2.7 Dryland salinity Key messages Condition and trend • More than one million hectares of agricultural land in the south-west of WA is severely salt-affected. • Dryland salinity has expanded throughout most of the south-west of WA since 1998, especially following episodic rainfall events, such as occurred in 1999, 2000, 2005, 2006 and 2007. • In cleared and developed for agriculture after 1960, most watertables continue to rise, despite a decline in annual rainfall. • As these areas approach a ‘new’ hydrological equilibrium, climate impacts will become the dominant controller of groundwater level trends and the extent of dryland salinity. • Hydrological equilibrium and the potential extent of dryland salinity may take many decades to develop, especially in drier areas. Management implications • The implications of dryland salinity to the agricultural industry are widespread and include reductions in crop yield, area of arable land and land capability. • The opportunity cost of lost agricultural production is at least $344 million per year. Salinity also physically and financially impacts rural infrastructure, public and private water resources and biodiversity, with costs exceeding those to agriculture. • Dryland salinity is a major cause of land degradation and remains a potential threat to 2.8–4.5 million hectares of highly productive, low-lying or valley soils, across the south-west of WA. • Management to contain or adapt to salinity is technically feasible using plant-based and engineering options, though recovery is economically viable in only a few areas. 2.7.1 Resource risk summary for risk of expansion of dryland salinity within hydrozones.
Table 2.7.1 Resource status and trends summary for dryland salinity number Hydrozone Summary Risk Groundwater Trends Confidence in condition Confidence in trend 1 Kalbarri Sandplain Extent of salinity very minor. Salinity could develop in the medium term. Variable trends in groundwater levels. Moderate Variable Adequate evidence and high level of consensus Limited evidence or limited consensus 2 Northampton Block Extent of salinity minor and unlikely to expand. Mostly rising groundwater trends as levels recover from drought. Low Deteriorating Adequate evidence and high level of consensus Adequate evidence and high level of consensus 3 East Sandplain Extent of salinity minor but will almost certainly develop in the medium term because groundwater trends are mostly rising. High Deteriorating Adequate evidence and high level of consensus Adequate evidence and high level of consensus 4 Irwin Terrace Extent of salinity moderate, no imminent threat of expansion. Variable trends in groundwater levels. Moderate Variable Limited evidence or limited consensus Adequate evidence and high level of consensus 5 Arrowsmith Extent of salinity Salinity could develop in medium term. Variable trends in groundwater levels. Low Variable Limited evidence or limited consensus Adequate evidence and high level of consensus 6 Dandaragan Plateau Extent of salinity minor but actively spreading with mostly rising trends in groundwater levels. Large area of high quality agricultural land at risk. High Deteriorating Limited evidence or limited consensus Adequate evidence and high level of consensus 7 Northern Zone of Ancient Drainage Salinity is extensive and continues to expand, but more slowly than prior to 2000. Variable trends in groundwater levels. Moderate Variable Limited evidence or limited consensus Adequate evidence and high level of consensus 8 Northern Zone of Rejuvenated Drainage Extent of salinity moderate and likely to expand but at slower rates than prior to 2000. Variable trends in groundwater levels. Moderate Variable Adequate evidence and high level of consensus Limited evidence or limited consensus quality quality quality quality quality
9 Southern Extent of salinity moderate with a low risk of expansion because trends in groundwater levels are mostly falling. Low Improving Limited evidence or limited consensus Limited evidence or limited consensus 10 South-eastern Zone of Ancient Drainage Salinity is extensive and will continue to expand, albeit at a slower rate. Variable trends in groundwater levels, but water levels in upland bores are still rising. Moderate Variable Limited evidence or limited consensus Adequate evidence and high level of consensus 11 South-western Zone of Ancient Drainage Salinity is extensive and likely to expand because groundwater levels are mostly rising. High Deteriorating Adequate evidence and high level of consensus Adequate evidence and high level of consensus 12 Southern Zone of Rejuvenated Drainage Salinity is extensive. Groundwater levels are mostly stable. The risk is moderating as catchments approach equilibrium. Moderate Stable Adequate evidence and high level of consensus Adequate evidence and high level of consensus 13 Eastern Darling Range Extent of salinity moderate, area of future expansion minor. Trends in groundwater levels are mostly stable. Moderate Stable Adequate evidence and high level of consensus Adequate evidence and high level of consensus 14 Western Darling Range Extent of salinity with low risk of expansion because groundwater levels are mostly falling. Zone mostly forested. Low Improving Limited evidence or limited consensus Limited evidence or limited consensus 15 Coastal Plain Extent of salinity very minor; future development possible in the north, but with low impact. Mostly stable trends in groundwater levels. Low Stable Limited evidence or limited consensus Limited evidence or limited consensus 16 Extent of salinity very minor and future development is unlikely because the zone is at hydrological equilibrium. Very low Unclear Limited evidence or limited consensus Limited evidence or limited consensus 17 Scott Coastal Plain Extent of salinity very minor. Future development is unlikely because the zone is at hydrological equilibrium. Very low Unclear Limited evidence or limited consensus Limited evidence or limited consensus
18 Extent of salinity minor with variable trends in groundwater levels. Salinity risk is moderate and extent will depend on future land use. Moderate Stable Adequate evidence and high level of consensus Limited evidence or limited consensus 19 Albany Sandplain Extent of salinity minor. Groundwater levels are currently deep with variable trends. Low Variable Limited evidence or limited consensus Adequate evidence and high of consensus 20 Stirling Range Salinity is extensive and groundwater trends are variable and equilibrium will be reached in the short term. Low Variable Adequate evidence and high level of consensus Adequate evidence and high level of consensus 21 Pallinup Extent of salinity moderate; expansion is likely but extent restricted. Variable trends in groundwater levels. Moderate Variable Adequate evidence and high level of consensus Adequate evidence and high level of consensus 22 Jerramungup Plain Extent of salinity moderate, expanding slowly and likely to continue. Mostly rising trends in groundwater levels. Moderate Deteriorating Adequate evidence and high level of consensus Adequate evidence and high of consensus 23 Ravensthorpe Extent of salinity minor; expansion is likely but extent restricted. Mostly rising trends in groundwater levels. Moderate Deteriorating Limited evidence or limited consensus Limited evidence or limited consensus 24 Esperance Sandplain Extent of salinity moderate but will almost certainly continue to expand because groundwater levels are mostly rising. High Deteriorating Adequate evidence and high level of consensus Adequate evidence and high level of consensus 25 Salmon Gums Mallee Extent of salinity moderate; expansion is possible because groundwater levels are mostly rising. Moderate Deteriorating Limited evidence or limited consensus Limited evidence or limited consensus
Table 2.7.7 Summary of dryland salinity assessment. NA = Not assessed; * = From Land Monitor areas of consistently low productivity (AOCLP 1998); † = From Land Monitor average height above valley floor (AHAVF) 0–2 m, except Hydrozone 24 0-1 m and Hydrozone 25 m; ‡ = from Resource management technical report 388 (Raper et al. 2013); § = from Salinity Investment Framework Phase 1 (George et al. 2005) of zone in 1998* % Proportion of zone within valley hazard† % trend Timing of salinity§ Risk of salinity Comments 1 Kalbarri Sandplain 0 NA variable medium term possible moderate moderate Rising, falling and stable groundwater trends are found throughout. Rising trends are observed where groundwater is less than 15 m deep, and falling and stable trends where groundwater is deep (> 15 m). The salinity risk is moderate because of the extensive areas of flat plains. 2 Northampton NA 17 mostly rising term unlikely minor low Prior to 2000, this hydrozone appeared to be in hydrological equilibrium with stable groundwater trends. From 2000 to 2007, drought led to significant groundwater falls. Since 2007, groundwater levels have been rising but generally remain below pre-2000 levels. The salinity risk is low because expanding salinity is unlikely and any consequences minor because of the incised topography restricting the extent of salinity. affected
12 Southern Zone of Drainage 8 24 mostly stable term likely moderate moderate Most monitored catchments appear to be approaching equilibrium but there are some bores with significant rates of groundwater level rise adjacent to valley hazard areas, so an expansion of the area affected by salinity is likely. Localised impacts are expected to be moderate as fresh to brackish groundwater resources occur. The moderate salinity risk in this zone is likely to be realised within the next 20 years. 13 Eastern Darling Range 2 3 mostly stable medium term almost certain minor moderate Stable groundwater trends have persisted for the last 10 years and much of the zone appears to be approaching a new hydrological equilibrium. However, a significant proportion of bores in areas of valley hazard show strong rising trends, despite lower than average rainfall. Furthermore, many bores in or adjacent to areas already show artesian heads. It is almost certain that the area affected by salinity will expand, though the additional area will not be great and hence the impact is assessed as minor. affected