Sponge function: indicators and metrics to assess water retention in Nature-Based Solutions with application to UK fluvial and agricultural sites

Climate extremes like floods and droughts pose significant threats to both human communities and natural landscapes. The EU Horizon SpongeScapes and SpongeWorks projects aim to enhance landscape resilience against these hydrometeorological extremes by exploring "landscape sponge functions" – the natural ability of landscapes to absorb, store, and gradually release water. The SpongeScapes project investigates various nature-based solutions (NBS) across diverse European sites with varying climates, geographies, and soil conditions, to address three main questions: (i) what is the longer-term effectiveness of sponge measures (and what indicators/metrics are more adequate); (ii) what is the overall effect of all sponge measures in a catchment (i.e. sponge strategies); (iii) what are the main co-benefits and tradeoffs of sponge measures and strategies.

Here we will present a framework of context-specific 'Sponginess' indicators and metrics, in particular to assess the sponge function of water retention capacity in fluvial and agricultural sponge measures and strategies (catchment-wide combination of measures), with applications to SpongeScapes UK sites in the river Thames basin where work has been done since 2017 and is ongoing. These sites include the Littlestock brook, a headwater catchment in an agricultural landscape where a diversity of nature-based solutions (woody leaky dams, field corner bunds, wet woodland planting) have been implemented, as well as several farms where regenerative agricultural practices (RAPs) have been followed to improve soils, surface and ground water management.

Results on applying our sponge indicators framework will be presented and discussed based on ongoing field investigations, including analyses based on novel low-cost telemetered water level data in the fluvial site, as well as survey data for soil bulk density, water retention functions, infiltration and hydraulic conductivity for the agricultural fields.