Since the 1990s, nature and water management policies have attempted to re-create natural rivers systems by mimicking curvy meandering planforms, based on the assumption that meandering is the natural channel-forming process. However, in low-energy river systems, the extent to which meandering plays a natural role is often minimal. This study aims to quantify contemporary lateral migration in the low-energy irregular sinuous lowland river system of the Drentsche Aa, The Netherlands, and to determine the factors influencing lateral channel migration in a heterogeneous valley fill. Although the river is classified as laterally immobile based on an empirical stability diagram, field observations prove that erosion and deposition are currently occurring. By analyzing historical and present-day maps, it was shown that lateral migration was highly spatially variable for the period 1924-2005. Sinuosity and valley gradient are not correlated to lateral migration rates, suggesting they are not a measure of lateral migration in the case study area, which is in line with the literature. Based on geomorphological and soil map analyses, it was shown that lateral migration rates are significantly higher in valley fills of aeolian sands than in clastic alluvial deposits, which on their turn are significantly higher than in peaty environments. Therefore, local conditions appear to be dominant over other factors such as stream power and bed grain size. These findings are important for river rehabilitation of low-energy rivers, because it shows that local valley fill conditions can greatly influence active lateral migration in the river.Processes and forms of individual river channels are influenced by a complex set of factors, such as flow energy (valley gradient, bankfull discharge, frequency of high discharge events), sediment load, sediment size, floodplain heterogeneity, and bank cohesion (composition and vegetation) (e.g., [9,10,[13][14][15][16][17][18][19][20][21]). Human interventions in hydrological systems also influence laterally moving behavior [22]. Although it is commonly perceived that in temperate lowland rivers, sinuosity tends to increase if the valley slope is steeper, and there are some examples of rivers where sinuosity and valley slope are positively correlated (e.g., [23]), specific relations between valley slope and sinuosity cannot be generalized for rivers with mean annual discharge of more than 10 m 3 /s [10]. In addition, it is also often perceived that in cases with a higher sinuosity, a higher lateral migration can be expected [24]. Sinuosity of a stream is often not a stable value, but is temporally and spatially variable. For example, vegetation influences, extreme weather conditions, clustering of meander cut-offs, or human influences can have an impact on the sinuosity [10].Rivers can be classified based on river channel processes or on their resulting planform [19]. Nanson and Croke [12] created a genetic classification, in which they distinguished river systems into high-energy non-cohesive floo...
