I have been working on the Monmouthshire and Brecon (M&B) canal recently. When we undertake some repairs to the canal, we need to empty it of water (known as dewatering). Water is emptied by opening up sluices or bed valves and these drain the water down into adjacent separate water courses. We have been asked by Natural Resources Wales (NRW), to look at the way we manage our dewatering work
NRW is worried that when we open up our sluices/bed valves we release muddy water into the receiving waters, which could impact on water quality and important fish spawning areas. I have been working with the local Waterway Supervisor, on the practical measures we can use to minimise impacts.
The site we were working on, was drained down by opening a sluice, which feed into a channel which led into a local stream. We needed to slow the water down as it came out of the sluice, the slow moving water would ensure that the majority of suspended sediment would sink to the channel bed. To do this the local team installed a series of straw bales covered in jute like material, to hold back the water and allow it to filter through at a reduced rate.
To ensure that this process worked, I went to site at the start of the dewatering works, to undertake suspended solid monitoring. Suspended solids are an indication of how muddy the flowing water is. I have a hand held meter which measures the amount of suspended solid in the water. NRW had set a suspended solid threshold of 60 mg/l, so suspended solid readings were not to exceed this. I am glad to say that process worked well.
Last date edited: 18 December 2014
About this blog
Sara has been with the Trust for 17 years, working in the environment team. She is a senior environmental scientist and will cover waste and water quality issues. She works closely with the South Wales and Severn Waterway team but her work will also pick up national issues, such as the Water Framework Directive.
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