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

Abstract

Abstract. Spatial patterns as well as temporal dynamics of soil moisture have a major influence on runoff generation. The investigation of these dynamics and patterns can thus yield valuable information on hydrological processes, especially in data scarce or previously ungauged catchments. The combination of spatially scarce but temporally high resolution soil moisture profiles with episodic and thus temporally scarce moisture profiles at additional locations provides information on spatial as well as temporal patterns of soil moisture at the hillslope transect scale. This approach is better suited to difficult terrain (dense forest, steep slopes) than geophysical techniques and at the same time less cost-intensive than a high resolution grid of continuously measuring sensors. Rainfall simulation experiments with dye tracers while continuously monitoring soil moisture response allows for visualization of flow processes in the unsaturated zone at these locations. Data was analyzed at different spacio-temporal scales using various graphical methods, such as space-time colour maps (for the event and plot scale) and binary indicator maps (for the long-term and hillslope scale). Annual dynamics of soil moisture and decimeterscale variability were also investigated. The proposed approach proved to be successful in the investigation of flow processes in the unsaturated zone and showed the importance of preferential flow in the Malalcahuello Catchment, a datascarce catchment in the Andes of Southern Chile. Fast response times of stream flow indicate that preferential flow Correspondence to: T. Blume (blume@gfz-potsdam.de) observed at the plot scale might also be of importance at the hillslope or catchment scale. Flow patterns were highly variable in space but persistent in time. The most likely explanation for preferential flow in this catchment is a combination of hydrophobicity, small scale heterogeneity in rainfall due to redistribution in the canopy and strong gradients in unsaturated conductivities leading to self-reinforcing flow paths.

The influence of soil moisture on threshold runoff generation processes in an alpine headwater catchment

“…For these events, the most important contribution to streamflow must have come from hillslopes, which likely became hydrologically active and started to release water once the soil moisture threshold was exceeded. We currently do not have isotopic or hydrochemical data to confirm these hypotheses but they agree with previous tracer-based results in other experimental catchments (Sidle et al, 2000;Burns et al, 2001;, which describe the dominant role of the riparian zone for runoff generation during small events/early in the event and low antecedent wetness conditions and, on the other hand, the major contribution from hillslopes for larger events/later in the event during wetter conditions. The observation of runoff production due to precipitation falling onto saturated areas and expanding over time is related to the variable source area (VSA) concept (Hewlett and Hibbert, 1967) from the riparian corridor to the foot of the hillslopes with increasing wetness but the threshold behaviour of hillslope activation and the subsequent abrupt increase in runoff is a mechanism not explained by the VSA concept (McDonnell, 2003).…”

“…Response times were computed following the methodology of Blume et al (2009). Time lags between storm onset and the start and peak of soil moisture, streamflow and water table response were calculated for all rainfall-runoff events.…”

“…Investigating the runoff generation processes in a small headwater catchment in Japan, Sidle et al (2000) identified saturated overland flow from the narrow riparian corridor as the main contributor to runoff during dry conditions whereas, as antecedent wetness increased, subsurface flow from adjacent hillslopes became the main source for streamflow with a corresponding decrease in the riparian contribution to streamflow. Burns et al (2001) assessed the role of riparian groundwater at the Panola Mountain Research Watershed (Georgia, USA) using end-member mixing analysis and concluded that riparian groundwater was the largest component of runoff during rising streamflow and throughout stream recession. Similarly, and McGlynn (2005) assessed the fundamental landscape controls on runoff generation and showed piezometric and tensiometric evidence for quicker responses to precipitation inputs of riparian zones than hillslope areas.…”

An experiment to gauge an ungauged catchment: rapid data assessment and eco-hydrological modelling in a data-scarce rural catchment

“…Similar to the present case, baseflow dynamics were of minor importance. Blume et al (2008Blume et al ( , 2009 successfully applied the same approach in a very humid catchment in Chile, where subsurface flow was the dominant process. Note that the Mod catchment is two orders of magnitude larger than the two latter catchments and that the money and time available for this study were much smaller.…”

The significance of soil moisture in forecasting characteristics of flood events. A statistical analysis in two nested catchments

“…This underlines the importance of direct soil moisture measurements to estimate antecedent wetness as shown in e.g. Blume et al (2009), Schädel (2006, Zehe and Blöschl (2004) or Zehe et al (2010). Thus, a set of distributed point measurements of soil water potential may yield representative information on temporal soil moisture dynamics at the headwater scale.…”