| A numerical process-imitating model, the Discrete Storm Event Sedimentation
Simulator (DSESS), has been developed to represent the climatic and hydraulic conditions of
drylands in modelling their geomorphological development and sedimentary facies distributions.
The ultimate aim is to provide insights into the lateral variability of permeability in the
Triassic Sandstone aquifers of the UK for the study of solute movement. DSESS employs discrete
storm-flood automata, released across a cellular landscape, to model sediment transport: erosion,
migration and deposition. Sediment classes with different grain sizes can be modelled. Empirical
process-based equations are used to quantify the movement of the automata, their erosion
potential, sediment-carrying capacity and interaction with the underlying sediments. The
approach emphasises the sequence of dryland storm events and associated floods rather than
their timing. Flood events are assumed to be discrete in time. Preliminary tests carried out
with DSESS using simple systems and idealised initial conditions produce lithological and land
surface features characteristic of dryland settings and indicate the potential of the model for
large-scale, long-time modelling of sedimentary facies development. Markedly different results
are observed across the range of tests carried out in response to the non-linear interactions
between the different elements of the landscape and the floodwaters simulated with DSESS.
Simulations show that sediment accumulations develop concave upward radial profiles,
plano-convex cross-profiles and possess a general lateral grading of sediment with distance
from source. The internal grain size architecture shows evidence of both persistent and
rapidly changing flow conditions, with both lateral and longitudinal stepping of coarse bodies
produced by ‘scour and fill’ events and random avulsions. Armoured layers form so that
near-surface sediments have increased likelihood of preservation. Future developments will
include representation of aeolian deposition, mass wasting and hyper-concentrated (debris)
flows.
Keywords: avulsion, channel, deposition, drylands, erosion, gravel armouring,
modelling, sheet-flood, transport capacity |