This paper assesses the extent to which a topographically defined
description of the spatial arrangement of catchment wetness can be used
to represent landscape hydrological connectivity in temperate river
catchments. A physically based distributed hydrological model is used
to characterize the space-time patterns of surface overland flow
connection to the drainage network. These characterizations are
compared with a static descriptor of the spatial structure of
topographically controlled local wetness, called here the Network
Index. Theoretically, if topography is the primary control upon
hydrological response, the level of catchment wetness required to
maintain connectivity along a flow path should be greater for flow
paths that have a lower value of the topographically controlled local
wetness. We find that our static descriptor can be used to generalize a
significant proportion of the time-averaged spatial variability in
connectivity, in terms of both the propensity to and duration of
connection. Although the extent to which this finding holds will vary
with the extent of topographic control of hydrological response, in
catchments with relatively shallow soils and impervious geology our
index could improve significantly the estimation of the transfer of
sediment and dissolved materials to the drainage network and so assist
with both diffuse pollution and climate change impact studies. The work
also provides a second reason for the concept that there are Critical
Source Areas in river catchments: these arise from the extent to which
that material can be delivered to the drainage network, as well as the
generation of risky material itself.