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Hazard

Water management systems

Hazard Knowledge

Water management systems are used to stabilise channels and manage water levels. The systems are used to manage flooding, maintain water supplies for irrigation, impound water for navigation and to control levels up or downstream of the system for ecological or other purposes.

Water management systems include sluices, weirs, pumping stations and locks. Individual features may appear in isolation, especially static weirs, but usually form part of a system of water management features. Where structures prevent navigation of the channel locks or man-made channels that bypass the system are usually present.

Locks are structures that allow navigation of a channel by vessels. Although lock gates are operated either manually or automatically by someone on site, it is possible for them to move as water pressure changes. This occurs if the gates have not been secured properly, have been poorly maintained or due to a failure of part of the system. Personnel should not work in the water near a lock gate without first taking control of the gates. In addition to the movement of lock gates themselves guillotine gates, used to reduce pressure to allow lock gates to open, can release water forming strong currents.

Pumping stations manage water levels between two separated bodies of water, for example a drain or dyke and a river. The size and design of pumping stations vary greatly, but most operate using an impeller system protected by a weed screen and secure hatches to prevent entry. Impellers may operate with little or no warning and will achieve a hazardous velocity almost immediately. The volume of water moved per second can be substantial, creating hazards upstream and downstream of the system. An upstream pull towards a filter designed to safeguard operating equipment can generate enough pressure to pin or trap a casualty, or rescuer, in a similar fashion to a strainer in fast flowing water. Downstream, large volumes of water can be released creating fast flows, recirculations, eddies and stoppers.

Sluices and weirs may be fixed in position but can often be lowered or raised, changing level depending on local requirements or weather conditions. Weirs are man-made features designed to regulate the flow of water downstream. The regulation of water can create increases in speed and dangerous currents. Changing levels can cause the formation of undertows, hydraulics or recirculations downstream of a weir. A person or object in the water may be drawn towards the face of the weir and forced under the surface. See Hazard Hydrology for further information on recirculations. Depending on the design and the presence of undercutting, a person caught in a recirculation may be flushed out further downstream or held below the surface. The recirculating water may also hold a person within it; self extrication from recirculations can be extremely difficult as the aerated water, strength of flow and disorientation caused makes swimming difficult. Personnel should avoid entering these features unless a well-informed risk assessment identifies that it is safe to do so.

Sluices operate in a similar manner to weirs but allow water to run underneath rather than over the top of the gate. Changes in position and conditions created are harder to identify and are likely to be submerged. Sluice gates restrict flow, by allowing the release of water below the surface which can create dangerous eddies, unseen recirculation, siphons and undertows.

Water management systems may be fixed, be operated manually, automatically or remotely. Activation of automated systems can be based on water level triggers, timed or seasonal programmes. Any decrease or increase in water levels will affect the flow and hydrology of a body of water. Decreasing or increasing flow rates can be hazardous, as unexpected hydrological features may form. When water levels decrease sub-surface objects may come closer to the surface and the risk of entrapment may. Any risk assessment of a water management system has limited currency. Changes in level and operation of the system will change the hazards associated with the system.

Although systems may have visual or audible warnings when activated, it is commonplace for no activation warning to be given. Changes in conditions may not be obvious, for example a sluice gate raised incrementally may not be obvious but conditions may change significantly enough to prohibit entry into an area that was previously safe.