Generally the turbidity of surface water increased tens or hundreds times rapidly by degree of rainfall and intensity. High turbid water have problems with lower alkalinity and many fine particles smaller than 1.0㎛. High turbid water needs higher coagulant dose for removing the particles especially fine particles which have comparatively larger specific area. But lower alkalinity can not react sufficiently with added coagulant to form aluminium hydroxide for removing the fine particles. Therefore lime is supplied for increasing raw water alkalinity, it is necessity increasing coagulant for good coagulation after lime added. For increasing particle to particle collision chance, high velocity gradient and longer flocculation time is needed. Though higher velocity gradient can increasing collision chance, can not make large floc so lower velocity gradient needed for making large floc to the last flocculation stage. Proper arrangement of baffles or compartmentalizations in the flocculation basin can reduce short-circuiting and extend flocculation time. The around-the-end and over-and-under baffled channel are more effective to prolong detention time than diffuser wall.