Use of soil moisture dynamics and patterns at different spatio-temporal scales for the investigation of subsurface flow processes

摘要

Spatial patterns as well as temporal dynamics of soil moisture have a majorinfluence on runoff generation. The investigation of these dynamics andpatterns can thus yield valuable information on hydrological processes,especially in data scarce or previously ungauged catchments. The combinationof spatially scarce but temporally high resolution soil moisture profileswith episodic and thus temporally scarce moisture profiles at additionallocations provides information on spatial as well as temporal patterns ofsoil moisture at the hillslope transect scale. This approach is better suitedto difficult terrain (dense forest, steep slopes) than geophysical techniquesand at the same time less cost-intensive than a high resolution grid ofcontinuously measuring sensors. Rainfall simulation experiments with dyetracers while continuously monitoring soil moisture response allows forvisualization of flow processes in the unsaturated zone at these locations.Data was analyzed at different spacio-temporal scales using various graphicalmethods, such as space-time colour maps (for the event and plot scale) andbinary indicator maps (for the long-term and hillslope scale). Annual dynamics ofsoil moisture and decimeter-scale variability were also investigated. Theproposed approach proved to be successful in the investigation of flowprocesses in the unsaturated zone and showed the importance of preferentialflow in the Malalcahuello Catchment, a data-scarce catchment in the Andes ofSouthern Chile. Fast response times of stream flow indicate that preferentialflow observed at the plot scale might also be of importance at the hillslopeor catchment scale. Flow patterns were highly variable in space butpersistent in time. The most likely explanation for preferential flow in thiscatchment is a combination of hydrophobicity, small scale heterogeneity inrainfall due to redistribution in the canopy and strong gradients inunsaturated conductivities leading to self-reinforcing flow paths.