Hasanuddin Hamid, Contributor, Makassar, South Sulawesi

Unchecked deforestation has brought closer to home the threat of Lake Tempe, some 200km northeast of Makassar in Wajo regency, disappearing in the not-too-distant future.

The lake's reduced capacity was blamed for the major flooding last May that claimed eight lives and inundated 15,795 houses and 7,669 hectares of rice fields. The worst-hit areas were those along the lake.

The flood was the biggest in almost five years, worse than in October 1998 when about 10,000 hectares of rice fields ready for harvest, were inundated. No lives were lost then.

During the 1998 flooding, the water level of the lake was at 7.5 meters, but last May, that level rose to 9.5 m. The latest flooding hit the neighboring regencies of Soppeng and Sidrap, causing considerable material damage and losses.

Ludvie Achmad, head of the South Sulawesi soil conservation and land rehabilitation center (BRLKT), said the popular lake was deteriorating due to sedimentation.

"If things continue to go unchecked, the lake's disappearance is simply a matter of time," he said.

During the wet season, the lake is about 30,000 hectares in area, but during the dry season it shrinks to half that size. Fifty thousand people live around it, with most making a living from agriculture and fishing activities, Wajo regent Naharuddin Tinulu, said.

Meanwhile, Ludvie said that a study conducted by the agency he heads had concluded that the Bila and Walanae rivers, which empty into the lake, carry some 50,000 tons of silt into the lake every year.

Soil and garbage make up the sediment that causes the bed of the lake to rise 5 centimeters to 7 cm annually.

Nine smaller rivers in five regencies located in the river basins of the Bila, Walanae and Beloka rivers also contribute in bringing mud into the lake. The lake's water, meanwhile, can drain only through one river, the Cenranae, which empties into Bone Bay.

"When there is a heavy rain, the water level in the lake increases to six or seven meters, causing the lake to overflow. During the dry season, the water level of the lake drops to only one meter," he said.

Ludvie also said that unless serious measures were taken soon, the sediment would increase by 10,000 tons a year. Over the past two decades, the lake's area has shrunk 900 hectares a year. This, he said, meant that the whole lake would be covered by sediment in 12 years time.

He added, however, that the lake could be saved if soil conservation measures were immediately taken. Unfortunately, the handling of river basins in this area is quite complicated and needs the cooperation of several agencies.

The siltation of the lake has not only made the lake shallow in depth and shrink in size, but it has also resulted in a reduction in the diversity of the lake's biota and a decrease in the fishermen's haul.

Over the past five years, the lake has generated 5,000 tons to 7,000 tons of freshwater fish a year. Two decades ago, the lake could yield 50,000 tons of fish a year and was the major source of fish for Java, said Tinulu.

He also said that to save the lake, the Wajo regency administration and other local administration agencies had conducted a special study on possible dredging and water control. The result of the study was submitted to the National Development Planning Board (Bappenas) for fund allocation.

Meanwhile, the head of the South Sulawesi water control service, Jantahin, said his office had drawn up a detailed plan for the construction of a flood control dam, but that they were waiting for a donor country that could finance the proposed project, which was estimated to need some Rp 250 billion (about US$27.7 million).

This dam, he said, would keep the water of the lake from overflowing and prevent the water level from drastically dropping in the dry season.

During the dry season, the dam would regulate the lake's water level, while during the wet season it would keep the lake's water at a desired level and channel any of the excess into the Cenranae River.

The local office for soil conservation and land rehabilitation has found it difficult to include forest rehabilitation in the lake's catchment as the community has cleared the areas around the forest.

Degradation of the lake has been largely attributed to deforestation in the upstream areas. Among those responsible is state-owned plantation company PT Perkebunan Nusantara XIV. The forests have also been badly affected by mining activities.

Sampe Paembonan, a professor at the School of Forestry at Hasanuddin University (Unhas), who is involved in forest conservation in South Sulawesi, said a study conducted by the university concluded that the mining and plantation activities had left most of the upstream area denuded.

Research undertaken by the Center for Environmental Studies of Unhas in cooperation with the Institute of Agriculture of Bogor (IPB) sometime ago showed that siltation of the lake had reached 5 cm to 7 cm a year. However, Paembonan estimated that the siltation level could be as high as 20 cm a year.

He said that immediate action must be taken by allowing the water to flow into other places. He agreed with a proposal for expanding the Cenranae's river basin.

Paembonan attributed the siltation process to two factors: the movement of the Earth's crust and siltation.

He said although Lake Limboto in the province of Gorontalo was also deteriorating and only 2 meters deep at present, Lake Tempe would undergo more rapid damage unless efforts were immediately taken to overcome the siltation problem.

He said to improve maintenance in the future, the local government needs to state the purpose of the lake: is it intended to boost fishery and recreation or agriculture? A clear purpose would determine how the lake would have to be redeveloped, he said.

To prevent Lake Tempe from drying up, Paembonan advised that the most important action to take was to establish an organization to oversee management of the lake.