sustainability Review A Review of Underground Pipeline Leakage and Sinkhole Monitoring Methods Based on Wireless Sensor Networking Haibat Ali and Jae-ho Choi * Civil Engineering, Dong-A University, Busan, P4401-1, 550 Bungil 37, Nakdong-Dero, Saha-Gu 49315, Korea * Correspondence: [email protected]; Tel.: +82-51-200-762 Received: 9 July 2019; Accepted: 21 July 2019; Published: 24 July 2019 Abstract: Major metropolitan cities worldwide have extensively invested to secure utilities and build state-of-the-art infrastructure related to underground fluid transportation. Sewer and water pipelines make our lives extremely convenient when they function appropriately. However, leakages in underground pipe mains causes sinkholes and drinking-water scarcity. Sinkholes are the complex problems stemming from the interaction of leaked water and ground. The aim of this work is to review the existing methods for monitoring leakage in underground pipelines, the sinkholes caused by these leakages, and the viability of wireless sensor networking (WSN) for monitoring leakages and sinkholes. Herein, the authors have discussed the methods based on different objectives and their applicability via various approaches—(1) patent analysis; (2) web-of-science analysis; (3) WSN-based pipeline leakage and sinkhole monitoring. The study shows that the research on sinkholes due to leakages in sewer and water pipelines by using WSN is still in a premature stage and needs extensive investigation and research contributions. Additionally, the authors have suggested prospects for future research by comparing, analyzing, and classifying the reviewed methods. This study advocates collocating WSN, Internet of things, and artificial intelligence with pipeline monitoring methods to resolve the issues of the sinkhole occurrence. Keywords: WSN; pipeline leakage; human-induced sinkhole; leakage detection; sewer pipeline; sensors 1. Introduction Sewer and water leakages in underground pipelines have become a critical issue for water-management authorities in most countries—developed and developing alike—worldwide. Leakages in sewer and water pipelines may lead to several problems such as a shortage of drinking water, groundwater contamination, and ground subsidence [1]. Numerous countries are investing a considerable amount of their annual budget towards the prevention and control of the probable effects of sewer and water pipeline leakage. These issues further exacerbate infrastructure and environmental conditions that support human socioeconomic activities. In recent years, developed countries, such as the United Kingdom, Australia, France, Spain, and the United States of America, have experienced shortage in domestic water supply because of leaking pipe mains [2]. The after effects of these leakages in pipelines cause ground subsidence and sinkholes [3]. These sinkholes result in damage to infrastructure (roads, highways, railways, and underground fluid transportation networks). A sinkhole refers to a cavity in the ground formed by underground erosion and the depression of the ground surface. In general, there exist two types of sinkholes—natural and human induced. Natural sinkholes are mainly observed in regions with large deposits of salt, limestone, and carbonate rocks. The accurate prediction of the location and time of the occurrence of these sinkholes is rather difficult [4]. Groundwater extraction, construction in adjoining areas, and leakage in underground Sustainability 2019, 11, 4007; doi:10.3390/su11154007 www.mdpi.com/journal/sustainability Sustainability 2019, 11, 4007 2 of 24 Sustainability 2019, 11, x FOR PEER REVIEW 2 of 25 pipelines are the leading causes of human-induced sinkhole formation in urban areas [5]. Among them, theNatural presence sinkholes of leakages, are mainly bursts, observed or in blockagesregions with inlarge sewer, deposits drain, of salt, and limestone,/or water and carbonate pipelines are the most frequentlyrocks. The reported accurate causesprediction of of sinkholes. the location and time of the occurrence of these sinkholes is rather difficult [4]. Groundwater extraction, construction in adjoining areas, and leakage in underground The issuepipelines of are sinkhole the leading creation causes of hashuman witnessed-induced sinkhole global formation escalation in urban in areas recent [5]. yearsAmong owing to ever-increasingthem, the urbanization presence of leakage and thes, burst continuouss, or blockage construction,s in sewer, drain, development, and/or water andpipelines expansion are the of urban areas [6]. Amost cavity frequently begins reported to develop causes as of leakedsinkholes. water erodes the soil surrounding pipelines. This reduces the bearing capacityThe issue ofof thesinkhole soil creation layer abovehas witnessed the cavity, global andescalation hence, in recent the groundyears owing collapses to ever- to form a increasing urbanization and the continuous construction, development, and expansion of urban areas sinkhole [7[6]].. A The cav sizeity begins of sinkholes to develop ranges as leaked from water 2 erodes m deep the andsoil surrounding 1.5 m wide pipelines. [5] to a This massive reduces scale of up to 15 m deepthe bearing and 30 capacity m wide of [the8], soil as reportedlayer above in the Jeju, cavity, South and Koreahence, the and ground Southwest collapses Japan, to form respectively. a Human-inducedsinkhole [7] sinkholes. The size of have sinkholes been ranges reported from 2in m Sandeep Antonio,and 1.5 m wide Texas [5] to [9 a]; massive Oakwood, scale of Georgia; up and Tracer, Coloradoto 15 m deep [10]. and These 30 m wide incidences [8], as reported have reportedlyin Jeju, South causedKorea and considerable Southwest Japan, economic respectively. damage and Human-induced sinkholes have been reported in San Antonio, Texas [9]; Oakwood, Georgia; and loss of humanTracer, lives. Colorado As reported [10]. These in incidences Fraser, USA have reportedly [10], the abruptcaused considerable collapse of e aconomic 44-year-old damage sewer and pipeline destroyedloss 22 homes,of humanand lives. the As reconstructionreported in Fraser, of USA the [10] damaged, the abrupt road collapse and sewerof a 44-year pipelines-old sewer cost the city administrationpipeline approximately destroyed 22 homes, $70 and million. the reconstruction More than of 20 the sinkholes damaged road have and been sewer observed pipelines cost in USA alone owing to thethe city failure administration of underground approximately pipe $70 mains million. [11 More]. Figure than 120 illustrates sinkholes have the been e ffects observed of underground in USA alone owing to the failure of underground pipe mains [11]. Figure 1 illustrates the effects of pipeline leakage.underground pipeline leakage. Figure 1. CausesFigure 1. Causes and eff andects effects of leakage of leakage in in underground underground water water systems systems and sewer and sewerpipeline pipeline systems. systems. Various hardware,Various hardware, software, software, mathematical mathematical formulas,formulas, and and algorithm algorithm-based-based methods methods have been have been proposed for monitoring, detecting, and preventing leakages in underground water pipelines and proposed forthe occurrence monitoring, of sinkholes. detecting, Conventional and preventing techniques, leakages such as acoustic in underground-based approaches, water have pipelines been and the occurrenceused of sinkholes.for this purpose. Conventional These techniques techniques, require an such expert as who acoustic-based scans a suspected approaches, area by listening have to been used for this purpose.leak sounds. These However, techniques such methods require are an extremely expert who time scansconsuming a suspected and their areaaccuracy by listeninghighly to leak sounds. However,depends on such the skills methods and experience are extremely of personnel time [12] consuming. Vibration analysis and their is another accuracy conventional highly depends technique utilized to locate leaks in pipelines [13]. However, in conventional vibration and acoustic- on the skillsbased and techniques, experience hydrophones of personnel must [12be ].placed Vibration on both analysis sides of is the another pipeline conventional section under technique utilized toconsideration locate leaks for leak in pipelines detection. Such [13 ].conventional However, techniques in conventional require the exact vibration length of andthe pipeline acoustic-based techniques,to hydrophonesaccurately locate must a leak. be In placedsuch cases on, the both length sides of ofthe the pipeline pipeline is measured section either under by considerationwalking for leak detection.with a Such measurement conventional wheel or techniques by utilizing requirethe recorded the exactdata from length maps of [14] the. The pipeline lengths to obtained accurately locate using these methods are inappropriate for locating or detecting a leak and result in errors of up to a leak. In such cases, the length of the pipeline is measured either by walking with a measurement wheel or by utilizing the recorded data from maps [14]. The lengths obtained using these methods are inappropriate for locating or detecting a leak and result in errors of up to 30% [15]. Various methods have been adopted to monitor and detect sinkholes. Over the years, wireless sensor networking (WSN) systems [16], Internet of things (IoT) [3], and image processing technology using artificial intelligence (AI) have been used for monitoring underground pipeline infrastructures