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Sewer Blockage Management: Australian Perspective
Abstract
The functions performed by sanitary sewers can be disrupted by blockages in the pipeline, especially in cities with aging systems and deteriorating pipes. The problem is acute in Australia, where the principal blockage cause is tree root intrusion. This paper presents an overview of the causes of sewer blockages, the scope of the asset management challenge, and the management practices employed by Australian water utilities. These views were developed through reviews of the literature and current management practices elicited in a collaborative research project involving a range of water sector partners and using qualitative techniques such as surveys, interviews, and workshops. This paper highlights that blockages occur because of a range of factors, of which root blockages are the most common in Australia. Issues that confound management of blockages are also described, along with a summary of management strategies. Optimizing the balance between proactive and reactive interventions was found to be a good management strategy to maximize service outcomes.
... Tree roots are the most common and widespread cause of blockages (or chokes) in sewer infrastructure globally (DeSilva et al. 2011, Randrup et al. 2001, Stål 1998. In Australia over 95% of pipe blockages serviced by water utilities are linked to tree roots (DeSilva et al. 2011). ...
... Tree roots are the most common and widespread cause of blockages (or chokes) in sewer infrastructure globally (DeSilva et al. 2011, Randrup et al. 2001, Stål 1998. In Australia over 95% of pipe blockages serviced by water utilities are linked to tree roots (DeSilva et al. 2011). This can have severe consequences for the performance of sewer systems including faster pipe deterioration, loss of conveyance capacity, and resultant contamination of the environment due to sewage overflow (DeSilva et al. 2011, Tran et al. 2010. ...
... In Australia over 95% of pipe blockages serviced by water utilities are linked to tree roots (DeSilva et al. 2011). This can have severe consequences for the performance of sewer systems including faster pipe deterioration, loss of conveyance capacity, and resultant contamination of the environment due to sewage overflow (DeSilva et al. 2011, Tran et al. 2010. ...
... Managing sewage systems is another substantial challenge faced by water utilities. While sewerage systems are designed to safely convey raw wastewater to treatment facilities, they often have decreased capacity due to blockages (e.g., accumulation of sediments or other nondegradable materials) or pipeline defects (e.g., joint failure), potentially resulting in overflows, environment pollution, public health hazards, and economic losses (e.g., fines, tourism loss) (De Silva et al., 2011). The prevalent management strategy among water utilities is either reactive, i.e., operate sewers until they block and then determine a course of action (De Silva et al., 2011;Tscheikner-Gratl et al., 2020), or preventative, i.e., regular schedule of maintenance activities to clean and inspect selected regions of the sewer system. ...
... While sewerage systems are designed to safely convey raw wastewater to treatment facilities, they often have decreased capacity due to blockages (e.g., accumulation of sediments or other nondegradable materials) or pipeline defects (e.g., joint failure), potentially resulting in overflows, environment pollution, public health hazards, and economic losses (e.g., fines, tourism loss) (De Silva et al., 2011). The prevalent management strategy among water utilities is either reactive, i.e., operate sewers until they block and then determine a course of action (De Silva et al., 2011;Tscheikner-Gratl et al., 2020), or preventative, i.e., regular schedule of maintenance activities to clean and inspect selected regions of the sewer system. Innovative solutions based on artificial intelligence have been proposed and trialled in Australia aiming to proactively manage sewers. ...
Developments in technology and data analytics bring opportunities for water utilities to proactively adapt their practices to better manage pressing challenges, such as water losses, ageing assets, and urban water scarcity due to climate change. Despite the increase in commercial digital technologies for monitoring urban water, wastewater and stormwater systems, digital transformation in water utilities has been occurring much slower than in other businesses (e.g., the energy sector). Leveraging from Australian best practices, this study aims to facilitate water utility’s digital transformation by establishing a targeted research agenda and a continuous improvement process for the successful implementation, operation, and improvement of smart water technologies. Four case studies on 1) automated and digital water consumption metering, 2) early warning of water mains breaks, 3) early detection of sewerage blockages and spills, and 4) smart rainfall reuse and flood mitigation are used to exemplify the potential benefits and hurdles of adopting digital technologies in water utilities, while highlighting pressing areas needing further research and development. Key research areas identified include: 1) development frameworks to map water utilities capacity and needs for ranking priority areas of investment, 2) improvements in sensor hardware, 3) integration of big, multi-sourced data and cybersecurity, 4) increase in generality of smart data applications for various field conditions (i.e., reduce the need for or level of customization), and 5) data-informed proactive asset management and water pricing. Key barriers to be overcome include 1) lack of internal capacity to develop, operate and integrate smart applications, 2) the risk conservative culture of water utilities when facing innovation, and 3) lack of operation standards among water utilities to promote benchmarking. It is imperative that water utilities actively drive the digital transformation process by perpetuating collaborations with research centres and the private sector, while simultaneously increasing in-house capacity through investments in skilled personnel and training.
... Sewer blockages pose a serious problem for wastewater network operators since the resultant spills contaminate the environment, endanger public health, and impact the economy (Fenner et al. 2007;DeSilva et al. 2011;Tizmaghz et al. 2022). Consequences of spillages and the costs of excessive preventative maintenance have encouraged innovation directed at developing economical sewer blockage detection techniques (Rodríguez et al. 2012;Mustafa Abro et al. 2019). ...
Blockage detection in circular open channels (partially filled pipes, e.g., gravity sewer pipes) has gained increasing interest in the water industry. While there have been significant advancements in monitoring technologies for such systems (e.g., smart sewer systems), there is a lack of quantification of the hydraulic impact of partial blockages in circular pipes, which is a limiting factor for cost-effective detection. This study presents and validates a numerical framework to quantify the changes in water depth caused by extended bottom blockages in circular open channels. The analysis is based primarily on continuity and energy conservation with the assumption of a lossless transition at the blockage. The proposed approach can determine the critical blockage height that would induce choking, therefore a change in the upstream depth. It can also calculate the changed upstream water depth for various bottom blockage height values (above the critical height) for both subcritical and supercritical conditions. The proposed approach is numerically implemented and then validated through a series of laboratory experiments under the subcritical flow condition (which is the most common condition for gravity sewer systems). The numerically determined water depth results are consistent with the experimental results, which confirms that the proposed approach can accurately estimate the new upstream depth under the choking condition induced by a bottom blockage in circular open channels. The results contribute to advancing the hydraulic understanding in circular open channels with extended partial blockages, which is useful in the development of smart sewer technologies.. This work is made available under the terms of the Creative Commons Attribution 4.0 International license, https://creativecommons.org/licenses/by/4.0/. Practical Applications: Spills and overflows out of the gravity sewer system damage the environment and bring risks to public health. The problem is typically caused by partial blockages, which can reduce the flow capacity of the sewer pipe and induce higher-than-designed flow depth on the upstream of the blockage (known as choked flow condition). This study helps water engineers and operators to understand how an extended bottom blockage affects the flow condition just upstream of the blockage in a circular gravity sewer pipe. Charts have been presented to enable the determination of (1) the critical height of an extended bottom blockage that would induce choking; (2) the expected upstream flow depth for blockages with various heights, with a given flow rate under choked flow condition; and (3) the expected upstream flow depth for various flow rates, with a given blockage height under choked flow condition. The results can be used to evaluate the risk of bottom blockage-induced spill for sewer pipes with various sizes, slopes and flow rates (e.g., some may be more tolerant to bottom blockages while some may be more sensitive). This information can then be used to prioritize preventative measures such as sewer depth monitoring or regular cleaning.
... In a survey of sewers with an aggregate length of 33.7 km in the Swedish cities of Malmö and Skokfjord, an average of 6.47 m per 100 m was found to have been invaded by roots (Östberg et al., 2012). In Australia, sewer blockage arose predominantly from root invasion, with about four blockage points found in every 10 km of sewers (DeSilva et al., 2011). In Poland, analysis revealed that rootinduced piping occlusion happened in >60 % of ceramic clay sanitary sewers and concrete storm sewers, and in >50 % of lowest-concrete sanitary sewers (Kuliczkowska, 2008). ...
Root damage from urban street trees represents a substantial concern arising from the conflict between root growth and limited growth spaces. Nonetheless, the phenomenon of root damage, which threatens the safety of urban facilities, appears to have received little scholarly attention. Moreover, the effectiveness of some proposed measures for root damage prevention and control has not yet received consistent evaluation. Accordingly, this review aims to examine root damage, including its causes and available prevention and control measures. Urban trees are found to have a high potential to exert root damage on infrastructures when the following factors exist. These include large and mature tree, fast-growing trees, trees planted in limited soil volumes, shallow-rooted tree with buttress roots, trees whose diameter at breast height exceeds 10 cm, old and cracked road paving, high soil surface moisture content, short distances between trees and sidewalks (<2 to 3 m), and underground pipes that are already broken and made of metals or stones. The phenotypic traits of trees may be the primary factor causing root damage when there is a mismatch between the root-soil requirements of urban street trees and the actual soil environment. The poor effectiveness of root damage prevention and control measures may be attributed to the lack of connection between the development of control measures and the mechanism of root damage.
... Futhermore, weak joints and cracks in old sewer pipes may lead to the intrusion of roots and other debris (Lu et al., 2000). Initially, intrusion of tree roots was identified as a great influence in spatial deposition (DeSilva et al., 2011;Ducoste et al., 2008) and Marlow et al., (2011) showed that blockages due to tree root intrusion can be of >75% for some utility areas in Australia. Since then, other solids such as disposable face masks, wet wipes, tampons, cotton buds, plastics, sanitary absorbents, grit and dirt have also been found in sewer networks. ...
Treatment of wastewater with high levels of fat, oil, and grease (FOG), produced by the growing number (annually 2%) of food service establishments (FSEs), is a major concern for water utilities. About 30-40% of sewer blockages are caused primarily by the formation of FOG deposits in sewer pipes, and an annual additional maintenance cost is required for sewer management. To manage FOG deposition, FSEs are required to recover the FOG at the point of generation by installing grease interceptors (GIs) before release to the sewer system. The successful control of FOG deposition is largely dependent on clear understanding of its complex properties, pre-treatment processes, deposition mechanism and public awareness. The objective of this study is to provide a comprehensive understanding of the physicochemical properties of FOG, including particle size distribution and their removal efficiencies by existing GIs. Nowadays, generation of FOG particles of ≤45 µm is increasing because of the increasing use of automatic dishwashers. Current hybrid processes which comprise pre-treatment prior to GI use are ineffective since they are unable to completely remove particle sizes of ≤45 µm. Hence, there is potential for these particles to be released into the sewer system and eventually cause blockages. This critical review discusses the characteristics of effluents, including the particle size distributions generated from automatic dishwashers and handwash sinks. It concludes by providing some case studies and a perspective of the future opportunities to develop a novel GI process integrated with pre-treatment to remove particles of all sizes, including colloidal particles.
Tree root intrusion can cause failures of underground sewer pipes and thus represent a major water asset management issue. If tree root intrusion is not detected early, this may lead to the interruption of wastewater services and high costs of repair to the pipeline. The objectives of this review are to assess the existing maintenance strategies, explore suitable strategies for Australia and similar settings around the world, and identify possible factors and predictive tools. Maintenance strategies can be divided into two categories: reactive and proactive approaches. The current reactive approaches are (1) mechanical techniques to clean the root mass in pipe networks and (2) chemical techniques to remove the root mass and control future growth. The literature suggests that the reactive approaches often provide only partial solutions. The proactive approaches, guided by a predictive model of tree root intrusion and its related factors, showed the potential to improve maintenance and limit the risk of the damage from re-occurring. Predictive models could help to evaluate the risk of planting trees in different conditions and minimise the damage of tree root intrusion after further multifactor investigations.
The semantic segmentation of pipe point clouds is a critical process for detecting defects in underground sewer systems. Traditional pipeline segmentation methods primarily rely on manual operations, which are laborintensive, time-consuming, and often result in suboptimal accuracy. While deep learning methods for point cloud processing have been investigated, existing networks demonstrate limited efficacy in segmenting multiscale defects. This study introduces a dual-scale layered deep learning network (DLnet) for 3D semantic segmentation of sewer pipelines from global and local perspectives. DLnet incorporates two complementary modules: ShellNeXt, designed for comprehensive pipe feature recognition, and ShellNeXt-mini, optimized for
detecting small-scale defects such as spalling. Specifically, ShellNeXt utilizes a novel Reshell convolution oper
ator for layered feature extraction, enabling detailed analysis of the entire sewer pipeline, while ShellNeXt-mini efficiently identifies subtle local defects with enhanced computational performance. The proposed network surpasses the state-of-the-art PointNeXt model, achieving a 13.6% improvement in mean Intersection over Union (mIoU) and demonstrating significant gains of 62.49% and 13.11% in intersection over Union (IoU) for spalling and corrosion, respectively. This study provides a valuable contribution to the assessment and measurement of sewer conditions and defects.
Adding herbicides to sewer lines, a common practice for controlling root intrusion in sewer pipes, may adversely impact downstream wastewater treatment by inhibiting nitrification and denitrification performance. This study investigated the effects of herbicides, namely diquat, triclopyr, and 2-methyl-4-chlorophenoxyacetic acid (MCPA)-dicamba, on these processes. Various parameters were monitored, including oxygen uptake rate (OUR), nutrients (NH3-N, TP, NO3-N, and NO2-N), chemical oxygen demand (COD), and herbicide concentrations. It was found that nitrification was not affected by OUR in the presence of each herbicide at various concentrations (1, 10, and 100 mg L-1). Additionally, MCPA-dicamba at various concentrations demonstrated minimal inhibition in the nitrification process compared to diquat and triclopyr. COD consumption was not affected by the presence of these herbicides. However, triclopyr significantly inhibited NO3-N formation in the denitrification process at various concentrations. Similar to nitrification process, both COD consumption and herbicide reduction concentration were not affected by the presence of herbicides during the denitrification process. Adenosine triphosphate measurements showed minimal impact on nitrification and denitrification processes when herbicides were present in the solution up to a concentration of 10 mg L-1. Tree root kill efficiency experiments were performed on Acacia melanoxylon. Considering the performance on nitrification and denitrification process, diquat emerged as the best herbicide option (concentration of 10 mg L-1), with a 91.24% root kill efficiency.
This literature review presents the state-of-the-art concerning sediment sewer transport modelling. After a description of solid particles found in domestic sewage and in storm water, the different steps taken into account in models are described: build-up over the catchment, washoff by rainfall, transfer through gully pots, transport, deposition and erosion in sewer pipes. For each step, several modelling approaches are presented with their basic equations. The paper ends with a short presentation of some models, and with some remarks about the comparison between models and field experimental data.
The invasion of sewer pipes by tree roots is a major cost to both the corporations managing urban infrastructure and to private landowners. There are a number of factors that may result in the growth of roots into and around the pipes. These include pipe material factors such as degradation of aging pipes and damage caused to pipes and environmental factors such as site conditions, tree proximity and tree species. Research into these issues will help in developing more efficient methods of controlling root invasion, benefiting both the management of sewer flow and the urban landscape. A study of root invasions in suburban Melbourne was carried out to examine relationships between site factors and root blockages. Common factors found associated with tree root blockages were Eucalyptus and Melaleuca species over 4m high within 6 m of sewers, pipe depth 2 m or less, rubber ring joined 150 mm diameter vitreous clay, 30 to 60 years old, soil types with sandy topsoils, and blockages occurring most frequently when temperatures and evaporation were at their lowest i.e. August to October. An experiment was conducted to evaluate chemical and physical treatments for preventing root growth in disturbed soil with high nutrient content and readily available moisture (modeling leaking sewers). Over a period of 177 days significant inhibition was achieved with the chemical treatments dichlobenil (278 g/m3 and 1392 g/m3), copper sulphate (1.5 g Cu/kg soil and 7.5 gCu/kg soil), oryzalin (1031 g/m3) and trifluralin (260 g/m3) and the physical treatments slaked lime (ratio of 10 soil:1 lime and 10 soil:5 lime) and cement slurry. The potential for the use of these treatments in areas where tree roots have damaged sewers is discussed.
Interference between trees and sewer systems is likely to occur in old systems and in cracked pipes. Factors that contribute to damage include old pipes with joints, shallow pipes, small-dimension pipes, and fast-growing tree species. Because roots are reported to cause >50% of all sewer blockages, costs associated with root removal from sewers is substantial. In smaller-dimension pipes, root removal every year or every other year is common. Major resources are put into replacement and renewal of existing pipes, which is sometimes accelerated because of root intrusion. Collapse repair costs are greater than new construction, but costs associated with root removal may be one-sixth the cost of pipe replacement/renewal due to roots. Major breaks and stoppages seem to occur more frequently in older systems than in new. Therefore, it seems worthwhile to carry out preventative maintenance of the older parts of the sewer system.
Why do tree roots penetrate pipes-and not only where the pipe is damaged? Root damage to the pipe connections of duly laid, intact pipes causes millions of damages per year. Engineers and biologists are searching for the reasons together. Their results are already turning past theories topsy-turvy and have consequences for laying pipes. Sewers are a rather inconspicuous property of cities and municipalities. But there are few things so important for the community. This becomes particularly obvious, if sewers do not work properly. A frequent cause are roots growing into the pipes.The estimated costs of repair and ultimately renewal of the pipes would rapidly exceed the total sum of a billion in Germany alone. While one can resort to bottled mineral water instead of drinking water, help out with aggregates in the case of electrical current and simply do without television occasionally, a defective sewage system is always an acute problem, that has to be solved quickly. We have investigated why roots represent a problem for piping systems at all in a cooperation project of the Chair for Systematic Botany and the Botanical Garden of the Ruhr-University with the IKT-Institute for Underground Infrastructure. Concepts to avoid this damage are to be developed, based on the accurate knowledge of what happens when roots penetrate. Sound precautions are particularly important, since it usually takes more than 10 years from pipe laying to the occurrence of damage and pipes should last for a long time (service life: 50 to 100 years). Biologists and underground engineers seem to be "natural enemies" in this respect, because one group argues, that nothing can happen, if the pipes are "decently" laid, while the other considers wood as an aggressive destroyer of the marvel of their engineering art. A biology student, who jobbed in underground engineering and returned to his academic roots with this problem, made the contact between both worlds.
Metham (sodium methyldithiocarbamate), applied alone or in combination with dichlobenil (2,6-dichlorobenzonitrile) in foam, was effective in killing roots of eucalyptus ( Eucalyptus camaldulensis Dehnhardt) or willow ( Salix hindsiana Benth.). An air-aqueous (19 to 1) foam of these herbicides was at least 20 times as effective as the aqueous mixture alone. Killing of the root with metham was rapid and extended above the lower treated portion, with the extent of necrosis resulting from translocation of the herbicide varying with concentration of metham that was used. The amount of the root killed with dichlobenil was limited to the treated area regardless of concentration. Four weeks were required to control the larger roots. Root killing with metham proceeded via both the aqueous and vapor phases. Results from labeling trees with ¹⁴ C-assimilates indicated that neither translocation nor accumulation were greatly affected by metham or dichlobenil except in the tissues actually killed. However, transport and accumulation into untreated roots were reduced for a few weeks by dichlobenil. Similar results were obtained with cotton ( Gossypium hirsutum L. ‘Acala’) treated with dichlobenil.
The recent California drought and attendant reduction in water utilization give a preview of the problems and potential benefits of reduced water use. The performance of sewer collection systems and treatment works operating at reduced flow conditions was analyzed. The effects of reduced water use on wastewater strength (biochemical oxygen demand, suspended solids, and nutrients) were evaluated from plant operating records of 14 treatment systems. The effects of reduced scouring velocities on sewer performance have been discussed with reference to sewer design correlation. Process performance of treatment plants has been analyzed with reference to a computer programmed process model. Operating problems and solutions are discussed. Potential benefits of reduced water utilization for existing and new systems are described.
Little is currently known about the nature, quantity or variability of WC derived sewer solids. This work describes results of a one week domestic WC usage survey in the UK. Specific attention is paid to solid production including faecal matter, toilet paper and sanitary refuse. Significant quantities of solids were found to be produced. The results illustrate distinctive diurnal usage patterns including the surprisingly low evening faecal related flush usage Weekend usage exceeded week day usage on average, but with reduced morning peaks. Differences between males and females usage were also noted, in particular the much larger toilet paper usage and sanitary refuse disposal associated with females.
Three sites with root intrusion problems in the City of Malmo were inspected to find different solutions to the problems. All sites had high maintenance costs due to the roots. Alternative measures for each site were selected. Each site was treated differently depending on the technical, aesthetical, cultural and economical values. At one site, pipes were relined, at another the trees were replaced with less aggressive species and at the third a decision is yet to be made. Tree roots entering sewer systems is a well- known phenomena. To be able to live and develop, a tree must have a sufficient soil volume and a good soil environment. One reason for the good environment for root growth around pipes is the condensation or accumulation of water outside or inside the pipe. The root tip follows the pipe and penetrates where there is a weakness. The design and type of the pipe is of utmost importance for root intrusion and the amount of root damage. Different materials can resist root intrusion differently. Older concrete pipes without rubber gaskets in the joints can resist root intru- sion the least and make up the majority of pipes with root intrusion problems. Concrete pipes with rubber gaskets in the joints have been found to have a higher resistance against root intrusion but are not fully reliable, especially not in older in- stallations. Pipes made of plastic (PVC) and fi- berglass (GAP) have, so far, been nearly resistant to root intrusion, if we disregard carelessness during construction, and the joints between these types of pipes and concrete pipes. Polythene pipes (PEH) are welded so there are no joints and no problems with root intrusion. The plastic pipes must have a very well-constructed and compacted gravel bedding, to get the stability to withstand a physical load, or there is a risk for deformation and cracking, with root intrusion as a result.
Australia cracked under the pressure of its longest recorded drought, with politicians and the public feeling the impact