Case Study: Oroville Dam Spillway Damage During Construction Repairs (2017)
Project Overview
• Name: Oroville Dam Emergency Spillway Repair
• Location: Oroville, California
• Year: 2017
• Project Size: $1.1 billion
• Scope: Emergency repair and reconstruction of main and auxiliary spillways after partial failure.
• Lead Agencies/Contractors: California Department of Water Resources (DWR)/
Category of the Issue, Problem, or Challenge
• Geotechnical
• Hydraulics
• Construction Management
Summary of the Issue, Problem, or Challenge
During the rapid construction repairs to the main and emergency spillways following the 2017 failure, issues arose with underdrain installation and foundation treatment. Improperly placed drainage elements and insufficient compaction led to water seepage beneath new concrete slabs, which raised concerns about slab uplift and long-term durability. This forced rework during the compressed construction timeline.
Root Cause Analysis
| Factor | Details |
| Inadequate Drainage Detail: | Drainage features beneath concrete slabs were installed without confirming alignment with geotechnical recommendations. |
| Accelerated Construction: | Compressed schedule to meet seasonal weather deadlines led to oversight in foundation prep. |
| Soil Compaction Deficiencies: | Compaction tests showed subgrade variability and some areas not meeting specifications. |
| Construction Sequencing Gaps: | Lack of coordination between excavation and drain crews resulted in rushed installation. |
Impacts Due to the Issue, Problem, or Challenge
• Portions of slab required demolition and reinstallation, causing delays.
• Increased cost due to emergency rework and equipment standby time.
• Strain on workforce and material supply chain due to compressed schedule.
• Raised concerns about the ability to maintain long-term dam safety under emergency-response contracting models.
Corrective Actions Taken
- Subgrade Rework: Removal of affected slab sections and re-preparation of foundation with stricter compaction protocols.
- Drainage Design Review: Third-party geotechnical engineers brought in to review and adjust underdrain layout.
- Enhanced QC Protocols: Daily geotechnical verification of subgrade and drainage prior to concrete placement.
- Sequencing Adjustments: Revised work plans to separate excavation, drainage, and slab crews with built-in hold points.
- Documentation System: Implementation of rapid-response documentation and approval workflows to reduce reactive field changes.
Lessons Learned
• Emergency timelines can jeopardize quality if not carefully managed with field-based quality verification.
• Subsurface drainage and foundation prep must be prioritized, even during rapid mobilization.
• Independent geotechnical review teams are vital in complex, fast-track repair projects.
• Modular sequencing and crew segmentation reduce coordination failures.
Audit & Prevention: Project Control Questions to Ask on Future Projects to Help Control the Situation for Future Projects
Foundation Preparation
• Are compaction requirements being independently verified before concrete placement?
• Has the geotechnical team approved final foundation prep in the field?
Drainage Installation
• Are underdrain systems properly coordinated with slab layout and hydraulics design?
• Are drain materials tested and logged upon delivery and installation?
Construction Sequencing
• Are key construction activities appropriately decoupled to avoid overlapping trades?
• Is there a clear chain of responsibility for foundation verification prior to slab placement?
Emergency Response Oversight
• Are rapid-response projects given special QA/QC scrutiny?
• Do emergency contracting models allow for sufficient oversight and documentation controls?