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A study of the groundwater flow and the saltwater intrusion phenomenon at the alluvial aquifer of Katapola at the island of Amorgos, using the grounwater flow model PTC

Siaka Markella

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URI: http://purl.tuc.gr/dl/dias/653A1687-39B0-4C6D-87A8-E114041F621C
Year 2015
Type of Item Diploma Work
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Summary

Saltwater intrusion is a common phenomenon in coastal aquifers that can degrade the quality of water intended for drinking and irrigation purposes. Small islands are small scale systems that are very vulnerable to saltwater intrusion. Especially, in dry periods, the problem is exacerbated, due to increased touristic activity and irrigation needs. This fact, makes water resources management, in small islands, a big challenge and, at the same time, an urgent need. Amorgos island, is one of the four most water demanding islands, of South Aegean Sea, receiving more than 30.000m3 of drinking water, from ships, annually. At the same time, Amorgo’s coastal communities are seriously affected by saltwater intrusion. In order to provide groundwater management options for the alluvial aquifer of Katapola, located on Amorgo’s island, a three-dimensional groundwater flow mathematical model was developed. Argus One was chosen for the simulation, coupled with Princeton Transport Code (PTC). PTC operates, using a combination of finite element and finite difference numerical methods, to solve a system of spatially varying equations. The model takes into account the system’s geomorphological characteristics, such as depth, hydraulic conductivity, storativity and porosity, while providing information on temporal and spatial variations of hydraulic heads and groundwater’s flow velocity. In order to study the extent of saltwater intrusion, the sharp-interface approximation combined with the Ghyben-Herzberg equation was used. Ghyben-Herzberg equation was used in conjunction with a correction factor that accounts for the hydrodynamic dispersion constant of the brackish zone. The model was calibrated until satisfactory agreement between simulated data and field measurements was achieved. To facilitate model evaluation, in terms of accuracy, model evaluation statistics were calculated, as well. The prediction model results show that under the current pumping strategies (overexploitation), the saltwater intrusion front will continue to move inland, posing serious and irreversible problem to the groundwater quality. The management goal is to find the optimal pumping rates from the existing wells, so as to prevent further spreading of saltwater intrusion. For this purpose, several water management scenarios were developed, taking into account the effects that climate change will have on rainfall, water supply, mean sea level and population growth. Controlling the expansion of seawater intrusion, in Katapola, includes the periodic deactivation of most pumping wells and the designing of alternative resources/plans for water supply.

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