22-27 September 2019
Trade Fairs and Congress Center (FYCMA)
Europe/Madrid timezone

Groundwater flow system of the North China Basin: Groundwater age, heat and flow simulations

27 Sep 2019, 11:15
15m
Multiuse room 3 ()

Multiuse room 3

Oral Topic 5.4 - Innovative approaches for understanding groundwater flow systems Parallel

Speaker

Dr Dongmei Han (Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences)

Description

Groundwater flow systems conceptualized according to topography and/or groundwater table configuration generally assume a near-equilibrium state with the modern landscape. However, the time to reach such a steady state, and more generally the timescales of groundwater flow system evolution are key considerations for large sedimentary basins. In the North China Basin (NCB), there remain contradictions between the generally accepted conceptual model of regional flow, and environmental tracer data. We re-examined a range of isotopic tracer data and conducted new three dimensional groundwater age and heat transport simulations in the NCB, for evaluating the impact of different combinations of hydraulic parameters and boundary conditions on groundwater flux, flow paths, groundwater age distributions and heat transport, and use coupled groundwater flow and solute transport modeling to estimate theoretical maximum groundwater ages under hydraulic conditions. It is more reliable to consider the Quaternary and Neogene aquifers together when evaluating regional groundwater circulation, and more reasonable to view the deep groundwater in the NCB below the central and coastal plains as virtually stagnant, at least on human timescales (i.e., decades) or even longer on thousand-year timescales. The model results show that in contrast to previously accepted conceptualizations, most groundwater is discharged in the vicinity of the break-in-slope of topography at the boundary between the piedmont and central plain. Groundwater discharge to the ocean is in contrast small, and in general there are low rates of active flow in the eastern parts of the basin below the central and coastal plain. This conceptualization is more compatible with geochemical and geothermal data than the previous model. Simulated maximum groundwater ages of ~ 1 Myrs below the central and coastal plain indicate that residual groundwater may be retained in the deep parts of the basin since being recharged during the last glacial period or earlier. The groundwater flow system has therefore probably not reached a new equilibrium state with modern-day hydraulic conditions. The previous hypothesis that regional groundwater flow from the piedmont groundwater recharge zone predominantly discharges at the coastline may therefore be false. A more reliable alternative might be to conceptualize deep groundwater below the coastal plains a hydrodynamically stagnant zone, responding gradually to landscape and hydrological change on geologic timescales. This study brings a new and original understanding of the groundwater flow system in an important regional basin, in the context of its geometry and evolution over geological timescales. There are important implications for the sustainability of the ongoing high rates of groundwater extraction in the NCB. The determination of the spatial distribution of the transition (mixing) zone between the active groundwater system with the deep stagnant groundwater is a challenging topic for future research.

Primary author

Dr Dongmei Han (Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences)

Co-author

Dr Guoliang Cao (China Institute of Water Resources and Hydropower Research)

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