Seawater infiltration method and water infiltration intake unit

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. Water or air is injected from the backwashing pipe to agitate and blow upward from the surface layer living organisms or sediments trapped in intermediate layers of the sand filtration layer, and the agitated water is sucked in by a suction pipe and recovered. The seawater infiltration rate can be maintained as high as possible under 400 m/day.

1 . A seawater infiltration method which uses water infiltration intake units combined to form a sand filtration layer at an installation site on an ocean floor, wherein each of the water infiltration intake units comprises 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 intakes seawater from the sea which has undergone natural infiltration in the sand filtration layer and been introduced into the water intake pipe, comprising:
 setting a seawater infiltration rate at less than 400 m/day, and   injecting water or air from the backwashing pipe to agitate and blow upward from the surface layer living organisms or sediments trapped in intermediate layers together with living organisms accumulated in the surface layer, thereby preventing clogging of the sand filtration layer.   
     
     
         2 . The seawater infiltration method according to  claim 1 , wherein the water infiltration intake units are further provided with suction pipes disposed above the sand layer, and are combined to form a sand filtration layer at an installation site on an ocean floor, the method further comprising:
 injecting water or air from the backwashing pipe to agitate and blow upward from the surface layer living organisms or sediments trapped in intermediate layers together with living organisms accumulated in the surface layer, after which the agitated water containing the living organisms or sediments is sucked in by the water suction pipes, thereby preventing clogging of the sand filtration layer.   
     
     
         3 . The seawater infiltration method according to  claim 2 , further comprising using a difference in settling rates of the living organisms or sediments blown above the sand filtration layer when sucking in the agitated water by the water suction pipes according to a timing at which the substances which are to be sucked in settle in the sand filtration layer. 
     
     
         4 . The seawater infiltration method according to  claim 1 , wherein the water infiltration intake units are further provided with water discharge pipes disposed above the sand layer, and are combined to form a sand filtration layer at an installation site on an ocean floor, the method further comprising:
 injecting water or air from the backwashing pipe to agitate and blow upward from the surface layer living organisms or sediments trapped in intermediate layers together with living organisms accumulated in the surface layer, after which the agitated water containing the living organisms or sediments is injected by the water discharge pipes to discharge it to outside of the sand filtration layer, thereby preventing clogging of the sand filtration layer.   
     
     
         5 . The seawater infiltration method according to  claim 4 , further comprising using a difference in settling rates of the living organisms or sediments blown above the sand filtration layer to inject water from the water discharge pipes according to a timing at which the substances which are to be discharged to outside of the sand filtration layer. 
     
     
         6 . A water infiltration intake unit used in the seawater infiltration method according to  claim 4 , wherein the water discharge pipe injects water in a direction other that in which the water infiltration intake units are adjacent, and the angle of injection of the water is in a range of 30-60° with respect to a horizontal plane. 
     
     
         7 . A seawater infiltration method which uses a water intake pipe embedded in a deep layer of a sand filtration layer and a backwashing pipe which injects water or air and which is embedded in the intermediate layers of the sand filtration layer, and intakes seawater from the sea which has undergone natural infiltration in the sand filtration layer and been introduced into the water intake pipe, the method comprising:
 setting a seawater infiltration rate at less than 400 m/day, and   injecting water or air from the backwashing pipe to agitate and blow upward from the surface layer living organisms or sediments trapped in intermediate layers together with living organisms accumulated in the surface layer, thereby preventing clogging of the sand filtration layer.   
     
     
         8 . The seawater infiltration method according to  claim 7 , wherein a water suction pipe is further installed above the surface layer of the sand filtration layer, and water or air are injected from the backwashing pipe to agitate and blow upward from the surface the living organisms or sediments trapped in the intermediate layers of the sand filtration layer together with living organisms or sediments accumulated on the surface of the sand filtration layer, after which the agitated water containing the living organisms or sediments is sucked in by the water suction pipe, thereby preventing clogging of the sand filtration layer. 
     
     
         9 . The seawater infiltration method according to  claim 7 , wherein a water discharge pipe is further installed above the surface layer of the sand filtration layer, and water or air are injected from the backwashing pipe to agitate and blow upward from the surface the living organisms or sediments trapped in the intermediate layers of the sand filtration layer together with living organisms or sediments accumulated on the surface of the sand filtration layer, after which water is injected from the water discharge pipe, thereby preventing clogging of the sand filtration layer.