* Barrier exacerbates seasonal floods, residents say
* Environment, livelihoods endangered
* Rare cooperation to alleviate floods in conflict hotspot
By Noah Browning
QALQILYA, West Bank, Jan 9 (Reuters) - Heavy winter downpours have turned some Palestinian lands in the occupied West Bank into a morass of filth and flooding as an Israeli barrier blocks the waters from draining away.
In Qalqilya, a town of 42,000 in the northern West Bank almost completely surrounded by the concrete wall, Khaled Kandeel and his family huddled by an open fire in a shed as trash-laden water swelled through his pear orchard.
"Before the wall, the water used to drain fine, and flowed down to the sea easily. They could just flip a switch and end our suffering, but they don't," Kandeel said, his breath steamy from the winter cold.
Israel started building the barrier, a mix of metal fencing, barbed wire and concrete walls, in 2002 in response to a wave of Palestinian suicide bombings.
Drainage channels run under the imposing ramparts but their automated metal gates are mostly closed and now clogged with refuse and stones that block the outflow of storm water.
The Israeli military, citing security reasons, generally bars locals from clearing the obstructions or digging their own channels close to the barrier.
Built mostly within occupied land and not on the "Green Line" which was Israel's de facto border before the 1967 Middle East War, the barrier inside the West Bank is deemed illegal by the U.N.'s International Court of Justice.
It directly impacts the farming, grazing and environment of about 170 communities, the United Nations Relief and Works Agency (UNRWA) says.
Hemmed-in residents of northern towns in the West Bank have been deprived of large swathes of rural land, forcing poorly-regulated waste dumping closer to farms and homes.
Driving rain could not mask the stench of raw sewage being unloaded from a tanker on a village road outside Qalqilya on Tuesday, its putrid contents mixing with the brown torrent pouring past olive trees clustered on the hills.
"Raw sewage is disposed near, or on, agricultural land resulting in the contamination of soil and groundwater," UNRWA said in a report.
Planning restrictions, inked as part of interim peace accords by Israeli and Palestinian negotiators almost two decades ago, widely limit locals' ability to build water infrastructure or repair damaged or polluted wells.
But in Hebron, whose old city is a flashpoint of conflict with Jewish settlers, rare coordination with the Israeli military allowed Palestinian officials to lift the concrete slabs which separate the ethnic enclaves to relieve flooding.
"We removed the concrete to prevent the passage of water to the old city souq, where flooding reached up to one meter," said Walid Abu Halawa of Hebron's construction commission.
"We also opened holes in the iron barrier built by the Occupation at the terminus of the souq," he told Reuters.
Ten years after work on the barrier began and with no suicide bombings against Israel for almost four years, construction has slowed amid opposition from local groups and international organizations.
Last month, Israel's high court and its Nature and Parks Authority urged the military not to build a wall near Battir, fearing it would damage the Palestinian village's millennia-old irrigation terraces.
In nearby Walaja village, dynamite and stone foundations used to embed a section of concrete wall degraded soil quality and impaired the natural flow of water downhill toward Jerusalem, residents said.
Plans to complete the wall and enclose the village on all sides, with a single gate for entty and exit comings and goings, are opposed by locals and even some neighboring Israeli settlers, who regard the barrier as unnecessary given the current calm.
(Additional reporting by Ali Sawafta; Editing by Angus MacSwan)