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The paper deals with complex hydrological/hydrogeological behaviour in the Rjecina karst spring and river basin located in the north-western part of the deep and developed Croatian Dinaric karst. The Rjecina Spring is one of the major karst springs in Croatia, used for water supply of Rijeka City and its surrounding area. Beside the use of Rjecina spring for water supply, the development of the Rijeka hydroelectric power plant (HEPP) also changed hydrological and hydrogeological regime of the whole catchment. In order to analyse the anthropogenic influences in the system, hydrological analysis of the Rjecina river and spring discharge was done, as well as the analysis of the available data of groundwater measurements. The analysis showed that, due to the increase of water caption and decrease of precipitation, the average annual spring discharge decreased for approximately 25% in the 1980-2016 period. Detailed analysis of groundwater measurements indicated aquifer behaviour and the need for additional measurements and catchment delineation. Key words: hydrology, hydrogeology, karst, Rjecina Spring, Rjecina River, Dinaric karst. Analiza vodnih virov kraskega izvira in reke Rjecina (Dinarski kras) Clanek obravnava zapletene hidroloske/hidrogeoloske razmere v zaledju kraskega izvira in reke Riecine v severozahodnem delu globokega in dobro razvitega hrvaskega Dinarskega krasa. Izvir Rjecina je eden najvecjih kraskih izvirov na Hrvaskem, zajet je za oskrbo s pitno vodo za mesto Reka in njeno okolico. Poleg rabe izvira Rjecine za oskrbo z vodo je razlog za spremenjen hidroloski in hidrogeoloski režim celotnega zaledja tudi gradnja hidroelektrarne Reka (HEPP). Za analizo antropogenih vplivov na sistem smo zato naredili hidrolosko analizo pretokov reke in izvira Rjecina pa tudi analizo razpoložljivih podatkov merjenja podzemne vode. Analiza je pokazala, da se je zaradi povecanja zajemanja vode in zmanjsanja kolicine padavin povprecen letni pretok izvira v obdobju 1980–2016 zmanjsal za približno 25 %. Podrobna analiza meritev podzemne vode je nakazala znacilnosti delovanja vodonosnika ter pokazala potrebo po dodatnih meritvah in dolocitvi zaledja izvira. Kljucne besede: hidrologija, hidrogeologija, kras, izvir Rjecina, reka Rjecina, Dinarski kras.

Debris flows generate important yearly human and property losses. Its analysis is important to assess the risk and to delimitate vulnerable areas where mitigation measures are required. Debris flows are a type of mass wasting processes. Mass movement processes can be categorized following some parameters such as the release mechanism, the sort of material, the sediment composition, the proportion of the solid phase, the velocity, the time of the event, the slope of the movement plane, the material behavior and the physical processes during the mass movement. Predicting both the runout distance and the velocity through mathematical modeling of the propagation can avoid important losses. Moreover data from modeling can be used as input in risk studies, where hazardous areas are defined and appropriate protective measures are designed. In the last decades, modeling of propagation stage has been largely carried out in the framework of the continuum mechanics, and a number of new and sophisticated numerical models are developed. Most of the available approaches handle the heterogeneous and multiphase moving mass as a single phase continuum. The Smoothed particle hydrodynamics model (SPH model) described here after consists on considering two phases, a granular skeleton with voids filled with either water or debris/mud. If the shear resistance of the fluid phase can be neglected, the stress tensor in the mixture can be decomposed into a "pore pressure" and an effective stress, and the mechanical behavior of the mixture can be described by a system of differential equations governing the dynamics of each of the phases. Once the required initial and boundary conditions are provided, the spatial and temporal integration of the system of differential equations can be carried out with numerical methods. In the SPH method, the state of a system is represented by a set of particles, which possess individual material properties and move according to the governing conservation equations. SPH method, as a meshfree, Lagrangian, particle method, has its particular characteristics. The key idea of the meshfree methods is to provide accurate and stable numerical solutions for integral equations or PDEs with all kinds of possible boundary conditions with a set of arbitrarily distributed nodes (or particles) without using any mesh that provides the connectivity of these nodes or particles. SPH method has some special advantages over the traditional grid-based numerical methods, the most significant one among which is the adaptive nature of the SPH method. This adaptability of SPH is achieved at the very early stage of the field variable approximation that is performed at each time step based on a current local set of arbitrarily distributed particles. The SPH depth integrated model is a 2D model able to predict runout distance, flow velocity, deposition pattern and final volume of debris flows. It is based on a mathematical model, on rheological models and on a numerical model. The basis of the mathematical model is a coupled depth integrated model coming from a velocity-pressure version of Biot-Zienkiewicz equations. The rheological models correspond to constitutive equations. The SPH depth integrated model is a calibration-based model, which means that the appropriate rheological parameters must be constrained by back analysis of previous real debris flows. In this paper are described the main characteristics of debris flow processes and point out the more relevant parameters and magnitudes describing debris flow. The paper also gives the main equations on which is based the SPH depth integrated model applied for Grohovo landslide. In this paper two erosion laws are presented, the Hungr erosion law and the Egashira erosion law. On the end of the paper was given a brief description of the SPH code, and some conclusions of this case study and the possible future research lines.

Surface sediments (fraction 6 ppm, that might cause lowest toxic effects. At the lower Rječina and in prodelta sediments Pb is also present at slightly elevated concentrations (>31 ppm) that could cause such effects. Concentrations of Zn in prodelta, corresponds to those occurring in moderately polluted sediments (90-200 ppm). In the prodelta sediments Hg is slightly below toxicity threshold (1 ppm), while Ag is present at toxicity threshold (0.5 ppm) or close to it. Rječina River could act as a good illustrative example for behavior of toxic metals in alogene karstic rivers, in which accumulation of anthropogenically introduced pollutants usually occurs in their estuaries, as result of fine particles transport and deposition.

This work presents first complementary geochemical and stable isotope investigations of Risnjak Mountain karstic aquifer system in north-western Croatia. This aquifer is an important source of drinking water for both countries Croatia and Slovenia. The two main rivers, namely the Kupa River and the Rjecina River discharge the same mountain range, but belong to two different watersheds. Their springs are only 22 km apart, and located in scarcely populated areas. Kupa flows through limestones and dolomites in National Park Risnjak until it meets its largest tributary Cabranka. Rjecina flows first through flysch and carbonates before it enters the Adriatic Sea. At its lower course it flows through the densely populated town of Rijeka. For effective management of water resources the baseline data were collected. Sediment fraction

The city of Rijeka (Croatia) developed from the old Tarsatica on the right and the newer Sušak on the left side of the River Rječina right on the river's mouth in the Adriatic Sea. The Rječina was the driver of the city, it moved mills, supplied the city with drinking water (and still does) and along its flow the first manufacture, and later industrial plants of this city in development, were raised. Today these areas and industrial buildings along the Rječina mostly do not fulfil their primary function and are waiting for their conversion and re-integration in the life of the city. This paper will show plans as well as already undertaken regulation, restoration and revitalisation works in the riverbed and the riversides of the Rječina. These solutions try to achieve social benefits by connecting the city and its citizens with “ their” river and the natural environment, valorise the areas along the river as well as the industrial and architectural heritage.

Hydrological and hydrogeological investigations of the karst river Rječina (Croatia), which has outflow in the Adriatic Sea, is presented. The paper treats a complex case o1 surface and groundwater circulation in a typical Dinaric karst catchment, which whole area is about 400 km2. In average 1500 1/s of karst groundwater in the catchment is used for water supply. On the central part of the Rječina River the Valići dam and reservoir for hydropower production are constructed. Both of mentioned reasons, as many others natural and anthropogenic, influenced strong changes of hydrological regime on the Rječina River and catchment. In paper special attention is paid on the analyses of the hydrological behaviour of the Rječina karst spring. Its exit is at the altitude of 325 m a. s. l., and mean annual discharge is 7.14 m3/s. The natural and anthropogenic influences on the decreasing of the Rječina spring discharges during the 1947-2003 period are explained.

Construction of the first large-scale hydrotechnical structures, especially reservoirs in Dinaric karst come to middle of 20th century. The development of industry in this time needed electric energy. It was the main reason for the beginning of intensive research and for the construction work of the large reservoirs in the Dinaric karst region. Generally, first purpose of all those reservoirs were production of electric energy, water supply, socio-economic development etc. During the last 50 years, numerous large regional water systems, hydro electric power plants (HEPP), hydrotechnical tunnels and other large structures have been built in the Dinaric karst (Bonacci 1987). Their construction has greatly influenced the surface and ground water regime in the region. All of these structures were built with the same objective, i.e. to improve the water regime, and hence, the living conditions. Past experience has shown that many of these works have been suboptimal. Paper presents three different examples: 1) Decreasing of the water level of the Vrana Lake at the island of Cres; 2) Consequences caused by the construction of Salakovac reservoir on the Neretva River; and 3) Changes of hydrologic regime of the Rje~ina River.

Mathematical model and calculated results of Rjecina estuary flooding are presented in this paper. Mathematical i.e. numerical model is based upon the finite volume method. Time discretization uses Runge-Kutta method of second order and space discretization is based on local Lax-Friedrichs scheme. Problem of tide variation and bridges implementation are successfully comprehended in this model. Obtained results confirm the robustness of presented mathematical model.