TY  - JOUR
A1  - Nguyen Le Duy, 
A1  - Nguyen Viet Du, 
A1  - Heidbüchel, Ingo
A1  - Meyer, Hanno
A1  - Weiler, Markus
A1  - Merz, Bruno
A1  - Apel, Heiko
T1  - Identification of groundwater mean transit times of precipitation and riverbank infiltration by two-component lumped parameter models
JF  - Hydrological processes
N2  - Groundwater transit time is an essential hydrologic metric for groundwater resources management. However, especially in tropical environments, studies on the transit time distribution (TTD) of groundwater infiltration and its corresponding mean transit time (mTT) have been extremely limited due to data sparsity. In this study, we primarily use stable isotopes to examine the TTDs and their mTTs of both vertical and horizontal infiltration at a riverbank infiltration area in the Vietnamese Mekong Delta (VMD), representative of the tropical climate in Asian monsoon regions. Precipitation, river water, groundwater, and local ponding surface water were sampled for 3 to 9 years and analysed for stable isotopes (delta O-18 and delta H-2), providing a unique data set of stable isotope records for a tropical region. We quantified the contribution that the two sources contributed to the local shallow groundwater by a novel concept of two-component lumped parameter models (LPMs) that are solved using delta O-18 records. The study illustrates that two-component LPMs, in conjunction with hydrological and isotopic measurements, are able to identify subsurface flow conditions and water mixing at riverbank infiltration systems. However, the predictive skill and the reliability of the models decrease for locations farther from the river, where recharge by precipitation dominates, and a low-permeable aquitard layer above the highly permeable aquifer is present. This specific setting impairs the identifiability of model parameters. For river infiltration, short mTTs (<40 weeks) were determined for sites closer to the river (<200 m), whereas for the precipitation infiltration, the mTTs were longer (>80 weeks) and independent of the distance to the river. The results not only enhance the understanding of the groundwater recharge dynamics in the VMD but also suggest that the highly complex mechanisms of surface-groundwater interaction can be conceptualized by exploiting two-component LPMs in general. The model concept could thus be a powerful tool for better understanding both the hydrological functioning of mixing processes and the movement of different water components in riverbank infiltration systems.
KW  - bank infiltration
KW  - groundwater
KW  - lumped parameter model
KW  - mean transit time
KW  - Mekong Delta
KW  - stable isotopes
Y1  - 2019
U6  - https://doi.org/10.1002/hyp.13549
SN  - 0885-6087
SN  - 1099-1085
VL  - 33
IS  - 24
SP  - 3098
EP  - 3118
PB  - Wiley
CY  - Hoboken
ER  -