Coarse Sediment Augmentation on Regulated Rivers. Scott McBain McBain & Trush, Inc.

Transcription

1 Coarse Sediment Augmentation on Regulated Rivers Scott McBain McBain & Trush, Inc.

2 Components Some geomorphic and ecological considerations Conceptual approach at understanding augmentation needs, locations, and rates Augmentation grain size considerations Augmentation methods

3 Thalweg Elevation Typical geomorphic responses Year of dam construction Present-day Distance Below dam

4 Potential ecological responsessalmonid spawning habitat, benthic macroinvertebrate habitat

5 Thalweg Elevation Potential ecological responsesabandoned side channels Side channel entrances Year of dam construction Present-day Distance Below dam

6 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

7 Conceptualizing the evolution in sediment budget and routing

8 Coarse Sediment Transport Capacity (tons/day) Tools to estimate coarse sediment transport rates Bedload transport measurements 100,000 10,000 1, Existing Condition Post-transfusion Sediment transport relationships Gravel Refresher Water Discharge (ft3/s)

9 Potential shortterm and longterm strategy Short-term transfusion to rapidly increase storage Long-term augmentation to maintain increased storage

10 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

11 Short-term transfusion sites-planning level locations and volume estimates

12 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) , ,600 22, , ,100 14, , 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

13 Grain size considerations Spawning Gravel versus Coarse Sediment Fines versus screening out fines Current and future transport rates (and augmentation needs)

14 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, mm cfs (6 in) 8 Size in (mm) Medium Gravel Cobble Boulder Coarse Bed Material Load

15 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

16 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 Existing Condition Post-transfusion Water Discharge (ft3/s)

17 Augmentation Introduction: Potential source areas Restore two sites for the price of one

18 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) Particle Size (mm)

19 Potential Coarse Sediment Augmentation Methods

20 Method #1: Instream placement method- Riffle and/or pool tail augmentation

21 Method #2: Instream placement method- Bar creation

22 Method #3: Fluvial placement method

23 Method #4: Selffeeding method (high flow recruitment pile)

24 Method #5: Restore more natural poolriffle sequence and redistribute slope

25 Modeling tools Additional information? Other Coarse Sediment Management Plans and brochures Implementation designs CALFED white paper Kristin Bunte review Monitoring plans