Pingtung Plain Research Articles

Deep submarine groundwater discharge indicated by tracers of oxygen, strontium isotopes and barium content in the Pingtung coastal zone, southern Taiwan

We have conducted detailed hydrographic surveys off the Pingtung Plain coast, SW Taiwan, using environmental isotope and trace element compositions (δ 18O, Δ 87Sr, and Ba) as the main tracers to investigate submarine groundwater discharge (SGD) in the region. The δ 18O values of seawater in this area show significant variability with heavy isotope enrichment relatively to groundwater, and two δ 18O-depleted layers are found at depths of 400-700 m and 1200 m along deep parts of Kaoping Canyon. Assuming two end-member mixing model, we estimate that fresh submarine groundwater may constitute a few percent of the total SGD in the canyon. This is reflected in lower salinity, higher Δ 87Sr values and Ba concentrations in deep canyon water than in adjacent seawater. Pore water samples collected from the canyon floor have light δ 18O values and low chloride concentrations, consistent with the overlying δ 18O-depleted water. Elsewhere, seabed pore waters have normal seawater compositions. The results of this study indicate that the deep SGD in the Pingtung Plain coastal zone is mainly fed by recirculating seawater with some admixture of fresh groundwater in canyon area (down to ~ 1200 m). Areas with notable SGD are located a long distance from the shoreline (~ 25 km), and the ‘deep’ SGD may be widespread off southern Taiwan. This discharge must be considered as a significant source of trace elements and other chemical constituents to the coastal ocean.

Probabilistically determining roles of groundwater use in aquacultural fishponds

Summary This work probabilistically determined roles of groundwater use in farmed fishponds in the Pingtung plain, southern Taiwan. According to the standard of water quality for aquaculture, three hydrochemical parameters were considered – manganese, arsenic and ammonium–nitrogen. A minimal utilization ratio (UR) of groundwater was obtained from integrating the hydrochemical parameters diluted with surface water or seawater. Through the integration process, safe groundwater used for aquaculture can be determined effectively. Indicator kriging was adopted to estimate spatial probability distributions of UR. A proper groundwater role – UR

Infiltration mechanism simulation of artificial groundwater recharge: a case study at Pingtung Plain, Taiwan

This paper discusses the artificial groundwater recharge effect of high-infiltration basins. For this purpose, the hydrogeological parameters of the study area are collected to construct a conceptualized physical model. The TOUGH2 numerical simulation software is then used to simulate the infiltration behavior of an artificial recharge into an underground aquifer. Four wells (MW-1, MW-2, MW-3, and MW-4) are observed at the field site, after which the groundwater levels are compared with the simulation results. It is found that good agreement exists between the observed and numerical data for MW-1 and MW-2. However, the observed groundwater level in MW-3 is higher than the simulated level. We also find that MW-3 is at the edge of the artificial recharge lake, and that the high groundwater level may well be the result of a portion of the infiltration load following the well border into the well screen. Conversely, the groundwater level in MW-4 is found to be lower than in the simulated well due to local permeability in the well location. Finally, the numerical results predict that the groundwater level will attain a steady state at approximately 47 h after the onset of infiltration.

Comparative analysis of temporal changes of multifunctionality benefit of two major rice paddy plains in Taiwan

Recently, free trade of farm land, changes of agricultural policy and global climate changes have resulted a significant reduction of rice planting area and the multifunctionality values of paddy field in Taiwan. This study aims to evaluate the temporal changes of multifunctionality benefit of two major rice paddy plains in Taiwan. The main agricultural production regions of the Chou-Shui river alluvial fan and Ping-Tung plain are selected for the comparative study. The replacement method is adopted to quantify the multifunctionality of the paddy field. The results show that percentage of cultivated paddy to the total paddy gradually decreases from 92 to 80% and the external value remains from 572,000 to 668,000 NT$/ha in the Chou-Shui river alluvial fan. Whereas, the percentage of area of cultivated paddy to the total paddy markedly decreases from 37 to 23% from 1999 to 2006 and resulting the external values of paddy only ranges from 156,000 to 258,000 NT$/ha in the Ping-Tung plain. To maintain the sustainable agriculture in the paddy field, government needs to formulate incentive policy to conserve the paddy farming, promote, and transmit the general understanding of the environmental and living-hood multifunctionality values to the people.

A Low Velocity Zone along the Chaochou Fault in Southern Taiwan: Seismic Image Revealed by a Linear Seismic Array

The Chaochou fault is one of the major boundary faults in southern Taiwan where strong convergence has taken place between the Eurasian and Philippine Sea plates. The surface fault trace between the Pingtung plain and the Central Range follows a nearly N-S direction and stretches to 80 km in length. In order to examine the subsurface structures along the Chaochou fault, a linear seismic array with 14 short-period stations was deployed across the fault to record seismic data between August and December 2001. Detailed examination of seismic data generated by 10 local earthquakes and recorded by the linear array has shown that the incidence angles of the first P-waves recorded by several seismic stations at the fault zone were significantly larger than those located farther away from the fault zone. This difference might reflect the lateral variation of velocity structures across the Chaochou fault. Further examination of ray-paths of seismic wave propagation indicates that a low-velocity zone along the Chaochou fault is needed to explain the significant change in incidence angles across the fault zone. Although we do not have adequate information to calculate the exact geometry of the fault zone well, the variation in incidence angles across the fault can be explained by the existence of a low-velocity zone that is about 3 km in width on the surface and extends downward to a depth of 5 km. The low-velocity zone along the Chaochou fault might imply that the fault system consists of several splay faults on the hanging wall in the Central Range.

Three-dimensionalQp- andQs-tomography beneath Taiwan orogenic belt: implications for tectonic and thermal structure

SUMMARY We determined the 3-D Qp- and Qs- structure of the Taiwan orogenic belt to enhance understanding of the related tectonic and thermal structure beneath the collision zone. The inversion used t* values measured from the spectra of P and S waves from the dense Taiwan strong motion network for moderate size earthquakes (ML 4.5–5.5) to avoid source complexity. The time period, 1991–2007, includes the aftershock sequence of the 1999 Chi-Chi earthquake that provides good ray coverage in central Taiwan. Over 18 000 velocity spectra from 883 earthquakes were analysed. A non-linear least square technique is applied to the spectra for t* determination by assuming a ω−2 source model for the frequency band of 1–30 Hz. A frequency-independent Q was assumed in this study. The corner frequency of a specific event was fixed for the corresponding stations, and a quality index was defined to assure good quality data for the inversion. The results reveal the sharp variation of Qp and Qs across the recently ruptured Chelungpu Fault, and the Kaoping and Chaochou Faults in Pingtung Plain. The Q values in the hangingwall are smaller by about 85 and 110 for Qp and Qs, respectively, relative to the footwall. The fault geometry is distinctly delineated by the contour of Qp/Qs of 1.2 that extends to the depth of the geologically identified decollement structure. Beneath the Central Range, the low Qp, low Qs and high Qp/Qs features coincide well with the aseismic zone. Comparison to the recent thermomechanical numerical models of Taiwan shows that the low Q zone corresponds to the exhumation of the lower crust. The low Qs regime (high attenuation) beneath the Central Ranges at the depth of 5–22 km coincides with predicted temperatures of 400–600 °C. The Qs comparison with the major tectonic and thermal mechanical models of Taiwan reveals that the shear wave attenuation model contains comprehensive rheological and thermal information of relevance to understanding mountain building processes. This technique appears particularly useful for distinguishing strong and weak crustal regions in the absence of other constraints.

An optimal water allocation for an irrigation district in Pingtung County, Taiwan

AbstractThis paper presents a linear programming model to study the conjunctive use of surface water and groundwater for optimal water allocation in Taiwan. Increasing demand for water emphasizes the proper need for effective planning and development of irrigated resources. A groundwater simulation model was performed to construct the hydrogeological structure of the regional Pingtung Plain in the southwest part of Taiwan and the optimal withdrawal of three irrigation areas in Pingtung Plain was analysed. The optimal ratios for allocating water of three canals are analysed in this research. The optimal distribution rate of each canal depends on the season, irrigation methods and crops, which are two paddy rice and one upland crop. After simulation of various scenarios, optimal simulation results show that the minimal amount of required groundwater and the maximum amount of excess water amounts in the area can be satisfied by current agricultural practices. Copyright © 2008 John Wiley & Sons, Ltd.

Does extrusion occur at both tips of the Taiwan collision belt? Insights from active deformation studies in the Ilan Plain and Pingtung Plain regions

We analyse the present-day deformation in two key areas of the Taiwan collision belt, the Ilan Plain to the NW and the Pingtung Plain to the SW. Our approach is mainly based on consideration of horizontal displacement revealed by recent geodetic (GPS) surveys, derived strain rate tensors indicating horizontal deformation and three-dimensional seismotectonic stress regimes issued from inversion of focal mechanisms of earthquakes. We reconstruct a consistent, albeit complex, tectonic pattern involving non-rigid rotations (clockwise in NE Taiwan, anticlockwise in SW Taiwan), transitions from pure compression near the mountains to transtension near the sea and simple shear affecting the deforming domain (NW–SE left-lateral in NE Taiwan, NNE–SSW right-lateral in SW Taiwan). These tectonic patterns reflect lateral extrusion processes towards mechanically weak domains with respect to collision zone, i.e., adjacent subduction zones (Ryukyu to the NE, Manila to the SW). The extrusion of the Ilan Plain area occurs towards the SE, whereas that of the Pingtung Plain area occurs towards the SW. The extrusion in NE Taiwan is facilitated by the opening of the Okinawa Trough, so that velocity and deformation rates are higher than in SW Taiwan despite less active collision in this northern area. The symmetry of the extrusion patterns is altered by differences in relative positions and orientations of collision belt and adjacent subduction zones, which depend on the plate tectonic configuration and tectonic history of the Taiwan region.

Contemporary deformation of tectonic escape in SW Taiwan from GPS observations, 1995–2005

The GPS velocity field in SW Taiwan inferred by 103 stations from 1995 to 2005 provides an opportunity to better recognize the contemporary crustal deformation under escaping tectonics. Horizontal velocities relative to the Chinese continental margin from east to west rotate counterclockwise from 42.0 mm/yr to 13.0 mm/yr along azimuths from 246° to 265° across SW Taiwan. The vertical velocity field in SW Taiwan shows a subsidence rate of 5 to 20 mm/yr concentrated on the coastal area of the Pingtung plain and an uplift rate of 10 to 20 mm/yr distributed along the mountain belt. Spatial velocity variation indicates the NE–SW-striking Chishan fault (CHNF) acting as reverse faulting with dextral motion, the N–S-trending Chaochou fault as nearly pure reverse faulting, and the Fengshan transfer fault zone (FTFZ) as left-lateral shearing, intersecting the aforementioned faults. The dominant WNW–ESE shortening and NE–SW dextral shear strain are subject to the fold-and-thrust belt of the Western Foothills west of the CHNF. A NE–SW extension and NW–SE contraction are represented near the FTFZ along the SW coastal area, showing a NW–SE sinistral shear strain. Our GPS data show that the movement of FTFZ greatly enhances the velocities of SW Taiwan rotating from nearly westward direction to WSW direction, sub-parallel to the edge of the basement high ( i.e., the rigid indenter) of the Chinese continental margin. The Chishan fault as a boundary fault separates the SW Taiwan into a western deforming domain and an eastern quasi-rigid block. A nearly E–W contraction and N–S extension escaping stress regime is accommodated by N–S-trending ductile flow within the upper mantle and by brittle conjugated-type fracture, formed by the CHNF and the FTFZ, within the crust. The different directions between N–S-trending upper mantle flow and southwestward crustal escape indicate that the crust and upper mantle are decoupled in the tectonic escape process of SW Taiwan.

Feasible groundwater allocation scenarios for land subsidence area of Pingtung Plain, Taiwan

Land subsidence basically is the deprivation of water and earth resources, further inducing social and economical undesirable impact. The principal direction of land subsidence prevention is properly management of groundwater. However groundwater management should be developed on the basis of combined technical, economical, social and institutional approaches to management that reflect local conditions and can be adapted and evolved. Therefore, the aim of this paper is to make land subsidence prevention strategies for government to refer. Before year 1969, agriculture was the main land utilization business in Pingtung Plain. Due to intensive development of fish breeding after 1970’s, the aquaculture area along the estuary region of Pingtung Plain have been dramatically increased. Groundwater thus became the main fresh water resource for aquacultural water diluting and flushing because of the insufficiency in surface water supply. The uncontrolled development of groundwater resources has led to undesirable effects, especially in the south where aquaculture is concentrated. These effects are land subsidence, saline water intrusion, lowering of water tables and reductions in well yields. Government stressed on the improvement of breeding technology in the past, which mainly focused on the water quality control in order to raise the culture density, however, it neglected the impact to the environment and quantity control. This paper promotes a reasonable aquacultural water consumption policy aims at finding out the most suitable breeding species considering water consumption and its reasonable breeding area under the premise that it will not depress the original profit of aquatic products trading.

Climate-induced hydrological impacts on the groundwater system of the Pingtung Plain, Taiwan

The Pingtung Plain is one of the most important groundwater-resource areas in southwestern Taiwan. The overexploitation of groundwater in the last two decades has led to serious deterioration in the quantity and quality of groundwater resources in this area. Furthermore, the manifestation of climate change tends to induce the instability of surface-water resources and strengthen the importance of the groundwater resources. Southwestern Taiwan in particular shows decreasing tendencies in both the annual amount of precipitation and annual precipitation days. To effectively manage the groundwater resources of the Pingtung Plain, a numerical modeling approach is adopted to investigate the response of the groundwater system to climate variability. A hydrogeological model is constructed based on the information from geology, hydrogeology, and geochemistry. Applying the linear regression model of precipitation to the next two decades, the modeling result shows that the lowering water level in the proximal fan raises an alarm regarding the decrease of available groundwater in the stress of climate change, and the enlargement of the low-groundwater-level area on the coast signals the deterioration of water quantity and quality in the future. Suitable strategies for water-resource management in response to hydrological impacts of future climatic change are imperative.

Designing an optimal multivariate geostatistical groundwater quality monitoring network using factorial kriging and genetic algorithms

The optimal selection of monitoring wells is a major task in designing an information-effective groundwater quality monitoring network which can provide sufficient and not redundant information of monitoring variables for delineating spatial distribution or variations of monitoring variables. This study develops a design approach for an optimal multivariate geostatistical groundwater quality network by proposing a network system to identify groundwater quality spatial variations by using factorial kriging with genetic algorithm. The proposed approach is applied in designing a groundwater quality monitoring network for nine variables (EC, TDS, Cl−, Na, Ca, Mg, SO 4 2− , Mn and Fe) in the Pingtung Plain in Taiwan. The spatial structure results show that the variograms and cross-variograms of the nine variables can be modeled in two spatial structures: a Gaussian model with ranges 28.5 km and a spherical model with 40 km for short and long spatial scale variations, respectively. Moreover, the nine variables can be grouped into two major components for both short and long scales. The proposed optimal monitoring design model successfully obtains different optimal network systems for delineating spatial variations of the nine groundwater quality variables by using 20, 25 and 30 monitoring wells in both short scale (28.5 km) and long scale (40 km). Finally, the study confirms that the proposed model can design an optimal groundwater monitoring network that not only considers multiple groundwater quality variables but also monitors variations of monitoring variables at various spatial scales in the study area.

The contribution to tectonic subsidence by groundwater abstraction in the Pingtung area, southwestern Taiwan as determined by GPS measurements

The three sets of Global Positioning System (GPS) data collected from 1996 to 1999 are used to investigate the contribution to tectonic subsidence by groundwater abstraction in the Pingtung plain, southwestern Taiwan. The horizontal station velocities varied from 32 to 54 mm/yr for azimuths ranging from 247.2° to 272.6° with respect to the permanent station S01R located in the Penghu islands. In the central and western part of the study area, GPS stations move generally towards the west, whereas in the Kaohsiung–Pingtung coastal area, the displacement vectors demonstrate a clear counter-clockwise deviation towards the SW. The southern part of the offshore coastal area shows remarkable extension rates of 0.6–2.0 μstrain/yr along azimuth 015–020°. The significant southward increase of extensional strain rates is attributed to the lateral extrusion of blocks bounded by major discontinuities in the study area. For the vertical movement, the station velocities are from ∼13 to −25 mm/yr. Significant subsidence rates from ∼11 to ∼25 mm/yr have been observed. These results clearly demonstrate the existence of transtensional deformation and the southward increase of extensional deformation in the along-strike direction throughout the study area. The comparison with the pattern of Holocene subsidence rates and the isopach of fine-grained sediments suggest that about 75% of this subsidence may result from the decrease in groundwater levels induced by over-pumping. These localized anthropogenic activities contributed to the natural risk that results from tectonic subsidence associated with tectonic extrusion and lateral extrusion at the southern tip of the Taiwan collision belt.

Estimation of subsidence using GPS measurements, and related hazard: the Pingtung Plain, southwestern Taiwan

Four years of GPS measurements were done since 1996 in southwestern Taiwan in order to investigate crustal deformation and land subsidence. The network of 48 stations revealed the velocity field in the Pingtung Plain. Horizontal velocities range from 31 to 54 mm yr −1 towards azimuths 247 ◦ to 273 ◦ . They show clear anti-clockwise deviation in the coastal area, consistent with tectonic transtension related to lateral escape at the transition collision–subduction. The deformation resembles a particle flow towards a free boundary, and is not a rigid rotation. Vertical velocities range from +13 to −25 mm yr −1 . Twenty stations show fast subsidence in the coastal area, with rates averaging −16 mm/yr. The comparison with Holocene subsidence suggests that about 75% of the present-day subsidence result from decreasing groundwater level induced by over-pumping, adding significant short-term component to the natural risk resulting from long-term tectonic subsidence. To cite this article: C.-S. Hou et al., C. R. Geoscience 337 (2005).

Grey degree and grey prediction of groundwater head

Boundary types and geologic conditions, which possess random and obscure characteristics, produce variations in groundwater heads. In this study, a groundwater flow system was regarded as a grey system and a grey degree defined and quantified those characteristics. Data were obtained from field records in Gao-Shu and De-Xie Stations, which are located in the upper and middle sites of Pingtung Plain, Taiwan, respectively. An estimated interval was used to represent the upper and lower groundwater head limits. The analyses showed that the grey degree in the wet season was smaller than in the dry season. This was due to the greater uncertainty in groundwater pumping and rainfall recharge in the dry season. With high confidence levels, the grey degree of the groundwater heads decreased. Under spatial distribution, the uncertainty of the groundwater pumping and rainfall recharge in the middle zone was greater than in the upper zone because the middle zone included residential districts and agricultural regions. Thus, the grey degree in the upper zone was less than the middle zone. The grey model can be used to predict a groundwater head based on the observed groundwater head data and the random degree in the groundwater head each month can be judged by the grey interval.

Radon distribution in groundwater of Taiwan

Radon levels were surveyed in 517 monitoring wells constructed in five major groundwater areas of Taiwan. The radon concentration in groundwater samples varied in a wide range from below the detection limit of 18 pCi/L up to 1,100 pCi/L. A worldwide comparison of reported groundwater radon levels was conducted. Overall radon levels in Taiwan groundwater are relatively low compared to other countries because the geology of Taiwan is mainly comprised of sedimentary rocks. Among the 517 wells monitored, only five wells were found with radon concentrations higher than 500 pCi/L. These five wells are all located near the Chaochou Fault in the Pingtung Plain. This study suggests that well sites near the Chaochou Fault could be good locations to monitor radon anomalies for earthquake prediction and should be avoided for developing domestic water supply. In the recharge area near the Chaochou Fault, the radon concentration in groundwater from shallow wells was approximately 1/2 to 1/4 of that from deep wells in the same cluster.

Land-surface deformation corresponding to seasonal ground-water fluctuation, determining by SAR interferometry in the SW Taiwan

Abstract In this study we implement the InSAR technique for identifying the seasonal surface deformation in the SW Taiwan. The focus of our investigation is on the Pingtung plain, a tectonic valley with a high water-pumping rate. Our preliminary results show that the land subsidence occurs specifically in the dry season and even ceases during the wet season. Whereas local land subsidence is usually caused by dewatering of sediments, we compare therefore our InSAR observations with the groundwater data of this area. This comparison shows that the subsidence rate is associated with the descending trend of groundwater level. Based on our research results, we infer that the dewatering during the dry season removes the buoyant support from the sediments and the effect of sediment compaction simultaneously results in local land subsidence. This successful test exhibits that with suitable images, the InSAR is a useful high-resolution tool for monitoring the earth surface deformation and can provide significant information for the issue of natural hazard mitigation.

Characteristics of the wedge-top depozone of the southern Taiwan foreland basin system

The wedge-top depozone in the southern Taiwan foreland basin system is confined by the topographic front of the Chaochou Fault to the east and by a submarine deformation front to the west. The Pingtung Plain, Kaoping Shelf and Kaoping Slope constitute the main body of the wedge-top depozone. In a subaerial setting, the alluvial and fluvial sediments accumulate on top of the frontal parts of the Taiwan orogenic wedge to form the Pingtung Plain proximal to high topographic relief. In a submarine setting, fine-grained sediments accumulate on the Kaoping Shelf and dominant mass wasting sediment forms the Kaoping Slope. Wedge-top sediments are deformed into a series of west vergent imbricated thrusts and folds and associated piggyback basins. A major piggyback basin occurs in the Pingtung Plain. Four smaller piggyback basins appear in the shelf-slope region. Many small sized piggyback basins developed over ramp folds in the lower slope region. Pliocene-Quaternary deep marine to fluvial sediments about 5000m thick have been deposited on top of the frontal orogenic wedge in southern Taiwan. Sedimentary facies shows lateral variations from extremely coarse fluvial conglomerates proximal to the topographic front (Chaochou Fault) to fine-grained deep marine mud close to the deformation front near the base of the slope. The stratigraphic column indicates that offshore deep-water mud is gradationally overlain by shallow marine sands and then fluvial deposits. The transverse cross- section of the wedge-top depozone in the southern Taiwan is a doubly tapered prism. The northern boundary of the wedge-top depozone in southern Taiwan is placed along the southern limit of the Western Foothills where the frontal orogenic wedge progressively changes southward to a wedge-top depozone (Pingtung Plain), reflecting ongoing southward oblique collision between the Luzon Arc and the Chinese margin. The wedge-top depozone is bounded to the south by the continent-ocean crust boundary. The deep slope west of the Hengchun Ridge can be viewed as an infant wedge-top depozone, showing initial mountain building and the beginning of wedge-top depozone.

Characteristics of the wedge‐top depozone of the southern Taiwan foreland basin system

AbstractThe wedge‐top depozone in the southern Taiwan foreland basin system is confined by the topographic front of the Chaochou Fault to the east and by a submarine deformation front to the west. The Pingtung Plain, Kaoping Shelf and Kaoping Slope constitute the main body of the wedge‐top depozone. In a subaerial setting, the alluvial and fluvial sediments accumulate on top of the frontal parts of the Taiwan orogenic wedge to form the Pingtung Plain proximal to high topographic relief. In a submarine setting, fine‐grained sediments accumulate on the Kaoping Shelf and dominant mass‐wasting sediment forms the Kaoping Slope. Wedge‐top sediments are deformed into a series of west‐vergent imbricated thrusts and folds and associated piggyback basins. A major piggyback basin occurs in the Pingtung Plain. Four smaller piggyback basins appear in the shelf–slope region. Many small‐sized piggyback basins developed over ramp folds in the lower slope region. Pliocene–Quaternary deep marine to fluvial sediments about 5000 m thick have been deposited on top of the frontal orogenic wedge in southern Taiwan. Sedimentary facies shows lateral variations from extremely coarse fluvial conglomerates proximal to the topographic front (Chaochou Fault) to fine‐grained deep marine mud close to the deformation front near the base of the slope. The stratigraphic column indicates that offshore deep‐water mud is gradationally overlain by shallow marine sands and then fluvial deposits. The transverse cross‐section of the wedge‐top depozone in the southern Taiwan is a doubly tapered prism. The northern boundary of the wedge‐top depozone in southern Taiwan is placed along the southern limit of the Western Foothills where the frontal orogenic wedge progressively changes southward to a wedge‐top depozone (Pingtung Plain), reflecting ongoing southward oblique collision between the Luzon Arc and the Chinese margin. The wedge‐top depozone is bounded to the south by the continent–ocean crust boundary. The deep slope west of the Hengchun Ridge can be viewed as an infant wedge‐top depozone, showing initial mountain building and the beginning of wedge‐top depozone.

Application of grey correlation analysis for evaluating the artificial lake site in Pingtung Plain, Taiwan

The overuse of groundwater in coastal areas of Taiwan has caused serious land subsidence, seawater intrusion, and soil salinification. Artificial lakes are one of the alternatives that increase groundwater water resources. The Pingtung Plain is one of the most bountiful groundwater resource areas in Taiwan. The grey correlation method was used to evaluate the four optimal sites in the Pingtung Plain. Evaluations were based on hydraulic conductivity, the amount and quality of source water, the distance between the potential artificial lake site and the source water intake position, and the quantity and quality of gravel dug from the potential artificial lake site. Based on groundwater recharge and water storage, the grey correlation method showed that site D (Dar-Shiang-Yung) was the best choice.Key words: artificial lake, grey correlation analysis, groundwater recharge, Pingtung Plain.