Multi-scale assessment of interactions between surface water and groundwater fluxes in hard rock, water limited environment

This is a PhD research dataset by S M Tanvir Hassan, Water Resources Department of the Faculty of Geo-information Science and Earth Observation (ITC), University of Twente, The Netherlands. The abstract of the research outcome is as follows: The multi-scale assessment of surface-groundwater interactions in hard rock (granite), water limited environments was carried out first in the ~80 km2 Sardon catchment and finally in a small, 7.6 ha Trabadillo study area (Western Spain). Three different thematic studies (Chapters 2-4) had been carried out applying various techniques including: field data acquisition, automated monitoring, remote sensing and integrated hydrological modelling using GSFLOW code. Chapter 2 addresses the assessment of dynamics of surface-groundwater interactions at the Sardon catchment scale; the main findings were: (1) intense groundwater exfiltration; (2) groundwater flow characterized by short groundwater flow-path and short residence time; (3) declining trend of catchment groundwater outflow; and (4) large variability of infiltration influenced by land cover type. That impact of land cover upon dynamics of surface-groundwater interactions triggered expansion of further research in Chapters 3 and 4, but also underpinned some hardcoded deficiencies of GSFLOW, related to formulation of driving forces. That initiated the study in Chapter 3, addressing spatiotemporal tree rainfall interception loss (Ei). Experimental measurements of Ei on selected evergreen Quercus ilex and deciduous Quercus pyrenaica oaks were carried out during two years and spatiotemporally upscaled into two homogeneous (1 ha) plots and into the entire Sardon catchment; the main findings were: (1) yearly Ei was larger in wet than in dry hydrological years but if reflected as percent of rainfall, then it was opposite; (2) Ei of Quercus ilex trees were larger than of Quercus pyrenaica but for the catchment scale Ei, it was opposite, because of much larger catchment population of the latter; (3) catchment Ei was primarily dependent on tree density and species type. The Chapter 4 focusses on simulating surface-groundwater interactions at very fine grid (5x5 m) and at temporal daily resolution, using 20-year time-series observation to assess the net recharge dependence upon land cover type expressed through hydrological terrain units (hydrotopes). The findings of this study confirmed all findings of the Chapter 2, adding the following: (1) hydrotope-dependent variability of water fluxes; (2) non-negligible grass interception; and (3) much lower net recharge under tree than grass hydrotopes, meaning more trees, less water resources.