Abstract

The research was aimed to find means how to handle water at Phetchaburi diversion dam for coping with stream pollution in Phetchaburi River through irrigation watershed management. There eight sampling points for collecting water samples since the year of 2002 to 2013 for analyzing water quality in relation to release water flow in consecutive velocity of 22.4, 100, and 377m³/s in order to obtain the better diluted stream water. Accordance with the same trends of water quality indicators, this study was taken in BOD and DO as the representatives for determining the role of flow velocity in dilution capability. The results found that the BOD were gradually decreased from Phetchaburi diversion dam all the way to agricultural zone and jumping up during passing the city zone, and still jumping up in estuarine zone. Whenever the BOD decreases, the DO values were also decreased because of bacterial organic digestion process occurring while it flows except very high flow velocity. The flow velocity not more than 30 m³/s is recommended to release from Phetchaburi diversion dam for eliminating stream pollution by dilution process.

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