Simulation of Rain Garden Effects in Urbanized Area Based on Mike Flood
An urban storm and surface water pollution model (MIKE FLOOD) was used to assess the impact of rain gardens on water quantity and quality for an urban area in Xi'an. After the rain garden measures were added, the results show that: (1) In the case where the total proportion of rain gardens was 2%, the overflow reduction rate was 6.74% to 65.23%, the number of overflow points reduction rate was 1.79% to 65.63%, the overload pipes reduction rate was 0% to 11.15%, the runoff reduction rate was
... uction rate was 1.93% to 9.69%; (2) Under different rainfall conditions, the load reduction rate of suspended solids (SS), chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) were 2.36% to 30.35%, 2.37% to 30.11%, 2.34% to 30.08%, and 2.32% to 31.35%, respectively; (3) The submersion ranges of different submerged depths and submerged durations were reduced by 0.30% to 64.18% and 7.12% to 100%, respectively. The statistics of the automatic modeling and intelligent analysis system (AMIAS) showed that the rain garden regulation range of the waterlogging risk area was 0.78% to 100%. The rain garden has a good control effect on urban storm runoff in terms of water volume and water quality, but as the rainfall recurrence interval increases, the control effect will decrease. 2 of 23 in LID. It uses the chemical, biological, and physical properties of plants, microorganisms and soils to remove pollutants, thereby achieving urban storm water runoff and water quality regulation targets  . Real-world data is needed to calibrate and validate LID simulations. At present, the most commonly used simulation softwares for LID are SWMM , MIKE URBAN , InfoWorks-ICM , SCS, HydroCAD and so on  . From the perspective of the simulation in different conditions of the region and the feasibility of LID measures, MIKE URBAN has the characteristics of fully simulating the process of runoff and confluence of single or continuous rainfall, accurately simulating the accumulation and migration process of various typical pollutants on different underlying surfaces of cities, and fully integrating with the simulated environment of GIS. This software is more suitable for simulation analysis of different land use scenarios and LID measures. The software has been used to implement the simulation of LID control measures for runoff, peak flow, and runoff pollutants  . At present, most of the research in China on the effectiveness of LID measures has been evaluated using the open source SWMM model. However, the MIKE series is able to fully simulate urban storm water and non-point source pollution and has rarely been used for the simulation of large areas. The objectives of this work are: (i) To establish a MIKE FLOOD model in the research area based on the existing pipe network system and measured data; (ii) To quantify the influence of rain gardens on urban rainfall runoff and pollutants through the results of the 1D rainwater pipe network and 2D surface, submerged under different rainfall recurrence intervals; and (iii) To offer waterlogging risk assessment of the study area and further evaluate the impact of urban storm on urban areas by the automatic modeling and intelligent analysis system (AMIAS),which utilizes the MIKE FLOOD calculation result file and analyzes the waterlogging risk level assessment map for the entire area or selected area based on the defined risk level, taking into account the water depth and the duration of the accumulated water. Materials and Methods Overview of Study Area The area of Xiying Road-Chanhe River in Xi'an City was selected as the study area, with an area of approximately 8.02 km 2 . This area belongs to the warm temperate semi-humid monsoon climate zone, with many northeast winds in winter and southwest winds in summer. The rainfall is moderate, and the average annual rainfall is 507-720 mm. Xi'an with the number of 741.14 million resident populations is a mega-city and the study area belongs to a non-central city area in Xi'an. Taking into account the nature of the study area, town types, topographical features, and climatic characteristics, the designed recurrence period of the rainwater drainage system in the study area is two years. The research area was bordered by city streets within the area shown in Figure 1 . Establishment of Study Area Model According to the urban planning map and storm water network map of the study area from Xi'an Municipal Engineering Design and Research Institute, MIKE URBAN was used to establish a one-dimensional drainage network model for the study area. The study area is bordered by independent drainage zones and was divided into 130 sub-catchment areas. The Tyson polygon method was used in the MIKE model to divide the catchment area automatically. The drainage pipe network system in the model had 139 pipelines. The pipelines were all reinforced concrete round pipes with diameters of 500-2500 mm. There were 132 inspection well nodes, one of which entered the Chanhe River. The results are shown in Figure 1a as a 1D drainage diagram. The first step in creating a two-dimensional surface flow model is to mesh the ground elevation model. The DEM whose source is the Geospatial Data Cloud is the Digital Elevation Model with a resolution of 1:1000. The overall terrain of the area is inclined from south to north and the site is relatively flat. This study is based on the MIKE FLOOD platform, coupling only the one-dimensional Water 2018, 10, 860 3 of 23 drainage network model (MIKE URBAN) and the two-dimensional surface flow model (MIKE 21). The specific coupling model generated is shown in Figure 1b.