PLANNING SEWER INSPECTION PROGRAMMES
Sewer inspections are not very affordable, and it’s, therefore, neither possible nor cost-effective to carry them out too frequently. Some sections may require more frequent monitoring than others and for that reason, as with care itself, it is frequently essential to set priorities for review. Methods for the identification of those elements of the sewer network which require inspecting most, and also for deciding the frequency of inspection, are thus required.
There are two big questions which need to be asked if planning a sewage inspection programme:
- What’s the risk or likelihood of a specific section of the network falling?
- What is the consequences or effects of such a collapse?
The danger of failure will depend on certain key characteristics of the part of the network being assessed, including the pipe material, the location inside the system, the age of the tube, the kind of bedding and service, characteristics of the surrounding soil and water table, the imposed loads, the present and expected flow levels, the diameter and thickness of the pipe, and any history of failures or sewer blockage clearing history in the area or in other similar area of pipe within the community.
The consequences of failure will incorporate the degree and extent of flooding likely to happen, potential contamination of watercourses and groundwater, interference with different sections of the sewerage network and sewage treatment facilities downstream, and, in the case of sewer collapses, disruption to traffic, commerce, other utilities and any further action in the area of the collapse.
Both the risk and the consequences of civil engineering failure need to be taken into account when setting priorities for sewage inspection. So as to do this in a reasonable and reasonable manner, a system of allocating points to each length of pipe within the system could be adopted. A range of points can be assigned to each factor affecting the threat and the results of failure, and then a total score could be calculated for every pipe span within the network. By way of instance, sewers under primary roads or at busy shopping areas would warrant a higher score compared to those under minor roads, and asbestos cement, large diameter, trunk sewers would bring in a higher score than small diameter PVC pipes serving only a few possessions. An understanding of this age, size and pipe materials must do this.
A programme of the review can then be drawn upon the basis of their scores and the review resources and budget available.
PLANNING SEWER MAINTENANCE PROGRAMMES
The purpose of a tactical maintenance program or programme is to ensure the continuous and effective operation of the entire sewerage system in the lowest cost commensurate with those objectives. Reactive, or catastrophe, maintenance — which is dealing with faults and insecurities just — is seldom cost-effective from the long-term.
A complete and accurate set of comprehensive records (rather stored in a computer database) of this system is necessary before trying to develop a strategic maintenance programme. These records should be as detailed as possible and should contain at least the following information relating to each part in the machine:
- Name and unique identification markers
- Accurate geographic information including the exact location on elevation and plan, relevant information on every component of the system. For pipelines, this should include the diameter, thickness, material, jointing procedure, type of bedding and service, and details of any coating, liner or alternative rust protection provided. Records for mechanical/ electrical equipment and the plant might include details normally supplied by the manufacturer, including power rating, voltage, working pressures and temperatures, type of lubricants required, etc..
- Historic information — this must include any previous failures, flaws or problems, results of surveys and testimonials, and details about any previous sewer repair attempts completed
- Other information on soil conditions, water table, traffic flow, the strategic importance of streets, etc..
The arrangement of the database must allow for easy updating of the documents in order that future faults, maintenance and modifications to the system could be included as and when they occur. The objective of the database is to help in identifying potential problems and prioritising maintenance activities.
A hierarchy of maintenance operations can be identified such that failure to carry out work at the same level will frequently lead to the requirement to perform work in a higher and more expensive amount at a later date.
A simple hierarchy for sewage maintenance might be described as follows:
- Level 1 — routine and regular cleaning (pre-emptive). If that is not carried out it may result in level two maintenance requirements.
- Level 2 — leaky pipes (reactive).
- Grade 3 — Local repair and root management (pre-emptive together with the requirement being identified through sewer inspections). If this isn’t done it may result in level 4 maintenance.
- Amount 4 — relining. Failure to reline when required could cause collapse and the need to completely replace the pipe (flat 5).
- Grade 5 — replacement.
A tactical maintenance programme should try to recognise the essential frequency of every amount of maintenance to minimise overall costs. This is going to be highly dependent on local infrastructure construction requirements, and understanding has to be built up over time, amending the strategy as conditions dictate. By way of example, if more material is eliminated from a specified sewer-cleaning operation than from the preceding one on the same length of pipe, then the period between cleanings should be shortened. This emphasises the need to keep accurate records of maintenance activities so that this type of informed decision could be made.
Besides a record of accurate records of the machine, a set of standards, where various maintenance options may be assessed is required. These criteria may include goals and objectives together with particulars of the effectiveness of different maintenance operations.
