The main goal of this thesis is to study linear and nonlinear catchment dynamics through the fairly new concept of “hydrologic connectivity”. Justification for the chosen approach lies in the fact that we want to look for the organizing principles and emergent properties of catchment dynamics, rather than focusing on the heterogeneity of point data at very small temporal and spatial scales. The concept of hydrologic connectivity emerges as a very powerful tool for explaining the growing numbers of nonlinear hydrologic behaviors documented around the world, because it gives us an indication of the functional relationship between storm runoff sources and the catchment outlet. Indeed, when we try to gather what we know about the connectivity concept so far, we realize that it is a term that is being increasingly applied. However there seem to be a lack of consensus among hydrologists, about what it is exactly, how to identify and measure it, and how to relate it to existing research. This therefore raises three major issues for future work in catchment hydrology, and these three issues form the core of the thesis: (1) How to identify and measure hydrologic connectivity?, (2) How to model hydrologic connectivity?, and (3) How to investigate the  time/space scale-dependence of hydrologic connectivity?

        In terms of research outline, two main objectives are pursued. In the experimentation part of the research, we aim at identifying and measuring hydrologic connectivity. A perceptual model of hydrologic connectivity is to be build using data on geochemical flow paths, multiple depths soil moisture and surface and subsurface topography. In the modelling part of the research, we rather investigate the representation of hydrologic connectivity in index-based hydrological models, especially TOPMODEL. These two main objectives are broken into more specific sub-objectives and the scaling issues are examined in both an experimental and a modelling context for small headwater, humid temperate catchments.