Summer Floods Research Articles

Characteristics and influencing factors of sediment deposition-scour in the Sanhuhekou-Toudaoguai Reach of the upper Yellow River, China

The annual changes of sediment deposition-scour on the riverbed in the Sanhuhekou-Toudaoguai Reach of the upper Yellow River during the years 1952–2010 were investigated based on runoff and sediment transport observations from the Sanhuhekou and Toudaoguai hydrological stations. Multiple influencing factors such as reservoir operations, tributary inflows, as well as runoff and sediment loads from the Shidakongdui area were analyzed. The results show that even though the sediment loads from the major sources, the Shidakongdui area as well as the upstream tributaries such as the Qingshui River and the Zuli River have reduced especially since the 2000s as a result of enhanced water-soil conservation measures and improvement of vegetation cover, the study reach was still generally in a status of cumulative aggradation. This is mainly due to the joint operations of the Liujiaxia Reservoir and the Longyangxia Reservoir, which significantly reduced the annual runoff and sediment loads at the Sanhuhekou Crosssection. The reservoirs also remarkably altered the summer flood characteristics of the study reach, inducing the shape of the annual flow curve changing from a ‘single-peak’ into a ‘double-peak’. These alternations sharply decreased the sediment transport capacity of flooding in the summer flood season which yields more than 90% of the sediment loads, leading to an unbalanced relation between the water and sediment. In addition, the estimated incoming sediment coefficient of the Sanhuhekou Crosssection ranged from 0.003 to 0.014 kg s/m6, of which 0.004 kg s/m6 was suggested as a rough critical value to determine the scour or deposition status of the study reach.

Improved flooding tolerance and carbohydrate status of flood-tolerant plant Arundinella anomala at lower water temperature.

BackgroundOperation of the Three Gorges Reservoir (TGR, China) imposes a new water fluctuation regime, including a prolonged winter submergence in contrast to the natural short summer flooding of the rivers. The contrasting water temperature regimes may remarkably affect the survival of submerged plants in the TGR. Plant survival in such prolonged flooding might depend on the carbohydrate status of the plants. Therefore, we investigated the effects of water temperature on survival and carbohydrate status in a flood-tolerant plant species and predicted that both survival and carbohydrate status would be improved by lower water temperatures.MethodologyA growth chamber experiment with controlled water temperature were performed with the flood-tolerant species Arundinella anomala from the TGR region. The plants were submerged (80 cm deep water above soil surface) with a constant water temperature at 30°C, 20°C or 10°C. The water temperature effects on survival, plant biomass and carbohydrate content (glucose, fructose and sucrose and starch) in the viable and dead tissues were investigated.Principal findingsThe results showed that the survival percentage of A.anomala plants was greatly dependent on water temperature. The two-month submergence survival percentage was 100% at 10°C, 40% at 20°C and 0% at 30°C. Decreasing the water temperature led to both later leaf death and slower biomass loss. Temperature decrease also induced less reduction in glucose, fructose and sucrose in the roots and leaves (before decay, p < 0.05), but only marginally significant in the stems (p < 0.05). However, the starch content level did not differ significantly between the water temperature treatments (p > 0.05). Different water temperatures did not alter the carbon pool size in the stems, leaves and whole plants (p > 0.05), but a clear difference was found in the roots (p < 0.05), with a larger pool size at a lower temperature.Conclusions/SignificanceWe concluded that (1) A. anomala is characterized by high flooding tolerance and sustained capability to mobilize carbohydrate pool. (2) The survival percentage and carbohydrate status of submerged A. anomala plants were remarkably improved by lower water temperatures. The survival of submergence seemed to be closely associated with the sugar content and carbohydrate pool size of the roots, which contained the lowest amount of carbohydrates. Three Gorges reservoir impoundment in winter is beneficial to the survival of submerged A. anomala in riparian area of the reservoir due to the low water temperature.

A Comparative Analysis of Exceptional Flood Events in the Context of Heavy Rains in the Summer of 2010: Siret Basin (NE Romania) Case Study

The Siret River crosses northeastern (NE) Romania from the north to the south, and it discharges into the Danube, near the city of Galati. Between 17 June and 10 July 2010, significant amounts of precipitations in the mountainous basin of Siret were recorded. The floods comprised two periods with four bimodal cycles, and they were counted as among the strongest on the Romanian territory. The exceptional floods occurred in the rivers of Siret, Suceava, Moldova, Bistrita, Trotus, and so on. The most important compound flood wave was determined by the precipitations, which fell between 29 June and 1 July 2010, when significant amounts of rain were recorded, sometimes exceeding 80 mm/day. The high discharges on the Bistrita River—downstream from the Bicaz Reservoir—were controlled by complex hydro-technical works. The maximum discharge for summer floods in the year 2010 was recorded at the Dragesti hydrometric station: 2884 m3/s (historic discharge) compared with the preceding historic discharge (2850 m3/s) of the year 2008. The effects of floods were strongest in the counties of Suceava, Neamt, and Bacau. The floods on the main course of the Siret River were analyzed in correlation with the tributaries within the mountainous sector.

REPERCUSSIONS OF WATERLOGGING STRESS AT MORPHO-PHYSIOLOGICAL LEVEL ON COTTON AND WAYS TO LESSEN THE DAMAGE TO CROP YIELDS

The volatility of the climate, which is characterized by intermittent heavy rainfall, causes flooding. The problem is exacerbated in soils with limited internal drainage by warm weather patterns. Cotton is commonly grown under these conditions, putting it at risk for yield losses due to summer flooding following heavy rainfall. This requires a deeper understanding of cotton's processes for waterlogging tolerance. This research analyses likely reasons of waterlogging-induced yield loss in cotton, as well as ways for boosting waterlogging tolerance, based on the little information available on cotton and recommendations from other species. The yield penalty is impacted by soil type, phenological stage, and the total time roots were exposed to less than 10% air-filled porosity. In addition to other soil-related issues, an oxygen deficiency in the root zone alters the redox state of nutrients, rendering some inaccessible (such as nitrogen) or potentially poisonous to plants. In addition, xylem-transported root hormones have long been linked to oxygen shortage. Reduced root growth, reduced nutrient uptake and transport, and disturbed hormone signaling are examples of subterranean effects on shoots that impact canopy formation, photosynthesis, and radiation utilization efficiency. Cotton has no evident root aerenchyma reaction and low fermentative activity compared to cereals with greater waterlogging tolerance. We believe that these traits have a significant effect on cotton's susceptibility to prolonged waterlogging. These subsurface components' effects on photosynthesis, shoot functionality, and yield components are discussed. Utilizing management techniques such as fertilizer application, soil aeration, and controlled watering helps prevent waterlogging. Reducing the expression of the genes directing ethylene production and introducing anti-ethylene compounds to limit ethylene biosynthesis are effective methods for preventing yield losses in cotton plants that have become waterlogged.

ЗООПЛАНКТОН НИЖНЕГО ТЕЧЕНИЯ РЕКИ БОРЗЯ

The diversity of plankton invertebrates in the lower stream of the Borzya river is formed by 72 species and subspecies, according to 2005, 2016 and 2018. Widespread and littoral species dominate in thezooplankton species composition. The species number varied from 11 to 42 species, the total abundance – from 0,22 to 92,20 · 103 ind./m3, the total biomass – from 0,77 to 740,14 mg/m3. The greatest diversity and high density of zooplankters were observed after the summer flood.

Climate affects fish-kill events in subtropical estuaries of eastern Australia

Fish kills following austral summer flood events (November–March) occur episodically in estuarine channels in Australia. We examined the climatic conditions associated with the historic record of such events in a subtropical region in eastern Australia to determine the effect of antecedent weather conditions on the probability of post-flood fish-kill events. Records, including regional county council logs, newspapers and New South Wales Fisheries annual reports, were analysed for reports of floods and fish kills following these events. Daily rainfall patterns preceding floods with fish-kill events tended to be drier than rainfall patterns preceding floods when a fish kill did not occur. Based on these observations, it is proposed that estuarine hypoxia resulting in a fish kill is increased by prolonged dry periods followed by rapid and intensive rainfall preceding the flood peak. This is most likely due to (i) accumulation of organic material on the floodplain due to vegetation stress and reduced decomposition processes in drier conditions; (ii) upstream migration of the salt wedge, allowing some estuarine fish species to maintain an optimum environment, followed by flooding with (iii) rapid consumption of dissolved oxygen during decomposition of accumulated organic material sourced from senescent vegetation; and (iv) fish becoming trapped upstream in discharging hypoxic floodwater during the flood recession phase.

Numerical simulation on the southern flood and northern drought in summer 2014 over Eastern China

In summer 2014, Eastern China suffered a typical “southern flood and northern drought” anomalous climate. Observational analyses indicated that the anomalous vertical motion, East Asian subtropical westerly jet stream, and the East Asian summer monsoon (EASM) played important roles in the formation of such precipitation anomaly. Furthermore, using the climate model (IAP-AGCM-4.1) perturbed by simultaneous observed sea surface temperature anomalies (SSTAs) in global scale and four different regions (North Pacific, Indian Ocean, North Atlantic, and Equatorial Pacific), this study investigated the potential contribution of ocean to such “southern flood and northern drought” over Eastern China in summer 2014. The simulations forced by global-scale SSTAs or North Pacific SSTAs displayed the most similarity to the observed “southern flood and northern drought” over Eastern China. It was revealed that the global-scale and North Pacific SSTAs influenced the rainfall over Eastern China via modulating the EASM. The related simulations successfully reproduced the associated atmospheric circulation anomalies. The experiment driven by Indian Ocean SSTAs could also reproduce the similar precipitation anomaly pattern and suggested that the Indian Ocean exerted pronounced influence on the North Pacific Subtropical High. Additionally, the simulations forced by SSTAs in the North Atlantic and Equatorial Pacific successfully reproduced the northern drought but failed to capture the southern flood. The simulations suggested that precipitation anomaly over Eastern China in summer 2014 was a comprehensive effect of global SSTAs and the dominant contribution to the “southern flood and northern drought” pattern came from the North Pacific and Indian Ocean.

Hurry up and wait: life cycle and distribution of an intermittent stream specialist (Mesocapnia arizonensis)

Species inhabiting intermittent streams must have life-history traits that confer resistance or resilience to flow cessation or drying. However, we lack basic life-history information for most aquatic invertebrate species, especially those from intermittent streams. I documented the life cycle and distribution of an unusual winter stonefly species, Mesocapnia arizonensis (Capniidae). The species was first described from 6 localities in 1969, but its natural history remained enigmatic. I surveyed >90 streams across the southwestern USA, documented the life cycle of M. arizonensis at 1 locality, and experimentally rehydrated dry streambed sediment in search of dormant stoneflies at another locality. Field surveys expanded the number of localities from 22 to 98, most of which were intermittent with flow durations as brief as 3 mo/y, and extended the known range of the species by 800 km. Nymphs were abundant within days of flow resumption, grew rapidly as a single cohort, and started emerging as adults 42 d after flow resumed. The brief appearance of a 2nd cohort of tiny nymphs 1 mo before the stream dried indicates direct hatching of at least some eggs. I failed to find dormant stoneflies in the top 30 cm of dry stream sediment, suggesting that M. arizonensis undergoes dormancy deep in the substrate, putting it safely out of reach of scouring summer floods that occur between favorable winter seasons. The remarkable ability of M. arizonensis to survive in short-flow duration streams and to endure multiple consecutive dry years, suggests that the species is well prepared for the drier climatic conditions predicted to occur across its range.

Social capital's role in recovery: evidence from communities affected by the 2010 Pakistan floods.

Pakistan suffered large-scale flooding in summer 2010 that caused damage amounting to approximately USD 43 billion, claimed the lives of at least 1,700 people, and negatively affected some 20 million others. Observers have debated the degree to which social capital plays a role in recovery after a catastrophe of this magnitude. Using new survey data on 450 residents impacted by the disaster, this study found that, controlling for various confounding factors, the social capital levels of victims serve as robust correlates of life recovery. Other important variables connected with recovery include education and income, family size, occupation, material damage suffered, stability of home, and trauma experience. The findings point to a number of relevant policy recommendations, most notably that during and following major shocks, disaster managers should work to keep the social networks of victims intact so that they can benefit from interaction with family, friends, and neighbours.

Calculation of precipitation during period of catastrophic flood 21-27 july 2008 in Ukrainian Carpathians

Intense precipitation event happened in Ukraine on 21-27 July 2008 leading to extreme flash floods in the Ukrainian Carpathians which are characterized by the return period of approximately 50 years. Besides favourable synoptic conditions leading to quasi-stationary low situated over Balkans and South-West part of Ukraine precipitation during this event was intensified by mountains. This lead to formation of the specific precipitation patterns in the Ukrainian Carpathians which was not adequately resolved by the existing measurement network.&#x0D; The purpose of this publication is application of the mesoscale meteorological model WRF with high resolution (1 km) for reconstruction of precipitation during flood in July, 2008 in the Ukrainian Carpathians and evaluation of the simulated results against measurements.&#x0D; Calculation of precipitation during the period of catastrophic summer flood in 2008 at the territory of Ukrainian Carpathians had been carried out with the use of meteorological model WRF. The precipitation field was well simulated for the period of maximum floods (July, 25-th) as compared to precipitation data measured at meteorological stations. However the second and lower peak of precipitation which happened during July, 27-th was underestimated by WRF. The reason of such underestimation is possibly the influence of boundary conditions on simulated results. The precipitation field formed during July, 25-th is elongated along the main ridge of the Ukrainian Carpathians and precipitation maximums on that date, reaching up to 70 mm/3 hours are situated above foothills of the Carpathians. On July, 27-th the precipitation maximums are shifted south-eastward, close to the boundary of the computational domain. The vertical crossections of the calculated meteorological fields demonstrate characteristic system of gravitational waves occurring in flow above mountains and sequence of convective cells situated mostly above the windward (north-eastern) hills and coinciding with the precipitation maximums. The depth of some of the convective cells reaches 10 km, which is supported by satellite data. The indirect evaluation of the calculated precipitation field is performed using the measured water discharge data at the watersheds of the rivers in Carpathians. For the period of maximum flood the relative precipitation amount at each watershed (over total precipitation amount at all water-sheds) appears to be approximately equal to relative water discharge of the corresponding watershed.&#x0D; In conclusion we could state that the precipitation field was well simulated by WRF for the period of maximum floods (25 July). High quality of simulated results is supported by comparison of the calculated and measured precipitation as well as with indirect juxtaposition of the calculated integral precipitation at the watersheds of Carpathian rivers and water discharges in the corresponding river outlets. The calculated results demonstratre that existing measurement network is too sparse to capture the details of the orographically enhanced precipitation field. The scarcity of the measurement network makes it difficult to evaluate integral and maximum characteristics of precipitation happening in the Ukrainian Carpathians.&#x0D; Directions for further research should include usage of the coupled mesoscale meteorological-distributed hydrological model chain for calculation and forecasting of meteorological and hydrological characteristics of floods.

Volcanic suppression of Nile summer flooding triggers revolt and constrains interstate conflict in ancient Egypt

Volcanic eruptions provide tests of human and natural system sensitivity to abrupt shocks because their repeated occurrence allows the identification of systematic relationships in the presence of random variability. Here we show a suppression of Nile summer flooding via the radiative and dynamical impacts of explosive volcanism on the African monsoon, using climate model output, ice-core-based volcanic forcing data, Nilometer measurements, and ancient Egyptian writings. We then examine the response of Ptolemaic Egypt (305–30 BCE), one of the best-documented ancient superpowers, to volcanically induced Nile suppression. Eruptions are associated with revolt onset against elite rule, and the cessation of Ptolemaic state warfare with their great rival, the Seleukid Empire. Eruptions are also followed by socioeconomic stress with increased hereditary land sales, and the issuance of priestly decrees to reinforce elite authority. Ptolemaic vulnerability to volcanic eruptions offers a caution for all monsoon-dependent agricultural regions, presently including 70% of world population.

Long-Term Downstream Effects of a Dam on a Lowland River Flow Regime: Case Study of the Upper Narew

Most European riverine ecosystems suffer from the negative influence of impoundments on flow regime. Downstream effects of dams lead to a number of environmental and socioeconomic risks and, therefore, should be thoroughly examined in specific contexts. Our study aims to quantify the downstream effects of the Siemianówka Reservoir (Upper Narew, Poland), using statistical analysis of key elements of the river’s flow regime, such as the flow duration and recurrence of floods and droughts. In a comparative study on control catchments not influenced by impoundments (the Supraśl and Narewka Rivers), we revealed the following downstream effects of the analyzed dam: significant shortening of spring floods, reduction of the duration and depth of summer droughts, decrease of the maximum discharge, and homogenization of the discharge hydrographs. Although we determined a significant decrease in the duration of summer floods in the “before” and “after” dam function periods, we showed that this issue is regional, climate-related, and replicated in control catchments, rather than an evident downstream effect of the dam. We conclude that significant hydrological downstream effects of the Siemianówka dam–reservoir system could have been the main driver inducing the deterioration of the anastomosing stretch of the Narew River downstream of the dam.

Empirical Subseasonal Prediction of Summer Rainfall Anomalies over the Middle and Lower Reaches of the Yangtze River Basin Based on Atmospheric Intraseasonal Oscillation

The middle and lower reaches of the Yangtze River basin (MLRYB) are prone to flooding because their orientation is parallel to the East Asian summer monsoon rain belt. Since the East Asian summer monsoon presents pronounced intraseasonal variability, the subseasonal prediction of summer precipitation anomalies in the MLRYB region is an imperative demand nationwide. Based on rotated empirical orthogonal function analysis, 48 stations over the MLRYB with coherent intraseasonal (10–80-day) rainfall variability are identified. Power spectrum analysis of the MLRYB rainfall index, defined as the 48-station-averaged intraseasonal rainfall anomaly, presents two dominant modes with periods of 20–30 days and 40–60 days, respectively. Therefore, the intraseasonal (10–80-day) rainfall variability is divided into 10–30-day and 30–80-day components, and their predictability sources are detected separately. Spatial-temporal projection models (STPM) are then conducted using these predictability sources. The forecast skill during the period 2003–2010 indicates that the STPM is able to capture the 30–80-day rainfall anomalies 5–30 days in advance, but unable to reproduce the 10–30-day rainfall anomalies over MLRYB. The year-to-year fluctuation in forecast skill might be related to the tropical Pacific sea surface temperature anomalies. High forecasting skill tends to appear after a strong El Niño or strong La Niña when the summer seasonal mean rainfall over the MLRYB is enhanced, whereas low skill is apparent after neutral conditions or a weak La Niña when the MLRYB summer seasonal mean rainfall is weakened. Given the feasibility of STPM, the application of this technique is recommended in the real-time operational forecasting of MLRYB rainfall anomalies during the summer flooding season.

Hydrology controls recruitment of two invasive cyprinids: bigheaded carp reproduction in a navigable large river.

In the Mississippi River Basin of North America, invasive bigheaded carp (silver carp Hypophthalmichthys molitrix and bighead carp H. nobilis, also referred to as Asian carp) have spread rapidly over the past several decades. In the Illinois River, an important tributary of the Upper Mississippi River, reproduction appears to be sporadic and frequently unsuccessful, yet bigheaded carp densities in this river are among the highest recorded on the continent. Understanding the causative factors behind erratic recruitment in this commercially-harvested invasive species is important for both limiting their spread and managing their harvest. We analyzed weekly catch records from 15 years of a standardized monitoring program to document the emergence of age-0 bigheaded carp in relation to environmental conditions. The appearance of age-0 fish was generally linked to hydrographic attributes, which probably serve as a cue for spawning. However, we found profound differences in the number of age-0 fish among years, which varied by as much as five orders of magnitude in successive years. The strong link between summer flooding and age-0 fish production we observed emphasizes the importance of understanding the hydrologic context in which sustained invasions occur. Despite evidence of sporadic recruitment, bigheaded carp populations in the Illinois River appear to be consistent or increasing because of particularly strong, episodic year classes.

Flood footprint of the 2007 floods in the UK: The case of the Yorkshire and The Humber region

International headlines over the last few years have been dominated by extreme weather events, and floods have been amongst the most frequent and devastating. These disasters represent high costs and functional disruptions to societies and economies. The consequent breakdown of the economic equilibrium exacerbates the losses of the initial physical damages and generates indirect costs that largely amplify the burden of the total damage. Neglecting indirect damages results in misleading results regarding the real dimensions of the costs and prevents accurate decision-making in flood risk management. To obtain an accurate assessment of total flooding costs, this paper introduces the flood footprint concept, as a novel accounting framework that measures the total economic impact that is directly and indirectly caused to the productive system, triggered by the flooding damages to the productive factors, infrastructure and residential capital. The assessment framework account for the damages in the flooded region as well as in wider economic systems and social networks. The flood footprint builds on previous research on disaster impact analysis based on Input-Output methodology, which considers inter-industry flows of goods and services for economic output. The framework was applied to the 2007 summer floods in the UK to determine the total economic impact in the region of Yorkshire and The Humber. The results suggest that the total economic burden of the floods was approximately 4% of the region's GVA (£2.7 billion), from which over half comes from knock-on effects during the 14 months that the economy of Yorkshire and The Humber last to recover. This paper is the first to apply the conceptual framework of flood footprint to a real past event, by which it highlights the economic interdependence among industrial sectors. Through such interrelationships, the economic impacts of a flooding event spill over into the entire economic system, and some of the most affected sectors can be those that are not directly damaged. Neglecting the impact of indirect damages would underestimate the total social costs of flooding events, and mislead the correspondent actions for risk management and adaptation.

Climatic seasonality, hydrological variability, and geomorphology shape fish assemblage structure in a subtropical floodplain

AbstractWe applied a multiscale approach to understand the patterns of longitudinal, lateral, and temporal variability in fish assemblage structure of a large floodplain river and explored their relationships with climatic seasonality, hydrological variability, and floodplain geomorphology. We studied the fish assemblage structure of 35 connected lakes along a 600-km section of the Parana River over 5 y. Longitudinal changes in fish assemblage structure were associated with a latitudinal climatic gradient, whereas temporal changes were associated with climatic seasonality and hydrological variability. Longitudinal and seasonal changes in assemblage structure were probably based on different thermal preferences of species that migrate seasonally along the main river axis. Extraordinary floods in summer promoted downstream dispersal of several species, which increased similarity between downstream and upstream regions. Thermal seasonality of this subtropical system was a strong factor driving temporal chang...

Recent Extreme Floods and Their Transformation Along the Danube River

The article discusses the considerable changes in meteorological conditions and hydrological regime in the Danube River basin over the period from the late 20th century to the early 21st century. Particular attention is given to the recent extreme hydrological events in the Danube River basin: the disastrous rainfall flood that occurred in August 2002, and the extremely high spring–summer floods in 2006 and 2010. Specific features in the development and transformation of flood waves along the Danube River are discussed in detail, including the impact of the Iron Gate I Reservoir on these processes. In addition, the influence of the backwater effect of the Black Sea was evaluated, and probabilities of extreme floods were approximately estimated.DOI: http://dx.doi.org/10.5755/j01.erem.73.1.17988

Run-off analyses using isotopes and hydrochemistry in Yushugou River basin, eastern Tianshan Mountains

Yushugou River basin of East Tianshan Mountains receives water from melting glaciers. In recent years, the glaciers retreated strongly due to global warming which intensified the water cycle in the river basin. For this reason, the relation of water bodies based on hydrochemistry and isotope in the summer flood was carried out. Hydrochemistry research showed that there was frequent hydraulic interaction between river water and groundwater. Studying the isotopes and $$\hbox {Cl}^{-}$$ of river water, glacier meltwater, groundwater and precipitation, indicated that Yushugou River was recharged by the glacier meltwater, groundwater and precipitation during the summer flood period. The analysis result based on the three-component mixing model showed that Yushugou River was recharged by 54.9% of glacier meltwater, 37.6% of the run-off came from groundwater, while less than 8% was contributed by precipitation. The study suggests that the role of glacier meltwater and groundwater, especially glacier meltwater, should be specially concerned in water resource protection and reasonable utilization, and the injection of glacier meltwater is the main reason for run-off variation in this alpine basin during the summer flood period.

Flooding tolerance of four floodplain meadow species depends on age.

Numerous restoration campaigns focused on re-establishing species-rich floodplain meadows of Central Europe, whose species composition is essentially controlled by regular flooding. Climate change predictions expect strong alterations on the discharge regime of Europe’s large rivers with little-known consequences on floodplain meadow plants.In this study, we aim to determine the effects of flooding on seedlings of different ages of four typical flood meadow species. To this end, we flooded seedlings of two familial pairs of flood meadow species of wetter and dryer microhabitats for 2 weeks each, starting 2, 4, 6, and 8 weeks after seedling germination, respectively.We show that a 2-week-flooding treatment had a negative effect on performance of seedlings younger than 6 weeks. Summer floods with high floodwater temperatures may have especially detrimental effects on seedlings, which is corroborated by previous findings. As expected, the plants from wet floodplain meadow microhabitats coped better with the flooding treatment than those from dryer microhabitats.In conclusion, our results suggest that restoration measures may perform more successfully if seedlings of restored species are older than the critical age of about 6 weeks before a spring flooding begins. Seasonal flow patterns may influence vegetation dynamics of floodplain meadows and should, therefore, be taken into account when timing future restoration campaigns.

Temporal variations of large wood abundance and mobility in the Blanco River affected by the Chaitén volcanic eruption, southern Chile

The aim of this study is to analyze the temporal variation in abundance and transport of in-channel wood along a river affected by a volcanic eruption, considering the mobility and retention rates in detail. The 2008 eruption of Chaitén Volcano (Southern Chile) severely affected the Blanco River basin, causing changes in channel morphology and large wood (LW) dynamics along the fluvial corridor of the river, a fourth-order stream on the southern slope of the volcano. Temporal dynamics of LW were investigated, from January 2015 until March 2016, in three 80m-long study reaches of the active channel in the lower course of the river. Every wood element (≥1m in length and ≥0.1m in diameter) within the active channel of each reach was georeferenced, measured, tagged, and characterized. Wood mobility rate, defined as the number of tagged wood pieces repositioned or not found within each study reach to total tagged LW in the same reach; and retention rate, defined as the number of tagged LW pieces found within each study reach to total tagged wood pieces in the same reach, were calculated considering two periods, one in summer and one in autumn-winter. A regional flood frequency analysis estimated flood magnitude, defining a recurrence interval of ~1year for summer floods, and 10–25years for autumn-winter floods. Results highlighted how, eight years after the eruption, the types of LW are still influenced by the impacts of pyroclastic density currents on riparian vegetation. The characteristics and abundance of monitored LW are typical of a river system with frequent wood transport. The mobility rate ranges between 42 and 94% during the summer and autumn-winter period, respectively; while the wood volume decreases during the summer and increases in autumn-winter. Large wood mobility was also found to vary according to the predominant morphological settings, with lower values in narrower channels compared to wider wetted areas. In this context the greatest abundance of LW was detected after the higher floods, corresponding to an input of LW up to 285.35m3·ha−1. Along the Blanco River ordinary floods deliver LW mainly through fluvial transport, and bank erosion during higher floods appears as an additional and important wood recruitment process. The bank erosion processes, with up to 5200m2 of eroded area, confirmed the widening tendency occurring in river systems following volcanic disturbances. As there are dead riparian trees along the easily erodible banks, it is reasonable to suppose that the Blanco River will continue to widen for a long period, recruiting and transporting downstream huge volumes of LW. In this context these analyses appear of fundamental importance to better manage the river system, also for decreasing hazards to the downstream village of Chaitén.