Groundwater depletion. Are Eco-friendly Energy Recharge Dams a solution?

Groundwater is a primary source of drinking water for almost two billion people worldwide. Moreover, it is critically important for energy, food security, human health and ecosystems. Yet, depletion of groundwater reserves is a common phenomenon in both humid and semi-arid regions of the world. Although non-sustainable groundwater exploitation has been documented on both regional and global scales, specific spatiotemporal characteristics need to be further studied and quantified. The phenomenon of groundwater depletion occurs when extraction from an aquifer exceeds the recharge, with the extent of the depletion effects being also determined by the aquifer type. A number of research challenges prevail, the most significant being the quantification of factors triggering groundwater depletion. Inevitably, depletion leads to increased pumping costs and the reduction of groundwater discharge to streams, springs and wetlands affecting ecosystems. Additionally, lowered water tables induce groundwater flow, which can lead to salinization by seawater intrusion in coastal aquifers. Eventually, groundwater depletion can even lead to dry wells. The main cause of groundwater depletion is the excessive extraction for irrigation especially in cases where an aquifer is only replenished in a slow manner, while climate change could potentially exacerbate the phenomenon in some regions. Global food production has increased dramatically since 1970 due to advances in well-drilling equipment and electrical pumping, and a large number of wells has been operated in a largely unregulated manner, often replacing surface-water resources. Over-irrigation may lead to crop evapotranspiration levels above those of aquifer inflow. Accordingly, in some areas, groundwater levels have declined at rates even exceeding 1 m per year. On the other hand, climate-related changes might also influence recharge rates and aggravate groundwater depletion as recharge rates are influenced by the distribution and seasonality of snow coverage as well as drought events. Projecting the effects of climate change on groundwater is a challenging task with uncertainties in all the steps of the process. So far, the impact of climate change on aquifer depletion has only moderately been compared with non-climatic drivers. Such a comparison although complex, can potentially divulge unknown aspects of groundwater depletion.

Effective strategies to mitigate groundwater depletion can be built on effective groundwater modeling incorporating land use, climate and water management scenarios. Nonetheless, groundwater modeling requires detailed hydrogeological and hydrological knowledge of a studied system in order to develop a robust conceptual model and increase reliability. Artificial groundwater recharge using treated wastewater or surface water could offer aquifer replenishment and reverses its depletion. However, artificial recharge is a complex and high cost option, and groundwater simulation models should evaluate it fully before its large scale in situ application. Artificial groundwater recharge faces certain limitations regarding location, timing, available water and its distance from the area to be recharged. Dams, can store surface water in periods of abundant precipitation, protect lowlands from flooding and provide in periods with increased water demands. Recent studies have shown that groundwater depletion may be offset if more surface water is stored in reservoirs behind dams. Additionally, these dams can be transformed into mini-scale hydropower facilities – multi scope dams – and produce clean energy. For instance, in Greece small hydroelectricity applications have a very good techno-economic performance and, therefore, a promising future. In Mediterranean countries, groundwater is an almost ubiquitous source of fresh water and covers about 60% of the water demand. Indisputably, preserving groundwater reserves is of outmost importance to support economic activities (food, tourism, industry, energy) as well as to ensure the health of humans and ecosystems. Due to its importance, the phenomenon of groundwater depletion needs to be further studied, adopting cutting edge methods and integrated approaches. In Greece, the first attempt to study groundwater depletion dates to 2013 and this was updated in 2018 through the development of the Water Resources Management Plans of Water Districts in Greece. These plans are limited to qualitative descriptions regarding only groundwater quantity and quality, however, they do provide unequivocal evidence that in certain regions of Greece groundwater is being depleted. For instance, since 1980 the decline in groundwater level recorded in the coastal area of the eastern Thermaikos Gulf has reached a rate of over 1 m per year and has caused salinization of the local aquifer up to 5 km towards the mainland. Similar problems have also been recorded in other Mediterranean countries such as Italy. Especially in coastal areas, the mismanagement of groundwater systems can lead to the drying-up of rivers and deterioration of groundwater quality. According to global practices, model-based strategies are an efficient tool to mitigate groundwater depletion. Mathematical models require a number of parameters to be measured and quantified before being introduced into the model. Vertical distribution and seasonality of snow coverage, drought events, and rainfall and temperature variations, are some of the climatic parameters that influence groundwater depletion. Additionally, the aquifer type, land use, population density, and availability of surface water for artificial groundwater recharge, all constitutes important aspects in the study of groundwater depletion. The critical step of every simulation process is the model validation and verification.

The present project aims to multi-model groundwater depletion in representative aquifers of both Greece and Italy and determine those parameters that have exacerbated this phenomenon. Moreover, various model-based strategies will simulate scenarios to inverse groundwater depletion. Field measurements in four pilot-sites will be used to validate the model parameters. The core of these scenarios will be the use of small recharge dams, while their transformation to mini-scale hydropower facilities will provide clean energy production, reduce CO2 emissions and lead to an economically feasible and eco-friendly strategy against groundwater depletion. For this purpose, an integrated software package will be developed and used to harmonize the dam operation for energy production, flood mitigation and managed aquifer recharge (MAR). Hence, in periods of high precipitation both energy production and aquifer water storage will support environmental sustainability and socioeconomic development. Accordingly, the proposed research will create interdisciplinary approaches based on a team that cross-cuts different scientific fields.