographic Area If No Curves Exist Consider Developing Smaller Scale, Site Specific Curves A B 1 10 100 0.1 1.0 10.0 Drainage Area (square miles) Bankfull Width (feet) Field Measurement Eastern U.S. Buffalo Run Ref

Calculate Bankfull Velocity & Discharge Velocity Equations Manning’s Chezy Darcy-Weisbach Relative Roughness R/D84 Discharge Equation Q = U*A

Sediment Transport Validation Stop, Store, and/or Transport Sediment Delivered to the System Procedures for Gravel Systems Typically Based on Sediment Transport Competency and Capacity Procedures for Sand Systems Typically Based on Sediment Transport Capacity Define Competency and Capacity

Module # 17 Overview of Geomorphic Channel Design Practice Iowa’s River Restoration Toolbox Level 1 / Base Training