SUNDAY, APRIL 18, 1993
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PROJECT TO TACKLE POLLUTION OF NULLAHS
A $135 MILLION PROJECT THAT SEEKS TO TACKLE POLLUTION OF THE NULLAHS IN YUEN LONG HAS BEEN SUBSTANTIALLY COMPLETED.
THE CHIEF ENGINEER OF NORTHWEST NEW TERRITORIES DEVELOPMENT OFFICE OF TERRITORY DEVELOPMENT DEPARTMENT, MR WONG CHI-YIN, SAID LIVESTOCKS WASTE WAS BEING DUMPED INTO THE WATERCOURSES IN THE CATCHMENT AREAS TO THE SOUTH OF YUEN LONG.
SAID.
THIS HAS SERIOUSLY POLLUTED THE FOUR NULLAHS IN THE TOWN, HE
THE NULLAHS ARE SUBJECT TO TIDAL INFLUENCE FROM THE SEA AND THE POLLUTED WATER MOVES BACK AND FORTH IN THE NULLAHS.
"THIS CREATES RAD SMELL, AND AN UNHYGIENIC CONDITION AFFECTING THE TOWN. THE SITUATION IS MORE SERIOUS IN DRY SEASON."
ACROSS
UNDER THE PROJECT, AN INFLATABLE DAM HAS BEEN INSTALLED THE MAIN NULLAH AT THE DOWNSTREAM END OF YUEN LONG TOWN NEAR CHUNG HAU TSUEN AT WANG CHAU TO EXCLUDE POLLUTED TIDAL WATER.
OTHER WORKS INCLUDE A 700-METRE CONCRETE LINING IN THE NULLAH AND A PUMPING STATION.
THERE IS ALSO A SERIES OF "LOW FLOW CHANNELS" OF FIVE KILOMETRES WHICH ENABLE POLLUTED LOW FLOWS ΤΟ MOVE QUICKLY FROM UPSTREAM TO THE INFLATABLE DAM.
AT THE DAM, A PUMPING STATION REMOVES THE FLOW ΤΟ DOWNSTREAM OF THE DAM. THIS KEEPS THE NULLAHS IN THE POPULATED AREAS DRY.
THE PUMPING STATION HAS DELIVERING LOW FLOWS ONLY WITH A METRES PER SECOND.
BEEN DESIGNED TO BE CAPABLE OF DISCHARGE CAPACITY OF 4.2 CUBIC
DURING THE "HIGH FLOW PERIOD" WHEN HEAVY RAIN IS FALLING, THE DAM WILL DEFLATE AUTOMATICALLY FOR FLOODS TO PASS THROUGH.
THE DAM HAS A CREST LEVEL OF 3.2 M PD (PRINCIPAL DATUM) WHEN
INFLATED.
IT NORMALLY REMAINS INFLATED BUT WILL AUTOMATICALLY DEFLATE WHEN THE UPSTREAM WATER LEVEL IS HIGHER THAN 2.0 M PD AND ABOVE THE DOWNSTREAM WATER LEVEL, OR WHEN THE UPSTREAM WATER LEVEL IS HIGHER THAN 2.5 M PD IRRESPECTIVE OF THE DOWNSTREAM WATER LEVEL.
LEVEL
THE DAM WILL AUTOMATICALLY INFLATE AGAIN WHEN THE WATER DROPS BELOW 1.0 M PD. DEFLATION WILL BE COMPLETED WITHIN BIGHT MINUTES WHILE INFLATION WITHIN 20 MINUTES.
MR WONG SAID THE EFFECTIVENESS OF THE PROJECT WOULD DEPEND ON PROPER MAINTENANCE OF THE WORKS.
/THE "LOW