Abstract
Long-term groundwater level analysis, which is usually based on traditionally defined hydrological years is essential in an era of global warming and other climatic and environmental changes, especially in urban areas. A complex interplay of multiple factors influencing the groundwater level makes the investigation of their interdependencies a challenge. Based on multiple data sets and a long time series available as well as specific geological and hydrological conditions, a semi-urban district of Wrocław/Poland was selected as a case study for investigating these dependencies. This paper presents an interdisciplinary approach to the analysis of groundwater level fluctuations by combining mathematics, signal processing, hydrogeology, and meteorology. Applying well-known methods from disciplines other than hydrogeology, the authors investigated seasonal behavior and similarity of groundwater level fluctuations during 15 hydrological years. Based on segmentation and agglomerative clustering (AHP), five classes of groundwater levels fluctuations for predefined hydrologic years and the corresponding seasons were identified and compared to the classification scheme by Pleczyński. Additionally, the relationship between precipitation and groundwater level was investigated using Pearson, Kendall and Spearman correlations. This led to the identification of “typical” and “untypical” seasons for the correlation between the cumulative precipitation sum and groundwater levels. The results presented here will be used for further investigations of groundwater level fluctuations using additional factors and statistical methods. These aim to identify periods that describe similarities better than the commonly used hydrological year.
Highlights
Groundwater, amounting to 23.4 million km3, is the second largest resource of freshwater in the world, after glaciers and permanent ice caps with a volume of 32.9 million km3, and the only widely accessible fresh water source [1,2,3]
If the observation point had been located in a undisturbed environment, it would be characterized as the type III or as a type IV
The best option to identify the character of the groundwater level fluctuations and the general shape of the groundwater level diagram during the hydrological year (HY) is clustering (Figure 12)
Summary
Groundwater, amounting to 23.4 million km , is the second largest resource of freshwater in the world, after glaciers and permanent ice caps with a volume of 32.9 million km , and the only widely accessible fresh water source [1,2,3]. Sci. 2020, 10, 3553 stress, especially in urban and semi-urban areas where global warming influences its quantity, and many artificial factors have a negative effect on the available volume of groundwater [4]. To manage this precious resource properly, we have to know how much water exists in the aquifer. We need long-term groundwater level observations, which are important for effective and sustainable water management, geoengineering as well as for a reliable freshwater supply
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