Author : Soulivanh Voravong

Summary : Water quality degradation in Phetchaburi River will still be present in the years to come, since water pollution from municipal wastewaters, industrial wastewaters, and agricultural practices are not visible to be handled effectively. The research aimed to find means on how to handle water at Phetchaburi diversion dam for coping with stream pollution in Phetchaburi River through irrigation watershed management. There were eight sampling points for collecting water samples since 2002–2013 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. In accordance with the same trends of water quality indicators, this study was taken in 10 water quality indicators, including water temperature, pH, TDS, BOD, DO, EC, NO , HN , TCB, and FCB as the representatives for determining the role of flow velocity in dilution capability. The results found that water temperature changed a little in municipal area, pH increased when water flow increased, EC and TDS

decreased when water flow increased, NO

increased if water flow increased, and

HN was not detected when water flow increased, TCB and FCB increased when
water flow increased particularly water flow throughout density communities, and BOD 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 also decrease because of bacterial organic digestion process occurring, while it flows except very high flow velocity. The flow velocity less 30 m3/s is recommended to release from Phetchaburi diversion dam for eliminating stream pollution by dilution process. These communities will not undertake activities that will lead to the deterioration of the resource. Based from these findings, the probability of identifying and implementing a sustainable management strategy for Nam Xong River will be high. The strategy should however, be based on the real needs not only of the community, but also of the resource. Again, the importance of public consultation and participation of the stakeholder should be taken seriously.