Wednesday, September 28, 2011

Interactions between rainwater harvesting and groundwater recharge


A paper recently published by Hubert Stahn and Agnès Tomini, «Rainwater Harvesting under Endogenous Capacity of Storage : a solution to aquifer preservation?», studies interactions between conjunctive rainwater harvesting and groundwater withdrawal.

Some of the issues explored in the article are particularly relevant given current trends towards increased rainwater harvesting. Previous posts (here and here) were pointing at possible interactions between rainwater catchment and environmental flows. Another set of underlying questions that should be addressed pertains to rainwater as a source for groundwater recharge and aquifer depletion. On these issues, interesting excerpts in the paper are as follows (the paper is too technical for me to follow, but the intro and conclusion are legible for the lay person):

«Rainwater Harvesting (RWH) is a simple technique that has been used for thousands of years. Today, this practice is enjoying a revival in popularity and an international network, the International Water Association, promotes and supports RWH initiatives worldwide as an important component in the sustainable provision of freshwater. However, the co-existence of this technique with groundwater withdrawals is not always a success story, as it can lead to depletion of the water table. (...)

(W)e are dealing with two water sources that are typically interdependent: rainwater that is harvested cannot reach the aquifer. This implies that the quantity of RWH a¤ects the dynamics of the aquifer and even the marginal pumping cost, which depends on the aquifer head. The idea of this paper is to explore this complex dynamics and especially to show that in the long run, the introduction of RWH negatively a¤ects the head of the aquifer. (...)

It is therefore interesting to wonder about the signicance of this result with respect to the principle of sustainable development. Groundwater also maintains the health of the ecosystem, which gives it a conservation value. In other words, the question must be addressed of whether the implementation of this technology might not jeopardize the sustainable level of groundwater for all its different functions

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