Drainage system of landscape space is design by experience or overestimated size because there is no criteria or guideline. On this study, a construction feasibility of landscape spaces is evaluated, a construction cost is estimated and a construction cost change ratio is analyzed.
The construction cost of landscape space drainage system is lineally increased on increasing a size of drainage system and the change ration of construction cost is constant. Therefore the more expensive cost is need, the larger drainage size is constructed. Other hand, many case of drainage system size can be proposed in same cost. But the ability of conveyance of flow is different. Adapting the Hydaulic Theory called Manning formula and conservation equation, the Optimal size can be determined.