Conclusion
This study shows that no individual suspended sediment monitoring method
is suitable for providing the necessary data to understand sediment
transport dynamics in a flowing gully. Rather, the application of a
combination of complimentary methods is necessary to reliably provide
representative data from these challenging aquatic environments. For
example, autosamplers provide multiple samples over a flow event but
fail to sample coarser particles accurately; the calibration of samples
collected by autosamplers with the time-integrated data from a PASS
sampler, which does sample coarser particles relatively accurately,
would result in a more reliable dataset than the use of either method
alone. Other configurations could be used to improve the spatial scale
of monitoring effort, for example, low cost methods (i.e., PASS and RS
samplers) could be deployed at various locations throughout a network of
gullies, whereas multiple methods (i.e., PASS and RS samplers, turbidity
logger, and an autosampler) would be deployed at the gully network
outlet.
The modified PASS sampler performed well in both laboratory and field
trials. The modification of the PASS sampler to operate in gullies is a
good example of how existing techniques can be customised to operate in
the harsh environments typical of gully systems. We aim to further
modify the PASS sampler by interfacing a flow meter and pump controller
so that its sample rate can be matched to stream velocity, thus allowing
the collection of a flow proportional (i.e., isokinetic) sample. Further
comparisons using the PASS sampler and other methods in different
gullies with varied suspended sediment dynamics are required to confirm
its validity as an automated sampling method for gully systems.