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River Lambourn Dredging Restoration – April 2019 update

Dredging Restoration Update 

This is our diary of the restoration of the River Lambourn in East Garston after unauthorised dredging in late 2018.

 

Seven weeks after the gravel bed of the River Lambourn was reinstated by the Environment Agency in March 2019, how is the river faring?

 

As reported here, there were incidents in late November and early December of unauthorised dredging the river bed in East Garston. Please see diary of events below.

Friday 8 March 2019

We had a chat with Environment Agency technical specialist Paul St Pierre on Friday 8 March about the progress of restoration work, the importance of the gravel bed of a chalk stream and the precious ecology of a Winterbourne (a stream that doesn’t flow year-round).

Monday 11 – Wednesday March 2019

This video from 11 March shows the last phase of the restoration work overseen by the Environment Agency where 100 tonnes of gravel was spread along approximately 80 metres of riverbed. 

They are using local flint gravel from the Kennet Valley to match the gravel native to the River Lambourn. In time, the river weed will begin to root again throughout the gravel, creating a habitat for the small invertebrate creatures that the fish and waterbirds feed on.

Two days later, on 13 March 2019 the stream flows beautifully clear over the new gravel.

The Background

 On 9 January 2019 the Environment Agency (EA) visited the site to assess the extent and nature of the restitution work required. We understand that this work will start some time after 16 January and will be carried out by, or the very least closely supervised by, the EA. 

On 23 January 2019, the EA said that no further comment was possible as investigations were still taking place but that they were viewing the matter ‘extremely seriously.’

On 30 January 2019, the EA confirmed it was using statutory powers to access Mabberley’s Stables in order to “remedy the effects caused by unauthorised flood risk activity”. This work will take place at a date to be confirmed in February and will include “establishing a site compound for contractors; delivering materials to the  site; undertaking remediation of the River Lambourn through the importation and placing of flint gravel on the bed of the river; and the redistributing of material currently placed on the bank as a result of non-permitted works.”

Note: the EA contacted Penny Post on 12 February to point out an error in the paragraph below which we have corrected.

On 6 February 2019, the EA started work in earnest, using the Mabberley’s Stables as its base. One of the first things discovered in the river bed was material which might be asbestos. Samples are currently being analysed and once the nature of the material has been established then appropriate removal and disposal will take place. Whatever this material proves to be, it had probably been there for some time and been disturbed by the dredging. Some aspects of the work can continue while these tests are being carried out.

On 22 February 2019, an EA spokesman contacted Penny Post with the following statement: “Tests on material found by the River Lambourn earlier this month have confirmed it was white asbestos. We are carrying out further checks on the soil, and any contaminated earth and the asbestos will be removed safely [it has since been established that the soil does not appear to be contaminated]. Our discovery is a timely reminder that people should only dispose of asbestos within the law, through a company registered with the Environment Agency to do so”. You can click here for advice and to check the EA register, or call  the EA on 03708 506 506.

On 7 March 2019, the local Flood Warden checked the groundwater levels at Mabberley’s. He estimates that these are about 45cm below the riverbed and rising at about 3cm a day. If this trend continues, the river should be flowing there at least in a bout two week’s time. It also appears that the EA expects to have completed its restoration work by then. About 30kgs of asbestos cement sheet has been removed and the next stage will be to put gravel back into the bed. A decision also needs to be taken as to whether the riverbank needs stabilising to prevent erosion until the vegetation returns.

The River Flow

For the latest on the river levels and a variety of issues to do with owning property that is vulnerable to flooding, listen here to our interview with East Garston river monitor Mark Brock (from 9 mins 15 seconds).

The early part of the year is a time for many things including diets, resolutions and thermal underwear. If you live in the upper reaches of the River Lambourn it’s also the time we start wondering when our chalk stream will return…

As all local residents know, the section of the River Lambourn from its source down to Maiden Court Farm (between East Garston and Shefford) is seasonal winterboure and generally tends to be dry between August and early January. This can vary depending on the level of the water table; the river is fed by springs from the underground chalk aquifer which in turn is fed by rainwater. Depending on rainfall, the river sometimes flows continuously for over a year and sometimes the river is dry for over a year.

Looking at the chart of the river flow between 1964 and 1999 in the book East Garston Past and Present the river is usually flowing between January and May and usually dry in September and October. Even this can’t be guaranteed. Between late July 1990 and mid November 1992 it didn’t flow at all but then did so without a break until early September 1994. Another odd period was 1975-76. The river dried up in July 1975 and stayed dry for the next 18 months. However, despite the notoriously hot summer that year, the flow began again in early January as if nothing odd had happened. This may (or may not) be an omen for this year.

I spoke to East Garston Parish Council’s appointed Flood Warden Mark Brock in early January. One of his tasks is to take measurements from various boreholes and report the findings to Thames Water, the Environment Agency and West Berkshire Council. “When the river will start flowing again will depend very much on the rainfall pattern over the next few months,” he explained.. “Groundwater levels are low for this time of year but a prolonged period of heavy rainfall could result in groundwater levels rising rapidly, though currently there is little or no rain in the forecast.”

On top of the unpredictable amount of rainfall, there is also the issue of how heavy it is, as heavy rainfall is less beneficial to the water table than lighter rain because after a downpour much of it will run off. And when it rains is also an issue as rain that falls in the summer is more likely to be soaked up by vegetation or lost to evaporation. On top of this, the chalk sub-strata is constantly changing which effects the amount of water that can be retained in any one part of it.

All in all, predicting the river flow is a bit of a dark art.

East Garston River Sweepstake – the winner

However, we’re not going to let that stop us trying. Our neighbour Hilary Reem, who’s lived, and tended a garden, next to the river for over 60 years, told us the other day that she felt it would be flowing again on 1 March. Defining what ‘flowing’ means is open to some debate as the various springs start at different times and there’s a period when the river might flow gently for 100 yards and then stop for another 100. However, we’ll take up her challenge and will define ‘flowing’ as when the river is clearly flowing as far as one can see on both sides of the bridge by the war memorial in East Garston.

Before casting my vote, I thought I’d seek some expert advice. What did Mark think about 1 March? “Not sure,” he said. “I think it’s unlikely unless we get some persistent and heavy rain in the next month. My readings show the water levels have been falling since May and still haven’t levelled off. If it stays dry it’s quite possible it won’t flow at all this year.” I asked him if he’d like to predict a date and he said he’d have another look at the figures and get back to me.

So, science and instinct, not for the first time, are in disagreement. Penny has gone for 15 March while I – with my natural pessimist’s supposition of apocalyptic weather just round the corner at any time of the year – have opted for 25 February.

Note (7 March). Various other estimates have been received. In the light of the current rise in groundwater levels at Mabberleys (see Dredging Update above), Penny’s bet of 15 March is looking quiet shrewd. However, the river comes to life in different places at different times and the part we’re using is up at the bridge by the war memorial (see first para in this section). So, there’s still time to enter and win the prize.

Note (13 March). The river was flowing today on both sides of the bridge by the war memorial today so we have a winner. Anthony Banfield was close with his guess of 19 March 2019; Ed James (who has lived his whole life within 15 metres of the river) was not close with his guess of 8 January 2020. Contrary to what I said yesterday, the winner is not Penny Locke (who guessed 15 March) but James Hoskins (whose guess was 13 March). Congratulations, James, for a nearly spot-on prediction. I’m quite relieved: for Penny to have won a sweepstake in her own newsletter would have looked a bit odd. 

Many thanks to Raymond Baker at the East Garston Social Club for donating the prize.

Tidying the river

Now the river has returned, there might be some detritus that’s been washed down from upstream. If so, pluck it out if it’s safe to do so. We strongly advise against doing anything more invasive than this unless you’ve first had a look at this article and perhaps contacted some of the organisations or sources of advice it refers to. And don’t do any dredging.

The river’s return

This is an almost magical experience, often spanning a week or so, and one of the great delights of living on this remarkable and almost unique little river. Click here to see a stop-action video Penny made charting is return in March 2017.

A search for ‘River Lambourn’ on this website will take you to a number of other related articles.

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