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A one‐dimensional analysis of the discharge passing under a tunnel gate and of the hydraulic downpull acting on it is presented. It is shown that the downpull is significantly affected not only by the geometry of the gate bottom, but also by the rate of flow passing over the top of the gate through the gate well. In fact, the downpull on a tunnel gate of a given form can be significantly reduced by appropriately controlling this overflow. To facilitate prediction of possble negative downpull, which might inhibit safe gate closure, the analysis is expanded to include the dangerous range of extremely large gate openings and the unsteady effect of gate movement. Data on all the significant flow and downpull parameters are given as obtained from systematic watertunnel experiments. In conjunction with these data, the analysis should prove useful as a design tool.

The pressure distributions and the energy losses were obtained in an air tunnel for the following penstock trifurcations: a two-wye arrangement, two types of plug-funnel proposal, and an abrupt junction. Published results of other types of trifurcation, namely, the one provided with a tie bar, and other wyes have been also included in this report in order to provide a comprehensive aid for the designing engineer in selecting the right type of trifurcation. The model tests were made for all the three operating conditions: one branch flowing, two branches flowing and all three branches flowing. It is found that the energy-loss coefficient depends only on fluid inertia for approach, flow Reynolds numbers greater than 10\U5\N. The plug-funnel trifurcation in which the central portion is recessed was found to be hydraulically better than the other models tested when all the three branches are flowing because the boundary geometry provides a smooth entry into all three branches. The double wye is, however, superior to all other types when only one branch is flowing.