A flood bypass is a region of land or a large man-made structure that is designed to convey excess flood waters from a

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

stream A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, a stream ...

in order to reduce the risk of

flooding A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrolog ...

on the natural river or stream near a key point of interest, such as a city. Flood bypasses, sometimes called ''floodways'', often have man-made diversion works, such as diversion

weir A weir or low head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the river level. Weirs are also used to control the flow of water for outlets of l ...

s and

spillway A spillway is a structure used to provide the controlled release of water downstream from a dam or levee, typically into the riverbed of the dammed river itself. In the United Kingdom, they may be known as overflow channels. Spillways ensure tha ...

s, at their head or point of origin. The main body of a flood bypass is often a natural

flood plain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...

. Many flood bypasses are designed to carry enough water such that combined flows down the original river or stream and flood bypass will not exceed the expected maximum flood flow of the river or stream. Flood bypasses are typically used only during major floods and act in a similar nature to a

detention basin A detention basin or retarding basin is an excavated area installed on, or adjacent to, tributaries of rivers, streams, lakes or bays to protect against flooding and, in some cases, downstream erosion by storing water for a limited period of time ...

. Since the area of a flood bypass is significantly larger than the cross-sectional area of the original river or stream channel from which water is diverted, the velocity of water in a flood bypass will be significantly lower than the velocity of the flood water in the original system. These low velocities often cause increased sediment deposition in the flood bypass, thus it is important to incorporate a maintenance program for the entire flood bypass system when it is not being actively used during a flood operation. When not being used to convey water, flood bypasses are sometimes used for agricultural or environmental purposes. The land is often owned by a public authority and then rented to farmers or ranchers, who in turn plant crops or herd

livestock Livestock are the domesticated animals raised in an agricultural setting to provide labor and produce diversified products for consumption such as meat, eggs, milk, fur, leather, and wool. The term is sometimes used to refer solely to animals ...

that feed off the flood plain. Since the flood bypass is subjected to

sedimentation Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to the ...

during flood events, the land is often very productive and even a loss of crops due to flooding can sometimes be recovered due to the high yield of the land during the non-flood periods.

Examples

Bonnet Carré Spillway The Bonnet Carré Spillway is a flood control operation in the Lower Mississippi Valley. Located in St. Charles Parish, Louisiana, about west of New Orleans, it allows floodwaters from the Mississippi River to flow into Lake Pontchartrain and ...

Eastside Bypass East Side or Eastside may refer to: Places Australia * East Side, Northern Territory Canada * Eastside, Ontario, a neighborhood in Sault Ste. Marie, Ontario * Downtown Eastside, Vancouver, British Columbia United Kingdom * Eastside, Bi ...

Yolo Bypass The Yolo Bypass is one of the two flood bypasses in California's Sacramento Valley located in Yolo and Solano Counties. Through a system of weirs, the bypass diverts floodwaters from the Sacramento River away from the state's capital city of Sac ...

{{DEFAULTSORT:Flood Bypass Hydraulic engineering Hydrology Flood control