ABSTRACT
Spillways are invariably provided in storage dams for safe disposal of the excess water flowing into the reservoir after it has filled up. Spillways may have simple overflow crests or may have controlled crests with gates. The controlled crests permit controlled release of surplus water in excess of the reservoir capacity and convey the same into the river channel below the dam or to any other drainage area in such a manner that the foundations are protected from erosion and scour. Overflow on the dam at floods cannot be allowed unless the downstream face is designed for passing the floods with requisite depth and the bed well protected to take the impact of falling waters. Many failures of dams have been attributed to inadequate spillways capacity with consequent overtopping of bund. In case of earthen dams if the water overtops there is no possibility of saving the dam from failure. Adequate spillway is a very important factor in the design of earthen dams. Thus the object of the spillway design should be to provide a safe and adequate spillway structure at most economical cost, without impairing the safety of the dam. Dam failure due to inadequate spillway capacity may result in heavy loss of life and property. In the hydraulic design of a spillway the following procedure is generally followed: (i) First, hydrological analysis to determine the magnitude of design flood (already dealt
with in Chapter 2). (ii) And thereafter detailed hydraulic analysis.
