Portland Water Bureau Preparing Portland s Water Supply for The Big One July 11, 2018 Tim Collins, P.E., G.E.
Presentation Outline Portland water system overview Pacific Northwest seismic hazards Building a resilient system
Do you know where your drinking water comes from?
Portland s Drinking Water System
Population and Consumption Total service population 935,000 566,000 retail 369,000 wholesale Average demand 100 million gallons Peak demand 162 million gallons per day Winter demand 85 million gallons per day
Surface Water Bull Run Watershed: Reservoirs 1 & 2
Climate, Topography and Geology 750 4,500 elev. 130 avg. annual precipitation Rain dominated system Underlying geology: Columbia River basalt
126 Years of Clean Water
Groundwater Columbia South Shore Well Field
System Components 2,200 miles of small pipe 2 dams 100 miles of large pipe 58 tanks 15,000 hydrants 40,000 valves 180,000 meters 38 pump stations
Pacific Northwest Seismic Hazards
Plate Tectonic Map of the Pacific Northwest: The Cascadia Region Interplate Crustal Intraplate Modified from 2010 issue of Cascadia, Oregon Dept. of Geology and Mineral Industries
Juan de Fuca Plate The interaction between Juan de Fuca and North American plate generate seismic sources.
Vertical Slice through Subduction Zone Source: http://pubs.usgs.gov/circ/c1187/
Between Earthquakes Seafloor goes down Coast goes up Source: http://pubs.usgs.gov/circ/c1187/
During an Earthquake Seafloor goes up Coast goes down Source: http://pubs.usgs.gov/circ/c1187/
Cascadia Subduction Zone Earthquakes Turbidites show how much of the subduction zone ruptured in ~42 earthquakes over the last 10,000 years. Recurrence Mw ~9 500 yrs Mw 8.5-8.8 430 yrs Mw 8.5-8.3 320 yrs Mw 7.6-8.4 240 yrs Modified from Goldfinger et al. (in press) by adding magnitude estimates and some labels. 20 earthquakes ruptured all of the subduction zone. 2 to 3 earthquakes ruptured three quarters of subduction zone. 19 earthquakes ruptured the southern half or quarter of the subduction zone.
Frequency of Cascadia Zone Earthquakes Comparison of the history of subduction zone earthquakes along the Cascadia Subduction Zone in northern California, Oregon, and Washington, with events from human history. Ages of earthquakes are derived from study and dating of submarine landslides triggered by the earthquakes. Earthquake data provided by Chris Goldfinger, Oregon State University; time line by Ian P. Madin, DOGAMI.
What Damaging Phenomena Do Earthquakes Generate? Liquefaction Lateral Spreading Landslides Ground Shaking Fault Rupture These are of greatest concern to the PWB.
Liquefaction Source: Sand Liquefaction Phenomena induced by the May 2012 Emilia Romagna Earthquake. ENEA
Liquefaction results from strong ground shaking. Occurs in saturated soil profiles with significant sand content Results in a semi-fluid state Loss of soil strength and bearing capacity Liquefaction
Lateral Spreading Occurs when liquefaction occurs on a slope or near an open face.
Lateral spread in the February 29, 2001, M6.8 Nisqually Earthquake.
Lateral spread at North Wharf. January 12, 2010 M7.0 Haiti Earthquake Source USGS/EERI
Landslides Earthquake induced Groundwater induced Headworks landslide shut down the Bull Run system for a month in 1995.
Recent Studies Bull Run Watershed Landslide Assessment (2016) Water System Seismic Study (2017)
Transmission Main Vulnerabilities
Breaks and Leaks
Wellfield Vulnerabilities
System Seismic Vulnerabilities Conduits: 10 or more failures on each conduit Backbone Pipelines: 200+ failures Distribution System: 3,000+ failures Columbia Wellfield: 150+ damage to multiple well casings, potential damage to collection tank Willamette River Crossings: All six crossings will be damaged Pump Stations and Tanks: Three pump stations and 10 tanks at high risk of damage
PWB Seismic Study Findings Existing water supply system will drain within hours Repair times will not meet the Resiliency Plan recommendations Significant resources will be necessary to bring to system into compliance with the Resiliency Plan Fill the tub!!!
Resiliency Actions
Oregon Resilience Plan Issued February 2013 Specifies likely impacts of a magnitude 9.0 Cascadia earthquake. Defines target states of recovery goals to be met within 50 years. Recommends changes in practice and policy.
Current System Recovery Targets & Status
PWB Resiliency Efforts Improve seismic resiliency of bridges Remove exposed portions of conduit Strengthen key facilities Improve river crossings Improve transmission backbone
Bridge Improvements Bowman s Bridge Seismic Upgrade, 1999 Bolt foundations to bedrock; structural improvements
Bridge Improvements Larson s Bridge Seismic Strengthening, 2003 Rock bolts; structural strengthening
Conduit Trestle Improvements Trestle removal, conduit hardening, scour protection, 2005
Groundwater Pump Station Seismic Upgrade Ground Improvements and structural improvements, 1999
Sandy River Crossing Tunnel Remove surface piping and bridge. Install new conduits 80 below the Sandy River bottom, 2007.
Sandy River Crossing Tunnel
Willamette River Crossing Currently no seismically hardened water main crossing Proposed alignment beneath liquefiable soils. Provide average daily demand after an earthquake Under design, complete 2020 Existing pipe New pipe
Questions?