Kung, Chen-Shan1, Wu, Su-Jen2,
Tsai, Wen-Hao3, Tao Fang Tse3
1Vice President, Sinotech Engineering Consultants, Ltd
2Manager, R&D Planning Department, Sinotech Engineering Consultants, Inc
3Senior Engineer, Hydraulic
Engineering Department, Sinotech Engineering Consultants, Ltd. Taiwan, China.
Abstract: Groundwater is an important water resource in
Chuoshui Alluvial Fan. Due to the uneven distribution of precipitation on this
2000 km2 area, people rely on groundwater to supplement the
insufficient surface water supply during dry season. Excessive withdrawal of
groundwater leads to serious environmental impacts: besides problems of
groundwater contamination, land subsidence and seawater intrusion impose immense
losses in land and property. Therefore, appropriate groundwater management
strategies are imperative in the region. This paper introduces several major
groundwater management strategies being applied in the Chuoshui Alluvial Region
which are groundwater and surface water conjunction use plan, groundwater
monitoring system, artificial recharge program. The effects of these groundwater
management strategies will be monitored, evaluated, and modified if necessary,
in order to achieve the goals of curtailing land subsidence and ensure
sustainable use of groundwater resource.
Keywords: groundwater and surface water conjunctive use plan, groundwater management strategies
Taiwan is located in subtropical zone, however, due to its peculiar topographic configuration, rainfall is unevenly distributed both in space and time. In the dry season, rainfall is generally scarce in most areas. Under this situation, water resources application is a difficult issue on the island. As a result of continuous economic growth, rapid increase of population, booming industrial development, and highly improved living standard, we see a continuous increase on water demand during the past decades. This increased demand on water renders water supply management all the more difficult than days past. This is especially true in groundwater management.
The major water supplies in Taiwan are surface water and groundwater. Statistics shows that the annual surface water supply is about 11 billion m3 (1995), amounting to about 65% of the total 17.0 billion m3 water used. The annual groundwater supply is about 6.0 billion m3, and constitutes about 35% of the total water use(1). The Chuohsui Alluvial Region straddles the Changhwa and Yunlin counties. Groundwater resource is a very important contributor to the total water supply, and groundwater is used all the year round in Chuoshui Alluvial Region. The aquifers of the Chuoshui Alluvial Region are constituted of four layers. Information from the observation wells and monitoring wells indicated that the groundwater consumption is 877 million m3/year, which is about 20.4% of total water use of 3088 million m3. The groundwater table draw- down due to this practice of groundwater retrieval is quite serious in the coastal areas of the Changhwa and Yunlin counties. In the past two decades there is a boom in aquaculture industry in Yunlin and Changhwa coastal areas, the demand of water increases tremendously in recent years. The aqua farming industry began to draw groundwater on a large scale, and caused serious land subsidence. It thus stands to reason that, in order to prevent land subsidence and ensure the sustainability of water resources, proper utilization and management of groundwater is an urgent task for the water resources sector(3).
This paper discusses the characteristics of groundwater and the current key issues of groundwater management in Chuoshui Alluvial Region. Action plans for improving groundwater management and the sustainable use of groundwater are also discussed. It is expected that these management strategies introduced will be effective measures that would curtail the practice of excessive groundwater withdrawal, and gradually, but eventually reduce the amount of land subsidence, and also achieve the goal of sustainable use of water resources.
Utilization of groundwater has its advantages and drawbacks. Using groundwater means low cost and readily available water for agricultural, domestic and industrial uses. On the other hand, excessive use of groundwater has imposed some serious problems. During the past forty years, the use of groundwater has created some critical issues on the management of groundwater resources.
The key issue related to groundwater management in Taiwan is that there is no bona fide management body for groundwater use. Traditionally, surface water is managed by the farmer organizations. In this connection, groundwater is only a supplemental water resource for the farmer organizations that distribute water to the farms. Under this system, groundwater management is wholly neglected during the last several decades. By legislature, the direct management authority for groundwater is the local government of each county, and there are commonly just a few clerks who perform the chore of registration only. Under the Water Law, there is no need to enter a registration in the local county government if the use of groundwater is less than 144 m3/day. This leads to loss of information, albeit the groundwater drawn is of small quantity in individual case, but the total cumulative quantity becomes quite substantial but is unknown. Another factor is that the farmers and private industries do not really understand the importance of groundwater cycle and the regulations of groundwater management. The combination of these factors explains why groundwater management is at best lax and ineffective, and sustainability remains a distant goal yet to be achieved. After forty years, the results show that only about 10% of water wells have been registered in the local county government.
The second issue related to groundwater management in Taiwan is that in the past forty years there were no effective groundwater monitoring systems. Recently, this situation has been improved by installation of monitoring systems in the Chuoshui Alluvial Region, Pingtung Plain Region, Chaiyi-Tainan Plain Region and the Lanyang Plain Region. The rest of the groundwater basins still do not have modern monitoring systems. Except Taipei basin, most groundwater basins do not have water meters on their wells. Hence, the actual groundwater consumption can only be estimated indirectly.
The third issue related to groundwater management in Taiwan is the incessant draw down of groundwater table and subsequent land subsidence. During the last forty years, groundwater is over drawn in most coastal plain aquifers because of the increased water demand and the insufficient surface water supply. The consequences of excessive groundwater use are the continuous draw down of groundwater table and the consequential land subsidence due to the consolidation process. Figure 1 shows the extent of land subsidence of the Chuoshui basins respectively. The consequences of land subsidence are drainage problems on low land, beach erosion and high risk of dikes on the coastal areas.
Fig. 1 The recharge and subsidence areas in Chuoshui Alluvial Region
In the Chuoshui Alluvial Region, the Yunlin Offshore Industrial Estate is developed from 1994 to 2020. The first phase is to develop 2200 hectares of land for petrochemical industry use. The Mailiao Project of the Formosa Plastic Group is scheduled to be completed from 1994 to 2000. The full extent water demand for industrial use is 300000 m3/day. The second phase development of the Hsing Hsing Zone started from 1998. A total of 1000 hectares of land is developed for basic industry. The estimated increased amount of industrial water demand is 220000 m3/day in 2009. The third phase development will be finished in 2020. The increased amount of water demand will be another 340000 m3/day. Besides the Yunlin Offshore Industrial Estate, there are other industrial developments in this region; these include the expansion of Touliu Industrial Park, the Yunlin High-Tec Park and the Changhwa Shuiwei Industrial Park, etc. It is foreseen that population growth, economic boom, and raised living standard will be future phenomena in this region consequent to the industrial development. In keeping with this promising industrial development, the total water demand will be increased up to 700000 m3/day in this area in the year 2010. The increased water demand curve is shown in Figure 2.
Fig.2 The water demand curve for Chuoshui Alluvial Region
Three stages of water supply schemes are implemented to cope with the rapid development in order to satisfy the increased water demand. The core concept of the conjunctive use is to satisfy the water demand by conjunction of the safety yield groundwater and the available surface water in a basin(3). In other words, the plan of conjunctive use of surface water and groundwater is to control the groundwater-pumping rate, and supplement by the surface water supply scheme for the future sustainable use of water resources. The conjunctive use of surface water and groundwater plan is currently being conducted in the Chuoshui Alluvial Region. Figure 3 shows the water supply schemes of the Chuoshui Alluvial Region on the conjunctive use bases. Based on the geological formation of the Chuoshui
Fig. 3 The water supply scheme Chuoshui Alluvial Region
Alluvial Region, the artificial recharge program is to evaluate and select suitable places in the alluvial fan deposits areas for groundwater recharge. During the wet season from May to October, surface water is the main water supply, whereas during the dry season, from November to April, the water supply mainly comes from reservoir and groundwater wells. In the wet season, the residual water is diverted to the recharging pond, or recharging lake, for groundwater recharge. Figure 4 illustrates the idea of the series weir structures in river channel program at work in the Chuoshui Alluvial Region.
Fig. 4 Sketch of the series weir structures in river channel program
The first stage is construction of the Chi-Chi Project. Major multipurpose functions of the Chi-Chi project include steady supply of agricultural water, meet the increased demand of 200000 m3/day for the domestic water supply, and fully supply the 860000 m3/day of water for industrial use in the wet season. During the dry season, the supply of the 300000 m3/day industrial water demand is reallocated from agricultural water supply.
The second stage scheme is to implement the Yunlin Reservoir Project, the Hushan and Hunan Reservoir. This reservoir provides 54 million cubic meters storage capacity for surface water during wet season. The project will be completed in 2009. The water supply will be 694000 m3/day in conjunctive use with the Chi-Chi Project. The industrial and agricultural water supply will be well stabilized upon completion of this reservoir. During this stage, the Mailiao Lake Project will also be implemented. The capacity of water supply from Mailiao Lake Project will be 30 million m3/year. The Channeling work of Chuoshuichi and artificial recharge project will also be implemented during this phase. An approximate 30 million m3/year reduction of groundwater consumption will be realized through this conjunctive use scheme.
Modern groundwater monitoring systems are now installed in the Chuoshui Alluvial Region. 188 monitoring wells were installed in its 4-aquifer layers. Under this monitoring system, groundwater tables are measured on the daily bases for the Chuoshui Alluvial Region from 1994. The data are entered onto the data log every day and analyzed every month. The information of groundwater tables is published every year, and is available for use by related organizations and interested parties. The information of groundwater table is also transferred to the local county for the purpose of groundwater management.
The third stage of this water supply scheme is to improve groundwater and surface water conjunctive use, to increase groundwater management and to reduce groundwater consumption. The program of encouraging reasonable water consumption will also be installed in this area for the purpose of reducing extra water demand. Under this stage, the Juifeng Reservoir Project will be implemented in accordance with the economic and social development plan for the Chuoshui Alluvial Region.
Groundwater is an important resource in Taiwan. On this island, almost 35% of water supply are from groundwater. The utilization of groundwater has its advantages, such as providing cheap water for domestic, agricultural and industrial uses. However, serious land subsidence problem occurred in many coastal zones due to inadequate withdrawal and excessive extraction of groundwater in these areas. During the last forty years, groundwater use in Taiwan is not sustainable in several areas; this culminated in high cost to the society and future generations.
To improve groundwater management in Taiwan and mitigate the consequence of non-sustainable use of groundwater, several measures are installed and planned on two pilot groundwater basins, the Chuoshui Alluvial Region and Pingtung Plain Region. The information of groundwater characteristics acquired through these measures will be transferred to the local county government, provincial government and central governmental agencies for the purpose of groundwater management.
The conjunctive use of surface water and groundwater is the best solution for increasing groundwater recharge and sustainable use of water resources. There are three major strategies of the conjunctive use, the artificial recharge program, the series weir structures in river channel program, and reservoir construction. These strategies are now operating in full throttle in the Chuoshui Alluvial Region and the Pingtung Plain Region. Similar program will be developed on other groundwater basins eventually. Following establishment of conjunctive use of surface water and groundwater policy, groundwater use in Taiwan will be sustainable in the future.
Land subsidence in the coastal zones is a serious problem in Taiwan. After the urbanization development together with water supply scheme, the groundwater use pattern will be improved in the future on the coastal areas. If the development proved to be a correct approach, land subsidence in the coastal areas will be eventually curtailed, and the water resources will progressively be sustainable in the future.
[1] Water Resources in Taiwan, Water Resources Planning Commission, 1995.
[2] Wan-Chuan Yang, the Delimitation on Groundwater Basin of Taiwan Area, Geographical Studies, No. 11, December 1987.
[3] Jing-San Hwang, The Water Resources Management in Taiwan, Symposium on Integrated Water Resources Management, Taiwan, May 1998, pp140-194.
[4] The Conjunctive Use of Surface Water and Groundwater in Chuoshui Alluvial Fan (Draft), TPGWRD, August 1998.
[5] The Water Resources Comprehensive Development Plan in Southern Part of Taiwan (Draft), Water Resources Bureau, August 1998.