Analysis of the hydraulic connection of the Plitvica stream and the groundwater of the Varaždin alluvial aquifer

Analiza hidrauličke veze potoka Plitvice i podzemnih voda varaždinskog aluvijalnog vodonosnika

Andrija Mohorovicic Geophysical Institute 2021

A combination of different statistical methods and flow duration curves was used to examine hydraulic connection between the Plitvica stream and the surrounding piezometers that capture the groundwater of the Varaždin alluvial aquifer. Also, rainfall quantities over a wider study area were considered to examine the effect of precipitation on Plitvica water levels and groundwater levels. The following statistical methods were used in this paper: the correlation method, the auto- correlation method, and the cross-correlation method. Correlation analysis show that there is generally a significant correlation between the Plitvica water levels and groundwater levels, with positive direction of the correlation. The analysis of auto-correlograms for groundwater and surface water shows that the correlation coefficient value drops below 0.2 after a longer period, which indicates a long-term memory of the system that can be explained by the slow flow and thus slow pressure transfer. Cross-correlation analyses of the time series of the Plitvica water levels and groundwater levels showed a time lag of 1-2 days with a fairly significant cross-correlation coefficient. For precipitation and groundwater levels, the relationship is much weaker, with a lag time of 4-5 days with a weak cross- correlation coefficient. The least time lag, within a day, was established between precipitation and Plitvica water levels. Analyses of the flow duration curves revealed that Plitvica almost completely drains groundwater, except in the vicinity of the piezometer 2178 where Plitvica recharges the aquifer about a quarter of the time.
Kombinacija različitih statističkih metoda i krivulja trajanja korištena je za ispitivanje hidrauličke veze potoka Plitvice i okolnih piezometra koji zahvaćaju podzemne vode varaždinskog aluvijalnog vodonosnika. Također, razmatrane su količine oborina sa šireg područja istraživanja kako bi se utvrdio utjecaj oborina na vodostaj Plitvice i razine podzemne vode. U radu su korištene sljedeće statističke metode: korelacija, auto-korelacija i kros-korelacija. Korelacijske analize pokazuju da generalno postoji značajna povezanost između vodostaja Plitvice i razina podzemnih voda, s pozitivnim smjerom korelacije. Analiza auto-korelograma za podzemne i površinske vode pokazuje da vrijednost koeficijenta korelacije pada ispod 0,2 nakon duljeg vremenskog razdoblja, što ukazuje na dugotrajnu memoriju sustava koja se može objasniti sporim tečenjem, odnosno sporim prijenosom tlaka. Kros-korelacijska analiza vremenskih nizova između vodostaja Plitvice i podzemnih voda pokazala je vremensko zaostajanje od 1–2 dana s prilično značajnim koeficijentom korelacije. Između oborina i podzemnih voda veza je mnogo slabija, s vremenskim zaostajanjem od 4–5 dana te slabim koeficijentom korelacije. Najmanje zaostajanje, unutar jednog dana, utvrđeno je između oborina i vodostaja Plitvice. Analizama krivulja trajanja utvrđeno je da Plitvica gotovo u potpunosti drenira podzemne vode, izuzev piezometra 2178 u blizini kojega oko četvrtinu vremena prihranjuje vodonosnik.

correlation; auto-correlation; cross-correlation; Plitvica stream; Varaždin alluvial aquifer; korelacija; auto-korelacija; kros-korelacija; potok Plitvica; varaždinski aluvijalni vodonosnik; text; info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion

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