Urban Drainage Infrastructure Research Articles

Sustainable Rainwater Management With the Use of Compensatory Urban Drainage Techniques: Case Study on The Maracanã Campus of the University of the State of Rio De Janeiro (UERJ)

Objective: The objective of this study is to evaluate the hydrological impact of using different compensatory techniques on the conventional urban drainage system in an intramural contribution basin to the Maracanã Campus of the State University of Rio de Janeiro (UERJ), located in the Maracanã neighborhood, in the city from Rio de Janeiro-RJ. Theoretical Framework: A bibliographical review was prepared with an approach to the urbanization process associated with urban drainage infrastructures, as well as the use of compensatory techniques to control urban flooding. Method: Rainfall and hydrological data, demand and consumption of non-potable water in the building, sizing of the microdrainage network and compensatory techniques and calculation of the runoff buffered by the techniques were obtained. Results and Discussion: The results obtained revealed that the hydrological impact of using compensatory techniques designed on the drainage network designed in the Maracanã Campus basin, which discharges a flow of 2,041.66 Lts/s, would have a reduction in the flow of around 19%, using only around 14% of the Campus area is a contribution area for techniques. Research Implications: The research brings a scientific contribution based on the analysis of the implementation of compensatory techniques on the microdrainage network as an alternative to be evaluated by municipal managers as a solution to be integrated into the infrastructure development of cities, in order to make them more resilient in terms of to intense rainfall events. Originality/Value: The study showed, based on the results obtained, the efficiency in the use of compensatory urban drainage techniques, with discussion in the scientific community to develop further studies in the context of water resources management.

An innovative diffusion-theory based assessment of inherent barriers in urban green drainage infrastructure systems

ABSTRACT Conventional urban drainage infrastructure is gradually failing to attain sustainable development goals. Effective techniques for adapting to climate change at the city level include the use of urban green drainage infrastructure (UGDI). This study aims to assess the inherent barriers to UGDI in Ghana. Primary data was gathered from 62 built environment professionals. Analytical tools included a component factor analysis and mean score ranking. A factor analysis revealed four components explaining 67.967% of the total variance in the barriers to UGDI. Lack of knowledge, information and awareness of UGDI was ranked as the most critical implementation barrier. It is recommended that the adoption of UGDI evolves from being an alternative to a “necessity” given that its significance is evident in the current climatic change crises. This is a novel attempt to expose the inherent barriers of UGDI systems in Ghana through the innovation diffusion theory.

Management of the designed risk level of urban drainage system in the future: Evidence from haining city, China

The design of urban drainage infrastructure is mainly based on historical conditions. Under global warming, more intense precipitation extremes will pose severe risk to current infrastructure. The evaluation of where and by how much design standards need to change, is urgently needed to help maintain well-functioning drainage systems. In this study, we used climate projections from the Coupled Model Intercomparison Project Phase 6 (CMIP6) and InfoWorks Integrated Catchment Modeling (ICM) to simulate urban flooding. According to the latest design standard of urban drainage infrastructure, we assess the risk of future urban flooding, and evaluate the effect and benefit of drainage infrastructure adaptation measures. The results showed that, under the shared socioeconomic pathway (SSP) 5–8.5 scenario, a 35% increase in extreme rainfall would be expected. Under a 1-in-30-year precipitation event, the maximum depth would increase by 5.59%, and the withdrawal time would rise by 2.94% in the future period, relative to the baseline level. After the enlargement of drainage infrastructure in local areas, 10% pipe enlargement has a better effect to reduce risk and higher benefits than 5% pipe enlargement. These findings provide valuable insights for policymakers in enhancing the drainage system and adapting to climate change.

A novel safe-fail framework for the design of urban stormwater drainage infrastructures with minimal failure and flood severity

The urban stormwater drainage structures (SDSs) are conventionally designed for their failure recurrences rather than addressing the consequences of the failures. Various methods that consider the effects of flooding in SDSs design largely rely on the overflow volume and do not consider actual inundation characteristics due to computational challenges. Hence, advanced methods are required to design SDSs while incorporating flood consequences. We introduce a novel method called the 'safe-fail framework' for designing SDSs, which determines the best design solutions that minimize flood consequences with computational efficiency. The safe-fail framework involves event-based simulations of urban flood inundation properties, iteratively to evaluate the flood consequences until the design return period satisfies the safe-fail criteria with acceptable failure consequences. We demonstrate the approach in an urban catchment in Chennai, India, by estimating the optimal design return periods of the SDSs to minimize the flood consequences. A structure-variable approach that reduces the complexities of multivariate problems to univariate to identify flood-causing extreme rainfall events was explored. We show that 12 conduits (among 30) in the catchment require design return periods ranging between 3 and 6 years (vis-a-vis initial 2 years) to achieve the safe-fail condition, evaluated through a newly developed Flood Severity Index. The results reiterate the inappropriateness of using a common design return period across the catchment due to the varying sensitivity of locations to flood flows. The safe-fail framework can potentially improve the SDSs design criteria while accounting for urban flood properties and deriving improved urban water resources management decisions.

Prioritization of the key underlying sustainability indicators of urban green drainage infrastructure systems

ABSTRACT Assessments of urban green drainage infrastructure (UGDI) have always been a headache in contemporary times which is a roadblock to enticing investors. This study prioritized the underlying sustainability indicators of UGDI systems in Ghana. After an exhaustive literature review, some identified sustainability indicators were compounded into semi-structured questionnaires. Sixty-two built environment professionals were asked to rate the significance of each indicator. A parametric test was used to prioritize the indicators. The results indicated that the most significant underlying sustainability indicators were; ‘Flood control’, ‘Compliance with sustainable development goals’, ‘multi-functionality’, ‘energy efficiency and GHG emissions’ and ‘Initial Construction Cost’. To understand how UGDI performs with regards to flood and pollution mitigation, specific geographical performance indicators are required. This is an under-explored area in the Ghanaian context. Hence, the indicators espoused in this study serve as a starting point for the development of appropriate frameworks to aid the implementation of UGDI.

Climate Change Flood Risk Analysis: Application of Dynamical Downscaling and Hydrological Modeling

Floods are a recurring natural phenomenon during the rainy season in many Brazilian municipalities. Nevertheless, shifts in weather patterns have contributed to an increased incidence of these events in urban areas, where their impact can be amplified by the way the surrounding catchment is occupied. Hence, the present study sought to evaluate the susceptibility of the urban drainage infrastructure in João Monlevade, Brazil, to the effects of climate change by undertaking a comprehensive assessment of the Carneirinhos catchment, including its morphometric characteristics. For this purpose, we employed a hydrological model driven by regional rainfall projections from a high-resolution climate model (HadGEM2-ES downscaled to 5 km resolution) under the Representative Concentration Pathways (RCP8.5) scenario. Several combinations of rainfall occurrence were simulated, incorporating temporal aspects (different durations and return times), as well as spatial aspects (concentrated and distributed rainfall within the catchment). The results showed that the area of exposed soil in the Carneirinhos catchment experienced an increase of more than 140% from 2016 to 2019, favoring runoff surface and evaporation, which contributed to the increase in the number of flood events in the region. In addition, only 1 of the 56 heavy rainfall event simulations performed did not exceed the capacity of the macro drainage gallery.

A study of 101 organic substances in gully pot sediments accumulated over a one-year period in Stockholm, Sweden

Stormwater runoff is a key pathway for diffuse pollutants to enter receiving waters. Mitigating measures include pollutant substitution, restricting their release into the urban technosphere and limiting the (re-)mobilisation of substances to minimise their negative impacts on receiving waters. Gully pots (GPs) are one of the most ubiquitous urban drainage infrastructure components, providing both a drainage function and limiting the onward transport of pollutants through in-pot sedimentation processes. In this study, sediments accumulated over a one-year period were collected from 26 GPs in catchments of four land-use types in Stockholm, Sweden. Sediments were analysed for 101 organic substances from eight substance groups (hydrocarbons, polycyclic aromatic hydrocarbons, alkylphenols, polychlorinated biphenyls, phthalates, organotins, per- and polyfluoroalkyl substances and brominated fire retardants) to inform an assessment of their occurrence and net accumulation rates over a typical unit operation period. A total of 63 substances were quantified in at least one GP, with aliphatic hydrocarbons, phthalates and organotins quantified in all GP sediments, highlighting their ubiquitous use. The identification of 14 and 21 organic substances in two pedestrian/bike path GPs emphasise the contribution of non-vehicular sources to diffuse pollutant loads. Significantly higher mass accumulation rates of 4-tert-octylphenol, 4-nonylphenols, formaldehyde, dioctyltin and dibutyltin are identified in commercial catchment GPs suggesting the need to enhance source-tracing and runoff quality-control measures within catchments of this land-use type. Sediments in 25 GPs were identified with at least one substance exceeding toxicology-based threshold values, highlighting the runoff quality-control function of GPs in reducing the potential ecotoxic impacts on recipients.

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.

The interface of disasters, sanitation, and poverty in Brazil: a sociological perspective

In Brazil, the high frequency and types of disasters are symptoms of misguided socioenvironmental public policies. While approximately 25% of municipalities decree emergency every year, over 75% of the occurrences are linked to sanitation issues. Such events range from the lack of urban drainage infrastructure to handle large volumes of rainwater to the insufficiency of backup water supply strategies during prolonged drought, both further impacting other precarious infrasystems such as solid waste management and sewage, with the most heavily and extensively affected group being the citizens facing poverty. Therefore, the issues of disaster, sanitation, and poverty are intertwined in Brazil. Using a network science approach, we investigate how the sociological debate is overcoming the fragmented approach about these subthemes and within the disciplinary fields in social sciences by analyzing the connections between the keywords of the open-access research articles from 2003 to 2022 from four databases. This mini review highlights the main contemporary axes between the themes, identifies the potential for tackling the gap at the interface, and clarifies the needs for future studies given the aims of the Sustainable Development Goals.

Urban Drainage: The Challenges and Failure Assessment Using AHP, Addis Ababa, Ethiopia

Urban drainage infrastructures are facing critical challenges due to a lack of integrated asset management, periodic maintenance, improper design, and construction methodologies. The objective of this study is to understand the urban drainage challenges and assess the failure causes and their impacts to recommend possible mitigation measures. Drainage failure causes and impacts are analyzed using the analytical hierarchy process (AHP) qualitative multicriteria decision model after conducting technical group discussions, interviews, and technical field surveys. The assessment was performed by taking representative samples from both cross- and longitudinal drainage infrastructures. The AHP analysis results showed that approximately 35.5% and 28.6% of failure causes are debris and various solid wastes for cross- and longitudinal drainage structures with correlation coefficients of 0.93 and 0.95, respectively. The result showed that design and construction defects are the second major failure causes. The research results showed that urbanization has a direct relationship with major drainage failure causes, resulting from man-made debris and solid waste clogging. On the other hand, drainage failure caused by siltation, drifts, and vegetation is higher in newly developing semi-urban and agricultural areas. The number of barrels in cross-drainage structures also contribute significantly to cross-drainage failure by creating a flow barrier due to the intermediate columns. The drainage failure impact assessment result showed that both cross- and longitudinal drainage failures primarily impact road pavement following transport disruption and traffic accidents, accounting for 38.5%, 18%, and 16%, respectively. Our research recommended that the mitigation measures for drainage failure are proper asset management and maintenance, appropriate construction supervision, and awareness creation, with weights of 36.3%, 15.5%, and 15.3%, respectively. As a drainage problem mitigation measure, the longitudinal drainage analysis results showed that the provision of a combination of cross-fall slopes, gutter slopes, and local depressions at the inlets can contribute to an increase in the trapping efficiency of the drainage system by 50%, which can reduce surface flooding substantially.

The Elephant and the Goddess: How Water Systems Models Could Help Preserve Civil Life

In this paper, the elephant in the room is the issue of projected longer-term population growths and declines in a finite world, while the Greek goddess Panacea is the opportunity to non-disruptively attain populations that live sustainably and solve some of the world’s most pressing problems. Particularly addressed in this paper is the potential of water systems models and modeling to facilitate a transition to planning for long-term sustainable lives of sustained quality. Anent “longer term”, for simplicity we consider both a typical period of family memory, for instance from 1880 to 2100, or 220 years, about seven or eight generations, as well as the anthropocene millenia. After setting down background definitions and introducing the underlying issues, we review key population and well-being trends, attitudes, and impacts, citing acknowledged experts. How, where, and when population and economic decline will occur is not covered; the paper rather suggests implications for water resources engineering and for water management modeling, even if the transition will be patchy in space and time. Confronting imminent degrowth, significant revisions of current water modeling practice are suggested: planned, phased, orderly removal of projected and existing urban development and drainage infrastructure and, for instance and where applicable, systematic restoration of keystone ecology and natural hydrology. Whether the imminent degrowth era will persist is uncertain, evidently. Also alluded to is degrowth’s countervailing assurance of improved well-being, providing more time for individuals to further their personal interests. The original PowerPoint presentation is at Robillynians.org and also at the CHI website (James 2023). Questions raised and the answers given at the presentation are included in the appendix to this paper.

Impacts of climate change on IDF curves for urban stormwater management systems design: the case of Dodola Town, Ethiopia.

Climate change impacts are one of the global challenges that change the intensity and frequency of rainfall. The Dodola town has previously experienced rainfall-induced flooding effects, and future floods may be more frequent and severe due to possible variations in rainfall intensity due to climate change. In this study, the rainfall intensity-duration-frequency (IDF) curves are updated for the design of urban stormwater drainage infrastructures under climate change to reduce flooding risks. To assess the variations in the rainfall intensity, the future IDF curves for the periods (2020-2100) and two GCMs (CanESM2 and HadGEM2-ES) were derived and compared to the current IDF curves. It was found that rainfall intensities for future climate conditions will differ from the current period for all durations and return periods. The comparison results show that the relative change between future rainfall intensities and historic rainfall ranges from 1.5 to 30.6%, 2.48 to 42.6%, and 3.7 to 23.24% for 2020-2040, 2041-2070, and 2071-2100, respectively. The IDF relationships revealed that as a result of climate change, urban flooding will increase in the future. This study will help to better understand the impacts of climate change on rainfall IDF relationships, as well as have implications for the design of current and future stormwater management systems in Dodola, Ethiopia.

Nitrogen loads in urban surface runoff from a major, cold-region North American city in 1991–2021

Long-term monitoring of pollutant loads in urban surface runoff is important but uncommon. In this study, we examined nitrogen loads in stormwater and snowmelt runoff from four urban catchments of a major, cold-region North American city over the past 31 years (1991–2021). Temporal variability of total organic nitrogen (TON), nitrate and nitrite nitrogen (NOx-N), total ammonia nitrogen (TAN), and total nitrogen (TN) were similar in the four catchments, which had an increasing trend from 1992 (TN: 1.3–3.4 kg/ha/year) to 2006–2011 (TN: 5.5–19.3 kg/ha/year) and a decreasing trend afterward. Trends and change points in the four urban catchments were influenced by storm/snowmelt events, land use, urban drainage infrastructure issues, and stormwater management facilities. The maximum monthly fluctuation occurred in March/April and July due to high variations of snowmelt and storm events. The ratios of monthly loads during the storm season (April to October) to the snow season (November to March) for TON, NOx-N, and TN were 1.31, 1.12, and 1.15, respectively; whereas it was 0.95 for TAN. TKN, TAN, and TN event mean concentrations (EMCs) in snowmelt were higher (18.0%, 94.0%, and 10.8%, respectively) than those in stormwater. However, the NOx-N EMC in snowmelt was lower (9.3%) than in stormwater.

A design framework for considering spatial equity in sustainable urban drainage infrastructure

• Traditional design methods may lead to inequity in water infrastructure services. • A trade-off between spatial equity and other goals may exist. • A multi-criteria design framework addressing spatial equity is proposed. The design of urban drainage systems has traditionally aimed for cost and service objectives without considering broader socio-economic implications of design decisions. This can result in designs with unequal distributions of infrastructure services among urban communities. In this paper, we propose a design approach for multi-criteria design of urban drainage systems which combines traditional design objectives, such as reliability and cost-effectiveness, with social goals like reducing inequality in the spatial distribution of infrastructure benefits. A multi-dimensional search algorithm is linked to an urban rainfall-runoff simulation model to identify portfolios of efficient (Pareto-optimal) and spatially equitable drainage infrastructure developments. A measure of the difference in flood damage between different subregions is also considered as a decision-making aide along with other criteria. An illustrative case study shows how the design framework can help planners make trade-offs, for example between spatial equity and cost-effectiveness, when selecting future interventions in urban water systems. The results imply that traditional optimisation models can lead to inequity in spatial distribution of urban drainage infrastructure services and that equality in spatial distribution of green drainage assets does not necessarily entail fair spatial distribution of flood damage between different urban neighbourhoods.

Sub-hourly resolution quality control of rain-gauge data significantly improves regional sub-daily return level estimates.

This research demonstrates how the use of high-resolution rain-gauge data for quality control (QC) significantly changes extreme rainfall estimates, with implications in scientific, meteorological and engineering applications. Current open QC algorithms only consider data at hourly or daily accumulations. Here we present the first open QC algorithm utilising sub-hourly rain-gauge data from official networks at a national, multi-decade scale. We use data from 1,301 rain-gauges in Great Britain (GB) to develop a threshold-based methodology for sub-hourly QC that can be used to complement existing, freely available hourly QC methods by developing an algorithm for sub-hourly QC that uses monthly thresholds for 1 hr, 15 min and 1 min rainfall totals. We then evaluated the effect of combining these QC procedures on rainfall distributions using graphical and statistical methods, with an emphasis on extreme value analysis. We demonstrate that the additional information in sub-hourly rainfall allows our new QC to remove spuriously large values undetected by existing methods which generate errors in extreme rainfall estimates. This results in statistically significant differences between extreme rainfall estimates for 15 min and 1 hr accumulations, with smaller differences found for 6 and 24 hr totals. We also find that extremes in the distributions of 15 min and 1 hr rainfall accumulations tend to grow more rapidly with return period than for longer accumulation periods. We observe similarities between the shape parameter populations for 15 min and 1 hr rainfall accumulations, suggesting that hourly records may be used to improve shape parameter estimates for extreme sub-hourly rainfall in GB. Sub-hourly QC moderates unrealistically large return level estimates for short-duration rainfall, with beneficial impacts on data required for the design of urban drainage infrastructure and the validation of high-resolution climate models.

A comparative study of the time of concentration methods for designing urban drainage infrastructure

Abstract The time of concentration (ToC) is an important parameter in rainfall−runoff simulation for designing and evaluating an urban drainage system (UDS). There are several lumped and distributed methods available in the literature for estimating the ToC. However, these methods lead to significantly varied values. Therefore, it is imperative to choose an appropriate and best-suited method for estimating the ToC. This study analyses eight lumped approach-based and two distributed approach-based methods for estimating the ToC in an urban area of Gurugram, a satellite city in the National Capital Region (NCR) of Delhi in India. Considering the ToC obtained by the Natural Resource Conservation Service (NRCS) method as the ‘true’ value, the Carter method among lumped methods and the SWDM method between the distributed methods results in ToC values in agreement with the NRCS method. Furthermore, to study the impact of the underestimation or overestimation of ToC on drainage, the system is evaluated in terms of variation in flood volume, duration, peak discharge, and the time to peak for different ToC values. The simulations were carried out by setting the model in SWMM, and it was found that flood volume increases by 4.25 times and the duration increases by 7.25 times if the ToC is increased from 0.1 to 6.14 h. The results infer that ToC estimation methods significantly impact the design and performance of an urban drainage infrastructure.

Application of weather research and forecasting (WRF) model in evaluating depth–duration–frequency estimates under a future climate scenario

Abstract Point precipitation frequency estimates (PPFEs) are used in the design of stormwater drainage infrastructures. The PPFEs for 1-year to 1,000-year recurrence intervals with durations ranging from 5 min to 60 days are published in the National Oceanic and Atmospheric Administration (NOAA) Atlas 14. NOAA's published PPFEs are accepted as a reliable resource for the design of urban drainage infrastructures, yet they are based on the stationary climate assumption. However, future climate change may affect the distribution, frequency, and intensity of precipitation events. To evaluate the potential impacts of climate change on the stationary climate assumption, a weather research and forecasting (WRF) model was developed based on the medium climate change emission scenario. Then, the PPFEs were determined for 2010–2015, 2030–2035, 2050–2055, and 2070–2075 at six different locations in the state of Arizona. The comparison of the published and simulated PPFEs revealed a varying trend in depth and frequency values dependent on location and climate. Additionally, depth values were diminished for <3-h events at a majority of the stations.

Dynamic Modeling of Inland Flooding and Storm Surge on Coastal Cities under Climate Change Scenarios: Transportation Infrastructure Impacts in Norfolk, Virginia USA as a Case Study

Low-lying coastal cities across the world are vulnerable to the combined impact of rainfall and storm tide. However, existing approaches lack the ability to model the combined effect of these flood mechanisms, especially under climate change and sea level rise (SLR). Thus, to increase flood resilience of coastal cities, modeling techniques to improve the understanding and prediction of the combined effect of these flood hazards are critical. To address this need, this study presents a modeling system for assessing the combined flood impact on coastal cities under selected future climate scenarios that leverages ocean modeling with land surface modeling capable of resolving urban drainage infrastructure within the city. The modeling approach is demonstrated in quantifying the impact of possible future climate scenarios on transportation infrastructure within Norfolk, Virginia, USA. A series of combined storm events are modeled for current (2020) and projected future (2070) climate scenarios. The results show that pluvial flooding causes a larger interruption to the transportation network compared to tidal flooding under current climate conditions. By 2070, however, tidal flooding will be the dominant flooding mechanism with even nuisance flooding expected to happen daily due to SLR. In 2070, nuisance flooding is expected to cause a 4.6% total link close time (TLC), which is more than two times that of a 50-year storm surge (1.8% TLC) in 2020. The coupled flood model was compared with a widely used but physically simplistic bathtub method to assess the difference resulting from the more complex modeling presented in this study. The results show that the bathtub method overestimated the flooded area near the shoreline by 9.5% and 3.1% for a 10-year storm surge event in 2020 and 2070, respectively, but underestimated the flooded area in the inland region by 9.0% and 4.0% for the same events. The findings demonstrate the benefit of sophisticated modeling methods compared to more simplistic bathtub approaches, in climate adaptive planning and policy in coastal communities.

An evaluation of temporal changes in physicochemical properties of gully pot sediments

Diffuse pollution is recognised as a major challenge in achieving EU Water Framework Directive compliance, with urban runoff being a key pathway connecting various sources to receiving waters. Gully pots, as one of the ubiquitous urban drainage infrastructures, are placed at the inlets of piped drainage pipe network and actively drain runoff from urban catchment with suspended solids proportionally retained. The physiochemical properties of these retained solids reflect the activities within the catchment during the accumulation period. In this work, seven gully pots in two catchment types (highway and housing) in Luleå, Sweden were fully emptied and sediments analysed for total mass, particle size distribution and selected metal concentrations by six size fractions. The results of this sampling campaign are compared with the results of a 2005 study of the same gully pots to identify changes in the physicochemical properties of sediments over time and examine whether changes identified can be linked to changes in wider catchment management practices. The results highlight the potential impacts of winter road maintenance operations (e.g. up to a 15-fold higher solids loading rate in road catchment gully pots), reaching a normalised solids accumulation rate of 0.176–0.819 kg m2 year−1. An increase in tyre and road wear associated with winter road maintenance operations is also understood to contribute to the temporal increase of several metals including Cu, Zn, Co, Cr and V in the < 63-µm solids fraction in the road catchment gully pots. The concentrations of As and Pb decrease in all size fractions in both catchments, with the implementation of unleaded fuels (for Pb in housing catchment only), End-of-Life Vehicle Directive (Directive 2000/53/EC) (for Pb in both catchments), and strengthened industrial emission reduction measures suggested as possible drivers. The high contamination load for Zn, Cu, Cd and Pb in < 63-µm sediments from low-traffic housing catchment also emphasised the necessity of tracing and restricting non-traffic-related metal sources. Further seasonal monitoring of gully pot sediments is recommended to fully follow up the development of metals loading in both catchments.

PROBLEMSOF LOCAL FLOODS AND THEIR RELATION TO BOGOR CITY DRAINAGE INFRASTRUCTURE SYSTEM

Highland areas are not necessarily without flood problems, especially local flooding. The problem of poor drainage can be the cause of a local flood, as happened in Bogor City, West Java. Development evaluation related to local flooding in a city is an exciting topic to study further. The purpose of this evaluation is to answer the need for public information about the philosophy of flooding in the highlands, existing policies, and factors causing local flooding in Bogor City. The benefits of this analysis can also provide policymakers with input on strategic steps in the planning of urban drainage infrastructure systems, both in terms of physical channels, social approaches, and aspects of land carrying capacity within the ecological framework. The method used in this evaluation is in the form of literature studies and direct field observations of Bogor City's drainage infrastructure at specific points. The recommendation for the Bogor City government is to carry out comprehensive data collection and re-topography, namely by collecting data on buildings and drainage, determining the slope and height of the channel, and implementing risk management at each stage of its implementation. In addition, strict supervision and community participation in overseeing the development process and reducing waste disposal in the river supports the improvement of drainage development.