Unpaved irrigation canal of total extension 21km exists in the central part of river Narusegawa alluvial fan, Akita Prefecture, Japan. The canal is still utilized for paddy field in 2005. A part of the unpaved irrigation canal (39°14´ 38´´ N, 140° 31´ 49´´E), of which full length is in 220m and average width is in 0.98m, was chosen for measurement of infiltration. The measurement has been performed in the period from May to August, 2005. As a result, average infiltration rate during the observation period was 15.4 l/s, and average infiltration capacity was estimated at about 18.8cm/h. As this numerical value, unpaved irrigation canals of this district have a superior groundwater recharge function. This is a function approximately equal to artificial recharge facility for groundwater.
