The Development and the Construction Method of a New Type of Sand Capping Method by Sand-upwelling System

As a water quality purification measure for areas such as lakes, a sand capping method by sand-upwelling system was developed. This method involves welling up clean sand from below contaminated sludge by using a water jet. The disposal of sludge and the acquirement of pure sand are not necessary like dredging and conventional sand capping works. Besides, the ecosystem will hardly be disturbed by this method. A scale model test and field tests at Lake Suwa were carried out to study sediment purification effects, sand capping conditions and turbidity range. As a result, it was demonstrated that sand capping was succeeded by this method. Some characteristics of this method were revealed, the thickness and the area of the sand capping depended on the jet discharge rate and the sand diameter, the turbidity range was very small caused by this method. After seven months later, the field observation was carried out in Lake Suwa. The thickness of the sand capping layer and the aerobic environment were maintained. Also, many Limnodius appeared in the sand capping area.