The impact of avulsion on groundwater level and peat formation in delta floodbasins during the middle-Holocene transgression in the Rhine-Meuse delta, The Netherlands

Abstract

By redistributing water and sediment in delta plains, avulsions of river branches have major environmental impacts, notably in changing hydrological and peat-forming conditions in floodbasins. The central part of the Rhine-Meuse delta, with its extensive databases including detailed lithological data and high-resolution age control, offers a unique opportunity to study middle-Holocene avulsion impacts on floodbasin groundwater level and peat formation. Avulsion has caused local accelerations of rising groundwater tables to be superimposed on decelerating base-level rise. This is evident from comparing single-site groundwater rise for multiple floodbasins in the river-dominated part of the delta, with regionally averaged groundwater-rise reconstructions. Floodbasin type (lacustrine versus terrestrial wetland), size and openness, partly through effects on discharge dispersal, affect how strongly the floodbasin groundwater tables respond to avulsion-diverted discharge. Cross-sectional lithology repeatedly indicates a shift from high-organic wood peat to low-organic reed peat in the vicinity of the avulsed channel, resulting from changes in water-table regime and nutrient status. Avulsive impact on the floodbasin groundwater table was most pronounced during the transition from transgressive to high-stand stage (between ca. 6000 and 4000 years ago), owing to developing floodbasin compartmentalization (size reduction, confinement) resulting from repeated avulsion. By way of environmental impacts on groundwater tables and vegetation, avulsions thus affect the heterogeneity of floodbasin facies.

Coastal peat‐beds and peatlands of the southern North Sea: their past, present and future

“…Differential compaction can also produce channel avulsion, bringing river systems to new areas (Van Asselen et al ., 2009) and raise groundwater levels and thereby change the distribution of vegetation. For example Van Asselen, Cohen & Stouthamer (2017) report the replacement of a highly organic wood peat by a low‐organic reed peat in the vicinity of an avulsed channel.…”

Projections of declining fluvial sediment delivery to major deltas worldwide in response to climate change and anthropogenic stress

“…Fluvial sediment delivery is therefore a vital precondition for aggradation, so we focus here on projecting sediment flux at the delta apex as an important, but not exclusive, control on delta aggradation, as aggradation can only occur if the available sediment is deposited within the delta area. Prior studies have highlighted how fluvial sediment delivery is a critical factor in offsetting relative sea-level rise (Syvitski et al 2009, Evans 2012, van Asselen et al 2017, but these previous studies have focused either on contemporary (Evans 2012, Tessler et al 2015 or past (Syvitski et al 2005b, Milliman and Meade 1983, Milliman and Syvitski 1992, Guillén and Palanques 1997, Darby et al 2016 changes in sediment flux. Few studies have projected future changes in fluvial sediment flux, and those that have were limited to a few rivers (Dunn et al 2018) while addressing a single driver of change, such as dam construction (Tessler et al 2018) or climate change (Darby et al 2015, Praskievicz 2016).…”

Holocene evolution of tidal systems in The Netherlands: Effects of rivers, coastal boundary conditions, eco-engineering species, inherited relief and human interference

“…Yet, assuming a fixed planform shape ignores dynamically evolving boundary conditions and possibly large effects of biogeomorphological interactions, particularly at the system margins (e.g., Temmerman et al, 2007;Kirwan and Megonigal, 2013). Eco-engineering species can significantly change their environment at the landscape scale (Jones et al, 1994) as is wellknown for rivers (e.g., Kleinhans, 2010;van Asselen et al, 2017), but at present large-scale effects on tidal system development remain poorly understood. Mapping shows that tidal system dimensions and development in many cases largely depend on pre-Holocene surface (e.g., Boyd et al, 1992Boyd et al, , 2006) while many other cases initiated largely independently from inherited relief, and as a result of storm-surge ingressions or river floods (van der Spek, 1995;van de Plassche et al, 2006;Vos, 2015;Pierik et al, 2017).…”