On-site machinery: Water management systems - Test

Hazard

On-site machinery: Water management systems

Hazard Knowledge

Water management systems are the various types of on-site machinery used to stabilise channels and manage water levels. The systems are used to:

  • Manage flooding
  • Maintain water supplies for irrigation
  • Impound water for navigation
  • Control levels up or downstream of the system for ecological or other purposes

Water management systems include:

  • Sluices
  • Weirs
  • Pumping stations
  • Locks

Individual features may appear in isolation, especially static weirs, but usually form part of a system of water management features. Locks or channels that bypass the system are normally found where structures prevent navigation of the main channel.

When these systems are activated or in use, they may create movement of water that can produce a range of hydrological hazards. For more information refer to Hydrological hazards.

Locks are structures that allow vessels to navigate a channel. 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 in the system. Guillotine gates are used to reduce pressure to allow lock gates to open; these can release water, which can form strong currents.

The Canal & River Trust website provides more information about lock gates and canals.

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, with secure hatches to prevent entry. Impellers may operate with little or no warning and will almost immediately achieve a hazardous velocity. The volume of water moved 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 person in water or rescuer, similar to a strainer in fast-flowing water.

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. 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.

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.

Activation of water management systems

Water management systems may be fixed, or 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, submerged objects may come closer to the surface and the risk of entrapment may increase. Any risk assessment of a water management system is time-limited. Changes in water levels 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 common for no activation warning to be given. Changes in conditions may not be evident, 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 assessed to be safe.