How to Protect Bandung City From Floods

Prohibit rain dances there and upstream.

You are doomed.

Halt development in the low lying areas and move it to higher ground.

Build dikes and dams and hope the sea level doesn't rise.

This forum is no place to ask a question of this magnitude.

This is a municipal/national problem and it will take millions of dollars to study and remedy.

only permit lawns to be watered on Wednesday

To get beyond facetious comments, you need to provide some workable information. Describing the topography around Bandung might not be easy, but some attempt is needed, along with seasonal rainfall data.

Flood control measures could include flood walls around the city, upland reservoirs to catch heavy rainfall, diversion channels to direct water around the city, etc. The details depend on the elevation contours for several miles in all directions.

With only one sentence to work with you really haven't got a chance.

The unfortunate answer is you can't. Every city in the world is a disaster waiting to happen. Build a city on a flood plane, and there will be floods. build a city in a tectonic active area, and there will be earthquakes and volcanoes. Build a city on the sea coast and there will be hurricanes, tsunamis, and sea level will change. And if none of the above, an occasional tornado will rip it apart.

Any time you have a lot of people living in a concentrated area, the random acts of nature will be a disaster.