Generally, polluted sea bottom sludge is disposed of in containment area when it is dredged to improve aquatic environment. However, it becomes impossible to obtain large containment area recently. On the other hand, it is reported that it is enough to dredge thinly on the surface of the bottom sludge to improve aquatic
environment. Therefore, technique to dredge thinly on the surface of sludge and in high mud content to reduce the volume of dredged sludge is needed.
　For this purpose, two types of thin layer dredging equipment using watertight belt conveyer were developed. One is pipe type conveyer dredging equipment and the other is sandwich type conveyer dredging equipment.Dredging characteristics were investigated by model experiment. The results were as follows:
(1)Dredging method of these two types are technically feasible, and both types can dredge efficiently compared with the conventional dredging method.
(2)The sandwich type conveyer dredging method is superior in both dredging characteristics and mechanism to the pipe type conveyer dredging method.