Catchments as Organised Systems

[G] Hydrological connectivity and its controls on hillslope and catchment scale stream flow generation

This subproject continues the work of project G within the first phase of the DFG Research Group FOR 1598 CAOS.

Observing and understanding connectivity within a catchment (including its spatial variability and organization as well as its temporal dynamics) is one of the central themes in advancing hydrological understanding for predicting rainfall-runoff response, solute and matter transport and in-stream variability of water quantity and quality. In this project, we will focus on functional connectivity between hillslopes, riparian zones and the stream network, which is the result of how spatial patterns of structural (static) connectivity translate into fluxes and export of water, sediment and solutes. In particular, we will advance the understanding of the relevance and role of diffuse vs channelled connectivity for surface and subsurface processes and possible feedback mechanisms.

In order to observe, understand and predict these different functional connectivities from the reach scale to the meso-scale watershed, we will develop and apply a range of novel observation and modelling techniques to measure functional connectivity at its appropriate scale and at the necessary repetition to draw statistically sound conclusions. In addition to the invaluable existing installations from phase 1 (subproject G) of 46 cluster sites and over 20 streamflow gauging sites within a nested catchment arrangement, we propose to install 100 time-lapse cameras and saturation sensors to track the surface contributions from hillslopes to the stream network as well as the expansion and contraction of the stream network itself. Subsurface connectivity will be observed at nested focus areas from the stream to a hillslope transect, based on snap-shot surveys of in-stream sampling and geophysical observation, continuous measurement in near-stream and hillslope piezometer networks and selected tracer experiments at hillslope transects. Finally, stream temperature signals, which will be monitored with a dense network of temperature loggers across the Attert basin, will be used as indicators of hillslope-stream connectivity and as tracers for consecutive mixing, but will also serve as a unique dataset for heat balance and heat transport modelling which is deemed to be an essential counterpart to the mere modelling of water flows.

This project will make an important contribution to catchment process hydrology and modelling and hence to the CAOS research unit, as a systematic assessment of hillslope-stream connectivity is paramount to linking local scale dynamics and runoff generation to overall catchment response. This systematic assessment of connectivity, its temporal dynamics, spatial patterns and the underlying controls will thus add to our understanding of landscape organization of water flow and transport, with the potential to improve regionalisation efforts considerably.

Signatures of connectivity

Fig 1. Signatures of connectivity will be investigated in the stream itself (A), at the stream- hillslope interface (the river bank - B), in the near-stream zone (C) and along the hillslope transect (D).