Multitemporal analysis of hydropeaking and surface water-groundwater interaction at regional scale

The management of hydropower plants affects the discharge of the rivers at multiple temporal scales, including daily, weekly and yearly signals, which in turn propagate into the aquifer. In this work, we apply wavelet analysis techniques to study how the weekly signal affects the groundwater table in an Alpine valley in the north of Italy. The valley is traversed by four reaches differently affected by hydropeaking. In our study, we prepared a transient model of the aquifer during two different hydrological years: 2009/10 and 2016/17, the second characterized by lower precipitation. We analyze both the river and the groundwater heads using continuous wavelet analysis and wavelet coherence analysis. Results show that hydropeaking displays a stronger weekly signal during drought conditions, not only in the river fluctuations but also in the groundwater heads and the exchanged water between the rivers and the aquifer. In addition, maps based on the weekly signal reveal that despite the stronger impact during the drought conditions, the area of the aquifer affected by hydropeaking is similar in the two compared years.