A tank cascade system consisting of several small earth dams has been developed for the irrigation system in Sri Lanka. The frequent flooding in recent years has led to the collapse of small earth dams or their spillways (Oka et al. 2013). Such collapse poses a danger to people living downstream. Therefore, disaster prevention measures including water management must be improved to prevent overflow of the embankments and the flooding of populated areas. Small earth dams and spillways frequently collapse in Japan as well. Systems have been developed for monitoring and predicting water levels in reservoirs to reduce the damage from flooding. This paper introduces the water level monitoring system and water level estimation system in tank cascades in Sri Lanka to improve disaster prevention measures. We successfully monitored the water level of small earth dams from a remote location, and the water level estimation system in Sri Lanka was used to calculate the water level of small earth dams.