Water management

Master Thesis Water Systems and Global Change Group in partial fulfilment of the degree of Master of Science in 2023 master program Climate Studies at Wageningen University, the Netherlands. This master thesis is a contribution in the context of the BO project: Duurzaam regenwaterbeheer BES-eilanden.

Abstract This study examines the impact of climate change and water management choices on infiltration and runoff in the case of the Salinja di Vlijt catchment on Bonaire. Climate change will affect precipitation, temperature will increase, sea level will rise (at least 0.2 meters), and tropical storms will be more intense. This will influence the catchments hydrology – runoff will decrease in base flow and increase in peak flow. The current water management measures – drain pipes, channels, reservoirs, and dams – lead to nuisance flooding and partly are in need of maintenance. Evaluating different water management scenarios, rain barrels and rooftop disconnection systems with water storage can reduce runoff and improve infiltration, while additional infiltration trenches decrease catchment discharge and increase infiltration in specific sub-catchments. Extra reservoirs have limited impact on overall runoff and infiltration. Implementing selected measures can help mitigate the effects of changing urbanization and climate change in the catchment. Further research is required to explore the combined effects of measures and assess spatial feasibility. This study contributes valuable insights for effective water management strategies in the Salinja di Vlijt catchment, and the approach presented can be applied to other catchments.

The climate in Curaçao is semi-arid to arid. Every century several extended periods of drought occur with practically no rain. A whole system of earthen dams for water conservation was developed since early colonial times. These dams force part of the rainwater into the ground and help maintain groundwater levels; they also help to combat erosion. A large number of smaller dams is more effective than a few large ones. This way ground water levels are influenced over a relatively large area. A few larger ones were constructed in the 20th century but even so these are relatively small; the very largest one having a capacity of 600.000 tons. The next one comes in at 450.000 tons; all the others are substantially smaller. The larger dams are less effective, they store more water above ground in a deeper temporary lake where a larger fraction of the water is subject to evaporation over a longer period of time as compared to a series of smaller dams with the same capacity.

Since most of the food production was local, this system was of the utmost importance. Curaçao is divided in 48 different watersheds (catchment areas). With time the water flows in practically all of these were all extensively dammed, except for the limestone and calcareous areas. Housing developments have lead to the destruction of many dams. There are still a few large ones and about 800 smaller ones which are still functioning. In the past there were at least 1500 of such dams.

This report was published in 2018 and information was added in 2021, and 2022.

This report gives an overview of the most prominent problems currently encountered at the Lac bay area. To change the currently negative situation at the Awa di Lodo area with dying mangrove and unfavorable conditions for fish, it is recommended to improve water circulation at the Awa di Lodo area. This will lead to a better water quality and especially to a lower salt concentration. Based on this analyses, recommendations are made for five specific management actions which individually or in combination could be part of a management plan for the ecological rehabilitation of Lac Bonaire.

Management actions are conducted both from the land and sea side, they are short or long term and they can be summarized as follows:

• To clear the upstream (north) section at the labado from sediments in order to restore its function as sediment trap.
• To clear the east and west side feeder channels from sediment and mangrove in order to improve water circulation in the Awa di Lodo area.
• To construct a new central feeder channel following an existing creek pattern to improve water circulation in the Awa di Lodo area. Whether or not this new feeder channel is going to be constructed, will depend on monitoring results of changes in salt concentration in the Awa di Lodo after the existing feeder channels have been cleaned.
• To start a discussion with livestock owners in the greater catchment area on how over-grazing by roaming livestock can be stopped while at the same time these owners can make a living from their business.
• To remove Rhizophora established propagules at the sea side in order to slow down mangrove occupation of the bay area.

Each operation can be separately budgeted and they can be phased in time.