محاكات شبكة الامطار بأستخدام برنامج EPA SWMM في منطقة مستجمعات المياه غير الحضرية في مدينة كربلاء

Simulation of Storm Network by Using EPA SWMM Program in Un–urban Catchment Area in Karbala City

Abstract
Rainfall patterns are affected by climate change in the region, which
leads to increased surface runoff and thus flooding the stormwater network
in the neighborhood. Most cities have adopted sustainable stormwater
management measures and objectives to conserve water resources. Changing
climatic conditions and seasonal fluctuations have led to increased rainfall
levels and accumulation on sidewalks and roads and their collection inside
roads. This study aims to find a modern way to shift from traditional
stormwater management methods to more sustainable methods, based on the
selection of Karbala city in Iraq, and more precisely, the Al-Wafa
neighbourhood located southwest of the city, and relying on collecting
historical data (rainfall and network data) to build a simulation model for the
stormwater network in the region using the Stormwater Management Model
(SWMM) program and studying the impact of floods on the stormwater
network in Al-Wafa neighbourhood. The effectiveness of the stormwater
network in the region was evaluated before and after rainfall for several
recurrence periods of 2, 5, 10, and 20 years. In addition, the model was
calibrated after its analysis by adjusting the characteristics of the important
sub-basins that were calculated based on the modelled and observed
discharges. The flood volume in the network after analysis reached 6921 m3
in the return period of 2 years and then increased to 9956 m3 when the return
period was extended to 20 years; this is due to climate change and thus led to
floods in the rainwater network in the vicinity, which negatively affects the
network infrastructure. The flood locations in the network were identified
through the program, and appropriate solutions were proposed for this
problem while maintaining the value of the normalized mean square error
(NMSE), which reached 1.16 in the return period of 2 years, and the
coefficient of determination (R2) 0.934, while in the return period of 20
years, the normalized mean square error (NMSE) was 0.93 and the
coefficient of determination (R2) 0.899 within the acceptable limits. Three
additional drainage lines were proposed for the network, and LID
technology was added to achieve sustainability, which led to a decrease in
the frequency of floods. Rain gardens are one of the basic methods for
complete control of surface water runoff during floods. This method was
also applied in the Karbala Al-Wafa area to control the initial floods caused
by the rainwater network. The maximum discharge was confirmed by
simulating the area before and after adding rain gardens. After simulation,
the flood reduction was 10.47%, 19.4%, 15.99%, and 15.46% over the return
periods of 2, 5, 10, and 20 years, respectively. The results showed a clear
difference in flood reduction. It was observed that the maximum number of
flooded manholes during the 2-year return period was 31 manholes without
rain gardens, while after adding rain gardens, the number decreased to 14
manholes. This demonstrates the effectiveness of rain gardens in reducing
floods