Coldham’s Common chalk stream dries up: lack of rain and over-abstraction blamed

Coldham’s Brook, one of the globally unique ecosystems base on the region’s chalk stream network, ceased flowing this week.

The Brook runs from Cherry Hinton to Barnwell Road and up to the Abbey stadium on Newmarket Road: it travels through large swathes of Coldham’s Common.

The alarm was posted to Twitter by Cambridge resident Monica Hone on September 26 whose caption to pictures of the stream read: ‘Another chalk stream death due to the greed of the unsustainable growth lobby and @Cambswater refusing to do anything that would genuinely reduce demand.’

Chris Smith in a tweet on Tuesday (September 27) said: ‘No water under the bridge: Coldhams Brook, Coldhams Common, Cambridge has run dry for first time that I have known. Brook is spring fed and this appears a direct result of water abstraction.’

The environmental group Keep Waterbeach Local replied: ‘Should development be progressed unless nailed-on assurance can be given that the provision of water can meet growth whilst guaranteeing no harm to the chalk streams and the life they support?’

Monica Hone pointed out there was still water up near the Sainsbury’s superstore off Coldham’s Lane yesterday, but that the water level ‘​​receded approx 6 metres in 24 hours’.

A walk round the worst-affected area raised several questions. How did the water level go down so fast? How much rainfall will be needed to restore the Brook – and will it ever happen? What is happening to the chalk stream underground? What happened to the government help that was promised last year?

Yet water deflectors were installed by The Wildlife Trust over the summer, with support from Abbey People, Friends of Cherry Hinton, Cambridge City Council, and Cambridge Water (whose grants aid the work). The buttressing and channeling work to support the stream now look rather forlorn. Just weeks ago the water around the bridge was about 20cm: now it is just rocks and dry wood.

Chris Smith noted: ‘These are flow deflectors installed in Coldhams Brook & intended to improve low flow speeds to help biodiversity. There is though no flow. They are funded by Cambridge Water and the council. Shouldn’t we be dealing with the over-abstraction?’

The Cam Valley Forum newsletter, published September 29, says: “It is not clear why the latter [part of the stream] barely reaches Coldham’s Lane at Sainsbury’s, whilst still flowing (feebly) further upstream. This year the more vulnerable Coldham’s Brook has dried up altogether much further upstream than usual.

“It takes up to four months of abundant rainfall to recharge the aquifer, until evapotranspiration takes charge again in the spring.”

Evapotranspiration is the sum of all processes by which water moves from the land surface to the atmosphere via evaporation and transpiration.

The current situation, says the update, is that the chalk streams have to all intents and purposes seized up. The ground water isn’t there any more. Plants, bright and green, that are usually growing on the bank are already growing in the bed. Effectively, the normal function of nature has been suspended.

The news briefing adds that ground water, “which had earlier been depleted by natural spring flow and over-abstraction due to human rapaciousness” is no longer being replenished by rain water.

Cam Valley Forum’s data reveals a significant soil moisture deficit and, with this year’s lack of rain for the streams to recharge, it comments of the situation: “There is no reason to be optimistic and no reward for being patient.”

Cambridge Water stated that “flows in the creek had receded… due to an exceptional dry spell”.

River, sea, groundwater and rainfall data recorded by the government shows that the water level on the River Cam is normal at Jesus Lock and ‘low’ – 0.19m – at Baits Bite Lock.

The Environment Agency said in a statement: “Recent rainfall hasn’t been enough to replenish groundwater and reservoir levels. 11 out of 14 Environment Agency areas remain in drought. We are working with water companies to manage water resources and reduce the impacts of drought next year.”

Chalk Streams are rare habitats, often referred to as England’s rainforests. Most drinking water in the east of England comes from rainwater stored in deep, natural limestone aquifers that feed limestone streams.