@article{NguyenLeDuyNguyenVietDuHeidbuecheletal.2019,
  author    = {Nguyen Le Duy, and Nguyen Viet Du, and Heidb{\"u}chel, Ingo and Meyer, Hanno and Weiler, Markus and Merz, Bruno and Apel, Heiko},
  title     = {Identification of groundwater mean transit times of precipitation and riverbank infiltration by two-component lumped parameter models},
  series = {Hydrological processes},
  volume    = {33},
  journal   = {Hydrological processes},
  number    = {24},
  publisher = {Wiley},
  address   = {Hoboken},
  issn      = {0885-6087},
  doi       = {10.1002/hyp.13549},
  pages     = {3098 -- 3118},
  year      = {2019},
  abstract  = {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.},
  language  = {en}
}
@article{LohFynnManuetal.2022,
  author    = {Loh, Yvonne Sena Akosua and Fynn, Obed Fiifi and Manu, Evans and Afrifa, George Yamoah and Addai, Millicent Obeng and Akurugu, Bismark Awinbire and Yidana, Sandow Mark},
  title     = {Groundwater-surface water interactions},
  series = {Environmental earth sciences},
  volume    = {81},
  journal   = {Environmental earth sciences},
  number    = {22},
  publisher = {Springer},
  address   = {New York},
  issn      = {1866-6280},
  doi       = {10.1007/s12665-022-10644-x},
  pages     = {15},
  year      = {2022},
  abstract  = {This research demonstrated the application of hydrochemical data and stable water isotopes of delta O-18 and delta D (or delta 2H) for evaluating the relationship between surface water in Lake Bosumtwi and the underlying groundwater system. It aimed at determining the presence or absence of a hydraulic relationship and for evaluating the possible direction of flow at the interface between the two reservoirs. The study also estimated evaporative losses of infiltrating rainwater as it transits the unsaturated zone and provided important information on the hydrological processes prevailing in the area. The results of Q-Mode hierarchical cluster analysis (HCA) clearly differentiate the lake water from the groundwater based on their spatial relationship. These results indicated that groundwater recharge occurs on the hilltops of the crater, where it is slightly acidic with low levels of dissolved ions, characterised by short residence time and rapid unrestricted vertical infiltration and recharge. The groundwater becomes more mineralized with longer contact times and deeper circulation with the host rock, while it flows from the recharge areas towards the lake at lower elevations. Analyses of delta O-18 and delta D showed a high evaporation rate on the lake surface (90\%) with a significant evaporative enrichment, whereas groundwater showed no significant isotopic variations. Thus suggesting that the aquifers have been recharged by recent meteoric water that has undergone some evaporative enrichment since the study established an evaporation rate of water infiltrating the unsaturated zone ranging from 54 to 60\%. Both reservoirs do not appear to be hydraulically connected, and where such a connection exists, it is expected to favour the lake.},
  language  = {en}
}