The Nicomekl Water Control Structure (WCS) project, initiated by the City of Surrey, is a critical component of its Coastal Flood Adaptation Strategy (CFAS). This project addresses the urgent need to replace the aging Nicomekl Sea Dam, an almost century-old structure vulnerable to projected sea level rise and seismic events. The new WCS is engineered to provide robust flood protection for Surrey’s lowlands, safeguarding agricultural areas and vital infrastructure.

Strategically located upstream of the existing sea dam and adjacent to King George Blvd, the new structure’s placement is designed to minimize disruption and integrate with the surrounding dyke system. A significant aspect of this project includes the relocation of existing Metro Vancouver and City of Surrey water mains, ensuring continuous flood protection and enhancing public access through integrated pathways.

My Role and Key Contributions

As a Structural Engineer-in-Training (EIT) on this pivotal project, I was entrusted with significant responsibilities spanning the initial project phases through to detailed preliminary design. My contributions were integral to developing a resilient and functional structure tailored to complex site conditions and operational requirements.

Project Initiation and Conceptual Design

My involvement began in the crucial initial phases. I assisted the Project Manager by:

  • Thoroughly reviewing the Request for Proposal (RFP) to establish a comprehensive understanding of the project scope and client objectives.
  • Collaborating closely with the project manager to develop a comprehensive proposal that meticulously addressed all RFP requirements.
  • Playing a key role in drafting responses to the RFP requirements, ensuring our proposed solutions were precisely aligned with the City of Surrey’s needs.
  • Upon contract award, I actively executed the work plan outlined in the proposal, taking the lead in creating and refining conceptual designs for the WCS, which were subsequently presented to the client for review and approval.

Preliminary Structural Design

My core responsibilities included the preliminary structural design of the WCS, focusing on durability and operational functionality:

  • I executed the overall structural design for the WCS, primarily utilizing reinforced concrete specified with a C-1 exposure class to ensure longevity and resilience against harsh coastal conditions, including seawater spray and freeze-thaw cycles.
  • I developed the structural configuration for seven gravity flow channels (each 3m wide x 4.67m high), innovatively designed to accommodate future hydraulic pumps.
  • I engineered the concrete base slab to function as a continuous pile cap, effectively connecting supporting piles and serving as the foundational floor for tunnels and approach wing walls.
  • I designed the roof slabs (discharge slabs) of the tunnels, which are suspended from channel walls. These slabs were engineered to protect critical water mains and conduits, while also supporting a multi-use pathway and occasional maintenance vehicles, demonstrating a multi-functional design approach.

Foundation System Design

I played a significant role in the design of the robust foundation system:

  • I contributed to the design of the foundation, which incorporates concrete-filled steel piles (610 mm diameter) extending to a competent hard stratum, providing a secure end-bearing foundation.
  • I ensured the pile-supported raft slab was designed for optimal stability against sliding and overturning forces, critical for a flood control structure.
  • I collaborated on preliminary pile design calculations for various pile sizes, which involved assessing axial capacities in both compression and tension, and developing P-Y curves essential for the detailed design phase.

Design of Specialized Structural Components

My design responsibilities extended to several specialized components crucial for the WCS’s long-term operation and maintenance:

  • I designed the downstream slab above the discharge level to support future pumps, incorporating knock-out panels for their efficient installation.
  • I detailed extended channel walls on the upstream side to accommodate future debris screens, trash rakes, and conveyor belts, ensuring future-proofing of the structure.
  • I engineered a 5m removable hatch in the roof slab, facilitating essential maintenance access to City utility pipes and the Metro Vancouver water main.
  • I incorporated openings in the north abutment wall specifically for fish passage gates, demonstrating a commitment to environmental integration.
  • I designed support channels cast into concrete dividing walls for stop logs in each tunnel bay, a critical feature for facilitating maintenance and dewatering operations.

Gate System Integration and Support

I provided key structural input for the integration of gate systems:

  • My work included designing for the installation of side-wall hinged gravity gates on the ocean side of each tunnel and stop logs on the riverside.
  • I analyzed and adapted structural supports to accommodate different gate supply options, including the potential reuse of existing gates versus new fabrications.
  • I engineered the structural support for two dedicated fish slots (300mm wide x 500mm and 1000mm tall) and their associated weir gates, designed to withstand a differential head of up to 3m.

Access, Amenities, and Dyke Integration

I also focused on the integration of access structures and the surrounding dyke system:

  • I designed various access hatches (e.g., a 5m x 3m central equipment access hatch) and manholes within the pavement slab. These were engineered for safe inspection and maintenance access while ensuring structural integrity and seamless integration with the pedestrian pathway.
  • I ensured the structural tie-in of the WCS with the extended dykes on both the north and south sides of the Nicomekl River.
  • A key aspect of my work involved addressing potential differential settlements between the on-grade dyke fill and the pile-supported WCS, ensuring long-term structural stability.

Key Engineering Challenges & My Contributions to Solutions

This project presented unique structural and logistical challenges, where I contributed to developing innovative and effective solutions:

  • Complex Geotechnical Conditions: The site’s variable soil conditions—ranging from silty sand to clayey silt/silty clay overlying very stiff glacial till at varying depths—demanded a sophisticated foundation design.

    • My work on the end-bearing concrete-filled steel pile design directly addressed these complexities.
    • I was involved in analyzing the impact of the variable pile capacities due to the dipping glacial till, ensuring the foundation design was robust across the entire structure.
    • I contributed to the strategies for managing significant estimated settlements (up to ~140 mm for the north dyke and ~230 mm for the south dyke), which included considering preloading, surcharge treatment, or increasing dyke height.
    • I actively addressed the challenge of differential settlements between the WCS and adjacent dyke fill, and along new water mains, through careful design considerations.

  • Construction Staging & Constructability: The full-width river construction necessitated a phased approach within dewatered zones.

    • I was involved in understanding the implications of coffer dam designs capable of supporting approximately 5.7 m of water. This included considering challenging installations of sheet piles into dense till.
    • I contributed to problem-solving for coffer dam bracing, including the innovative consideration of a lower concrete working slab placed by tremie method to act as the lower brace, thereby optimizing the work zone.
    • My design considerations included provisions for leaving downstream face sheet piles in place to act as a seepage cut-off wall.

  • Material Selection & Durability in Coastal Environments:

    • I ensured long-term durability by specifying C-1 exposure class concrete, a critical decision for a structure exposed to seawater spray and freeze-thaw cycles.
    • I participated in the evaluation of gate material options, supporting the recommendation for stainless steel due to its superior long-term performance and lower maintenance requirements in a corrosive environment.

  • Integration of Multiple Utilities & Functions:

    • My design work for the WCS structure directly accommodated two major water mains (City of Surrey 300 mm DI and Metro Vancouver 750/1,050 mm STL), including designing a water main casing with flexible sleeve connections to protect dyke integrity.
    • I integrated provisions for future hydraulic pumps, debris screens, and fish passage facilities directly into the structural design, enhancing the project’s adaptability and functionality.

Project Highlights & Achievements

I am proud to have contributed to a project with such significant positive impacts and engineering achievements:

  • Significantly Enhanced Flood Protection: My structural design work directly contributed to a critical infrastructure upgrade, substantially bolstering flood defenses for Surrey’s lowlands against sea-level rise and seismic events.
  • Commitment to Environmental Integration: I actively incorporated features for improved fish passage, including the structural design for two dedicated fish slots and weir gates, addressing key ecological considerations.
  • Multi-Functional and Community-Oriented Design: I designed elements supporting the WCS’s role not just as a flood control structure, but also as a community asset integrating a multi-use pathway and amenities.
  • Future-Proofed Engineering: My designs accommodated future hydraulic pumps and debris removal systems, ensuring the structure’s long-term operational flexibility and adaptability.
  • Robust and Durable Structure: Through careful material specification (C-1 concrete) and foundation design, I contributed to ensuring a long service life with minimized maintenance for the WCS.
  • Successful Stakeholder Collaboration: My role in the initial proposal development and conceptual design phases supported the project’s alignment with the diverse expectations of key stakeholders.
  • Comprehensive and Informed Design: My structural engineering work was part of a comprehensive design approach, informed by detailed geotechnical investigations, CFD modelling, and salinity modelling.