Floods that occur on the north coast of Central Java are caused by high rainfall and the presence of ROB including floods that occur in the Catchment area of the Semarang city banger, where there is high rainfall, where when there is high rain, water flows from upstream to downstream carrying waste material. In the form of used bottles, plastics, tree branches, leaves and other rubbish in the presence of this garbage will disrupt and inhibit the flow of water, which both happens in the longstrage banger and in channel A2. Semarang by optimizing longstorage. To find out the water level in the longstorage the method is to install a peil schal or measuring meter in the long storage banger in addition to installing a Diver device that is paired with the peil schal tool if the water has reached a certain elevation according to the stipulated provisions, the water in Longstorage banger then the pump is discharged into the BKT river in Semarang City. Based on the results of measurements and field observations, when it rains in the Banger cathment area, it is directly proportional to the observation using the Diver tool and is juxtaposed with the observation results at the nearest rainfall station, namely BMKG maritin. Observation and installation of tools were carried out on 24 February to 5 March 2020 based on observations and reading data on your maximum elevation diver on 24 and 25 February 2020 while based on daily and hourly rainfall data obtained from BMKG, Maritime Station, the rainfall intensity is 25 mm. and the flood discharge is 34 m3/s and the water level in the Banger longstorage is 0.8 m, based on these data, it is a straight line with good observation using the Diver tool and with the data obtained at the bulk station.