Investigation of Permeable Pavement Implementation in Baghdad Using PCSWMM Model

One of the most important reasons for the frequent occurrence of rainwater flooding in Baghdad in general and Al-Huryai, part of Baghdad, in particular is the lack of runoff drainage systems in conventional pavement. Incidents of flooding have occurred on an average three times per year in many parts of the town due to heavy rain of high intensity and short duration. Using permeable pavement will help to control flooding and improve public health. The objective of this study is to investigate the important factors that describe the possible implementation of permeable pavement in Al-Huryai city using PCSWMM software and to quantify the effectiveness of this technique on the hydrologic response of the case study by comparing the simulation analyses of the site under its undeveloped condition, after development, and after implementing permeable pavement. The simulation results showed that permeable pavement approach has a significant impact on runoff reduction.


Introduction
When the rate of population growth increases, the rate of land development will also increase causing more flooding problems.It is estimated that from 2010 to 2050 the Iraqi population will increase by 3.6 percent.This rate is considered very high.It was recommended to be reduced to 1.9 percent (El-Mooty et al., 2016).Stormwater runoff is generated when precipitation from rain does not percolate into the ground, eventually causing reduction in the groundwater recharge and increasing in flooding events (USEPA, 2012).In addition, the hydrologic systems are currently being impacted by extreme rainfall events with high intensity and short duration.For instant, (Shen et al., 2018) showed a strong relationship between high temperatures and heavy rain as a result of climate change.This will lead to increases in the probability of flooding in the near future.Baghdad, the capital of Iraq, is subject to flooding at many areas due to heavy rain.Incidents happen on an average of three times per year.Recently on Feb 16, 2018, an incident caused road flooding and economic loss from pumping water out of ponded areas.Therefore, a new design for Baghdad's drainage system is needed.Low Impact Development (LID), a new stormwater management, is widespread around the world and could be used in any type of soils and in different methods to decrease the runoff problems by increasing both infiltration and evaporation (Abaas, 2013).
Permeable pavement, one of the most important applications of LID, has been widely used nowadays in many countries for its effectiveness in reducing the amount of runoff as close to the source as possible (Gupta, 2017;Eckart, 2017).Many studies have been done on permeable pavement.For instant, Abaas, 2013 recommended using LID techniques in the Faculty Housing Complex in Baghdad University.The study suggested a number of solutions and viable strategies in order to develop the study area to a sustainable residential project by using green infrastructure.One solution is establishing permeable pavement in children's play areas, parking lots, tennis courts, and football fields for ensuring the possibility of infiltration.In addition, another study in Dubai was conducted by Kfoury et al., 2015 where similar conditions to Iraq exist.The study demonstrated how permeable pavement greatly effects runoff reduction.The researchers examined four porous concrete mixture designs using the available materials to achieve acceptable strength, permeability, and surface quality.Out of the four, the porous concrete with acceptable permeability (0.005 cm/s), flexural strength (3.2 MPa) and compressive strength (22 MPa) was recommended to be used.The clogging factor for porous concrete due to sand and dust exposure is acceptable, and it is not an obstacle for permeable pavement implementation.Moreover, the study revealed that porous concrete disadvantages including high susceptibility to freeze-thaw cycles and low flexural strength are not considered a problem in the Middle East where no freezing and thawing occur.
Al-jumaili, 2016 compared the influence of two modifier types (styrene-butadiene styrene [SBS] and propylene modifier [PP] on the porous asphalt mixtures performance using local materials in Iraq.The porous asphalt mixture (PAM) evaluation was based on void, asphalt flow drain, and abrasion resistance.Porous asphalt with 5% was the most effective while the PP had no effect on mixture strength.A mixture with marshal stability 12.4 KN, marshal flow 2.8 mm and marshal stiffness 4.43 KN/mm elucidates high marshal stiffness among other porous mixture.The results showed that porous stiffness is the most important parameter that causes failure.To improve mixture stiffness, a modifier can be added.Rojas et al., 2018 analyzed the hydrologic response of three types of permeable pavement which were implemented in Granada, Spain to assess the impact on runoff reduction, and 70 % efficiency was obtained for delaying the catchment area response.Globally, many studies have been conducted on LID techniques in general and permeable pavement in particular.Chang, 2018 presented a brief study of the (LID) implementation in several countries such as China, Japan, Australia as well as Los Angeles in the United States.The study effectively explained how these techniques are perceived in different attitudes by the western and eastern communities around the global.For instant, the western parts such as United States have focused on restoring water quality whereas Eastern parts pay more attention to flood control and rain water harvesting.Public participation in LID implementation is very important.The increase in community education in implementing LID practices in their properties will help these communities understand its benefits.In China, the requirement of implementing LID elements was issued in 2013.The requirements include no less than 500 cubic meters of rainwater storage facilities for every hectare of hard ground no less than a 70% porous flow rate for pavement.Permeable pavement allows water to infiltrate up to 80 percent of annual runoff volume, needs less concrete collection pipes and storage systems, and improves driving safety.Other advantages are reducing pollutant load, recharging groundwater and reducing tire-pavement noise (Al-jumaily, 2016; Kfoury et al., 2015).Stormwater reuse can help meet the growing water demand, and permeable pavement is valuable in accomplishing this task.
Al-Huryai city, located in Baghdad, Iraq, has currently experienced an increase in population and land development during the last decades.This led to stormwater flooding in many parts of the town including residential areas.This study examines the possibility of implementing permeable pavement in garages, parking lots; children's plays areas at schools, and people yards to minimize the negative impact of streets flooding during heavy rains.The permeable pavement was undertaken using PCSWMM software.PCSWMM, one of the most comprehensive urban runoff models and support system for EPA (SWMM5), was chosen for use in this study for its ability to effectively simulate continuous runoff quantity in urban areas.The runoff components in PCSWMM function on a collection of subcatchment areas that receive precipitation and generate runoff.The routing components transport this runoff through a system of pipes, storage units, and other structures (James et al., 2010).Computerized solutions can be more detailed than hand calculations with less error and with less amount of time (Haestad Press, 2004).The objective was to create three models.The first model represents the study area in its undeveloped state (Al-Huryai as-is).The second represents the site condition after development (Al-Huryai_PosDev), and the third model simulates the site after implementing permeable pavement (Al-Huryai-PP).The three scenarios were modeled and compared to see the effect of permeable pavement on runoff reduction.The simulation results revealed that the permeable pavement has a significant impact on runoff reduction and thus, decreases the possibility of flooding problems.

Site Description
Al-Huryai is located in the west of Baghdad, Iraq.It has a climate between continental and subtropical with average annual precipitation of about 213mm per year (Al-Ansari et al., 2014) and average temperatures ranging from 48 C˚ in summer to below 0 C˚ in winter (Shubbar et al., 2016).The site is currently managed with combined sewer systems where both sanitary and storm flow can be disposed.The system consists of subsidiary and main sewer networks that are insufficient during heavy rain which frequently causes streets to flood.The soil consists of sand, silt and clay (Abdullah, 2013) which is referred to (B) NRCS (Natural Resources Conservation Service) soil type.The Green-Ampt Method was used for modeling the infiltration.The three most important input parameters in this method are the hydraulic conductivity (0.152 cm/hr), suction head 21.99 cm, and initial deficit (0.136) (James et al., 2012).Depression storage (Dstore-Imperv) defines as a volume that must

Results
The water many area areas (ND Al-Huryai simulation controls.T end of sim -Huryai as-is a ulation period

Table 2
EnFigure 4. P e pre-developm of the pre-dev