Flow Recovery Following Abstraction Reduction

The Chalk Streams First coalition has CSF has commissioned an independent investigation (CLICK HERE) into flow recovery following abstraction reductions in the Colne and Lea chalk streams.

This is an important piece of work because currently what are – in our view – irrationally precautionary and unrealistically low estimates of flow recovery are shaping WRSE and Affinity Water plans.

Chalk Streams First (CSF) welcomes and supports the circa 150 Ml/d abstraction reductions indicated for chalk stream tributaries of the Colne and Lea in Affinity Water’s WRMP. This would be sufficient to almost fully re-naturalise the flows in the Colne and Lea chalk stream tributaries, the primary goal of the CSF coalition.

However, the majority of the proposed reductions are not scheduled until after 2040 and are framed as being dependent upon a large strategic resource option such as either the Abingdon Reservoir or the Severn to Thames transfer. This would push the ecological recovery of the chalk streams decades down the line. CSF could and should be a self-contained and timely solution and should not become dependent on distant future schemes.

The contingency / delay appears to be based on an estimate of 17% flow recovery from chalk stream abstraction reduction at very low flows, Q95 – Q100, meaning the strategic resource is necessary to underwrite the abstraction reductions. The 17% figure derives from a triangulated process of analysis conducted by Affinity Water and consultants, summarised in Technical Appendix 5.6 “Deployable Output Benefits from Abstraction Reduction”.

CSF has commissioned an independent investigation into flow recovery from abstraction reductions, the results of which suggest that the 17% figure is unjustifiably conservative.

The results of our own report suggest that average flow recoveries at the relevant percentiles are considerably higher: in the region of 50 to 60% of upper catchment reductions translates into increased deployable output in downstream reservoirs at the average percentiles through the 1921 and 1933/34 droughts.

The delay in implementing the reductions is therefore unnecessarily precautionary.