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Protecting water quality while dredging the Somerset levels

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Dredging the levels.

A special monitoring system is helping protect water quality on the Somerset Levels and Moors where a major dredging operation is under way following severe flooding.

The system, which was supplied by OTT Hydrometry and installed by Wavelength Environmental, is designed to protect the river ecology by issuing email alerts if water quality deteriorates beyond pre-set conditions. Any such alerts would immediately be relayed to the project team and an assessment of conditions would then be undertaken, so that working practices can be reviewed and continued.
The flood caused extensive damage to properties in the area and many residents had to leave their homes. Approximately 170 homes and businesses were affected. The Environment Agency estimated there were more than 65 million cubic metres of floodwater covering an area of 65 square kilometres.
On Monday 31st March 2014, three months after the flooding began, dredging work started on the banks of the river Parrett between Burrowbridge and Moorland, just a few minutes from Junction 24 of the M5 in the south west of England. Costing £1 million per mile, 5 miles of river bank will be dredged (3 miles of the river Parrett and 2 miles of the river Tone), based on restoring the river channels to their 1960’s profile and improving their drainage capability.
In recent years, an accumulation of sediment has narrowed the river channel and this is believed to be just one of the reasons for the severe flooding that took place. A network of mobile real-time water quality monitors is therefore being deployed to continuously monitor water quality upstream and downstream of the dredgers. This work complements the Environment Agency’s wider environmental monitoring.

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The Adcon telemetry system plus Hydrolab WQ sonde.

Automatic alerts
The monitors consist of Hydrolab water quality ‘sondes’ and Adcon telemetry systems which transmit near-live data during the dredging operation that is due to run until the Winter of 2014. The monitors are anchored to the river bed and suspended in the river by means of two small buoys. Each sonde is fitted with sensors for the measurement of dissolved oxygen (DO), ammonium, temperature, pH, conductivity and turbidity. A short cable connects each sonde to an Adcon telemetry unit on the bank, which transmits data via GPRS every 10 minutes. The sondes contain internal dataloggers, however the transmitted data is available to project staff in near real-time via a web-based data portal. If water quality meets the pre-set alert conditions (for temperature, dissolved oxygen or ammonium), email messages are issued via the telemetry units. It is important to note that poor water quality can be caused by a number of factors including low flow levels and high nutrient levels arising from many sources in the area.
The project plan has allowed for up to eight dredging teams, and the monitors are being installed approximately 50 metres upstream and 100-150 meters downstream of the dredgers – to allow sufficient mixing.
Simon Browning from Wavelength Environmental has been monitoring the data from the sondes and says: “The monitors are quick and easy to deploy, and have performed very well; however, portability is extremely important because the instruments have to be moved and redeployed as the dredging work proceeds.
“We have also started fitting GPS units to the telemetry systems so that we can keep track of the monitoring locations. This is important because each dredging team is constantly moving, so the monitors have to be moved regularly.”
Matthew Ellison, a telemetry specialist from OTT Hydrometry, was delighted to be involved in this high profile project and recommended the Adcon systems because they are extremely small and therefore portable, and have been designed to run on very low power, which means they can be left to run in remote locations for extended periods of time with just a small solar panel.

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The Adcon downstream monitor from OTT Hydrometry.

In January, Owen Paterson, Environmental Secretary of State asked for a 20 year Action Plan to be developed to look at the various options for the sustainable management of flood risk on the Somerset Levels and Moors. The plan is supported by a £10m investment from the Department for Transport with a further £500k from the Department for Communities and Local Government, on top of the £10m previously announced by the Prime Minister. This plan has now been published and is available at: http://somersetnewsroom.com/2014/03/06/a-big-step-forward
Whilst the plan recognises that it will not be possible to stop flooding completely, it has 6 key objectives:
1. Reduce the frequency, depth and duration of flooding.
2. Maintain access for communities and businesses.
3. Increase resilience to flooding for families, agriculture, businesses, communities, and wildlife.
4. Make the most of the special characteristics of the Somerset Levels and Moors (the internationally important biodiversity, environment and cultural heritage).
5. Ensure strategic transport connectivity, both within Somerset and through the county to the South West peninsula.
6. Promote business confidence and growth.
“Dredging is one of the one things the local community has really been pressing for and people are going to check the Environment Agency is doing the work properly. The water quality monitoring undertaken by the mobile monitors and by our own static monitors will help provide assurance that the environment is not compromised by this work,” said Graham Quarrier for the Environment Agency.

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