Infiltration pools can help alleviate floods, drought

Infiltration pools can help alleviate floods, drought

David Solaiman, Lecturer, Civil Engineering, Universitas
Pelita Harapan, Tangerang, Banten

There is still hope for the alleviation of the floods that
usually occur at this time of year. However, despite this, people
continue to be subjected to stress as they are told to prepare
for another traumatic disaster.

The river desilting work currently being carried out by the
government is good, but it represents a passive approach toward
flood alleviation. What is really needed now is action that is
aggressive in nature; as in football, attack is the best method
of defense. Something must be done in the catchment areas in the
upstream reaches of the 13 rivers that caused severe inundations
in Jakarta early last year.

At any time, rainfall causes run-off. The Ciliwung river is
the biggest and has the largest catchment area among the 13
rivers flowing through Jakarta. The West Flood Canal was not able
to accommodate the excess flow from the Ciliwung and its banks
overflowed at several locations.

Population growth in Jakarta, estimated at an annual 2
percent, entails the need for new residential areas. And,
unfortunately, these are mostly constructed in the catchment area
of the Ciliwung and the other rivers, which in turn increases the
run-off of rainwater into the rivers because the residential
areas are no longer available for the infiltration of rainwater.

If the same intensity of rain were to fall again this year,
the discharge from the Ciliwung would be even greater than last
year because of changes in land use.

In 1996, the Ciliwung produced its biggest flow so far
recorded at 743 cubic meters per second, a flow that has a return
period of 100 years. Between 1981 and 1985, the greatest
discharge was never more than 275 cubic meters per second, but
after 1985 the discharge kept on increasing in the direction of
400 cubic meters per second.

A security system is needed to deal with the issue, otherwise
there will be a never-ending flood problem in Jakarta. Attention
has to be paid to catchment dynamics in terms of development
plans for residential and industrial areas. Human needs and
desires cannot be met without manipulation of the water cycle and
the landscape.

Development must be based on environmental consciousness, as
solving the flood problem is no simple matter.

In the development of new commercial and residential areas,
the increase in run-off must be controlled by providing
infiltration pools and wells or pits.

By providing such tools, run-off will certainly be reduced to
an extent that will depend on the volumetric capacity of the
pools and pits.

This is what is meant by an attacking football strategy. These
measures will not only alleviate flooding but will also increase
the ground water available, which will be of crucial importance
in alleviating drought during the dry season.

The pools and wells should be built by the householders or the
real-estate developers themselves. So this idea is really like
taking small steps with a view to achieving big results, and
therefore needs social participation, acceptance and the
understanding of political decision-makers.

It would be really worthwhile to try and implement this idea,
preferably in the catchment area of the Ciliwung river throughout
the entire Puncak and Bogor areas. If 40,000 house compounds were
each provided with a pool with an average capacity of 10 cubic
meters, then 400,000 cubic meters of rainwater would be retained.

And if the duration of rainfall averaged one hour, this would
reduce the river discharge by 111 cubic meters per second, quite
a significant amount in preventing rivers from overflowing their
banks. The water collected in the pools and pits would infiltrate
into the soil and increase groundwater capacity, which would
emerge several months later in the downstream reaches of the
rivers and in domestic wells.

Even in Japan, people make use of tennis courts as retention
pools by enclosing them with brick walls of up to 30 centimeters
in height. When the time of flooding is over, the pools are
allowed to drain. Outdoor parking lots are treated in the same
way. The flat concrete roofs of high-rise buildings are also used
as retention pools.

Efforts are needed to bridge the gap between public knowledge
and scientific understanding. Erect billboards to show the need
for infiltration pools, or place advertisements in the media to
urge people dig such pools!

Since infiltration pools will have to be dug independently by
individual householders. This work could, however, be carried out
simultaneously, so that thousands of pools would be completed in
not more than two weeks.

The infiltration pools and pits would certainly truncate the
peak flows of our river whenever rain falls, so let us dig them
now!