Types and scales of changes in connectivity in dryland fluvial systems

Connectivity within fluvial systems can change over time at a variety of spatial and temporal scales, and can be due to differing agencies and drivers.  Here, the range and scale of alterations in dryland systems, where flow is ephemeral, are analysed, using evidence of field sites and catchments documented over several decades.

Three main types of agency or drivers are examined:  anthropogenic alterations, which may be deliberate or inadvertent; alteration from vegetation changes; effects of extreme flows.  The modifications of connectivity vary from gradual and progressive to very sudden. The persistence of the alteration also varies. Examples of each type of change are provided and the spatial scale of modification assessed. The morphodynamics and feedbacks into the operation of the systems are discussed.  Changes that are exemplified include effects of structures such as check dams on differing timescales, and the modifications produced by growth and destruction of vegetation. The connectivity of varying flows in these ephemeral changes is related to event characteristics and channel state.  The extent of human impact and their repercussions in these systems are discussed.  The various modifications of connectivity present challenges to modelling and prediction of impacts at varying spatial and temporal scales. The implications for sustainable management and functioning of the systems are considered.