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Investigating the applicability of water sensitive urban design techniques for Güzelyurt, Northern Cyprus

Elham, Jahani
Water Sensitive Urban Design (WSUD) is a method used to mitigate the negative effect of urbanization on the water cycle. Due to a high percentage of impervious surfaces in urban area and reduction in the share of infiltration and evaporation, a considerable amount of rainfall is converted to runoff. This increase in runoff portion in urban areas causes serious problems for public and private properties. Moreover, the impact of climate change on more intensive rainfall events would cause serious problems that need the close attention of different stakeholders. In addition, water scarcity in semiarid regions and groundwater depletion are the issues which can be mitigated by applying WSUD practices. Harvesting rainwater not only reduce the pressure of rainfall runoff on the drainage system but can also be considered as a source of none potable water for irrigation and household usage. In this study, the effect of harvesting water in existing drywells in Güzelyurt city is investigated as to quantify to what extent connecting drywells to the drainage system can reduce the pressure on the system. To achieve this goal, a map of existing drainage inlets is generated in Geographic Information System (GIS) environment in which it includes six parameters (X, Y, Z, inlet picture, inlet width, inlet length) for each of the inlets. Furthermore, a close range observation of urban characteristics results in a comprehensive rainfall runoff model simulated in SWMM software. The whole city is divided into four main subcatchments and the maximum design rainfall event that cause no problem for the drainage system is obtained as 19, 20, 20 and 23 mm/hr for subcatchments A, B, C, and D, respectively. All the results are verified and approved by technical department of the municipality since there is no measured data for verifying the results. In this study, harvesting water in existing drywells considered as a Low Impact Development (LID) controls. Both subcatchments A and B are chosen for applying LID, for Subcatchment B is the most populated region with highest impervious ratio located at the central part of the city and Subcatchment A is the subcatchment with the least impervious area. Results indicate that applying LID controlsto Subcatchment B increases drainage system capacity from 20 mm/hr rainfall event to 40 mm/hr rainfall event and for Subcatchment A the increase is from 19 mm/hr to 35 mm/hr. On the other hand, in case of conventional method for improving the drainage capacity, for such an improvement in the drainage system in Subcatchment B, 909 m existing pipelines need to be replaced with 100 cm-concrete pipes which costs approximately 356,000 TL. However, in case of applying LID controls for Subcatchment B, this cost reduces up to approximately 172,000 TL. The economic comparison shows that for improving drainage system capacity in Subcatchment B, by the use of LID controls approximately 182,000 TL would be saved in compare with conventional method.