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Physical Model Investigations on Nappe Instabilities at Labyrinth Weirs
No full textFree overflow hydraulic structures operating at low heads tend to develop nappe instabilities when there is no ventilation. A detailed investigation has been undertaken with a relatively large-scale labyrinth weir in the hydraulic laboratory of the BAW. A quarter-round crest was selected, because nappe instabilities mainly occur at sharp-crested weirs, which favor the development of an air pocket behind the nappe. The headwater ratios for which nappe instabilities could be observed were determined. Pressure fluctuations were measured and the frequencies determined. Adding splitters to the crest is one way to vent the air pocket and to avoid vibrations. Another possibility is an artificial ventilation to stabilize the pressure behind the nappe. This paper presents the results and observations and discusses them against the background of the existing literature
Experimental and Numerical Investigation of A-type Rectangular Side Piano Key Weir
No full textA side weir is a structure installed along the side wall of a channel, serving multiple purposes, such as raising water levels for irrigation and drainage and diverting excess flow from rivers or channels during floods. Most studies have focused so far on linear rectangular and labyrinth side weirs, with relatively limited research conducted on side Piano key weirs. In this paper, an experimental and numerical simulation was performed on an A-type rectangular side piano key weir and a rectangular sharp-crested side weir. The diversion discharge of Piano key side weirs was within the range of ± 10% with numerical results. The diverted discharge over the rectangular side piano key weir was 1.5 to 6.7 times greater than the linear rectangular side weir. Water surface profile and velocity variations along the rectangular side Piano key weirs were also investigated experimentally and numerically
Piano Key Weir With Orifice Sluice
No full textIn recent years, many Piano Key Weirs (PKW) have been built around the world. In Vietnam there are more than 18 PKWs in operation to the present. However, during the operation, some experience has been drawn on the design and application conditions. This paper is about the Dak Mi 3 reservoir with a PKW that operated well for more than 4 years until an exceptional flood following typhoons in October 2020, making reservoir fully filled with mud and sand. The result is the PKW became ineffective and the hydropower plant unable to operate. In order to dredge the reservoir and prevent mud deposits again, a part of the PKW was replaced by two deep orifice sluices. The lesson is that using orifice sluices in combination with PKW is an effective solution for sand flush of reservoir in catchment areas sensitive to landslides and under climate changes
Nachtigal Dam: A 4917 m Long Labyrinth Spillway
No full textThe Nachtigal Dam, part of the Nachtigal Amont Hydropower Project in Cameroon, features a 4917-meter-long labyrinth spillway, designed to safely manage floodwaters. This spillway was optimized for hydraulic safety, cost efficiency, and environmental considerations. Physical scale modeling (at a relatively rare 1:12.5 scale) and detailed design adjustments ensured robust performance under various flow conditions. Despite construction challenges for such a large-scale nonlinear structure, the project achieved reliable spillway operations, demonstrating the suitability of labyrinth weirs for large-scale hydraulic infrastructure
Introduction to the Vegetable Session & USU Vegetable Production Lab
No full textOutline
I. Meet the specialist & current role at USU
II. USU vegetable programs/Utah\u27s Unique challenges
III. Overview of current & Upcoming studies
IV. Survey/Poll
V. Q&
2D Probabilistic Scour Model for Predicting the Time-Rate of Scour for Spillways and Overtopping Dams Based on the Erodibility Index Method
No full textTime-dependent prediction of rock scour for dams and spillways has largely remained elusive given limited available data on rock erosion rate parameters in literature. Recently, a theoretical framework for determining the rate of rock scour was developed by Annandale (2025), enhancing the Erodibility Index Method (EIM). The EIM is the most commonly used and accepted approach for evaluation of scour in rock for dam applications. This theoretical framework has been incorporated into the 2D probabilistic jet impingement scour model (George & Annandale, 2023) so that scour progression due to head-cutting in a spillway channel (lined or unlined) or overtopping onto a dam foundation can now be simulated over the duration of a flood hydrograph. Currently, back-analysis of observed scour due to prior flood events is needed to calibrate a rock-specific erosion rate coefficient. Prediction of rock erosion rates allows for greatly improved decision making when considering the impacts of scour on civil structures
Modulation of the Semi-Annual Oscillation by Stratospheric Sudden Warmings as Seen in the High-Altitude JAWARA Re-Analyses
No full textThe semi-annual oscillation (SAO) dominates seasonal variability in the equatorial stratosphere and mesosphere. However, the seasonally dependent modulation of the SAO in the stratosphere (SSAO) and mesosphere (MSAO) by sudden stratospheric warmings (SSWs) in the Arctic has not been investigated in detail. In this study, we examine the seasonal evolution of the SAO during 16 major SSW events spanning 2004 to 2024 using the Japanese Atmospheric General Circulation Model for Upper Atmosphere Research Data Assimilation System Whole Neutral Atmosphere Re-analysis (JAWARA). Basic features of the SAO are well captured by JAWARA, as evidenced by the SSAO and MSAO appearing at around 50 km and 85 km, respectively. The different responses of the SAO to early and late winter SSWs are particularly strong during the Northern Hemisphere winter of 2023/24. Early winter SSWs tend to significantly intensify the westward SSAO, while late winter SSWs tend to weaken the eastward SSAO. Similarly, the eastward MSAO is amplified during early winter SSWs, whereas the westward MSAO is slightly weakened during late winter SSWs. The weak MSAO response is probably due to its smaller climatological magnitude. Modulation of the SAO by SSWs is related to meridional temperature changes during SSWs through the thermal wind balance. Our findings contribute to the understanding of coupling between the tropics and high latitudes, as well as interhemispheric coupling
