The "Dredger" was developed as a specialized vessel for improving the water quality of lake Kasumigaura by dredging its muddy bottom ooze.Unlike normal dredging with a dredger, ooze dredging is a dredging operation performed under difficult constraints, namely, removing only the very oozy sludge built up on the surface layer of the lake bottom (about 30 cm thick) having a water content rate of 200-400% and including much phosphorus and nitrogen. Up till now, ooze dredging has presented many problems: because the mud content ratio is low and has a wide variation and the positioning of the ship and operation of the ladder is done by hand, ooze dredging has been of poor precision, with the dredging being either too deep or too shallow, and the operating efficiency has been low because the actual mud lifting time amounts to only a small fraction of the dredging time, and many workers are required.By working to overcome these technical problems, developing and improving the dredging equipment, and developing a dredging automatic control algorithm to greatly automate the operations, an automated dredger dubbed the "Kasumizaurus" has been completed.The automated system is divided broadly into an automatic control part for the dredging operation and an operation monitoring part for the operation of work management.The Kasumizaurus, which began operation in March 1995, is designed to be considerably better than a conventional ship in dredging efficiency, high-mud-content-ratio dredging, operational precision, and labor saving.

A 1.5-meter channel runs along the bank foot of Lake Kasumigaura, Ibaraki Prefecture. From fields and rice paddies that surround the area, soil drains into this channel and accumulates in the bottom. Unless removed, the accumulated soil degenerates the functions of the channel, and in the long run, possibly drain into .Lake Kasumigaura.With such anticipation, the Ministry of Construction has introduced the "Bank-foot channel cleaning work truck," a compact, highly mobile 11-ton truck installed with apparatuses necessary from absorbing to dewatering soil accumulated. Major advantages of the truck are: a suction robot, operated by wireless controller, runs pulling a suction hose by own driving system; and all apparatuses mounted on the truck are automatically-operated.Each apparatus was designed based on calculation and experiment, and specifications were designed to satisfy each function. Special attention was paid to the design of the suction robot, as well as to the balance between apparatuses mounted on a limited space on the truck bed.After factory testing, we conducted a site test, and confirmed that the truck has a soil collection capacity even higher than expected. However, repeated testing has shown that the truck requires further improvement. We intend to institute changes that will enhance its functions.