Gabion weirs are a type of hydraulic structure made of wire mesh baskets filled with stones or other suitable materials. They are commonly used for river training, erosion control, and water conservation purposes. The flow characteristics of gabion weirs play a crucial role in their effectiveness and overall performance.
The primary flow characteristics of gabion weirs include the following:
Flow capacity: The ability of a gabion weir to pass a certain amount of water is known as its flow capacity. It depends on the size and number of openings in the weir structure and the velocity of the water passing through it.
Discharge coefficient: The ratio of the actual flow rate to the theoretical flow rate through a gabion weir is called the discharge coefficient. It depends on the geometry and roughness of the weir structure and the approach velocity of the water.
Energy dissipation: The process by which the energy of the flowing water is dissipated as it passes through a gabion weir is known as energy dissipation. It depends on the size and shape of the weir structure and the velocity and depth of the water.
Flow pattern: The pattern of water flow through a gabion weir depends on the weir's geometry and the flow rate and direction of the water. The flow pattern can be classified as submerged flow, free flow, or surcharged flow.
Sediment transport: Gabion weirs are often used for sediment control, and the flow characteristics of the weir affect sediment transport in the river or stream. The size and shape of the weir structure and the velocity and depth of the water play an essential role in sediment transport.
The flow characteristics of gabion weirs must be carefully considered during their design and construction to ensure optimal performance and effectiveness.
Weirs are generally used to measure and regulate the flow in open channels. They are
constructed of concrete or metal depending on the shape and size of river and open channel. Gabion
weirs are the simplest form of rectangular broad-crested porous weirs that usually span the full
width of a river. Being highly porous and good in the availability of boulders in the hilly
areas, weirs constructed of gabions are hydraulically and economically effective. Concrete
structures constructed across the open channels bring ecological changes in the flow. Such
changes affect the environmental conditions of the river, among that include adverse effects on
fish spawning and migration. The flow that passes through the rocks, stones, and gravel enhances
the dissolved oxygen content of water, making the structures environmentally and ecologically
friendly. Physical and chemical materials, such as sediments and suspended organic matter, can
pass through the porous body of these structures, which results in the reduction of the
sedimentation behind the weirs.
Moreover, bacteria in the crevices and pores of a gabion weir facilitate the degradation of
particulate organic materials in the water. This biochemical activity results in the
purification of the water passing downstream through the weir. Also, the flow turbulence through
these porous structures increases the flow aeration and may lead to river water refinement.
