Concave-down green space is a simple rainfall collection technique in urban setting.It has advantages such as simplicity

low investment and high efficiency.The storage and infiltration efficiency can be improved with increases of the depth of concave and the area of green space.According to the actual situation in Tianjin City

the experimental tests and theoretical calculations suggested that the depression depth should be 100 mm in the environmental setting of Tianjin City.With 30% green space rate

the storage-infiltration efficiency could reach up to 70% for the storms with recurrence interval of 1 or 2 years

which will reduce the flow peak and at the same time

minimize effectively the water demands of green oases and increase ground-water resources.