  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.
