Igor Ružić

Coastal cliff geometry derived from structure-from-motion photogrammetry at Stara Baška, Krk Island, Croatia

The aim of this study was to examine the capability of structure-from-motion photogrammetry in defining the geometry of cliffs and undercuts in rocks of complex geomorphology. A case site was chosen along pocket beaches near the village of Stara Baška on the Adriatic Sea island of Krk, Gulf of Kvarner, Croatia, where cliff erosion of 5 m in breccias was identified by comparison of aerial photographs from 1960 and 2004. The 3D point cloud was derived from approx. 800 photos taken on 9 January 2014 by a single camera from various elevations and angles, and processed using the online software ReCap (Autodesk). Data acquisition was found to be quick and the method easy to implement. The difference between the georeferenced 3D cloud points and an RTK-GPS survey was 7 cm, i.e. within the limits of RTK-GPS precision. Quantifying the spatial variation in undercut geometries revealed that the deepest and largest (17 m3) undercut was in the south-eastern sector of the beach. Reconstructing the detailed geomorphology of this 3.8-m-deep undercut convincingly demonstrates the high efficiency of the method. Such assessments of spatiotemporal changes in undercut and overhang volumes can prove useful for evaluations of cliff erosion risk. Coupled with the low cost and relatively simple application, this is evidently an attractive technique for meaningful geotechnical and coastal engineering monitoring in the future on the island of Krk and, for that matter, also on other Adriatic islands and in similar settings worldwide.

Coastal Erosion and Instability Phenomena on the Coast of Krk Island (NE Adriatic Sea)

This paper presents the influence of the marine erosion on slope stability in the south eastern coastal area of the Krk Island (north-eastern part of the Adriatic Sea). The bedrock (Paleogene marls and flysch) is occasionally covered with talus breccia from Quaternary period. The coast is strongly exposed to wave attack and thereby to marine erosion. Comparison of few orthophoto map generations shows significant coastal retreat during the fifty-year period. This phenomenon has been a fundamental trigger off different instability phenomena. The type of instabilities is a consequence of local geological fabric and resistivity of rock mass to marine erosion. In the investigated area, rock falls and slumps prevail in cliffs formed in talus breccias. Extremely high tides from 2008 and 2012 have caused significant coastal erosion. This is obviously an indicator of the possible higher hazard degree caused by the sea-level rise.

Analysis of a historical landslide in the Rječina River Valley, Croatia

BackgroundLarge landslides triggered by rainfall and floods were registered on both sides of the Rječina River Valley, near City of Rijeka, in Croatia, where numerous instability phenomena in the past 250 years have been recorded, and yet only some locations have been investigated. The paper presents investigation of the dormant landslide located on the south-western slope, recorded in numerous historical descriptions from 1870. Due to intense and long-term rainfall, the landslide was reactivated in 1885, destroying and damaging houses in the eastern part of the Grohovo Village.Results2D stability back analyses have been performed based on landslide features, in order to approximate the position of the sliding surface and landslide dimensions. Because of the very steep landslide topography and the slope covered by unstable debris material, a Remotely Piloted Aircraft System (RPAS) was used to provide the data about the present slope topography. The landslide 3D point cloud was derived using Structure-from-Motion (SfM) photogrammetry. In order to verify the cloud of georeferenced sliding points obtained from images, it was compared with the existing models acquired from terrestrial photogrammetry and laser scanning, showing good accordance and small changes through the years. Based on the classification and Uniaxial Compressive Strength test results, rock mass strength was defined using generalised Hoek-Brown’s failure criteria.ConclusionsStability analysis results of the present slope conditions show that the slope is marginally stable for dry conditions, and that the critical seismic coefficient of about 0.14 would generate inertial forces corresponding to the factor of safety equal to 1. Analyses were performed with the purpose to predict the possible reactivation of a dormant landslide, and the presented results could be used in the establishment of an early warning system.

Marine Erosion and Slope Movements: SE Coast of the Krk Island

This paper presents the interaction of the marine erosion and slope movements on the south eastern coastal area of the Krk Island, Croatia. Larger parts of the coastal bedrock are carbonate rocks, and smaller parts are marls and flysch. The bedrock is occasionally covered with Quaternary sediments, which are characterized in terms of engineering soil properties. Complex geological fabric of the coastal area around Stara Baska settlement, in the south western part of the Krk Island, caused different movements on the coast. Due to the different grade of fissuring and karstification, as well as different weathering grade, carbonate and siliciclastic rock mass have wide range of resistance to the sea effects including wave attack. Exposure to the wave attack generated due to winds from the south directions contributes to the decreased resistivity. Additionally, occasional torrent flows and intensive erosion cause sporadic higher slope instability. The, effect of the previously registered extremely high tides, as well as the possible hazard increase due to the estimated sea level rise, is also analysed in the paper.

New approach to flap-type wavemaker equation with wave breaking limit

ABSTRACT The limitations of the classical wavemaker theory motivated the development of a new equation that can directly predict both regular and broken waves based on the flap-type wavemaker setup. This is achieved first by coupling a commonly accepted wave breaking formula with the linear wavemaker equation. Both these equations were then rewritten in terms of the paddle stroke, water depth, and frequency instead of the wave number. Additionally, the validity range for each equation was explicitly defined to predict the maximum wave height before breaking. Comparison with both classical wavemaker theory and measurements confirms the reliability and accuracy of the proposed equation.

Coastal erosion and instability phenomena at Stara Baška, Krk Island, Croatia

The paper describes the influence of the marine erosion and slope instabilities on cliff retreat in the coast near Stara Baška settlement on Krk Island (northeastern channel part of the Adriatic Sea). The bedrock is occasionally covered by breccia from Quaternary period. The coast around Stara Baška is exposed to wave attack and thereby to marine erosion. By comparison of orthophoto maps from 1966 and 2004, the significant coastal retreat was determined. This phenomenon has been a fundamental trigger off different instability phenomena. The type of instabilities is a consequence of the local geological fabric and rock mass resistivity marine erosion. In the investigated area, rock falls and slumps prevail in cliffs formed in breccia. Extremely high tides with the combination of strong waves from southern direction have a significant influence on the coastal erosion. This is an indicator of the possible higher hazard degree caused by the sea-level rise.

Observations of shoreline changes on a pocket gravel beach: Baška beach, Croatia

The Baška beach, one of the largest gravel beaches in Croatia was monitored over 3 years. This paper presents analysis of the shoreline position derived from these measurements. The shoreline position and the beach width were calculated from beach profile measurements. Overall changes in shoreline positions were quite small except in areas affected by fresh-water input (stream and urban runoff) and near a groyne. Several storm events were covered during the observation period. In most of these cases, the shoreline retreat was registered as expected. This would be followed by a rapid beach recovery and resulting shoreline advancement. After NE (Bura) storm wind event the shoreline advancement was registered. However, the close inspection of the beach profiles showed that this registered shoreline advancement was due to accumulation of sediment at the toe of the beach. This material was eroded at the upper beach. This finding and the lack of beach rotation indicate that the cross-shore sediment processes dominate during the energetic events.

Analysis of interrelation between water quality and hydrologic conditions on a small karst catchment area of sinking watercourse Trbuhovica

Sinking watercourse Trbuhovica is located at the topping karst of Gorski Kotar in Croatia, near the Slovenian border. About 900 inhabitants live in Trbuhovica catchment area. Sewage system had not been built. The project KEEP WATERS CLEAN (INTERREG III A project) was approved by EU commission and has a purpose of investigating water resources of that area, their appropriate protection and improving management of those resources. This paper presents projects 1st phase investigation results: hydrologic conditions and water quality at several locations on stream and at the springs of Trbuhovica, Mlake and Obrh. Climatologic (precipitation, air temperature and snow cover), basic hydrologic characteristics (flow and water temperature), water quality parameters (pH, electric conductivity, alkalinity, oxygen regime, nutrients and mineral oils) and microbiology indicators have been monitored. Samples of micro invertebrates and samples of periphyton have been collected in the field. Biological results have been elaborated via Saprobial Index according to Pantle-Buck. Analyses results showed a strong connection between hydrologic condition and selected water quality parameters. The groundwater quality changes are very quick. Maximum pollutions occur during the period of intensive rain. Water at the spring of Mlaka is very clean and is classified in the first to second water category, while Trbuhovica shows higher organic pollution.