Flood Episodes Research Articles

Landscape diversity vs. population resilience of a wetland species near the limits of its range (the root vole Microtus oeconomus in Poland) – Implications for species conservation

Loss of connectivity between habitat patches is particularly important for small, environmentally specialized species with short migratory capacity. Taking the root vole as an example, we studied whether variation in the landscape (its geomorphological evolution) may affect the genetic differentiation exhibited by a wetland species, and thus the resilience of its population. We did so by testing the genetic differentiation at 9 sites located in two areas in the peripheral zone of the root vole’s range limit in Poland (the Sandomierz Basin and Western Polesie), and confronted the results with the differing origins and geomorphological characteristics of the hydrogenic environments in those two areas. Based on the analyses of 12 microsatellite loci (N = 118) and the 908 bp of cytochrome b sequences (N = 107), higher genetic variability was found in individuals from Western Polesie than from the Sandomierz Basin. Geomorphological analysis conducted with the use of DTM, satellite images, geological maps and cartographic fieldwork showed that the habitats optimal for the root vole are configured differently in the two areas considered, occurring mainly in river valleys and in isolated wetlands of lake-land plains, respectively. Simultaneous analysis of both the spatial configuration and connectivity of habitats, and the voles’ evolutionary directions and genetic parameters, supports the conclusion that the linear character of highly fragmented riverine habitats, additionally inundated during episodic flooding, is less favorable for the gene dispersal of small mammals than extensive marshy wetlands, even despite locally occurring barriers. These findings indicate that the genesis and geomorphological evolution of the landscape may influence the ecological changes taking place there, including habitat reduction and fragmentation. They may therefore be important for the persistence/resilience of particular species and therefore should be taken into account in conservation management of hydrogenic habitat areas, especially those close to the range limit of species with demanding habitat requirements.

Extreme precipitation events in the Mediterranean area: contrasting two different models for moisture source identification

Abstract. Concern about heavy precipitation events has increasingly grown in the last years in southern Europe, especially in the Mediterranean region. These occasional episodes can result in more than 200 mm of rainfall in less than 24 h, producing flash floods with very high social and economic losses. To better understand these phenomena, a correct identification of the origin of moisture must be found. However, the contribution of the different sources is very difficult to estimate from observational data; thus numerical models are usually employed to this end. Here, we present a comparison between two methodologies for the quantification of the moisture sources in two flooding episodes that occurred during October and November 1982 in the western Mediterranean area. A previous study, using the online Eulerian Weather Research and Forecasting (WRF) Model with water vapor tracer (WRF-WVT) model, determined the contributions to precipitation from moisture evaporated over four different sources: (1) the western Mediterranean, (2) the central Mediterranean, (3) the North Atlantic Ocean and (4) the tropical and subtropical Atlantic and tropical Africa. In this work we use the offline Lagrangian FLEXPART-WRF model to quantify the role played by these same sources. Considering the results provided by WRF-WVT as “ground truth”, we validated the performance of the FLEXPART-WRF. Results show that this Lagrangian method has an acceptable skill in identifying local (western Mediterranean) and medium-distance (central Mediterranean and North Atlantic) sources. However, remote moisture sources, like tropical and subtropical areas, are underestimated by it. Notably, for the October event, the tropical and subtropical area reported a relative contribution 6 times lower than with the WRF-WVT. In contrast, FLEXPART-WRF overestimates the contribution of some sources, especially from North Africa. These over- and underestimates should be taken into account by other authors when drawing conclusions from this widely used Lagrangian offline analysis.

Exploring the benefits of a Hi-EnKF system to forecast an extreme weather event. The 9th October 2018 catastrophic flash flood in Mallorca

The afternoon of 9 October 2018 a catastrophic flash flood episode (above 500-y return period) hit the town of Sant Llorenç, in northeastern Mallorca (Spain), leading to 13 casualties and economic losses over 91 M€. Operational models, including HARMONIE-AROME run at the Spanish Meteorological Agency, missed this event and thus no relevant warnings were issued to take preventive actions. Satellite, radar and conventional observations indicate the presence of convective activity along a convergence line, forming during the morning east of Menorca and moving westwards. This convective line is identified as a key factor for the initiation of the moist deep convection responsible for the extreme rain rates associated to this episode. Indeed, the failure of operational numerical models in predicting the flash flood is most likely attributable to their inability to properly simulate the convergence line and the associated convection. To further understand the predictability of this case, we assess multiple different high-resolution ensemble generation strategies, including data assimilation. Results show that among all, only configurations that assimilate reflectivities have the potential to predict significant precipitation amounts over useful lead times in Sant Llorenç basin. In any case, simulated precipitation values are underestimated, and we prove that the predictability of the responsible moist convective systems drops off near the 3–4 h lead times. Numerical predictability challenges of this episode and limitations of the EnKF in these situations are discussed in detail. Overall, the study shows that accurate prediction of this episode is beyond the current prediction capabilities of state-of-the art numerical models and data assimilation techniques.

Observed changes in heavy daily precipitation over the Nordic-Baltic region

Study regionThe Nordic-Baltic region has experienced numerous flooding episodes resulting from heavy rainfall. Such events are costly and may potentially threaten the safety of the population. In this paper we present a temporally long and spatially dense dataset of annual maximum daily precipitation and their date of occurrence measured in a large region covering Fennoscandia and the Baltics (Dyrrdal et al., 2021, doi:10.11582/2021.00015). Study focusWe analyse the long-term (1901–2020) changes at 138 stations and short-term (1969–2020) changes at 724 stations for both annual maxima and their date of occurrence. Further, we assess the climatology of heavy precipitation including record evens, as well as changes in design values. New hydrological insight for the regionResults show a majority of positive trends in daily annual maxima and the 5-year return level, with hotspots in southeast of Norway, southern Sweden and southwest of Finland. Generally, annual maximum precipitation events occur somewhat later in the year now compared to the beginning of the last century. The 5-year return level is relatively homogeneous across the Nordic-Baltic region, with values between 30 and 50 mm, except for a few lower values in Finland and high values mainly exceeding 70 mm at the west coast of Norway.

Effect of Energy Dissipation on Scour Hole Development Downstream of the Chute

An energy dissipation on hydraulic structures is a scientifically highly examined field of study. Gained knowledge can be used to ensure the safety of the hydraulic structures and the channels which is crucial during floods. Above that, those structures are also part of the critical infrastructure therefore their function is necessary. It is assumed that in the Czech Republic the precipitation distribution is changing due to climate change thus episodes of extreme floods may be observed more often. The paper brings brand new knowledge on the kinetic energy dissipation on the chute and in the stilling basin and its impact on the riverbed scour hole development. The presented research was conducted in the Water Management Experimental Centre of Czech Technical University in Prague, Faculty of Civil Engineering. The research aimed to examine the energy dissipation mechanism on different geometric modifications of the construction of spillway chute and stilling basin and its impact on the process of scour hole development. These various types of dams’ flood safety equipment were examined in the hydraulic laboratory: an elementary form of the spillway without any stilling basin; the elementary form of the spillway and the stilling basin (crest and spillway channel had the same width); the chute width was reduced, and the stilling basin had the full width; steps were added on the narrowed chute and the and stilling basin had the full width; only the spillway crest was reduced to a half-width; only the stilling basin width was smoothly reduced; the chute’s width was smoothly reduced along the chute and the stilling basin had full width; the chute’s width was smoothly reduced along the chute and the stilling basin had the width reduced to a half. The flow, water levels, scour hole and deposit dimensions were measured. Then the amount of energy dissipated was computed. The correlation and connection between energy dissipation and scour hole development was investigated. These outcomes can be used as a recommendation of an appropriate construction design to provide better flood safety of the hydraulic structure.

Contested flood risk reduction: An analysis of environmental and social claims in the city of Genoa

The most recent significant episodes of floods in terms of victims and damages in the city of Genoa occurred in 2011 and 2014. After 2014, the Italian government has changed its approach to flood risk management (FRM), adopting what has been called a change of direction towards flood risk reduction (FRR). Accordingly, the city has been involved in a process of governance and urban restructuring. In the wake of these governance and infrastructural transformations, I have conducted thirty-five semistructured interviews with local stakeholders. I use the results to discuss the adopted measures and their acceptability for the local community, focusing in particular on identifying the reasons and different narrative frames that move social dissent. The main reasons for dissent have been identified following two situations: no-recognition of the effectiveness of some works, and lack of adequate measures. Conclusions are that such manifestations of dissent could generate a discussion about the validity by the adopted FRR measures and claim for a more participative approach to the analysis of benefits and impacts produced by such measures. What emerges is in line with last international calls to overcome a technocratic approach to post-disaster, giving more space to community's needs.

Geographic variability of post-disaster mental health: case study after the 2017 flood in Bangladesh.

Every year Bangladesh faces enormous damages due to flooding. Facing these damages the Government adopts various recovery approaches. However, the psychological dimension of any disaster is generally overlooked in disaster management. Researchers have found that the spatial distribution of post-disaster mental health can help the authorities to apply recovery procedures where they are most needed. For this research, Posttraumatic Stress Checklist (PCL-5), Patient Health Questionnaire (PHQ-9) and Generalized Anxiety Disorder-7 (GAD-7) were used to estimate posttraumatic stress, major depressive disorder and anxiety following three episodes of severe floods in 2017 that affected at least 8 million people. To better understand the spatial pattern of psychological vulnerability and reach a comprehensive scenario of post-disaster mental health, Moran's I was applied for spatial autocorrelation and Pearson's correlation and regression analysis for a study of the relationship between the psychological aspects. It was found that psychological vulnerability showed a spatial clustering pattern and that there was a strong positive linear relationship among psychological aspects in the study area. This research might help to adopt disaster management policies that consider the psychological dimension and spatial distribution of various psychological aspects to identify areas characterized by high vulnerability and risk so that they can be reached without delay.

Geomorphological Appraisal of the Madogo-Mororo Floods using Neuro-Fuzzy Inference and the Multinomial Logistic Regression Models

The Tana River County has had serious issues relating to management of its riparian corridors and gazetted catchments. Floods have been an annual episode in Madogo-Mororo areas, with disastrous consequences every time they occur. Lives of both humans and livestock have been lost in every such episode, alongside the destruction of infrastructures and damages to properties, valued in the range of millions of Dollars. The causes do not directly relate to the rainfall volume registered whenever it rains, but rather to myriads of anthropogenic, geomorphological and hydrological variables. A combined statistical - and Artificial Intelligence-aided mapping of the study area was deemed a necessity as a DESK-TOP planning tool for flood risk assessment in the Study Area, as well as for detailed flood-risk mapping. The objective of this study was to identify all these three components, which involved mapping the longitudes, latitudes, elevations, soil types prevalent, vegetation density, grainsize of rocks or soil particles deemed prevalent in the surficial geology, culvert types constructed in the areas visited, hosing types, nearness of settlement to rivers, erosional intensity status of an area, as the input variables, to predict the output variable, flooding probability of an area. Visits were made to the Madogo -Mororo areas and the coded weightings of the aforementioned variables assigned, as deemed appropriate by researcher. For instance, soil erosion intensity was coded as 1, 2, and 3, with the numbers respectively coding for low intensity, moderate intensity and high intensity. The R software modeling libraries were used in this exercise. The neuro-fuzzy algorithms were then used to develop prediction models for floods, based on these coded parameters to assess then accuracy levels of the algorithm test datasets were used, generating over 98.4 percent levels of accuracies. The logistic regression models were then used, for comparison, also recording accuracy levels of 98.4 percent. This affirmed the supremacy of fuzzy logic and logistic regression as useful assessment tools for floods probability mapping in the study area. A code value of 1, represented a high probability of an area being flooded (flood risk areas), and a code of 2 was used to represent high-probability of moderate risk to flooding, whereas the value of 3 signaled a risk-free high-probability in an area. These probability codes were then plotted in a GIS map to help display the geospatial models of flood risk in Madogo and Mororo areas. The study notes the role of human activities and geomorphic factors in exacerbating the propensity to flooding episodes in the study area. Summarily, this study validates the use of neuro-fuzzy inference and logistic regression as dependable mapping tools for flood episodes in Madogo Mororo areas, used alongside the GIS techniques.

Glacial outburst flood in the marginal zone of the Wartanian Glaciation: An example from Adamów, central Poland

In this study, a glacial lake-outburst flood was documented in the immediate foreland of the maximum phase of the Wartanian (Warthian, Late Saalian, MIS 6) Glaciation at Adamów in south central Poland. The structural and textural analyses of the sediments, as well as palaeohydraulic analysis, were carried out in the proximal part of the outwash plain where a fragment of the floodwater drainage system comprising buried erosional channels have been documented. Their fill reached a thickness of up to 11 m and was composed of poorly sorted, massive gravels with boulders, as well as horizontally, sub-horizontally, low-angle, and cross-stratified gravels. The coarse sediments were found to be inversely and normally graded. These sediments constituted the records of two subsequent flooding episodes. In the channel fill, the lenticular accumulations of gravel were identified and interpreted as buried large gravel dunes, while exhibiting a thickness of up to 2.5 m. Traces of sediment diapirism at the contact of channel fill and underlying sediments were also documented. Deformation was observed to originate from liquefaction caused by the rapid depositional loading of flood deposits. The example used in this study exhibited that the impact of glacial lake-outburst floods in shaping the marginal zones and foreland of ice sheets in the North European Plain was higher than that considered earlier. This example also showed a different case of glacial outburst flood in the foreland of the Middle Pleistocene ice sheets of Europe than that already known, which includes the discharge of sub- or englacial meltwater reservoirs emanated from a large proglacial ice-dammed lake.

Flood deposits characterization in Citarum Riverbank Area in Bandung Regency, West Java, Indonesia

Citarum River, the longest river in West Java, is one of the most strategic rivers yet one of the most polluted rivers causing a series of floods throughout history. Understanding shallow flood deposits characteristics may infer the past flooding episode and predict future flood deposits distribution. This research aims to analyze grain size and elemental distributions of flood deposits found in the Citarum Riverbank Area at several districts in Bandung Regency, West Java. Shallow coring resulted in soil samples showing that the samples were dominated by clay and silt. Element analysis revealed that Si and Al are the major elements followed by high concentrations of Fe-oxide in all soil samples. Based on these findings, it is presumed that there were two major episodes of past-floods that occurred in the research area.

Assessing the skills of inter-sectoral impact model intercomparison project climate models for precipitation simulation in the Gongola Basin of Nigeria

The study quantitatively assesses the ability of five Global Circulation Models (GCMs) in the fast track of Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP) to reproduce the observed precipitation climatology over the Gongola river basin of Nigeria for the period 1982−2004. The recent occurrences of recurrent flooding episodes in the basin is alarming. Hence, the models' present-day precipitation is evaluated relative to Global Precipitation Climatology Centre (GPCC) observational datasets based on spatial analysis, statistical measures and climate indices at annual, monthly and daily cycles to identify the most appropriate GCM for impact model in the basin. The results show that climate models replicate the annual precipitation pattern well, both spatially and in magnitude with varying margins. Moreover, the GCMs captured the orographic pattern in the Jos plateau and the general decreasing precipitation trend towards the basin's northeast. amongst the GCMs, IPSL-CM5A-LR better captured the rainy season in the basin extents from April to October and May to October respectively over the Jos plateau and other regions, with maximum rainfall occurring in August, exhibiting a unimodal pattern. The HADGEM2-ES however, better represented the most occurring rainfall intensity in the basin (5 to 50 mm hr−1) in most regions. The degree of pattern correspondence was found highest for IPSL-CM5A-LR with a correlation coefficient of 0.73. Only HADGEM2-ES was able to capture the spatial variability of maximum consecutive dry days over the study domain, increasing from 150 days around the Jos plateau to 200 days over Uba plain. In any case, the HADGEM2-ES appeared to be the most promising model for simulating the extreme conditions over the Gongola basin and can therefore be selected for the application of hydrological impact model for adaption strategy.

Remote Sensing of Ecosystem Structure—Part 2: Initial Findings of Ecosystem Functioning through Intra- and Inter-Annual Comparisons with Earth Observation Data

This study examines the response of a cold-regions deltaic wetland ecosystem in northwestern Canada to two separate and differing seasonal wetting cycles. The goal of this paper was to examine the nature of reflected electromagnetic energy measured by earth observation (EO) satellites, and to assess whether seasonal wetland hydroperiod and episodic flooding events impact the information retrieved by the Sentinel-2 sensors. The year 2018 represents a year characterized by a large spring freshet and ice-jam flooding, while 2019 represents a year characterized more by summer open-water flooding. We applied the Modified Normalized Difference Wetness Index (MNDWI) to address the effects of the wetting cycles. The response of the vegetative cover was tracked using the fraction of the absorbed photosynthetically active radiation (fAPAR) and the Leaf Area Index (LAI). All three indices were viewed through the lens of cover classes as derived through a previously published study by the authors. The study provides a framework for designing longer-term studies where multiple intra- and inter-annual hydrological cycles can be accessed via EO data. Future studies will enable the examination of lag times inherent in the response to the various water sources applied to spectral response and incorporate this EO approach into a monitoring framework.

New titanosaurian sauropod tracks with exceptionally well-preserved claw impressions from the Upper Cretaceous of Argentina

A new titanosaur sauropod ichnotaxon named Teratopodus malarguensis gen. et sp. nov is erected based on a unique association of ten characters. It is represented by new tracks discovered in the upper section of Anacleto Formation outcropping in southern Mendoza province (middle Campanian, Neuquén Basin, Argentina). Teratopodus diagnosis includes suboval-shaped pes tracks, with a slightly obtuse V-shaped heel (PLM° = 95°–100°) and three large, laterally deflected claw impressions corresponding to digits I, II and III, and symmetrical kidney-shaped manus tracks with a slightly concave posterior border. Teratopodus has a medium-gauge trackway and a medium degree of heteropody (~1/3). In addition, a new characterization of heel impressions in sauropod tracks is herein proposed taking into account a distinction between ‘V-shaped’ and ‘U-shaped’ heel impression morphology and the ‘postero lateral-medial angle’ (PLM°). The trackmakers are two titanosaurs specimens of a relatively small-medium size of ca. 11 m and 14 m in length. These tracks are preserved in poorly drained floodplain deposits with ephemeral channels controlled by flash flood episodes. In this context, the trackmakers walked from a humid ground to a more flooded one, leaving behind one of the best-preserved sauropod pes tracks ever recorded in South America.

Sedimentary evolution of distributive fluvial systems within intraplate tectonic active basins: Case study of the Early Cretaceous Araripina Formation (Araripe Basin, NE Brazil)

The Lower Cretaceous Araripina Formation records deposition in a distributive fluvial system that is a part of the post-rift sequence of the Araripe Basin, NE Brazil. Following the opening of the Brazilian Equatorial Margin, the reactivation of regional faults of the Paleoproterozoic basement resulted in tectonic subsidence and formation of a regional-scale DFS. The Araripina Formation is an up to 40-m-thick succession of rhythmically interbedded sandstone and mudstone, organized in two depositional sequences separated by a regional disconformity. We recognized and grouped nine sedimentary facies into six facies associations that we interpreted as deposits of meandering channels, ribbon channels, minor channels, floodplain, lateral and terminal splays, and distal floodplain. The lower sequence facies associations suggest deposition in the medial to distal part of a distributive fluvial system in a tectonically active, interior basin subjected to episodic flooding. The periodic inundations were responsible for activating ephemeral channels and producing sheetfloods, followed by deposition of lateral and terminal splays in distal flooded areas. Syn-sedimentary deformation structures are present in rhythmite facies (truncating surfaces, load structures, injectite and convoluted folds) in the upper part of the lower sequence. The upper sequence was formed after a period of intense tectonic activity in a large distal floodbasin dominated by suspension. The deposition culminates in an interval with pedogenetic deposits cross-cut by a regional disconformity with the upper Exu Formation. Paleocurrent data from both depositional sequences indicate paleodepositional slope towards southeast and east with source-areas located to the northwest and west. This pattern is similar to that observed in the lower Santana Group and opposite to the westward direction of sedimentary transport in the overlying Exu Formation implying significant change of source region, basin topography and continental paleodrainage in the Araripe Basin after the Albian.

Costal sea level variability and extreme events in Moñitos, Cordoba, Colombian Caribbean Sea

Flooding episodes occur frequently in the Colombian Caribbean and cause damage to coastal settlements. However, there is little knowledge about these episodes and about how changes in associated variables affect coastal flooding. This paper presents the results obtained from analyzing the temporal variability of flood levels in Moñitos-Córdoba on the Colombian Caribbean coast, as well as the contribution their components make to different time scales. To achieve this, the total sea level (TSL) was estimated indirectly as the sum of the variables involved (sea level anomalies, astronomical tide, storm surge and wave runup). These variables were obtained by applying numerical and empirical modeling using satellite altimetry data, tidal modeled data and wind, waves and atmospheric pressure from reanalysis. Data Trends and contributions were analyzed using statistical methods, including variance analysis, exceedance distributions, linear regressions, Sen-Slope and the Mann Kendall test. The results indicate that the total sea level has a semi-annual cycle with its highest maximum levels in the months of December to March and its lowest maximum levels in the months of April and September. The total sea level variability in Moñitos is dominated by the runup component at monthly, intra-annual and inter-annual scales, while at longer-term timescales (2–7 years and greater) variability is dominated by the sea level anomaly. Runup is the greatest contributor to the total sea level, followed by the sea level anomaly in average conditions and the astronomical tide in extreme conditions. There was a trend of increasing total sea level, related to the trend in sea level anomaly, with a consequent increasing trend of frequency and magnitude of extreme sea levels.

Acidosis-induced activation of anion channel SLAH3 in the flooding-related stress response of Arabidopsis

Plants, as sessile organisms, gained the ability to sense and respond to biotic and abiotic stressors to survive severe changes in their environments. The change in our climate comes with extreme dry periods but also episodes of flooding. The latter stress condition causes anaerobiosis-triggered cytosolic acidosis and impairs plant function. The molecular mechanism that enables plant cells to sense acidity and convey this signal via membrane depolarization was previously unknown. Here, we show that acidosis-induced anion efflux from Arabidopsis (Arabidopsis thaliana) roots is dependent on the S-type anion channel AtSLAH3. Heterologous expression of SLAH3 in Xenopus oocytes revealed that the anion channel is directly activated by a small, physiological drop in cytosolic pH. Acidosis-triggered activation of SLAH3 is mediated by protonation of histidine 330 and 454. Super-resolution microscopy analysis showed that the increase in cellular proton concentration switches SLAH3 from an electrically silent channel dimer into its active monomeric form. Our results show that, upon acidification, protons directly switch SLAH3 to its open configuration, bypassing kinase-dependent activation. Moreover, under flooding conditions, the stress response of Arabidopsis wild-type (WT) plants was significantly higher compared to SLAH3 loss-of-function mutants. Our genetic evidence of SLAH3 pH sensor function may guide the development of crop varieties with improved stress tolerance.

Implementation of WRF-Hydro at two drainage basins in the region of Attica, Greece, for operational flood forecasting

Abstract. An integrated modeling approach for forecasting flood events is presented in the current study. An advanced flood forecasting model, which is based on the coupling of hydrological and atmospheric components, was used for a twofold objective: first to investigate the potential of a coupled hydrometeorological model to be used for flood forecasting at two medium-size drainage basins in the area of Attica (Greece) and second to investigate the influence of the use of the coupled hydrometeorological model on the precipitation forecast skill. For this reason, we used precipitation and hydrometric in situ data for six flood events at two selected drainage regions of Attica. The simulations were carried out with the Weather Research and Forecasting (WRF) model (WRF-only) and the WRF-Hydro system in a fully coupled mode, under which surface, subsurface, and channel hydrological processes were parameterized at a fine-resolution grid of 95 m approximately. Results showed that the coupled WRF-Hydro system was capable of producing the observed discharge during the flood episodes, after the adequate calibration method applied at the studied basins. This outcome provides confidence that the model configuration under the two-way atmospheric–hydrological coupling is robust and, thus, can be used for operational flood forecasting purposes in the area of Attica. In addition, the WRF-Hydro model showed a tendency to slightly improve the simulated precipitation in comparison to the precipitation produced by the atmospheric-only version of the model (WRF), demonstrating the capability of the coupled WRF-Hydro model to enhance the precipitation forecast skill for operational flood predictions.

Stream Hydrochemical Response to Flood Events in a Multi-Lithological Karstic Catchment from the Pyrenees Mountains (SW France)

Hydrological variations hold a significant influence over the water chemistry in the karstic critical zone. In this context, the karstic Baget Catchment (BC) has been monitored at a high resolution over two years at the outlet in order to set up a typology of the flood events. The objective was to assess the multiple streamwater physico-chemical patterns in response to hydrological variations, streamflow component (quick-response, subsurface, and baseflow) and lithological contributions, and biogeochemical processes. The karstic catchment exhibited an impulsive response to flood events in relation to the typical structural and morphological characteristics of the karst. In addition, this response was constrained by the magnitude of the rainfall and the preceding hydroclimatic conditions. The variability of the dissolved load in streamflow was closely associated with the characteristics of the weathered rocks and the hydrological conditions throughout the year. Two simple indicators allow to characterize the concentration–discharge relationships with different hysteresis patterns on a set of floods with various intensities and shapes of the hydrograph and under different hydrological conditions before the flood. Almost all elements exhibited either clockwise loops or more complex behaviors, suggesting a higher overall concentration when the major water contribution comes from the quick-response flow (karst and surface runoff fraction). Besides, the epikarst flushing under dry conditions led counterclockwise hysteresis patterns for calcium (Ca2+) and bicarbonate (HCO3−) which revealed an overall chemostatic behavior as a result of carbonate dissolution in the karst. On the contrary, sulfate (SO42−) exhibited the widest relative variation during flooding and showed a significant sensitivity to the dilution process with increasing discharge. For medium flood episodes (Qmax < 4.4 m3·s−1), an overall concentration increase or chemostatic behavior could be observed during the rising limb of the hydrograph. On the opposite, under extreme flood episodes (Qmax > 8.3 m3·s−1) occurring after several rain events, a dilution pattern was noted for all elements originating from rock weathering. Finally, high-frequency sampling during storm events improved the understanding of the factors controlling the hydrochemical dynamic in karstic catchments.

The January 2014 Flashflood in the Ambato River (Catamarca, Argentina)- A Case Study of Megaboulders Fluvial Transport

Megaboulders mantle the steep channels of mountainous rivers, and moderate incision rates by increasing channel roughness. Direct measurement of the transport of boulders in natural rivers is difficult, therefore there are few field studies on the subject. The transportation of megaboulders downslope in catastrophic floods in urban environments releases a destructive power. This study analyses the Ambato river flood that occurred in Argentina in January 2014 with an assumed recurrence interval of 1:100 years. The flood was caused by concentrated rainfall in the upper basin, at an elevation of 4000 m.
 The Ambato river forms a boulder alluvial fan drained by episodic floods. The 2014 flood caused casualties and economic losses in the village of El Rodeo in the province of Catamarca. Several houses and a bridge were destroyed and vehicles were swept away. All bedload sizes- including megaboulders with 2000 mm b-axis- were transported during the flood. The empirical equation for stream power value and the unit bedload transport rate of megaboulders were validated.
 An assessment of boulder mobility is necessary to mitigate flow hazards in mountainous urban areas. The effects of climate change in semi-arid environments would be greater if they involved increased precipitation or more extreme rainstorms due to events such as El Niṅo.

Укрепление и защита берегов в Калачевском районе Волгоградской области с помощью кустарниковой растительности

The critical abrasion situation manifests itself on the coastal part of the Kalachevsky district due to the increasing anthropogenic load. The most important element of the complex of measures to combat silting of reservoirs and coastal abrasion, as well as an effective measure to strengthen the banks is forest vegetation. The objectives of the research were to study the soil, forest and climatic conditions of the object under study, to develop an assortment of shrubs and features of the formation of protective forest stands, as well as criteria for selecting an adapted assortment of tree and shrub vegetation and methods of caring for the soil and plantings. During the research, the most promising types of shrubs for creating upper protective forest stands were identified: Ligustrum vilgare L., Berberis vulgaris L., Cotoneaster lucidus Schltdl., Amelanchier Medik., Ribes aureum Pursh., Rosa canina L. It was found that the useful role of forest stands is manifested in their ability to convert surface runoff into subsurface runoff, to clean surface stock water from fine-grained soil, to weaken the speed of movement and to extinguish the energy of waves, binding the soil with roots. Recommendations are given for the creation and placement of anti-abrasion plantings, depending on the steepness and height of the slope. It is stated that one of the main measures for the care of the aboveground part of the plantings is the pruning of the crown, carried out taking into account the biological characteristics of their growth and development, including the removal of dry and damaged branches, thinning of the crown, preservation of the previously given crown size, rejuvenation of the crown. It is recommended to place shrubs depending on the landscape, soil and climatic conditions and features of abrasive processes in areas of constant, periodic, episodic flooding and strong moderate and weak flooding of the coastline.