Gully Pot Research Articles

Impacts of seasonal activities and traffic conditions on the contamination and accumulation of gully pot sediments: Metal(loid)s and organic substances

Gully pots (GPs) are an integral urban drainage component, transferring surface runoff into piped systems and reducing sediment and contaminant load on downstream sewers and receiving waters. Sediment build-up in GPs impairs their hydraulic performance, necessitating maintenance for hydraulic function recovery. The variations in sediment accumulation rates between GPs suggested by earlier studies challenge the effectiveness of adopting a generalised maintenance frequency. This study addresses the knowledge gap regarding how various factors influence sediment contamination in GPs. The impacts of seasonal activities and traffic conditions on the contamination of sediments in 27 GPs in areas with varying traffic intensities and street features (roundabouts, intersections, and straight roads) were examined. Over one year, GPs were emptied twice, with sediments collected for winter-spring and summer-autumn accumulation periods. These sediments were analysed for 84 substances, including metal(loid)s, hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), alkylphenols, phthalates, per- and polyfluoroalkyl substances and organotins. Significant temporal changes were identified in key parameters such as electrical conductivity, total organic carbons, tungsten (W), heavy-molecular-weight PAHs (PAH-H) and diisodecyl phthalate (DIDP) in GP sediments, influenced by winter road safety measures and autumn leaf abscissions. Significantly higher concentrations of 4-tert-octylphenol, DIDP, diisononyl phthalate, antimony and W were identified in GP sediments from roundabouts compared to those at the other two street features, exclusively during the winter-spring period. This is attributed to the synergistic effect of winter road safety measures and stop-and-go traffic patterns at roundabouts. No consistent spatial and temporal patterns were identified for substance concentration and mass accumulation rates. Results underscore the potential to develop a prioritisation-based maintenance strategy as an opportunity to enhance the efficiency of GP maintenance operations, ensuring better resource allocation and reduced environmental impact.

Microplastics in gully pot sediment in urban areas: Presence, quantities and characteristics

Stormwater is widely recognized as a pathway for transporting pollutants, including microplastics, from sources in urban environments to receiving waters. Gully pots are often where urban runoff drains into the piped network; they typically include a trap where sediments accumulate. The aim of this work was to contribute to a better understanding of the fate of microplastics as they enter into the urban drainage system, and the role of gully pots in trapping microplastics. Sediment samples collected from 29 gully pots were analysed for non-carbon-black and carbon-black (e.g. tire wear particles) microplastics larger than 40 μm using μ-FTIR and ATR-FTIR, respectively. Commonly found polymers in descending order were PP > EPDM > EVA > PS > SBR, PP was most common both by mass and by number of microplastics. The total concentration of carbon black and non-carbon black microplastics ranged from 709 to 10 600 items/100 g dry matter (DM), (median: 2960 items/100 g). Estimated mass of non-carbon black microplastics ranged from 0.19 to 490 mg/100 g, (median: 3.66 mg/100 g). In total 21 different types of microplastics were detected, the majority of these (13) were carbon black and eight non-carbon black polymer types. By number and the carbon black particles accounted for up to 68% of the microplastics (average 30%), this stress the importance of using analytical methods enabling the detection of both carbon-black and non-carbon black microplastics. Furthermore, the results indicate that gully pots can act as temporary sinks for microplastics, mainly for microplastics larger than 125 μm. The amount of microplastics found in gully pots, together with the very large number of gully pots sited in urban areas, indicates that gully pots can potentially trap large amounts of microplastics, and thus if gully pots are fitted and maintained properly they could significantly contribute to reducing the amount of microplastics reaching receiving waters.

Investigation of uniform and graded sediment wash-off in an urban drainage system: Numerical model validation from a rainfall simulator in an experimental facility

Understanding sediment wash-off in urban environments plays an essential role in sediment transport management; and is critical for accurate pluvial flood control to assist in adaptation and mitigation strategies. Sediment transport models have been researched previously, though challenges still arise due to the complicated nature of graded sediment transport. This study tested the accuracy of the van Rijn model using a sparse distribution of particle sizes using the geometric mean. As such, this study used high-resolution datasets collected in a water laboratory to investigate sediment wash-off and transport on an urban street. This included the interaction of two gully pots receiving sediment loads that were washed off from a hypothetical urban surface by three rainfall intensities. The results showed that the model was able to simulate uniform sediments entering the gully pots accurately when the sediment size was assigned to a median diameter. Using the grain diameter to represent the geometric mean can improve the model performance for simulating a graded sediment.

Influence of seasonal activities and traffic conditions on the accumulation and particle size distribution of gully pot sediments

Gully pots (GPs) are ubiquitously used in urban catchments, to direct surface runoff into piped sewer systems, reduce the risk of sediment-induced pipe blockages and the loading of solids and associated contaminants on the receiving waters. Over time, the build-up of sediments in GPs will lead to impaired hydraulic performance, putting the urban catchment at risk of flooding. However, GP maintenance strategies lack both a robust evidence base and clear aims against which their effectiveness can be benchmarked. An improved understanding of the factors influencing long-term in-situ solids accumulation in GPs is required for further assessment and optimisation of the GP maintenance scheme. As a contribution to addressing these knowledge gaps, sediments from 27 GPs located in urban catchments associated with three street feature types (roundabout; crossing; straight road) and varied traffic intensities were collected on two occasions, representing two distinct seasonal accumulation periods. Parameters including GP fullness levels, particle size distribution (PSD), and solids mass accumulation rates were evaluated with regards to the impacts of seasonal activities, traffic conditions as well as configuration and dimension of GPs. The results indicate impacts of seasonal activities on solids accumulation rates were not consistent across all GPs, with the magnitude of the difference larger following winter-spring catchment practices. Additionally, synergistic impacts of seasonal activities and traffic conditions on PSD and solids accumulation rates were observed. For example, the winter road safety measures may enhance the impacts of the characteristic vehicle turning motions at roundabouts, contributing to the negative correlation identified between traffic intensities and solids accumulation rates. The overall exhibited large variations in sump fullness levels (4 %–73 %) and solids dry mass (0.5–51 kg) directly challenged the commonly adopted generalised GP maintenance frequency without taking the catchment-specific activities into consideration.

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.

A Study of 101 Organic Substances in Gully Pot Sediments Accumulated Over a One-Year Period

A Study of 101 Organic Substances in Gully Pot Sediments Accumulated Over a One-Year Period

The mismatch between long-term monitoring data and modelling of solids wash-off to gully pots

ABSTRACT Urban runoff remobilises solids and their associated pollutants from urban-built environments and transports them to drainage systems via gully pots. This study presents an extensive monitoring campaign on the solids loading to drainage systems, including 104 gully pots as sampling locations and lasting 2 years. The solids loading is modelled with Build-Up and Wash-Off (BUWO) models and a Regression Tree (RT). The performance of the RT is substantially better than the performance of the BUWO models, such that it is not recommended to use a single BUWO model to predict the loading of a set of gully pots/catchments. It is discussed whether the generally observed mismatch between monitoring data and wash-off models, both in this study and in literature, points to a fundamental misunderstanding of the underlying processes. Finally, the results show that an increased street sweeping frequency does not significantly reduce the solids loading to drainage systems.

Monitoring and characterising the solids loading dynamics to drainage systems via gully pots

ABSTRACT Runoff (re)mobilises solids and their associated pollutants from streets and transports them via gully pots to the drainage system. As the solids negatively impact the performance of the drainage systems, knowledge on the solids loading in terms of mass and composition is essential. However, monitoring data on the solids loading, in particular, covering all seasons and a number of sites, is scarce. This article presents the results of a monitoring campaign on the solids loading to a drainage system via 52 gully pots over a period of 2 years at a sampling rate of once per 3–4 weeks. The loading shows a maximum during the tree phases ‘leaf growth’ and ‘full capacity’ and is correlated with the rain intensity during these phases. The organic fraction and D50 of the solids are correlated with leaf abscission. The settling velocity of the particles <1800 µm is strongly correlated with their organic fraction.

An assessment of gully pot sediment scour behaviour under current and potential future rainfall conditions

Gully pots actively trap sediments transported by urban runoff to prevent in-pipe blockages and surface flooding. However, due to poor maintenance (resulting in sediment build-up) and increasingly extreme wet weather events, the scour of previously-deposited sediments from gully pots is identified as a potential contributor to EU Water Framework Directive failure. While basal sediment scour deterministic models have been developed and validated using laboratory and field gully pot data sets, the ability of these models to predict behaviour at sites other than those for which they were established has not been addressed. Nor has the impact of future rainfall predictions on the role of gully pots as sediment sources been systematically examined. As a contribution to addressing these knowledge gaps, the performance of two gully pot basal sediment scour models of distinct complexity levels are evaluated under current and future rainfall conditions. The output from Model One suggests that the scour-induced total suspended solids in gully pot discharge can be kept well below 25 mg/L if the gully pot fullness level is maintained at under 60%. Results identify the opportunity to incorporate the actual/targeted ecological status of recipients in scheduling gully pot maintenance operations and that proactive gully pots maintenance will reduce the impacts of increased rainfall intensity/duration on the magnitude of sediment scour. Results from Model Two suggest that fine sediments are particularly susceptible to in-pot scour. For example, sediment with a specific gravity of 1.1 and diameter of >63 μm accounts for 50% of scour-induced total suspended solids in gully pot discharge. The effluent suspended solids concentrations predicted by the two models differ by up to two orders of magnitude. However, without further empirical field data pertaining to their respective competences/applications, neither model could be discounted at this stage. For example, the use of Model One is more appropriate in the establishment of gully pot maintenance schedules, with Model Two more suited to the dimensioning of gully pots based on performance requirements. This application, however, relies on the development and adoption of a more stringent regulation on gully pots discharge.

Sediment Morphology and the Flow Velocity Field in a Gully Pot: An Experimental Study

Urban runoff (re)mobilises solids present on the street surface and transport them to urban drainage systems. The solids reduce the hydraulic capacity of the drainage system due to sedimentation and on the quality of receiving water bodies due to discharges via outfalls and combined sewer overflows (CSOs) of solids and associated pollutants. To reduce these impacts, gully pots, the entry points of the drainage system, are typically equipped with a sand trap, which acts as a small settling tank to remove suspended solids. This study presents data obtained using Particle Image Velocimetry (PIV) and Laser Doppler Anemometry (LDA) measurements in a scale 1:1 gully to quantify the relation between parameters such as the gully pot geometry, discharge, sand trap depth, and sediment bed level on the flow field and subsequently the settling and erosion processes. The results show that the dynamics of the morphology of the sediment bed influences the flow pattern and the removal efficiency in a significant manner, prohibiting the conceptualization of a gully pot as a completely mixed reactor. Resuspension is initiated by the combination of both high turbulent fluctuations and high mean flow, which is present when a substantial bed level is present. In case of low bed levels, the overlaying water protects the sediment bed from erosion.

Hydraulic, wash-off and sediment transport experiments in a full-scale urban drainage physical model

This paper presents a dataset obtained from hydraulic and sediment transport experiments performed in a full-scale urban drainage physical model of 36 m2. The study seeks to accurately measure sediment mobilization through the different parts of the model (surface, gully pots and pipe system), also obtaining a precise characterization of water flow and using realistic rainfall simulator to ensure the transferability of the results. Three different rain intensities and five sediment granulometries were tested in 6 hydraulic and 23 wash-off and sediment transport experiments. The following experimental data were produced: surface elevations and 2D runoff velocities measured by visualization techniques; surface and in-pipe water depths; flow discharges, total suspended solids concentrations and particle size distribution at the entrance of the gully pots and at the pipe system outlet; and sediment mass balances. This data is optimal for developing and validating wash-off and sediment transport formulations in urban drainage models, towards better treatment and management techniques for minimizing the impact of urban surface pollutants on the environments of towns and cities.

Do Sustainable Drainage Systems favour mosquito proliferation in cities compared to stormwater networks?

ABSTRACTWith the recent emergence of dangerous mosquito species in cities, Sustainable Drainage Systems used to manage stormwater are sometimes suspected to favour their development. In the metropolis of Lyon, the density of mosquitoes were studied in 15 retention, detention and/or infiltration sites, two green roofs, seven swales and 20 gully pots in traditional sewer networks. None of the swales retained water long enough to be sampled. No larvae were detected in the green roofs. Four classical species were found in the retention/detention basins (Culex pipiens, Culex hortensis, Anopheles maculipennis sl and Culiseta longiareolata). They appeared in May, mainly in the artificial habitats (e.g. concrete parts). Gully pots were colonized by Culex pipiens, Culiseta longiareolata during summer and by Aedes albopictus, ‘tiger mosquito’ in autumn. Vegetated systems where water was drained rapidly (i.e. green roofs, infiltration basins or swales) were not significant breeding sites compared to more artificial sites.

Study of Gully Pot Monitoring System for Urban Areas

Sewer failure occurs is one of the major problem in urban areas. The major cause of flooding is due to overflow of sewers. Several manholes across residential areas are overloaded due to excess sewage load. This is the main reason for the occurrence of Chennai flood. Inefficient gully pot network is the major reason for the over flooding of mainstream sewage pipes. There is a need for an efficient system design for monitoring a gully pot which is capable of providing required information about sewage block is prior to the occurrence. Wireless Sensor Network (WSN) has been used to monitor the sewer blockages. The blockage will be detected and the detected information has been transmitted to the authority through a GSM and developed in mobile application.

Quantifying the effect of proactive management strategies on the serviceability of gully pots and lateral sewer connections

Gully pots and lateral connections represent the anterior part of the sewer infrastructure responsible for the majority of flooding events in public areas. This study provides a statistical procedure to quantify the effectiveness of proactive management strategies to improve their performance. The first part consists of non-parametric methods to determine the evolution of gully pot blockages. The second part presents a Bayesian approach to quantify the development of reported flooding events when lateral connections are subject to proactive strategies. To this end, call data were collected from areas that were maintained proactively instead of reactively. Application of the procedure revealed a significant call decrease in one area. In addition, an increasing blockage likelihood over time indicated cyclic cleaning to be effective to improve sewer serviceability. By linking management strategies to performance, this flexible procedure can support sewer managers to balance the merits of proactive and reactive management strategies.

Dynamic optimisation of preventative and corrective maintenance schedules for a large scale urban drainage system

Gully pots or storm drains are located at the side of roads to provide drainage for surface water. We consider gully pot maintenance as a risk-driven maintenance problem. We explore policies for preventative and corrective maintenance actions, and build optimised routes for maintenance vehicles. Our solutions take the risk impact of gully pot failure and its failure behaviour into account, in the presence of factors such as location, season and current status. The aim is to determine a maintenance policy that can automatically adjust its scheduling strategy in line with changes in the local environment, to minimise the surface flooding risk due to clogged gully pots. We introduce a rolling planning strategy, solved by a hyper-heuristic method. Results show the behaviour and strength of the automated adjustment in a range of real-world scenarios.

Monitoring and statistical modelling of sedimentation in gully pots

Gully pots are essential assets designed to relief the downstream system by trapping solids and attached pollutants suspended in runoff. This study applied a methodology to develop a quantitative gully pot sedimentation and blockage model. To this end, sediment bed level time series from 300 gully pots, spanning 15 months, were collected. A generalised linear mixed modelling (GLMM) approach was applied to model and quantify the accumulation of solids in gully pots and to identify relevant physical and catchment properties that influence the complex trapping processes. Results show that the retaining efficiency decreases as sediment bed levels increase. Two typical silting evolutions were identified. Approximately 5% of all gully pots experienced progressive silting, eventually resulting in a blockage. The other gully pots show stabilising sediment bed levels. The depth of the sand trap, elapsed time since cleaning and the road type were identified to be the main properties discriminating progressive accumulation from stabilising sediment bed levels. Furthermore, sediment bed levels exhibit no residual spatial correlation, indicating that the vulnerability to a blockage is reduced as adjacent gully pots provide a form of redundancy. The findings may aid to improve maintenance strategies in order to safeguard the performance of gully pots.

An initial appraisal of waste decomposition by microbial processes within roadside gully pots

Despite their importance in urban drainage systems, gully pot internal processes have received little scientific study. Therefore, gully pot contents were examined to gain a basic understanding of these processes and to establish the decomposition characteristics of the contents ex situ. Moisture content, organic matter content, enzyme activity and pH were measured to investigate seasonal and geographical effects, in addition to a 5-week composting trial to determine the rate and characteristics of decomposition. Little difference was observed in the content processes, especially between seasons, and the composting trial illustrated organic content decreased at an average rate of 0.1 g of organic matter per 13 g of organic matter per day. The results from this study indicate an as yet unknown initial decomposition rate. Activity monitored between gully pots also suggests they are relatively similar systems across space and time; enabling gully contents to be evaluated universally in future research.

The role of settling velocity formulation in the determination of gully pot trapping efficiency: comparison between analytical and experimental data

Roadside gully pots are the connecting points between surface runoff and the underground drainage network; therefore they can be considered as the most superficial component of urban drainage systems. Gully pots are supposed to trap particulate matter washed off the catchment surface, but also to collect and convey stormwater into the network. The continuous accumulation of particulate matter results in a progressive loss of the gully pot hydraulic conveyance, thereby increasing the probability of urban flooding during rainstorm events. This study has therefore the objective to determine which variables influence the gully pot capability of retaining solids (efficiency), both experimentally and analytically. Several laboratory tests have been performed on a simple plastic gully pot, with different inflow rates and using both mono and hetero-disperse particle samples. Particular attention has been given to the influence exerted by the way particle settling velocity is expressed: efficiency has been analytically determined by means of multiple settling velocity formulas proposed by various authors and eventually compared to experimental data. Results deriving from the adoption of each single settling velocity formula have been extensively analysed, showing fairly different outcomes.

A Low Power Wireless Sensor Network for Gully Pot Monitoring in Urban Catchments

Sewer and gully blockages are the main cause of residential sewer flooding in the U.K. A low-cost and power efficient wireless sensor mesh networking communication system has been designed, developed and implemented to provide adequate warning on potential blockage incidents to prevent sewer failure. By monitoring the water level of the gully pot at each residential property, the water company will be proactively informed of the best course of actions to eliminate the causal problem, i.e., blockage and leakage within the sewer infrastructure. Hence, the number of residential sewer flooding and pollution incidents can be reduced. The prototype system consists of eight Zigbee based wireless sensor nodes and a GPRS enabled data gatherer. Each Zigbee sensor node comprises of a radio transceiver, a data acquisition board and an acoustic sensor probe. Field trials were carried out in an outdoor scenario to cross-validate the theoretical and practical performance of the prototype system. The results in terms of durability of sensors, sensor nodes and gateways and reliability of communication under real operational conditions and within a typical inner city urban environment are discussed. The problems encountered and solutions to tackle these problems were addressed.

Urban sediment particle size and pollutants in Southern Brazil

Background, aim and scope Studies of particulateassociated pollutants, or PAPs, in urban areas have become necessary due to their potentially deleterious effects on the environment. However, it is not just the sediments themselves which are problematic but also their particle size composition, which has a great influence on their capacity to adsorb and transport pollutants. This paper presents the particle size distributions and concentrations of five metals (Cr, Cu, Ni, Pb and Zn) of urban sediments collected from paved streets and gully pots from 20 cities in southern Brazil. The cities have different characteristics and hence sources of PAPs associated with differing geologies, soil types and type of urbanisation. Studies of this nature enable elucidation of the relationship between diffuse sources such as streets and gully pots and the likelihood of PAPs to subsequently pollute the urban aquatic environment. Materials and methods Sediment samples were taken at random from paved streets and gully pots in 20 cities in Rio Grande do Sul state, southern Brazil by means of a portable vacuum cleaner to avoid loss of finer particles. The particle sizes of the samples were measured using a Cilas® 1180 laser particle analyzer, and the concentrations of five metals (Cr, Cu, Ni, Pb and Zn) were determined by wet acid digestion (HCl–HF–HClO4–HNO3) followed by inductively coupled plasma atomic emission spectroscopy on the <63-µm fraction. Results It was found that in comparison to sediments collected from the streets, gully pot sediments were more heterogeneous in terms of particle size and also that sediment samples from the gully pots were predominantly coarser than those originating on the streets. From the gully pot results, analysis of the modal particle diameter enabled the cities to be divided into three categories. The concentrations of metals in the street sediments were similar across all 20 cities, with all concentrations above background values. Discussion The fact that concentrations of metals in the street sediments were above statutory guideline values and that the coarser material was deposited in the gully pots suggests that the finer, more polluted sediment is not retained in the gully pots but is transported to the nearest local receiving watercourse. This finding has implications for management strategies for reducing pollution in urban environments. Conclusions High concentrations of Cr, Cu, Ni, Pb and Zn in the <63-µm fraction of street sediments, in combination with coarse material retained in the gully pots, indicate that metals could be transferred quite rapidly from the diffuse source of pollutants, on impermeable street surfaces, to receiving watercourses.