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.