# Statistical and Numerical Assessments of Groundwater Resource Subject to Excessive Pumping: Case Study in Southwest Taiwan

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## Abstract

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## 1. Introduction

## 2. Study Area and Data

## 3. Methodology

#### 3.1. Statistical Assessment

#### 3.1.1. Trend Analysis

#### 3.1.2. Change-Point Analysis

#### 3.2. Numerical Assessment

#### 3.2.1. Groundwater Model: WASH123D

#### 3.2.2. Hydrogeological Analysis

#### 3.2.3. Mesh Generation

#### 3.2.4. Boundary Conditions

## 4. Results and Discussion

#### 4.1. Interannual Variations in Hydro-Meteorological Conditions

#### 4.2. Calibration/Validation of WASH123D

#### 4.3. Assessment of Unregulated/Illegal Pumping Using WASH123D

## 5. Conclusions and Recommendations

- At the annual scale, quasi-stationary rainfall is not able to provide enough recharge to the PAP aquifers with the observed decline of GLs, especially over the eastern-southeastern part. The decline, aggravated after the identified change points around 2005–2008, suggests a clear association with land subsidence.
- The pumping-free numerical experiment reveals significant discrepancies between simulated and observed GLs, and these discrepancies develop in both space and time. Our findings not only corroborate the evidence of unregulated/illegal pumping, but also propose a remote connection between pumping and land subsidence.

## Supplementary Materials

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 2.**Spatial locations of various stations, including groundwater level, streamflow, rainfall, and weather stations.

**Figure 3.**The (

**top**) panel illustrates the hydrogeological units (please refer to Table 1 for the definition of each unit), and the (

**bottom**) shows the 3D mesh over the PAP used for WASH123D simulations.

**Figure 4.**The (

**top**) and (

**bottom**) panel shows the spatial distribution of annual rainfall amounts (mean rainfall intensity) and the corresponding trend over the PAP.

**Figure 5.**The (

**top**) panel shows the spatial distribution of mean groundwater levels in Aquifers 1, 2, and 3-1, and the (

**bottom**) shows the estimated trends in the corresponding aquifers over the PAP.

**Figure 6.**Histograms of identified change points for each aquifer, representing frequency distributions of identified years when groundwater level series at any gauges experience a shift in the mean.

**Figure 7.**The (

**top**) and (

**bottom**) panel shows the estimated trends in groundwater levels prior (posterior) to the identified change points at each gauge.

**Figure 8.**Annual series of average effective precipitation and groundwater level anomalies in Aquifer 3-1 and corresponding linear trends.

**Figure 9.**Validation results of river stages in the Gaoping River (

**left**) and groundwater levels (

**right**) from 8 June–8 July of 2012 when Tropical Storm Talim affected Taiwan.

**Figure 10.**Comparisons between simulated and observed groundwater level series at selected sites along the downstream of the Gaoping River from 2003–2013.

**Figure 11.**As in Figure 10, but for the downstream of the Donggang and Linbian Rivers.

**Figure 12.**Evolution of the spatial patterns of groundwater level differences (simulated minus observed data) for the 10-year simulation.

**Figure 13.**Annual series of observed and simulated groundwater level anomalies and corresponding linear trends. GL, groundwater level.

**Table 1.**Hydrogeological units in the PAP and associated hydraulic conductivity (K) values used on this study.

Hydrogeological Unit | ID | Pumping Test Results | Lateral K | |||
---|---|---|---|---|---|---|

Name | Abbr. | No. Tests | Ave.K | Std. Log(K) | ||

Mud Layer | M | 13 | - | - | - | $7\times {10}^{-8}$ m/s |

Fluvial Deposit | F | 14 | - | - | - | $2\times {10}^{-5}$ m/s |

Aquifer 1/A1 | F1/A1 | 1 | 7 | $2.12\times {10}^{-3}$ m/s | 0.32 | $2\times {10}^{-3}$ m/s |

Aquifer 1/A2 | F1/A2 | 2 | 8 | $5.69\times {10}^{-4}$ m/s | 0.33 | $7\times {10}^{-4}$ m/s |

Aquifer 1/B | F1/B | 3 | 13 | $3.31\times {10}^{-4}$ m/s | 0.5 | $4\times {10}^{-4}$ m/s |

Aquifer 1/C | F1/C | 4 | 13 | $2.32\times {10}^{-4}$ m/s | 0.75 | $1.9\times {10}^{-4}$ m/s |

Aquifer 2/A1 | F2/A1 | 5 | 4 | $9.84\times {10}^{-4}$ m/s | 0.06 | $1\times {10}^{-3}$ m/s |

Aquifer 2/A2 | F2/A2 | 6 | 18 | $8.39\times {10}^{-4}$ m/s | 0.44 | $6\times {10}^{-4}$ m/s |

Aquifer 2/B | F2/B | 7 | 15 | $2.69\times {10}^{-4}$ m/s | 0.38 | $3\times {10}^{-4}$ m/s |

Aquifer 2/C | F2/C | 8 | 4 | $2.27\times {10}^{-4}$ m/s | 0.23 | $5\times {10}^{-5}$ m/s |

Aquifer 3-1/A | F3-1/A | 9 | 30 | $1.91\times {10}^{-4}$ m/s | 0.5 | $5\times {10}^{-4}$ m/s |

Aquifer 3-1/B | F3-1/B | 10 | 12 | $1.86\times {10}^{-4}$ m/s | 0.59 | $2\times {10}^{-4}$ m/s |

Aquifer 3-1/C | F3-1/C | 17 | 5 | $4.31\times {10}^{-4}$ m/s | 0.48 | $4\times {10}^{-5}$ m/s |

Aquifer 3-2 | F3-2 | 11 | 16 | $5.13\times {10}^{-4}$ m/s | 0.55 | $5\times {10}^{-4}$ m/s |

Aquitards | T1–T3 | 15 | - | - | - | $1\times {10}^{-8}$ m/s |

Lingkou Cg † | LK | 12 | - | - | - | $2\times {10}^{-5}$ m/s |

Bedrock | R | 16 | - | - | - | $1\times {10}^{-8}$ m/s |

Channels (1D) | Land Surfaces (2D) |
---|---|

$\mathit{Mn}$ | $\mathit{Mn}$ |

0.028–0.040 | Agricultural (0.20) |

Forestry (0.30) | |

Traffic (0.10) | |

Water (0.05) | |

Building (0.10) | |

Other (0.15) |

Year | Hengchun | Kaohsiung | Year | Hengchun | Kaohsiung |
---|---|---|---|---|---|

1981 | 25.21 | 25.00 | 1998 | 26.06 | 25.83 |

1982 | 24.82 | 24.83 | 1999 | 25.12 | 25.19 |

1983 | 24.90 | 24.76 | 2000 | 25.32 | 25.13 |

1984 | 24.54 | 24.33 | 2001 | 25.20 | 25.16 |

1985 | 24.72 | 24.22 | 2002 | 25.44 | 25.66 |

1986 | 24.21 | 24.43 | 2003 | 25.27 | 25.43 |

1987 | 25.30 | 25.16 | 2004 | 25.12 | 25.22 |

1988 | 25.16 | 24.87 | 2005 | 25.05 | 25.05 |

1989 | 24.77 | 24.95 | 2006 | 25.90 | 25.68 |

1990 | 25.12 | 25.13 | 2007 | 25.77 | 25.46 |

1991 | 25.14 | 25.34 | 2008 | 25.37 | 25.14 |

1992 | 24.95 | 24.88 | 2009 | 25.40 | 25.35 |

1993 | 25.20 | 25.11 | 2010 | 25.37 | 25.44 |

1994 | 25.37 | 25.21 | 2011 | 24.72 | 24.95 |

1995 | 24.95 | 24.65 | 2012 | 25.48 | 25.43 |

1996 | 24.97 | 24.83 | 2013 | 25.56 | 25.55 |

1997 | 24.97 | 24.98 | 2014 | 25.59 | 25.59 |

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## Share and Cite

**MDPI and ACS Style**

Shih, D.-S.; Chen, C.-J.; Li, M.-H.; Jang, C.-S.; Chang, C.-M.; Liao, Y.-Y.
Statistical and Numerical Assessments of Groundwater Resource Subject to Excessive Pumping: Case Study in Southwest Taiwan. *Water* **2019**, *11*, 360.
https://doi.org/10.3390/w11020360

**AMA Style**

Shih D-S, Chen C-J, Li M-H, Jang C-S, Chang C-M, Liao Y-Y.
Statistical and Numerical Assessments of Groundwater Resource Subject to Excessive Pumping: Case Study in Southwest Taiwan. *Water*. 2019; 11(2):360.
https://doi.org/10.3390/w11020360

**Chicago/Turabian Style**

Shih, Dong-Sin, Chia-Jeng Chen, Ming-Hsu Li, Cheng-Shin Jang, Che-Min Chang, and Yuan-Ya Liao.
2019. "Statistical and Numerical Assessments of Groundwater Resource Subject to Excessive Pumping: Case Study in Southwest Taiwan" *Water* 11, no. 2: 360.
https://doi.org/10.3390/w11020360