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Title:Characterization of a karst aquifer in the recharge area of Malenščica and Unica springs based on spatial and temporal variations of natural tracers
Authors:Kogovšek, Blaž (Author)
Petrič, Metka (Mentor) More about this mentor... New window
Jemcov, Igor (Mentor) More about this mentor... New window
Files:.pdf Blaz_Kogovsek.pdf (18,38 MB)
 
Language:English
Work type:Doctoral dissertation (mb31)
Tipology:2.08 - Doctoral Dissertation
Organization:FPŠ - Graduate School
Abstract:The aim of the present study is to characterize and improve the still insufficient knowledge of the recharge processes that have an important influence on the flow and solute transport in karst aquifers and thus also on the quantity and quality of karst water sources. A binary karst aquifer in the recharge area of the Malenščica and Unica springs, which covers an area of about 820 km2 in SW Slovenia, was selected as the study area. A dense monitoring network was established at 20 observation points (six springs, four ponors, seven water-active caves and three surface streams) for simultaneous monitoring of the hydrological characteristics and the physicochemical properties of the water, the so-called natural tracers. Data-loggers were installed to measure water pressure, temperature and conductivity. During selected storm events, samples were taken for chemical and microbiological analyses and discharge measurements were made. The meteorological and hydrological data of the Slovenian Environment Agency complemented the extensive dataset. Collected data allowed the analysis and comparison of the spatial and temporal variations of the natural tracers under different hydrological conditions. Frequent discharge measurements allowed the generation of rating curves and proved to be a crucial element for understanding the hydraulic processes that determine the functioning of this system. The calculation of the water budget allowed an assessment of the proportion of autogenic and allogenic recharge of the springs and a quantitative estimate of autogenic recharge under different hydrological conditions. The hydrological analysis, i.e. the flow duration curve, the hydrograph separation techniques and the recession analysis, revealed that the Malenščica spring has a higher storage capacity, a greater proportion of autogenic recharge, especially at low-flow, and a slower recession than the Unica spring. This was also confirmed by correlation and spectral analyses, which were also used to investigate the relationships between discharges at ponors and springs. However, the results of the cross-correlation analysis showed hardly any difference between the two springs and in this case proved to be unsuitable for studying the influence of allogenic recharge. Instead, partial cross-correlation analysis was used to control the input parameters of effective precipitation and discharge of one of the sinking streams to determine the contribution of the other sinking stream to the observed spring. The results confirmed differences in allogenic recharge of the Unica and Malenščica springs. Hysteresis analysis has been applied as a complementary method to time series analysis and represents an improved approach to the characterization of the karst hydrological system. The hydraulic approach to the construction of hysteresis enabled a detailed analysis of allogenic and autogenic water interaction and its influence on the Malenščica and Unica springs under different hydrological conditions. Narrow shapes of the hysteresis indicate a direct hydraulic connection between the ponor and the spring and thus a well-developed drainage system. Any deviation towards a convex or concave shape indicates a less developed, more matrix-related drainage system or the influence of other recharge sources. Analysis of physicochemical hysteretic function of individual locations confirmed the differences in the recharge characteristics of the two springs. Compared to the Unica spring, the Malenščica spring has specific recharge characteristics that result in lower vulnerability to the effects of the sinking streams. A greater proportion of autogenic recharge in the initial phase of the storm event is important, as it allows for a time delay of the possible negative effects of the sinking stream. However, possible pollution from the area of autogenic recharge can have strong negative effects, as in this initial phase with low discharges the dilution effect is negligible.
Keywords:karst aquifer, dynamics of natural tracers, storm events, discharge measurements, time series analysis, hysteresis, Unica spring, Malenščica spring
Year of publishing:2022
Source:Nova Gorica
COBISS_ID:99189763 Link is opened in a new window
URN:URN:SI:UNG:REP:O3CVRSAR
Views:524
Downloads:31
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Secondary language

Language:Slovenian
Title:Analiza časovne in prostorske spremenljivosti naravnih sledil za določitev značilnosti kraškega vodonosnika v zaledju izvirov Malenščice in Unice
Abstract:Namen doktorske disertacije je opisati in izboljšati nezadostno poznavanje procesov napajanja, ki pomembno vplivajo na pretok in prenos snovi v kraških vodonosnikih ter s tem tudi na količino in kakovost kraških vodnih virov. Za študijsko območje je bil izbran kraški vodonosnik, ki se nahaja v JZ delu Slovenije, v zaledju izvirov Malenščice in Unice, in obsega skoraj 820 km2. Dosedanje raziskave in poznavanje območja so omogočili učinkovito načrtovanje meritev, rezultate obdelav podatkov pa smo preverjali in vrednotili z nekaterimi že znanimi metodami in drugimi na novo uvedenimi za to študijsko območje. Vzpostavili smo mrežo samodejnih merilnih postaj, ki so zvezno beležile meritve tlaka, temperature in električne prevodnosti vode. Meritve hidroloških in fizikalno-kemijskih značilnosti vode, t.i. naravnih sledil, so potekale na šestih izvirih, štirih ponorih, sedmih jamah z dostopom do podzemne vode ter treh površinskih vodotokih. Na izbranih vodotokih so bile opravljene številne meritve pretokov, med izbranimi padavinskimi dogodki pa so bili odvzeti vzorci za kemične in mikrobiološke analize. Obsežen nabor podatkov so dopolnili meteorološki in hidrološki Agencije RS za okolje. Zbrani podatki so omogočili analizo in primerjavo prostorskih in časovnih razporeditev naravnih sledil v različnih hidroloških razmerah. Meritve pretokov so omogočile izdelavo pretočnih krivulj, podatki o pretokih so se izkazali kot ključni element za razumevanje hidravličnih procesov, ki določajo delovanje opazovanega sistema. Izračun vodne bilance je omogočil oceno deleža avtogenega in alogenega napajanja izvirov ter količinsko oceno avtogenega napajanja v različnih hidroloških razmerah. Hidrološka analiza (krivulja trajanja pretoka, indeks baznega odtoka, analiza recesijske krivulje) je omogočila izračun različnih kazalnikov. Rezultati razkrivajo, da ima izvir Malenščice večjo zmogljivost uskladiščenja vode, večji delež avtogenega napajanja, zlasti v času nizkih voda ter počasnejše upadanje pretokov kot izvir Unice. To sta potrdili tudi metodi analize časovnih vrst, avtokorelacija in spektralna analiza, s katerima smo raziskali tudi povezave med pretoki na ponorih in izvirih. Vendar pa so rezultati križne korelacije prikazali komaj zaznano razliko med preiskovanima izviroma; v tem primeru se je metoda izkazala za neprimerno pri preučevanju vpliva alogenega napajanja izvirov. Namesto tega je bil inovativno uporabljen pristop parcialne križne korelacije. Analiza je omogočila kontrolo vhodnih podatkov efektivnih padavin in pretokov enega od ponorov za določitev vpliva drugega ponora na opazovani izvir. Rezultati so potrdili razlike v alogenem napajanju izvirov Unice in Malenščice. Analiza histerez je bila uporabljena kot dopolnilna metoda k analizi časovnih vrst in predstavlja izboljšan pristop pri karakterizaciji kraškega hidrološkega sistema. Hidravlični pristop za izdelavo histerez je omogočil podrobno analizo vzajemnega delovanja alogene in avtogene vode ter njun vpliv na izvire Malenščice in Unice v različnih hidroloških razmerah. Ozke oblike histerez kažejo na neposredno hidravlično povezavo med ponorom in izvirom in s tem na dobro razvito odtekanje vode skozi sistem. Vsako odstopanje v smeri konveksne ali konkavne oblike kaže na manj razvit sistem, vezan na pretakanje vode v slabše prepustnih delih vodonosnika ali vpliv drugih virov napajanja. Analiza fizikalno-kemijskega pristopa k izdelavi histerez za posamezne lokacije je potrdila razlike v lastnostih napajanja obeh izvirov. V primerjavi z izvirom Unice ima izvir Malenščice posebne lastnosti napajanja, zaradi katerih je manj ranljiv na vpliv ponikalnic. Pomemben je večji delež avtogenega napajanja v začetni fazi padavinskega dogodka, saj omogoča časovni zamik možnih negativnih učinkov ponikalnice. Vseeno pa ima lahko morebitno onesnaženje na območju avtogenega napajanja močne negativne učinke, saj je v tej začetni fazi, v času nizkih voda, učinek redčenja zanemarljiv.
Keywords:kraški vodonosnik, dinamika naravnih sledil, padavinski dogodki, merjenje pretokov, analiza časovnih vrst, histereza, izvir Unice, izvir Malenščice


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