Water monitoring
River level monitoring lowers bridge scour risk
The trial was conducted at a bridge over Vales Burn near Hawick in Scotland, and the monitoring equipment was provided by OTT HydroMet. OTT’s Wendy Strain says: “The system was set to deliver alarms at pre-set water levels, which enhanced the timing and efficiency of site inspections.” Climate change is increasing the frequency
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and severity of extreme weather events such as storms and floods. This presents a growing threat to structures that could be susceptible to scour during periods of high water flow. The trial was therefore established to determine whether access to remote water level measurements could enhance the protection of critical transport infrastructure.
BACKGROUND
The stability and integrity of structures such as bridges, culverts and walls can be compromised by ‘bridge scour’ which is caused by fast-flowing water that removes material from around the footings of bridge abutments or piers. There are three main types of scour. Local scour is caused by the faster water flow that occurs around piers and abutments. Constriction scour is created by water accelerating through a narrow opening, and degradation scour can lower a river bed over a longer period, both upstream and downstream of a structure. The effects of bridge scour can be
disastrous. For example, during a flood in 1987, the Glanrhyd Bridge in Carmarthenshire partially collapsed, causing a train to plunge into the River Towy, killing the driver and three of the passengers. In 2009, failure of the Malahide Viaduct in Dublin, Ireland was caused by foundation scour. Two commuter trains packed with hundreds of passengers were just seconds away from disaster when a 20-metre section of the viaduct collapsed after they passed over it. Nobody was killed, but travel chaos ensued. Today, highways and rail authorities conduct regular inspections in order to asses scour risk.
BRIDGE SCOUR IN SCOTLAND Transport Scotland is split into four operational regions, and Jim Brown is South East Unit bridge manager. Prior to this position, Brown spent 42 years as a civil engineer with Network Rail, 13 years of which he headed the geotechnical discipline in Scotland – so it is fair to say that Brown knows a thing or two about bridge scour. “The most important objective is the early detection of increased risk,” Brown explains. “Once we have established which structures are more vulnerable during flooding, we are able to implement different levels of mitigation.
44 April 2022 Instrumentation Monthly
ngineers at Transport Scotland have investigated the potential for water level monitoring systems to help mitigate risks where transport infrastructure interacts with moving water.
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