Deficit and Dry
Sedimentation of Bali’s Four Major Lakes Contributing to Bali’s Water Deficit
The volcanic lakes of Bali’s Highlands that form reservoirs of precious water supplies are suffering degradation. These lakes contribute to a network of 1,300 rivers and streams that provide most the Island's water supply.
As reported by Balipost.com, among the four major lakes of Bali, the most severely polluted lake is Danau Buyan in Bali’s mountain-lake district. The head of the Bali-Penida Lakes and Waterways Department, I Keteut Jayada, said on Thursday, November 1, 2018: “This is the result the change of land usage in the Baturiti area. In the past, the land was used for coffee cultivation but is now used for villas. This change of usage has resulted in sedimentation of the lake’s bottom. The depth of the lake has become shallow meaning the volume of water held by the lake is less.”
Jayada said the potential air production from lakes and rivers in Bali is 239 cubic meter per second per year. Meanwhile, the need for air in Bali stands at 103 cubic meters per second per year.
Explaining further, Jayada said while the figures suggest a surplus, these figures do not reflect Bali true water supply situation. Of the 391 rivers in Bali, only 162 flow during the entire calendar year. The remaining number of rivers only carry water for a part of the year and some only flow carrying run-off when it’s raining.
Jayada said most water potential in Bali is used for irrigation. Water taken from rivers and streams by the traditional subak system of irrigation has become one of the impediments to Bali’s meeting its water requirements.
In the Sarbagita Region (Denpasar, Badung, Gianyar, and Tabanan) a water deficit of 5 cubic meters per second already exists. “Sarbagita represents a concern because the service of the State Water Board (PDAM), especially in Denpasar, is very low at 48 percent. “This means that 62% of the residents of Denpasar are not adequately served by PDAM. This has not caused the (expected) outcry because almost every house has an alternative supply of water of a reasonable quality,” said Jayada.
At the same time, Jayada warns, however, that the heavy reliance on well water is dangerous. Areas such as Nusa Dua, Kuta and Sanur are already listed as “red zones” due to the heavy intrusion of seawater into the water table. The intrusion of seawater is the result of the over exploitation of ground water. Moreover, the over-use of subterranean water sources brings the frightening prospect of land subsidence and sink holes that can swallow up homes and businesses.
Authorities are working to create new reservoirs for fresh water. This is being achieve by outlawing the drilling of water wells and the creation of dams. “We need to create dams. Our rivers and streams are small. When there is heavy rain and flooding water quickly runs off into the oceans. By making reservoirs, we can contain rain water for later use,” said Jayada.
Jayada said reservoirs are being constructed in Sidan (Belok Sidan, Bandung) and Tambland (Sawan, Buleleng). The Sidan dam is being developed in anticipation of the water requirements for a new airport at Kubutambahan.
The new reservoir at Sidan will be unable to meet the current water deficit of 5 cubic meters per second in Sarbagita, with the Sidan reservoir projected to produce only 1.7 cubic meters per second.
Jayada said additional reservoirs, capable of producing 10 cubic meters per second, are needed to alleviate Sarbagita’s current water deficit.