ASDSO Dam Safety Toolbox

Hydraulics

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Analysis of spillway hydraulics using Computational Fluid Dynamics (CFD). CFD can be used to model three-dimensional hydraulic conditions (such as the standing waves downstream of the control section in this picture) that are important in evaluating spillway capacity and the adequacy of spillway training walls.

The hydraulic design of a dam includes a knowledge of the following foundational topics: pressurized and free-surface flow, uniform flow, gradually and rapidly varied flow, steady and unsteady flow, energy and momentum principles, energy losses, and cavitation. [1]

Types of Evaluations

Empirical Hydraulic Calculation Methods

Empirical equations are based on observations and experience as opposed to theoretical relationships. Several empirical calculation methods have been developed to represent various hydraulic flow conditions. These include the following:

Types of Hydraulic Modeling

Selection of either a one-, two-, or three-dimensional hydraulic model is necessary depending on both the complexity of the flow conditions and the level of accuracy required of the model. Hydraulic modeling helps to attain a higher-optimized level of operation of the dam and reduce uncertainty.

“Maintaining the high efficiency of a spillway requires careful design of the spillway crest, the approach configuration, and the piers and abutments. For this reason, when design considerations require departure from established design data, model studies (or three-dimensional computer models) of the spillway system should be accomplished”. Physical model studies or three-dimensional Computational Fluid Dynamics (CFD) models are recommended to confirm any design that involves complex geometric considerations and/or large discharges and velocities. [1]

Best Practices Resources

Design Standards No. 14: Appurtenant Structures for Dams (Ch. 3: General Spillway Design Considerations), USBR, 2022

Technical Release 210-60: Earth Dams and Reservoirs, NRCS, 2019

Federal Guidelines for Inundation Mapping of Flood Risks Associated with Dam Incidents and Failures (FEMA P-946), FEMA, 2013

Selecting and Accommodating Inflow Design Floods for Dams (FEMA P-94), FEMA, 2013

Hydraulic Design of Spillways (EM 1110-2-1603), USACE, 1992

Design of Small Dams, USBR, 1987

Hydraulic Design of Reservoir Outlet Works (EM 1110-2-1602), USACE, 1980

Trainings

On-Demand Webinar: Hydraulics 101: Intro to Hydraulics for Dam Safety

On-Demand Webinar: Hydraulics 201 for Dam Safety

On-Demand Webinar: Inlet and Outlet Hydraulics for Spillways and Outlet Structures

On-Demand Webinar: Designing Spillways to Mitigate Failure Modes

On-Demand Webinar: Introduction to Addressing Inadequate Conveyance Capacity at Dams


Citations:




Revision ID: 6693
Revision Date: 03/17/2023