Stop 19: Water management

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The River Severn feeds water into the canal near Newtown, whilst the River Tanat feeds in further north at the northern end of the Welsh section, at Carreghofa. The canal is further fed by various small land drains, ditches and streams along its length, whilst other watercourses are culverted underneath the canal.

Many of these smaller watercourses drain nearby road run-off and agricultural land, increasing the risk of pollutants entering the canal. The effects can be extremely harmful to the aquatic ecosystem. During persistent and heavy rainfall the quantity of water flowing down via these watercourses increases, with further diffuse run-off from agricultural land down the steep hillsides.

Containing elevated levels of nutrients, sediments and other pollutants, this can directly poison wildlife and reduce the amount of oxygen available to plants and organisms needed for survival. The addition of pollutants can also alter environmental conditions, which promotes the growth of more aggressive plants, to the detriment of the less competitive species.

Life in the slow lane

The slow-flowing nature and managed water levels are what create this unique habitat that is such a vital resource for wildlife. However, maintaining the right conditions is fundamental to the sustainability of this sensitive ecosystem. The species that thrive here are especially reliant upon sufficient availability of water throughout the year, to discourage invasion of competitive marginal plants, as sediment gradually builds up and water levels drop.

Invader alert!

A certain level of intervention is necessary to manage the water levels and flow and conserve the ecological interest. In summer, rapid growth of the more competitive and invasive weeds can take over much of the water column, blocking out light which is crucial for the more sensitive plant species to flourish. This can further restrict flows and volume of water needed to sustain the canal downstream. Routine aquatic weed management is often undertaken to help maintain the balance of open water extent with marginal fringe and promote the preferred conditions for the more specialised species, whilst securing the operational needs of the water resource. Dredging may also be used to target silt build-up in the channel.

The water levels and flow rates in the canal can also be controlled by structures including overflow weirs and sluices, which provide a channel for taking a flow of excess water away from the canal to surrounding watercourses.