An Overview of the Geological Control on Groundwater Potential in Lacamutu River, Alaua Kraik Area, Baucau Municipality, Timor-Leste

Abstract

Timor island has a tropical climate with relatively little rainfall and surface water is often not available throughout the year with groundwater relied on to fulfill daily domestic necessities. Geological reconnaissance mapping, hydrogeological investigation, and resistivity survey were undertaken in this study to systematically understand the hydrogeologic system (e.g., aquifer system, hydrostratigraphic units, groundwater flow direction) and its potentiality for water supply to human consumption in Alaua Kraik area, Baucau Municipality, Timor-Leste. Res2DInv, Dips 5.1, Surfer 16, Global Mapper 13, and ArcGIS 10.6 software was used to create geological reconnaissance maps, resistivity interpretation profile lines, and a hydrostratigraphic model. Rainfall precipitation, rainfall intensity, maximum rate of runoff and infiltration data are also used to interpret the groundwater potential in the study area. Two rock units occur in the study area; permeable alluvial deposits which unconformable overlie impermeable interbedded red marl-chert and calcareous shale. Structurally the area comprises the Lacamutu anticline, thrust fault, left slip fault, and normal right slip fault. Resistivity lines indicate three (3) types of lithologies: alluvial deposit, an intercalated layer of red marl-chert, calcareous shale and wet calcareous shale. The alluvial deposit and red marl-chert layer intercalated with calcareous shale units are classified as a hydrostratigraphic unit of intergranular and localised aquifer systems with low productivity. The groundwater flows through the existing fractures of the shear joint and tends to flow towards the left slip fault plane zone from the North to South direction. Much of the rainwater in the study area is most likely intercepted, evaporated, and or transpiration as opposed to running off and infiltrating into the ground. The permeable and heavily fractured impermeable rock units in the study area have good porosity but low permeability and represent poor aquifers. The springs and Lacamutu River have low discharge and are generally dry in the dry season as it does not have an adequate aquifer that can accumulate and pass groundwater with significant volumes even if the rainfall in the study area is classified as moderate rainfall.