Mekong River Commission

4.1 General situation

In Cambodia conditions during the 2006 flood season were below average both in terms of peak and volume. The flood peak was, in fact, amongst the lowest recorded over the last 80 or more years. The maximum discharge for the year occurred in mid August, after which water levels decreased considerably until early October and the passage across the region of Severe Tropical Storm Xangsane. This weather system generated a slightly lower second peak in mid October, an uncommon feature of the annual hydrograph. As a result of these below normal seasonal flows no significant crop losses were reported, with the exception of the fact that the unseasonally late second peak led to the inundation of some low lying areas. Some early flood recession rice plantings were lost and a second replanting was required.

No flood damage to infrastructure was recorded for the year.

4.2 Lessons learnt from a field trip to Kampong Cham, Kratie and Stung Treng—24th to 26th October 2006

• Kampong Cham: The major flood related issues here are river bank erosion, the regular loss of crops and damage to property, domestic and commercial disruption, low levels of social awareness of the flood hazard, inadequate institutional capacity to receive and disseminate flood warnings and inadequate investment in flood mitigation and rehabilitation measures.
• Kampong Cham: The present warning flood stage of the Mekong at Kampong Cham needs urgent review since in the recent past, during 2000, 2001, 2002, parts of the city were flooded despite the fact that the flood stage of 16.20 masl had not been reached. Frequency analyses of long term annual maximum water levels between 1930 and 2006 indicate that the flood warning stage of 15.20 masl has a return period of less than 4 years.
• Kratie: The western part of the town was flooded at a Mekong River level of 22.05 masl, noting that the flood level at the hydrometric gauge is 21.9 masl. (Appendix 2). The 2006 maximum flood did not reach the warning level at any of the villages equipped with flood referencing facilities. It would be useful to establish the flood marks from the most recent 2000–2002 floods at each village as reference levels for issuing flood warning.
• Kratie: The province has identified a total of 97 safe areas. Some provide emergency living accommodation during floods while others provide refuge for farm stock, which is generally the major family asset. Accessibility can be difficult during the dry season since access roads can be very poor. During the flood season, however, they are easily accessible by boat. One pilot site with an area of 55 ha has been identified and will be equipped with facilities such as water supply, sanitation and proper access roads.
• Stung Treng: The town has no protection from flood inundation, which is mainly caused by high water levels in the Mekong mainstream and backwater in three major local tributaries.
• Stung Treng:The strategic location of the Stung Treng hydrometric station at the head of the major part of the Cambodian floodplain downstream is a key element within the regional flood forecasting network. The reliability of the station is not, however, what it should be under these circumstances. Forecasting accuracy could be improved in conjunction with data observed at Siem Pang and Chant Ngoy on the Sekong, at Andaung Meas, Veun Sai and Ban Kamphun on the Se San and at the Lumphat on the Sre Pok. Some of these stations, however, have ceased to operate and transmit data due to poor maintenance schedules and a lack of investment
• Stung Treng. The reference levels used by the Regional Flood Management and Mitigation Centre at the Stung Treng are 10.7 masl for the alarm stage and 12.0 masl for the flood stage. These correspond to annual return periods of two and slightly less than fifteen years, which appears to be inconsistent and illogical.
• Stung Treng: Provincially, 116 flood refuges have been identified, though only a few are equipped with even basic facilities such as water supply and toilets. Effective evacuation to them during a flood emergency is a village responsibility, though the capacity to organise and coordinate the process is not well developed. Nor are the means in place to transmit prompt flood warnings to vulnerable villages.