Identifying how the dominant runoff processes of sub-catchments integrate to determine hydrological responses at larger scales (> 1000 km2) remains a major challenge in hydrology. At these larger scales, major environmental differences such as climate, geology and land use may have increased influence on runoff dynamics. While process investigations at smaller scales (< 10km2) have been important in establishing the influence of topography and soils on runoff generation, more research at larger spatial scales is needed, since it is at such scales where important water management decisions are made in relation to applied problems such as floods and droughts. Tracers, such as stable isotopes of water, have proven utility as tools since they reflect the integration of processes at much smaller scales. In addition, geochemical tracers, such as alkalinity, help identify the geographical sources of runoff in larger catchments. This thesis focuses on their use to study catchment hydrological processes in the River Dee (~2,100 km2), NE Scotland, and to determine how these processes integrate at larger scales. Runoff from soil derived hydrological responsive pathways dominates during high flow facilitating a relatively rapid translation of precipitation isotope signatures into the channel network. Increased coverage of responsive soils resulted in reduced Mean Transit Time (MTT) estimates. High coverage of freely draining soils and certain landscape features often resulted in greater MTT estimates. Small scale heterogeneity appears to be averaged out at larger scales with MTTs indicating that the montane headwaters of the river are the dominant source of runoff. Transit Time Distributions (TTDs) suggest that catchment waters may have transit times of less than 2 weeks during high flows and greater than 10 years in summer baseflows.