National-Scale Optimized Design of Cost-Effective Water Supply and Transfer Systems

Many countries contain some regions with water surpluses and others with deficits, and with differences in the marginal cost of future water supply development. These factors imply to some extent an opportunity to attain or maintain water supply service levels at lower cost by sharing resources regionally through water transfers. There is then the question of which transfers to select, in conjunction with which existing and new supply options. In countries with strong disparities in regional water availability and population density, a least-cost design may imply some transfers which are less attractive from a political or environmental point of view. Political, social, and engineering preferences may push toward relying on local sources rather than imports, but how far should planners stray from least-cost infrastructure upgrade programs? One way to address this question is to identify how national-scale water supply and transfer infrastructure development would change as planners stray from the least-cost design toward systems more aligned with their preferences (e.g., fewer imports). We demonstrate such an approach on a national-scale problem: the water supply infrastructure of England and Wales for the year 2050 under various demand, drought resilience, and environmental sustainability scenarios. National-scale results show how insufficient transfers may strand surplus water, and that water sharing at regional and national scales reduces costs and helps balance supply and demand.