A new modelling framework to simulate transport in highly unsteady river-groundwater systems

Diogo Costa, Paolo Burlando, Shie-Yui Liong

Thursday 2 july 2015

12:15 - 12:30h at Oceania Foyer (level 0)

Themes: (T) Water resources and hydro informatics (WRHI), (ST) Surface and subsurface flow interactions

Parallel session: 11L. Water resources - Flow interactions

River and groundwater have been typically modelled separately. In dynamic river-groundwater systems, however, this approach may not always be the most appropriate. Neglecting the simulation of river flow and transport explicitly, for instance when looking at river to groundwater contamination, raises two considerable problems: first, infiltration and the respective downward flux of contaminants are computed from an average river water level and concentration provided by the user, thus disregarding spatial and temporal variability; second, the effect of exfiltration from groundwater to the river system cannot be addressed. This study summarizes the restructuring, improvement and modular coupling of independent source codes from some state-of-the-art distributed river and groundwater flow and transport models. The combined use of these source codes through a fully coupled model framework translates into a more detailed, realistic and physically based representation of the mechanisms affecting the way the two systems interact. The tool can be used to either study phenomena occurring at the interface (i.e. hyporheic zone) or to look at the impact either system has on the quality of the other. Through a real world application in the heavily polluted Ciliwung River in Jakarta, Indonesia, we demonstrate how the model can be used to study the impact of riverine flooding, by showing, for instance, how this can increase the levels of oxygen in the hyporheic zone, benthic layer and the shallow aquifer, this potentially increasing natural aerobic degradation rates. Results show that the infiltration of both water and dissolved oxygen clearly varies both in space and time. Most oxygen recharging the subsurface occurs upon the rise of the flood wave seemingly due to it being accompanied by higher levels of oxygen in the river. The additional volumes of water infiltrating into the groundwater throughout the event and model domain add little more than 20% to the existing background values. However, in the case of oxygen, results suggest that the river to groundwater oxygen recharge more than doubles.