# Changes in long-term properties of the Danube river level and flow induced by damming

## TL;DR

This study investigates how dam construction on the Danube River altered its long-term flow and level dynamics, revealing significant changes in natural cycles and scaling properties upstream and downstream of the dams.

## Contribution

It applies advanced time series analysis methods to quantify the impact of damming on river dynamics and identifies specific changes in scaling and cyclic behavior over large spatial scales.

## Key findings

- Damming caused human-made cycles to appear or enhance in downstream data.
- Large-scale cycles diminished or disappeared, especially upstream, affecting river dynamics.
- Upstream stations showed a loss of annual cycles extending up to 220 km from dams.

## Abstract

In this paper we assessed changes in scaling properties of the river Danube level and flow data, associated with building of Djerdap/Iron Gates hydrological power plants positioned on the border of Romania and Serbia. We used detrended fluctuation analysis (DFA), wavelet transform spectral analysis (WTS) and wavelet-based modulus maxima method (WTMM) to investigate time series of river levels and river flows recorded at hydrological stations in the vicinity of dams and in the area of up to 480 km upstream from dams, and time series of simulated NOAA-CIRES 20th Century Global Reanalysis precipitation records for the Djerdap/Iron Gates region. By comparing river dynamics during the periods before and after construction of dams, we were able to register changes in scaling that are different for recordings from upstream and from downstream (from dams) areas. We found that damming caused appearance of human-made or enhancement of natural cycles in the small time scales region, which largely influenced the change in temporal scaling in downstream recording stations. We additionally found disappearance or decline in the amplitude of large-time-scale cycles as a result of damming, that changed the dynamics of upstream data. The most prominent finding of our paper is a demonstration of a complete or partial loss of annual cycles in the upstream stations' data that we found to extend as far as 220 km from dams. We discussed probable sources of such found changes in scaling, aiming to provide explanations that could be of use in future environmental assessments.