| 摘要 |
<p>PROBLEM TO BE SOLVED: To divide a water-retentive material into an upper water-retentive material not coated to enable a water flow to be acknowledged by sight and a lower water-retentive material coated at its surface to prevent deterioration of the water-retentive material.SOLUTION: A water-retentive material 30 is divided into an upper part and a lower part of a double-layer structure in which the upper part is an upper water-retentive material 30a and the lower part is a lower water-retentive material 30b. The surface of the lower water-retentive material 30b is coated and the surface of the upper water-retentive material 30a is not coated. A height size of the upper water-retentive material 30a with respect to a height size of the water-retentive material 30 is about 10 to 15%. The surface of the lower water-retentive material 30b is coated to enable itself to be prevented against deterioration with ultraviolet ray. The surface of the upper water-retentive material 30a can be acknowledged by sight against water-flowing and visualized. Although the upper water-retentive material 30a is deteriorated, it is sufficient that only the upper water-retentive material 30a is replaced with a new one and its price can be restricted to a less-expensive price. In addition, its replacing work is also easy.</p> |
