Uplift Pressure and Flow through Open Offset Joints in Spillway Chutes

Project ID: 19170
Principal Investigator: Tony Wahl
Research Topic: Condition Assessment
Funded Fiscal Years: 2019 and 2020
Keywords: None

Research Question

Can uplift pressures and flow rates through open joints and cracks in high-velocity spillway chutes be related to a characteristic boundary layer velocity, instead of the depth-averaged mean velocity? Previous tests in short flumes with no significant boundary layer (uniform-velocity flumes) have related uplift pressures to the mean velocity. New testing in a "boundary layer flume" could show that uplift pressures are significantly lower due to boundary layer effects.

Need and Benefit

Reclamation has many aging spillways and high-velocity conveyance channels that are cracked or have open joints
susceptible to hydraulic jacking. Some of these create Dam Safety deficiencies for the facilities (when underlying
geology consists of erodible materials that could allow a headcutting breach into the reservoir). Even when underlying
materials are erosion resistant, hydraulic jacking failures have the potential to create difficult operational conditions
and to severely impact the public (e.g., Oroville Dam evacuation order).
Available information from previous testing addresses only the uplift pressure component of the problem, since flow
rate measurements were unreliable. The quantity of flow through a joint and the demands that the flow will place
upon the underdrain system below the slab cannot be quantified at this time. Furthermore, uplift pressure estimates
based on past research may be overly conservative (predicting higher uplift pressures than actually occur) due to the
fact that previous testing did not utilize a facility that could produce a realistic boundary layer velocity profile over a
Initial steps have already been taken through a literature search and review of past research that was conducted in
FY18 using Dam Safety Office Technology Development funding.
The information gained from this research will be used in risk analysis studies of spillways throughout Reclamation.
The estimates of uplift pressure will be more accurate, and potentially lower due to the consideration of boundary
layer effects.
Reclamation has many aging spillways and is annually exposed to the possibility of its own "Oroville incident". The
PI has participated in two Value Planning studies in the last 6 weeks relating to spillways in poor condition (Glen Elder
Dam in Kansas due to freeze-thaw deterioration compromising joints and chute surfaces, and Hyrum Dam in Utah
plagued by seepage beneath the slab that has eroded the underlying soil and created voids).

Contributing Partners

Contact the Principal Investigator for information about partners.

Research Products

Bureau of Reclamation Review

The following documents were reviewed by experts in fields relating to this project's study and findings. The results were determined to be achieved using valid means.

Uplift Pressure and Flow through Open Offset Joints in Spillway Chutes (final, PDF, 2.8MB)
By Tony Wahl
Research Product completed on November 30, 2019

This research product summarizes the research results and potential application to Reclamation's mission.

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Last Updated: 6/22/20