Alamo Dam Simulated Breach Impact on Colorado River Flooding – Storage vs. 2D Areas

Cameron Jenkins, P.E. Senior Hydraulic Engineer WEST Consultants Inc. Thanks to the following:

USACE Los Angeles District

Modeling, Mapping, and Consequences (MMC) Production Center Purpose of Presentation

 Provide project background information and discuss the HEC-RAS setup  Discuss the impacts of the Alamo Dam Breach on the Colorado River  Compare 2D HEC-RAS vs. 1D HEC-RAS Storage Areas floodplain results Project Description and Setup Project Location

Alamo Dam • Alamo Dam on Bill Williams River u/s of Lake Havasu (39 miles) • Colorado River u/s of Lake Havasu (67 miles) • Colorado River d/s of Lake Havasu

Yuma (191 miles) • Gila River (13 miles) • ~1250 cross-sections Flood Inundation Scenarios

Maximum High Pool Top of Active Storage Pool

Security Scenario (1% DEP) Normal High Pool (10% DEP) Normal Low Pool (90% DEP)

DEP = Duration Exceedance Pool Boundary Conditions and Breach Hydrographs

• Bill Williams– PMF, scaled PMF, or constant inflow • Colorado River – constant inflow • Gila River – constant inflow PMF • Dam failures on Alamo Dam only • Normal Depth at d/s end Dam Information and Inputs

Physical Data Dam Type Zoned Earthfill Dam Length (ft) 975 Top of Dam Elev 1,267.34 (ft, NAVD 88) Spillway Crest 1,237.34 Elev (ft, NAVD 88) Detached, broad- Spillway Type crested Spillway Width (ft) 110 Credit: Andy Pernick, US Bureau of Reclamation Outlet Structure 3- 5′ x 8.5′ slide gates Lake Havasu River Characteristics Parker Dam

Wide Valleys

Canyons Alamo Lake Colorado River Alamo Dam

 Flows through a series of narrow canyons (200 ft) and with wide valleys (1.5 mile)  Potential to meander across valley  The average slope between Alamo Dam and Lake Havasu is 0.003 Elevation Data

•Detailed topographic data for Bill Williams Reach •USGS 10 meter DEM data for all other reaches •Channels were burned into the USGS cross-sections Related Projects

Palo Verde Parker Dam Diversion Dam Parker Dam

Headgate Rock Dam Related Projects

Morelos Dam Imperial Diversion Dam Laguna Diversion Dam Levees Flood Inundation Scenarios Levees Gila River

Colorado River

Yuma City

Storage Area – Areas that are protected by a Federal Levee Calibration

• 23 observed discharges and WSE along the Bill Williams River • No calibration was done for the Colorado and Gila Rivers • WSE within 1 ft in 10 locations and 2 ft in 20 locations • Observed WSE are based on discharges less than 6,500 cfs Challenges

• How wide to make cross-sections • Not having topographic data for the channel of the Colorado River and Gila Rivers • Lack of information on dams downstream of Alamo Dam Challenges

• Incorporating multiple dams as inline structures with gates and rules associated with operation • Extending model due to water flowing upstream Lake Havasu • Additional interpolated cross-sections were needed to stabilize the model for the different runs Results Flood Inundation

• All dam breach and Max High non- Distance Location of Results failure runs caused flooding/damage Downstream Reported of Dam (mi) • Floodwave travels downstream to Lake Alamo Dam 0 Havasu and continue both upstream Lake Havasu City1 58 and downstream Needles1 90 Blythe 113 • Floodwave takes ~400 hours to travel to Yuma 200 the end of the model (Mexico border) Somerton 220 San Luis 230 Critical infrastructure (schools and • 1Bill Williams River failure wave traveling hospitals) impacted upstream in the Colorado River Flood Inundation Mapping

Inundation Atlas – Aerial Map Series (Example) Flood Inundation Scenarios

Google Earth – Interactive Display of Flood Inundation Map Data (Example) Flood Inundation Scenarios

Inundation Atlas – Flood Profile (Example) Human Impacts

Population Distance Ranges at Risk (PAR) Daytime Nighttime Total PAR* Total Life Total Life PAR within 0 and 3 miles PAR Loss PAR Loss PAR within 3 and 7 miles PAR within 7 and 15 miles PAR within 15 and 60 miles PAR within 60 and 230 miles (end of model domain) Economic Impacts

• Assets Repair/Replacement Cost • Structures, equipment, and on-site property of Dam • Repair cost estimated by using 33% of original construction costs updated to 2014 prices • Total Remediation Costs • Repair/replace downstream property • Environmental restoration/emergency response not included • HAZUS data from 2006 with updated price level used • Largest cost

*Costs were estimated using MMC/USACE District input and USACE economic guidance. Storage Area and 2D Comparison Computer Hardware: 8 I7 Intel Processors, 3.60 GHz CPU, 16 Gb of RAM ,64-Bit OS Comparison Information

• Convert levee protected storage areas to 2D areas • Max High Pool Dam Breach run only • Other runs did not overtop levees • 2D areas used 500 ft x 500 ft elements 1D Run Time 2D Run Time • Full Momentum equation used for 2D 8 min 46 sec 41 min 55 sec • Manning Roughness of 0.06 used in 2D • Same time step of 30 sec Levees Flood Inundation Scenarios Levees Gila River

Colorado River

Yuma City

Storage Area – Areas that are protected by a Federal Levee Levees Levees Gila River

Colorado River

Yuma City

2D Model– Areas that are protected by a Federal Levee Flood Inundation Scenarios

Storage Area Floodplain for Max High Dam Breach Flood Inundation Scenarios

2D Model Floodplain for Max High Dam Breach

Comparison Challenges

• USGS 10 meter data used • lateral structure information was lost when opened in RAS 5.0 Beta • Levee elevations don’t match well with the USGS topo and caused problems with lateral structures being lower than terrain in 2D • Testing different element sizes required adjusting lateral structure elevations for each size • How to split up storage areas – take a lot to get similar results as 2D Comparison Summary

• 2D HEC-RAS has a more accurate floodplain than storage area model west of Yuma • The floodplains are similar north and northeast of Yuma for both model runs • The economic cost would be larger for the 2D model due to larger floodplain near Yuma Comparison Summary

• The runtime for the 2D model is ~5 times as long as the 1D model • Smaller element would take longer to run with not much change in results • Having better topographic data would impact results Questions???