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.

Proposal of the “Wastewater Use Basin” Concept as an Integrated Sewage and Rainwater Management Unit in Semiarid Regions—A Case Study in the Southeast of the Iberian Peninsula

“…Both in the Campo of Cartagena-Mar Menor and the Vega Baja districts, the sanitation network is unitary (sewage and rainwater in the same collector), although in some areas they have a mixed sanitation network (sewage in one collector and rainwater in another collector), and gather rainwater from urban areas, in addition to the wastewater flows generated. With the objective of reducing the danger of urban floods, many cities have begun to design sustainable systems for the circulation of rainwater, through the construction of large-capacity collectors, environmental tanks or stormwaters [42] and flood parks, at the same time incorporating green infrastructure [54].…”

“…Bearing in mind all the costs of production, extraction and transport, desalination is the most expensive option compared to the other sources (stormwater and IPR) [32]. Nonetheless, it depends on the decisionmakers and the final use of the water, as Diogo, Resende, and Oliveira [42] show in the case of Cape Verde, where the most suitable source for landscape irrigation was freshwater and reclaimed water, while for water distribution it was groundwater and desalinated water. In the area of study, due to the marine intrusion into the sewerage system, STPs' effluent must be treated once more with reverse osmosis, in order to adjust the salinity levels.…”

Humanitarian Assistance in G5 Sahel: Social Sustainability Context of Macrologistics Potential

“…It usually erodes the surface of the fields and housing soils. Furthermore, the water supply and landscape irrigation are complex issues in the Western African Sahel, especially due to performance with surface water and reused wastewater [53]. Very sensitive vegetation of the semiarid zone and lack of forests constitutes another challenging field for Sahelian space [54], especially when water governance is still being developed [55].…”

How to Prioritize the Attributes of Water Ecosystem Service for Water Security Management: Choice Experiments versus Analytic Hierarchy Process

“…where N is the number of attributes. Finally, the Consistency Ratio (CR), also proposed by Saaty, is evaluated, as in Equation (9).…”

“…In addition, WES attributes need to be weighted to support decision making, e.g., in the face of water scarcity situations [8]. In situations of scarcity, it is possible to identify optimized solutions for water supply and irrigation based on multi-criteria models [9].…”