Water Level and Groundwater Dynamics across a Sandur-Wetland Landscape in Response to Seasonal and Episodic Events, South-East Iceland

A 2.5 km stretch of a sandur (glacial outwash plain) neighbouring a wetland in South-east Iceland was monitored from 1 September 2015 to 2 September 2016. Improved understanding of the hydrological regime at this sandur-wetland boundary is warranted as local farmers are losing ground to the frequent flooding of their wet meadows despite the existence of elevated berms. A series of water wells were installed across a sandur-wetland boundary, to monitor water table fluctuations, determine flooding extent and assess groundwater inflow. Flooding occurred rapidly in the sandur during 19 weather events, which included modest and heavy rainfall, and glacial outburst floods (jökulhlaups). Water levels on the South-western edge of the wetland responded in sync with the sandur during flooding, indicating a connectivity via groundwater exchange across the coarse, non-vegetated berm. We estimated that between 6 June and 31 August, 11,275 m of groundwater flowed from the sandur to this part of the wetland. This contrasted with the South-eastern edge of the wetland, which had an older, vegetated berm. Here, only 7446 m of groundwater flowed from the sandur to the wetland. Overall, these modest water inputs accounted for 76% of seasonal evaporation loss from the wetland (191 mm).