Emergence of an ephemeral chalk stream in 2014 at Assendon, Oxfordshire

JBA Trust monitored and documented the emergence and flow of the Assendon Stream in 2014 to provide a resource for researchers and practitioners interested in understanding more about this type of rare groundwater flooding event.

Assendon Stream at its source in February 2014

Assendon Stream near Henley-on-Thames is an extremely ephemeral watercourse that is normally completely dry, even during a wet winter. Prior to the winter of 2013-14, it rose briefly in 2003 and last experienced sustained flow in 2001, when there was prolonged flooding to roads and property. Before that it had flowed in the 1960s and 1981.

Rainfall recorded by the Met Office from 1 December 2013 to 28 February 2014 made this one of the wettest winters since records began in 1766 and following exceptional rainfall during January 2014, the Environment Agency identified the possibility that rising ground water levels may begin to drive flows in Assendon Stream.

In February 2014 the spring started to flow and this presented a very rare opportunity to monitor the emergence of the stream, and gather first hand data in relation to the its response to groundwater levels and the mechanisms of flooding.

JBA Trust carried out a study to monitor and document this event and use the information collected to produce a resource for researchers and practitioners with the aim of helping those interested in understanding the mechanisms for flow and flooding on ephemeral watercourses of this type.

The full report is available to download here and summarises the data and evidence collected as part of the study including detailed documentation of the emergence pattern, groundwater records, monitored stream flows, levels and photographic evidence.

The supporting data and evidence collected as part of this study is available on request, please contact us for more information.

Assendon stream making its way to Henley-on Thames in April 2014

Assendon Stream caused flooding of roads and property in April 2014