By Roland Buerk BBC correspondent in Dhaka

Land grabbers have crippled Dhaka's natural drainage system

The United Nations has requested $210 million in aid for flood stricken Bangladesh, the largest appeal since the earthquake in Bam in Iran last year.

Much of the money will be spent on immediate needs, healthcare and food.

But it will also be used to help rebuild the country's infrastructure.

In the capital, Dhaka, pumps are still clearing away the water, sending it gushing over the embankment and out of the city.

'City damaged'

Weeks after the floods began to subside, many areas are still to be drained.

But the efforts are being hampered by rogue developers.

"During the flood time it's a race because while we're pumping the water out, they're pumping it in," said Akhter Hossain, the managing director of Dhaka Water Supply and Sewerage Authority.

Damage done by the floods has been made worse by pressure for space

"The developers use the silt in the water to build up land inside the embankment for housing.

"It makes me angry because they don't understand the damage they are doing to the city."

For decades the developers have been allowed to build unhindered.

They have grabbed lakes, wetlands and even rivers.

Government inaction

It has crippled the Dhaka's natural drainage system.

When monsoon floods come much of the water has nowhere to go but the streets.

But now an environmentalist is taking them on, challenging the developers in court and winning.

"It has created a sensation," said Rezwana Hasan who is a lawyer.

A lot of the water has nowhere to go

"Not only among the general people but also in the law implementing and enforcing agencies."

She explains how the grabbers have got away with it for so long.

"They start cases on the basis that that the land is recorded in their names, and there you find government inaction so in most of these cases the government has lost.

"Secondly in ensuring that these lands are not going out of their hands they establish some sort of slum settlement, allowing them to go ahead with other forms of construction.

"Then when they win in the court they take possession of those lands."

Clamour for space

Bangladesh does have planning laws, but they are poorly enforced.

Developers have to be stopped, say environmentalists

Rajuk, the government body in charge of planning in Dhaka, has too few staff to control a building boom in the city, and the developers often have political influence.

"The land grabbers are very powerful people," said Shahid Alam who became chairman of Rajuk this week.

"They are musclemen and they have a lot of cash flow. Definitely we are stopping them but we cannot succeed all the times. Grabbers are very active they are continuously grabbing land."

Rezwana Hasan says her legal action is a good start, but court rulings may not be enough to hold back the clamour for space.

Bangladesh is among the world's most crowded countries.