Analysis of Inflow and Infiltration in a Low-Pressure Sewer System

Alves, Billy Michael (2022) Analysis of Inflow and Infiltration in a Low-Pressure Sewer System. [USQ Project]

Text (Project)

Download (5MB) | Preview


Inflow and Infiltration (I/I) have a significant impact on the hydraulic capacity of sewer systems. Whilst the impact this has on traditional gravity sewer system has well been researched in previous literature, the quantifiable impacts I/I has on Pressure Sewer System’s (PSS) is largely unknown. The aim of this project was to quantify the I/I in an existing PSS within the Eurobodalla local government area, and determine the operational costs associated with the collection, transfer, and treatment of the I/I.

The existing methods for estimating the various components and parameters of sewage flows in PSS vary depending on the guideline used for the design of the PSS. Whilst these guidelines provide a good benchmark for design factors and objectives in greenfield systems, there is little evidence that the guidelines are relevant to retrofit of PSS in backlog sewerage areas.

The methodology for quantifying I/I followed existing methods used from previous literature related to management of I/I in sewerage systems. In this research, several methods which improve the accuracy and reliability of determining Dry Weather Flow (DWF) were implemented through an iterative process, with an improved technique for quantifying hourly and daily DWF recognised. This technique includes derivation of the diurnal flow pattern and an appropriate return to sewer factor for the system, based on analysis of existing flow monitoring data during dry weather periods. Daily water consumption data for the system is also used as a model input for determining the DWF values for a selected period.

Once an accurate and reliable DWF pattern had been established, a customised hydraulic model was developed to quantify the Rainfall Derived Inflow and Infiltration (RDII) that occurred during significant rainfall events. The model was calibrated, validated, and optimised to ensure a good representation of the RDII response to rainfall events was observed and appropriate outputs were quantified using the model.

The comparison of the model outputs with the values from relevant design and management guidelines demonstrated that further investigation into the sources of I/I is warranted, due to the high quantities of I/I flows entering the PSS. The I/I flows that can be expected during and after a rain event are consistent and predictable.

Whilst the increased I/I volumes may result in increased risk of environmental, public health, and social issues occurring, there is only a relatively minor economic impact associated with I/I in the PSS analysed.

The results from the research provide opportunity to develop appropriate design parameters for design and construction of pressure sewer systems in backlog sewerage areas. The key parameters for a PSS which were identified by this research were daily water consumption, and the percentage of water consumption being returned to sewer. These parameters should be included when establishing DWF values as part of analysis of the RDII component of I/I flows.

Statistics for USQ ePrint 51865
Statistics for this ePrint Item
Item Type: USQ Project
Item Status: Live Archive
Faculty/School / Institute/Centre: Current – Faculty of Health, Engineering and Sciences - School of Engineering (1 Jan 2022 -)
Supervisors: Aravinthan, Vasantha
Qualification: Bachelor of Engineering (Honours) (Civil)
Date Deposited: 19 Jun 2023 01:52
Last Modified: 20 Jun 2023 01:05
Uncontrolled Keywords: Inflow and Infiltration (I/I); hydraulic; sewer systems

Actions (login required)

View Item Archive Repository Staff Only