AB STRA CT The south-western part of Croatia, i.e. the area of central Istria, comprises the research area, (approximately 500 km2). It is characterized by a fl ysch complex with a great number of isolated relief landforms, termed badlands. The im­ portance of badlands (areas with sparse or no vegetation) lies in the fact that sediment production from these areas is 8000 times higher than from areas with vegetation. Here, the badland inventory presents 5568 distinguishable bad­ lands (polygons) with a total badland area of 10.7 km2. Spatial analysis of the badland inventory showed that erosive channel fl ow at the steep slope foot is the most important factor in badland formation and development for the area of central Istria. Keywords: badland, inventory, spatial analysis, fl ysch complex, central Istria  Geologia Croatica 67/1 1–15 17 Figs. Zagreb 2014 Geologia CroaticaGeologia Croatica The analysis of the � ysch badlands inventory in central Istria, Croatia  Vlatko Gulam*, Davor Pollak* and László Podolszki* * Department of Hydrogeology and Engineering Geology, Croatian Geological Survey, Sachsova 2, 10000 Zagreb, Croatia; (vlatko.gulam@hgi­cgs.hr, davor.pollak@hgi­cgs.hr, laszlo.podolszki@hgi­cgs.hr) doi: 10.4154/gc.2014.01 1. INTRODUCTION The long period of time necessary for the majority of the Earth’s relief formation presents a problem in measuring the processes which occur during that period (HOWARD & KERBY, 1983). On a smaller scale (in area and time), the badlands as landforms can be used as case studies for research and understanding the bigger systems (WAINWRIGHT & BRAZIER, 2011) because all the exogenetic processes: weathering, denudation and depo­ sition occur and interweave there. Changes which occur on bad land relief are dynamic, and can be measured because they happen in a relatively short time span. Badlands are also very common worldwide (Mediterranean environment: Tunisia, DE PLOEY, 1974; Morocco, IMESON et al., 1982.; WAIN­ WRIGHT & THORNES, 2003., drylands in Africa: BOARD­ MAN et al., 2003.; ERIKSSON, et al., 2003.; FEOLI et al., 2002.; ACHTEN et al., 2008; Chile: MAERKER et al., 2008; India: JOSHI et al., 2009; China: LIU et al., 1985). These are the main reasons for the large number of scientifi c papers in which badland detection, description and measurements of dif ferent processes are presented. The term badland originates from the early French colo­ nists in northern America who encountered terrain that was bad, or diffi cult to cross (WAINWRIGHT & BRAZIER, 2011). There are many defi nitions of badlands in the litera­ ture but they all refer to the relief with or without sparse ve- getation cover, steep slope inclination, a dense hydrographic network, with or without a thin regolith, and the materials are usually unconsolidated or weakly consolidated clay rich bedrock. Marls and recent alluvium in particular can erode rapidly and they have a great denudation value. There are also some scientifi c papers in which the denudation values are smaller because some badlands or at least some parts of badlands can be stable for thousands of years (WISE et al., 1982; WAINWRIGHT, 1994; HOWARD, 1997; DÍAZ­ HERNÁNDEZ & JULIÁ, 2006). Badlands can also be de­ fi ned as areas where intensive piping, erosion and mass wast­ ing processes combine with fl uvial processes to produce a rugged, hummocky, dissected and strongly gullied topogra­ phy (BRYAN & YAIR, 1982). A large number of factors and processes have an infl u­ ence on badland formation and maintaining it as a complex relief form. The analysis and research of badlands can be undertaken at a variety of different scales. Although nume­ rous factors and processes infl uence badland development, most areas in which natural badland development is exten- sive share certain lithological and climatic characteristics (BRYAN & YAIR, 1982). Also in badland defi nitions sparse or no vegetation at all is one of the most important factors for the persistence of badlands and not the cause of badland formation. In recent times the anthropogenic infl uence is im­ portant in badland development, as in many locations the vegetation cover is disappearing due to human activity. Geologia Croatica 67/1Geologia Croatica 2 Badlands in central Istria are isolated relief units (in the terms of area they are smaller than 1 km2), not like the glo- bally known type and investigated localities (which can stretch over more than a dozen square kilometres): Dinosaur Provincial Park, Alberta, Canada (BRYAN et al. 1987) or the Henry Mountains, Utah, SAD (GILBERT, 1880; HOWARD, 1994). The small areas of badlands in central Istria (the big- gest badland has an area of 0.08 km2) suggest that an unsta- ble chain of exogenetic processes exist in that area which dictates badland formation, development and persistence in conditions (lithological, geomorphological and climatic ones) which are characteristic for the central Istrian area. These are detailed in this paper. In the majority of the literature which refers to the inves- tigation of erosion in the area of central Istria, it is stressed that the aforementioned area is characterized by very intensive exogenetic processes (JURAK et al., 2002; PETRAŠ et al., 2008; ZORN, 2009a, 2009b). Here, the badlands are marked as locations with excessive erosion (JURAK & FABIĆ, 2000), with sediment production up to 8000 times higher than in lo- cations which have some kind of vegetation cover. High se­ diment production from bare flysch in combination with inten- sive surface flows (flysch is characterized by low infiltration values and rapid runoff formation) are very common causes of backfilling of artificial accumulations, retention dams and drainage canals in traffic infrastructure. The goal of this work is to present the badland inventory and results of spatial analysis which can help in understand- ing the conditions necessary for badland formation and de- velopment in the flysch area of central Istria. 2. BASIC CHARATERISTICS OF THE ISTRIAN PENINSULA Geographical, geological and morphological characteristics of the Istrian peninsula differ from the rest of Croatia. This is the main reason why the Istrian peninsula is usually regarded as a separate unit (VRESK, 1987; VLAHOVIĆ et al., 2003.) in the scientific literature, and also why Istria is treated as a separate administrative unit. 2.1. Geographical characteristics of the Istrian peninsula The administrative unit of Istria is located in the southwestern part of Croatia (Fig. 1) with an area of 2820 km2. The climate of the Istrian peninsula is also variable, par- ticularly in big differences in arithmetic mean of annual va­ lues of precipitation. In the south-west and west these vary from 800–900 mm/year, in the middle part from 1200–1300 mm/year and in the north­east (mountainous area) from 2000–2500 mm/year (GAJIĆ­ČAPKA et al., 2003). Similar differences can also be noticed in the arithmetic mean of an- nual values of temperature: from 14°C in the south­west to 6°C in the north­east (ZANINOVIĆ et al., 2004). So, there are three types of climate on the Istrian peninsula (OGRIN, 2005): two types of submediterranean climate and a medi- terranean one. According to Köppen, these types are: Cfb (in the central part), Cfa (in the eastern and western coastal part) and Cs (in southern coastal part). The Istrian peninsula is mainly covered by forest (61.1 %). Agricultural land 35.4 %, urban and artificial areas 3.3 % and water surfaces account for around 0.2 % of the land surface (AZO, 2006). 2.2. Geological characteristics of the Istrian peninsula Postsedimentation tertiary tectonics has influenced the com- plex structure of deposits of the Adriatic carbonate platform, but the Istrian peninsula is one of the „stratigraphic oases” where it is possible to study all major events from geologi- cal history (VELIĆ et al., 2003). From the geological aspect, the Istrian peninsula can be divided into three major regions (which also correspond to the division into historical regions according to the local population): 1) Red Istria – Jurassic­Cretaceous­Eocene plains (south­ ern and western part of the peninsula): the term ori- ginates from the thick Quaternary deposits of terra rossa which overlie carbonate bedrock of Mesozoic and Tertiary age; 2) White Istria – Cretaceous­Eocene carbonate platform and clastic zone (mainly the massifs of Ćićarija and Učka) with characteristically imbricated structure: the term originates from the white colour of Cretaceous and Eocene weathered limestones; 3) Grey Istria – Eocene flysch basin (central Istria): the term originates from the grey colour of the marls which are interbedded with sandstones which toge­ ther form the flysch complex. Tectonic units of the Istrian peninsula can generally be divided in the Laramian tectonic unit (numbered 1 in Fig. 2) and Postlaramian tectonic units (2­5 in Fig. 2; POLŠAK & ŠIKIĆ, 1973). Here, the most important unit is unit 3 (Pazin synclinorium) and part of unit 4 (Trieste synclinorium). The Pazin synclinorium represents the tectonic unit formed from the Eocene to the Oligocene, during which time flysch sedi- mentation occurred in central Istria (BERGANT et al., 2003). Figure 1: Research area in the central part of the Istrian peninsula (marked by brown). Gulam et al.: The analysis of the flysch badlands inventory in central Istria, Croatia Geologia Croatica 3 2.3. Geological characteristics of the research area The research area includes almost the entire flysch complex on the Istrian peninsula. Only tectonic unit 5 is not included in the research area (the imbricated and overthrusted struc- ture of the Ćićarija, Učka and Labin basin), although it con- tains flysch deposits (Fig. 2). The reason for the exclusion of this unit lies within the goal of this research: determina- tion of the conditions necessary for badland formation and development (ie. which of the exogenetic processes is im- portant). In unit 5, the tectonic movements are one of the main factors in relief formation and those movements are hard to measure and quantify (they appear in geological time), so unit 5 was not taken into consideration. The re- search area is in the central part of the Istrian peninsula (ap- proximately 487 km2, Fig. 1). The research area mainly consists of deposits of Globige- rina marl and flysch which have low durability and high ero­ dibility, confirmed by JURAK et al. (2002), PETRAŠ et al. (2008) and GULAM (2012), and predetermined by the litho- logical, mineralogical, physical and mechanical properties of these materials. These properties of the Globigerina marl and flysch develop under a special set of conditions. The strati- graphic setting of the marl and flysch deposits of middle Istria is shown on a simplified geologic column in Fig. 3, from which it can also be seen that the base of the flysch complex and Globigerina sediments is composed of foraminiferal lime- stones with thin transitional sediments (marls with crabs). The term Globigerina marl originates from the plank- tonic foraminifera Globigerina and contains different ratios of carbonate and siliciclastic components. The carbonate component is mainly crypto- to microcrystalline calcite, while the siliciclastic components are mainly quartz and clay which originated from the mainland (BERGANT et al., 2003). Globigerina marls are deposited in a deep sea envi- ronment as confirmed by their constituent microfauna (JURAČIĆ, 1980). Flysch of the central Istria is superpositioned on the Glo- bigerina marl and can be divided into the upper and lower parts (BERGANT et al., 2003), with the complex thickness of about 90­100 m (Fig. 3). The lower part of the flysch com- plex is composed of a rhythmical exchange of marl and car- bonate sediments varying in thickness from 0.3 up to 7 m. Carbonate deposits can be conglomerates, foraminiferal bre- ccia, arenites and siltstones. Within the lower part of the flysch complex, carbonate megalayers of various thicknesses are very common (up to couple of metres, BERGANT et al., 2003). In the upper part of the flysch complex there are de- posits of carbonate-siliciclastic turbidite sediments which are thinly bedded and represent only the upper part of the Bouma turbidite sequence (Tb­e, Tc­e and Td­e, BERGANT et al., 2003), so called the undercut turbidite sequence (BER- GANT et al., 2003). 3. RESULTS 3.1. Relief dissection The relief dissection map generally indicates the areas of higher relief energy which equates to areas of potential higher Figure 2: Tectonic units of the Istrian peninsula (according to POLŠAK & ŠIKIĆ, 1973); 1. West Istrian Jurassic - Cretaceous anticline; 2. Savudrija - Buzet anticline; 3. Pazin synclinorium; 4. Trst synclinorium; 5. Imbricated and overthrusted structure of Ćićarija, Učka and Labin basin; A – Autoch- ton; B - Transitiona structures; C – Paraautochton. Figure 3: A simplified geological column of Kotli in central Istria (accor ding to BERGANT et al., 2003). Geologia Croatica 67/1Geologia Croatica 4 values of denudation and vice versa (MARKOVIĆ, 1983). For some areas the value of relief dissection is determined by lithology, type and thickness of the engineering soil, tectonic activity and the type of dominant exogenetic processes. The relief dissection map of Istria was generated using a topographic map at 1:25.000 scale. Categorization of the relief dissection was carried out according to GAMS et al. (1985) and is shown in Fig. 4. It can be concluded that the map of the relief dissection (Fig. 4) also corresponds to the potential zones of exogenetic processes intensity. The south­ western part of the Istrian peninsula is mainly characterized by plains of low dissection (6.6 %) and the relief of low dis- section (46.9 %). These attributes are predefined by: low erodible carbonate rocks of Jurassic and Cretaceous age and the „modest” tectonic activity in that area. The central part of Istria, where the flysch complex de- posits lie, is characterized by the relief of moderate dissection (100­300 m). Although the tectonic activity is not emphasized in this area, the relief of moderate dissection is the conse- quence of high erodibility and low durability of these flysch sediments. Because of these properties the central part of Is- tria is characterized by intense exogenetic processes. All the canyons on the Istrian peninsula (Mirna, Lim, Raša) and the mountain massive of Ćićarija occur in this category (moder- ate dissection). The mountain massif of Učka, in the eastern part of Istria is composed mainly of carbonates of Cretaceous age and they are in the category of relief of extensive dissec- tion (2.8 %) which reflects the effects of tectonics. 3.2. Badlands inventory Worldwide, there are many methods for the detection and for sorting out the areas with excessive erosion, but gene­ rally they can be divided into two main groups: • field mapping and • remote sensing. Figure 4: Map of the relief dissection of Istria. Figure 5: Badland inventory of central Istria; 1. Badland boundary, 2. Watershed boundary, 3. Studied area boundary. Gulam et al.: The analysis of the flysch badlands inventory in central Istria, Croatia Geologia Croatica 5 The research area (Fig. 1) is almost 500 km2 with a re- latively high percentage of badlands. For example, accord- ing to JURAK & FABIĆ (2000) badlands in the catchment of the Krbunski stream constitute 6 % of the catchment area. Field mapping was impractical and expensive for the re- search area due to terrain configuration and the large area of interest. Therefore the logical, practical and adequate method for producing a badlands inventory in the research area, is the usage of remote sensing. The method used in this re- search, consisted of reviewing the orthophoto maps at 1:5.000 scale (digital orthophotos of Croatia) and marking every single badland with the unique ID and contour of bad- land border on the terrain surface on these photos. The badland inventory of the middle part of Istria was used for: 1) determining the ratio of badlands in the research area, 2) determining the spatial distribution of badlands and de- termining the areas with the maximal and minimal ratios of badlands and 3) spatial analysis in order to determine the most important conditions/factors necessary for badland formation and development in the flysch area of central Istria. The badland inventory (data base) contains: (i) unique ID of each badland, (ii) contour of badland border on the terrain surface (polygon) and (iii) total area of each badland. In the research area, 5568 badlands were singled out, with the sum of the total areas of badlands of 10.7 km2, which is 2.2 % of the research area. The research area with contour of badland border on the terrain surface (polygons) is shown in Fig. 5. Also the larger detail with the orthophoto as the background is given in Fig. 5. On that orthophoto the badlands are easily recognizable. In the upper left corner of Fig. 5 the detail of the database (from the badland inventory) is shown. 4. DISCUSSION 4.1. Chain of exogenetic processes at the badlands The combination of exogenetic processes which takes place in the badlands needs to be explained to clarify the condi- tions under which badlands develop. Two very important factors for badland development in the central part of Istria are (GULAM, 2012): 1) Low durability sediments – badlands develop on the terrains where the bedrock is characterized by a very high susceptibility to periodic cycles of drying and wetting. As a result strong physical weathering oc- curs and the bedrock is covered with a thin, highly erodible, eluvium (10­20 cm). 2) Erosive stream – badlands in the central part of Istria are attached to gullies and valleys with very erosive periodic channel flow. Badland development in central Istria in terms of the geological time scale is explained on the theoretical and sim- plified model of a flysch terrain shown in Fig. 6. Most of the flysch terrain is covered by regolith which is the consequence of chemical and physical weathering and very low bedrock durability (Fig. 6a). Periodic concentrated channel flows erode the regolith overlying the flysch sediments, since its erosivity easily surpasses the erodibility of the regolith (Fig. 6b). This process leads to gully incision (Fig. 6c). The for- mation of gullies redirects sheet surface waters into channel flow causing an increase in the flow rate of waters running through them. Deepening of the gullies is facilitated by this increase in water quantity, and the flanks steepen until even- tually the regolith layer is detached and fresh rock is exposed – which is considered here as a badland (Fig. 6d). Further processes which determine badland „life” are cyclical and interdependent. The main phases of this chain of exogenic processes can be schematically represented as shown in Fig. 6, (I­IV) and below: I Fresh rock. Low durability intact rock material very prone to physical weathering is one of the basic pre- requisites for badland formation. II Weathering. In reality, fresh rock is rarely exposed at the very surface. On the steep badland slopes, fresh rock is not protected by a thick regolith layer and is exposed to physical weathering. Perpetual cyclical processes of drying and wetting of fresh rock mate- rial easily and rapidly degrades the mechanical cha­ racteristics of bedrock and form a thin layer of highly erodible material – eluvium. III Denudation - deposition. It is important to differen- tiate the processes by which eluvium is transported into the bottom of the gullies (Fig. 6, III). These pro­ cesses interact with slope inclination: • Denudation 1) Sheet erosion – occurs if the slope inclination is less than the angle of internal friction of eluvium (usually less than 35°). 2) Mass movements (usually rockfalls) – result when the slope inclination is higher than the angle of inter- nal friction of eluvium (usually more than 45°). 3) A combination of sheet erosion and mass movements – occurs if the slope inclination is near the value of the angle of internal friction of eluvium (usually be- tween 35° and 45°). • Deposition. IV Erosion. Talus sediment accumulated in the central part of the gully is eroded by periodic channel flow. The relationships between the four aforementioned main phases of badland evolution over time will determine whether badlands will develop (Fig. 6e) or die out (Fig. 6f). In conditions favourable for badland progress, the deepen- ing of the gullies takes place until the periodic channel flow reaches the erosion base. At this point, the rockwall retreat (CURRY & CHRIS, 2004; SEONG et al., 2009; ZORN, 2012) of the gullies takes place. The magnitude of badland rockwall retreat is also guided by relationships between the major processes (I to IV) described earlier. If badland slopes are in close contact with periodic channel flow, erosion will take place. But if the position of the periodic channel flow does not change over time, rockwall retreat will diminish Geologia Croatica 67/1Geologia Croatica 6 Figure 6: Badland development and the chain of exogenetic processes. Gulam et al.: The analysis of the flysch badlands inventory in central Istria, Croatia Geologia Croatica 7 leading to badland extinction. The same will happen if the water energy drops. The cyclical process is mainly continuous and has three constants – the same intact rock material with the same weathe- ring potential, and the same mechanical properties of the re- sulting eluvium. According to these parameters, the denuda- tion rate should be constant, but it also depends on the only variable in this cycle – climate. Climate change or climate ex- tremes dictate both very important and periodic factors in this cycle: wetting and drying periods, and erosion of the talus sediment by periodic channel flow. It should also be noted that the equilibrium cycle can also be disturbed by a change of erosion base level (for example by endogenic movements – geological time) or by anthropogenic activity (for example in civil engineering by changing the position of the periodic channel flows caused by road buildings – engineering time). Explanations given for Fig. 6, suggest the conclusion that the last link in the chain of exogenetic processes is the weakest – erosion by periodic channel flow (Fig. 6, IV). In middle Istria there is a periodic (or constant) channel flow of high erosivity in almost every stream order, but it is not necessary that the channel flow is in close contact with the steep flanks of valley or sediment accumulation (formed by sheet erosion or mass movements). It is clear from the discus- sion that the contact is necessary for the badland formation, development and reactivation, i.e. the contact is necessary for erosion and redeposition of the accumulated mate rials at the slope foot. The next logical question is: Which factors cause formation of this close contact? The answer is given by spa- tial analysis described below. 4.2. The importance of bedding inclination on badland development Big badlands in central Istria (for example badlands in the vicinity of St. Donat or Boljun, Fig. 5 and Fig. 8) are char- acterized by bedding inclination between 5° and 20°. Bed- ding steeper than 5° influences the forming of channel flows at the badland foot, shown in theoretical model in Fig. 7. The model presents the terrain with constant channel flow in a gully where bottom is being eroded with equal rate (Fig. 7a, f). By gully deepening (in bedrock) badlands are being formed on the flanks of the gully (rockwall) and the chain of exogenetic processes commences (Fig. 6). When the channel flow reaches resistant, none or low erodible com- ponents of the flysch deposits (for example calcarenite sedi- ments, Fig. 7b, g), widening of the gully takes place (rockwall retreat). If the bedding is horizontal (e.g in the south ­eastern part of the Ričica catchment) the rockwall retreat of the gully is equal on both flanks. If the bedding is inclined (for exam- ple badlands in vicinity of St. Donat and Boljun) the rock- wall retreat of the gully takes place in one direction – in the direction of bedding inclination. In Figs. 7c and 7h continuation of rockwall retreat is shown, while in Fig. 7c the retreat is slowing as the flow wid- ens (a larger area of flow means lower energy of flow i.e. lower erosivity). In Fig. 7h the retreat value remains the same (as the flow energy remains the same). In Fig. 7e the end stage is pre- sented – gully without rockwall retreat with wide flow with very low value of erosivity (or none). In Fig. 7j, on the other hand, a gully with the same level of activity is shown. On the far side (opposite side) of the flow, sediment accumulation takes place and eventually that side of the gully/valley will become inactive. The rockwall retreat continues (on the active side) until the appearance of some hindering factors stop it. Hindering factors can be: bedding inclination change to a smaller value, a greater sediment production value than flow erosivity, as a result of a larger badland area, etc. Initial bedding inclination has a great influence on bad- land formation and development, i.e. on the flow concentra- tion at the slope foot. The results of spatial analysis of slope Figure 7: Rockwall retreat influenced by bedding inclination. Geologia Croatica 67/1Geologia Croatica 8 aspects (in badland and non-badland areas) in the south-east- ern part of the Ričica catchment and in the vicinity of St. Donat and Boljun (Fig. 8) provide confirmation of this. 4.2.1. St. Donat badland catchment St. Donat badland catchment is approximately 2.7 km south of Buzet in the centre of Grey Istria (Fig. 8). The term originates from the village of St. Donat, which is west of the badlands. St. Donat badland catchment area on which the analysis was undertaken is 0.46 km2. The badland area in the catchment is 0.05 km2, which is approximately 9.2 % of the catchment area. The main flow is the Kameršiač stream (its spreading is 112­292°). According to the Basic Geological Map (1:100.000 scale), (PLENIČAR et al., 1969), the catchment consists of a flysch complex (intervals of marls and sandstones with centimetre thick beds) of Middle Eocene age (3E2). The average bed- ding values in the catchment is 179/13°. The diagram in Fig. 9 clearly shows that the maximum development of the badlands aspects is almost directly op- posite to the bedding azimuth in the analyzed catchment (in correspondence with discussion associated with Fig. 7), while the actual situation on the analyzed catchment is sim- ilar to that presented in Fig. 7j. The areas with vegetation approximately correspond to the bedding surfaces (Fig. 10), i.e. the maximum aspects of the areas with vegetation (Fig. 9) are in the same direction as the bedding azimuth. The areas of blue and grey polygons in Fig. 9 are almost symmetrically divided by the arrow which represents the value of azimuth for the Kameršiač stream. This type of „butterfly” distribution (in which the values of aspect for badland and non-badland areas of the catchment are shown), is very common for the catchment areas of central Istria when the whole catchment is characterized by uniform bed- ding values. This conclusion is also confirmed by the exam- ple of the Boljun badland catchment analysis which is in the south­eastern part of flysch basin in Boljunščica catchment (Fig. 8). 4.2.2. Boljun badland catchment The Boljun badland catchment is in the north­western part of Boljunšćica catchment area (Fig. 8). The name ori­ ginates from the village of Boljun which is south­east of the badlands. Boljun badland catchment area on which the anal- ysis was undertaken is 1.33 km2. The badlands in the catch- ment cover 0.16 km2, which is approximately 12.0 % of the catchment area. The main flow is the western confluent of the Boljunšćica stream with an approximate north – south direction of flow. According to the Basic Geological Map (1:100.000 scale) (ŠIKIĆ et al., 1969) the catchment consists of flysch complex (intervals of marls and sandstones) of Middle and Upper Eocene age (E2,3). Average bedding value on catchment is 262/8°. Figure 8: Spatial distribution of the analyzed locations; 1. Horizontal bedding, 2. Inclined bedding. Gulam et al.: The analysis of the flysch badlands inventory in central Istria, Croatia Geologia Croatica 9 The „butterfly” distribution in Fig. 11 is very similar to Fig. 9. The maximum of the badlands aspect is opposite to the bedding azimuth and to the maximum aspect of slo­ pes with vegetation (non­badland area). This also confirms the discussion concerning Fig. 7, i.e. confirms the fact that badlands on the catchments with uniform bedding are de- veloping on the flanks which are opposite to the bedding azimuth. Boljun badland catchment in 3D is shown in Fig. 12 and it clearly shows that non-badland areas correspond approxi- mately to bedding planes and that most of those areas are on the left side of the main flow in the catchment. These slopes are characterized by lower slope inclination and a higher area of spreading. 4.2.3. South-eastern part of the Ričica catchment area The Ričica catchment area is part of the southern part of the Botonega catchment (Fig. 8) with an area of 1.75 km2. The badland area in the catchment is 0.13 km2, which is ap- proximately 7.4 % of the catchment area. The main flow is the Ričica stream (spreading is 130­310°). The Ričica catchment is in the central part of the flysch synclinorium and it is characterized by horizontal bedding. This is also the reason for the somewhat different badland aspect distribution in relation to the non-badland area, shown in Fig. 13 by the blue arrow (presenting the flow of the highest order in that catchment area) as a division of the grey polygon into two parts, almost equal in area. This means that badlands form equally on each slope which is confirmed by the high overlapping of non­badland area (ar- eas with vegetation, blue polygon) and badland area (grey polygon). The south­eastern part of the Ričica catchment in 3D is shown in Fig. 14. It is clearly visible that badlands develop and form on both flanks of the main valleys. The terrain is Figure 9: Analysis of slope aspect and badlands and their connection with the average value of bedding in St. Donat badland catchment. Figure 10: St. Donat badland catchment in 3D; 1. Watershed boundary, 2. Badland boundary, 3. Main stream Geologia Croatica 67/1Geologia Croatica 10 Figure 12: Boljun badland catchment in 3D; 1. Watershed boundary, 2. Badland boundary, 3. Main stream Figure 11: Analysis of slope aspect and badlands and their connection with the average value of bedding in the Boljun badland catchment. similar to that presented in Fig. 7a–7e, i.e. the horizontal bedding predefines approximately equal development of badlands on each slope of each valley. 4.3. The influence of the valley cross section morphology on badland development After the badland inventory was prepared and visually ana- lyzed, some general conclusions were reached: there is regu­ larity in the ratio of badlands in some smaller catchments to periodic channel flows (also for some larger constant flows). The ratio of badlands in some areas is increasing as the dis- tance from the mouth of the river is growing, i.e. as the ero- sion base is becoming more distant. This conclusion is con- firmed by simple spatial analysis in which the connection between the badland ratios on some parts of the analyzed catchment (segment) and the distance of the centroid of that part of the analyzed catchment (segment) from the mouth of the catchment is observed. These segments are formed by the principle of concentric clips where the centre is the mouth of the catchment. The spatial analysis for the Bo- tonega catchment is shown below (Fig. 15). 4.4. Botonega catchment area The Botonega catchment represents the left tributary of the Mirna river and has an area of 104.6 km2 with the height dif- ference of 485 m. The highest elevation in the catchment area is 500 m while the lowest is 15 m above sea level. The catchment is fan shaped with Botonega as the main flow and also as the flow of the highest order (6th order defined by the contour lines at 1:25.000 scale according to the methodo logy suggested by STRAHLER, 1957). The badland area in the catchment is 2.0 %. The central valley (the Botonega river valley) corre- sponds with the axis of the flysch basin which is bath shaped Gulam et al.: The analysis of the flysch badlands inventory in central Istria, Croatia Geologia Croatica 11 Figure 13: Analysis of slope aspect and badlands and their connection with the average value of bedding in the south-eastern part of the Ričica catchment. Figure 14: South-eastern part of the Ričica catchment badlands in 3D presentation; 1. Watershed boundary, 2. Badland boundary, 3. Main stream ment and the badland ratio of each segment. This correlation confirms the visual analysis and it can be described with a linear function (with a very high factor of determination – 0.85). Graduation of the red colour (Fig. 15) shows this line ar distribution, i.e. light red marks the segments with low bad- land ratios and vice versa (dark red marks the segments with high badland ratios). To clarify, the very high value of the factor of determi- nation means it is necessary to take into consideration the described chain of exogenetic processes (Fig. 6). The flow concentration at the steep slopes foot, as one of the most im- portant links in the chain, can be predefined by the shape of the valley cross section. If the cross section is U shaped there is a very high probability that the channel flow in the centre of the valley will not be in close contact with flanks (rock- wall). The situation is reversed if the cross section is V shaped, then there is a very high probability that the cannel flow is in a close contact with the steep flanks of the valley (rockwall). If the valley cross sections for each segment on the branch of the hydrographic network marked with thicker blue line (Fig. 15) are analyzed there will be 12 profile po- sitions and 12 values. This branch is approximately in the centre of the Botonega catchment area and it stretches from the river mouth to the final segment. The cross sections for each profile position were made and analyzed (Fig. 17a & 17b) and four characteristic cross sections are also shown in Fig. 15. On the cross sections, the vertical scale is en- larged by x 20 to emphasise the shape of the cross section. and stretches from the north­west to south­east. According to the Basic Geological Map (1:100.000 scale, (sheets: Tri- este, PLE NI ČAR et al., 1969; Ilirska Bistrica, ŠIKIĆ et al., 1972; Ro vinj, POLŠAK & ŠIKIĆ, 1969; Labin, ŠIKIĆ et al., 1969)), flysch deposits cover approximately 86 % of the catchment area and the rest is alluvium (11 %) and carbon- ate deposits (3 %). Spatial analysis for the area of the Botonega catchment were undertaken as described in Section 4.3 (Fig. 15). Seg- ments are defined at 1 km intervals. Fig. 16 shows the correlation between the distance of the centroid of each segment from the mouth of the catch- Geologia Croatica 67/1Geologia Croatica 12 Figure 15: Spatial analysis for the area of the Botonega catchment with 1 km segments and characteristic valley cross sections. Figure 16: Correlation between the distance of each segment centroid from the mouth of the catchment and the badland ratio on each segment. The total height of each cross section is 10 m. In these cases the values which can determine the cross section shape are their width and area. The width is expressed in km and re- presents the distance between the two highest points of each cross section. The area of exaggerated cross section is ex- pressed in km2 and it is defined by a horizontal line which connects the two highest points of the cross section and the profile line, (the area defined in this way is shown on four examples of exaggerated cross sections by a green colour in Fig. 15). From the values shown in Fig. 17, it is clearly visible that the badland ratio in the segments is reducing as the width and the area of cross section increases. Both correla- tions result in very high factors of determination, approxi- mately 0.76. The logical conclusion is that the cross section shape of the valley is very important in badland formation Gulam et al.: The analysis of the flysch badlands inventory in central Istria, Croatia Geologia Croatica 13 and development as it is in direct connection with the chan- nel flow concentration at the foot of steep valley flanks (rockwall). 5. CONCLUSION The area of central Istria is characterized by low tectonic ac- tivity but the relief dissection is moderate i.e. relief energy values are also moderate. This is the result of very intense exogenetic processes which are predefined by the combina- tion of existing specific lithology and climate. As the product of these specific set of conditions the bad- lands in central Istria are very common isolated morphologi- cal landforms. A badland inventory of the research area, based on orthophoto pictures, contains 5568 identified badlands (poly­ gons). Badlands in the research area are isolated landforms, and therefore very small, since the biggest has an area of 0.08 km2. Badland area overall in the research area is 10.7 km2, which is 2.2 % of the total research area. Badlands of central Istria are also characterized by some sparse vegetation. Generally, on all badlands of central Istria there is strongly connected chain of exogenetic processes. In the chain of exogenetic processes most of exogenetic processes take place: weathering, denudation (erosion and mass move- ments on slopes), deposition or accumulation. The research results prove that the last link in the chain of exogenetic processes – erosion of the channel flow is the most important one, the link that defines the badland initia- tion, development and formation, i.e. close contact of the channel flow with the accumulated material at the badland slope foot is the most important factor in badland develop- ment and formation. As an argument for these statements, spatial analysis was undertaken on bedding orientation and cross section shape of the valley. Analyses proved that both factors can influence the erosion by the channel flow, i.e. can dictate the concentration of channel flow at slope foot and conditions under which badlands can be formed. Bedding orientation was analyzed at three locations: the south­eastern part or the Ričica catchment area, St. Donat badland catchment and Boljun badland catchment. The analy­ sis showed that in the catchments with horizontal bedding (south­eastern part or the Ričica catchment) badlands are equally developed on each slope, while on the catchments with inclined bedding (St. Donat badland catchment and Boljun badland catchment) badlands are developed on slopes which have the opposite aspect to bedding inclination. Analyses of the cross section shape of the valley were undertaken on the Botonega catchment where the ratio of badland increases from the mouth of the catchment towards the south-east border. The area of the cross section of the valley in that direction (north-west to south-east) is reduced, i.e. the valley width is smaller. This means that the cross sec- tion of the valley changes in shape from a U shape (higher order of valleys closer to the river mouth) to V shape (lower order of valleys more distant from the river mouth). The V shape of the valley influences the concentration of the chan- nel flow at the slope foot which contributes to the badland formation and development. Based on the present research, it can be concluded that close contact of the channel flow with the accumulated ma- terial at the badland slope foot is frequently the most impor- tant factor in maintaining an erosively active badland rock- wall. Therefore such situations, at locations of interest, should be artificially controlled or regulated if we wish to preserve fertile soil material and enable conservation of ve- ge tation. REFERENCES ACHTEN, W.M.J., DONDEYNE, S., SAMWELI, M., ELLY, K., JEAN, P., JOZEF, D. & BART, M. (2008): Gully erosion in South Eastern Tanzania: Spatial distribution and topographic thresholds.– Zeit­ schrift für Geomorphologie, 52, 225–235. AZO (2006): Corine Land Cover.– Baza podataka, Agencija za zaštitu okoliša, Zagreb. Figure 17: Analysis of 12 profile positions: a) correlation of the width of cross section and badland ratio for each segment b) correlation of the area of cross section and badland ratio for each segment. Geologia Croatica 67/1Geologia Croatica 14 BERGANT, S., TIŠLJAR, J. & ŠPARICA, M. (2003): Eocen carbonates and flysch deposits of the Pazin basin.– In: VLAHOVIĆ, I. & TIŠ­ LJAR, J. (eds.): 22nd IAS meeting of sedimentology – Opatija. Field trip guidebook, 57–63. BOARDMAN, J., PARSONS, A.J., HOLLANDC, R., HOLMESC, P.J. & WASHINGTOND, R. (2003): Development of badlands and gullies in the Sneeuberg, Great Karoo, South Africa.– Catena, 50, 165–184. BRYAN, R.B., CAMPBELL, I.A. & YAIR, A. (1987): Postglacial geo- morphic development of the Dinosaur Provincial Park badland, Alberta.– Canadian Journal of Earth Science, 24, 135–146. BRYAN, R.B. & YAIR, A. (1982): Perspectives on studies of badland geomorphology.– In: BRYAN, R.B. & YAIR, A. (eds.): Badland geomorphology and piping. GeoBooks, Norwich, 1–12. CURRY, A.M. & MORRIS, C.J. (2004): Lateglacial and Holocene talus slope development and rockwall retreat on Mynydd Du, UK.– Geo morphology, 58, 85–106. DE PLOEY, J. (1974): Mechanical properties of hillslopes and their re- lation to gullying in central semi­arid Tunisia.– Zeitschrift für Ge- omorphologie Supplementband, 21, 177–190. DÍAZ­HERNÁNDEZ, J.L. & JULIÁ, R. (2006): Geochronological po- sition of badlands and geomorphological patterns in the Guadix– Baza basin (SE Spain).– Quaternary Research, 65, 467–477. ERIKSSON, M., REUTERSWÄRD, K. & CHRISTIANSSON, C. (2003): Changes in the fluvial system of the Kondoa Irangi Hills, central Tanzania, since 1960.– Hydrological Processes, 17, 3271–3285. FEOLI, E., GALLIZIA VUERICH, L. & WOLDU, Z. (2002): Pro cesses of environmental degradation and opportunities for rehabilitation in Adwa, Northern Ethiopia.– Landscape Ecology, 17, 315–325. GAJIĆ­ČAPKA, M., PERČEC TADIĆ, M. & PATARČIĆ, M. (2003): Digitalna godišnja oborinska karta Hrvatske [Digital annual map of precipitation of Croatia – in Croatian].– Hrvatski meteorološki časopis, 38, 21–33. GAMS, I., ZEREMSKI, M., MARKOVIĆ, M., LISENKO, S. & BOG- NAR, A. (1985): Uputstvo za izradu detaljne geomorfološke karte SFRJ u razmeru 1:100.000 [Manual for the production of detailed geomorphological map of SFRY in scale of 1:100.000 – in Ser- bian].– Radna grupa Naučnog veća međurepubličko­po krajin skog projekta za geomorfološko kartiranje, Beograd, 80 p. GILBERT, G.K. (1880): Report on the geology of the Henry Moun- tains.– US geographical and geological survey of the Rocky Moun- tain region, 2nd editon, Washington, DC, 170 p. GULAM, V. (2012): Erozija ogolina u flišu središnje Istre [The erosion of flysch badlands in the central Istria – in Croatian].– Doctoral thesis. Faculty of Mining Geology and Petroleum engineering, University of Zagreb, 276 p. HOWARD, A.D. (1994): Badlands.– In: ABRAHAMS, A.D. & PAR- SONS, A.J. (eds.): Geomorphology of Desert Environments. Chap- man &Hall, London, 213–242. HOWARD, A.D. (1997): Badland morphology and evolution: Interpreta­ tion using a simulation model.– Earth Surface Processes and Land­ forms, 22, 211–227. HOWARD, A.D. & KERBY, G. (1983): Channel changes in badlands.– Bulletin of the Geological Society of America, 94, 739–752. IMESON, A.C., KWAAD, F.J.P.M. & VERSTRATEN, J.M. (1982): The relationship of soil physical and chemical properties to the devel- opment of badlands in Morocco.– In: BRYAN, R.B. & YAIR, A. (eds.): Badland Geomorphology and Piping. GeoBooks, Norwich, 47–70. JOSHI, V., TAMBE, D. & DHAWADE, G. (2009): Geomorphometry and fractal dimension of a riverine badland in Maharashtra.– Jour- nal of the Geological Society of India, 73, 355–370. JURAČIĆ, M. (1980): Dubina sedimentacije „lapora s rakovicama“ iz odnosa planktonskih i bentičkih foraminifera [Depth of sedimenta­ tion of „marl with crabs“ estimated from the ratio between plank­ tonic and benthic foraminifera].– Geološki vjesnik, 31, 61–67. JURAK, V. & FABIĆ, Z. (2000): Erozija kišom u slivu bujičnog vodo- toka u središnjoj Istri [Torrential Catchment Raindrop Erosion in the Cetnral Istria].– In: VLAHOVIĆ, I. & BIONDIĆ, R. (eds.): Zbornik radova 2. Hrvatskog geološkog kongresa, Cavtat – Dubrov­ nik, 603–612. JURAK, V., PETRAŠ, J. & GAJSKI, D. (2002): Istraživanje ekscesivne erozije na ogoljelim flišnim padinama u Istri primjenom terestičke fotogrametrije [Research into excessive erosion of bare flysch slopes in Istria by use of terrestrial photogrammetry – in Croatian].– Hr- vatske vode, 10/38, 49–58. LIU, T., AN, Z., YUAN, B. & HAN, J. (1985): The loess­palaeosol se- quence in China and climatic historiy.– Episodes, 8, 21–28. MAERKER, M., CASTRO, C.P., PELACANI, S. & BAEUREL, M.V.S. (2008): Assessment of soil degradation susceptibility in the Chaca­ buto Province of central Chile using a morphometry based response units approach.– Geografia Fisica e Dinamica Quaternaria, 31, 47–53. MARKOVIĆ, M. (1983): Osnove primenjene geomorfologije [Basics of applied geomorphology – in Serbian].– Posebna izdanja, Knjiga 8., Geoinstitut, Beograd, 174 p. OGRIN, D. (2005): Istarska enciklopedija [Istrian encyclopedia – in Cro- a tian].– In: BERTOŠA, M. & MATIJAŠIĆ, R. (eds.): Leksikograf- ski zavod Miroslav Krleža, Zagreb, online edition (http://istra.lzmk. hr/clanak.aspx?id=1369). PETRAŠ, J., HOLJEVIĆ, D. & PATRČEVIĆ, V. (2008): Mjerenje pro- dukcije erozijskog nanosa na istraživačkom poligonu „Abrami“ u Istri [Measuring of the erosion sediment yield at the „Abrami” re­ seach polygon in Istria].– In: OŽANIĆ, N. (eds.): Savjetovanje – Hidrološka mjerenja i obrada podataka. Nacionalni park Plitvička jezera, 190–206. PLENIČAR, M., POLŠAK, A. & ŠIKIĆ, D. (1969): Osnovna geološka karta SFRJ, list Trst u mjerilu 1:100 000 [Basic Geological Map of SFRY, sheet Trieste in scale of 1:100.000 – in Croatian and Slove- nian].– Savezni geološki zavod, Beograd. POLŠAK, A & ŠIKIĆ, D. (1969): Osnovna geološka karta SFRJ, list Rovinj u mjerilu 1:100.000 [Basic Geological Map of SFRY, sheet Rovinj in scale of 1:100.000 – in Croatian].– Savezni geološki za- vod, Beograd. POLŠAK, A. & ŠIKIĆ, D. (1973): Osnovna geološka karta SFRJ, tumač za list Rovinj [Basic Geological Map of SFRY, Guide for sheet Rovinj – in Croatian].– Savezni geološki zavod, Beograd. SEONG, Y.B., OWEN, L.A., CAFFEE, M.W., KAMP, U., BISHOP, M.P., BUSH, A., COPLAND, L. & SHRODER, J.F. (2009): Rates of basin­wide rockwall retreat in the K2 region of the Central Ka- rakoram defined by terrestrial cosmogenic nuclide 10Be.– Geomor- phology, 107, 254–262. STRAHLER, A.N. (1957): Quantitative analysis of watershed geomor- phology.– Transactions of the American Geophysical Union, 38/6, 913–920. ŠIKIĆ, D., POLŠAK, A. & MAGAŠ, N. (1969): Osnovna geološka kar- ta SFRJ, list Labin u mjerilu 1:100.000 [Basic Geological Map of SFRY, sheet Labin in scale of 1:100.000 – in Croatian].– Sa vezni geološki zavod, Beograd. ŠIKIĆ, D., PLENIČAR, M. & ŠPARICA, M. (1972): Osnovna geološka karta SFRJ, list Ilirska Bistrica u mjerilu 1:100.000 [Basic Geolo­ gical Map of SFRY, sheet Ilirska Bistrica in scale of 1:100.000 – in Croatian and Slovenian].– Savezni geološki zavod, Beograd. VELIĆ, I., TIŠLJAR, J., VLAHOVIĆ, I., MATIČEC, D. & BERGANT, S. (2003): Evolution of the Istrian part of the Adriatic carbonate platform from Middle Jurassic to Santonian and formation of the Gulam et al.: The analysis of the flysch badlands inventory in central Istria, Croatia Geologia Croatica 15 flysch basin durnig the Eocene: Main components and regional com parison.– In: VLAHOVIĆ, I. & TIŠLJAR, J. (eds.): Field trip guidebook, 22nd IAS Meeting of sedimentology, Opatija. 3–17. VLAHOVIĆ, I., TIŠLJAR, J., VELIĆ, I., MATIČEC, D., SKELTON, P. W., KORBAR, T. & FUČEK, L. (2003): Main events receorded in the sedimentary succession of the Adriatic carbonate platform from the Oxfordian to the Upper Santonian in Istria (Croatia).– In: VLA­ HOVIĆ, I. & TIŠLJAR, J. (eds.): Field trip guidebook, 22nd IAS Meeting of sedimentology, Opatija. 19–56. VRESK, M. (1987): Polarizacijski efekti urbanizacije Istre [Polarization effects of the urbanization of Istria – in Croatian].– Acta Geogra­ phica Croatica, 22, 43–53. WAINWRIGHT, J. & BRAZIER, R. (2011): Slope systems.– In: THO- MAS, D.S.G. (ed.): Arid zone geomorphology. 3rd Edition, 209–233. WAINWRIGHT, J. (1994): Anthropogenic factors in the degradation of semi­arid regions: A prehistoric case study in Southern France.– In: MILLINGTON, A.C. & PYE, K.U (eds.): Effects of Environmental Changes on Drylands. John Wiley & Sons, Ltd. Chichester, 285–304. WAINWRIGHT, J. & THORNES, J.B. (2003): Environmental issues in the Mediterranean: Processes and perspectives from the past and present.– Routledge, London, 479 p. WISE, S.M., THORNES, J.B. & GILMAN, A. (1982): How old are the badlands? A case study from southeast Spain.– In: BRYAN, R.B. & YAIR, A. (eds.): Badland geomorphology and piping. Geobooks, Norwich, 259–277. ZANINOVIĆ, K., SRNEC, L. & PERČEC TADIĆ, M. (2004): Digital- na godišnja temperaturna karta Hrvatske [A digital annual temper­ ature map of Croatia – in Croatian].– Hrvatski meteorološki ča so­ pis, 39, 51–58. ZORN, M. (2009a): Erosion processes in Slovene Istria. Part 1, Soil ero- sion.– Acta geographica Slovenica, 49/1, 39–87. ZORN, M. (2009b): Erosion processes in Slovene Istria. Part 2, Bad- lands.– Acta geographica Slovenica, 49/2, 291–341. ZORN, M. (2012): Geomorphic activity in flysch badlands of the Istria peninsula (SW Slovenia).– Zeitschrift für Geomorphologie, Suppl., 56/3, 53–79. Manuscript received September 23, 2013 Revised manuscript accepted December 18, 2013 Available online March 21, 2014