Wells, lakes best way to fight floods

Wells, lakes best way to fight floods

By Sapto HP

JAKARTA (Antara): The huge flood which swamped Jakarta in 1996 is still fresh in our minds. It wrought havoc on the lives of people living near riverbanks from Manggarai to the Thamrin- Sudirman area.

The flood was exceptionally widespread. Communities previously spared from inundations were saddled with the tedious task of clearing away mud and debris left after the water subsided.

Later floods were confined to those areas traditionally prone to flooding, including Cipinang in East Jakarta and Sunter in the north of the capital.

Does this mean other areas are now safe? Unfortunately, the answer is apparently not.

A survey conducted by M. Fakhrudin, a limnologist of the Center for Limnology Research and Development of the Indonesian Institute of Sciences (LIPI), concluded that floods in the future will be even bigger.

Causes are clear. Upstream and downstream areas of rivers have become places for settlement, and water catchments like lakes and swamps are rapidly disappearing.

Fakhrudin said preventive measures against flooding were not difficult technically because they could be controlled by constructing a dam in the upstream area of the river, from Depok to the Puncak area of West Java.

"But from the socioeconomic aspect such a project is hard to implement, in consideration of the high density of the population in the area," he said.

He proposed two more feasible ideas -- to build wells as catchment areas in residential areas from Depok to Puncak, or preserve existing lakes -- which he said would not cause social problems.

Wells

Fakhrudin said the construction of wells at residences in the Puncak area was a way to reduce the quantity of rain water flowing directly into the soil's surface, because it is this water which was the main cause of floods.

As a result of the increasing density of settlement areas in the upstream areas of the river flowing to Jakarta, rain water in these areas directly flows on the surface rather than entering the ground.

Fakhrudin said open fields in the upstream areas of the Ciliwung River which could function as catchment areas were decreasing. In the past 10 years, settlement areas increased by about 20 percent and dry land decreased by 37 percent.

The result is that the water flow at the Manggarai flood gate, measured at 370 cubic meters per second in 1973, is now 570 cubic meters per second, an increase of 54 percent.

"It would be very hard work to restore the previous condition of the area because various factors are involved," he said.

Therefore, he added, it would be beneficial to issue a regulation making the construction of wells compulsory in residential areas in the region. The Jakarta administration formerly had such a regulation.

Lakes

The maintenance and rehabilitation of lakes in Greater Jakarta is also key to flood prevention in the area, Fakhrudin said.

Lakes are believed to be important in flood control because water flows into the lakes during rains. The water gathers over time and then flows out of the lakes, so a reduction takes place, both in the rapidity of the flow and in the quantity of water.

Research by Olivier Klepper in 1994 at Sentarum Lake in West Kalimantan showed that it could reduce the debit by 25 percent during rains and increase the flow of the Kapuas River by 50 percent in the dry season.

Fakhrudin found the same was true of the Bojongsari Lake at Sawangan, Bogor. From August to October 1988, the lake water could supply ground water, but from November to January it could absorb additional ground water.

"Therefore, if the existing lakes could be preserved, the threat of floods for Jakarta could be reduced," he said.

But considering the present condition and the number of lakes in the greater Jakarta area, such efforts should be made immediately because the latter are continuing to disappear.

Data from the West Java Planning and Development Board (Bappeda) in 1986 showed there were 173 lakes in Greater Jakarta, consisting of 122 in Bogor regency, 42 in Tangerang regency and nine in Bekasi regency. Even then, some of the lakes were reportedly drying up.

The Directorate General of Waterworks of the Ministry of Public Works says there are 193 lakes in Greater Jakarta, 45 percent to 50 percent of which they list in critical condition.

It would be economically and socially taxing to make new lakes, he added.

The government, he said, should instead give priority to the preservation of existing lakes rather than constructing artificial lakes, because it is cheaper and does not carry the potential of creating social unrest.

Research also needs to be done on the potential commercial benefits of using the lakes.

"Direct or material benefits are apparently more feasible than ecological advantages that would reduce the risks of floods," he said.

The more lakes that can give economic benefits, such as tourist sites, the easier will be the case for their preservation, he said.

"If there are lakes that have high esthetic value, there should be consideration about giving concessions to the private sector to manage the areas."

History may be the best teacher. "It is said the Dutch in colonial times made many lakes in the framework of controlling floods," Fakhrudin said.