Water & Wastewater Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/1144867
10 | AUGUST 2019 | WWT | www.wwtonline.co.uk In Focus: Abstraction been made to the resilience of water supplies through reductions in leakage, there is justifiable concern. APEM, named Consultant of the Year at the 2019 Water Industry Awards, has worked extensively in the field of abstraction alongside water companies and the various UK regulators. "There have been problems in some places – there's no question about that," Dan Cadman, APEM's head of hydrol- ogy, says. "Chalk streams are sometimes impacted and they are valuable and vis- ible, so there's a lot of attention. There are similar issues elsewhere too, with reduced water tables in sandstone aquifers and issues downstream of reservoirs and catchwaters in upland areas. "It's not just the volume of water that's taken but the effects of the abstraction structure so, with reservoirs or catch- waters, the structure itself is probably stopping sediment going downstream and may well be a barrier to fish passage." Cadman also highlights problems with changing the pattern of flows – which can mean salmon do not receive the required pulses of flow to trigger their migrations upstream and downstream – as well as rivers that may appear quite natural but where, as the result of a dam upstream, the sediment is seldom disturbed, and they lack the oxygenation required for fish spawning. APEM has worked alongside Stantec to develop a 'hydroecology model' for Severn Trent that manages the impacts of groundwater abstraction, combin- ing macroinvertebrate indices with flow reductions from groundwater models to develop flow targets. The company also won the Data Project of the Year prize at the 2018 Water Industry Awards for its work with Welsh Water and Natural Resources Wales, looking at the impact of water abstraction on shad populations, using field and aerial surveys alongside hydraulic modelling to estimate the likely loss of spawned shad eggs caused by abstraction changes. Having studied the impact of abstrac- tion in some depth, Cadman stresses that – while it can cause problems – it is o˜en not as straightforward as might be sug- gested. When the EA identifies an issue during screening, APEM may be called in to pinpoint the precise causes. "Obviously you want to resolve ab- straction problems, but you don't want to be resolving problems that aren't real," he says. "Quite o˜en you'll actually find ab- straction is actually two or three in terms of significance, not number one." Diffuse pollution and changes to chan- nel form, which have straightened and simplified river habitat and disconnected the channel from floodplains, are fre- quently found to be the primary culprits. Wood technical director Rob Soley also has extensive experience in this area, having spent the last two decades helping the Environment Agency develop the catchment abstraction management strategy process for EU Water Framework Directive reporting, with a particular focus on groundwater abstractions and their impact on wetlands and rivers, as well as serving as an expert peer reviewer for Defra on its abstraction reform model- ling work. "We should be doing things that bring about ecological benefit," Soley says. "I think too o˜en the experience of reducing groundwater abstraction, particularly in relation to chalk streams, leads to disap- pointment in terms of the resulting flow recovery. "Many people come at the abstraction reduction problem thinking: 'If we reduce pumping from that borehole by a mega- litre a day, we will get a megalitre a day back in that river.' This may sometimes be true, but flow recovery is o˜en consider- ably less than expected during low flow and drought periods. "There's a lot of hope that we'll have gushing flows in summer periods in chalk valleys that wouldn't naturally have gush- ing flows during hot and dry times." The Environmental Flow Indicator (EFI), which highlights deviation from natural river flow, is used in England and Wales to indicate where abstraction may start to cause an undesirable effect on river habitats and species. Wood has carried out work to establish how much groundwater abstraction would need to cease in order to prevent flows falling beneath the EFI's screening Chalk it up: Southern Water plans to spend £800 million over the next 10 years to contend with new restrictions on abstraction from the River Itchen (above) and River Test APEM carrying out macroinvertebrate sampling, which can provide an indication of abstraction impact