ASSESSING SEDIMENT REGIME ALTERATION OF THE LOWER DRAVA RIVER

Alterations to the sediment regime of the lower Drava River were assessed using the rescaled adjusted partial sums (RAPS) method and possible causes of these changes are discussed in this paper. The sudden alteration to sediment regime and the sharp decreases of suspended sediment concentration (SSC) at the two gauging stations in the lower Drava River began in the 1980s. Suspended sediment load decreased about 65% between 1967–1981 (0.922×106 t/year) and 2003–2017 (0.323×106 t/year) for the Botovo station. For the Donji Miholjac station, suspended sediment load decreased about 81% between 1971–1981 (1.383×106 t/year) and 2007–2017 (0.263×106 t/year). The construction and operation of reservoirs were the main reasons for these sharp alterations. SSC and flow discharge (Q) relationships were assessed by proposing a new form of a sediment rating curve (SRC). Compared with the traditional SRC approach, the new form of the SRC can better capture seasonal dynamics of SSC at daily and monthly time-scales

Beitrag zur Verbesserung des Systems für hydrologische Messungen von Übergangsgewässern: hydraulische Analyse und Spektralanalyse von Durchflüssen am Fluss Neretva

U priobalnim rijekama koje su pod utjecajem uspora mora često nije moguće odrediti protok na osnovu izmjerenih vodostaja, odnosno jednoznačno definirati protočnu krivulju. Iz toga se razloga u Hrvatskoj još uvijek ne raspolaže pouzdanim podacima o dnevnim količinama slatke vode koja utječe u Jadransko more. Tehničkim razvojem ultrazvučnih strujomjera postigli su se uvjeti za poboljšanje hidroloških mjerenja prijelaznih voda. Prvi takav sustav kontinuiranog mjerenja protoka postavljen je 2015. godine na rijeci Neretvi u Metkoviću. U ovome radu provedena je hidraulička i spektralna analiza nove generacije mjerenja. U prvom je koraku pomoću numeričkog modela istražen utjecaj dinamike pridnenog sloja slane vode na izmjerene protoke u Metkoviću. Potom je provedena nestacionarna spektralna analiza kako bi se usporedili vremenski nizovi izmjerenih i modeliranih razina mora te vodostaja i protoka u Metkoviću, te kako bi se identificirao i okarakterizirao uzrok unutar-dnevnih oscilacija protoka. Provedene su analize pokazale da dinamika slane vode u pridnenom sloju može imati značajan utjecaj na izmjerene vrijednosti protoka, posebno tijekom sušnog perioda. Numerička i spektralna analiza sugeriraju da unutar-dnevne oscilacije izmjerenih vodostaja i protoka djelomično imaju uzrok u plimnim oscilacijama, ali u većoj mjeri uzrok treba potražiti u oscilacijama dotoka s uzvodnog dijela sliva.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.An den küstennahen Flüssen, die wegen des Meeres langsamer fließen, ist es oft unmöglich, den Durchfluss auf Grund von gemessenen Wasserständen zu bestimmen, bzw. die Durchflusskurve eindeutig zu definieren. Aus diesem Grunde stehen in Kroatien zuverlässige Angaben zu den Tagesmengen an Süßwasser, die in das Adriatische Meer fließen, noch immer nicht zur Verfügung. Dank der technischen Entwicklung von Ultraschall-Durchflussmessern konnten die hydrologischen Messungen von Übergangsgewässern verbessert werden. Ein erstes System zur kontinuierlichen Durchflussmessung wurde 2015 am Fluss Neretva in Metković eingesetzt. In dieser Untersuchung wurden die hydraulische Analyse und Spektralanalyse einer neuer Generation von Messungen durchgeführt. In der ersten Phase wurde anhand eines numerischen Modells der Einfluss der Dynamik der bodennahen Salzwasserschicht auf die gemessenen Durchflüsse in Metković untersucht. Danach wurde die nicht-stationäre Spektralanalyse durchgeführt, um die Zeitreihen von den gemessenen und von den modellierten Meeresspiegeln sowie Wasserständen und Durchflüssen in Metković zu vergleichen und die Ursache von täglichen Durchflussschwankungen zu bestimmen und zu beschreiben. Die durchgeführten Analysen zeigen, dass die Salzwasserdynamik in der bodennahen Schicht auf die gemessenen Durchflusswerte einen großen Einfluss haben kann, besonders während der Trockenzeit. Die numerische Analyse und die Spektralanalyse deuten darauf hin, dass die täglichen Durchflussschwankungen von gemessenen Wasserständen und Durchflüssen teilweise ihre Ursache in Flutschwankungen haben. In größerem Maße soll aber die Ursache in Zulaufschwankungen im oberen Teil des Einzugsgebietes gesucht werden

Beitrag zur Verbesserung des Systems für hydrologische Messungen von Übergangsgewässern: hydraulische Analyse und Spektralanalyse von Durchflüssen am Fluss Neretva

U priobalnim rijekama koje su pod utjecajem uspora mora često nije moguće odrediti protok na osnovu izmjerenih vodostaja, odnosno jednoznačno definirati protočnu krivulju. Iz toga se razloga u Hrvatskoj još uvijek ne raspolaže pouzdanim podacima o dnevnim količinama slatke vode koja utječe u Jadransko more. Tehničkim razvojem ultrazvučnih strujomjera postigli su se uvjeti za poboljšanje hidroloških mjerenja prijelaznih voda. Prvi takav sustav kontinuiranog mjerenja protoka postavljen je 2015. godine na rijeci Neretvi u Metkoviću. U ovome radu provedena je hidraulička i spektralna analiza nove generacije mjerenja. U prvom je koraku pomoću numeričkog modela istražen utjecaj dinamike pridnenog sloja slane vode na izmjerene protoke u Metkoviću. Potom je provedena nestacionarna spektralna analiza kako bi se usporedili vremenski nizovi izmjerenih i modeliranih razina mora te vodostaja i protoka u Metkoviću, te kako bi se identificirao i okarakterizirao uzrok unutar-dnevnih oscilacija protoka. Provedene su analize pokazale da dinamika slane vode u pridnenom sloju može imati značajan utjecaj na izmjerene vrijednosti protoka, posebno tijekom sušnog perioda. Numerička i spektralna analiza sugeriraju da unutar-dnevne oscilacije izmjerenih vodostaja i protoka djelomično imaju uzrok u plimnim oscilacijama, ali u većoj mjeri uzrok treba potražiti u oscilacijama dotoka s uzvodnog dijela sliva.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.An den küstennahen Flüssen, die wegen des Meeres langsamer fließen, ist es oft unmöglich, den Durchfluss auf Grund von gemessenen Wasserständen zu bestimmen, bzw. die Durchflusskurve eindeutig zu definieren. Aus diesem Grunde stehen in Kroatien zuverlässige Angaben zu den Tagesmengen an Süßwasser, die in das Adriatische Meer fließen, noch immer nicht zur Verfügung. Dank der technischen Entwicklung von Ultraschall-Durchflussmessern konnten die hydrologischen Messungen von Übergangsgewässern verbessert werden. Ein erstes System zur kontinuierlichen Durchflussmessung wurde 2015 am Fluss Neretva in Metković eingesetzt. In dieser Untersuchung wurden die hydraulische Analyse und Spektralanalyse einer neuer Generation von Messungen durchgeführt. In der ersten Phase wurde anhand eines numerischen Modells der Einfluss der Dynamik der bodennahen Salzwasserschicht auf die gemessenen Durchflüsse in Metković untersucht. Danach wurde die nicht-stationäre Spektralanalyse durchgeführt, um die Zeitreihen von den gemessenen und von den modellierten Meeresspiegeln sowie Wasserständen und Durchflüssen in Metković zu vergleichen und die Ursache von täglichen Durchflussschwankungen zu bestimmen und zu beschreiben. Die durchgeführten Analysen zeigen, dass die Salzwasserdynamik in der bodennahen Schicht auf die gemessenen Durchflusswerte einen großen Einfluss haben kann, besonders während der Trockenzeit. Die numerische Analyse und die Spektralanalyse deuten darauf hin, dass die täglichen Durchflussschwankungen von gemessenen Wasserständen und Durchflüssen teilweise ihre Ursache in Flutschwankungen haben. In größerem Maße soll aber die Ursache in Zulaufschwankungen im oberen Teil des Einzugsgebietes gesucht werden

Numerische Analyse der Wirkung der Schleuse auf die Verhinderung von Salzwasserintrusion entlang des Flusses Neretva

3D numeričkim modelom provedena je numerička analiza dinamike pronosa slane vode u koritu rijeke Neretve na dionici 0+000.0 m - 25+000.0 m. Osim postojećeg stanja korita rijeke analizirane su i hipotetske situacije sa izvedbom jedne brane u profilu 2+000.0 m (velika dubina i mala širina) ili 4+000.0 m (mala dubina i velika širina), te izvedbom 4 brane u profilima 2/4/6/8+000.0. Regulacija podizanja i spuštanja brane vezana je uz srednji izmjereni protok na mjernoj postaji Metković u prethodnom razdoblju od 24 h (QSR-24) ili 6 h (QSR-6). U situacijama QSR-24 > 300 i 350 m3/s, odnosno QSR-6 > 300 m3/s, brana je potpuno spuštena, dok se za manje srednje vrijednosti protoka brana podiže do određene razine (od -2 m do -5 m) kroz jedan sat. Korišten je 3D numerički model Mike 3fm, zasnovan na metodi konačnih volumena. Za kalibraciju numeričkog modela korišteni su izmjereni protoci, razine i salinitet na monitoring postajama u 2018. godini, dok su za validaciju modelskih rezultata korišteni podaci iz 2017. godine. Podaci o temperaturi i salinitetu mora u akvatoriju ušća Neretve preuzeti su iz nacionalnih programa praćenja morskog okoliša. Modelska dinamika uzvodno-nizvodne translacije slanog klina u nestacionarnim uvjetima strujanja u suglasju je s mjerenjima. Modelska debljina razdjelne zone između slatke i slane vode veća je od izmjerene, kao posljedica numeričke difuzije i usvojene proračunske diskretizacija u vertikalnom smjeru od 1 m. Mjerene vrijednosti i rezultati modeliranja upućuju na zaključak da pri nestacionarnim protocima većim od 700 m3/s dolazi do potpunog istiskivanja slanog klina iz riječnog korita, dok pri protoku manjem od 150 m3/s slani klin napreduje do uzvodne stacionaže 20+909.0 m (Metković) i dalje uzvodnije. Ukoliko se želi spriječiti intruzija slanog klina uzvodno od stacionaže brane (2+000.0 m ili 4+000.0 m) potrebno je izvesti branu s podizanjem do dubine -2 m, uz uvjet podizanja brane QSR-24 300 and 350 m3/s and QSR-6 > 300 m3/s, the dam was fully lowered whereas at smaller mean discharge values the dam is lifted up to a certain level (from -2 m to -5 m) during one hour. The 3D numerical model Mike 3fm, based on the finite volume method, was implemented. The discharges, levels and salinity measured at monitoring stations in 2018 were used for the model calibration and the 2017 data for the model results validation. Data on the sea temperature and salinity in the waters of the Neretva river mouth were taken from the national marine environment monitoring programmes. The model dynamics of the upstream-downstream translation of the salt “wedge” in non-stationary circulation conditions is in line with the measurements. The model thickness of the dividing zone between the freshwater and saltwater is larger than the one measured as a result of the numerical diffusion and adopted discretization of the calculation in the vertical direction of 1 m. The measured values and modeling results point to the conclusion that a complete extrusion of the salt “wedge” from the riverbed occurs at non-stationary discharges larger than 700 m3/s whereas the salt “wedge” advances upstream to 20+909.0 m (Metković) and further at discharges lower than 150 m3/s. If the intrusion of the salt “wedge” upstream of the dam (2+000.0 m or 4+000.0 m) is to be prevented, a dam with a lifting to the depth of -2 m, under the condition of dam lifting at QSR-24 300 und 350 m3/s, bzw. QSR-6 > 300 m3/s, ist die Schleuse geschlossen, während im Falle von niedrigeren mittleren Durchflusswerten die Schleuse bis zu einer bestimmten Höhe (von -2 m bis -5 m) auf eine Stunde geöffnet wird. Das numerische 3D-Modell Mike 3fm, das auf der Methode der finiten Elemente gründet, wurde eingesetzt. Zur Kalibrierung des numerischen Modells wurden die in 2018 an Überwachungsstationen gemessenen Werte von Durchflüssen, Wasserständen und Salinität genutzt, während zur Validierung der Modellergebnisse die Angaben aus dem Jahr 2017 genutzt wurden. Die Angaben zur Temperatur und Salinität an der Mündung der Neretva wurden aus den nationalen Programmen zur Überwachung der Meeresumwelt übernommen. Die Modelldynamik des Vordringens des Salzkeils flussaufwärts und flussabwärts bei der nichtstationären Strömung stimmt mit den Messungen überein. Die Modelldichte der Übergangszone zwischen Süßwasser und Salzwasser ist höher als die gemessene Dichte, was als Folge der numerischen Diffusion und angenommenen Diskretisierung in der vertikalen Richtung von einem Meter gesehen wird. Die gemessenen Werte und die Ergebnisse der Modellierung weisen auf die Schlussfolgerung hin, dass bei nichtstationären Durchflüssen, die großer als 700 m3/s sind, zu einer völligen Verdrängung des Salzkeils aus dem Flussbett kommt, während bei dem Durchfluss unter 150 m3/s der Salzkeil bis zur Stationierung 20+909.0 m (Metković) und weiter flussaufwärts vordringt. Wenn man die Intrusion des Salzkeils flussaufwärts von der Stationierungsschleuse (2+000.0 m oder 4+000.0 m) verhindern will, sollte eine Schleuse gebaut werden, die bis zur Tiefe -2 m unter der Bedingung der Schleusenöffnung QSR-24 < 300 m3/s geöffnet wird

Izvješće Hrvatskog odbora za geodeziju i geofiziku o provedenim aktivnostima od 2019. do 2022. - podneseno Generalnoj skupštini Međunarodne unije za geodeziju i geofiziku, Berlin, Njemačka, 2023.

Content: Introduction Geodesy in Croatia, 2019–2022 Geomagnetism and aeronomy in Croatia, 2019–2022 Hydrology and physical limnology in Croatia, 2019–2022 Meteorology in Croatia, 2019–2022 Physical oceanography in Croatia, 2019–2022 Seismology in Croatia, 2019–2022Sadržaj: Uvod Geodezija u Hrvatskoj, 2019.–2022 Geomagnetizam i aeronomija u Hrvatskoj, 2019.–2022 Hidrologija i fizikalna limnologija u Hrvatskoj, 2019.–2022 Meteorologija u Hrvatskoj, 2019.–2022 Fizička oceanografija u Hrvatskoj, 2019.–2022 Seizmologija u Hrvatskoj, 2019.–202

Megafloods in Europe can be anticipated from observations in hydrologically similar catchments

Megafloods that far exceed previously observed records often take citizens and experts by surprise, resulting in extremely severe damage and loss of life. Existing methods based on local and regional information rarely go beyond national borders and cannot predict these floods well because of limited data on megafloods, and because flood generation processes of extremes differ from those of smaller, more frequently observed events. Here we analyse river discharge observations from over 8,000 gauging stations across Europe and show that recent megafloods could have been anticipated from those previously observed in other places in Europe. Almost all observed megafloods (95.5%) fall within the envelope values estimated from previous floods in other similar places on the continent, implying that local surprises are not surprising at the continental scale. This holds also for older events, indicating that megafloods have not changed much in time relative to their spatial variability. The underlying concept of the study is that catchments with similar flood generation processes produce similar outliers. It is thus essential to transcend national boundaries and learn from other places across the continent to avoid surprises and save lives

Assessing the Long-Term Production of Suspended Sediment and the Climate Changes Impact on Its Deposition in Artificial Lakes—A Case Study of Lake Trakošćan, Croatia

A prevalent engineering task in practice is calculating the annual balance of sediments on some watercourses. This is particularly challenging when assessing the backfilling of river reservoirs that have a multifunctional purpose. Trakošćan Lake was built in the period from 1850 to 1862 as a pond and landscape addition to the park and Trakošćan castle. After 60 years, the lake was drained in 2022, and the work began on sediment excavation to improve the lake’s ecological condition due to about 200,000 cubic meters of deposited silt in the lake. In this research, the annual sediment production is calculated for the long-term period 1961–2020, based on empirical parametric methods (Fleming, Brunne). The results are compared with results from previous projects and recent sediment deposit investigations. Since there are no changes in LC/LU on this natural catchment, the decreasing trends in long-term sediment transport were compared with meteorological values, daily rainfall, and snow days. It is concluded that the intensity characteristics of the rainfall should be investigated more in detail and could provide much more tangible information regarding climate change impacts. Some targets for future monitoring design and research techniques are set

Assessing hydrological parameters in coastal rivers using artificial intelligence

U ovom radu će biti prikazani preliminarni rezultati znanstvenog projekta čiji je cilj razvijanje prikladne računalne metode, potpomognute umjetnom inteligencijom, za procjenu vodostaja i protoka u priobalnim rijekama. Kao pilot područje odabrana je rijeka Neretva, najveća rijeka u istočnom dijelu Jadranskog sliva. Istraživanja su usmjerena na prevladavanje ograničenja postojećih pristupa procjene protoka u priobalnim rijekama koje su pod utjecajem uspora mora. Naime, zbog nelinearne interakcije između plimnih valova i protoka rijeka postojeći pristupi za procjenu protoka temeljeni na fizikalnim modelima nisu pouzdani, stoga su potrebni novi koncepti i metode proračuna. Kombiniranjem naprednih metoda strojnog učenja i numeričkog modeliranja, postignuta je preciznija i pouzdanija procjena protoka slatke vode koja se ulijeva u Jadransko more, kao i prognoza vodostaja na kritičnim lokacijama uzvodno od ušća. Prikazano istraživanje i razvijene metode imaju široku primjenu u upravljanju vodnim resursima i doprinose održivosti priobalnih ekosustava.This paper presents the preliminary results of a scientific project aimed at developing a suitable computer method, supported by artificial intelligence, for the assessment of water level and flow in coastal rivers. The Neretva River, the largest river in the eastern part of the Adriatic basin, was selected as a pilot area. The research aims to overcome the limitations of existing approaches to flow estimation in coastal rivers, which are affected by the slowness of the sea. Due to the nonlinear interaction between tidal waves and river flow, existing approaches to estimating flow based on physical models are not reliable, and new concepts and computational methods are needed. By combining advanced machine learning and numerical modeling methods, more accurate and reliable estimation of freshwater flow into the Adriatic Sea and prediction of water level at critical locations upstream of the mouth were achieved. The presented research results and the developed methods have wide application in water resources management and contribute to the sustainability of coastal ecosystems