Labyrinth weirs are often a favorable design option to regulate upstream water elevations and increase flow capacity; nevertheless, it can be difficult to engineer an optimal design due to the complex flow characteristics and the many geometric design variables of labyrinth weirs. This study was conducted to improve labyrinth weir design and analyses techniques using physical-model-based data sets from this and previous studies and by compiling published design methodologies and labyrinth weir information. A method for the hydraulic design and analyses of labyrinth weirs is presented. Discharge coefficient data for quarter-round and half-round labyrinth weirs are offered for sidewall angles of 6° to 35°. Cycle efficiency is also introduced to aid in sidewall angle selection. Parameters and hydraulic conditions that affect flow performance are discussed. The validity of this method is presented by comparing predicted results to data from previously published labyrinth weir studies. A standard geometric design layout for arced labyrinth weirs is presented. Insights and comparisons in hydraulic performance of half-round, trapezoidal, 6° and 12° sidewall angles, labyrinth weir spillways located in a reservoir with the following orientations are presented: Normal, Inverse, Projecting, Flush, Rounded Inlet, and Arced cycle configuration. Discharge coefficients and rating curves as a function of HT/P are offered. Finally, approaching flow conditions and geometric similitude are discussed; hydraulic design tools are recommended to be used in conjunction with the hydraulic design and analysis method. Nappe aeration conditions for trapezoidal labyrinth weirs on a horizontal apron with quarter- and half-round crests (sidewall angles of 6° to 35°) are presented as a design tool. This includes specified HT/P ranges, associated hydraulic behaviors, and nappe instability phenomena. The effects of artificial aeration (a vented nappe) and aeration devices (vents and nappe breakers) on discharge capacity are also presented. Nappe interference for labyrinth weirs is defined; the effects of nappe interference on the discharge capacity of a labyrinth weir cycle are discussed, including the parameterization of nappe interference regions to be used in labyrinth weir design. Finally, the applicability of techniques developed for quantifying nappe interference of sharp-crested corner weirs is examined.

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 recent years, magnitudes of flood estimates used in hydraulic design have increased for many reservoirs. Consequently, many existing spillways are now deficient as they do not meet current discharge capacity requirements. To rehabilitate existing, fixed-width spillways, labyrinth weirs are often viable solutions. For reservoir applications, arcing labyrinth weirs into the reservoir increases hydraulic efficiency. This results from better cycle orientation to the approaching flow field. This study supplements available arced labyrinth weir hydraulic data by observing flow characteristics of three laboratory-scale physical models and two numerical (CFD) models. Physical model results provide head (energy)-discharge data and empirical coefficients for hydraulic design. Results also show that increasing the arc angle improves efficiency at H/P<0.3, where H/P is upstream piezometric head divided by weir height; after which, efficiency improvements diminish as downstream submergence also increases. The purpose of the CFD analysis was to assess the appropriateness of CFD as a design tool for arced labyrinth weir head-discharge relationship development. The CFD model results found good agreement with the physical model data indicating CFD’s usefulness as a hydraulic design tool; however, it is recommended that CFD models be calibrated to reliable laboratory or field data. This study’s data may be used, with sound engineering judgement, to aid in hydraulic design of arced labyrinth weirs