The heart of the matter: unevenness, not scarcity
The Gaoping River, with its watershed of 3257 square kilometers, is Taiwan’s largest river and the main source of water for Kaohsiung and Pingtung. Nevertheless, although average yearly rainfall in the Gaoping watershed exceeds 3000 mm, 90% of its precipitation falls in the period from June to September. The ratio of rainfall between the rainy season and the dry season can exceed 100:1.
The Gaoping watershed had already long been suffering drought conditions in late March when flow rates in the river dropped to 12 cubic meters (m³) per second, an all-time low. A raging river had become a trickling stream. Water resource agencies practically had to suck the flow dry (extracting about 11.5 m³ per second) just to barely meet the water-use needs of Kaohsiung.
And Kaohsiungers cannot relax during the rainy season either, because turbidity then is often higher than what is allowed by water treatment plants, thus raising the possibility of suspension of water supply.
The risk of water shortages in Kaohsiung puts water resource agencies frequently on edge. “Kaohsiung’s biggest problem is that it doesn’t have ‘water savings’ in an account that it can withdraw from!” says Lai Chien-hsin, director of the Southern Region Water Resources Office of the Water Resources Agency (WRA), under the Ministry of Economic Affairs.
According to Lai, who holds a doctorate in soil and water conservation from National Chung Hsing University, greater Kaohsiung has only the small reservoirs of Agongdian, Fengshan, and Chengqing Lake to draw from. Even though the Gaoping runs strong during the wet season, without large reservoirs to store the water, there are naturally minimal reserves to draw upon when the dry season rolls around.
In addition to those natural limitations, growth in water use has greatly added to the problem.
Lai points out that current water use in Kaohsiung stands at about 1.62 million cubic meters a day, but the city’s own water supply system can only supply 1.42 million m³. That extra 200,000 m³ comes from various places. “The city government predicts that by 2026 water usage will have risen to 1.78 million m³, so the city will be faced with even greater supply challenges.”
In order to extend the life of the Shimen Reservoir, the Northern Region Water Resources Office has to dredge silt from it every year. The office also plans to add a special channel that will be devoted to removing silt from the reservoir.