No abstract

This paper reports on the development of a low-cost, rapidly deployable sensor for surveying live sewers for blockages and structural failures. The anticipated cost is an order of magnitude lower than current techniques. The technology is based on acoustic normal model decomposition, The instrument emits short coded acoustic signals which are reflected from any sewer wall defect. The acoustic signals can be short Gaussian pulses or longer sinusoidal sweeps and pseudo-random noise. The processing algorithms used on the reflected signal can predict the extent and geometry of the pipe deformation, and the locations and approximate size of common blockages. The effect of the water level on the frequency of the fundamental mode has also been investigated. It is shown that the technique can be adapted to work reliably in relatively large 600 mm diameter sewer pipes.

& It is the purpose of combined sewerage systems to convey a variety of solids, and associated liquid wastes, for treatment and return to the environment. The movement of the solids in sewers has come under increased scrutiny in recent years, due to the pollution and maintenance concerns associated with this material. The real or perceived physical, biochemical, ecological and aesthetic impacts of sewage spills into the environment, via separate storm sewers, combined sewer over¯ow (CSO) structures and treatment plants, have recently entered more prominently into public awareness and perception. Worldwide, engineers have become increasingly aware that the methodologies currently in use to design sewers to prevent solids deposition and minimize the hydraulic and other eects, are inadequate. A modi®ed design approach, recently proposed by the Construction Industry Research and Information Association (CIRIA), aims to address these problems by providing a standardized procedure to minimize sedimentation in sewers. This approach relies substantially on laboratory-based work for calibrating the sediment transport, and to a lesser extent, hydraulic resistance relationships. This paper examines the basis of the CIRIA design methodology, and compares the laboratory work with real sewer conditions (based on real sewer sediment data collected in the UK, and other European sewers). The aim is to provide sewerage designers, managers and planners with information about the general applicability of current methodologies regarding the design of sewers, to manage sediment problems. This information is presented in the context of the current understanding of the physical processes which control the movement and deposition of real sewer sediments, rather than those studied in laboratories.

Sediments within sewers can have a significant effect on the operation of the sewer system and on the surrounding natural and urban environment. One possible method for the management of sewer sediments is the use of slotted invert traps. Although invert traps can be used to selectively trap only inorganic bedload material, little is known with regard to the design of these structures. This paper presents results from a laboratory investigation comparing the trapping performance of three slot size configurations of a laboratory-scale invert trap. The paper also presents comparative results from a two-dimensional computational model utilising stochastic particle tracking. This investigation shows that particle tracking consistently over-predicts sediment retention efficiencies observed within the laboratory model.

A greater understanding of the erosion behaviour of sewer sediments is necessary in order to reliably estimate the amount and nature of the sewer sediments released from deposits in sewers and transported either to waste water treatment plants or discharged into the environment. Research has indicated that microbial activity in sediment can influence the physical release of sediment from in-pipe deposits. This paper reports on a series of erosion tests in which sewer sediments from different sewer networks are kept under different environmental conditions and their resistance to erosion is examined. The erosion tests are carried out under aerobic and anaerobic conditions and two temperatures, one representing ambient sewer temperatures and a lower temperature that significantly suppresses bacterial activity.