Assessing Mechanisms and Rates of Levee Erosion in the Sacramento-San Joaquin Delta Douglas Sherman, Texas A&M University Bernard Bauer, University of British Columbia, Okanogan Mark Lorang, University of Montana Jean Ellis, NASA Stennis Space Center Mark Lange, University of Southern California David Hansen, East Bay Municipal Utilities District Frank Hopf, Texas A&M University
Research Programs Concerning Levee Erosion by Boat-wakes 1. Monitoring 44 Sites for Bank Changes Biased toward eroding sites Monitored seasonally 2. Monitoring Boat Traffic Boat type, size, speed Characteristics of wakes 3. Mapping and Characterizing Levee Waterlines 4. Measuring Boat Wake Dissipation by Brush Bundles 5. Measuring Boat Wake Dissipation by Tule Stands
Bank Change Monitoring Erosion Pin Network 44 sites 4-12 pins each site Seasonal Data 2-10 yrs of data 4 surveys per year Vertical and horizontal change Spatially Distributed Process Distributed
Erosion Pin Concept Each Site Has Four or More Pins
Site Selection
Railroad Cut Site 24 Stagnant water No boat traffic No wind waves Minor tides
Sacramento River (below Walnut Grove) Site 10 Strong current Boat wakes Wind waves Medium tide
Bank Change Rates, By Site HE = 0.13 m/yr and VE = 0.03 m/yr 60 0 1 2 3 4 5 6 7 8 9 10111213141516171819202122232425262728293031323334353637383940414243444546 44n 44 Erosion Accretion Bank Change Rate (cm/yr) Change Rate (cm/yr) 40 20 0-20 -40-60 horizontal vertical Accretion Erosion + 20-20 0 1 2 3 4 5 6 7 8 9 10111213141516171819202122232425262728293031323334353637383940414243444546 43n 44 Site Site Number
Bank Change Rates, By Season Su '98 Su '99 Su '00 Su '01 Su '02 Su '03 Su '04 Su '05 Su '06 Bank Change Bank Change Rate (cm) (cm/30day) 4 2 0-2 -4-6 -8-10 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 horizontal vertical Elapsed Time (days) Elapsed Time (days)
Site 5: September 2000
Site 17: December 2000
100 SITE 5 - Cumulative Bank Change Su '98 Su '99 Su '00 Su '01 Su '02 Su '03 Su '04 Su '05 Su '06 Bank Bank Change (cm) (cm) 50 0-50 -100-150 Site 5: Across Georgiana Slough From Site 17 Exposed Mud Bank Bank Collapse in 2004 Brush Bundle in 2005-200 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 horizontal vertical Elapsed Time (days) Elapsed Time (days) 0 SITE 17 - Cumulative Bank Change Su '98 Su '99 Su '00 Su '01 Su '02 Su '03 Su '04 Su '05 Su '06 Site 17: Restored in 1997 Brush Bundle in 2000 Woody Debris Emplaced Vegetation Colonizes Bundles Deteriorate in 2003 Bank Change (cm) Bank Change (cm) -50-100 -150-200 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 horizontal vertical Elapsed Time (days) Elapsed Time (days)
Monitoring Boat Traffic Observations Over Summer Holiday Weekends Boat data Wake data Bank response data 500 and 1000 Boat Pass Experiments Video Monitoring
ms -1 0.6 0.3 0.0-0.3 EM5 gl -1 3 2 1 OBS5-0.6 40 60 80 100 120 140 160 180 TIME (seconds) 0 40 60 80 100 120 140 160 TIME (seconds)
Monitoring Boat Traffic Summer Holiday Weekends Labor Day 2000 (n=108): 0.03-0.05 mm/pass Memorial Day 2001 (n=256): 0.03-0.18 mm/pass 4 th of July 2001 (n=32): <0.01-0.04 mm/pass Labor Day 2001 (n=68): 0.03-0.08 mm/pass 500 and 1000 Boat Passages Ski Boat (x500): 0.03-0.05 mm/pass Fishing Boat (x1000): 0.01-0.03 mm/pass
Video Monitoring Program Georgiana Slough
Weekly Boat Traffic Since October 1, 2006 200 2833 Boats Through August 23, 2007 Boat Passages BOAT PASSAGES 150 100 50 0 0 5 10 15 20 25 30 35 40 45 50 WEEKS SINCE 10/1/2006 Weeks Since October 1, 2006
Mapping and Characterizing Levee Waterlines Map, with GPS, 800 Miles of Levee Waterline Categorize as 1 of 9 types Use as Indicator of Erosion Vulnerability
Selected Bank Types Partial Rock Partial Concrete Unprotected Trees Trees Trees Vegetation
800 Miles Of Bank Types
Summary of Bank Types Levee Bank Types by Length length (km) 500 450 400 350 300 250 200 150 100 50 0 Partial Rock 75 mi 65 mi 50 mi Most Vulnerable To Erosion Partial Concrete Type Rock1 Type 3 Unprotected Type 7 Vegetated Type 6 Type Trees5 Developed Type 8 Type Concrete 2 Type Undet. 9 Type 4
Boat Wake (wind wave) Dissipation by Brush Bundles: Georgiana Slough Eroded Levee Brush Bundles
Experimental Design Outer PTs Inner PTs
Results: Brush Bundles Dissipate 60% of Boat Wake Energy 2.0 r 2 =0.031 p=0.442 CONTROL r 2 =0.578 p=0.136 2.0 r 2 =0.730 p=0.000 y=0.901x-0.331 R 2 = 0.73 BUNDLE r 2 =0.101 p=0.313 1.5 1.5 E n E n 1.0 1.0 0.5 0.5 0.0 0.4 0.6 0.8 1.0 1.2 0.0 0.4 0.6 0.8 1.0 1.2 Normalized h Normalized h
Boat Wake (wind wave) Dissipation by Tule Stands: Sacramento River Based on Concepts in Markel (1967) and Dean (1979) Dissipation Function of Stem Size, Stand Density, Stand Width
Dean s (1979) Model For Wave Attenuation H ( x) H 1 = 1 AH o + o x H 0 is offshore wave height x is distance from edge of stand A = C D 3πs D 2 s h C D is drag coefficient D s is stalk diameter s is stalk spacing h is water depth
Experimental Design Ten Data Runs of Five Boat Passes Each Wake Height Measured at 2 m Intervals Over 10 m Distance Tule Stand Thinned Between Runs Until Open Water Remained Measurements Compared to Dean Predictions Attenuation Ratio 1.0 0.9 00m 2 4 6 8 10 m Distance in Stand
Observed vs. Predicted Wave Heights 0.19 Observed H (m) 0.15 0.13 0.09 R 2 = 0.51 050 0100 0150 0200 0 250 0300 0350 0400 0.10 0.20 0.30 Dean s Predicted H (m)
Summary of (Preliminary) Findings Average Erosion Rates for Unprotected Sites: HE = 0.13 m/yr and VE = 0.03 m/yr. Boat Wake Erosion Averages about 0.09 m/yr (or less). Annual Boat Traffic on Georgiana Slough > 3000 About 200 Miles of Levee Vulnerable to Boat Wake Erosion Brush Bundles Dissipate About 60% of Wake Energy Tule Stands Dissipate 15-30% of Wake Energy