Assessment of pluvial flood events based on monitoring and modeling of an old urban storm drainage in the city center of Yangon, Myanmar

Pluvial flooding is a critical issue in cities worldwide, particularly in lowland areas with old and deteriorating drainage systems. The primary driver of pluvial flooding is extreme rainfall; other drivers include urbanization, inadequate drainage systems, improper solid-waste management, and the tidal backwater effect. However, the interplay between these drivers makes predicting pluvial floods difficult and complex. Previous studies in de - veloping countries seldom used water-level data or simulation modeling to identify the causes of pluvial flooding. In this study, rainfall data and water-level variations in an open channel drain and a receiving river controlled by sluice gates were collected and evaluated in detail to investigate pluvial flooding events. To predict these events, we generated a hydrodynamic model using InfoWorks ICM and verified its results using water logger data and official field reports. Analysis shows that drainage-system failures due to solid blockage and receiving water-level variation contribute more to pluvial flood occurrence than heavy rainfall. Lastly, we discuss measures to mitigate pluvial flooding in Yangon, Myanmar. The proposed monitoring and modeling approach can suitably predict pluvial flooding occurrence and provide useful quantitative data for flood risk management.


Introduction
Pluvial flooding is one of the most frequent disasters, causing contaminant and pathogen exposure, traffic congestion problems, and damage to property and urban critical systems in many cities worldwide (Hammond et al. 2015).Pluvial flooding occurs when drain water exceeds the drainage capacity owing to intense or prolonged rainfall (Dawson et al. 2008;Falconer et al. 2009).Most cities, particularly low-lying areas near the coast and along tidal riverbanks, witness pluvial flooding not only because of the large quantity of storm water received by the inadequate drainage system, but also because of the direct or indirect effects of tidal waves on receiving water bodies (Chan et al. 2018;Pervin et al. 2019).
Developing countries are particularly susceptible to urban pluvial flooding because their drainage systems are inadequate, mismanaged, and often congested for a variety of reasons, including solid waste being disposed into drains and canals (Chan et al. 2018, Zurbrugg 2003).Waste clogging is seen not only in the drainage channels but also at the inlets and drainage throats.Therefore, owing to this clogging effect, surface water cannot escape through the drain throat and enter the drainage system even if the drain has sufficient capacity to carry the surface water, increasing the severity of the flood (Despotovic et al. 2005;Guo 2017;Palla et al. 2018).Before and after extreme flooding, drain throat blockages and sediment deposition in drain channels are more frequent (Asia-Pacific Network for Global Change Research 2018).The drain throats and channels in most open-channel drains are only periodically cleaned.The deposition of soil, sand, and waste reduces the drainage capacity.The simulation results for urban drainage reveal that the presence of various sediment deposits in drain channels has a significant impact on the severity of floods, particularly in terms of flood discharge and duration (Min and Tashiro 2020).This is a recurring problem in the big cities of developing countries because of the lack of an effective waste management system and the unacceptable behavior of residents (Asia-Pacific Network for Global Change Research 2018).Sedimentation and waste accumulation in drainage systems are due to irregular street sweeping, solid-waste disposal, and poor coordination between different local government authorities (Parkinson and Mark 2005).Moreover, leaves and small litter can block the grates; this issue can be resolved by good design considerations as observed in Japanese cities such as Kitakyushu.It has been estimated that half of the grate area can be blocked by leaves and small pieces of litter (Kitakyushu Model Subsector 2017).Urban drainage systems in developing countries are also heavily obstructed by sediment which reduces their carrying capacity, resulting in floods of varying magnitudes (Kolsky et al. 1996;Nyameche 2007).Construction materials, such as sand, gravel, wood, and construction wastes, have also been found in drainage systems; they aggravated existing blockages (Cherqui et al. 2015).
The novelty of this research lies in its integrated approach proven to be the most effective method for identifying and understanding the occurrence and severity of floods in developing countries, particularly relevant in areas where the impact of garbage clogging and sediment deposition significantly affects the conveyance capacity of stormwater drainage systems.Pluvial flooding in developing countries has been rarely studied because of the lack of quantitative flood data, input data scarcity, and uncertainties in flood modeling.Governments in Southeast Asia are preparing for water-related disasters through collaboration with other nations, predominantly Japan and Korea, to enhance their readiness for waterrelated disasters (Abdullah 2017).However, they emphasize more on river flood mitiga-tion measures than those for pluvial floods because of the lack of high-resolution rainfall and recorded monitoring data for the latter.In developed countries, high-resolution elevation data can be easily accessed online.Researchers have widely used water-depth loggers to measure water-level variations for storm-water management worldwide (Ertezaei et al. 2018;Toran 2016).In addition, detailed rainfall data are important for simulations and can help correlate rainfall and pluvial flood events (Bruni et al. 2015;Ochoa-Rodriguez et al. 2015;Schellart et al. 2011).
A flood inundation model is effective for planning, designing, and analyzing urban drainage systems and flood events in cities (Bulti and Abebe 2020;Fan et al. 2017;Nkwunonwo et al. 2020;Teng et al. 2017).Conventional modeling methods, such as one-dimensional (1D) sewer models or the combination of a 1D sewer model and a 1D surface network model (1D-1D), fall short in delivering precise results when floodwaters surpass curbs in urban regions (Mark et al. 2004).Currently, the 1D-two-dimensional (2D) coupled model represents a powerful tool for simulating the hydraulic behavior of flooded urban areas due to excess runoff not conveyed by the drainage networks (Chang et al. 2015).The most wellknown models are the storm water management model (SWMM), which is an open-source model with complete functions for 1D models (Rossman 2015), and commercial packages such as XP-SWMM and TUFLOW (XP Solutions).Other software packages with hydraulic solvers, such as MIKE URBAN (DHI A/S 2020) and InfoWorks ICM (Wallingford 2015), are popular in industrial practice.The InfoWorks ICM model is widely used for many functions, such as risk assessment (Cheng et al. 2017) and pre-and post-analysis of earthquake effects on sewer networks (Biswas 2017).Most studies involving interviews and complaintdata evaluation have identified pluvial flood occurrences due to gully pot blockages and waste blockages (Peter et al. 2015;Ten Veldhuis et al. 2009;Thecla 2014).Sörensen & Mobini (2017) clarified the mechanism and characteristics of pluvial flood occurrence in Malmo, Sweden, using insurance data.However, insurance data for identifying the causes of pluvial flooding events are rarely available in developing countries, where the insurance system is not widely used.The conventional approach for identifying pluvial flood events involves applying simulation models to evaluate the impact of climate change and drainage capacity (Russo et al. 2015(Russo et al. , 2020;;Salike and Pokharel 2017;Semadeni-Davies et al. 2008).Accurate prediction and correct identification of pluvial flood events are essential steps for devising flood mitigation measures.Systematic approaches, such as monitoring with water depth loggers, simulation modeling, and information collection from drainage system authorities, have not been employed to assess pluvial flooding in developing countries.
This study has two objectives: (1) comprehending and precisely identifying the incidence of pluvial floods in the downtown areas of Yangon City, Myanmar, distinguished by an obsolete drainage system consisting of open channel networks.The region is susceptible to recurrent pluvial floods, particularly during the rainy season, characterized by varying rainfall intensities and sediment deposition.(2) the manuscript emphasizes the benefits associated with the utilization of an integrated approach for evaluating pluvial flood events.In this study, we adopted an effective monitoring method (Tashiro et al. 2020) to analyze the mechanism of pluvial flood occurrence by utilizing inexpensive level gauges to collect onsite data.Moreover, InfoWorks ICM modeling was used to predict flood events in the studied area.In the model, coupled 1D-2D approaches consider the interactions between the "minor drain system" with open channel networks and the "major runoff system" formed by streets, sidewalks, and squares.The drainage system of Yangon was built more than several decades ago; therefore, some data provided by the Yangon City Development Committee (YCDC) were unsuitable for creating the model.The inference tool in InfoWorks ICM can generate reasonable values when accurate data are not available.

Study-site description
Yangon (16°48'19.01"N,96°9'22"E) is the largest industrial and commercial city in Myanmar and is situated along the Yangon River and Irrawaddy delta (Fig. 1).In recent years, Yangon has experienced more frequent pluvial floods compared to the early 2000s owing to urban expansion.Around the year 2000, the city expanded from 357 to 673 km², resulting in a reduction in pervious surrounding land area and natural flood retention storage (Win and Win 2010).Currently, the Central Business District (CBD) in Yangon has witnessed severe flooding on most of the main roads after a heavy precipitation of 50 mm or more (YCDC 2018).
The study area is located in the Yangon CBD, which experiences severe floods during the monsoon season.The Yangon Central Business District (CBD) features a flat terrain, encompassing a study area of approximately 2.62 km², and is nearly 100% urbanized.Sluice gates are installed at each outfall to prevent backwater flow from the Yangon River, and all the gates are manually controlled.The Yangon River water level is directly related to astronomical tide conditions, and the tidal gate is closed during high tides for approximately 4 or 5 h (YCDC 2019).In the following section, we describe the data and current problems in Yangon associated with urban pluvial flooding, as well as meteorological and hydrological factors, and other factors related to the drainage system.

Land-use pattern in downtown area
The study area is situated in the downtown area of Yangon, where there are many commercial, cultural, and government buildings such as government offices, religious structures, historical monuments, commercial areas, and hospitals.This area is highly urbanized, and most structures consist of impermeable surfaces such as concrete and asphalt.Therefore, heavy rainfall can lead to runoff because the non-porous surfaces do not allow water to seep in, and water runoff flows faster with little absorption.

Topography
For this study, the digital terrain model (DTM), provided by YCDC, has been rectified.The DTM resolution is 1 × 1 m, obtained by LIDAR (laser imaging detection and ranging) surveys from 2014.The existing land is flat and highly urbanized with a peak ground elevation of 16.5 m above the mean sea level (MSL) (Fig. 2).Fairly rolling terrain partially exists in the Latha Township, whereas rest of the area is flat and below 5.0-m MSL, with some areas at the marina being as low as 1.0 m above MSL (Fig. 2).Prevailing land slopes in the CBD area vary from 1.75% at the higher strips to 0.10% in the areas next to the Yangon River.

Climate and precipitation
Myanmar has three different seasons because of its location within the tropical monsoon climate region, characterized by the northeast and southwest monsoon wind systems.It has an average annual rainfall of 2700 mm during the monsoon period from mid-May to October with about 129 annual average rainy days.The maximum 24-h rainfall observed in the past 35 years was 343 mm in 2007 (YCDC 2014).The frequencies of early and late monsoon rainfalls have decreased, whereas that of peak-monsoon rainfall has marginally increased (Khaing 2021).The month with the most precipitation is July.

Drainage
The drainage system of Yangon consists of open channels, constructed more than 80 y ago, and some parts have deteriorated (Fig. 3).The system has no pump and relies on a gravity drainage system.The recent decade has witnessed a remarkable increase in flooding events due to rapid urban development in the CBD.Periodical inundation worsens when heavy rainfall coincides with the spring tide because the existing drainage system relies exclusively on gravitational flow.Owing to such frequent severe flooding, with up to 0.50 m depth in the most populated and largest business centers of Myanmar, there has been significant economic, social, and environmental despair.

Drainage problems in Yangon downtown
illustrate a few problems associated with the Yangon CBD drainage system.Solid-waste dumping in the drainage routes reduces the carrying capacity of the drainage system (Fig. 4), causing undesirable waterlogging after heavy rainfall.Waste-collection coverage in Yangon is approximately 53% owing to limited public awareness of cleanliness, inadequately organized street cleaning as pushcart vendors act both as street sweepers and waste collectors, and insufficient income from solid-waste management services to cover the costs of solidwaste collection and disposal.In Myanmar, illegal waste disposal into the water bodies is also common.Approximately 40%, 30%, and 15% of the total waste products are disposed into water bodies in the nearby villages, towns, and cities, respectively (Gamaralalage et al. 2017, Heinrich Böll Foundation andBreak Free From Plastic 2020).Consequently, a substantial quantity of waste is illegally dumped, resulting in blocked drainage systems; this adds to the drainage system cleaning workload of the Pollution Control and Cleansing Department (PCCD) (World Bank, Country Environmental Analysis 2019) Sediment dredging is vital for reducing flood severity in downtown Yangon, and drainage departments conduct sediment dredging before and during the rainy season (Fig. 5).During dredging operations, workers often find many types of solids, such as solid waste, food waste, sediments, water bottles and, sometimes, construction materials such as sand and gravel.Some of these products are due to illegal disposal of construction materials and waste into the drainage system owing to the non-enforcement of waste-disposal regulations in the downtown areas of Yangon (Fig. 6).Therefore, the sediment deposition rate is difficult to predict, and these areas have higher pluvial flood severity due to sediment and waste blockage.
Other problems associated with the drainage system are caused by garbage clogging and the severity of flood.Figure 7 highlights the garbage clogging with water pipe and cables in a drain channel.major challenges such as the fragmentation and overlapping of responsibilities exist in YCDC due to the lack of coordination among the different departments responsible for drainage, telecommunication, water supply, and sanitation.In Yangon city, significant drain-throat clogging occurs during the rainy season, and water on the roads cannot flow into the open-channel drain (Fig. 8).If the inundation is severe, residents call on the Drainage and Wastewater Management Authority (DWMA) of the YCDC office to unclog the drain throats and drain channels.Although the DWMA claims it plans to upgrade the current drainage system to help the city withstand a 10-y return period storm, some drainage facilities cannot accept all the storm water even for a 2-y return period storm because of their reduced water conveyance capacities due to clogging as well as deterioration due to aging (YCDC 2018).The DWMA has been expanding some drain channels to increase the conveyance capacity of the system; however, these efforts are hampered by the lack of effective planning and strategies.

Pluvial flood monitoring
In this study, we used water-depth loggers to measure the water-level variations in the drains and river.In addition, we installed a tipping bucket rain gauge to obtain input rainfall data for modeling.

Materials and methods
We deployed water-level loggers (Onset, HOBO U20L-01) at eight locations in the storm drainage system of the study area and on the banks of Yangon River.We also installed one tipping bucket-type rain gauge (resolution = 0.5 mm; Climatec, Inc., CTFK-1) with a data logger (Onset, HOBO CO-UA-003) (Fig. 9).The loggers have advantageous characteristics, including simple and quick deployment, low cost, reusability, and durability in harsh environments.Conventional flood monitoring methods, such as resident and chalk gauges, cannot accurately determine the inland flood frequency and duration.Monitoring systems with sensors are more practical than manual measurements because they can accurately obtain continuous water fluctuation, flood duration, and flood frequency accurately (Tashiro et al. 2020).These sensors can measure water-level data with an operating range of approximately 0-9 m (up to 30 ft) in freshwater.
Channel properties such as width, height, and location were measured at each station (Table 1).During data collection, a flood event is declared when the water level reaches the rim of the storm drainage channel.

Results and discussion
Data were collected from June to December, and the total monitoring period was approximately 200 days during the monsoon season of 2019.During this monitoring period, the total recorded rainfall was approximately 1920 mm, and the heaviest rainfall was 41.5 mm/h measured on October 10, 2019.Moreover, according to the logger results, 12 flood events occurred in the 2019 rainy season in Yangon.Table 2 lists the details of each observed flood event, including inundated locations, preceding one-hour and three-hour rainfall intensity, and the water levels at Yangon River.
According to the logger measurements, twelve flood events occurred during the 2019 rainy season in Yangon (Table 2).The rainfall data from the tipping bucket were compared with the logger results, and we did not find a strong correlation between the rainfall intensity and the flood events recorded by the loggers.Therefore, we established that flooding is related not only to the rainfall intensity preceding the flood, but also to the Yangon River Fig. 8 Cleaning at the drain throat clogged during flooding events water level.For example, the sluice gates are opened when the river water levels are low and closed when the river water levels are high due to high tide.Some flood events are related to high rainfall intensity, whereas others are not directly related to the rainfall intensity.The results suggest that some severe floods occur even under low-intensity rainfall when the sluice gates of Yangon River are closed for high tide.

Info Works ICM model building methodology
The following sections outline the methodology adopted for constructing the ICM model for Yangon CBD, including information related to the model input data, approach, and software.The storm drainage has an open-channel length of 73 km with 609 nodes included 16 outfalls, as shown in Fig. 9. Figure 10 illustrates the 1D-2D ICM computation model.

Computational domain
The model was constructed and executed using InfoWorks ICM Version 11 modeling software (Innovyze 2019).An existing 1D drainage model within InfoWorks ICM was created using drainage data provided by DWMA (2019) and incorporated into the InfoWorks ICM model.It represents the 2D model surface using irregular triangles (of varying size, which Fig. 9 Storm drainage system and monitoring-device locations in Yangon make up individual elements within the mesh).For this mode, the maximum triangle area is 100 m 2 , minimum element area 25 m 2 , minimum angle approximately 25°, and mesh total 20,023 elements.
The InfoWorks ICM model utilized a direct rainfall model and applies a rainfall hyetograph to every element in the 2D surface model for every storm event.The hydrological model mainly contains parameters for the runoff and flow-convergence processes.The channel parameters applied in this model include the roughness of the concrete channel walls for the 1D open channel network model and the roughness of the surfaces for the 2D hydrodynamic model.Within the 1D open-channel model, roughness values in the network were set to a standard Colebrook-White value of 3.00 for old brick work in good conditions, and the Manning roughness for 2D elements was set to 0.04 (Butler et al. 2018;Xu and Zhao 2016).
The Thiessen polygon method was used to divide the sub-catchments whose runoff flows into the nearest manholes.The total number of sub-catchments was 599.The 2D flood-type ever, we did not consider water exchange through these inlets because of the lack of data according to their treatments in existing studies (Bertsch et al. 2017).The mass of water flowing into the open-channel drainage or sewer system is limited by the capacity of the inlets; nonetheless, this phenomenon has not been adequately considered in the extant urban drainage models (Chang et al. 2015).In the simulation, we assumed that the virtual manholes-as nodes of the channel junctions-connect the 1D and 2D models.Water exchange between all the manholes and the surficial mesh was calculated using the Weir equations, assuming a Weir crest level at the node ground level and a crest length equal to the node shaft circumference (Innovyze 2019).A flooding discharge coefficient of 0.5 equivalent to the weir discharge coefficient was specified for the node according to the model's default value, whereas the chamber and shaft areas of each manhole were considered 4.0 m 2 as in practical examples (Innovyze 2019).In this "inlet-manhole method," the water discharged through inlets was assumed to be instantly transported to a manhole, where one manhole can be connected to several inlets.

Computational condition
Of the 12 flood events listed in Table 2, we selected the following nine situations with six hour rainfall and water level data as the computational conditions in the InfoWorks ICM modeling, such as July 28, August 2, 7, 17, 24, September 10, October 10, 14, and 28.
Additionally in these cases, we controlled the openness of sluice gates by referring to the tide table provided by the Myanmar port authority and correlated the rainfall and river water level data.

Results and discussion
Seven flood events could be partially reproduced with InfoWorks ICM simulations.Most flood events occurred when the water level of Yangon River was high.We selected three flood events (one flood event where the simulation and logger results coincide under the closed flood gate condition, and two other flood events for which the logger and simulation results do not coincide) for analysis.First, we selected the flood event on 2 August 2019 when the sluice gates were closed.A comparison of the logger data, DWMA field reports (DWMA, 2019) and photographs, and simulation results reveals that the model can accurately predict the time and location of a flood (Figs.11 and 12).The measured and simulated water levels at L3 and P2 are illustrated in Fig. 13.These values were directly compared, but the results were not calibrated.Model calibration is an essential step in modeling, and conventional calibration approaches include the adjustment of model parameters and other activities such as model structural and functional validation, data checking and preparation, sensitivity analysis, and model verification (Mark 2014).However, the effects of sedimentation and garbage blockages in the open-channel network are severe and cannot be accurately assessed by the calibration process for pluvial flooding.
The other two flood events were evaluated using logger data, DWMA field reports (DWMA 2019) and photographs, and simulation results.The simulation results and logger data did not match the DWMA account of flooding on the 7th of August 2019, where the sluice gates were open (Fig. 14).A similar mismatch was observed for the flood on 14 Octo-ber 2019 where the sluice gates were also open (Fig. 15).According to the official reports (DWMA 2019), workers cleaned the waste blockage at the drain throat and drain at those locations after the floods.These floods might have been caused by the limited capacity of the drainage system due to gully pot blockages due to sediment and driftwood, as reported in Ten Veldhuis et al. (2009).Despite uncertainties, clogged drains were shown to be the primary causes of urban flooding according to a questionnaire administered in Thailand  (Thanvisitthpon et al. 2018).Conventionally, most pluvial-flood assessments relied on interviewing residents or local authorities.
In a previous study, we emphasized the drainage performance sensitivity to sediment deposition (Min and Tashiro 2020).Varying sediment percentages (such as 0%, 20%, and 50%) in drains significantly influence floods, particularly discharges and duration, as observed in downtown Yangon.The maximum variation in flood discharges between channels with 0% and 50% sediment depositions is approximately 0.2 m³/s.Specifically, for a clean channel, flooding lasted 15 min, while flooding lasted for 22 min for the scenario with 50% sediment deposit.Additionally, deposited sediments in drain channels reduce carrying capacities and impede water drainage, increasing flood duration, as confirmed by simulations employing different sediment depths, which provide a comprehensive analysis of these phenomena.
Our simulations could not reproduce these flood events because we adopted the inletmanhole method and did not consider clogged drains (Figs. 4,5,6,7 and 8) in our modeling.Jang et al. (2018) demonstrated that the inlet-manhole method could numerically overestimate flood severity; however, we suggest that the clogging effects are predominant, as indicated by Lamond et al. (2012), because inundations in the real-world is more severe than that obtained numerically.These effects were also supported by the convergence of the simulation results and measurements under the closed the sluice gate condition as the river water level increased (Figs. 11,12 and 13).This phenomenon is an interesting challenge in Yangon, and we could identify the possible causes of flood events by simulation, monitoring in situ data, and collection of verifying information from the local engineering department.These findings related to pluvial flood assessment in this case study highlight that the combined approach is more effective than the traditional ones, such as interviews and surveys, and the simulation approach in developing countries.
Furthermore, variation in the water levels of receiving water bodies was a prominent factor affecting the pluvial flood severity in this study.Therefore, local authorities should consider receiving water-level fluctuation as an important factor for determining pluvial flood severity.According to the IPCC AR6 report, the frequency and intensity of heavy precipitation events have increased since the 1950s, whereas the global mean sea level has risen at 3.  sea levels, which are caused by climate change, cities situated in the coastal and delta areas of developing countries should rapidly upgrade their drainage systems for high-intensity rainfalls and provide adequate interventions.In 2022, the Drainage and Wastewater Management Authority implemented the installation of pumps at flood gates to make floods less severe during rising water levels and flood gate closure.As indicated in the 2023 report by DWMA, areas near flood gates that previously experienced frequent severe floods witnessed significantly less severe floods after the pumping station was installed.(DWMA, 2023).This observation is of particular significance given that the simulations conducted for flood assessments in 2019 were intricately linked to the closure of flood gates, thereby accentuating the consequential influence of the pumping station on flood mitigation when river levels rise.

Conclusions
In this study, we introduced a process for investigating the local pluvial flooding events in the downtown area of Yangon using water-depth loggers and model simulations.We verified that the simulation can correctly predict the flooding events under closed sluice-gate conditions by comparing the logger measurements with the simulation results.This research employed an integrated approach, demonstrating that it is the most effective method for discerning and comprehending the incidence and magnitude of floods in developing countries.However, the simulation approach cannot be used to clearly identify the occurrence of pluvial flooding in urban areas in developing countries owing to the discrepancies between the design and actual capacities of the drainage system.In particular, we identified a mismatch between the simulation results and the observed situations for the downtown areas of Yangon.By comparing the results with field information obtained from the drainage management authority, we found that this was the reason why pluvial flooding was often caused by sediment blockage in the drain channels and garbage accumulating at the drain throats.This is notably relevant in regions where the negative consequences of waste accumulation and sediment deposition markedly impede the conveyance capacity of stormwater drainage systems.Furthermore, we identified that the severity of pluvial flood was also dependent on the variation in the water-level of the receiving water bodies.
During site inspection, a few drainage covers were found to be damaged, and the curb inlets lacked bar screens, which resulted in the clogging of the drainage system by garbage and sediments.Preventing solid waste and sediments from entering the drainage system is important for reducing the severity of pluvial floods.Therefore, based on an understanding of the effect of sediment blockage in storm water drainage systems on pluvial flooding, the municipal authorities should clearly explain the consequences of illegal waste disposal on the increase in risk and severity of flooding.In addition to introducing good waste management practices in schools, universities, and other establishments in the public and private sectors, it is essential to ensure that they are implemented well and that sediment dredging and ad hoc cleaning of drainage systems are scheduled regularly.Further, installing sediment traps, covering open channels, and adding bar screens at curb inlets can reduce the severity of floods in the city, while creating flood water detention ponds can reduce water levels in the receiving water bodies during heavy rainfall.Therefore, the integration of these measures could mitigate pluvial flooding in urban areas in developing countries.

Fig. 1
Fig. 1 Study-site location and area in Yangon City, Myanmar.(Source: Google Earth)

Fig. 2
Fig. 2 Digital Terrain Model (DTM) of the study area.(Data source: Yangon City Development Committee)

Fig. 11
Fig. 11 Flood condition near Logger P2: Inundation map (top) generated by ICM software and photograph of the actual location (bottom) captured during the flooding event on 2 August 2019

Fig. 12
Fig. 12 Flood condition near Logger L3: Inundation map generated by ICM software (top) and photograph of the actual location (bottom) captured during the flooding event on 2 August 2019

Fig. 13
Fig. 13 Observed and simulated water levels at (a) P2 and (b) L3 logger locations during the 2 August 2019 flooding event 7 [3.2-4.2]mmyr − 1 from 2006 to 2018 (IPCC 2021) over most of the land area.Because of the increased occurrence of rainfall over shorter intervals of time and the rising

Fig. 15
Fig. 15 Flood condition near Logger L1: Inundation map generated by ICM software and photographs of the actual location (top left) including maintenance activities (bottom left) captured during the flooding event on 14 October 2019