Effects of climate change on the design of subsurface drainage systems in coastal aquifers in arid/semi-arid regions: case study of the Nile delta

The influence of climate change on the availability and quality of both surface- and ground-water resources is well recognized nowadays. In particular, the mitigation of saline water intrusion mechanisms in coastal aquifers is a recurrent environmental issue. In the case of the Nile delta, the presence of sea level rise and the perspective of other human-induced stressors, such as the next operation of the Grand Ethiopian Renaissance Dam, are threats to be taken into account for guaranteeing resilient agricultural practices within the future possible scenarios. Subsurface drainage offers a practical solution to the problem of upward artesian water movement and the simultaneous downward flow of excess irrigation water, to mitigate the salinization in the root zone. Subsurface draining systems can contribute to mitigate the vulnerability to climate change and to the increased anthropic pressure insofar they are able to receive the incremented flow rate due to the foreseen scenarios of sea level rise, recharge and subsidence. This paper introduces a rational design of subsurface drainage systems in coastal aquifers, taking into account the increment of flow in the draining pipes due to future possible conditions of sea level rise, artificial recharge and subsidence within time horizons that are compatible with the expected lifespan of a buried drainage system. The approach proposed in this paper is characterized by the assessment of the incremental flow through the drains as a function of various possible scenarios at different time horizons. Our calculations show that the impact on the discharge into the existing subsurface drainage system under the new foreseen conditions is anything but negligible. Thus, future climate-related scenarios deeply impact the design of such hydraulic structures, and must be taken into account in the frame of the next water management strategies for safeguarding agricultural activities in the Nile delta and in similar coastal contexts.