Hrvatske vode, Vol. 29 No. 118, 2021.
Preliminary communication
A contribution to improving the system of transitional waters’ hydrological measurements: Hydraulic and spectral analyses of the Neretva River flow rate
Nino Krvavica
orcid.org/0000-0001-5014-5476
; Sveučilište u Rijeci, Građevinski fakultet, Rijeka, Hrvatska
Goran Lončar
; Sveučilište u Zagrebu, Građevinski fakultet, Zagreb, Hrvatska
Dijana Oskoruš
; Državni hidrometeorološki zavod, Zagreb, Hrvatska
Igor Ružić
; Sveučilište u Rijeci, Građevinski fakultet, Rijeka, Hrvatska
Abstract
It is often not possible to determine the flow rate based on the measured water levels, i.e. to unambiguously define the stage-discharge curve, in coastal rivers affected by sea backwater. For this reason, reliable data on the daily quantities of fresh water flowing into the Adriatic Sea are still not available in Croatia. The technical development of ultrasonic flow meters has created the conditions for improving hydrological measurements of transitional waters. The first continuous flow measurement system was installed on the Neretva River at Metković in 2015. This paper is comprised of the conducted hydraulic and spectral analyses of the new generation of measurements. In the first step, the influence of the seawater bottom layer dynamics on the measured discharges at Metković was investigated using a numerical model. This was followed by a non-stationary spectral analysis aimed at comparing the time series of measured and modelled sea levels and water levels and flow rates at Metković, as well as at identifying and characterising the cause of fluctuations in intra-day flow. The conducted analyses showed that seawater dynamics in the bottom layer can have a significant impact on measured values of discharge, especially during a dry period. The numerical and spectral analyses suggest that intra-day fluctuations of measured water levels and discharges are partly caused by tidal fluctuations; however, to a greater extent, their cause should be looked for in inflow fluctuations from the upstream part of the basin.
Keywords
transitional waters; Neretva River; flow measurements; numerical model; STREAM 1D; salinity stratification; spectral analysis; continuous wavelet transformation
Hrčak ID:
274289
URI
Publication date:
30.12.2021.
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