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What Is a Flood Crest?

"Flood crest" refers to the highest phase of a flood wave when it passes through a particular location. This highest point prompts people controlling the water flows to issue flood warnings when an inundation is expected near a dam or a river over a dry area. Flood crest is controlled by gates specially made for controlling the swirling waters.

  1. Calculation

    • The river normally flows at certain amount of feet, say 23 feet, usually measured as normal river depth. Flood crest is also an elevation-type number that is measured by subtracting normal water level of the river from the total height of the water level during the flood (e.g. 47 feet). In this case the flood crest is 24 feet.

    Prediction

    • Flood crest prediction is a challenging task. It involves hundreds of readings of water flows and river stages (river stage is an elevation of the water surface in reference to a predetermined height). These readings can be obtained from geological surveys that monitor water flows and river stages through automatic measuring devices and satellite transmitters.

    Flood Crest Gates

    • Flood gates are also known as crest gates. They are made to control water flow in a reservoir or river. Crest gates are not fixed, but adjustable by lowering or raising them. Because these gates control the rise of water surface by rerouting the water or by sending it to a storage dam, they are called the “crest gates.” These gates can stop water flow to control the surging waters. The gates are installed to adjust and divert water flow in sluices or canals.

    Types of Flood Crest Gates

    • Bulkhead gates are designed as parallel walls with removable sections. These can be elevated to allow water to flow beneath. Sometimes these crest gates slide to sides, especially while controlling large water systems.

      Hinged crest gates are also sections of a wall that rotates vertically from its horizontal base, as a result of which the height of the dam can vary. These gates are controlled by the mechanical properties of water.

      Apart from these two types of gates, which are designed to control flood crest, recently some other types of gates (i.e. radial and drum crest gates) have been introduced for similar purpose.

    Other Definitions of Flood Crest

    • Flood crest is the highest point of a flood wave. Hydrological terms refer to a flood crest as the highest level of the flood wave when it passes a particular point, which may be a dam, spillway, dike or a weir, to the height of which water has to rise before it can pass over the structure. Flood crest width means the dam’s width at the crest level or topmost point of the dam. Flood crest width is referred to in terms of thickness in the case of arch-type dams and as width in the case of other dams.

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