The methods of measuring unevenness of gravels,laying multiple-orifices filter blocks and stainless nets during the filter reconstruction were used in four water purification plants in Yokohama to assure the normal and effective operation of the filters.

• 横滨市水道局下属的4座水厂采取测量砾石起伏程度、滤池翻修时铺设多孔双层滤砖和不锈钢丝网等措施来保证滤池的正常有效运行;