The cover (cap) over the tailings pit at Nabarlek uranium mine must be
structurally stable as it will act as a barrier to radon gas emission and have
to contain other long-lived radionuclides. Structural stability is primarily
an issue of erosional stability in the context of a design life of thousands
of years. The primary agent of erosion is fluvial, dominated by rainwash,
overland flow, filling and gullying in the local area. Other agents of
erosion are of less concern although biogenic agents of erosion (eg
termites and windthrow) may enhance fluvial activity. Several methods may be used to assess erosional stability. They fall
into two main categories, namely erosion modelling and geomorphic
modelling. The former is illustrated by the Universal Soil Loss Equation
in which parameters describing aspects of the geotechnical and
hydrological properties of the rehabilitated surface are used as input for
the modelling of erosion rates. The latter is illustrated by estimates of
gully and valley erosion using empirical models. Estimates of the erosion
rates and stability of the Nabarlek cover are presented. The two main techniques are complementary and it is argued that
rehabilitation design must make use of both approaches when estimating
erosion and geomorphic stability. More recent developments in
geomorphic modelling using numerical techniques incorporate both
approaches.