Aquifer characterisation in Timor-Leste using ground electromagnetics

[摘要] A combination of population increase and economic development in Timor-Leste has resulted in greater demands being placed on the country’s water resources. In a number of areas, including thecapital Dili, these demands are currently being met by extraction of groundwater from the aquifers, with government regulated bores in some urban areas, but also from an increase in the number ofunregulated spear point bores which tap the shallow aquifer systems. In a project entitled “Assessment on Climate Change Impacts on Groundwater Resources in Timor-Leste”, Geoscience Australia in partnership with the Government of Timor-Leste’s National Directorate for Water Resource Management (DNGRA), is aiming to build Timor-Leste water agencies’ capacity for assessing, monitoring and managing the growing demands on its groundwater resources in a changing climate. The project, funded by Department of Climate Change and Energy Efficiency (DCCEE), involves a multifaceted investigation, including the application of hydrogeophysical methodsfor groundwater and aquifer characterisation.This report details results from the use of ground based time domain electromagnetics (TDEM), as a technique used to help characterise sedimentary coastal aquifers near Dili, the capital of Timor-Leste.The primary objectives of the study were to better define aquifer architecture, the spatial variations possibly associated with groundwater quality and to define the extent of saltwater intrusion between pumping wells on the coast. TDEM Soundings were acquired in over 35 locations mostly within and around Dili, along the Comoro River and around the Tasi Tolu Lakes, west of the capital, and in two other areas, one along the Laleia River some 80kms east of Dili and another near Baucau the second largest city in Timor-Leste.While this study was limited in scope, and consequently only provided a small sample of the variability associated with the aquifer systems on the north coast of Timor-Leste, it demonstrates the potential of hydrogeophysical methods in defining their character, their extent (depth), and the quality of the water they contain.Results from investigations of the alluvial aquifer in Tasi Tolu near Dili, indicate the presence of a highly saline ground water system. The saline groundwater appears to extend over several kilometresinland from the coast in places. Additional soundings would help trace and better delineate the shape and extension of this saline body. In Dili itself, the limited soundings suggest the alluvial aquifer may contain relatively good quality groundwater. The Dili aquifer is presumably being recharged during the monsoonal season and remains fresh as a result of high recharge resulting from high flow events along the Comoro River and other tributaries. In the Baucau area, the results suggest the limestone aquifer to be of good quality, but by inference, of variable quantity. Accessibility seems to be mostly dependent on the limestone thickness, although further work linked to stratigraphic drilling and hydrochemical and environmental tracer studies are required to explain the observed conductivitystructure which underlies the limestone and its hydrogeological significance.Realising the full benefit of the hydrogeophysical results described here requires that they be incorporated into a more extensive hydrogeological investigation on the aquifer systems of the region.

[发布机构] CSIRO

[学科分类] 地球科学(综合)