Date of Award:

12-2012

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Civil and Environmental Engineering

Committee Chair(s)

Blake P. Tullis

Committee

Blake P. Tullis

Committee

Brian M. Crookston

Committee

John D. Rice

Abstract

The need to accommodate larger reservoir discharge events has prompted the improvement or replacement of existing spillways. One possible spillway modification is the use of an in-reservoir arced labyrinth weir in place of a linear weir. Arced labyrinth weirs can increase crest length (more cycles) and have improved hydraulic efficiency in non-channelized approach flow applications, compared to traditional labyrinth weir applications.

In this study, arced labyrinth weir flow characteristics were observed for eleven different laboratory-scale model geometries at the Utah Water Research Laboratory. Rating (Cd vs. HT/P) data and observations were recorded for each configuration, and discharge efficiency was determined. Cycle efficiency, which is representative of the discharge per cycle, was also reported.

In-reservoir labyrinth weirs with larger sidewall angles ( ≥ 20°) were found to have higher discharge efficiency than in-reservoir weirs with smaller sidewall angles ( < 20°). On the other hand, arced labyrinth weirs with longer crest length (occurring on geometries with α < 20°) were more efficient per cycle than α = 20° weirs. Aeration characteristics, inlet modification options, weir placement options, and nappe breakers were also investigated for arced and non-arced labyrinth weirs (in-reservoir).

As the upstream head increases, the outlet cycles of the arced labyrinth weirs experience local submergence (beginning at the upstream apex region). Eventually, the entire weir structure can become submerged when the inflow exceeds the weir’s free-flow discharge capacity. When this occurs, the head-discharge control point can move to a location downstream of the weir. Larger cycle arc angles (θ) are more susceptible to this phenomenon. Flow separation also contributed to decreased capacity at higher discharges (higher heads). Adding cycles to the weir length (from 5 cycles to 7 and 10 cycles) was also found to have slight to negligible effect on discharge efficiency, but due to increased weir length, discharge increased proportionally.

No current design method exists for arced labyrinth weirs, and limited hydraulic data (specific to arced labyrinth weirs) is currently available. This study continues the dialogue for arced labyrinth weir hydraulics and increases the repository of data available for their design. This data may be used, with sound engineering judgment, to better understand the flow characteristics of arced labyrinth weirs.

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