Palaeochannels as hidden pathways of water flow in agricultural alluvial landscapes: A review of concepts and suggested future directions for modelling

• Palaeochannels are key subsurface conduits in agricultural alluvial landscapes. • Coupled models provide the most realistic representation of palaeochannel flow. • Virtual experiments enhance understanding of palaeochannel hydrology. • Field mapping and monitoring are essential to support model development. Sustaining agricultural productivity while reducing off-site impacts on water quality requires a detailed understanding of water and nutrient movement through alluvial landscapes. Within these settings, palaeochannels − old river courses infilled with coarse sediments − represent major but poorly quantified subsurface flow pathways. Their influence on water and solute transport is rarely incorporated into hydrological assessments or models, despite their widespread occurrence and hydraulic connectivity with surface drains, aquifers and streams. This paper reviews current knowledge of palaeochannel structure, distribution and hydrologic function within agricultural alluvial systems, and evaluates approaches for their identification, characterisation and representation in hydrologic models. We examine the suitability of existing coupled modelling frameworks − such as HYDRUS-MODFLOW, SWAT-MODFLOW, MIKE-SHE and HydroGeoSphere − for simulating palaeochannel-mediated flow and material transport. Conceptual similarities between palaeochannels and engineered tile-drain networks are used to illustrate how established drainage formulations can inform future model development. We highlight virtual experimentation, combining numerical simulation with targeted field monitoring, as a practical means of exploring how palaeochannel geometry, depth and connectivity influence water and nutrient fluxes at field to catchment scales. Integration of direct and remote sensing with coupled hydrological models will enhance the capacity to parameterise and validate palaeochannel networks. Collectively, these advances provide a pathway towards more realistic representations of subsurface flow heterogeneity, improving predictions of water and solute movement and informing management strategies in intensively farmed alluvial landscapes.