The Diquini Tunnel is the largest single source of water supply in Haiti, accounting for 24-percent of the water produced for the metropolitan water system of Port-au-Prince. The 1.5-km tunnel was conceived during the United States occupation of Haiti in the early 20th Century, and was completed in 1940 by the J.G. White Engineering Corporation. The tunnel penetrates the Eocene-age Massif de la Selle limestones, targeting a fault and karst zones to produce a gravity-fed water supply for the city. Tunnel flows range from 11,085 to 73,265 m3/day, averaging approximately 28,000 m3/day.
A reconnaissance and forensic research effort was undertaken to characterize the hydrology of the tunnel and better understand the origin of its flow and its relationship with local and regional groundwater and surface water systems. The study included field mapping, terrain assessment using recent LiDAR data, and laboratory analysis of the tunnel water for physiochemistry, stable isotopes, chlorofluorocarbon (CFC), and sulfur hexafluoride (SF6).
Several decades of historical monitoring data were uncovered and synthesized with the new results to bring light to the complex hydrology of the tunnel, and the importance of large recharge events and El Niño-Southern Oscillation cycles in maintaining productive tunnel flows to serve the Port-au-Prince metropolitan area. The findings of the study also provide important insights for groundwater development and management related to the Massif de la Selle aquifer.