A%R – abstraction as a % of recharge in chalk streams

A key recommendation in the CaBA Chalk stream restoration strategy was for an independent review of abstraction as a % of catchment recharge. The basic findings of that report were published in the CaBA restoration strategy but now we have the full report and not before time …

You can read the report HERE

With the regional plans out for consultation, it is vital that we now make the case for a) prioritising chalk streams in absolute terms and b) for careful strategising and planning of abstraction reductions on the chalk streams, so that we see ecological gains in the places they are needed most urgently.

We all know that we have been leaning heavily and are dependent on groundwater in the chalk for a large chunk of public water supply across southern and eastern England. We know that the impact this has on the ecology of chalk streams is unacceptable and yet we also know that we cannot replace water resources overnight. It has taken too long to get to this point but at least we now have a chance – via the regional plans – to make significant reductions to chalk aquifer abstractions.

However, the scale of the flow deficits identified in the regional plans is enormous: so enormous that some form of prioritisation and expediency will surely be necessary, at least in terms of what comes first, if not in absolute returns.

That’s one place where this A%R report can play a very useful role in the public debate. Until now we stakeholders have had no real insights into the scale or spatial distribution of over-abstraction in chalk streams, even if we have felt sure our streams were over-abstracted. The public-facing WFD assessment gives a binary status of does or does not support good (flow being – absurdly – only a supporting element in the WFD assessment process).

John Lawson’s report is first and foremost an exercise in democratising that knowledge. Quantifying groundwater abstraction as a % of the total effective recharge of the chalk aquifer in a given catchment – or even across a region of catchments – is a very simple and accessible way of assessing the relative impact of that abstraction on flows. It is not infallible: we empirically know what the abstraction is, but effective rainfall estimates are subject to uncertainty and inconsistency. However, so are all the other forms of assessing impact while these are a) not available to the public and b) more complex.

A%R, therefore, is about bringing stakeholders, into the discussion armed with knowledge.

The A%R modelling in this report uses modelling of abstraction impacts on the River Ver to derive a correlation between A10%R (where groundwater abstraction uses no more than 10% of effective recharge) and the Environment Agency’s target for flows in an ASB3 (abstraction sensitivity band 3 being the most sensitive) chalk stream. It has been pointed out that this correlation may not hold for other chalk streams and that is true: it will vary from stream to stream according to variations on hydrogeology and land-use. On the other hand, the modelling was also accurate on the River Kennet and is proving a good fit in preliminary surveys of streams like the Beane and Mimram.

2 thoughts on “A%R – abstraction as a % of recharge in chalk streams

  1. Dear Sir,

    i was excited to read your arguments that A%R is a good way to compare the degree of overabstraction of rivers, and that the report covers some 55 UK rivers. Unfortunately my local river, the Ems, is not on the list, so I am naturally very interested in calculating its A%R.

    You say that calculating A%R is ‘very simple’, but there is a concern amongst the few hydrologists that I have talked to that different people will calculate A%R using slightly different methods, especially citizen scientists such as myself; I have a degree in computer science but no education in hydrology. *Is there any kind of cookbook, or “A%R for dummies”, that can spell out exactly how citizen scientists can calculate he A%R for their own rivers and add them to your list of 55 rivers?* I feel that this is a real need if we are going to promote the use of A%R up and down the country. The Ems is a small simple river, roughly 10Km long and fed by a catchment of 60.1 Sq Km, and we have a good relationship with the local EA who are currently modelling the hydrology of the river, so we should not have too hard a time getting any required raw data, but we want to use the exact same methodology as used in your report. In particular I have tried to reverse engineer your appendix B in the report, but how do we calculate ‘effective rainfall’ from actual rainfall? Also, our river is very seasonal – the flow in February can be over 500 times the flow in September, so should we calculate A%R on a monthly basis?

    On a related subject, given that the WRSE consultation suggests that the following rather subjective seven criteria will be used for deciding which rivers will have abstraction reduced over the next 20+ years: [image: image.png] ..*.will you be recommending alternative criteria such as A%R and WFD EFIs to the WRSE consultation*? It would be good if our response could be aligned with your views.

    Yours faithfully, Nick Rule (A member of the ‘Friends of the Ems’ – see https://e-voice.org.uk/greening-westbourne/friends-of-the-ems-fote/ and/or https://www.youtube.com/watch?v=lqxpjfW40gA )

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