Water storage changes as a marker for base flow generation processes in a tropical humid basement catchment (Benin): Insights from hybrid gravimetry

Abstract

In basement catchments of subhumid West Africa, base flow is the main component of annual streamflow. However, the important heterogeneity of lithology hinders the understanding of base flow generation processes. Since these processes are linked with water storage changes (WSCs) across the catchment, we propose the use of hybrid gravity data in addition to neutron probe-derived water content and water levels to monitor spatiotemporal WSC of a typical crystalline basement headwater catchment (16 ha) in Benin. WSC behaviors are shown to provide insights into hydrological processes in terms of water redistribution toward the catchment outlet. Hybrid gravimetry produces gravity change observations from time-lapse microgravity surveys coupled with gravity changes monitored at a base station using a superconducting gravimeter and/or an absolute gravimeter. A dense microgravity campaign (70 surveys of 14 stations) covering three contrasted years was set up with a rigorous protocol, leading to low uncertainties (<2.5 lGal) on station gravity determinations (with respect to the network reference station). Empirical orthogonal function analyses of both gravity changes and WSCs from neutron probe data show similar spatial patterns in the seasonal signal. Areas where storage and water table show a capping behavior (when data reach a plateau during the wet season), suggesting threshold-governed fast subsurface redistribution, are identified. This observed storage dynamics, together with geological structures investigated by electrical resistivity tomography and drill log analysis, make it possible to derive a conceptual model for the catchment hydrology.

Dynamics of water vapor and energy exchanges above two contrasting Sudanian climate ecosystems in Northern Benin (West Africa)

“…As shown by Hector et al . [] and Séguis et al . [], river flows over recent years in this area mainly originate from perched, seasonal water tables and the contribution of deep (10–20 m) groundwater is negligible.…”

“…However, despite drastic deforestation since in Benin 1973 (from 70% to 25% of the total surface), the upper Oueme river discharge (a 15,000 km 2 catchment in which the Donga catchment is embedded) has not shown any great change [Lelay and Galle, 2005;Peugeot et al, 2011]. As shown by Hector et al [2015] and Séguis et al…”

Geophysics From Terrestrial Time‐Variable Gravity Measurements

“…Nowadays, gravimetric techniques allow us to monitor hydrogeological effects at a scale of up to 1 km 2 , for signal ranging a few thousands of nm/s 2 to less than 1 nm/s 2 . Several studies have demonstrated the strength of gravity observations for monitoring quantities related to the water cycle, such as soil moisture, rainfall, groundwater storage, hydrothermalism, or snow covering (Creutzfeldt et al, ; Hector et al, ; Hemmings et al, ; Imanishi et al, ; Jacob et al, ; Pool & Eychaner, ; Van Camp et al, ; Wilson et al, ).…”

“…Ground‐based gravimetry can determine the change of gravity related to Earth rotation fluctuations, to celestial body and Earth attractions, to the mass variations in the direct vicinity of the instruments, and also to distant sources, and to displacement of the instrument itself due to ground deformation. Gravity measurements contribute to risk assessment and mitigation, by improving our understanding of past and present ice mass changes (Kazama et al, ; Lambert et al, ; Larson & van Dam, ; Mazzotti et al, ; Mémin et al, ; Omang & Kierulf, ; Ophaug et al, ; van Dam et al, ), subsidence of low‐lying areas (Van Camp et al, ; Zerbini et al, ), ground water resources (Creutzfeldt et al, ; Fores et al, ; Hector et al, ; Imanishi et al, ; Jacob et al, ; Kennedy et al, ; Lampitelli & Francis, ; Van Camp, de Viron, Pajot‐Métivier, et al, ; Van Camp et al, ), and earthquakes (Imanishi, ; Montagner et al, ; Van Camp et al, ). Concurrently, terrestrial gravity measurements play a key role in the new definition of the kilogram (Stock, ), and our understanding of environmental effects affecting the gravity measurements will be useful to assess the Newtonian noise affecting gravitational wave detectors (Coughlin et al, ; Harms & Venkateswara, ).…”

Resolving Geophysical Signals by Terrestrial Gravimetry: A Time Domain Assessment of the Correction‐Induced Uncertainty

“…For reducing tides, Tanaka et al (), for instance, used the Baytap program (Tamura et al, ); other studies preferred ETERNA (Wenzel, ), for example, in Meurers et al (), or VAV program (Venedikov et al, ), for example, in Arnoso et al (). Much of the same variety can be found even in studies focusing on identical or similar phenomena, like local water storage changes, where for the correction of global atmospheric gravity effects; some studies (Hector et al, ) chose the École et Observatoire des Sciences de la Terre (EOST) atmospheric loading (Boy & Hinderer, ); and others (Creutzfeldt et al, ) preferred Atmacs (Klügel & Wziontek, ). Similar examples can by found for continental hydrology and nontidal ocean loading (e.g., Hector et al, ; Mikolaj et al, ).…”