Objective To understand the distribution of Oncomelania hupensis snails in source areas of the east route of Southto-North Warter Diversion Project and evaluate the effects of the snails on the safety of water transfer.Methods The investigation of snail distribution was carried out in the source areas of the east route of South-to-North Warter Diversion Project every spring.The method of the random sample combined with environmental sample was used for the field investigation.The beach land in the stilling pool of Jiangdu Pumping Station was selected as a surveillance site to observe the snail spread.Results The areas of the snail habitats and infected snails were 256.11,184.55,164.92,121.16 hm~2 and 8.27,1.0,1.0,0 hm~2 respectively in the source areas of the east route of South-to-North Wafter Diversion Project from 2006 to 2009.The densities of living snails had a downtrend,too.Google Earth showed that the areas of snail habitats distributed mainly in the Jiajiang River and Mangdao River in the source areas.The snail habitats were detected in the beach land in the stilling pool of Jiangdu Pumping Station.The research results showed that the snail spread related to the wastes from the river of drawing water.Conclusion There are the risks of snail spread in the source areas of the east route of South-to-North Wafter Diversion Project,so that the long-term surveillance and control on the snails is very necessary.

Objective To study the drifting law of floats and potential risks of Oncomelania hupensis diffusion in the water diversion rivers of the east route of South?to?North Water Diversion Project. Methods The O. hupensis snails in the river chan?nels were monitored by the salvage method and snail luring method with rice straw curtains,and the diffusion possibility of snails along with water was assessed through the drift test of floats with GPS. Results In the flood seasons from 2006 to 2013, totally 8 338.0 kg of floats were salvaged,and 2 100 rice straw curtains were put into water in the Li Canal and Jinbao shipping channel,but no Oncomelania snails were found. The drift test of floats with GPS before water diversion showed that the flow ve?locity on water surface(northbound)was 0.45 m/s,the average drift velocity of the floats was 0.56-0.60 m/s,and the average drift distances each time were 999.70- 1 995.50 m in the Gaoshui River section,while there were no obvious drift in Jinbao shipping channel section. During the water diversion period,the flow velocity on water surface(northbound)was 0.45 m/s,the average drift velocity of the floats was 0.35-0.41m/s,and the average drift distances each time were 1 248.06-1 289.44 m in the Gaoshui River,while in Jinbao shipping channel section,the flow velocity on water surface was 0.28 m/s,the average drift velocity of the floats was 0.25- 0.27 m/s,and the average drift distances each time were 477.76- 496.38 m. The drift test showed that the floats gradually closed to the river bank as affected by water flow,wind direction and ship waves,when blocked by the reeds,water plants or other obstacles,and they would stopped and could not continue to drift without outside help. Con?clusions There are no Oncomelania snails found in the river channels of the east route of South?to?North Water Diversion Proj?ect. The drifting distance of the floating debris along with the water is restricted by the flow rate and shore environment.