Model of the Effect of Advanced Sea Water in Lamong Bay Due to Global Warming on the Drainage System in Surabaya City

The Lamong Bay area of the city of Surabaya is one of the areas with frequent inundation. The lamong bay area has several primary channels from the drainage system which where the primary canal empties into the lamong bay. The West Surabaya area, especially in the lower reaches of Tandes Rayon, has a high level of inundation due to several factors, one of which is the influence of sea level rise. So that times in the Tandes Rayon area it is unable to accommodate the tide from the sea. Therefore a puddle map is needed which is one of the efforts to minimize the impact of inundation that occurs in the downstream area of tandes Rayon by using 4 scenario conditions that occur in the field, namely the scenario when the existing conditions, second, the scenario when the water level rise is low, third is the scenario at the time of rising middle water level, fourth is the scenario when the water level rise is high. Data on global warming changes that occur in Indonesia are obtained from several studies on global warming, so that we get a change in sea level per year. Hydrological data processing can use HEC-HMS software and for hydraulic data processing requires primary channel profile data and can be processed in HEC-RAS 1D. Inundation map modeling in the Lamong bay area uses 2D HEC-RAS which is used to determine flood-prone locations caused by sea level rise in 4 simulated scenarios .From the results of this study, an analysis of sea level rise on global warming using IPCC data with predictions in 2030 with sea level rise as high as 8 cm for low, 18 cm for middle, and 29 cm for high Sea Level Rise. The effect of backflow from the sea greatly affects the conditions in the channel section. When the highest tide occurs 2.10 m, the water from the sea enters the channel cross section and causes the cross section of the channel not to be able to accommodate the discharge from rainwater and tide. In conditions at the Balong, Kandangan, and Sememi channels, they have a water depth of 1-3 meters. The largest inundation area is in the third scenario, which is high Sea Level Rise and 10 year return period of 9.24 km2. From the results of this simulation it can be seen that the inundation that occurs is strongly influenced by sea level rise and return period discharge. Especially in the downstream area it has a very large puddle and is very influenced by the tide of sea water.