تقييم تأثيرات الشدة المطرية على شبكة الأمطار ومشاريع البنى التحتية (منطقة الدراسة الحر-كربلاء كحالة دراسية)

Evaluation the Effects of Rainfall Intensity on Storm Network and the Infrastructure Projects

     The variation of rainfall intensity higher than the design standards due to the global warming considers as one of the big problems that are facing the urban area.

    Urbanization in cities led to the spread of impervious area quickly and the increase in the amount of the runoff quantity due to the decrease in the infiltration rate. The misuse of the storm drainage system by the inhabitants decreases the drainage capacity and led to urban flooding. Modeling of the urban flooding considers as an important method that help in discovering and managing the flooding problems.

    In this research Storm Water Management Model [SWMM] has been used to simulate the flooding of the storm drainage network in Al-Eskari quarter, Kerbala, Iraq. The hydrological data (i.e. rainfall intensity, temperature and wind speed) was collected for a period from 2008 to 2016 by Agricultural Meteorology Iraqi Network (AMIN) . The hydraulic data was provided for the storm drainage system of Al-Eskari quarter regarding to the manholes, pipes and pumps. The calibration data was used for two rainfall events in 18/1/2016 with rainfall intensity 2 mm/hr and 22/1/2016 with rainfall intensity of 4mm/hr.

     The major aim of this study is to develop a model to evaluate the effect of the climate variation and the misuse of the storm drainage system through adding an illegal sewage quantity to the storm network by the inhabitants. Also, this study aims to specify the damage cost of the infrastructure that caused by flooding.

     Finally, this study tries to provide a technical support for the decision makers by developing and accessing a solution to mitigate the flooding in the study area.

    The results indicate that the storm drainage network is suitable for the design intensity of 2-years return periods [9.6 mm/hr intensity for 1-hour] without considering the effect of an illegal sewage quantity. The climate variation plays the major role in the flooding of the study area with a rainfall intensity reach in an event to more than three times the design intensity with 33.54 mm/hr for 1-hour.

    Under 33.5 mm/hr rainfall intensity and without considering the sewage quantity, the equivalent water depth in the outlet reached to 5.55 m measured from the invert of the outlet, 47% from the manholes of the system flooding with discharge greater than 0.04 m3/sec and the flooding duration was 43 hours. The existent of sewage increases the flooding problem due to the clogging that happened in the system, where the system started to flood under rainfall intensity lower than the design intensity. The equivalent water depth with the maximum rainfall intensity in addition to the sewage amount reached to 5.62 m, 48% of the manholes in the system flooding with flow reach to 0.04 m3/sec and the flooding duration was 72 hours. The sewage quantity doubled the flooding duration. The flooding event with long duration led to damage in the infrastructure, especially the roads and houses.

    The total cost of flooding damage reached to 354800 $ and it’s a repeated cost if no solutions are provided to mitigate the flooding. In this study a solution was suggested by adding a transmission pipe line with cost of 1154 $ for each meter of the pipe. This performance of this solution under the maximum rainfall intensity and with consider the sewage amount was as follow: The equivalent water depth with the maximum rainfall intensity and with consider the sewage amount reached to 5 m, the volume of water flooding reached to 129 m3, 33% of the manholes flooding with discharge reached to 0.04 m3/sec and the flooding duration was 20 hours. The results of adding a pipe line is so promising and decreasing the flooding in the study area. The simulation results can offer resilient technical support for the urban drainage system controlling and planning.