Stormwater Drainage Research Articles

Evaluating the Capacity of Existing Stormwater Drainage System in Kapan, Kathmandu via SWMM Mode

Overflowing drainage systems in the Nepalese cities are the most significant issue due to unplanned urban expansion and inadequate drainage networks. As the city's drainage networks are not designed to handle the extra runoff from catastrophic flooding incidents, flash floods typically occur during short-duration, and high-intensity rainstorm storms frequently. In the vicinity of Kapan, Kathmandu, and many other Nepalese cities, particularly during the rainy season, roads are seen changing into the streams. This study employs a hydrological analysis model to examine the storm water drainage system existing currently in the Kapan area. Being the EPA Storm Water Management Model (SWMM) physically based, deterministic type that simulates the inflows, outflows, and storages of water within a sub-catchment efficiently, it is chosen here mainly to model the catchments specifically. Though it has not been employed frequently in the context of Nepal, despite its popularity in the industrialized countries such as United States of America for the proper management of the storm water, the SWMM is particularly employed here to model the catchments due to its publicly available, easy to obtain, simple data input parameters, and simple processing steps in compared to other relatively more expensive yet sophisticated models. The catchment's overall area of 360.57 hectares was at first separated into the 86 sub catchments using the SWMM based on its surface elevation and existing drainage network, and the attributes of each sub-catchment were then assigned accordingly. After the proper identification of the sub-catchments, the runoff from the relevant sub-catchments was routed to the respective nodes, and finally to the outlet via conduits. In the current study, the drain system (Combined Sewer line) is given along the center of the road network. The storm network are represented by junctions, conduits, and outfalls. The longitudinal and velocity profiles of the drain were obtained. The critical runoff and capacity of existing drains were determined, as well as their validation with discharge derived using the rational technique. With the runoff generated during peak rainfall 45.08 mm/hr., the Kapan area's existing drainage system was found to be insufficient. This study suggests that the SWMM would be the most effective model to be employed for predicting the sudden surface runoff and for prior managing of the storm water, particularly in Kathmandu and other vulnerable parts of main cities in Nepal, where overflow has caused serious problems during rainfall.

Conservation of Rain Water in Urban Area Using Ground Water Recharge

Abstract: Water scarcity is serious problem throughout the world for both urban & rural community. As the world population increases, the demand increases for quality drinking water. Urbanization, industrial development & increase in agricultural field & production has resulted in overexploitation of groundwater & surface water resources and resultant deterioration in water quality. The conventional water sources namely well, river and reservoirs, etc. are inadequate to fulfill water demand due to unbalanced rainfall. . Surface andgroundwater resources are being utilized faster than they can be recharged. Rainwater harvesting (RWH) is an option that has been adopted in many areas of the world where conventional water supply systems have failed to meet people’s needs.It is a technique that has been used since antiquity. It is an environmentally sound solution to address issues brought forth by large projects utilizing centralized water management approaches. Water harvesting is the activity of direct collection of rainwater, which can be stored for direct use or can be recharged into the groundwater. Water harvesting is the collection of runoff for productive purposes. According to Kim et al. (2005), rainwater harvesting may be one of the best methods available to recovering the natural hydrologic cycle and enabling urban development to become sustainable. The harvesting of rainwater has the potential to assist in alleviating pressures on current water supplies and storm water drainage systems. Rainwater collection has the potential to impact many people in the world. As water harvesting is an ancient tradition and has been used for millennia in most dry lands of the world, many different techniques have been developed the aim of the present study is to use rainwater andthus taking close to the concept of nature conservation. In this study, the rain water harvesting (RWH) system is analyzed as an alternative source of water in Gwalior Town in the state of Madhya Pradesh, India and the results were elated. By our calculation we have come to the conclusion that 108 days water can be stored for the entire city by the means of rain water harvesting method and that too only if we assume that only 70% of the water is being stored and remaining 30% of the water is getting wasted in the form of runoff. Even though, after this we are able to get 108 days of water for the entire city.

Experimental Study &Analysis of Polypropylene Fiber Reinforced Pervious Concrete

Abstract: At many projects water logging at parking and walkways is the major issue especially during monsoon as pavements and floors are normally impermeable. This results inconsiderable amount of investment in repairs and providing storm water drain systems, which may get clogged during peak over flow. Besides this there are many other problems that arise due to the above. In such situations it is very important to think about an economical solution which helps in getting rid of all above problems. The best solution to above problem is pervious concrete. When we used the polypropylene fiber in pervious concrete in various proportions 0.05%, 0.1%, 0.15%, 0.2%, 0.25% and 0.3% of volume of concrete the optimum result obtained for compressive strength at 0.2% of Polypropylene fiber. This paper discuss the art of pervious concrete; materials and possible mix proportions, properties such as compressive strength, flexural strength, shrinkage ,permeability with initial tests done at Innovation & Application and the principal advantages , major disadvantages and principal applications

Designing Stormwater Drainage Network for Urban Flood Mitigation using SWMM: A Case Study on Dhaka City of Bangladesh

Designing Stormwater Drainage Network for Urban Flood Mitigation using SWMM: A Case Study on Dhaka City of Bangladesh

Assessment of the drainage systems performance in response to future scenarios and flood mitigation measures using stormwater management model

Urban Flooding represents a significant problem in developing urban areas caused by inadequate stormwater drainage systems, increased impervious surface areas, and climate change. The performance of drainage systems can be evaluated using simulation models such as the stormwater management simulation model (SWMM). In this study, the potential impacts of future design rainfall on the performance of stormwater management systems were assessed by altering a hyetograph derived from rainfall intensity duration curves from three climate models. In addition, the effects of continued urbanization on the systems have been simulated by changing the percentage of imperviousness from current land use conditions. According to the findings, existing drainage systems cannot manage the expected flooding risks caused by a slight change in future rainfall intensity under each climate model. As a result of urban development, increasing the imperviousness ratio from 10% to 70% has increased peak runoff from 51.3 to 82.4 m3/s, flooding volume amplified from 24,320.5 x103 to 33,647.4 x103 m3 (representing 38.4% of the increase), and flooded nodes risen from 64 to 196 (representing 67.12% of raise). Overall, flooding locations and magnitude were identified, while drainage systems failed to safely convey surface runoff at baseline conditions, implying that future flooding will be more intense. As a result, selected mitigation strategies should be considered to alleviate the flooding risks that disrupt the socio-economic environment and the resulting significant property and life losses in Dodola, Ethiopia.

Sources of contamination in sediments of retention tanks and the influence of precipitation type on the size of pollution load

Densification of cities and urban population contributes to increased runoff and suspended solids and alteration of the urban water cycle. Nowadays, Blue-Green Infrastructure is promoted to increase a city’s resilience to floods; however, stormwater drainage systems, supported with retention tanks are still important in protecting urban areas against floods. Sediment accumulation in stormwater infrastructure relates to an issue of pollutants such as heavy metals, nutrients etc. Research on the origin of the pollutants associated with the suspension and ultimately sediment accumulated in sewage can bring new insights about processes in urban catchment areas. This is the first study, which is focused on the analysis of stable carbon and nitrogen isotopes in bottom sediments collected from municipal retention tanks to verify the origin of the deposited pollutants immediately after pluvial floods. The research was additionally extended with water quality analyzes immediately after three types of weather: a dry period, typical precipitation (< 30 mm) and torrential rainfalls (2 events with daily precipitation over 30 mm which caused pluvial flooding of the city area). Analyses of sediments indicated that the main source of carbon and nitrogen in the bottom of the retention tanks had been brought with stormwater runoff from the city area. Organic nitrogen fertilizers appeared to be the main source of nitrogen, while the sources of organic carbon were mixed: C3 land plants, wood, and oil. Additionally, it was found that torrential rainfall caused a 23-fold increase of N-NO3 concentration, a sevenfold increase of P-PO4 concentration, and an over fivefold increase of concentration of organic matter, in comparison to typical precipitation.

Analysis of (G+3) Hostel Building

Abstract: The principal objective of this project is the comparative study on design and analysis of hostel building (G+3) of area 2050 sqm, by AUTOCAD, STAAD.Pro and ETABS software’s. Our project deals with the plan and style of Hostel Building. Designing involves identifying the forces and stresses which arise within that structure, perform analysis to urge moments and shear forces on different elements of the structure then design the structure for ultimate loads, dead load, wind load, live load, earthquake load (Indian Earthquake zone 3) and moments etc. AUTOCAD, ETABS and STAAD.Pro may be softwares tool to style functional design of plan. Estimation includes finding the quantities of materials required for the development of the structure and requirements of labour etc. During this project work, an effort is formed consistent with Building by laws and style of hostel building as per is: IS-456-2000, IS-1200 and SSR. The layout planning may be a part of urban development it includes planning of hostel houses, commercial complexes, service roads, primary health centers, school...&amp; other amenities sewerage system for whole layout (includes treatment, sewer main, storm water drains), water distribution system. This article includes design &amp; estimation of hostel building in plot of layout planned.

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.

Prediction of Future Urban Rainfall and Waterlogging Scenarios Based on CMIP6: A Case Study of Beijing Urban Area

Extreme weather events will become more frequent and severe as a result of climate change, necessitating an immediate need for cities to adapt to future climate change. Therefore, the prediction of future precipitation and waterlogging is of utmost importance. Using Beijing as an example, the simulation capability of different models was evaluated, and the optimal model for the study area was screened using Taylor diagrams and interannual variability scores, along with actual monthly precipitation data from Chinese weather stations from 1994 to 2014 and historical monthly precipitation data from 10 coupled models from Coupled Model Intercomparison Project Phase 6 (CMIP6). The SWMM model was then used to simulate future rainfall and waterlogging scenarios for the study area using precipitation forecast data for 2020–2050 from the best model to investigate the impact of climate change on future rainfall and waterlogging in urban areas. CMIP6 brings together the most recent simulation data from major climate models on a global scale, providing a broader and more diverse range of model results and thereby making future predictions more accurate and dependable, and its findings provide a theoretical foundation for the emergency management of and scientific responses to urban flooding events. The following major conclusions were reached: 1. The best-performing models are EC-Earth3, GFDL-ESM4, and MPI- ESM1-2-HR. EC-Earth3 is a modular Earth system model developed collaboratively by a European consortium. MPI-ESM1-2 is a climate precipitation prediction model developed in Germany and promoted for global application, whereas the GFDL-ESM4 model was developed in the United States and is currently employed for global climate precipitation simulations. 2. Under future climate circumstances, the total annual precipitation in the example region simulated by all three models increases by a maximum of 40%. 3. Under future climatic conditions, urban surface runoff and nodal overflow in the study area will be more significant. The node overflow will become more severe with the increase in climate scenario oppression, and the potential overflow nodes will account for 1.5%, 2.7%, and 2.9% of the total number of nodes under the SSP1–2.6, SSP2–4.5, and SSP5–8.5 scenarios, respectively. 4. In the future, the effectiveness of stormwater drainage systems may diminish. To increase climate change resilience, the impacts of climate change should be considered when planning the scope of stormwater optimization and the integrated improvement of gray–green–blue facilities.

ENVIRONMENTAL POLLUTANTS OF THE RAINWATER DRAINAGE SYSTEM OF MYKOLAIV

The article is devoted to the study of the chemical composition and quantitative volume of pollutants entering the Bug Estuary with the rainwater sewage of Mykolaiv. It is known that sewage from industrial and municipal enterprises poses a threat of a significant additional burden on limited regional water resources. First and foremost, uncontrolled stormwater runoff is a major concern. In Mykolaiv, there are 49 registered stormwater drains, of which 19 are directly discharged into open water bodies. The purpose of the study was to investigate the chemical composition and volume of urban stormwater runoff into the Bug Estuary. The study was based on the results of chemical analyses of water samples from four storm sewers in Mykolaiv, performed in 2022. The materials of chemical analyses of water samples from five storm sewers of Mykolaiv in 1997 were also included. It was proved that phosphates, oil products, and nitrite nitrogen are present in the stormwater runoff from Mykolaiv to the Bug Estuary. The multiplicity of exceedances of the maximum permissible concentrations is: for biological oxygen consumption - 14-37 times; nitrite - 10-39 times; chemical oxygen consumption - 7-18 times. It has been shown that lead, nickel, iron, copper, chromium, and zinc are released into the Bug estuary with rainwater runoff. Excessive pollution of rainwater with suspended solids is associated with contamination of territories with dust, soil, clay, etc. Excessive pollution with oil products and heavy metals is associated with the operation of motor vehicles and industrial enterprises. It has been shown that unauthorized connections of domestic and industrial sewage systems are mostly responsible for some of the substances that pollute stormwater (phosphates, nitrates). Prospects for further research are the study of the sorption capacity of bottom sediments for the retention of pollutants and the assessment of the ecological capacity of the bottom sediments of the Bug estuary..

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.

Microplastics and microorganisms in sediments from stormwater drain system

Research has already confirmed the occurrence of microplastics (MPs) in sediments of stormwater drain system (SDS). However, the microplastic pollution remains to be elucidated well in sediments, especially the spatio-temporal distribution and the impacts of MPs on microorganisms. In this study, the averaged abundance of MPs in SDS sediments was 479 ± 688 items·kg−1 for spring, 257 ± 93 items·kg−1 for summer, 306 ± 227 items·kg−1 for autumn and 652 ± 413 items·kg−1 for winter. As expected, the abundance of MPs was the lowest in summer due to runoff scouring, while the highest in winter attributed to infrequent low-intensity rainfall. The major polymers of MPs were polyethylene terephthalate and polypropylene plastics, occupying 76 % to 98 % of the total number. Fiber MPs were the most regardless of season (41 % to 58 %). MPs with size of 250–1000 μm accounted for over 50 %, which is in accordance with the previous study that MPs of <1000 μm were the major. High-throughput sequencing of analysis shows that MPs provided an ecological niche for bacterial communities different from that of SDS sediments. Actinomycetes and bacteria with chemoheterotrophic genes tended to be enriched on the surfaces of MPs. In addition, Acidobacteria and bacteria with nitrification genes would not like to present in microplastisphere. A strong positive correlation (R from 0.74 to 0.83, P < 0.01) was found between the abundance of MPs in sediments and the abundance of functional genes for denitrification and nitrogen respiration of microorganisms on the surfaces of MPs. It indicates that MPs may influence the nitrogen transformation processes in SDS sediments via the occurrence of denitrification processes on the surfaces of MPs. The abundance of MPs had no significant relationship with the various functional genes of microorganisms in the sediments (P > 0.05), which means that MPs could not profoundly influence the expression of microbial functional genes in SDS sediments.

The effects of unplanned land use and heavy seasonal rainfall on the storm-water drainage in Dhaka metropolitan city of Bangladesh

ABSTRACT The capital city of Bangladesh, Dhaka, faces several challenges including significant rainwater congestion. With the holistic depiction of the current status, this study quantified rainfall, estimated land cover change and analyzed the drainage system in the western part of Dhaka. Statistical analysis and logarithmic graph fitting methods were used to develop a strong correlation between short-duration and daily rainfall. Land cover maps from 1990 to 2020 were generated using supervised classification in ERDAS IMAGINE, and the future land cover was predicted using the Terrset software with the CA Markov method. This research found that the build-up region increased by about 70% during the last 30 years while about 15.64 km2 of wetland was encroached during the past 15 years leading to the failure of existing drainage network. The assessment of rainfall demonstrated that the extreme events aggravated the issue. Restoration of natural canals is required for activating proper drainage system in the city.

Derivation of short-term design rainfall intensity from daily rainfall data for urban drainage design using empirical equations in robe town, Ethiopia

Flooding is a significant impact that regularly affects the majority of cities/towns in developing countries due to inadequate drainage systems that were designed without considering hydrological-hydraulic efficiency caused by design rainfall intensity. Design rainfall intensity is essential to urban stormwater management systems; however, obtaining long-term, short-term design rainfall in developing countries such as Ethiopia is challenging. As a result, this study is conducted to derive short-term design rainfall intensity from daily rainfall data for Robe town using three empirical equations for urban drainage design: Indian Meteorological Method (IMD), Modified Indian Meteorological Method (MIMD), and Ethiopian Road Authority Method (ERAM). The results show that the estimated design rainfall by IMD is greater than other methods; the relationship between IMD, MIMD, ERAM, and existing ranges from 0.57 to 1.001, 1.015 to 1.218, and 0.890 to 1.027, respectively. According to the findings of this study, the design rainfall intensity of all empirical equations is not the same in all return periods and durations. Furthermore, the peak stormwater that caused flooding will vary due to variations in rainfall intensity. Thus, this study strongly suggested that the experts consider each empirical equation and select the accurate design rainfall to design adequate stormwater drainage systems for Robe Town. To manage unexpected urban inundation caused by urban development, short-duration design rainfall and other sub-catchment characteristics will need to be considered.

Space and Functional Efficiency for Waterfront Architecture: Ibom Power Company Housing Estate, Ikot Abasi, Akwa Ibom State, Nigeria

Purpose: This paper seeks to demonstrate the technical, structural, professional, legal, ethical, and financial setup involved in designing Ibom Power company housing estate within the waterfront of the Qua river estuary in Ikot Abasi Local Government Area of Akwa Ibom State.&#x0D; Methodology: Field observation/measurement, base map, site analysis and weather analysis were employed to generate data for the study. The qualitative study approach was further used to highlight the specific innovations brought into the design to overcome the spatial impediment posed by the waterfront and guarantee space and functional efficiency for the housing estate.&#x0D; Findings: Findings showed that space and functional efficiency can be achieved by adopting common design elements for managing site shape and topography to foster storm water drainage as well as providing well landscaped open spaces and&#x0D; Recommendations: Based on these findings, Architects and other allied professionals are encouraged to be flexible, innovative and creative while adopting common design elements for enhancing space and functional efficiency for waterfront development.&#x0D;

Effects of Air Void Content, Crumb Rubber, and Pozzolanic Fillers on OGFC Laboratory Performance

Open-graded friction course (OGFC) is recognized for its ability for rapid stormwater drainage and effective noise reduction. Yet, several state highway agencies have limited its use because of concerns about its durability. The objective of this study was to investigate the impacts of air void (AV) reduction, crumb rubber (CR), and pozzolanic fillers on OGFC durability. Six mixtures were fabricated in the laboratory and their performance was evaluated. A control mix, 9.5-NMAS mix, two mixes incorporating CR, and two mixes prepared with pozzolanic fillers (i.e., Portland cement and fly ash) were evaluated. The test factorial was designed so that each mix would be evaluated at three different stages (i.e., production, construction, and field performance). A suite of laboratory tests was conducted including draindown, prediction of compaction effort, Cantabro abrasion loss, Hamburg wheel-tracking, Texas overlay tester, modified Lottman test, and boiling test to evaluate production, compaction, and OGFC resistance to raveling, permanent deformation, cracking, and moisture damage. Results showed that the reduction in AV and the use of CR and pozzolanic fillers considerably enhanced OGFC durability while maintaining appropriate functional performance (i.e., permeability).

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.

Two-dimensional (2D) flood analysis and calibration of stormwater drainage systems using geographic information systems.

In recent years, there has been severe flooding in urban areas as well as coastal and river flooding. Urban flooding is exacerbated by climate change, urbanization, growing population, and the increase of impervious surfaces in urban areas. Stormwater drainage systems that discharge stormwater to a safe location in urban areas are becoming increasingly important. The objective of this study is to analyze and calibrate the flood performance of stormwater drainage systems currently used in the central region of Malatya in a potential flood situation using geographic information systems and the InfoWorks ICM. The model was created using the land use type, buildings, and digital elevation model (DEM), and the analysis was performed by exposing stormwater drainage systems to rainfall events of 5, 10, and 15 min of duration for return periods of 2, 5, and 10 years. The model was then validated using field-observed rainfall and flood data and its performance was evaluated using R2, NSE, RMSE, and MAE metrics. The results showed that the eight stormwater drainage systems currently in operation cannot fully convey stormwater and may pose a risk of loss of life and property in residential areas. In addition, the severity of the flooding was found to increase with an increasing return period.

Investigating the Relationship between the Manning Coefficients (n) of a Perforated Subsurface Stormwater Drainage Pipe and the Hydraulic Parameters

Subsurface perforated pipes drain infiltrated stormwater runoff while attenuating the peak flow. The Manning roughness coefficient (n) was identified as a fundamental parameter for estimating roughness in various subsurface channels. Hence, in this work, the performance of a six-row non-staggered sand-slot perforated pipe as a sample of the subsurface drainage is investigated experimentally in a laboratory flume at Universiti Sains Malaysia (USM) aimed at determining the Manning roughness coefficients (n) of the pipe and assessing the relationship between the Manning’s n and the hydraulic parameters of the simulated runoff flow under the conditions of the tailgate channel being opened fully (GFO) and partially (GPO), as well as the pipe having longitudinal slopes of 1:750 and 1:1000. Water is pumped into the flume at a maximum discharge rate of 35 L/s, and the velocity and depth of the flow are measured at nine points along the inner parts of the pipe. Based on the calculated Reynolds numbers ranging from 38,252 to 64,801 for both GFO and GPO conditions, it is determined that most of the flow in the perforated pipe is turbulent, and the calculated flow discharges and velocities from the outlets under GFO are higher than the flow and velocity rates under GPO with similar pipe slopes of 1:750 and 1:1000. The Manning coefficients are calculated at nine points along the pipe and range from 0.004 to 0.009. Based on the ranges of the calculated Manning’s n, an inverse linear relationships between the Manning coefficients and the flow velocity under GFO and GPO conditions are observed with the R2 of 0.975 and 0.966, as well as 0.819 and 0.992 resulting from predicting the values of flow velocities with the equations v = ((0.01440 − n)/0.009175), v = ((0.01330 − n)/0.00890), v = ((0.02007 − n)/0.01814), and v = ((0.01702 − n)/0.01456) with pipe slopes of 1:750 and 1:1000, respectively. It is concluded that since the roughness coefficient (Manning’s n) of the pipe increases, it is able to reduce the flow velocity in the pipe, resulting in a lower peak of flow and the ability to control the quantity of storm water in the subsurface urban drainages.

A planning framework to mitigate localized urban stormwater inlet flooding using distributed Green Stormwater Infrastructure at an urban scale: Case study of Dallas, Texas

Mitigation of localized pluvial flooding is one of the major resiliency goals in urban environments, and Green Stormwater Infrastructure (GSI) has the potential to deliver such an outcome. However, there is a lack of systematic approaches to prioritize investment in different candidate areas. This study provides a framework to identify vulnerable stormwater drainage inlets and their contributing areas, prioritize them, identify dominant factors in their selection, assess the potential of GSI in mitigating their overflows, and compare the impact and its cost to gray infrastructure upgrade alternatives. Using SWMM 5.1.013, decision trees, and a volumetric-based assessment of GSI overflow capture, we applied the framework to the City of Dallas, Texas, for three design storms with three GSI practices— bioretention cells, raingardens, and rainwater harvesting tanks. Results showed that there was a significant increase in the number of overflowing stormwater drainage inlets, referred to as hotspots, and their contributing subwatersheds, referred to as opportunity areas, with more intense storms especially in problematic watersheds. Also, prioritization results provided a series of maps to rank the opportunity areas based on overflow severity, recurrence of the overflows, and GSI availability. Moreover, classification results showed that inlet features, especially the inlet depth, were the dominant factors in the identification of the non-problematic inlets. Finally, the GSI impact assessment showed substantial overflow mitigation even at the “very high” severity levels when GSI is comprehensively deployed across opportunity areas. Despite gray infrastructure upgrades yielding higher reduction levels, their cost per cubic meter was higher than GSI. Therefore, a combination of GSI and gray results in maximum overflow reduction at a lower cost compared to common practices.