NATURE OF PROJECT: BASIN SCALE MODELLING FOR GROUNDWATER RESOURCE DEVELOPMENT
CLIENT: JABATAN MINERAL DAN GEOSAINS MALAYSIA (JMG) SELANGOR / WILAYAH PERSEKUTUAN
DURATION: JUNE – NOV 2018
INTRODUCTION
Selangor State in Malaysia have reached a decision that a quick fix to the water deficit is to develop groundwater as supplementary raw water supply for various users. Groundwater modelling is considered the most valuable and powerful management tool that is useful to effectively perform the complex task. For the basin scale groundwater modelling, Jabatan Mineral Dan Geosains (JMG) Selangor, Malaysia awarded the groundwater modelling project to Geomapping Technology (GMT) Sdn. Bhd. to develop a regional groundwater flow model for the aquifer at Sungai Kelang Basin (1,288 km2). The primary objective is to estimate the groundwater reserve and maximum sustainable extractions from the aquifer to support technical decision for planning and groundwater resource development of the Basin.
METHODOLOGY
The approach used in this study include:
- Desktop review and previous data gathering
- Data processing and management
- Field investigation for new data capture
- Numerical Modelling
Modular finite-differential flow (MODFLOW) by U.S. Geological Survey was used for finite differential solutions for the reserve estimates, MODPATH (modular finite differential path lines) and ZONE BUDGET was used to assess the availability of groundwater in five (5) zones and sub-catchment areas.
REGIONAL CONCEPTUAL MODEL OF KELANG BASIN
Kelang Basin was modelled as three (3) main hydrostratigraphic unit and comprise of two aquifer system (upper aquifer and fractured bedrock aquifer). The layers comprise of one unconfined layer (Layer 1), one confined upper aquifer (Layer 2) and semi-confined fractured bedrock aquifer (Layer 3). Layer 1 is Quaternary Alluvium/completely weathered soil (sandy clay /sandy silt). Average thickness is estimated to be 12.3 m. Layer 2 (Alluvium clayey sand/silty sand) is the upper aquifer (10.7 m). Layer 3 is fractured bedrock and comprises of relatively less permeable Kuala Lumpur Limestone Formation, Kenny Hill Formation (mainly sandstone) and Hawthornden Schist Formation (schist, and phyllite). Assumed thickness for the fractured bedrock is 250 m.
Figure 1: Conceptual site model of Kelang River Basin
RESULT & DISCUSSION
(i) The model calibration performed well: standard error of estimate is 0.47 m, RMSE: 9.56 m and correlation coefficient: 0.78. The regional movement o of groundwater is northwest-southwest towards the west coast (Strait of Melaka). (ii) Total inflow of fresh groundwater to the Basin is ≈6.1 million m3/day (6,132,655 m3/day). Groundwater reserve (∆s) is 589,422.25 m3/day). The Basin is recharged at 260 mm/yr (10.5 % of average annual rainfall of 2465mm/yr). The bulk of recharge to the aquifer comes from rainfall (918,899.06 m3/day).
CONCLUSION
For groundwater development to be sustainable, maximum sustainable extraction for the Basin is recommended at 50 % of natural recharge.
