Modeling 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 toward 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. Floodplain vegetation
strongly influences local-scale transport timescales within the deltaic
floodplain but minimally affects water age distributions within
distributary channels. Furthermore, network-scale water age distribution
remains largely unaffected by vegetation density and spatial
arrangement, except for slight modifications in the heavy right tail of
the distribution. 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.