Karst Polje Research Articles

Flooding and flood water storage in karst systems of the Mediterranean region

Flooding is a recurring natural phenomenon that can have both life-giving and destructive aspects. In natural environments, floods are often an important element of the seasonal hydrologic cycle that provides water and nutrients to soil, supporting unique, rich and diverse ecosystems. However, flood events can also represent a destructive force that can endanger lives and cause significant damage in urban areas. Karst areas, in particular, are unique because of their special hydraulic characteristics in terms of flood occurrence, the dependence of ecosystems on such events, and attempts to actively store and manage floods. In this article, the hydraulic response of karst aquifers to heavy precipitation events, flood generation, and engineering interventions for flood control are discussed using several examples from karst areas in the Mediterranean region. Flooding mechanisms and regulatory structures in karst poljes are considered using several typical examples from the Dinaric mountain range. In addition, different variants of groundwater abstraction for increasing storage capacity and flood control are presented using examples from France and Montenegro. Managed aquifer recharge in karst areas and adjacent aquifers is demonstrated with examples from Jordan and Algeria. Finally, failed attempts at flood storage in karst reservoirs are presented with examples from Spain and Montenegro. These examples of flood retention in karst areas show the wide range of planning and technical measures and remind us of possible risks and failures in implementation as well as some positive and negative impacts on the environment and especially on ecosystems.

Floods in Dinaric Karst fields: a case study of the Dicmanjsko-Bisko Polje (Croatia)

ABSTRACT Karst areas are characterized by extreme heterogeneity and variability of geologic, morphologic, hydrogeologic, hydrologic, hydraulic, ecologic and other parameters in space and time. Therefore, the occurrence of floods under such condition manifests in different forms, intensities, and durations. Heavy precipitation in karst areas leads to a considerable increase in groundwater levels and the activation of temporary springs. Karst fields that have not been properly meliorated are particularly vulnerable to such phenomena and, can remain flooded for several weeks. In Dalmatia, in the southern Croatian region, there are 12 karst poljes with an area larger than 1000 ha, including Dicmanjsko-Bisko polje (1700 ha). Our study presents a conceptual model of the interaction of underground and surface water in the Dicmanjsko-Bisko polje, as well as the process of flooding. The input data were geological mapping and measured precipitation. The paper describes the December 2021 flood in detail. The average 11-day precipitation recorded in the field catchment area was 292 mm, which led to the flooding of 230 ha (approximately 14% of the field area). The main cause of the flooding in the western part of the field was a large amount of surface runoff, resulting in insufficient capacity of the existing drainage channels. In the eastern lowest part of the field, flooding was even more intense due to the insufficient capacity of the sinkhole. The flood caused damage to agricultural lands, infrastructure, and economic facilities. The paper proposes flood mitigation measures. The study is an example of the practical application of karst research, that can be used for different purposes (spatial planning, hydrologic monitoring, modeling hydrogeological processes).

Poljes in the Sivas gypsum karst, Turkey

Karst poljes, despite their large dimensions and significant applied interest, have received limited attention in the geomorphological literature, and references to gypsum poljes are incidental. This work analyses the morpho-structural setting, characteristics, origin and controlling factors of thirteen poljes mapped in the gypsum karst of Sivas, Turkey. The poljes occur along a 38 km long belt associated with the allogenic Kızılırmak and Acısu rivers, which constitute the regional base level of the karst system. The path of these drainages is controlled by the trailing morpho-structural trough of the antiformal ridge associated with the front of the active Sivas Thrust. The floor of most of the poljes is connected with the floodplain of the main rivers, but largely lies at lower elevation, functioning as semi-closed basins that can be flooded by water table rise and the incorporation of floodwaters from the adjacent fluvial systems. The depressions, with their floors situated within the epiphreatic zone, are classified as base-level poljes. Three types of base-level poljes are differentiated based on cartographic relationships and attending to their evolutionary path: poljes associated with relict valleys; poljes developed in abandoned valley sections, poljes related to the coalescence of bedrock collapse sinkholes. The poljes expand by lateral solution planation, involving the retreat of the marginal slopes and their replacement by a solution plain (polje floor) controlled by the water table. The retreat of the slopes is mainly achieved by solutional undercutting during floods, mass movements, and the rapid removal of the gypsiferous landslide deposits. These processes are expected to operate in gypsum bedrock at much higher rates than in carbonate rocks. Dissolution acting at the foot of the scarped gypsum slopes during floods locally produce floodwater footcaves with the typical water injection features (e.g., spongework, solution pockets, tapering dead-end passages). These caves locally produce bedrock collapse sinkholes that can be incorporated into the polje depressions generating characteristic embayments. The main factors that seem to favor the development of poljes in Sivas include: (1) a morpho-structural trough with relatively low uplift rate that confined the path of the main drainages; (2) abundant aggressive water supplied by allogenic rivers; (3) a fluviokarst landscape including fluvial landforms that can transform into poljes; and (4) presence of clusters of bedrock collapse sinkholes that experience rapid expansion.

Characteristic of Lang Son Karst Poljes in Vietnam and Geohazards

In the karst regions of Vietnam, there are many different terrains. The most important one is karst polje. Because there are a lot of residential areas and important economic regions. Based on the study of Geomorphology, geological structure analysis, Geophysics document analysis, and karstification process research at Lang Son karst polje. The author gives conclusions: Lang Son karst polje was formed from the limestone of Bac Son Formation, 700 – 800 m thick. Lang Son karst polje was formed from anticline structure, the limestone of Bac Son Formation that has high karstification level. Lang Son karst polje has only one karst aquifer which is a water supply source for residential areas in Lang Son city. This karst aquifer distributes in limestone blocks of the Bac Son Formation. Geohazards on Lang Son karst polje include collapse, sinkhole, flood, and pollution of water. Among them, the most dangerous one is the collapse of the underground karst caves.

Comparative Phylogeography of Phoxinus, Delminichthys, Phoxinellus and Telestes in Dinaric Karst: Which Factors Have Influenced Their Current Distributions?

The waters of the Dinaric Karst drain into both the Adriatic and the Black Sea basins. Precipitation is high, yet surface waters are scarce, with the exception of sinking streams. Dinaric Karst is a biodiversity hotspot, with diverse speleo- and epigean freshwater fauna. The distribution patterns of taxa in Dinaric Karst have arisen from a combination of vicariance and dispersal and their alteration over time. Within fishes, there are genera that include both species that are widespread and species with restricted ranges (e.g., Phoxinus, Telestes), and genera with only restricted distributions (e.g., Delminichthys, Phoxinellus). Some (Delminichthys, Phoxinellus and Dinaric Telestes) have a similar lifestyle, specialized for dwelling in sinking streams in karst poljes. The present study compares the distribution ranges of Phoxinus, Delminichthys, Phoxinellus and Telestes in Dinaric Karst based upon their mitochondrial genetic lineages, including dating of divergence times and reconstruction of ancestral geographic ranges. The biology of Phoxinus has played a major role in its wider distribution than the other three genera, which exhibit some limited ability to migrate underground, but which cannot disperse along main river courses due to their specific adaptation for dwelling in the sinking streams of karst poljes.

Late Quaternary Evolution of a Submerged Karst Basin Influenced by Active Tectonics (Koločep Bay, Croatia)

Koločep bay is a 30 km elongated karst basin located between the Elafiti Islands and the mainland with a NW–SE general direction. The bay lies within the seismically active southern Dalmatia zone. Irregular grid sub-bottom profiles and two legacy reflection seismic profiles have been used to determine the overall morphology of the bay and to establish the seismic stratigraphy of its sedimentary infill. Three major seismic–stratigraphic units have been identified in the upper ~50 m of the ~120-meter-thick sedimentary sequence that lies above the karstified limestone bedrock. The karst polje basin was flooded due to sea-level rise before 12.1 kyr BP. The morphology of the bay implies complex influences of Late Glacial meltwater discharges, aeolian sand deposition, the existence of paleo–ponor/karst spring zones and buried Pleistocene river channels. The Pleistocene seismotectonic units are deformed in the NW and SE parts of the basin. The central part of the basin has no signatures of intensive tectonic activity during the Holocene. A major erosion event was identified that led to the formation of a basin within the older sedimentary infill. In the southern part of the basin, we have evidence of Holocene tectonic activity with the formation of erosional scarps on the seafloor of the bay.

The challenges of bird conservation on an intermittent karst lake: The interplay between changing water level and agriculture

1. Intermittent karst lakes are important for forming wetland habitats in otherwise dry karstic landscapes. With characteristic water regimes they are unable to retain water owing to their underground drainage system. 2. Many Dinaric intermittent karst lakes (karst poljes) have gone through severe human disturbances in the past, aimed at fluctuating water levels in karst poljes. These measures had the goal of achieving either permanent dry agricultural land or permanent lakes for various purposes. Usually dams were built for water storage to achieve these goals. 3. This research aimed to determine the population responses of bird species that are important for conservation, to water level changes on Cerknica Lake (Slovenia), a large Dinaric intermittent karst lake, to inform effective conservation for such systems. 4. Water level and vegetation were strong drivers of waterbird diversity and abundance, based on analysis using canonical correspondence analysis and boosted regression trees. 5. Water level was critical for the conservation of important bird species. Water and reed specialists (e.g. water rail Rallus aquaticus) require management of refugia in wetlands to create mosaics of water and reedbeds. The formation of nature reserves, quiet zones and habitat restoration is needed for these specialist species. In these areas, mowing should be limited or not present at all. 6. Measures dealing with land-use change and connectivity between habitats, for instance agri-environmental measures, are more appropriate for rare bird species with wider niche breadths (but still narrower than generalists), e.g. skylark (Alauda arvensis) and linnet (Linaria cannabina).

Distribution of Vascular Plant Communities in Slovenian Watercourses

Rivers and streams are heterogenous ecosystems that host a great number of vascular plant communities. The territory of Slovenia is highly diverse regarding geomorphologic, geologic, climatic, and edaphic conditions. We presumed that environmental variability will also affect the distribution of hygrophilous vascular plants in running waters and consequently the structure of plant communities they form. We analyzed macrophyte, spatial, and environmental parameters in 906 stretches of the watercourses occurring in the Dinaric, Pannonian, and Po lowland hydro-ecoregions. We determined 87 vascular plant taxa. The most abundant were Myriophyllum spicatum, Phalaris arundinacea, and Potamogeton nodosus. Submerged macrophytes presented about one third of total species abundance, while amphiphytes were somewhat less abundant. Canonical correspondence analysis (CCA) revealed that distance from the source explained 15.1% of the growth form type variability, and current velocity and latitude explained 4.1% each. With the assessed parameters, we explained 31.6% of the variability. When CCA was run with taxa, only 20.9% of their variability was explained with statistically significant parameters. We distinguished 25 different plant associations belonging to five classes and nine alliances. The majority of defined plant communities were distributed in different watercourses belonging to different hydro-ecoregions. Only seven communities had a narrower distribution range, three of them on karst poljes. Among them, the new association Mentho aquaticae-Oenanthetum fistulosae from the river Mali Obrh on the Loško polje was described in this contribution.

Determination of inundation areas within karst poljes and intermittent lakes for the purposes of ephemeral flood mapping

The karst environment presents a special challenge when it comes to identifying groundwater/surface-water interactions. Existing definitions of areas of regular flooding in karst regions are too general and lack a measurable approach for the determination of flood-liable land. This paper proposes a means of specific definition and quantitative determination of intermittently flooded karst areas, which takes into account the extent, duration and frequency of flooding, and includes the identification of data sources and processing methods. The procedure, involving spatial layers, was developed using a pilot area and tested in three additional areas in Slovenia. The derived definition determines that flood-liable land within karst poljes and intermittent lakes comprise areas where stagnant water or stream overflow is present for at least 10 days/year over a period of 30 years, and these waters have direct contact with groundwater. The results show that the proposed procedure is applicable to areas with different geomorphological settings and to areas where the quantity and quality of available data vary. The study is an example of the practical application of knowledge on karst, as the findings can be used for short-term purposes (mapping flood areas, determination of habitats) and long-term purposes (study of impacts of environmental changes). Attention should be drawn to the lack of available data and the fact that the national networks of hydrological observatories are often too sparse for this purpose. This study raises awareness of these shortcomings and improves the planning or expansion of such a network in collaboration with experts.

Flood protection and water utilization of karst poljes: example of Gatačko Polje, Eastern Herzegovina

Eastern Herzegovina is highly karstified area, with porosity of karstified rock mass between 0.8 and 2%. It is an area with high precipitation (average annual values in wet year are around 2450 mm), but its distribution is uneven, with 70% of annual precipitation occurring during the wet season (late fall to early spring). The outflow coefficients are very high, between 0.7 and 0.8. The ratio between flow in the low water period (Q95%) and in the period of high water flow (Q1%) is 1:4000(5000). Due to such hydrological conditions, with limited dewatering capacity of karst channels and ponors, floods of karst poljes occur frequently. This article presents, in very general terms, the properties of the natural water regime of the Gatacko Polje, highest polje in Eastern Herzegovina, including some hydrological and hydrogeological specificity. Special attention is referred to floods and possible ways to mitigate such events, as there are coal mine and coal power plant “Gacko” situated in the polje. Several possible measures are presented in the paper, such as passive protection measures, active flood protection by proper reservoirs management, as well as spatial planning measures. Also, the possibility of transferring part of the water from the Gatacko Polje watershed to the multipurpose hydrosystem Trebisnjica for usage in hydropower production, irrigation, water supply and other secondary benefits is considered.

Late Pleistocene and Holocene paleoenvironmental reconstruction of a drowned karst isolation basin (Lošinj Channel, NE Adriatic Sea)

The results of a comprehensive study of submerged paleoenvironments developed along the karstified eastern Adriatic coast during the Late Quaternary are presented in this study. The Lošinj Channel is a drowned karst basin filled with sediments. A multi-proxy analysis of two sediment cores (LK-12 and LK-15) recovered from water depths of 62 and 64 m was conducted. We used magnetic susceptibility, grain size, mineralogy, XRF core scanning, organic and inorganic carbon, total nitrogen, and paleontological data, supplemented with AMS 14C dating results and high-resolution seismic data, to reconstruct the infill history of the Lošinj basin during the Late Pleistocene and Holocene. Our findings include the first detailed description of the presumed Marine Isotope Stage (MIS) 5a marine sediment succession along the eastern Adriatic coast. Deposition in the brackish-to-freshwater lacustrine body (Lošinj paleolake) occurred during MIS 3. Sea level lowstand that followed caused the formation of environmental conditions typical of a karst polje. The post-Last Glacial Maximum (LGM) sea level rise led to the establishment of a brackish marine lake with seawater seepage through the karstified sill at 13.7 cal kyr B.P. The transition to the present-day marine conditions commenced at 10.5 cal kyr B.P. Paleoenvironmental changes in the investigated area can be linked to the presence of a sill at −50 m depth that separates the Lošinj basin from the Kvarnerić Bay. The sill depth determines the isolation or inundation of the investigated basin in response to the changes in sea level. Paleoenvironments reacted sensitively to these changes, and therefore, the study area represents an ideal setting to track regional sea level and climate variabilty.

An Intermittent Karst River: The Case of the Čikola River (Dinaric Karst, Croatia)

Intermittent and ephemeral streams (IRES) are responsible for transporting about half of the water on Earth’s surface. Their hydrological behavior is different in various landscapes. IRES are found more often in karst terrains than in any other regions, as a consequence of strong and direct interaction between groundwater and surface water. This paper presents a hydrogeological and hydrological analysis of the intermittent Čikola River and Spring catchment, which is located in deeply karstified and developed parts of the Dinaric karst in Croatia. Hydrological calculations determined that the catchment area covers approximately 300 km2 and very probably changes in accordance with rapid variations in groundwater level. The karst spring of the Čikola River is a cave, extracted for a public water supply with four drilled extraction wells. The results of the interrelated hydrological and hydrogeological analysis show interesting phenomena from an intermittent karst spring (cave) and its catchment, flowing downstream through a karst polje with several smaller confluences, then entering a karst canyon (where the river sinks during certain periods), and ending in an estuary before contributing to the larger Krka River. The research presented was based on water balance calculations, climatic and hydrological time series analyses, spring pumping tests, and thorough hydrogeological interpretation.

Distributed hydrological-hydraulic modeling of the karst polje water balance

The paper presents developed 3Dnet-HET, a distributed hydrologic model coupled with the discrete channel network concept for groundwater circulation simulation in the karst environment. The hydrologic part is driven by the spatially distributed precipitation input and characteristic air temperatures to produce surface runoff and groundwater infiltration as a result. This represents input for the “horizontal water balance” module in which the groundwater flow is simulated by the system of discrete conduits representing known groundwater paths. In this study, the model is applied for simulation of the Dabarsko polje water balance in Bosnia and Herzegovina, as well as the river Bregava catchment runoff. The model is firstly calibrated based on recorded water levels in the Dabarsko polje and flow discharges at the Bregava spring. Obtained model is utilized to analyze the Dabarsko polje water balance and possible effects of the planned hydropower plant “Dabar”. Results indicate a high flow variation and necessity of integrated real-time water management of the whole Trebisnjica system.

Hydrogeological characterization of Dasht-e-Arjan Lake (Zagros Mountains, Iran): clarifying a long-time question

Dasht-e-Arjan Lake is located in the southern Zagros mountain ranges of Iran. It is a tectonic karst polje, fed by a single spring plus local surface runoff, and drained by a single ponor. The fate of sinking water from the ponor had not been determined before this study. Previous investigations suggested two alternatives: (1) underground flow ~ 24 km southwest to Parishan Lake and/or springs in the Kazeron area, and (2) underground flow ~ 20 km southeast to springs at Domeasb Gorge. To clarify this question, an integrated hydrogeological study including a dye tracer test was undertaken. Comparison of the discharge into the Arjan ponor and the discharge of the Domeasb springs shows a reliable correlation. Further, annual water balance analysis reveals that the discharge at the Domeasb springs is too great for its topographic catchment, requiring a major additional source. The dye tracer test, using 5 kg of uranine, was detected only at the Domeasb springs. Flow through time after the dye injection was 210 h. The tracer breakthrough curves are very simple and sharp, with a clear peak concentration of 7 ppb. The total tracer mass recovery and groundwater flow velocity were estimated to be 58% and 105 m h−1, respectively. The results indicate a simple and direct limestone karst hydraulic connection along the geologic strike between Dasht-e-Arjan Lake and the Domeasb springs. The results clearly suggest the possibility of designing a dam around the ponor to protect drying up the lake during drought periods.

Juxilyocypris kempfi, a new species of the genus Juxilocyprus (Ostracoda, Ilyocyprididae) from the Late Pleistocene-Holocene of Eastern Adriatic coast (Croatia)

ABSTRACT A new non-marine species of the ostracod genus Juxilyocypris (Kempf, 1967) is described from the late Pleistocene and Holocene sedimentary succession of Lake Vrana (Dalmatia) and Pirovac Bay in the central part of Eastern Adriatic coast in Croatia. The species has been previously recorded as Juxilyocypris cf. schwarzbachi from Lake Vrana (Dalmatia). Juxilyocypris kempfi sp. n., is a cold-temperate species of flooded karst polje habitats characterized by clastic carbonate-rich facies, followed by an organic-rich, low-energy wetland, and periodically shallow waters with muddy bottoms. The presence of a new species of the genus Juxilyocypris (Kempf, 1967) in Croatia extends the known biostratigraphical and biogeographical range of this taxon.

Quaternary Depositional Environments in the Vrgoračko Polje/Lake (SE Croatia)

The Vrgoracko polje is a karst field with a surface area of 37 km2 and an altitude of between 20 and 28 m above sea level, situated at the southern edge of the Dalmatian Zagora. During the Quaternary the polje was flooded for variable periods of time and a lacustrine environment was established. A multidisciplinary study of drill-cores, outcrops and geoelectric measurements recognised five main sedimentary facies: laminated sediment, redeposited sediment, coarse grained carbonate debris, littoral clay and lacustrine chalk. Based on the facies analysis, depositional environments developed during the Holocene include aquatic lacustrine littoral and deeper-water environments. The terrestrial environment is represented by a desiccated lake phase. The littoral clay facies (filling depressions and caverns in the karst relief) is laterally equivalent to the deep-water laminated facies (varves?). A stratigraphic break between littoral claya nd lacustrine chalk could be time-equivalent to disturbed laminated sediments deposited in deeper-water and to local intercalations of coarse-grained carbonate debris in shallow-water facies sediments. These features could have been the result of a neotectonic event (earthquake), which triggered debris flows of colluvial material from slopes around the lake, and this could also have changed the hydrological regime of the Vrgoracko polje and affected subsequent depositional facies. According to 14C dating, deposition of the lacustrine chalk started at the beginning of the Mid-Holocene Warm Period (7686±36 aBP) with a sedimentation rate of approximately 0.51 mm a-1 during the Middle, and 0.58 mm a-1 during the Late Holocene to today. Calculated carbonate production was estimated at 1050 gm-2 a-1. A temporary phase of subaerial exposure of the lake is indicated by desiccation cracks and two bioturbated palaeosol horizons. The described depositional environments and sediment facies found in the Vrgoracko polje could be considered to represent a typical Quaternary lacustrine sedimentation pattern for other Dinaric karst poljes.

Spatial distribution of soil organic carbon and total nitrogen stocks in a karst polje located in Bosnia and Herzegovina

Karst poljes in the Dinaric Mountains have a complex hydrological regime and high potential for crop production. Little information is available about soil organic carbon (SOC), total nitrogen (TN), carbon stocks (SOCS), and nitrogen stocks (TNS) in karst poljes located in the Dinaric area. The objective of this paper was to study the spatial distribution of SOC and TN in topsoil (ranged from 9 to 53 cm depth) and whole profile SOCS and TNS (ranged from 15 to 160 cm depth) in the Livno karst polje depression (Bosnia and Herzegovina) using kriging and co-kriging approaches. We used the following properties as co-variates: distance from hills (DFH), distance from the lake (DFL), sand, silt, and clay content, TN, SOC, SOCS, and TNS. We only used the properties that had a significant correlation with the estimated properties as co-variates. The results showed that soils in the study area had high average SOC (7.92%), TN (0.79%), SOCS (191.05 t ha−1), and TNS (17.91 t ha−1) values. Histosols had the highest SOCS and TNS and Arenosols the lowest. The experimental variogram of LogSOC and LogTN was best-fitted by the spherical model, while the exponential model was the most accurate for LogSOCS and LogTNS. The spatial dependence was moderate for all studied soil properties. The incorporation of auxiliary variables increased the precision of the estimations from 35.7% (SOC × TN) to 49.2% (TNS × SOCS).

Holocene environmental record from lake sediments in the Bokanjačko blato karst polje (Dalmatia, Croatia)

The Bokanjačko blato karst polje (field) is a typical depression along the eastern Adriatic coast that is filled with lake sediments. This large-scale structure is also an hydrologically important region as wells in southern part of the karst polje comprise the water supply for surrounding towns and villages. The evolution of this polje, however, remains poorly understood. A 7.8 m long sediment core from the south-eastern part of the karst polje is utilized in this study to enable a multiproxy approach to the reconstruction of depositional processes that have occurred over the last 10.3 ka cal BP. The sedimentological, mineralogical and geochemical characteristics, as well as palynological analyses of this core indicate that the whole sediment sequence consists of lake sediments alongside a variable amount of carbonates and silicates. The lake existed for approximately 10,300 years before it was drained for agricultural purposes in the 1960s. Depositional changes are also evident throughout the core; between 10.3 and 4.2 ka cal BP, a higher values of magnetic susceptibility (MS) and concentrations of lithogenic elements indicate increased erosion and input of material from the catchment and therefore wetter climatic condition. Deposition of siliciclastic detrital material gradually decreased from 4.2 ka cal BP onwards, replaced by carbonate sedimentation alongside minimal input of the former. The carbonate-based sandy silt sedimentation remains until hydromelioration of the depression. The results of this study show that the lake level gradually increased between 4.2 and 2.9 ka cal BP, evidenced by a higher carbonate content and a lower proportion of detrital material, reaching a maximum between 2.9 and 1.6 ka cal BP. Data also show that at 1.6 ka cal BP, the lake level was likely lowered due to higher nutrient content, including sulfur (S) and phosphorus (P), as well as organic compound levels, prior to human intervention and hydromelioration for agriculture. High concentrations of the nutrient elements, lead (Pb), copper (Cu), and zinc (Zn) in the upper 40 cm of this sequence are indicative of the influence of agricultural activities across the karst polje as well as anthropogenic atmospheric pollution. Geochemical and sedimentological proxies illustrate centennial-scale variability in carbonate deposition and erosional runoff processes comparable with the natural climatic and anthropogenic factors that are known to influence the evolution of Holocene karst poljes across the central Mediterranean.

Measurements of the Outflow Along the Eastern Border of Planinsko Polje, Slovenia

Planinsko Polje is the westernmost active polje of Dinaric karst. It is a typical overflow-structural polje, with springs on the southern side feeding the superficial flow of Unica River. The river meanders over the polje towards the terminal outflow area on its northern side, where it sinks back into the aquifer through several ponors. Along the reach in proximity to the eastern border of the polje, the Unica River loses water through several outflow zones into distinct ponors and into a set of small openings and fracture zones. To estimate the outflow rate along these zones, the Unica discharge was measured upstream and downstream to the outflow zone. Seven velocity profiles were recorded with an Acoustic Doppler Current Profiler and the corresponding discharges were calculated. The measurements were taken within four hours during the flow recession following a partial flooding of the Planinsko Polje. Therefore, six outflow zones were evaluated with an outflow rate ranging between 1 m3/s and 5.6 m3/s. The total loss of water along the eastern border summed up to 18 m3/s under the given hydrological conditions. These results give new insight into the functioning of karst poljes and provide an important input for eventual future hydrological modelling of the area. Key words: polje, outflow, ponors, discharge, Acoustic Doppler Current Profiler, Planinsko Polje, Unica.

Socio-geografska preobrazba Mostarskog blata

This paper analyzes the process of socio-geographic transformation of rural settlements in Mostarsko Blato, karst polje in the Neretva River drainage area. Many changes in spatial organization and landscape have been determined by deagrarization and deruralization, which had been, on the other hand, influenced by various geographic factors: neighboring towns, inadequate infrastructure, profound changes in job offers related to the problems of economic development at the end of socialist period and in transitional period, and particularly by Serbian aggression on Croatia and Bosnia and Herzegovina.Despite numerous problems, socio-economic development of Mostarsko Blato is possible due to natural and human resources. Its development should be based on organic farming, and on development of different types of tourism (ecologic, rural, camping, fishing and summer tourism).