Id. Jolly et al., SALT ACCUMULATION IN SEMIARID FLOODPLAIN SOILS WITH IMPLICATIONS FOR FOREST HEALTH, Journal of hydrology, 150(2-4), 1993, pp. 589-614
Dieback of native Eucalyptus largiflorens forests is an increasing pro
blem on the floodplains of the lower River Murray, southern Australia.
Salinisation of floodplain soils, as a result of the changed hydrolog
ical management of the River Murray, appears to be a primary cause of
the dieback. Regulation of the River Murray has reduced the frequency
of large flood events by a factor of approximately three and caused gr
oundwater levels beneath floodplains to rise. The higher water tables
have resulted in increased discharge of the naturally saline groundwat
er in the floodplains by evapotranspiration, and the decreased-inciden
ce of large floods has reduced floodwater recharge and hence leaching
of salt from floodplain soils. Use of soil physical properties for a r
ange of floodplain soils, combined with measurements of groundwater di
scharge from bare and vegetated sites, suggests that the time-scale fo
r complete soil salinisation can, at worst, be less than 20 years. Mor
eover, salt accumulation at most sites will continue to occur as the p
resent flooding regime (of which there is limited scope for improvemen
t) appears incapable of providing the leaching required to counteract
accumulation. The analyses carried out here suggest that the 'critical
' water table depth (below which groundwater discharge is balanced or
exceeded by floodwater recharge) needs to be increased by 14-55% (the
more clayey the soil, the larger the increase) to prevent salt accumul
ation. Failure to implement schemes which lower the water tables benea
th the floodplain may, in the long term, cause serious damage to these
important riparian forests.