Degrees of separation: hillslope-channel coupling and the limits of palaeohydrological reconstruction.

John Wainwright

Catena 66(1-2): 93-106.

According to qualitative analysis of conditions of hillslope-channel coupling, internal catchment configuration strongly influences water and sediment transfer through the fluvial system. Subsequently, similar climatic inputs into catchments with otherwise similar characteristics can result in very divergent responses. A cellular modelling approach has been used to assess the potential magnitude of this effect, and to investigate the implications for palaeohydrological investigations. The model subjected simple catchments with coupled and progressively uncoupled conditions to simulated climate change using a 740 ka proxy climate record. Dynamic flow and sediment routing were simulated, and soils and vegetation were allowed to evolve in parallel. The results suggest that the configuration of the catchment has a very strong effect producing a complex system response based on the output of sediment from the catchment and that there are no simple relationships between climate and catchment output. There is an evolution of the complex response itself time as the catchment dynamically reorganizes, implying that system trajectory and historical contingency are also significant factors. Although events may be captured in the sedimentary record, these events will often relate to pulses of sediment working their way through the system, rather than being directly related to climate changes or variability. Consequently, the complex, non-equilibrium behaviour of the system suggests that climate proxies derived from even high-resolution palaeohydrological records should be treated with extreme caution.

Key words

Catchment hydrology; Climate proxies; Geomorphic modelling; Complex response; Landform evolution; Equifinality; Divergence

Different interactions of slope diagram