Groundwater control measures for salinity management and agriculture in the Khon Kaen area, north east Thailand

• Department of Mineral Resources, Thailand

About six million hectares of northeast Thailand are salt affected (34% of the NE region). Rice yields and economic returns from salt-affected soils are about one-third of those from non-affected soils. The Thai Government has recognised the problem of salinity and has introduced a long-term reforestation program, allocating approximately 5 million rai for tree planting in the most recent (199296) development plan.

Usually, however, the best results for the management of land degradation caused by salinity, have been obtained by combining many strategies. Dryland salinity is mainly the result of saline groundwater discharging at the ground surface. Shallow groundwater salinity is caused by deep groundwater dissolving salt from thick salt deposits that come within 60 metres of the surface in some places.

The objectives of this project are to study the hydroecology of an area of 108 000 hectares in the Khon Kaen area of northeast Thailand. The study will include: local and regional flow systems; location of recharge and discharge areas; origins of salinity; water-use requirements of tree species targeted for planting on recharge areas; and the causes and distribution of high nitrate levels in groundwater.

Further objectives involve the evaluation of selected management methods including deep-well injection of brine and the development of methods for forecasting potential salinisation problems that could occur with changing land use.

Initially scientists will conduct a hydrogeological survey using existing reports, water-level records and air photo and remote sensing analysis.

They will drill groundwater bores to determine groundwater pressure distribution and for seasonal water quality monitoring. Shallow drilling in recharge and discharge areas will be used for solute and isotope studies for recharge/discharge rates. Deep and shallow drilling will be sampled to establish possible relationships between salinity and nitrate levels.

To locate the origin of soil and groundwater salinity, scientists will use geophysical surveys to locate salt domes and major fractures linking subsurface salt to surface salinised land. Using element and isotope evidence from deep and shallow drilling, salt distribution in the deep rock and soil zones can be determined.

Reseachers will evaluate the distribution of groundwater salinity by statistically analysing the water quality database and constructing salinity and groundwater models for the area using the hydraulic groundwater flow model MODFLOW. The model will be used to evaluate different management scenarios.

CSIRO's new 'sap zap' instruments will measure evapotranspiration rates of trees. They are attached to tree trunks and measure the flow of water. These instruments will be used to evaluate water use for mango, mulberry and eucalyptus trees.