Investigation of Desalination Process with Underground Drainage Pipes at Tsunami Affected Farmland in Miyagi, Japan.

After the 2011 Tohoku earthquake, thirteen thousand hectares of farmlands were damaged by massive Tsunami near coastal site in Miyagi, Japan. Some eighty percent of the damaged farmlands have been recovered, but subsidence and high salinity groundwater make it difficult to completely remove salinity from the soil. We monitored soil moisture, electric conductivity (EC), groundwater level with the remote sensing technology for Field monitoring system (FMS) at paddy fields where underground drainage pipes were installed. Underground drainage pipes facilitated desalination process due to rainfall and fresh water irrigation. However, we found high EC of groundwater (> 35 dS m^-1) at a paddy field near coastal site where severe subsidence occurred. The shallow groundwater provided salinity to the soil surface. The groundwater level reached the soil surface after heavy rainfall, so the leaching effect due to rainfall was not investigated. Thus, the recovery of agricultural production near the coastal site would need to raise the ground level and utilize underdrain system.