Modelling the Effects of Vegetation Distribution and Density on Hydrological Connectivity and Water Age in a River Delta

Abstract

Water transport timescales (WTTs) quantify how long it takes for water to travel through or remain in a system and are often cast as indicators of ecosystem function and health. Such timescales are known to be affected by vegetation in various environments. We quantify the impact of floodplain vegetation on WTTs within the Wax Lake Delta (WLD), a river delta system in Louisiana, USA, using a high-resolution Delft3D Flexible Mesh (DFM) model incorporating vegetation-induced flow resistance. We show that increased vegetation density leads to extended WTTs within vegetated sections of WLD while fostering flow localization and accelerating transport within distributary channels. We find that the presence or absence of floodplain vegetation significantly influences the volumetric flow directed towards the floodplain, with spatial distribution exerting more control than vegetation density. Vegetation density and spatial arrangement have minimal impact on flow directed out of the deltaic floodplain, indicating that vegetation does not constrain flow across the bayward boundary. Furthermore, network-scale water age distribution remains largely unaffected by vegetation density and spatial arrangement, except for slight modifications in the distribution's right tail. These findings contribute to a better understanding of how vegetation affects deltaic hydrology across scales, highlighting the importance of considering multi-scale vegetation influences for coastal restoration and management strategies.