Single-stage overboard consists of five parts.
① Inlet connection section, that is, the gradual transition section between the upstream channel and the control weir. Commonly used forms are twisted surface and splayed wall.
② Control gap: it is the throat to control the water level and flow of the upstream river, also called control weir. It controls and regulates the upstream water level and the flow through it. The common cross sections of notches are rectangular and trapezoidal, with or without thresholds and with or without gates. Rectangular gap can only make the water level at the gap close to the water level of the channel when passing through the design flow, while backwater or sedimentation will occur in the upstream channel at other flows. Trapezoidal notch is widely used in practice because it can adapt to the change of the relationship between water level and discharge in upstream channels. In order to reduce the length of the upstream water falling section, the bottom of the gap can also be raised to form a weir lifting gap. When the channel bottom is wide and the flow rate is large, it can be arranged into multiple gaps. Sometimes a gate is set at the control gap to adjust the water level of the upstream river.
(3) The falling water wall, that is, the retaining wall at the falling ridge, is used to bear the pressure of filling behind the wall. There are two types: vertical and inclined. Structurally, the falling wall should be connected with the control gap and the control weir.
(4) Stilling basin, located under the sill, has two forms: diffusion and equal width. The cross section is rectangular, trapezoidal and compound, which is used to eliminate the kinetic energy of water flow caused by water droplets.
⑤ Outlet connection section: Its function is to regulate the outflow water flow and guide the water flow to the downstream river smoothly. When the drop is more than 5 meters, multi-stage falling into the water is generally adopted. The structure of multi-stage falling water is similar to that of single-stage falling water. At the end of the upper stilling basin of the middle stage is the control weir of the next stage falling water. The number of multi-level water falls and the size of water falls at all levels should be determined according to the comprehensive comparison of topography, foundation, engineering quantity, building materials, construction conditions and management application. Generally, all levels of falling water adopt the same drop and arrangement. The main problems to be solved in the design of falling water are the steady inflow in the upstream and the full energy dissipation in the downstream.