overshot weir manufacturer

WATERMAN TILTING WEIR (OVERSHOT) GATESare an overflow-type gate used to control levels in canals, basins and other agricultural, municipal and industrial applications.

Waterman Tilting Weir (Overshot) Gates are an overflow-type gate used to control levels in canals, basins and other agricultural, municipal and industrial applications.

Overshot gates (also known as pivoting weir gates) are used to control upstream water levels. Versatility, efficiency, and safety are the primary reasons the Fresno Overshot Gate is the method of choice for municipal, agricultural, and industrial canal water control.

... TILTING WEIR GATES allow for precise upstream water control to tight tolerances. An inherently safe option, the gate allows for surge flows and debris to pass over.

... bottom-up discharge flow control, debris sluicing, and automatic emergency dump, and top-downsurface control and/or measuring weir. Easily deployed and programmed, cost efficient, reliable. Debris control made easy.

An overflow style adjustable weir that consists of a rectangular steel panel, hinged across the bottom, which is raised and lowered by two cables attached to the upper corners of the gate leaf. Basically, liken it to a drawbridge placed in a canal.

York Civil Pty Ltd engaged AWMA to custom design vertical water control gates, fishway gates and hydraulic actuation systems for SA Water’s Pipeclay and Slaney Weirs.

Five large AWMA Fixed Base Overshot (decant) gateswere developed to simulate overshot flow patterns of the existing stoplogs, whilst Segmented Stopboards were supplied for the new environmental fishways.

The overshot gate leaves were manufactured from marine grade aluminium with grade 316 stainless steel embedded frames and stainless steel dual cylinder actuation systems.

Marine grade aluminium segmented stopboards and AWMA lifting ladders were supplied for the fishway gates. Design features include overshot flows with low velocities for safe fish passage.

During his doctorate work in southeastern Australia, Pflugrath examined weirs, or small dams built across rivers, and how they impact fish passage. His findings were recently published in the paper, “,”in Ecological Engineering.Craig Boys of New South Wales Department of Primary Industriesled the project. The work was supported by the Australian Centre for International Agricultural Research.

Pflugrath focused his study on two weirs commonly used in rivers—the overshot weir and undershot weir.An overshot weir, or sharp-crested, passes water over the top of a downward opening, or gate, and an undershot weir, or sluice, passes water under an upward opening. Both weir designs aim to control water flow and increase water level upstream.Undershot and overshot weirs are used at major hydropower dams, including those on the Columbia and Snake rivers.

Thesestructures also can cause physical stressors likestrike, fluid shear, and rapid decompression. Strike is defined as when a fish collides with a part of the weir structure and injures its eyes, scales or gills. Fluid shear occurs when there is a change in water velocity and the fish is pulled in different directions, causing injury to gill flaps and eyes. Fish exposed to rapid decompression may suffer from barotrauma—any injury, mild or severe, that is the result of changes in pressure—which occurs becausebubbles form in the blood and gas in organs such as the swim bladder.

Overshot weirs have been widely regarded as the safest of the two weir designs for freshwater fish passage—something Pflugrath tested and confirmed using the PNNL-developed in Deniliquin, Australia.

“The overshot weir is generally safer for fish than an undershot weir because it eliminates rapid decompression, greatly reduces the chances of exposure to shear, and if the plunge pool is designed correctly can reduce the chances of strike,” Pflugrath explains.

In this study, the Sensor Fish were dropped upstream of the Colligen Creek Weir and the data was collected downstream by boat. Using pre-determined pressure calculations, the Sensor Fish were assessed for physical stressors fish may experience when passing through weirs.

The team found the undershot weir creates more risks of injuries overall than the overshot weir. The researchers concluded that although strike is a concern for overshot weirs, it can be easily fixed by changing weir design. Since there’s a low risk of fish suffering injuries from shear and decompression, “the overshot weir should be considered as the safer alternative to an undershot weir for low-head structures,” Pflugrath found.

The undershot weir was more likely to expose fish to barotrauma because rapid decompression occurred when the Sensor Fish traveled quickly under the weir opening and immediately entered more shallow water. In contrast, fish experienced very little pressure change when they passed the overshot weir because they were released near the surface of the water.

Strike and shear were recorded in all Sensor Fish deployments at the overshot and undershot weirs. However, the severity of shear was higher at the undershot weir. It is more likely that the undershot weir would create higher levels of fluid

Additionally, Pflugrath found both weir designs at Colligen Creek Weir have the potential for more strike impacts which occur when fish collide with some part of the structure. Strike was recorded in 83 percent of the deployments at the overshot weir and at 72 percent of the undershot weir deployments.

The Sensor Fish data showed that operating an overshot weir with an insufficient depth of water will likely cause fish collisions with objects submerged downstream of the weir.Strikes could be decreased by modifying the structure of the weir.

“The simplest way to reduce strike through an overshot gate is make the plunge pool deeper,” Pflugrath said. “The plunge pool is the area of the structure that the water falls into. Our findings suggest that the plunge pool depth should be at least 40 percent of the distance that the water falls from the upstream to the downstream water surface. For example, if the water falls 10 feet, the plunge pool should be at least four feet deep.”

Pflugrath cited other research that has shown redesign improvements at the Removable Spillway Weir, an overshot weir at Ice Harbor Dam on Washington’s Snake River. The weir was modified so that the spillway slope and deflectors would be less likely to injure fish. Using the Sensor Fish and then live fish, it was determined that the redesign improved hydraulic conditions.