Morphological Modeling of the Alameda Creek Flood Control Channel Rohin Saleh, Alameda County Flood Control District Søren Tjerry, Ph.D., DHI Portland, Oregon David E. Rupp, Ph.D., DHI Portland, Oregon (presenter) 11 th December 2008 Alameda County

Background San Francisco Public Utilities Commission (SFPUC) has decommissioned the Sunol and Niles dams on Alameda Creek. Temporary increase in sediment discharged to Alameda Creek. The dams and their removal are under the jurisdiction of SFPUC, while the Alameda County Flood Control and Water Conservation District (District) is responsible for Alameda Creek and the Alameda Creek Flood Control Channel (ACFCC).

Background Additional sediment deposition in channel system due to increased sediment supply to the creek. Increased inundation in the advent of a flood could result from additional sediment influx, although the volume and timing of sediment discharged to the creek is unknown. This poses a burden for the District responsible for the creek and the flooding that occurs along the creek.

Objective and Approach Objective: Quantify the largest increase in the 100-yr floodplain that can be experienced as the sediment pulse from the dam removal migrates through the Alameda Creek Flood Control Channel (ACFCC). Approach: Develop “MIKE 21C” graded sediment morphological model. Calibrate model by matching observed morphological development. Apply the model with and without dam removal to determine the morphological developments in the two cases. Develop “MIKE FLOOD” floodplain model that can simulate the 100-yr floodplain around the ACFCC as function of the updated ACFCC bathymetry (i.e., feed updated bathymetry to floodplain model).

Objective and Approach Objective: Quantify the largest increase in the 100-yr floodplain that can be experienced as the sediment pulse from the dam removal migrates through the Alameda Creek Flood Control Channel (ACFCC). Approach: Develop “MIKE 21C” graded sediment morphological model. Calibrate model by matching observed morphological development. Apply the model with and without dam removal to determine the morphological developments in the two cases. Develop “MIKE FLOOD” floodplain model that can simulate the 100-yr floodplain around the ACFCC as function of the updated ACFCC bathymetry (i.e., feed updated bathymetry to floodplain model).

Outline What is MIKE 21C? Examples of MIKE 21C applications A MIKE 21C model of the ACFCC Calibration of the MIKE 21C morphological model

MIKE 21C model features Depth-integrated hydrodynamic model that can simulate quasi-steady and dynamic flow fields with time-varying boundary conditions. Curvilinear grids (follow streamline curvature). Graded sediment (up to 16 grain sizes from fine sand to coarse gravel). Cohesive sediment (clay, silts).

MIKE 21C model features cont. Suspended load model with several transport formulas available; accounts for helical flow and adaptation in space (AD equation). Bed-load model with several transport formulas available; accounts for helical flow and bed slope. Dynamic update of the bed level; true morphological model. Dynamic update of bed composition by grain size. Parallel code! Can use as many processors as you have available. Allows computations on fine grids, over long time, with many sediment fractions.

ADCPMIKE 21C Hydrodynamics: Snake River ADCP Pine Bar, below Hells Canyon Dam, 24,300 cfs

Curvilinear hydrodynamics Fish resting pools Example from San Lorenzo Creek, complex flow fields Fish resting pool

Jamuna River, Bangladesh

Jamuna River, Bangladesh, Q=45,000 m 3 /s, d 50 =0.16 mm, eroding sandy banks, ~10 km width (decreasing towards the Ganges confluence), 100 km reach modeled (200 km North-South in Bangladesh). Simulation of braiding 0 years30 years3 years6 years12 years24 years18 years

Example of morphological model calibration Observed morphological development over 9 years based on 10 bathymetry surveys. Un-calibrated means we assume that standard sediment transport formulas are valid. Calibrated model has substantially (up to 60 times) higher sediment transport than what “accepted” formulas yield. Calibration is critical. The calibrated model matches the observations incredibly well; this is what an accurate morphological model can do – when calibrated!

Morphological Modeling of the Alameda Creek Flood Control Channel Model Development and Calibration

Alameda Creek Alameda Creek and Alameda Creek Flood Control Channel (ACFCC) Niles gage Active rubber dams SF Bay Dams removed, Autumn 2006 ACFCC

Longitudinal Profile of Thalweg, ACFCC (Tidally influenced)

Grid ResolutionGrid Extent Longitudinal: ~300 ft 200 x 10 cells Transversal: 30 – 90 ft Curvilinear Grid of Flood Control Channel

Elevation (m) Bathymetry of Flood Control Channel

Transport formula: Engelund and Hanson 10 non-cohesive sediment grain sizes: mm to 64 mm Cohesive sediment: < mm Time step: 2 seconds Simulation period: Oct – Sep (158 million time steps in ~2 days real time) ACFCC MIKE 21C Model Properties

Bed Sediment Particle Size Distribution at Niles Gage Initial Bed Sediment Conditions A.Bed Sediment Particle Size Distribution B.Sediment thickness Assumptions: Distribution the same throughout ACFCC at time = 0. Sediment layer thickness = 0.4 m

Largest discharge events dominate deposition and erosion. No suspended sediment and bedload measurements for largest events. Therefore, boundary conditions are uncertain! Model Calibration Challenges

? At least 14 events between 1999 and 2007 exceeded 3,000 cfs Model Calibration Challenges ?

1.Generate rating curves for sediment inflow based on least- squares fit to available data. 2.Apply rating curves to discharge time series at Niles Gage to calculate sediment inflow for calibration period (2003 to 2007). 3.Failure! Less estimated sediment inflow than measured deposition. Initial attempt:

Measured Cumulative Change in Sediment (2003 to 2007) Zone IZone III Zone II

Assumptions: Model Calibration 1.Nearly all non-cohesive sediment input to the ACFCC between 2003 and 2007 was deposited in Zones I and II. 2.Deposition in the tidally-influenced zone (Zone III) was mostly cohesive between 2003 and Both the SF Bay and Alameda Creek are cohesive sources to Zone III.

1.Adjust non-cohesive sediment rating curve parameters so sediment influx matches total deposition in upper channel (Zones I and II). 2.Adjust sediment transport factor (per grain size) to achieve match to cumulative longitudinal deposition pattern. 3.Adjust cohesive sediment parameters and SF Bay cohesive sediment concentration to achieve match to cumulative longitudinal deposition pattern in tidally-influenced channel (Zone III). Model Calibration Methodology

Observed and Modeled Suspended Sediment Transport vs. Discharge Cohesive Non-cohesive

Observed and Modeled Bedload Transport vs. Discharge

Calibration Results Following Steps 2 and 3 Cumulative Deposition (2003 – 2007)

Measured and modeled change in bed level in the upper ACFCC between 2003 and 2007 Model Calibration Results Measured Modeled

Measured and modeled change in bed level in the lower ACFCC between 2003 and 2007 Model Calibration Results Measured Modeled

Simulated morphology: Rubber Dams Upper channel Lower channel

Simulated morphology: Difference in bed level due to presence of rubber dams Upper channel Lower channel

Conclusions and Future Work Next step: Simulate additional sediment due to removal of Sunol and Niles Dams. Conclusions: Successfully simulated general morphological development in the ACFCC between 2003 and Have a calibrated model that will permit us to evaluate scenarios.

Thank You!