Water and Effluent Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/579379
16 WET NEWS october 2015 from flash floods. The design meets sustainable principles, by attenuating (holding back) excess flows and allowing them to discharge at a controlled rate. "The Hydro-Brake FAS controls have been installed in specially-constructed below- ground concrete culverts. The storage basin will be grassed over so the flood defences tie in with the local agricultural landscape." The cone-shaped Hydro- Brake Flood Alleviation vortex flow control devices installed in the culverts are based on an industry-standard method of flow attenuation, most frequently used in much smaller dimensions as part of urban surface water drainage designs. Hydro's UK Stormwater Operations manager, Andy Kane, explains: "The Hydro- Brake Flood Alleviation vortex flow control's internal geometry is designed so that water can flow unrestricted through the device for as long as possible, before a self-activating vortex is triggered when the water reaches a pre-determined head. In a flood, water is throttled back and released at a controlled rate. We have individually-sized both the controls at Northallerton to create an optimal internal geometry that delivers best-pos- sible hydraulic performance with the minimum amount of upstream storage. "Compared to alternative flood control devices such as orifice plates or penstocks, the vortex flow controls have a larger opening, so more water is able to flow through the culvert unimpeded, meaning less flood storage is needed. At the same time, there is less risk of blockages. This, together with fact that the flow controls have no moving parts or power requirements, means they require minimal maintenance." Trash screens On the Turker Beck, an 857mm outlet diameter Hydro-Brake Flood Alleviation vortex flow control has been installed with a maximum design flow is 1m3/ sec, requiring a back-up storage volume of 12,500m3. The Sun Beck installation, sited upstream of the junction with Turker Beck, has a 684mm Hydro-Brake Flood Alleviation vortex flow control with a maximum design flow of 0.58m3/sec and requiring 1,500m3 of back-up storage. To protect the inlets of the flow control devices, a series of new stepped trash screens have been installed. The low flow channels to the control device's back-up storage areas are sited in the original stream beds. Shallow grassed banks lead up to the same level as the original banks, thereby remaining unobtrusive while providing the amenity of grass meadows outside of high flood events. The installation at North- allerton follows successful flood alleviation schemes built on the White Cart Water in Glasgow, the River Douglas in Wigan and at Weedon Beck in Northamp- tonshire since 2002. Low flow channels to the control device's back-up storage areas are located in the original stream beds the Northallerton catchment is in a low lying river valley surrounded by steep, well-drained agricultural land, makes it susceptible to flash flooding