Assessing Mechanisms and Rates of Levee Erosion in the Sacramento-San Joaquin Delta

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1 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

2 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

3 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

4 Erosion Pin Concept Each Site Has Four or More Pins

5 Site Selection

6 Railroad Cut Site 24 Stagnant water No boat traffic No wind waves Minor tides

7 Sacramento River (below Walnut Grove) Site 10 Strong current Boat wakes Wind waves Medium tide

8 Bank Change Rates, By Site HE = 0.13 m/yr and VE = 0.03 m/yr n 44 Erosion Accretion Bank Change Rate (cm/yr) Change Rate (cm/yr) horizontal vertical Accretion Erosion n 44 Site Site Number

9 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) horizontal vertical Elapsed Time (days) Elapsed Time (days)

10 Site 5: September 2000

11 Site 17: December 2000

12 100 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) Site 5: Across Georgiana Slough From Site 17 Exposed Mud Bank Bank Collapse in 2004 Brush Bundle in 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) horizontal vertical Elapsed Time (days) Elapsed Time (days)

13 Monitoring Boat Traffic Observations Over Summer Holiday Weekends Boat data Wake data Bank response data 500 and 1000 Boat Pass Experiments Video Monitoring

14 ms EM5 gl OBS TIME (seconds) TIME (seconds)

15 Monitoring Boat Traffic Summer Holiday Weekends Labor Day 2000 (n=108): mm/pass Memorial Day 2001 (n=256): mm/pass 4 th of July 2001 (n=32): < mm/pass Labor Day 2001 (n=68): mm/pass 500 and 1000 Boat Passages Ski Boat (x500): mm/pass Fishing Boat (x1000): mm/pass

16 Video Monitoring Program Georgiana Slough

17 Weekly Boat Traffic Since October 1, Boats Through August 23, 2007 Boat Passages BOAT PASSAGES WEEKS SINCE 10/1/2006 Weeks Since October 1, 2006

18 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

19 Selected Bank Types Partial Rock Partial Concrete Unprotected Trees Trees Trees Vegetation

20 800 Miles Of Bank Types

21 Summary of Bank Types Levee Bank Types by Length length (km) 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

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24 Boat Wake (wind wave) Dissipation by Brush Bundles: Georgiana Slough Eroded Levee Brush Bundles

25 Experimental Design Outer PTs Inner PTs

26 Results: Brush Bundles Dissipate 60% of Boat Wake Energy 2.0 r 2 =0.031 p=0.442 CONTROL r 2 =0.578 p= r 2 =0.730 p=0.000 y=0.901x R 2 = 0.73 BUNDLE r 2 =0.101 p= E n E n Normalized h Normalized h

27 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

28 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

29 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 m m Distance in Stand

30 Observed vs. Predicted Wave Heights 0.19 Observed H (m) R 2 = Dean s Predicted H (m)

31 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