NATURE OF PROJECT: BASIN SCALE MODELLING FOR GROUNDWATER RESOURCE DEVELOPMENT
CLIENT: JABATAN MINERAL DAN GEOSAINS MALAYSIA (JMG) KEDAH / PERLIS / PULAU PINANG
DURATION: JUNE – NOV 2018
INTRODUCTION
Muda Basin in Kedah and its neighboring states of Pulau Pinang as well as a part of the state of Perlis are faced with the problem of water shortage which persist year in year out. Jabatan Mineral Dan Geosains Malaysia (JMG) is faced with the task to resolve the problem. Systematical evaluation of the groundwater potentials in the Basin is carried out by JMG. For this purpose, JMG Kedah/Perlis/Pulau Pinang awarded the groundwater modelling project to Geomapping Technology (GMT) Sdn. Bhd. to develop a groundwater flow model for the aquifer at Sungai Muda Basin (4,210 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 using state-of-the-art software e.g. ArcGIS, Rockworks, Surfer and Aquifer Test to aid groundwater development.
- Numerical Modelling
The three-dimensional numerical code, Modular finite-differential flow (MODFLOW) by U.S. Geological Survey was used for finite differential solutions for the reserve estimates, ZONE BUDGET was used to assess the availability of groundwater in six (6) zones and sub-catchment. Data were integrated on the platform of Visual MODFLOW flex software.
CONCEPTUAL MODEL
Three (3) hydrostratigraphic unit were considered for Muda Basin. This comprises of two aquifer system: (i) upper aquifer and (ii) fractured bedrock aquifer. The layers are: one unconfined layer at the top of the model (Layer 1:Quarternary Alluvium), one semi-confined layer (convertible from confined to unconfined) that defines the main Muda Basin aquifer (Layer 2:coarse sands and weathered rocks) and lastly one confined, underlying fractured bedrock aquifer (Layer 3) from Semanggol (sandstone/siltstone, shale), Mahang (shale, sandstone) Baling (shale, siltstone, sandstone , limestone) and Granite Formations.
Figure 1: Conceptual site model of Muda River Basin Kedah overlain with photo map of the study area
RESULT & DISCUSSION
(i) The model performed well with standard error of estimate at 0.29 m, RMSE (9.8 m) and correlation coefficient of 0.92. The regional trend of groundwater is north-southwest towards the coast (Strait of Melaka). (ii) The total flow of groundwater through the Muda Basin is ≈14.1 million m3/day. Groundwater storage (∆s) is ≈11.7 million m3/day (11,766,812.45 m3/day). The Basin is recharge at 180 mm/yr (7.2 % of average annual rainfall of 2477.78mm/yr). The bulk of recharge comes from rainfall (2,098,631.00 m3/day).
CONCLUSION
For groundwater development to be sustainable in the basin, maximum sustainable extraction (safe yield) for Muda River Basin is by making all abstraction less than 50 % of natural recharge.
