4:45 PM - 5:00 PM
[AHW22-21] Groundwater Gains and Losses Between Catchments in Saxony, Germany using Effective Catchment Index
Keywords:Groundwater, Catchment, Hydrogeology, Inter-catchment groundwater flow, Effective catchment, Topographic area
Hydrological models and simulations have often adopted the closed catchment concept for the estimation and management of water resources in a catchment, thereby neglecting the possibility of intercatchment groundwater flow (IGF). However, a comprehensive understanding of both the hydrological and hydrogeological process in a basin is essential for an integral management of water resources to avoid overestimating or underestimating the available water resources in a catchment. In this study, the effective catchment index was adopted using three global precipitation datasets (MSWEP, GLDAS, and ERA5), two global evapotranspiration datasets (GLEAM, and MODIS), and discharge observations. The hydrological fluxes of 140 catchments in Saxony considering two periods (1980-1990, and 2012-2022) were processed and accounted for bearing in mind the uncertainties, and afterwards their respective effective catchment areas were estimated. Similarly, the ECI result was evaluated and compared to individual catchment attributes obtained for the Digital Elevation Model (DEM) SRTM 30.
The result obtained identified approximately 42% of the 140 catchments which are smaller than their topographic catchment (losing catchment) with an effective catchment area lesser than topographic catchment area, while about 20% are effectively larger than their topographic catchment (gaining catchment). Moreover, about 3% of the 136 conclusive catchments have an effective area of twice or more the topographic catchment area, while less than 17% have an effective area of half or less the topographic area most especially in the arid region. In addition, 16% of the catchments considered for this study are closed catchments (flood regions) with an ECI value between -0.05 and 0.05. The reason for smaller effective areas in the arid region was traced to the mining activities (opencast mining) which required the pumping and lowering of groundwater level. The attributes of the catchments showed significant relationship with the ECI estimates, slope and mean elevation exhibit an increasing trend with ECI (R=0.75, and 0.76), while aridity index shows a decreasing trend with ECI. The result obtained from this study shows that the effective area of catchments in Saxony are either smaller or greater than the topographic catchment area which violates the hydrologists’ concept of a closed catchment mostly adopted by governmental and non-governmental agencies for the management of water resources in a watershed. Therefore, a more integral approach requires the consideration of IGF in water balance models and simulations for a better representation of the hydrological and hydrogeological processes over a basin.
The result obtained identified approximately 42% of the 140 catchments which are smaller than their topographic catchment (losing catchment) with an effective catchment area lesser than topographic catchment area, while about 20% are effectively larger than their topographic catchment (gaining catchment). Moreover, about 3% of the 136 conclusive catchments have an effective area of twice or more the topographic catchment area, while less than 17% have an effective area of half or less the topographic area most especially in the arid region. In addition, 16% of the catchments considered for this study are closed catchments (flood regions) with an ECI value between -0.05 and 0.05. The reason for smaller effective areas in the arid region was traced to the mining activities (opencast mining) which required the pumping and lowering of groundwater level. The attributes of the catchments showed significant relationship with the ECI estimates, slope and mean elevation exhibit an increasing trend with ECI (R=0.75, and 0.76), while aridity index shows a decreasing trend with ECI. The result obtained from this study shows that the effective area of catchments in Saxony are either smaller or greater than the topographic catchment area which violates the hydrologists’ concept of a closed catchment mostly adopted by governmental and non-governmental agencies for the management of water resources in a watershed. Therefore, a more integral approach requires the consideration of IGF in water balance models and simulations for a better representation of the hydrological and hydrogeological processes over a basin.