HGS RESEARCH HIGHLIGHT – How Does Topography Control Topography-Driven Groundwater Flow?
Zhang, X., Jiao, J. J., & Guo, W. (2022). How Does Topography Control Topography‐Driven Groundwater Flow? In Geophysical Research Letters (Vol. 49, Issue 20). American Geophysical Union (AGU). https://doi.org/10.1029/2022gl101005
“Numerical simulation of groundwater-surface water flow is conducted using HydroGeoSphere, by simultaneously solving the Richards equation for variably saturated groundwater flow and wave approximations of the Saint Venant equation for surface flow”
Fig. 1. The average flow patterns of Cases 1–7. Darcy velocity magnitude Log(V) (|V|, m/day) contours (in color bands).
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In a study led by Xiaolang Zhang, Jiu Jimmy Jiao, Wensi Guo, researchers have comprehensively explored the mechanisms governing topography-driven groundwater flow. Their research showcases the complexities between varying rainfall patterns, topographic features, and groundwater flow dynamics, offering invaluable insights into hydrological processes.
After utilizing a sophisticated two-dimensional groundwater-surface water coupled model, and by integrating surface water watershed characteristics and topographic indices, the researchers have uncovered the relationship between topography and groundwater flow patterns, and shined a new light on how landscape features influence subsurface water movement.
One of the key revelations from this study is the impact of topography on the penetration depths of local flow systems. From their analysis, the researchers have demonstrated that these penetration depths are linked to the capture zone size and topography rise of local flow systems, providing a deeper understanding of groundwater behavior in diverse landscapes.
Furthermore, the research clarifies the formation of stagnant zones as a result of the movement of stagnation points, offering critical insights into groundwater flow behavior under varying climatic conditions. By examining the dynamics of these stagnant zones, the study unveils the intricate response of groundwater flow systems to changes in rainfall recharge rates and hydraulic conductivity, highlighting the complexities between topography, climate, and geology.
By using advanced modeling techniques provided by HydroGeoSphere they have been able uncover the complexities of topography-driven groundwater flow. By simulating a wide range of hydrological processes, from storm surge scenarios to changing recharge rates and erosion dynamics, these models provide researchers with the flexibility to explore different scenarios and deepen our understanding of groundwater dynamics.
Plain Language Summary:
This study explains which topographic indices control topography-driven groundwater flow. Our study demonstrates that the groundwater subsystems are not controlled by the size and topography rise of a surface water watershed, but by the size and topography rise of each groundwater subsystem. In previous studies, identifying surface water divide was usually thought to be important before setting up a model to investigate groundwater flow patterns, but this study indicates that groundwater divide is totally independent of surface water divide. And it comes to an opposite conclusion when we base on capture zone size of groundwater subsystems. Our research also indicates that the control of topography on stagnant zones and variations of groundwater flow system can become weakened when the hydraulic conductivity or rainfall rate is reduced. The combined effect of topography, climate, and geology on groundwater flow patterns should be considered to fully understand the dominant factors on topography-driven groundwater flow.
Fig. 2. The trajectories of the five internal stagnation points. SZ means stagnant zone and A1 to A5 represent their corresponding area of Case 1.
Abstract:
How topography controls topography-driven groundwater flow is investigated with varying rainfall and topography using a two-dimensional groundwater-surface water coupled model. Results show that the penetration depths of local flow systems present a good relation with capture zone size (Cl) and topography rise (Hl) of local flow systems, but poor and opposite relation with the two topographic indices of the surface water watershed. The stagnant zones are formed due to the movement of stagnation points, whose velocity magnitude is almost zero. The area and depth of stagnant zones below the mountains have a good or no relation with the mountain size, depending on the hydraulic conductivity. The fractal behavior of penetration depth variations with rainfall presents a good or no relation with Cl and Hl, depending on the rainfall rate and hydraulic conductivity. The topography control may be less important when rainfall rate or hydraulic conductivity is significantly reduced.