Id. Jolly et al., FLOODWATER RECHARGE PROCESSES IN THE CHOWILLA ANABRANCH SYSTEM, SOUTH-AUSTRALIA, Australian Journal of Soil Research, 32(3), 1994, pp. 417-435
We report the results of a study into the interaction between floodwat
ers and an unconfined alluvial aquifer in the Chowilla anabranch syste
m of the River Murray during a large flood. Data on watertable elevati
on, groundwater chemistry and unsaturated zone salt storage were colle
cted before, during and after a flood in 1990 which inundated all but
the very highest points of the floodplain. These data, combined with a
nalytical modelling of the watertable behaviour throughout the flood,
led us to conclude that diffuse vertical recharge of floodwater to the
unsaturated zone is of little importance. As a consequence, only limi
ted teaching of salt from this zone to the groundwater occurs. This ap
pears to be due to a reduction in the infiltration capacity of the sod
ic clay surface soils of the floodplain which disperse and swell when
wetted with the low salinity floodwater. This suggests that the unsatu
rated zone is not the major source of salt which enters the River Murr
ay following floods. However, from previous studies it is clear that t
he floodplain is an important source of saline groundwater which is ad
ded to the river following floods. An alternative hypothesis to explai
n the observed salt accessions is that areas of the floodplain where t
he Coonambidgal Clay is thin or absent are zones of localized recharge
which cause displacement of in situ groundwater into the floodplain s
treams. This hypothesis should be tested in further work.