Groundwater Recharge in the Irrigated Upstream Area of the Regulating Gate in the Lower Nam Kam River, Thailand

There is soil salinity problem in northeastern Thailand. Particularly, in the lower Nam Kam River which is a branch of the Mekong River, have salinity problem in groundwater. Then, farmers cannot get agricultural water in the dry season. Because water level in the Mekong River is highly change in the dry and wet seasons. Royal Irrigation Department(RID) make a plan to set a regulator in the Nam Kam River to control water level before flowing to the Mekong River and build a reservoir in the lower part of this river basin. As the results, a reservoir existing in the lower Nam Kam River area through the year, and infiltration volume in this area will be increased by ponded water in this reservoir. This is caused by the Nam Kam control gate operation.The authors observed continuously groundwater levels in shallow aquifer over 7 years. And we have collected land use crop pattern, water levels and climate data in the Mekong and the Nam Kam River. Moreover, we have observed infiltration capacity 54 points and made the distribution map of infiltration capacity in this area. Using these data, the authors calculated the infiltration rate change during these periods. This paper shows those results and estimates the influence to groundwater level by setting the control gate in the lower Nam Kam River