Water restrictions were implemented in two zones of Taichung from Tuesday last week, with water supplied for five days and cut off for two. People with large-capacity water storage tanks at home might not be feeling the effects, but businesses that use large amounts of water, such as restaurants, hair salons and car washes, are in dire straits.
Only twice in the past 22 years has Taichung been divided into zones for water rationing: In 1999, the Shihgang Dam (石岡壩) was badly damaged by the 921 Earthquake and in 2004 the inlet sluice gate of the Liyutan Reservoir (鯉魚潭水庫) became detached, leading to water restrictions for less than a week. The dam has since been repaired and a second raw water pipe was installed at the reservoir, so these incidents are unlikely to recur.
How long will the rationing continue this time and how can similar incidents be prevented?
The current water restrictions were prompted by low rainfall since June last year and drying reservoirs. From 2011 to 2016, reservoirs in central Taiwan supplied companies with about 100 million tonnes of water per year, but from 2017 to 2019, the amount exceeded 130 million tonnes, reservoir data showed.
Industrial water consumption has dramatically increased and this inevitably has an impact in drought years. The only way to improve the situation is to ask water companies not to be overly optimistic when estimating supply, and to require those who use water to do so more sparingly.
Taichung relies on two major reservoirs: the Liyutan Reservoir and the Shihgang Dam.
The off-stream Liyutan Reservoir, which has storage capacity of 110 million cubic meters, supplied more than 300 million cubic meters in 2019, but also released 200 million cubic meters in overflow discharge. As well as being difficult to operate, the reservoir’s storage capacity is clearly insufficient.
A joint water usage and transfer project for the Daan (大安) and Dajia (大甲) rivers passed an environmental impact assessment last year, but if the reservoirs’ storage capacity remains inadequate, what difference does it make having more plentiful water resources?
The government should consider raising the reservoir’s height, as was done at the Zengwen Reservoir (曾文水庫).
Another important water source for Taichung is the Shihgang Dam, but this is basically a weir — a low dam built to raise the level upstream or to regulate flow — from which water can be drawn. The dam does not hold enough water to supply Taichung for one day, and it depends on the Deji Reservoir (德基水庫).
All of the reservoirs along the Dajia River, except for the Deji Reservoir, have little capacity. This is not a problem for the generation of electricity, but even the Deji Reservoir, with its 180 million cubic meters of capacity, still had to discharge overflow in 2019. As a result, the Shihgang Dam supplied about 540 million tonnes of water that year, but also released nearly 290 tonnes downstream.
The Deji Dam (德基水壩) is the tallest in Taiwan, but due to the curvature in the arches and in the crown cantilever, raising its walls is not feasible.
However, the downstream Qingshan (青山), Tianlun (天輪) and Maan (馬鞍) dams are all concrete gravity dams. Their walls could be raised or back pool weirs could be added.
The Tianlun Dam (天輪水壩) has two back ponds with a capacity of 800,000 cubic meters. The addition of retention basins, or their enlargement, between the Deji Reservoir and the Shihgang Dam would help Taiwan Power Co to build a Dajia River pumped-storage hydropower system, modeled after the one on Sun Moon Lake (日月潭) in Nantou County.
Taichung provides Changhua County with about 140,000 tonnes of water per day. Once the Niaozueitan (鳥嘴潭) artificial lake project and downstream running water systems are completed, Taichung could keep the water for its own use, but there is still scope for utilizing the water resources of the Dadu River (烏溪).
The Dadu Weir project, which has been aborted due to the shutdown of the Guoguang Petrochemical project near the Port of Taichung, could be reconsidered. Despite the poor water quality in the lower reaches of the Dadu River, it should be good enough for industrial use.
If the Dadu Weir was completed, it could, in conjunction with water recycling plants, supply water for industrial use on the lower reaches of the river, which would ease water use in Taichung.
Taichung uses only 100,000 tonnes of groundwater per day and more groundwater could be used. The most difficult part is the transfer of well water to water purification plants for treatment.
To accomplish this, pipelines need to be built from drought-relief wells to water purification plants. If drought-relief wells were widely distributed throughout the Taichung Basin, water could be extracted from wells near construction sites, thereby reducing the strain on water resources when sites are being excavated and there are signs of drought.
However, as well as giving the public access to well water, well water should be integrated with the water supply system without giving rise to public health concerns.
Of the water flowing through irrigation channels overseen by the Irrigation Agency’s Taichung Management Office, 36 to 47 percent is lost through leakage. Improving this situation would allow water resources to be used more efficiently and the irrigation system could be extended to a wider area.
Experience can be a guide for the future. Water restrictions have a heavy impact. Aside from forcing Taiwanese to buy containers to get through the drought and use water sparingly, the drought will hopefully be an opportunity to review all water supply and demand systems, to avoid water restrictions in the future.
Chang Yen-ming is a former section chief of the Water Resources Agency and author of a book about Taiwan’s reservoirs.
Translated by Julian Clegg
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