Design Principles that are involved in the Design of Flow over an Ogee Crest Spillway

The ogee-crested spillway�s ability to pass flows efficiently and safely, when properly designed and constructed, with relatively good flow measuring capabilities, has enabled engineers to use it in a wide variety of situations as a water discharge structure (USACE, 1988; USBR, 1973). The ogee-crested spillway�s performance attributes are due to its shape being derived from the lower surface of an aerated nappe flowing over a sharp-crested weir. The ogee shape results in near-atmospheric pressure over the crest section for a design head. At heads lower than the design head, the discharge is less because of crest resistance. At higher heads, the discharge is greater than an aerated sharp-crested weir because the negative crest pressure suctions more flow. The spillway is among the most important structures of a dam project. It provides the project with the ability to release excess or flood water in a controlled or uncontrolled manner to ensure the safety of the project. It is of paramount importance for the spillway facilities to be designed with sufficient capacity to avoid overtopping of the dam, especially when an earth fill or rockfill type of dam is selected for the project. In cases where safety of the inhabitants downstream is a key consideration during development of the project, the spillway should be designed to accommodate the probable maximum flood. Many types of spillways can be considered with respect to cost, topographic conditions, dam height, foundation geology, and hydrology. In this study, the ogee-crested spillway�s or overflow spillways discussed in this paper. A section on design of spillways that considers cavitation and aeration.