Understanding Overflow Dams and Spillways

The question asks for another name for an overflow dam. An overflow dam is essentially a structure built across a river or stream to retain water, and it is designed in such a way that excess water can flow over its crest or a specific part of it. This controlled overflow is crucial for managing water levels and preventing damage to the dam structure during floods or periods of high inflow.

Analyzing the Options

Let's examine the given options to determine which one best fits the description of an overflow dam:

• Rockfill dam: A rockfill dam is a type of embankment dam that uses rock and compacted earth or impervious materials. While it retains water, the primary way it handles excess water is typically through a separate spillway structure, not by overflowing the main rockfill body itself. Overflowing a rockfill dam without a properly designed overflow section can lead to erosion and failure.
• Spillway: A spillway is a structure used to provide the controlled release of excess water from a reservoir or dam downstream. It acts as a safety valve. Many dams incorporate a spillway directly into the dam structure, or it can be a separate structure. When a dam is designed specifically to allow water to flow over its crest or a dedicated section of it during high flow periods, that overflow section functions as a type of spillway. Therefore, an overflow dam often refers to a dam where the crest itself or a section acts as the spillway.
• Reservoir: A reservoir is the artificial lake or body of water created upstream of a dam by the impounding structure. It is where water is stored, not a type of dam or an overflow mechanism.
• Gravity dam: A gravity dam is a massive concrete dam that resists the horizontal thrust of the water primarily by its own weight. Gravity dams can be designed with overflow sections or spillways built into their structure, allowing them to function as overflow dams in some cases. However, 'gravity dam' describes the structural principle, not necessarily the overflow function itself. Not all gravity dams are designed for crest overflow.

Identifying the Correct Term

Based on the analysis, the term that most directly relates to the concept of an overflow dam, where water is allowed to flow over a specific part of the structure, is a spillway or a dam incorporating a spillway designed for overflow. A dam designed primarily for controlled overflow over its crest is a type of overflow structure, and the term "spillway" is closely associated with this function.

Specifically, some types of dams, like certain weirs or overflow spillways built into the dam body, are often referred to as overflow dams because they allow water to flow over their top. This function is the defining characteristic of a spillway designed to handle excess flow.

Therefore, an overflow dam is also known as a Spillway.

Revision Table: Dam Types and Functions

Additional Information on Spillways and Overflow Dams

Spillways are critical safety features for any dam. They prevent the dam from being overtopped by floods, which could lead to structural failure. There are different types of spillways, including:

• Overflow or Ogee Spillway: Designed with a curved profile (like an 'S' on its side) to allow water to flow smoothly over the crest. This is a common type associated with the term 'overflow dam'.
• Chute or Trough Spillway: Water flows through a channel down a slope.
• Shaft or Morning Glory Spillway: Water enters through a vertical or inclined shaft.
• Side Channel Spillway: Water flows into a channel parallel to the spillway crest before discharging.

An overflow dam, particularly one with an Ogee-shaped crest, is essentially a dam structure designed specifically to function as an overflow spillway. The term "spillway" refers to the *function* and the *structure* that facilitates controlled overflow, making it the most appropriate alternative name for a dam designed for overflow.