Optimised Selection of Water Supply and Irrigation Sources—A Case Study on Surface and Underground Water, Desalination, and Wastewater Reuse in a Sahelian Coastal Arid Region

Abstract

This paper presents a general conceptual procedure and an economic, sustainable, resilient, and integrated solution for the water supply and landscape irrigation of a large touristic complex projected in an arid to semi-arid southwest coastal region of the island of Santiago in Cape Verde, in the Western African Sahel. It is assumed that underground water can be explored, but at a minimum level to avoid aquifers depletion or any eventual saline intrusion, and that surface water can be mobilised with the construction of a dam. Other important sources of water that were identified, assessed, and compared include treated wastewater produced in the complex, which can be reused for irrigation after undergoing tertiary treatment, and desalinated sea water, which requires the construction of a desalination plant. The devised procedure includes the definition of all feasible alternatives by a deterministic complete enumeration, and the selection of the optimised solution that may be determined by a single objective cost function to be minimised, as well as by a multi-criteria decision-making process that considers a conventional 1–5 score to be maximised. Beyond the cost, four additional criteria are considered and scored for each solution, namely, Environmental Sustainability,Water Quality, Resilience, and Local Integration, and for the relative weighting between criteria a weighted sum model is assumed. For the parameters and cost models used, the best solution that was found considers that the landscape irrigation is performed with surface water and reused wastewater, and that the water distribution network is supplied with underground and desalinated water. Other solutions more or less close can be selected based on different scores or different decision maker weighting preferences.