2012 NGWA Ground Water Summit: Innovate and Integrate

Spatially Periodic Boundaries in Hyporheic Zone Numerical Models

Wednesday, May 9, 2012: 2:10 p.m.
Royal Ballroom C (Hyatt Regency Orange County)
Tariq Laattoe, Flinders University;
Vincent Post, Ph.D., NCGRT; Flinders University;
Adrian D. Werner, National Centre for Groundwater Research and Training, Flinders University;
Craig T. Simmons, Flinders University, National Centre for Groundwater Research Training;

Hyporheic zone groundwater models are increasingly used to understand the hydrodynamic, solute transport and the thermal regime of groundwater below streams (Fleckenstein et. al., 2010). Models of individual bedforms have been developed by several researchers to study local-scale flow and transport driven by pressure differences at the river bed (Cardenas & Wilson, 2007; Jin et. al., 2010, 2011). These implicitly assume an infinite number of adjacent, identical bedforms by adopting spatially periodic boundary conditions for flow and solute concentrations. A recently developed spatial periodic flow boundary package for MODFLOW is used to simulate flow below a single bedform model. From this a series of models composed of multiple bedforms, each with an identical flow pattern, are constructed using the MT3DMS code. The objective was to investigate the applicability of the assumption of spatial periodicity of solute concentration patterns, which has been adopted in a number of recent studies. A range of dispersivities are investigated. The results show that spatial periodicity for solute concentrations are generally not observed. This is attributed to transverse mixing of solutes, which causes mass exchange between the bedform-driven flow system and the groundwater underflow that traverses multiple bedforms. These results show that the assumption of spatial periodicity for solute concentration can lead to non-physical model behaviour, and is not generally applicable.

References

Cardenas, M. B. and J. L. Wilson (2007). "Effects of current-bed form induced fluid flow on the thermal regime of sediments." WRR  43(8).

Jin, G. Q., et al. (2010). "Transport of nonsorbing solutes in a streambed with periodic bedforms." AWR 33(11): 1402-1416.

Jin, G. Q., et al. (2011). "Hyporheic flow under periodic bedforms influenced by low-density gradients" GRL 38(L2240).

Fleckenstein, J. H., et al. (2010). "Groundwater-surface water interactions: New methods and models to improve understanding of processes and dynamics." AWR 33(11): 1291-1295.