Groundwater Modeling Study case : Central Plain of Thailand December 16, 2009 Werapol Bejranonda Department of Geohydraulics and Engineering Hydrology University of Kassel, Germany

Contents Study Area / Groundwater hydro. Methodology Groundwater Modeling Application of the model

Research Objectives Investigate use-patterns of conjunctive water between groundwater and surface water in the upper central plain of Thailand Estimate the impact of groundwater use via the use-patterns

Study Area GW Basins Geological Map of Thailand Upper Central GW Basin of great central basin Agricultural Bangkok (Capital) *The first upper central regional GW Model Lower Central GW Basin of great central basin Industrial Agricultural Hydrogeological map of upper central GW basin GW Basins

Study Area Surface Water cover 5 main surface-water basins Study Area Boundary 4 Main Streams Yom Rive Nan River Ping River Sakaekrang River cover 5 main surface-water basins Surface Water

Study Area Project study area covers 6 Provinces 47,000 km2 UTD SKT PSL KPP PCT 47,000 km2 NKS Project study area covers 6 Provinces

Existing Conjunctive Use Irrigation area Rainfed area Personal GW pumps

Study flowchart

GW use ?? Field data collection (pumping behavior) area crops/year season pumping/crop day/pumping hours/day irrigation 2.5 dry 6.0 2.6 19.3 wet 3.8 2.3 rainfed 2.0 6.5 3.1 22.0 2.1 16.0 pilot area (irrigation) 5.4 4,9 20.4 3.5 4.5 23.8

Layer Classification Flood Deposit & Low Terrain High Terrain

Upper Layer (Semi-confined) Lower Layer (Confined) GW Model (MODFLOW) 2 Layers Conceptual Model 10 km. Upper : 320 grids Lower : 346 grids 10 km Upper Layer (Semi-confined) Lower Layer (Confined)

Upper Layer Lower Layer thickness 40-100 m. thickness 100-300 m. Recent Flood Plain Deposits Low Terrace Deposits High Terrace Deposits Rock Upper Layer thickness 40-100 m. Lower Layer thickness 100-300 m.

Calculation Method Steady Calibration : 2003 Transient Calibration : 1993-2003 Model Verification :2003-2005 1.Steady State for Hydraulic Conductivity 1993 2.Transient State for Specific Storage 2003 2005 3.Verification

Calibration & Verification Steady Calculation Average Error (m) Root Mean Square Error(m) Calibration (Steady) -0.97 2.75 Calibration (Transient) 3.83 4.53 Verification (Transient) 1.77 5.34 Transient

Observed Simulation (steady) Groundwater Level in dry season of 2003

Surface Water Budget Situation

water demand : SW : GW (all in wet year) Space Dimension Aquifer types pump yield GW use to demand M3/hr flood deposits 10-20 17% Low terrace deposits 5-12 7% high terrace deposits 1-10 2% GW Use Ratios Basin water demand : SW : GW Irrigation area rain-fed area Ping 1 : 0.54 : 0.08 1 : 0.83 : 0.17 Yom 1 : 0.90 : 0.01 1 : 0.87 : 0.13 Nan 1 : 0.53 : 0.30 1 : 0.97 : 0.03 Chaophraya 1 : 1.00 : 0.02 1 : 0.99 : 0.01 Sakaekrang 1 : 0.83 : 0.01 all basins 1 : 0.62 : 0.17 1 : 0.93 : 0.07 Water situation water demand : SW : GW (all in dry season) Wet 1 : 0.49 : 0.27 Normal 1 : 0.32 : 0.36 Dry 1 : 0.47 : 0.52 Drought 1 : 0.63 : 0.68 Time Dimension Irrigation condition water demand : SW : GW (all in wet year) rainy season dry season whole year irrigation area 1 : 0.74 : 0.05  1 : 0.50 : 0.29 1 : 0.66 : 0.13 rain-fed (no irrigation)  1 : 0.98 : 0.02 1 : 0.54 : 0.46 1 : 0.94 : 0.06

Surface and Groundwater Use Conjunctive Use Patterns Ratio of Groundwater Use to total water demand

Different GW Level from Calculation Approach

Application#1 : GW Level in pilot area GW yield awareness Agricultural well yield Simulated as Drought year

Application#2 : Regional GW table 2005 Application#2 : Regional GW table 2018 Simulated groundwater table using conjunctive use ratio 2003 2026

Conclusions Groundwater use varies on deficit of surface water supply Conjunctive use pattern significantly varies with surface water situation, season, aquifer characteristic and irrigation-rainfed area Conjunctive use pattern is a key factor to estimate groundwater consumption and simulate groundwater-level fluctuation

References Faculty of Engineering, Chulalongkorn University (2002), Groundwater Potential in Lower Central Part of Thailand. Koontanakulvong, S. and Siriputtichaikul P. (2003), Groundwater Modeling In the North Part of the Lower Central Plain, Thailand, International Conference On Water and Environment, Bhopal, India, Vol.Ground Water Pollution No.19, pp. 180-187. Panot (2000), Groundwater Modeling of Lower Central Part of Thailand.

Acknowledgement Department of Groundwater Resources Royal Irrigation Department Water Resources System Research Unit, Chulalongkorn University

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