Mountain block recharge (MBR) mechanisms are an important component of the water budget for many alluvial aquifers worldwide. The MBR dynamics are complex, difficult to constrain, and quantification is highly uncertain. These challenges are magnified in data-scarce study areas, including the Cul-de-Sac and Leogane plains, two of Haiti’s largest alluvial aquifers, which are flanked by the Massif de la Selle mountain block. The associated groundwater supplies the regional metropolitan area of Port-au-Prince (RMPP) and it is facing increasing pressure, requiring improved understanding of the aquifer system to guide management and protection. This report introduces the aquifers and investigates the significance of river infiltration from flows originating from the mountain block. The approach to derive important insight on recharge included analysis of broad datasets on piezometry, isotopes, hydrochemistry, and streamflow. The findings indicate that river infiltration is a major source of recharge to the alluvial aquifers. Grise and Blanche river infiltration may account for >80% of recharge to the Cul-de-Sac aquifer, exhibiting temporal variation correlated to climate events such as cycles of the El Niño/La Niña Southern Oscillations. Momance and Rouyone river infiltration may account for >50% of recharge to the Leogane aquifer. The results direct attention to the Massif de la Selle carbonate aquifer system, where bulk recharge is estimated to be four times greater than both alluvial aquifers. The Massif not only supplies the RMPP with ~65% of its water supply from karst springs, but its streamflow also recharges the alluvial aquifers that supply the balance of RMPP supply.

A reconnaissance was performed for Tunnel Diquini and Source Mariani in the metropolitan region of Port-au-Prince, Haiti, to address concerns of decreasing flows and to evaluate potential impacts of a proposed river diversion scheme in the study area. The tunnel and spring are the two largest water sources serving the Port-au-Prince municipal water system and discharge from the Massif de la Selle carbonate aquifer. Considering their significance and importance to the water security of the region, there are limited data or studies specific to the water sources. An introductory framework was established regarding the flow regimes, the origin of waters, and recharge dynamics of the sources. Field reconnaissance and stable-isotope, tracer, and chloride-mass-balance techniques were applied to strengthen the conceptual understanding of the water sources. Recharge to this portion of the Massif de la Selle carbonate aquifer is variable depending on monthly rainfall intensity and 3–7-year climatic cycles. Rather than a consistent long-term decreasing flow trend, a particularly intense period from 2007 through 2010 resulted in the highest flows on record, which have steadily recessed to historical norms in recent years. The recharge characteristics and catchment areas indicate that neither water source is connected to the River Momance; however, a connection to the River Froide is possible, particularly related to the tunnel. Finally, recharge rates and an estimate of renewable groundwater in the Massif de la Selle show the regional significance and importance of the carbonate aquifer for current supplies and future water development.

ABSTRACT

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