Much concern has been expressed about the potential impacts of changing
climate upon future flood risk. However, there has been much less
attention given to the ways in which changes in catchment function in
general, and sediment delivery in particular, might themselves impact
upon flood risk. This includes the effects of climate change upon
sediment delivery and hence upon changes in river channel conveyance
and hence flood risk. In this paper, we present the results of two
types of modeling. The first presents predictions of future sediment
delivery rates under future climate changes (estimated for the 2050s
and 2080s) in order to provide first order estimates of rates of
channel aggradation in an upland river with a gravelly bed. The second
couples measured channel geometry changes, over short timescales, to
flood events with 1 in 0.5 year and I in 2 year return periods, for
both the present, and for future climates (the 2050s and 2080s). This
coupling is achieved through a coupled 1D-2D model, with a full
solution of the 1D St.Venant equations for the channel and a 2D
diffusion wave treatment on the floodplain. Our results show that, for
the system and flood return periods studied, sedimentation rates are
the primary control upon the frequency of overbank flows and the
magnitude of flood inundation extent. However, these interact
non-linearly with future climate changes to increase future flood risk
dramatically. This leads us to make three important observations: (1)
we must consider what happens when historical flood events are modelled
contemporary geometrical surveys in aggrading systems, as this is
likely to yield unrealistically low friction parameters during the
parameterization process; (2) we must factor the indirect impacts of
future climate change upon sediment delivery into estimates of future
flood risk; and (3) we must think about how river management activities
impact upon the sedimentation process and make sure that the mechanisms
by which a channel maintains conveyance when subject to sediment
delivery are not undermined by river management activities.