Coarse Sediment Augmentation on Regulated Rivers Scott McBain McBain & Trush, Inc. scott@mcbaintrush.com
Components Some geomorphic and ecological considerations Conceptual approach at understanding augmentation needs, locations, and rates Augmentation grain size considerations Augmentation methods
Thalweg Elevation Typical geomorphic responses Year of dam construction Present-day Distance Below dam
Potential ecological responsessalmonid spawning habitat, benthic macroinvertebrate habitat
Thalweg Elevation Potential ecological responsesabandoned side channels Side channel entrances Year of dam construction Present-day Distance Below dam
Potential Objective: Re-establish and maintain coarse sediment balance Dam induced changes in coarse sediment supply Degrade Aggrade Dam induced changes in coarse sediment transport capacity
Conceptualizing the evolution in sediment budget and routing
Coarse Sediment Transport Capacity (tons/day) Tools to estimate coarse sediment transport rates Bedload transport measurements 100,000 10,000 1,000 100 10 1 Existing Condition Post-transfusion Sediment transport relationships Gravel Refresher 0 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000 15000 Water Discharge (ft3/s)
Potential shortterm and longterm strategy Short-term transfusion to rapidly increase storage Long-term augmentation to maintain increased storage
How could we implement shortterm and longterm strategy? Depends on: Impact of dam on sediment supply and storage Geomorphic and ecological restoration objectives Cost Timeline Others
Short-term transfusion sites-planning level locations and volume estimates
Sum up the introduction areas Approx river mile location Approx length (ft) Approx width (ft) Estimated depth of sediment to be placed (ft) Approx. surface area to be constructed / enhanced (ft2) Estimated volume of coarse sediment to be added (yd3) 111.48 2,030 100 3.0 201,600 22,400 111.05 1,520 40 7.0 56,100 14,540 110.73 110 40 3.0 4,400 490 Then consider: Access, logistics, and land ownership Risk Cost Ecological benefits Conceptual models Regulatory requirements Prioritization and sequencing TOTAL: CONSTRUCTION LEVEL DESIGNS AND SPECIFICATIONS 37,430 cy yds
Grain size considerations Spawning Gravel versus Coarse Sediment Fines versus screening out fines Current and future transport rates (and augmentation needs)
Coarse Sediment vs Spawning Gravel 8 mm (0.3 in) 25 mm (1 in) Spawning Gravel Coarse Sediment Augmentation 101 mm (4 in) Mobilization Threshold at 11,000 152 mm cfs (6 in) 8 Size in (mm) 32 256 Medium Gravel Cobble Boulder Coarse Bed Material Load
Fines versus screening out fines Instream placement in California usually requires fines to be screened out, and placed material to be double washed (turbidity, mercury, sand) However, fines are a natural component of substrate, and reasonable amounts of sand can be beneficial to incubating salmonid eggs
Coarse Sediment Transport Capacity (tons/day) Potential changes in grain size and coarse sediment transport rates 100,000 10,000 1,000 Increased transport rates via decreased grain size 100 10 1 Existing Condition Post-transfusion 0 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000 15000 Water Discharge (ft3/s)
Augmentation Introduction: Potential source areas Restore two sites for the price of one
Augmentation source areas: materials testing to estimate net yield from source area Percent Finer 100% 90% 80% 70% 60% 50% 40% 30% 20% 37% sample weight removed by processing for coarse sediment between 9.5 mm and 127 mm 10% 0% Total distribution (D84=73 mm, D50=19 mm) Distribution with particles <9.5 mm removed (D84=96 mm, D50=36 mm) Distribution with particles <9.5 mm and > 127 mm removed (D84=72 mm, D50=31 mm) 1 10 100 Particle Size (mm)
Potential Coarse Sediment Augmentation Methods
Method #1: Instream placement method- Riffle and/or pool tail augmentation
Method #2: Instream placement method- Bar creation
Method #3: Fluvial placement method
Method #4: Selffeeding method (high flow recruitment pile)
Method #5: Restore more natural poolriffle sequence and redistribute slope
Modeling tools Additional information? scott@mcbaintrush.com Other Coarse Sediment Management Plans and brochures Implementation designs CALFED white paper Kristin Bunte review Monitoring plans