Abstract: To provide a cleaning apparatus suitable for removing clogging substances trapped in a surface layer of a sand filtration layer. A cleaning apparatus equipped with drive wheels serving as a driving device configured to move across a surface of a sand filtration layer. A pump and a jet nozzle are provided as an agitation device configured to agitate a surface layer portion of the sand filtration layer only at a desired depth, and which blows the clogging substances upward into the seawater in a turbid water intake pit together with a filtration sand. A perforated pipe for suctioning turbid water, a pump, an ejector, and a discharge pipe for dilute turbid water are provided as a suction and discharge device configured to suction turbid water blown upward into seawater in the water intake pit by the agitation device, and discharge it to outside of the turbid water intake pit.

Abstract: To provide a cleaning apparatus suitable for removing clogging substances trapped in a surface layer of a sand filtration layer. A cleaning apparatus equipped with drive wheels serving as a driving device configured to move across a surface of a sand filtration layer. A pump and a jet nozzle are provided as an agitation device configured to agitate a surface layer portion of the sand filtration layer only at a desired depth, and which blows the clogging substances upward into the seawater in a turbid water intake pit together with a filtration sand. A perforated pipe for suctioning turbid water, a pump, an ejector, and a discharge pipe for dilute turbid water are provided as a suction and discharge device configured to suction turbid water blown upward into seawater in the water intake pit by the agitation device, and discharge it to outside of the turbid water intake pit.

Abstract: To clean sediments and the like trapped not only in a top layer of a sand filtration layer, but also in intermediate layers. A seawater infiltration method which uses a water infiltration intake unit which is formed in advance and provided with a water intake pipe embedded in a gravel layer which forms a deep layer of the sand filtration layer, and a backwashing pipe embedded in a sand layer which forms an intermediate layer and a surface layer of the sand filtration layer, and a water suction pipe which is disposed above the sand layer. A desired number of water infiltration intake units are combined to form a sand filtration layer at an installation site on an ocean floor, and they intake seawater from the sea which has undergone natural infiltration in the sand filtration layer and this is introduced into the water intake pipe. The seawater infiltration rate is set at less than 400 m/day.