Burdass, W.J. (1985). Draining a saline seep. Western Australia Journal of Agriculture, Vol. 26. No. 4, p. 130-132.

Based on early successes with the use of sub-surface drains in treating saline seeps, a drainage trial was initiated to investigate its effectiveness in treating a saline seep on a property at Punchmirup Siding, on the closed Katanning Donnybrook railway line, Western Australia. The aim of the project was to measure the quantity and salt content of effluent from subsurface drains and to assess the changes in the composition of the pastures, as well as providing experience in laying sub-surface drains and assessing installation costs

Sandplain seeps are derived from a shallow groundwater system which flows from the deep sandplain soils upslope. The seeps result in small areas of salinity and waterlogging, which can be the focus of soil erosion. Sandplain seeps may represent as much as 10 % of the Western Australia's salt problem in the drier agricultural area.

The saline seep at Punchmirup Siding, Western Australia, is typical of many hillside seeps in the district. It is located towards the foot of the south facing slope that runs down from Punchmirup to a creek more than a kilometre away. The eye of the seep is situated at a distance of approximately 160 metres from the creek.
It is suggested that the salty seepage was caused by groundwater being 'dammed' up behind a rock bar and leaking upwards through preferred channels, resulting in a seepage eye or 'mound springs'.

Based on a detailed geological and hydrogeological knowledge of the site, the layout of the drains was planned and three drains, each 200 metres in length, with 30 metre spacings were installed. The drains were excavated to 2 metres below the surface to intercept groundwater as it leaked upwards.
The drains were excavated with a back-hoe fitted with a 46 cm wide bucket. The trench floor was trimmed with a blade to create a groove in which to bed the pipe. The pipe was covered with local pit gravel to a depth of 20 cm and thereafter back filled using a blade on the front of a wheeled tractor. Grade was maintained using a line and boning rod. The line was set at pre-determined heights on posts located to the side of the trench every 20 metres.

Since the drains were installed, surface flows of water from the eye have ceased. Capeweed and grasses are growing on three - quarters of the previously bare area and clovers are invading the areas that previously only carried sea barley grass.
The salinity of the surface soil was substantially reduced over the first year and has remained at that lower level. Similarly, water levels adjacent to the drains decreased rapidly (up to 70 cm) within 24 hours of installation. The combined discharge from the three drains ranges between 6 L/minute in summer and 26.5 L/minute in mid-winter.

Although the sub-surface drainage system has proven to be technically feasible, with regards to lowering soil salinity and water levels, and associated increased productivity, the high cost of the capital, installation and maintenance has meant that the system is not economically feasible at this site.
Only if the sub-surface drainage system was protecting higher value crops or discharging effluent water of suitable quality for stock purposes, would the engineering option be considered practicable at this site.

The following are key determining factors for the successful implementation of sub-surface drains to control saline seeps in dryland areas:

• drain spacing adequate to maintain the water table at a particular depth below the ground surface;
• a level of economic return from the land subject to the drains;
• a level of economic value of the re-used water;
• ability to re-use the drained water; and
• a suitable drainage disposal or storage strategy.