Types of Spillway: Comprehensive PDF Guide

Spillways are critical components of dams, serving to control water levels and prevent overtopping during high flow events. They are designed to safely pass excess water, ensuring the structural integrity and safety of the dam. Understanding the different types of spillways is essential for their effective design, maintenance, and operation. This article explores the various types of spillways, their features, and applications.

Spillways can be broadly categorized into two main types based on their location and function: overflow spillways and bypass spillways. Each type has its unique characteristics and use cases, which we will delve into in detail.

Overflow Spillways

Overflow spillways, also known as free overflow spillways, are designed to pass excess water by allowing it to flow over the top of the dam. They are simple in design and construction, making them cost-effective and commonly used in small to medium-sized dams.

Overflow spillways can be further classified into two sub-types based on their crest design:

Rectangular Crest Spillway

Rectangular crest spillways have a straight, horizontal crest, which is easy to construct and maintain. The crest width is designed to pass the maximum expected flood without causing excessive scour downstream. However, they can be prone to cavitation, a phenomenon that can cause damage to the spillway structure over time.

Examples of rectangular crest spillways include the Hoover Dam in the United States and the Three Gorges Dam in China.

Circular Crest Spillway

Circular crest spillways have a curved, semicircular crest, which helps to minimize cavitation and reduce the risk of damage to the spillway structure. They are more complex and expensive to construct than rectangular crest spillways but offer improved performance and longevity.

An example of a circular crest spillway is the Grand Coulee Dam in the United States.

Bypass Spillways

Bypass spillways, also known as controlled spillways, are designed to pass excess water through a controlled channel or tunnel, bypassing the dam crest. They offer greater control over water flow and can be used to pass larger flood events than overflow spillways. However, they are more complex and expensive to construct.

Bypass spillways can be further classified into two sub-types based on their location:

Morning Glory Spillway

Morning glory spillways are named for their distinctive shape, which resembles a morning glory flower. They are located at the base of the dam and pass excess water through a tunnel or channel that leads to a downstream outlet. Morning glory spillways offer excellent control over water flow but can be expensive to construct due to the need for excavation and tunneling.

An example of a morning glory spillway is the Glen Canyon Dam in the United States.

Chute Spillway

Chute spillways are located on the side of the dam and pass excess water through a controlled channel or chute that leads to a downstream outlet. They are simpler and less expensive to construct than morning glory spillways but offer less control over water flow.

An example of a chute spillway is the Aswan High Dam in Egypt.

Understanding the different types of spillways and their features is crucial for the effective design, maintenance, and operation of dams. Each type of spillway has its unique advantages and limitations, and the choice of spillway will depend on the specific requirements and constraints of the project. By selecting the appropriate spillway type and designing it correctly, engineers can ensure the safety and longevity of dams, protecting lives and infrastructure downstream.