Flexible design : an innovative approach for planning water infrastructure systems under uncertainty

Abstract

This thesis develops a framework for a flexible design approach to support decision-making in water supply infrastructure planning. It contrasts with a conventional, deterministic planning approach that uses past data or forecasts to anticipate future needs. This thesis surveys current approaches that attempt to consider uncertainty, including scenario planning, decision analysis, sensitivity analysis, real options, dynamic strategic planning, and adaptive management. A flexible design approach builds on current approaches and explores flexibility through infrastructure size and function. The approach intends to be applicable across various water infrastructure systems. This thesis describes real world and theoretical applications of flexible design, including climate change adaptation planning for water utilities, flexible planning for water infrastructure investments, and flexibility in urban drainage systems. The proposed flexible design approach employs probabilistic and simulation methods to anticipate a range of future circumstances and identify top-performing strategies. The engine of the framework is a time-series stochastic analysis that uses simulation in a discounted cash flow Excel model. First, it identifies key inputs and performance metrics, characterizes uncertainty distributions, and defines strategies of varying flexibility. Next, it employs Monte Carlo simulation and compares strategy performance through target curves and multiple criteria analyses. Singapore's water resources system inspires the characteristics of the model. The best-performing flexible approach introduces a cost savings of 15% over a 50-year timespan. To successfully implement a flexible design approach, leaders in the profession must guide the shift to planning methods that explicitly recognize the role of uncertainty in the planning process. While some implementation barriers present difficulties, the proposed flexible design approach enables substantial cost savings and fosters a deeper understanding of a water resources system in the face of future uncertainty.