Dams, Spillways, and Outlet Works

What We Can Do:

Designing dams and weirs with their spillways and associated outlet works so as to function correctly often requires a wide range of hydraulic studies. These studies may include capacity and stage-discharge analyses, energy dissipation performance, fish passage, total dissolved gas (TDG) abatement, sediment accumulation and bypass, dambreak analysis, and decommissioning of obsolete structures.

British Columbia:
Kara Hurtig
Tom Demlow
Gary Van Der Vinne
Ed Wallace
Brent Wolfe
Marc Villeneuve
Asia and Africa:
Alan Clark
+44 (0)7790041055
Latin America:
Mike Okun

NHC's specialists apply a range of tools to evaluate spillways and outlet works. These include physical hydraulic modeling, advanced numerical modeling, and specialized engineering analysis. Spillway models for structures in North America and elsewhere have been conducted in NHC's hydraulic laboratory for over 40 years. Recently, advanced numerical methods, including 1-D, 2-D, and 3-D (CFD) numerical models, have been used to evaluate spillway capacity and energy dissipation. Studies involving downstream effects, fish passage, and TDG often rely on the expertise of NHC specialists in river morphology, sedimentation, and fisheries engineering.


NHC's services for dams, spillways, and outlet works include:

  • Spillways and Energy Dissipation
    Creating physical model studies and advanced numerical analyses of gated spillways and energy dissipation facilities to verify analytical calculations or to develop innovative, cost-reduction solutions.
  • Fish Passage and TDG Abatement
    Conducting engineering analyses and preparing computational fluid dynamics (CFD) and physical models to evaluate alternatives for reducing TDG downstream of existing spillways and for providing safe passage of fish around dams, spillways, and other instream structures.
  • Dambreak Studies and Dam Decommissioning
    Advanced numerical modeling methods and engineering analyses used to predict the consequences of a dam failure to downstream morphology, aquatic habitat, lands, and communities.


The following examples were selected from a large number of NHC studies related to dams, spillways, and outlet works:

  • Spillway for High Multi-purpose Dam (Philippines)
    NHC built a 1:50 scale physical model to evaluate a gated spillway with aeration steps. The result helped improve approach flow conditions in the reservoir and to assess erosion in the plunge pool below the spillway flip bucket.
  • Spillway Replacement (British Columbia)
    For a seismic upgrade, NHC conducted CFD and physical model studies to confirm safe passage of the probable maximum flood (PMF), develop gated and ungated stage-discharge rating curves, and assess TDG abatement alternatives for the proposed spillway replacement.
  • CFD Analysis of Dam Overtopping (California)
    CFD modeling was used to estimate depth and velocity of flow overtopping the abutment of an existing dam.
  • Total Dissolved Gas Abatement Evaluation (Washington)
    We performed engineering analysis and CFD modeling to evaluate six alternatives for TDG abatement downstream of an existing spillway. The preferred alternatives were then examined in detail and refined using a 1:50 scale physical model to develop an efficient and cost-effective design for reducing downstream TDG levels.

San Roque multipurpose dam,

Ruskin spillway replacement, BC

Pit 3 dam overflow analysis, CA

Long Lake Dam TDG abatement, WA

Benefits & Results:

  • Our experience allows us to perform quality analysis and meet tight schedules at competitive costs.
  • All aspects of hydraulic and aquatic issues are fully addressed.