Evaluation of throughflow interceptors for controlling secondary soil and water salinity in dryland agricultural areas of southwestern Australia : II. Hydrological study

Short-term hydrological measurements at one site show that throughflow provided the dominant input of water but not of soluble salts to the salt-affected land. Interceptors will therefore reduce saltland waterlogging caused by inputs of throughflow from valley sides. Leakages through and beneath the monitored interceptors are problems which are partly attributable to incorrect design and construction, and partly to unfavourable soil properties.The salinity of deeper groundwaters was also too low to account for the quantities of soluble salts being exported from the site. This finding suggests that a proportion of the salts accumulated in situ and have only recently been mobilized within the site by increased inputs of fresh throughflow and relatively fresh groundwaters from the catchment of the salt-affected area.Control of deeper groundwater movements as well as throughflow is probably necessary in most locations, but the precise combinations in different situations, and the most appropriate techniques for controlling these water movements, require further research. Increased groundwater discharges are attributed to reduced transpiration by the replacement of deep-rooted, indigenous vegetation with shallow-rooted, seasonally growing exotic crops and pastures, rather than to increased groundwater recharge. The ideal method of controlling both water systems is likely to involve farm management strategies on saltland catchments, employing commercially useful vegetation which simulates the hydrological role of the native species, in conjunction with improvement of soil properties.