EFFECTIVENESS OF HIGH-RISE BUILDING RUN OFF REDUCER

The current development concept is no longer a horizontal building but a vertical building. In fact, there isn't enough space for open land. However, high-rise buildings contribute to an increase in the volume of rainwater on each side of the building walls by an average of 8%. To reduce the addition of surface water runoff to urban drainage, it is necessary to build a water reservoir with an outlet system as a flood reducer. This study was conducted in East Surabaya with the highest rain distribution pattern for 4 consecutive hours, and the rain intensity data was converted to a design rainfall with 5 years return period (R5) = 134.206 mm. For the calculation of runoff discharge, simulations are carried out using several building area measurements. Furthermore, to control the discharge, a simulation is carried out using several reservoir dimensions and the size of the outlet. To control the outflow discharge, single reservoir and double reservoir systems are installed in series. From the analysis, it is found that the reservoir dimensions and outlet holes are the most effective as a flood reducer. For a single reservoir measuring 2 m × 1 m × 1 m and 3 m × 2 m × 1.25 m with an outlet hole diameter of 2.50 cm, it can reduce flood discharge by 50.13%. Meanwhile, for double reservoirs installed in series, the effective dimensions are 2 m × 2 m × 1 m and 1 m × 1 m × 1 m with an outlet hole diameter of 1.25 cm which can reduce flood discharge by 94.33%.