Predicted variable river response at high and low flows due to groundwater abstraction changes in Chalk catchments

Improving low flows in Chalk streams by relocating groundwater abstraction further downstream is an idea that has become popular in the UK in recent years. Simulations using the Environment Agency's Hertfordshire Chalk Groundwater Model predict that reducing groundwater abstraction close to ephemeral or intermittent Chalk streams is more likely to increase river flows during high flow conditions than during low flows. This finding helps to explain the apparent lack of observed benefit to river flows during drought periods, in catchments where abstractions have been reduced. If abstraction reductions are predicted to result in more increase to high river flows than to low flows, they may risk contributing to increased flood likelihood downstream, without providing significant habitat protection during low flows. Conversely, it has also been found that under certain circumstances, preferential benefits can be predicted for low flows. Simulations show that such benefits are most likely to manifest by relocating abstraction to downstream locations where groundwater levels are already below the base of the river bed (e.g. due to existing abstraction or artificial channel modifications). Here, the varying degree of hydraulic connection between groundwater and river can result in preferential benefits to downstream low flows and reduced downstream flood risk. Thematic collection: This article is part of the Karst: Characterization, Hazards & Hydrogeology collection available at: https://www.lyellcollection.org/topic/collections/karst