At Stiver Engineering, we provide specialized design and engineering services for lake raw water intake structures. These facilities are critical infrastructure that supply untreated water from lakes and reservoirs to treatment plants, industrial operations, or power facilities. Because they connect directly into bodies of water, they present unique geotechnical and structural design challenges These structures must be designed to withstand substantial hydrostatic loads, variable subsurface conditions, and the construction challenges associated with working at depth beneath and adjacent to a body of water.
Depth and Design Considerations
Raw water intake structures are typically constructed at significant depths below the lake surface to ensure consistent flow, reliability during drought cycles, and protection from surface contaminants. Reaching these depths requires precision engineering, careful sequencing, and thorough consideration of soil and rock conditions.
The subsurface conditions at lake intake sites typically dictate the design approach. When lacustrine deposits, overburden soils, or mixed strata are encountered, caisson structures are a common solution. These can be designed as open caissons with cutting edges, sunk through soil with excavation proceeding inside the shaft, or as slurry-assisted excavations where stability must be maintained in highly permeable soils. Key considerations include:
- Bearing strata identification for final seating of the caisson.
- Differential settlement control to prevent uneven loading of the intake structure.
- Buoyancy resistance, requiring base slabs and keying into rock or dense soils to handle uplift pressures.
- Seepage control through watertight joints and cutoff walls.
When the intake is founded in competent rock, construction typically employs drill-and-blast methods, rock doweling, and systematic installation of rock bolts with shotcrete lining. These methods stabilize excavation walls and control raveling or spalling in high-stress environments. Shotcrete can be fiber-reinforced or include lattice girders, depending on loading conditions, with rock bolt patterns designed to resist both short-term construction loads and long-term operational stresses.
Hydraulic and Operational Considerations
From a hydraulic engineering perspective, intake structures must ensure:
- Consistent headwater pressure to maintain reliable conveyance across fluctuating lake levels.
- Sediment and debris control, either through intake bell design, screening systems, or sedimentation chambers.
- Velocity control across intake openings to prevent fish entrapment and minimize turbulence.
Intakes may discharge into vertical shafts or horizontal tunnels, often several hundred feet in length, constructed with slurry tunnel boring machines (TBMs) or drill-and-blast excavation depending on geology. These conveyance tunnels must be designed for both internal hydraulic pressures and external earth and hydrostatic loads.
Stiver Engineering’s Role
Raw water intake projects combine elements of geotechnical, structural, and hydraulic engineering, making them uniquely multidisciplinary. Each project demands careful calibration of analytical models, including analyses for soil-structure interaction, stability assessments under seismic loadings, and uplift resistance evaluations to validate safety and performance.
Stiver Engineering routinely solves complex problems involving tunnel entries, shaft stability, and hydrostatic uplift. We work directly with contractors to bring constructible solutions to projects where precision engineering is fundamental to delivering reliable, long-term water supply infrastructure.
Whether the project requires a massive concrete caisson sunk into soft soils or a rock-bolt-and-shotcrete stabilization system carved from bedrock, our engineers provide the field-tested design experience needed to deliver.
