Sewer inflow and infiltration for catchments with high rainfall and aging infrastructure

Keily, Rhys (2019) Sewer inflow and infiltration for catchments with high rainfall and aging infrastructure. [USQ Project]

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As traditional gravity sewer systems age, they become less efficient due to an increase in Inflow and Infiltration (I/I) of stormwater and groundwater into the system. The current sewage estimation methods used throughout Australia do not reflect actual flow data, sometimes not even considering major extraneous flows. These methods adopt the use of crude blanket values, causing great inaccuracies and misleading sewage flow estimations data.

The aim of this project was to explore methods to adequately identify and quantify I/I, then determine the implication it has on a sewerage network. By utilising a combination of respectable existing identification and quantification methods, and modifying as necessary, a customised hydraulic estimation method was designed.

The methodology was to consider and evaluate a sewerage catchment in a holistic manner. With significant emphasis placed separately on rainfall, groundwater table, watercourses, potable water consumption and sewerage infrastruction conditions. These factors are major contributors or have a substantial influence on sewage flows.

Once this customised hydraulic estimation method was derived, it was implemented into a case study catchment for refinement. The township of Gordonvale was used, as it experiences large peaks in sewage flows due to high annual rainfall and prolonged sewage flows after rain events due to the deteriorating sewerage infrastructure. The researched sewage flow estimation methods were all implemented for comparison against historic sewage flow data. The customised hydraulic estimation method generated results and compared against the other estimation methods.

The results revealed that the designed custom sewage estimation method accurately predicted sewage flows for the trial periods. It was able to quantify sources of I/I and revealed that the ageing and defective sewage infrastructure to be the foremost contributing factor, with ground water infiltration of major concern.

A remediation model was also undertaken that provided a comparison of the expected results to repair this increasing issue. Full sewer replacement with conventional PVC and the more recent NuSewer system were investigated, along with repair of house connection branches.

Overall, the customised estimation method adequately achieved to identify and predict sewage flows with greater accuracy than the current methods used. The customised hydraulic model that was developed identifies areas of concern and better estimates sewage flows without the need for adopting blanket estimation values. This method provides a greater level of confidence in determining the makeup of the sewage flows and identifying the major contributing factors.

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Item Type: USQ Project
Item Status: Live Archive
Faculty/School / Institute/Centre: Historic - Faculty of Health, Engineering and Sciences - School of Civil Engineering and Surveying (1 Jul 2013 - 31 Dec 2021)
Supervisors: Aravinthan, Vasantha
Qualification: Bachelor of Engineering (Honours) (Civil)
Date Deposited: 11 Aug 2021 02:05
Last Modified: 26 Jun 2023 22:39

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