Gibby Road Bridge Revetment Scour Analysis

Southern Orange County, CA


PACE designed a unique impermeable revetment as part of the replacement of the Gibby Road Bridge to reestablish natural flows along San Juan Creek. The existing 70-foot-wide low-flow Arizona crossing earthen embankment conveyed flows through three culverts under the roadway crossing, restricting sediment transport and fish passage. PACE prepared the initial bridge hydraulic sizing, fluvial modeling, and scour analysis to identify alternatives to the culvert crossing. A range of 33 different bridge geometries were analyzed, and the final design consisted of a 220-foot-long single-span, pre-stressed concrete box girder bridge that would allow passage of the 100-year flow of 36,100 cubic feet per second along the creek.

The proposed bridge abutment fill encroached upon the creek floodplain and required armoring of the slopes to prevent erosion. The revetment design consisted of grouted rock for the exposed portion above the channel invert and jet grouted columns for the buried portion that extends to the anticipated scour depth, while the active streambed bottom remains unarmored earth.

The design approach overcame multiple constraints, both regulatory (environmental permitting and riparian protection) and physical (high groundwater, high sediment loads, and flow capacity continuity). Installation of the new bridge restored the creek to a natural flow condition, allowing for fish passage and preventing frequent roadway crossing closures during storm events. The bridge was constructed using cast-in-place concrete to minimize service interruption and environmental disturbance during the project.


Key Features:

  • Bridge hydraulic analysis
  • Fluvial model / scour analysis
  • Revetment feasibility study and plans, specifications, and estimates (PS&Es)
  • Fish passage hydraulic impact assessment
  • Jet grout columns
  • Alternatives formulation and screening

Rancho Mission Viejo

Hydraulic Modeling / Research, River Engineering, Stormwater Management / Flood Control