Urban Stormwater Drainage Systems Research Articles

Analysis of rainwater utilization technology and current situation in the roof garden

The urban water environment has been deteriorating over the last decade due to land development and climate change, increasing the pressure on urban stormwater drainage systems. With economic development, the value of buildings has also been challenged at a higher level. Roof garden, as a new form of roof treatment, can effectively increase the urban greening area and compensate for the ecological and water environments that have been damaged by building development and utilization. This paper analyzes the advancement of roof garden by comparing it with the traditional sloped roof. The analysis finds that roof gardens can store water and control drainage, and have significant advantages in reducing rainwater discharge, reducing building water demand, and improving the urban water cycle. Roof gardens not only have the ability to utilize rainwater efficiently, but also come with a series of economic, ecological, and social benefits, such as improving the urban heat island effect, saving the amount of water demanded by buildings, and energy consumption. By analyzing domestic and international cases of roof gardens, it is verified that roof gardens are designed as a combination of utility and aesthetics.

Study rainfall intensity duration frequency relationships under climate change for design of efficient urban stormwater drainage systems in Dodola town, Ethiopia

Study rainfall intensity duration frequency relationships under climate change for design of efficient urban stormwater drainage systems in Dodola town, Ethiopia

Analysis of Stormwater and Rainwater Harvesting Potential Based on a Daily Water Balance Model: A Case Study of Korea

The increasing intensity of rainfall resulting from climate change is projected to worsen the inundation of urban areas by floods. As a viable alternative, stormwater harvesting presents an opportunity to enhance water supply reliability while reducing pressure on both water resources and urban stormwater drainage systems. The stored rainwater can be supplied with a radius of one kilometer around the storage facility, so less pumping energy is consumed compared to supplying the stored rainwater far away from the storage facilities. To visually depict the characteristics of the selected storage facility, land cover maps were created using ArcGIS. These maps were created for a circular region with a radius of one kilometer around each studied storage facility. In this study, a daily water balance model was formulated using spreadsheets to assess the potential of harvesting stormwater and rainwater for various pre-existing storage facilities. Five different types of storage facilities were selected for this study. The term “SRWH facility evaluation criteria” as a whole is used for the storm or rain (SR) water supply satisfaction rate, the SR guarantee rate, and the SR utilization rate. The results provide evidence that, for each selected studied storage facility, the SR water guarantee rate can potentially surpass 70% under conditions of low water demand. Moreover, we investigated the potential of the existing storage facilities to work as multifunctional resources, while the original purpose for which each facility was constructed remains un-affected.

Exposure of the US population to extreme precipitation risk has increased due to climate change

The magnitude and frequency of extreme precipitation events in the early twenty-first century have already proven to be increasing at a rate more quickly than previously anticipated. Currently, the biggest consequence of the change in extreme precipitation is the lack of a climate-adjusted national standard taking into account these recent increases that could be used to prevent life and property loss from catastrophic precipitation-driven floods. Here, we address how severe the change in extreme precipitation compares against the current national standard for precipitation climatology (NOAA Atlas 14) and how much of the population is affected by the underestimation of this risk in the contiguous United States (CONUS). As a result, extreme precipitation in the early twenty-first century has outpaced our current national standard in half of CONUS, and the heavy precipitation events experienced recently are quickly becoming a “new normal”, which will increase in severity and frequency in a continually changing climate. Over three-quarters of the U.S. population will likely experience this new normal occurrence of extreme precipitation. As much as one-third of the population is expected to experience the current definition of a 1-in-100-year storm as often as three times in their lifetime. Additionally, the current precipitation standards for designing transportation infrastructure and urban stormwater drainage systems that are built upon Atlas 14 may be insufficient to protect the public's safety and personal/community property from severe flooding. Areas where flood risk is mitigated by operating hydraulic and adaptation structures urgently need to assess the impact of the increased-hourly extreme precipitation and reevaluate their applicable operation rules. Understanding and predicting patterns and the likelihood of short-duration heavy precipitation would be beneficial in preparing for severe precipitation-driven disasters, such as flash floods and landslides, which would happen more frequently in a changing climate. Following the results of this analysis, accelerating the development and dissemination of the next generation of the national standard that has been climatically adjusted to adapt to the new normal is strongly recommended.

Predicting the Overflowing of Urban Personholes Based on Machine Learning Techniques

Urban stormwater drainage systems, which include many personholes to collect and discharge precipitation within a city, are extensively constructed to prevent streets and buildings from flooding. This research intends to build a machine learning model to predict whether a personhole will overflow soon, which is crucial to alleviate the damage caused by floods. To address the challenges posed by many diverse personholes, we proposed segmenting the personholes into several groups and have designed two methods employing different personhole features. The first, the geography-based method, uses the geographical locations of the personholes for the grouping. The second, the hydrology-based method, uses the characteristics that are directly related to the overflowing situation, such as the depth of the personhole, and the average and the maximum water level of the personholes. We also investigated several machine learning techniques, such as the multilayer perceptron (MLP) model and a fine-tuning architecture. The study area was located in the new Taipei city and the experimental results have shown the impressive predictive ability of the proposed approaches. Particularly, by applying the hydrology-based grouping method, and using a hybrid model combining the machine learning model prediction results with heuristic rules, we can obtain the best prediction result, and the accuracy is over 99%. We have also noticed the influence of the activation function used in the neural network and the number of frozen layers in the fine-tuning architecture. Particularly, using the tanh function with one frozen layer is good in some cases. However, since it is not general enough, we suggest the readers perform empirical studies before choosing the best setting in their own environment.

Coupled effects of future rainfall and land use on urban stormwater drainage system in Tampa, Florida (USA)

Future rainfall and land use are two important factors for flood management since they both directly and indirectly affect the functionality and performance of urban stormwater drainage infrastructures. Although some studies have already examined the coupled effects of future rainfall and land use conditions, they have not concluded how such effects on both surface runoff and flood areas would change with regional surface elevation variation and infrastructure conditions. This paper analyzed the coupled effects of future rainfall and land use on urban drainage systems in terms of surface runoff quantity and flood area changes using EPA SWMM. Future downscaled and bias-corrected precipitation projections for 2040–2060 and 2080–2099 from “Downscaled CMIP3 and CMIP5 Climate and Hydrology Projections” Archive and future land use for 2050 s and 2090 s from EPA ICLUS project were used for the City of Tampa in Florida (USA). It was shown that potential runoff volume and flood area changes ranged from −40% to 160%, and −40% to 400% due to rainfall change, while potential changes induced by land use change ranged from 0% to 3.5%, and 0% to 18% respectively. Additionally, this study examined the coupled effects of future rainfall and land use changes on flood area variations, considering the capacity of drainage infrastructure and elevation variation of study site. Results showed that flood area variations are not solely influenced by runoff quantity changes due to the two external drivers, but also by other factors. Specifically, in low-relief areas with inadequate drainage infrastructure and less elevation variation, these two drivers have no additive effects on the percentage of flood area changes. In contrast, in areas with adequate drainage infrastructure and greater surface elevation variation, there are additive effects from rainfall and land use changes on flood area expansions. These findings have important implications for stakeholders involved in city planning and flooding control, particularly for urban areas facing future precipitation and urbanization challenges.

Direct discharge of sewage to natural water through illicitly connected urban stormwater systems: An overlooked source of dissolved organic matter

The illicit connection of sewage pipes to stormwater pipes commonly occurs in urban stormwater systems. This brings problems that sewage might be directly discharges into natural water and even drinking water sources without treatment, posing risks to ecological safety. Sewage contains various unknown dissolved organic matter (DOM), which could react with disinfectants and lead to the formation of carcinogenic disinfection byproducts (DBPs). Thus, understanding the impacts of illicit connections on downstream water quality is of significance. This study firstly investigated the characteristics of DOM using fluorescence spectroscopy and the formation of DBPs after chlorination in an urban stormwater drainage system in the case of illicit connections. The results found that the concentrations of dissolved organic carbon and dissolved organic nitrogen ranged from 2.6 to 14.9 mg/L and from 1.8 to 12.6 mg/L, respectively, with the highest levels occurring at the illicit connection points. Concerning DBP precursors, pipe illicit connections introduced considerable precursors of highly toxic haloacetaldehydes and haloacetonitriles into the stormwater pipes. Furthermore, illicit connections introduced more contents of tyrosine-like and tryptophan-like aromatic proteins, which may be related to foods, nutrients, personal care products, etc. in the untreated sewage. This indicated that the urban stormwater drainage system was a significant input source of DOM and DBP precursors to natural water. The results of this study are of great significance for protecting the security of water sources and promoting the sustainability of urban water environment.

Combining green roofs and rainwater harvesting systems in university buildings under different climate conditions

Rainwater Harvesting Systems (RWHS) are an alternative solution with the potential to increase water supply security and reduce the pressure on water resources and urban stormwater drainage systems. Likewise, Green Roofs are a nature-based solution with several ecosystem services able to improve well-being in densely urbanized areas. Despite these benefits, the combination of both solutions is still a knowledge gap to be explored. To address this issue, the paper explores the potential of integrating traditional rainwater harvesting systems (RWHS) with extensive green roofs (EGR), while simultaneously evaluating the performance of traditional RWHS in buildings with high and variable water consumption patterns across different climatic conditions. The analyses were carried out assuming two university buildings hypothetically located in three distinct climates (Aw - Tropical Savanna, Cfa - Humid Subtropical, and Csa - Hot-summer Mediterranean). The results show that the relationship between available water and demand is the key factor that defines if the system is most suitable for saving water, reducing stormwater runoff rates, or dual-purpose (when there is a balance between non-potable water supply and capture of stormwater). Combined systems were most effective when there is a balanced rainfall distribution over the year, as in humid subtropical regions. Under these conditions, a combined system designed for dual purposes could potentially have a green roof coverage of up to 70% of the total catchment area. Conversely, climates that have well-defined rainy and dry seasons such as Aw and Csa, may limit the effectiveness of a combined system (RWHS+EGR), being not able to supply water demands during certain periods of the year. However, if the primary objective is effective stormwater management, a combined system should be strongly considered. Because green roofs provide other ecosystem benefits that can contribute to enhancing urban resilience in the face of climate change.

Calculating the volume of Tan Mieu lake in Thanh Noi area, Hue City, for the urban stormwater drainage system

Detention lakes, which are effective means of flood control, are highly effective in sustainable drainage solutions. Numerous factors diminish the regulating reservoir's function for urban drainages, such as the lake's small volume, an inadequate drainage system, and restricted outflow from the lake. Therefore, this study applies the method of limited rainfall intensity to calculate the stormwater flow into the lake and determine the volume of the detention lakes according to TCVN 7957: 2008 [1] to the sub-basin of Tan Mieu. It is confirmed that the volume of the lake in the region and the level of outflow from the lake, which are essential factors in flood mitigation, is not suitable for the rainfall characteristics of the area. The results show that with the planned outflow of Qx = 1/3 × Qt, the lake's actual capacity is roughly a half of the required lake capacity. With the option Qx = 1/2 × Qt, the actual volume of the lake is 1.2 times smaller than the calculated capacity. Therefore, increasing the lake's volume and outflow volume from the lake minimizes local flooding.

An Online Data-Driven Evolutionary Algorithm–Based Optimal Design of Urban Stormwater-Drainage Systems

To reduce flood risk in urban areas, an optimal design of drainage networks for urban areas is essential for flooding control and drainage management of the urban stormwater drainage system (USDS). A conventional design is generally used for drainage networks, resulting in high computational costs and limited flooding reduction effect. In this study, based on an on-line data-driven evolutionary algorithm coupled with the storm water management model (SWMM), a novel approach for USDS drainage network optimization design was developed. A case in Xi’an City, China, was then selected for practical implementation, where the performances of the local planning scheme, the particle swarm optimization algorithm (PSO) and the proposed approach were compared. Results confirmed that our proposed methodological approach is feasibility and highly efficiency, leading to a 32% reduction in total flooding from that resulting from the local planning scheme. In addition, the average computational time was reduced by 57%, while the flooding control effect was better, compared to PSO algorithm optimization. These results suggest that our optimization design approach is reliable and applicable, and can benefit and assist designers in practice.

Urban storm water drainage system optimization using a sustainability index and LID/BMPs

• A new comprehensive sustainability index for urban stormwater drainage systems was developed. • The developed sustainability index applied to the western part of Tehran stormwater drainage. Results showed that the study area suffers from significant performance degradation. • Two multi-objective optimization models, with the objectives of maximizing sustainability and minimizing costs, were introduced to rehabilitate the stormwater drainage system. • The effects of considering channels rehabilitation along with BMPs implication were studied. • Results showed that rehabilitating the stormwater networks by BMPs implication and rehabilitating the channels would result in more cost-effective solutions. Urban stormwater drainage systems (USDSs) play an essential role in protecting cities from excessive rainfalls and urban floods. To quantify the performance of the USDSs, a new sustainability index is proposed based on reliability, resiliency, and vulnerability indices. These performance indices evaluate different aspects of a USDS with a comprehensive view of the system's level of service. Using the proposed sustainability index, two USDS design/rehabilitation optimization models are introduced and compared to see which one offers a more sustainable solution and lower implementation cost. The first model ( Case I ) applies Best Management Practices (BMPs) to an existing USDS to improve sustainability with minimum costs. The second model rehabilitates the channel sizes along with using BMPs. A part of the Tehran Stormwater Drainage System (TSDS) is chosen as the study area to evaluate the proposed methodology. Optimization models are developed by linking the NSGA-II optimization algorithm with the EPA SWMM model. The best solutions are extracted from both cases’ Pareto fronts and compared using the Nash bargaining method. Results showed that designing/rehabilitating USDSs by optimizing the BMPs size and channel size would result in a higher sustainability index and lower costs.

Effects of sediment deposit on the hydraulic performance of the urban stormwater drainage system

Sediment deposit is a critical factor strongly affecting the drainage capacity of the conduits due to its cross-section area narrowing and roughness increasing. In this study, a numerical model was applied to investigate the influences of sediment deposit on the hydraulic performance of the drainage conduits. The Nhieu Loc - Thi Nghe (NL-TN) basin, located in Ho Chi Minh City, Vietnam, was selected as a case study. The drainage network of the NL-TN basin was simulated by using the EPA-SWMM model. The effects of sediment deposit were assessed by a non-dimensional comparison of the simulated peak flows of the sediment-deposited conduits and the clean ones. The results indicated that the sediment deposit significantly affects the flow capacity of the conduits and could cause severe inundation. Narrowing of the cross-section area has more impact on the hydraulic performance of the conduit than the increase in the roughness. A 40% increase in the Manning coefficient could decline the peak flow to approximately 80-90%, while a 40% increase in sediment thickness depth could degrade the peak flow by about 60-70% to compare with the peak flow of the clean conduit. The findings could support decision makings on the operation and maintenance of the sewer system and adaptation to extreme rainfall events.

Study rainfall intensity duration frequency relationships under climate change for design of efficient urban stormwater drainage systems in Dodola town, Ethiopia

Study rainfall intensity duration frequency relationships under climate change for design of efficient urban stormwater drainage systems in Dodola town, Ethiopia

3D CFD simulations of air-water interaction in T-junction pipes of urban stormwater drainage system

ABSTRACT A 3D computational fluid dynamics model based on a volume of fluid (VOF) approach is presented to simulate air-water interactions and transient pressures in T-junction pipes of urban stormwater drainage system. The effective heat transfer due to compressible air pocket, and various k-ε and k-ω turbulence models, are considered to account for the potential energy attenuation during air-water interactions. One effective meshing method considers the boundary layer of the pipe wall and the effect of grid density. The proposed approach with RNG model can accurately reproduce the experimental pressure oscillations, including the pressure peaks and periods and the pressure damping, and is importantly helpful to explore the complicated flow characteristics. Rapid filling of T-junction pipe with trapped air undergoes: (a) with the air movement and expulsion in vertical pipe, but without any geyser; or (b) involving the air movement and expulsion in vertical pipe, accompanying the violent geyser.

Surface water quality assessment for the management of hydrological regimes: Kalu Oya and Mudun Ela catchment in Sri Lanka

This study aims to assess the relationship between surface water quality and the land-use of an urban catchment named ‘Kalu Oya and Mudun Ela catchment’ located in the western province, Sri Lanka. Ten judgmental sampling locations of the streamflow were selected to measure water temperature, pH, salinity, conductivity, Total Dissolved Solids (TDS), Biological Oxygen Demand (BOD₅), Chemical Oxygen Demand (COD), oil & grease, nitrate and dissolved phosphorous levels, flow rates over five months of the period from June to October 2018. All these parameters varied independently with a significant difference from other sites (ANOVA, p < 0.05). Water temperature and nitrate levels showed a strong clustering pattern with positive Moran’s index values supported by higher Z-scores. (Moran’s index 0.557 and 0.5106, Z-score 2.773 and 2.419 respectively). Higher oil & grease levels exceeding the accepted levels were observed at all the sampling sites. Oil & grease values showed a strong positive correlation with the flow rate (Coefficient-0.807, P value-0.005) revealing that higher oil & grease levels in the stream may be resulted by subsurface flushing. Site 02 is affected by the effluent discharged by the Colombo fish market having higher phosphate and TDS levels. Clustering pattern of nitrate and dispersed pattern of oil & grease of the Kalu Oya and Mudun Ela catchment show evidence of the poor drainage system in the catchment. Improving the drainage system may enhance water infiltration by reducing the volume of runoff and improve the water quality by that it can be used as an effective urban storm water drainage system in the hydrologic water regime.

Hydrological and Hydraulic Analyses of Urban Storm Water Drainage System of Major Area of Pokhara, Nepal

The immense increase of the structural activity which decreases the pervious area of the city is alarming danger situation pertaining to drainage. Urbanization and improved area of imperviousness are the major contributors that make the existing drainage network insufficient while inadequate maintenance and haphazardly throwing rubbish on the road and drain are other issues. The major objective of the study is to analyze the hydrological and hydraulic status of the urban storm water drainage system of the major area of Pokhara City of Nepal and to compare the calculated result with existing situation, using Rehm tools HYKAS and GraPS under AutoCAD environment. The results of this study show that the size of the existing road side drains is inadequate to handle all the surface runoff. It is found that the existing situation of the drainage system is quite poor and need to be redesign or reconstruct immediately. The hydraulic load of almost all the conduit is beyond the limit assigned. The hydraulic design of the most of the drainage conduit is inadequate and re-design of the drain is essential based upon accurate flow estimation methods. This study concludes that the applicability of the current drainage system is quite poor and needs to make certain changes with their construction immediately in order to avoid any danger and adverse effect possessed by surface flooding over the road surface and other paved surfaces. The surface runoff is significantly increased compared to the situation before the construction of existing drainage system and therefore for the appropriate storm water management of the urban area of Nepal, it is critical to design the drainage system based on both hydrological and hydraulic analyses considering reliable data.

Effects of bottleneck blockage on the resilience of an urban stormwater drainage system

ABSTRACTSevere urban floods have frequently caused social and financial infrastructure problems due to a lack of hydraulic capacity of urban drainage systems or the structural failure of network elements. Conventional, reliability-based design methods of drainage networks only provide acceptable performance under expected conditions of loading. In this study, a new approach based on resilience is proposed for the rehabilitation of urban drainage systems; this approach is able to maintain a predefined service level under both external and unexpected internal loads, including different scenarios of blockage and a severe rainfall event. The performance of different design methods: resilient, non-resilient, deterministic and uncertain models, is comprehensively compared and the most appropriate approaches are introduced. The results show that the new resilient approach outperforms conventional design/rehabilitation methods in terms of flood volume reduction. Additionally, the single blockage scheme and the Poisson distribution-based model show the best performance to enhance the resilience of the network.

Infiltration Rate of Pervious Concrete on Street Curb Application

The street curb and stormwater inlets are among the component often found on the road which serve as part of the urban stormwater drainage system. They act as a stormwater removal and discharge it into the underground drainage system. However, the current stormwater inlet practiced in Malaysia has limitations which often cause water ponding and consequently lead to road flooding. Rather than improving the performance of stormwater inlet, the flow interception and rate of stormwater removal may be enhanced by introducing a new technology called the pervious curb. It isto be made of pervious concrete which provide an ability to allow water to pass through it.This paper attempts to adapt the existingtwo pervious concrete mix design and applied it into the so-called pervious curb. Herein, a newly designed infiltration rate test was used to test the pervious concrete performance under the effect of infiltration through side surface of the concrete curb. While doing so, the infiltration rate of the pervious concrete will be investigated under varying slopes. Results showed that the infiltration rate is quite high and the rate of infiltration increases as the inclination gutter increases. Thus, it is proven that the new infiltration rate test is applicable and can be used for other similar applications. Furthermore, the test has significantly revealed that the pervious concrete has high potential in enhancing flow interception and able to reduce water ponding as a street curb.

Flooding Control and Hydro-Energy Assessment for Urban Stormwater Drainage Systems under Climate Change: Framework Development and Case Study

Flooding issue and energy shortage have become the common concerns impeding the urban development under climate change scenarios. Exploiting potential hydro-energy from urban stormwater drainage system (USDS) has multiple beneficial perspectives for controlling flooding, relieving energy shortage and mitigating the greenhouse gases emission, which has not yet been systematically investigated in previous works. In this paper, a systematical analysis framework is developed to design the flooding risk control measures and to assess the feasibility and capacity of the hydro-energy development in USDS. The GCMs and HBV models, integrated within the SWMM computation platform, are adopted to simulate the hydrological and hydraulic processes during rainfall events, with the results used to manage the flooding situation and evaluate the energy generation capacity under the influences of both historical and future climate changes. The framework is then applied to a practical case in Tung Chung town of Hong Kong. The analysis result shows that, in the studied area, it is significant and worthwhile to develop the hydro-energy in USDS, which is evidenced to be beneficial to the energy generation and the flooding risk control as well as water resources management in the urban drainage system. The developed method and obtained results of this study may provide a new perspective and technical guide for effective USDS management and operation.

Hydrodynamic simulation of urban stormwater drain (Delhi city, India) using iRIC Model

Flooding in urban areas takes place mainly due to increased urbanization, decrease in infiltration rate and poor infrastructure for stormwater drainage network. Nays2DFlood is a recently developed solver by iRIC for the simulation of river flow regime. The number of input data requirement is few which makes this solver superior to other models but has been rarely applied to urban catchments. In this paper, a hydrodynamic model was developed to assess the model’s feasibility to simulate urban stormwater drainage system of Delhi, capital city of India for mapping inundation extents using Nays2DFlood solver. The data used in this model is a DEM (5 × 5 m resolution) and daily discharge data of the drains. The simulated drainage is analysed keeping in mind the constraints which were observed during the collection of field data; the storm-water drains are choked, the drains have improper flow gradient or damaged flow gradients. Based on the simulated results, the water depth and velocity profiles were analysed for the drain. The model identified four critical locations where the problem like zig-zag bed slope of the drain, undersized cross-section of the drain and last but not the least the backflow problem which were in close agreement with the observed field data. The flood propagation exactly predicting the inundated area. Thus, Nays2DFlood solver model can also be applied to urban catchments for identifying the flood extent.