Nature – River Mel Restoration Group

Nature

River Mel Restoration Group

A dry spring, followed by this autumn’s Indian summer has led to some of the lowest river levels seen in recent years. As we write this, in mid-October, the upper Mel is almost completely dry through the length of Stockbridge Meadows.

These low levels are a cause for concern for several reasons. Apart from the obvious and hopefully temporary effect on the wildlife, the river also forms an integral part of Melbourn’s sewage treatment system. The treated effluent from the sewage treatment works is discharged into the Mel on a three hourly cycle. This effluent is clean and, with normal river flows, is sufficiently diluted and dispersed so that it has no detrimental affect on either the wildlife or the environment. However, this natural balance can be disrupted to the detriment of the river in times of low flow, high rainfall, or both.

When it does rain, there is a time lag between rainwater soaking through the ground to reach the aquifers. A further problem is that in the summer, or after a period of drought, the ground is often so dry that the rain does not soak in, but instead runs off the baked ground into the drainage system. Besides causing local flooding, the run off from roads and driveways can then overwhelm the sewage treatment works. If this happens untreated storm water mixed with incompletely treated sewage can spill over into the river. If the river is flowing normally this is not a problem, as the storm overflows are quickly diluted and dispersed. But if the river flow is reduced then these storm overflows cannot disperse in the same way and in effect the river would become an extended sewer.

Ideally we wouldn’t want these ‘events’ to happen at all, but we live in an imperfect world, so the best we can hope for is some form of mitigation. This is one of the reasons why the Environment Agency supports the river flow in summer by pumping water into the river from aquifers elsewhere in the region. This pumped support to the river is triggered by low flows through a gauging station downstream in Meldreth that automatically sends readings back to the Environment Agency. This year the Environment Agency has struggled to provide sufficient support to the river, even though water has been pumped into the Mel throughout the spring and summer.

The drought has also put pressure on the wildlife that lives in and around the river. We hope that there are enough deeper pools within the river to enable the survival of the fish, but concentrating fish and wildlife into small areas makes them much more vulnerable to attack by predators. It is very difficult to assess accurately what is happening to the various populations of wildlife without some form of systematic survey. The Environment Agency and the River Restoration Centre have already carried out some baseline surveys of the fish and invertebrate populations that live in the river. Now we need to systematically monitor and identify the small mammals that rely on the Mel for their survival. This we are doing by using a series of in-river monitoring stations that have been loaned to us by the Countryside Restoration Trust. This study will provide a much better understanding of the number of species of small mammals that frequent the river and also where along its stretch they are located. The study should also give some indication of how they suffer when their habitat is under intense pressure, such as in times of drought. Working Party Dates 10th December 2011 - Meldreth 7th January 2012 - Melbourn 28th January 2012 - Meldreth 18th February 2012 - Melbourn

All working parties meet at 9.15am for a 9.30am start and we endeavour to finish by about 12.30pm. In Melbourn we meet at the Pavilion on the Recreation Field and in Meldreth at 14 Flambards Close. For further information, please contact info@rivermel.com or telephone Maureen Brierley on 01763 262752.

The dry river bed behind Dolphin Lane The dry river bed in Stockbridge Meadows

Chris Thomas

Cambridge Carpet & Upholstery Cleaning

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