GIS-Driven Site Selection for the Pitt River Water Supply Tunnel: A Systematic Approach to Shaft and Alignment Optimization

Abstract

This paper presents the application of Geographic Information System (GIS) technology to optimize site selection and determine the preferred alignment for the Pitt River Water Supply Tunnel. The methodology integrates geotechnical, environmental, social and spatial data within a 1,500-hectare study area to identify and evaluate potential shaft locations and tunnel alignments. A key benefit of this GIS-driven approach is its ability to function as a living analysis model, allowing for iterations throughout the design process without compromising previously completed works. Decision criteria, such as tunnel length, seismic hazards, and land use constraints, were structured as layers within the GIS model, enabling dynamic assessments. These layers could be toggled on and off to analyze the impact of individual factors on site suitability, making the decision-making process more transparent and flexible. Layering of the decision criteria was done to develop a composite heat map which used color gradients to convey the most to the least favorable locations for shaft placement, visually representing site suitability across the project area. This analysis initially identified 61 candidate sites, which were then refined through geotechnical and constructability assessments, ultimately shortlisting four sites for detailed field investigations. The selected alignments accommodate a 2.4 m diameter steel water main, with a shaft and valve chamber in the City of Port Coquitlam as well as an underground valve chamber and shaft in the City of Pitt Meadows, near Lougheed Highway. This GIS-driven methodology optimized decision-making, minimized project risk, and provided a scalable framework for future infrastructure planning.