Floods that occur on the north coast of Central Java are generally caused by high rainfall, where water flows from upstream to downstream carrying waste material. In the form of used bottles, plastics, tree branches and others, other so that the presence of garbage will disturb and inhibit the flow of water, the government's efforts to deal with flooding in the city of Semarang by optimizing there are retention ponds in Semarang City, for example, retention ponds in Tawang, Muktiharjo, Tanah Mas and Banger, these pools are useful. to accommodate water and later the water will be disposed of using a pump into the river then heading to the sea, if there is high tide that inundates the roads and houses, the pump is turned on Meanwhile, if the water recedes and does not inundate residential areas, the pump is turned off. The purpose of this study is to formulate a correlation between pumps and retention ponds, The research method used is quantitative by simulating a pool and pump prototype model in the laboratory, field observations using a diver, numerical modeling with the help of SWMM version 5.1 software. flood control using a return period of 50 years, the method used is SWMM. The depth of the pool is 3 meters, the reservoir volume is 406,000 m3. The pump is set to start at a water depth of 2.5 meters, and to stop at a depth of 0.5 meters. Pump capacity 22.34 m3 / s