Grille Monitoring in Scottish Borders
Hydro-Logic was appointed to supply 4 trash screen monitors to the Scottish Borders Council. They were installed to monitor the level upstream of the screens and to provide alarms when the level reached a set threshold. This alarm was to be used by the council to indicate a build up of debris in front of the screen that would have created a flood risk potential. The alarms are transmitted along with collected data back to an IDQTel system operated out of the Councils Border Care Office.
The grilles were trouble spots for local flooding - they often became blocked with leaves and other debris and during periods of heavy rain would cause local flooding as the burns which flowed through them backed up behind the blocked grille.
One of the alarms systems is installed on Jedburgh's Skiprunning Burn, which was the cause of severe flooding on 3rd - 4th January 1982.
In autumn 2005 the area was hit by heavy rainfall and the systems began to show their worth. The system in Jedburgh dialled out for three flood events in the early hours, and the prompt response of maintenance personnel clearing the material blocking the grille saved local residents from waking up to flooded basements.
The Hawk loggers use pressure transmitters to measure the depth of water in front of the grille. If the water exceeds a threshold (approximately halfway up the grille), the Hawk dials out with its GSM modem and sends an alarm message to an IDQTel alarm forwarding system in the council offices. The IDQTel system then forwards the alarm via SMS and email to various destinations, including the DLO responsible for cleaning the grilles.
At one particular site in Selkirk, the Long Philip Burn rose so quickly that there was insufficient warning time available to monitor water-levels only.
In May of 2006 Scottish Border Councils (SBC) approached Hydro-Logic to add a tipping bucket rain gauge to their network as part of their early warning plan.
The solution is to install a telemetered tipping bucket rain gauge to measure the intensity of rainfall. An Isodaq Hawk XT outstation transmits an alarm message to the IDQTel system based in SBC's 24-hour call centre (Bordercare). This system operates by a GSM modem connected to the Hawk XT outstation.
Early monitoring means vulnerable areas can be inspected on receipt of the warning message delivered to Bordercare. If riverbank locations are at risk of overtopping the banks, Emergency Planning Officers (using the raingauge information) can provide residents registered in the flood warning group of this flood-prone area with an early warning by automated phone messages, so that they can protect themselves and their property.
Continuous records of levels in the burns at the trash screens are maintained by IDQTel. Records can be viewed graphically by council staff at any time. These clearly show when the grilles become blocked, and the speed in which the blockage was cleared - vital information for a council keen on delivering a high level of service.
Performance of the system is constantly monitored with daily check-in calls from each outstation, where the 15m level time series data is transferred to IDQTel - even if no alarms are present.
The Hawk loggers, sensor and modems in this application are completely battery powered, using a combination of replaceable lead-acid external batteries and an internal alkaline backup battery. Battery -low alarms are triggered when either battery falls below a pre-set threshold; these are delivered to the maintenance staff in the same way as the level alarms.
David Campbell, Flood Prevention Officer at Scottish Borders Council, is very pleased with the performance of the systems:
'I would certainly use the system again for any problem drainage grilles.'
The system has since been used in future flood prevention plans.