Investigating the effectiveness of low impact development practices in flood control in densely built-up cities and cost analysis

The most important processes that form the foundations of today's modern world include the First Industrial Revolution, with the invention of the steam engine in the 18th century. The most important impact of the industrial revolution on the world is the transformation it has brought about in societies. Before the industrial revolution, the world economy was mostly based on agriculture and the majority of the population lived in rural areas. After the industrial revolution, with the intensification of industrial activities and the increase of mechanization in agricultural areas, migration from rural areas to cities accelerated. In addition, in cities; social and economic conditions, job opportunities and diversity in job opportunities, developed infrastructure services, a livable modern life, easy access to education and health opportunities are other factors that accelerate migration from rural areas to cities. Continuous migration from rural areas to cities has brought about intense urbanization and concreting. Infrastructure problems in big cities and the increase in concrete surfaces have caused a significant decrease in the infiltration capacity of surface waters formed after sudden rains due to the climate change experienced in the world in recent years. This decrease in infiltration capacity accelerates the surface flow of water, which leads to floods and inundations. Economic losses and loss of life occur with the floods experienced. In addition, the rapid surface runoff due to concreting on the ground makes it difficult to retain water in basins, which poses a major obstacle to storing sufficient amounts of water for the population living in cities. The study was carried out by defining the data of an area of 43.53 ha, which includes the entire Yıldıztepe Neighborhood and a part of İnönü Neighborhood in Bağcılar district of Istanbul province, where the population and urbanization are dense and have high concreting rates, into the SWMM program. In this study; rainwater infrastructure sewerage data of Bağcılar district of Istanbul province were obtained from Istanbul Water and Sewerage Administration General Directorate (İSKİ), meteorological data of the region were obtained from Istanbul Florya Marmara Station of General Directorate of Meteorology (MGM) and effective zoning plans of the district were obtained from Bağcılar Municipality, and hydraulic and hydrological rainwater model of Bağcılar district was created on EPA SWMM program. First of all, Low Impact Development (LID) applications that can be defined in the program were defined in the model created on the SWMM program. The effects of these applications on reducing rainfall flows to existing stormwater sewer systems in areas with intense urbanization were examined by creating 6 different scenarios for 2, 5, 10, 25, 50 and 100-year rainfall recurrence periods, and their effectiveness in flood control was investigated. The rain garden, rain barrel and permeable pavement DEK applications used within the scope of the study were applied to the impermeable surfaces in the study area at limited and fixed rates for each scenario, taking into account the valid zoning plans received from Bağcılar Municipality. Therefore, the effectiveness of the green roof LID application, which is one of the LID applications used in 6 different scenarios created within the scope of the study, in reducing the maximum flow rates coming to the stormwater infrastructure sewer system with precipitation was tested. In each scenario, green roof application rates were defined on the SWMM program by increasing them as 0% (Scenario 1), 9% (Scenario 2), 17% (Scenario 3), 26% (Scenario 4), 34% (Scenario 5) and 42.5% (Scenario 6). As a result of these scenarios, the effect of the green roof application, one of the LID applications used in the model, on the flow rates at the two outfall points in the study area and the costs of the green roof LID application and conventional sewerage applications were interpreted.