Flood Regime Research Articles

Impact of flood regime on phytoplankton communities in the large African reservoir, Lake Nasser, Egypt

Lake Nasser is a reservoir of freshwater for drinking and irrigation in Egypt and it constitutes an important share in the fisheries sector. This study aims to acquire a better understanding of the status of phytoplankton distribution in Lake Nasser under the current flood regime and before the construction of the Grand Ethiopian Renaissance Dam (GERD). Samples were collected from fifteen sites representing different lake sectors along the main channel of the lake during 2016−2017. Approximately 103 species were recorded, belonging to six different classes, dominated by Cyanobacteria, Bacillariophyceae, Chlorophyceae, whereas Euglenophyceae, Dinophyceae and Chrysophyceae were rare. Based on the abundance of phytoplankton species, the pre-flood and post-flood seasons were very well discriminated. A major blooming of Cyanobacteria in the Tushka sector was detected during the pre-flood season, whereas this phenomenon diminished in the post-flood period when Bacillariophyceae and Chlorophyceae appeared. The results of this study indicated that the most important factors affecting phytoplankton species distribution during pre-flood and post-flood seasons are temperature, nutrients and total dissolved solids. The study confirms that flood regime substantially affects the phytoplankton abundance and distribution in Lake Nasser.

Effective planting arrangement on floodplains to reduce soil loss in a flood regime: Study using physical models

In Taiwan, many floodplains are used for agriculture because flood discharge cannot be blocked, and farmers must be willing to accept the noncompensation offer from the government should their plants be destroyed by floods. Moreover, a scour problem has been observed in floodplains with some kinds of plant, such as bananas. Through a series of laboratory experiments, physical modeling was conducted to develop a planting design to reduce the erosion problem. Five different interval spacings between successive plant models were designed to observe the three-dimensional flow field and sediment transport. The results showed that four low-velocity zones formed around plants when a flood bent them. Among them, the fourth low velocity had the largest influence range. However, if the length of the interval spacing was less than the length of the bent plant, it would cause a shelter effect. This effect would limit the appearance of the fourth low-velocity zone and diminish downstream erosion. In addition, it is suggested that plants be planted using the half length of bent plants as an interval spacing to reduce soil loss. The transverse distance between plant rows should be larger than the half length of the bent plant to avoid contraction scour effects on floodplains. This practical planting method could meet human needs (through added profits) and prevent environmental damage (reduce erosion) simultaneously, making it an effective management strategy for ecological engineers in floodplains.

Impactos del cambio climático frente al cambio del uso del suelo en el reciente régimen de inundaciones del río Lijiang, Sur de China

espanolEl cambio climatico causado por el hombre, sincronizado con el rapido desarrollo en el sur de China, ha inducido varios desafios ambientales criticos en dicha region. Este trabajo compara los impulsores de los cambios del flujo hidrologico y la recurrencia de inundaciones en la cuenca del rio Lijiang. Se llevaron a cabo analisis estadisticos de los cambios climaticos y de uso/cobertura de la tierra (LULCC) utilizando imagenes satelitales, los modelos SWAT y HEC-HMS, pruebas de tendencia de Mann-Kendall y Minitab. Los mapas de uso del suelo se utilizaron para observar la conversion del suelo de la cuenca hidrografica durante el desarrollo previo/posterior a traves de GIS. Aunque se detecto un aumento de hasta el 76 % en las areas urbanizadas, solo el 0.6 % de LULCC se noto en toda la cuenca y habia causado un cambio de 0.1 % en el numero de curva (CN) en toda la cuenca. Los resultados del modelo HEC-HMS revelaron cambios insignificantes de hidrogramas con y sin LULCC. Los datos hidrometeorologicos diarios se analizaron cuantitativamente durante 1967-2016, para determinar el regimen de fluctuaciones y el reconocimiento de patrones. Se encontro un patron de lluvia mas desigual en las ultimas decadas vinculado con una escorrentia excesiva. La temperatura media y la humedad relativa han aumentado continuamente en 0.96 °C y disminuido en un 3 %, respectivamente, durante los ultimos 50 anos. Nuestro estudio sugiere que la causa principal de las recientes tendencias al alza del volumen de escorrentia se atribuye a los cambios en el patron de precipitacion como respuesta al calentamiento global en lugar de LULCC. El resultado esta respaldado por un aumento en la frecuencia del evento de lluvia de intensidad extrema. Los resultados respaldaron la necesidad de un desarrollo sostenible para adaptarse a la nueva situacion. EnglishRapid development synchronized with human-caused climate change, have induced several critical environmental challenges in south China. The current work compares the drivers of hydrological flux changes and flood reoccurrences in the Lijiang River basin. Using satellite images, SWAT and HEC-HMS models, Mann-Kendall and Minitab trend tests, analysis on climatic as well as land use/land cover changes (LULCC) were carried out statistically. Daily hydrometeorological data were quantitatively analyzed during 1967-2016 for fluctuation regime and pattern recognition. A more uneven rainfall pattern in recent decades was found aligned with the excessive runoff. The average temperature and relative humidity have continuously increased by 0.96 °C and decreased by 3 %, respectively during the last 50 years. Land use maps were used to observe the watershed land conversion during pre/post-development via GIS. Although up to 76 % increase in urbanized areas was detected; however, only 0.6 % of LULCC was noticed which had a 0.1 % change in the curve number (CN) in the entire watershed. HEC-HMS model results revealed negligible changes of hydrographs with and without LULCC. Our study suggests that the main cause of the recent flood upward trends is ascribed to the precipitation pattern changes as a response to global warming, rather than LULCC. The result is underpinned by a rise in the extreme intensity rainfall event’s frequency. The need for sustainable development to adapt to the new situation was supported by the outcomes.

Detection of Spatial Shift in Flood Regime of the Kabul River Basin in Pakistan, Causes, Challenges, and Opportunities

Recent evidence of regional climate change impacts on hydrological cycle directed us to study the floods in a high elevated and rapidly urbanized river basin, the Kabul River basin (KRB), Pakistan, which is susceptible to frequent flooding. Therefore, we analyzed the changes in flood regime at various spatial and temporal scales and their possible causes, which is accomplished by using flood indicators, trend analysis, change point analysis, and hydrological modeling. The results showed that the northern and northwestern parts of the KRB were more exposed to flood hazard than the southern parts under long-term scenario (1961/64-2015). However, after the change points, the flood risk decreased in the northern and increased in the southern regions. This spatial shift increased the vulnerability of population to the flood hazard, because the majority of population resides in the southern region. The extreme precipitation has also increased, especially the maximum one-day rainfall and maximum five-day rainfall throughout the basin. Particularly, the major cause of the decrease in different flood indicators in the northern parts of the KRB is the corresponding decrease in the annual and monsoonal rainfall and corresponding positive mass balance of glaciers in the northern region after the occurrence of change point in flood regime. However, the major cause of the increase in flood hazard on the southern part of the KRB is associated with maximum five-day rainfall. A 68% variability of annual maximum flood for the Kabul River at Nowshera and an 84% variability of annual maximum flood for Bara River at Jhansi post are explained by maximum five-day rainfall. In addition, a considerable decrease in forests (–5.21%) and increase in the urban area (88.26%) from 1992–2015 also amplifies the risk of higher flood peaks. The results of hydrological modeling suggest that the six-hourly flood peak increased by 6.85% (1992–2010) and 4.81% (2010–2015) for the extreme flood of 2010 for the Kabul River at Nowshera. The flood peak per decade will increase by 8.6%, as compared to the flood peak under the land use scenario of 2010. Therefore, consideration of proper land use planning is crucial for sustainable flood management in the KRB.

Restored river-floodplain connectivity promotes woody plant establishment

Riparian forest ecosystems are declining globally. Many floodplains no longer flood and thus cease to satisfy the hydrologic requirements for riparian tree maintenance and regeneration. To promote woody riparian plant recruitment where flood regimes have been altered by flow regulation, effective approaches to restoration need to be developed. We implemented a landscape-scale experiment in a remnant, temperate floodplain forest. By constructing two weirs within channelized reaches of a stream, we redirected flows into networks of historic distributary channels, which facilitated widespread floodplain inundation. Using a control-reference-impact study design, we assessed the establishment and growth of planted seedlings of three woody species (Eucalyptus camphora, Leptospermum lanigerum and Melaleuca squarrosa) over 13 months in response to flooding achieved by floodplain reconnection. Planted seedlings had higher height and diameter growth rates at both induced (19–29 cm, 1 mm) and naturally flooded (34–44 cm, 3–5 mm) than at non-flooded (4–10 cm, −5 to −3 mm) sites. However, survival rates and temporal growth patterns differed between species according to variation in flood duration and soil moisture, illustrating the different hydrological requirements of the coexisting species. This highlights that variable flooding and drying patterns are essential to create recruitment niches for different riparian plant species and shows the importance of river-floodplain connectivity for providing adequate flooding regimes. Our study demonstrates the suitability of two complementary restoration approaches – restoring hydrology and active revegetation – for promoting the regeneration of riparian forests.

Flood regime alters the abiotic correlates of riparian vegetation

AbstractQuestionsPredicting the influence of climate change on riparian plant communities improves management strategies. The sensitivity of riparian vegetation to climate and other abiotic factors depends on interactions between properties of the ecosystem, like flood regime, and plant characteristics. To explore these interactions, we addressed three questions: (a) does the composition and diversity of riparian vegetation vary with the flood regime; (b) do abiotic correlates of vegetation, including climate and groundwater, differ between sites that flood compared to locations that did not experience floods; and (c) which plant functional groups account for differential plant community sensitivity to abiotic factors between flood regimes?LocationMiddle Rio Grande Valley, New Mexico.MethodsWe used long‐term observations of plant community composition, groundwater depth, precipitation and interpolated temperature from 24 sites spanning 210 km of the Rio Grande riparian cottonwood–willow forest to explore the relative importance of climate and hydrologic correlates of riparian vegetation diversity and composition.ResultsRiparian plant diversity was higher at sites flooding compared to non‐flooding sites. Plant diversity positively tracked shallower groundwater depth at flooding sites, but was best predicted by intra‐annual groundwater variability at non‐flooding sites. Plant community composition correlated with groundwater depth and air temperature at all sites, but at non‐flooding sites, also with intra‐annual groundwater variability and precipitation. Relationships between native plant cover and potential environmental drivers diverged strongly between the two flood regimes; non‐native plant cover had only weak relationships with most environmental predictors.ConclusionsThe current flood regime of a site determined the climate and hydrologic factors that best predicted riparian plant community composition and diversity. Relationships between plant diversity or total cover and groundwater, temperature, precipitation, or groundwater variability can change in strength or direction depending on a site's flood history, highlighting the importance of flood regime to predicting the sensitivity of riparian woodlands to future environmental change.

Documentation of Riparian Biodiversity of an Urban River Stretch - A Citizen's Initiative

Rivers in urban areas are facing multidimensional threats ranging from untreated sewage discharge, garbage and debris dumping, developmental projects to illegal encroachment on banks. Still few river stretches in urban areas harbor rich riparian biodiversity. Such areas need protection to avoid further degradation. These river stretches serve as ideal river ecosystem adding to ecological value of the area. The present study deals with documentation of riparian biodiversity of river stretch in Pune, Maharashtra. This area is a confluence zone of Mula and Ram rivers. River undergoes ecological processes during her flow and flood regimes. This adds to making the region not only rich in biodiversity but acts like a sponge for flooding water, temperature control, ground water recharge and creating green lungs for local region. Ecological processes include formation of an island, braiding of channel, rocky outcrops, riffles and pools etc. All this together create specific habitats for diverse species. This river stretch is part of flood plain area and has presence of live springs. The objective of the study was to document the floral and avian biodiversity of the riparian area with help of public participation with a view of protecting this area. During the study we have recorded about 70 floral species and 60 avian species at this riparian zone. The riverbank harbours a thick patch of typical riparian vegetation comprising of Pongamia pinnata, Syzygium cumini, Syzygium heyneanum, Salix tetrasperma and Ficus racemosa. Regular monitoring and observations at the river stretch are being carried out by a group of active citizens who are members of Jeevitnadi Living River Foundation. This vigilance, year round monitoring and documentation is helping in protecting the river stretch. Some major threats and stresses faced by this serene riparian forest are sewage discharge, debris dumping, encroachment and developmental projects. Point and non-point sources of pollution include release of untreated sewage from Sewage Treatment Plant situated at confluence, discharge of sewage and waste dumping by slum dwellers situated along Ram River.

ВЛИЯНИЕ КЛИМАТИЧЕСКИХ ИЗМЕНЕНИЙ НА МАКСИМАЛЬНЫЕ УРОВНИ ПЕРИОДА ПОЛОВОДЬЯ РЕКИ АБАКАН

Актуальность работы обусловлена воздействием изменений климата на гидрологические режимы рек южной Сибири, увеличением повторяемости опасных гидрологических явлений. Наблюдаемые и прогнозируемые изменения в режимах половодий вызываются множеством факторов и требуют различных подходов для характеристики типов этих изменений. Цель: стохастическое моделирование сумм твердых осадков в исследуемом бассейне р. Абакан, установление их связи с максимальными уровнями воды в р. Абакан периода половодья в условиях пространственно-временной изменчивости гидрометеорологических факторов. Методы: комплексный географо-гидрометеорологический анализ, выявление зависимостей по данным многолетних гидрометеорологических наблюдений с использованием методов математической статистики, а также методики оценки количества осадков в бассейне с учетом орографический добавки к скорости вертикальных движений во фронтальной зоне, разработанной В.П. Галаховым. Результаты. Основным фактором формирования максимальных уровней периода половодья является количество зимних осадков. Обильные жидкие осадки на спаде половодья могут вносить значительные коррективы в максимальные уровни. Однако для бассейнов горных рек юга Западной и Восточной Сибири в последние десятилетия в связи с климатическими изменениями отмечается влияние условий промерзания почвогрунтов в осенний период на формирование максимальных уровней вследствие снеготаяния. Для бассейнов со значительной долей предгорных равнин в отдельные годы возможно уменьшение максимальных уровней периода половодья. Для бассейнов, имеющих в основном горный ландшафт, подобного эффекта не наблюдается. Разработана методика расчета сумм зимних ежегодных осадков в бассейне Абакана, учитывающая физические особенности формирования осадков в горах, в частности орографическую добавку к скорости вертикальных движений. На примере независимых данных показано, что алгоритмы расчета максимальных уровней за счет снеготаяния, основанные на регрессионных зависимостях, не всегда дают адекватные результаты. Необходима их корректировка с учетом процессов промерзания на предгорной равнине. Для получения общей статистической зависимости требуются дополнительные данные наблюдений.

Amazon floodplain hydrology and implications for aquatic conservation

Abstract The amplitude, duration, frequency, and predictability of runoff and inundation of aquatic habitats are key hydrological characteristics linked to aquatic ecosystem functioning and biodiversity, but they are seldom integrated into analyses of Amazon floodplain ecology. Remote sensing approaches, measurements and modelling of floodplain hydrology provide a basis for this integration. Effective legislation to protect floodplains and other wetlands depends on operational definitions that require application of hydrological data. Extent and changes of flooded areas are linked to fish diversity and to presence and growth of flooded forests and floating plants. Dam construction reduces river system connectivity and modifies the flood pulse, with major negative implications for floodplain ecosystems adapted to and dependent on a natural flood regime. Trends and variability in climate plus deforestation are altering the Amazon's hydrological cycle, causing changes in discharge and flooded area with concomitant ecological impacts.

Ontogenetic Structure and Temporal Patterns of Summer Ichthyoplankton in Upper Course of the Xijiang River, SW China

The summer ichthyoplankton characteristics in the Laibin section of the Xijiang River were analyzed based on a survey during summer 2017. The ontogenetic structure and temporal patterns of ichthyoplankton and the correlation between environmental parameters and the temporal patterns were investigated. A total of 10,665 eggs and 447 larval belonging to four orders, ten families, and 28 species were collected. According to the flood regime, summer is divided into three periods (pre-flood, flood period, and post-flood). Ichthyoplankton proved to be heterogeneous between periods in summer with differences in the composition and abundance. The assemblages were distinguished by multiple analytical tools, and presented a chronological pattern of marked variability in composition of the species between the periods, and under the strong influence of flood. The assemblages were mainly represented by eggs of S. wui Fang and S. robusta in the pre-flood period, S. argentatus and S. macrops in the flood period, and H. leucisculus and S. curriculus in the post-flood period, while, the larval occurred mainly in the flood period. Understanding these temporal patterns of the upper course of the Xijiang River is useful for the recruitment of fish resources and conservation of fish community diversity.

Agricultural Innovations to Reduce the Health Impacts of Dams

Dams enable the production of food and renewable energy, making them a crucial tool for both economic development and climate change adaptation in low- and middle-income countries. However, dams may also disrupt traditional livelihood systems and increase the transmission of vector- and water-borne pathogens. These livelihood and health impacts diminish the benefits of dams to rural populations dependent on rivers, as hydrological and ecological alterations change flood regimes, reduce nutrient transport and lead to the loss of biodiversity. We propose four agricultural innovations for promoting equity, health, sustainable development, and climate resilience in dammed watersheds: (1) restoring migratory aquatic species, (2) removing submerged vegetation and transforming it into an agricultural resource, (3) restoring environmental flows and (4) integrating agriculture and aquaculture. As investment in dams accelerates in low- and middle-income countries, appropriately addressing their livelihood and health impacts can improve the sustainability of modern agriculture and economic development in a changing climate.

Relationship between Flooding Regimes, Time of Year, and Seed Coat Characteristics and Coloration within Fruits of the Annual Monocarpic PlantSesbania emerus(Fabaceae)

Premise of research. Many plant species produce propagules of different shapes and sizes on the same plant or within an inflorescence. These differences influence seed dispersal and germination and seedling growth. We investigated the relationship between the flooding regime, time of the fruiting season, and position within the fruit on seed coloration, seed abortion, and seed predation in Sesbania emerus.Methodology. We studied the production of seeds of different colors within fruits of S. emerus in Palo Verde National Park, Costa Rica, during the months of fruit maturation and seed dispersal. We sampled fruits in natural stands along a flooding gradient, and for each seed, we recorded the color of its coat, its position within the pod, and whether it was healthy, aborted, or predated. We also studied the structure of seed coats of seeds of different colors using scanning electron microscopy (SEM) and thermal gravimetric analysis (TGA) to determine their chemical characteristics.Pivotal results. Our study reveals that S. emerus produced seeds of different colors within the same fruit and that their proportion varied along a flooding gradient and during the fruiting season. The proportion of seeds of different colors also varied among the positions within the fruit. Seed abortion and seed predation predominantly occurred for brown seeds and changed between flooding levels and fruiting season. SEM showed no differences in the seed coats’ thicknesses or structures among seed colors, but TGA showed differences in water, cellulose, hemicellulose, and lignin content.Conclusions. The production of seeds of different colors in S. emerus is related to differences in the flooding regime, time within the fruiting season, and position within the fruit. Seed color affects seed germination and the likelihood of seed abortion and predation, and we discuss the potential factors determining these differences.

Extreme floods of the Changjiang River over the past two millennia: Contributions of climate change and human activity

Climate change and human activity have exerted significant influences on the sediment load and channel morphology of the Changjiang River system, China. However, our knowledge of their influence on flood regime on the centennial to millennial timescales remains limited, and this is mainly because of the difficulty in directly determining the long-term hydrological variability of the Changjiang River over the period before hydrological gauges were established. Based on multiproxy analysis that combines chronological, sedimentological, and geochemical analysis of a 4.8-m-long sediment core retrieved from the subaqueous delta of the Changjiang River, this study establishes a flood history for the Changjiang River during the late Holocene. Our palaeoflood reconstruction revealed 14 multi-decadal periods of extreme floods (19–66 BCE, 25–80, 255–350, 415–475, 550–710, 740–835, 970–990, 1080–1130, 1170–1235, 1275–1390, 1440–1500, 1560–1730, 1810–1830, and 1950–2011 CE). These flood units match well with the observed large floods, documentary records of floods, and sedimentary flood deposits, confirming that the coarse units in the sequence are flood-derived and are regionally representative. Comparing with regional and global palaeoclimate records indicates that major flood events of the Changjiang are strongly modulated by the Asian summer monsoon and the El Niño–Southern Oscillation (ENSO), but that anthropogenic impacts (e.g. artificial channelization and land clearance) have also greatly amplified the flooding frequency over the past 600 yr.

Larger floods reduce soil CO2 efflux during the post-flooding phase in seasonally-flooded forests of Western Amazonia

Seasonally-flooded várzea forests of Western Amazonia are one of the most productive and biodiverse wetland forests in the world. However, data on their soil CO2 emissions, soil organic matter decomposition rates, and soil C stocks are scarce. This is a concern because hydrological changes are predicted to lead to increases in the height, extent, and duration of seasonal floods, which are likely to have a significant effect on soil C stocks and fluxes. However, with no empirical data, the impact of altered flood regimes on várzea soil C cycles remains uncertain. This study quantified the effects of maximum annual flood height and soil moisture on soil CO2 efflux rate (Rs) and soil organic matter decomposition rate (k) in the várzea forests of Pacaya Samiria National Reserve, Peru. The study was conducted between May and August 2017. The results showed that Rs (10.6–182.7 mg C m−2 h–1) and k (0.016–0.078) varied between and within sites, and were considerably lower than the values reported for other tropical forests. In addition, Rs was negatively affected by flood height (P < 0.01) and soil moisture (P < 0.001), and it decreased with decreasing river levels post flooding (P < 0.001). In contrast, k was not affected by any of the above-mentioned factors. Soil moisture was the dominant factor influencing Rs, and it was significantly affected by maximum flood height, even after the floods had subsided (P < 0.001). Consequently, we concluded that larger floods will likely lead to reduced Rs, whilst k could remain unchanged but with decomposition processes becoming more anaerobic.

Hydromorphological characteristics of the rivers of Algeria

The article presents the results of a study on the water regime of the rivers of Algeria, which are characterized by a flood feeding regime. The flood regime is mainly formed from heavy rains, the flow of which is 80-90 % of the annual flow. Due to the short duration of rain floods, stationary hydrological posts do not always register them, so they can be characterized as single-modal, which simplifies their design possibilities. For the design of hydrographs of rain floods, a parabolic model-a flood scheme is adopted, and the main characteristics of hydrographs are determined according to this scheme.

Beaver dams attenuate flow: A multi-site study.

Beavers can profoundly alter riparian environments, most conspicuously by creating dams and wetlands. Eurasian beaver (Castor fiber) populations are increasing and it has been suggested they could play a role in the provision of multiple ecosystem services, including natural flood management. Research at different scales, in contrasting ecosystems is required to establish to what extent beavers can impact on flood regimes. Therefore, this study determines whether flow regimes and flow responses to storm events were altered following the building of beaver dams and whether a flow attenuation effect could be significantly attributed to beaver activity. Four sites were monitored where beavers have been reintroduced in England. Continuous monitoring of hydrology, before and after beaver impacts, was undertaken on streams where beavers built sequences of dams. Stream orders ranged from 2nd to 4th, in both agricultural and forest‐dominated catchments. Analysis of >1000 storm events, across four sites showed an overall trend of reduced total stormflow, increased peak rainfall to peak flow lag times and reduced peak flows, all suggesting flow attenuation, following beaver impacts. Additionally, reduced high flow to low flow ratios indicated that flow regimes were overall becoming less “flashy” following beaver reintroduction. Statistical analysis, showed the effect of beaver to be statistically significant in reducing peak flows with estimated overall reductions in peak flows from −0.359 to −0.065 m3 s−1 across sites. Analysis showed spatial and temporal variability in the hydrological response to beaver between sites, depending on the level of impact and seasonality. Critically, the effect of beavers in reducing peak flows persists for the largest storms monitored, showing that even in wet conditions, beaver dams can attenuate average flood flows by up to ca. 60%. This research indicates that beavers could play a role in delivering natural flood management.

Rainfall-Runoff Simulation and Modelling Using HEC-HMS and HEC-RAS Models: Case Study Tabuk, Saudi Arabia

Flooding regimes in arid regions are heavily influenced by climate change, water shortage, water regulations, and increased water demands. The low amount of annual precipitation due to the desert climate may lead to false estimations of flooding hazards. This study analyzed flash floods caused by short-intense rainstorms. The objective of this study was to determine flood risk related to identified precipitation depths. The project quantized the runoff corresponding to different design storms and used hydraulics and geospatial data to determine flood elevations. The study constructed hydrologic and hydraulic models to quantify flood hazards in the adjacent area of Wadi Abu Nashayfah. Peak discharges for the wadi were computed by using observed rainfall data, and the output of this process was applied to compute water surface elevations within the flow channel. At upstream, there is a high potential of flooding when Wadi Abu Nashayfah receives a minimum of 25 mm of rain which generates 40.60 m3/s of peak discharge, thus, at this point the stream will overtop its banks and risking the adjacent area. In the second case, flow will overtop its banks when the channel receives at least 35 mm of rain and peak discharge level to 67.20 m3/s. While flow will reach bank full point if wadi Abu Nashayfah receives 10.00 mm of rain and generates 14.80 m3/s of streams downstream. The depth of precipitation at which the channel was overtopped was determined in several locations. The predicted overtopping was compared to historic events with good agreement.

Сучасна динаміка рівнів вод та їх паводкових підйомів у верхів’ї річки Прут у межах ландшафту Чорногора (Українські Карпати)

This article presents the results of the analysis of modern water levels of the upper reaches of the largest river named Prut in the mountain landscape of Chornohora for the period from 2010 to 2019, based on data from own long-term hydro-meteorological observations on the basis of Landscape Monitoring Laboratory of Ivan Franko National University. The studied river is characterized by a dense river network, a peculiar hydrological regime and periodic formation of heavy floods, as well as the presence in its basin of valuable landscape complexes and environmental facilities, high landscape diversity and recreational and tourist potential, which determines the relevance of this study. As a result of the study, the peculiarities of the formation and modern features of the hydro network of the Prut river basin were established, its heterogeneity in the mid-mountain and high-mountain landscape tiers was characterized. It is established that during the period 2010-2019 in the upper reaches of the Prut River there was an increase in river water levels, as well as identified the main factors and their impact on current changes in the hydrological regime of the river. The annual changes in the water level in the upper reaches of the Prut River for the period 2010-2019 were also analyzed and it was found that its mountainous nature causes high dynamics of river water levels at different times of the year and in certain months. It was important to identify the relationships between their indicators and the characteristics of the annual distribution of precipitation and snowmelt during studying the annual cycles of water level fluctuations. Particular attention is paid to the study of the formation and spread of floods as the most dangerous hydrological phenomenon of the upper reaches of the Prut River, characterized by a sharp rise in water levels, high erosion capacity, etc. The study found that more than 75 % of floods occur during the spring snowmelt in April and May where the average daily river water levels usually do not exceed 60-70 cm. The analysis of flood rises in terms of years and months shows that the most severe catastrophic floods are formed in November-December due to heavy rains, which cause the formation of powerful destructive water flows and catastrophic growth of river water levels over 90-100 cm. The total annual number of flood rises in the Prut River was also analyzed according to certain categories of indicators (over 60 cm, 70 cm, etc.) and it was found that the total number of floods in the upper reaches of the river is increasing.

Assessment of the livelihood sustainability of rice farmers in the upper floodplains of the Vietnamese Mekong delta

Rural areas and rural livelihoods in many countries have been affected by changes in natural and environmental conditions. In areas where livelihoods relied on the floodwater, changes in flood regimes and the natural environment had significantly impacted many farmers' livelihoods. In the Mekong Delta flooded areas, flood patterns changed mainly due to the hydropower development and the climate change. The livelihoods of many farmers, primarily rice farmers, were facing challenges and needed changes to adapt to the sustainable livelihood development. This study used a sustainable livelihood framework of DFID to assess factors affecting the sustainability in agricultural livelihoods in flooded areas of An Giang province, specifically at Phu Hiep and Phu Long communes of Phu Tan district. We interviewed 60 farmers based on the structured questionnaire and conducted two focus group discussions with more than 40 participating farmers. Our results of the Livelihood Capitals Index (LCI) showed that natural and physical capitals had less impact on household livelihoods. Phu Long is less affected than Phu Hiep by assessing five capitals. Farm households' current livelihoods were mainly affected by the lack of human resources and the unstability of market prices. The rate of consensus on transition to sustainable farming models was not high due to many factors. However, the transition is possible if their production and output are secured by the government.

Frequency of occurrence of flow regime components: a hydrology-based approach for environmental flow assessments and water allocation for the environment

ABSTRACT Hydrological methodologies are the most efficient approaches for environmental flow (eflow) assessments. This paper presents a hydrological methodology for determining eflows in rivers with scarce development to promote proactive environmental water allocations that limit flow alteration and unsustainable water use. The analysis includes the natural intra-annual and inter-annual ranges of flow variability. Eflows are determined based on four hydrological low-flow conditions and a flood regime. The main contribution is that the flow regime components are adjusted to a four-tiered environmental objective class system based on a novel “frequency-of-occurrence” approach. The method is applied in three rivers in western Mexico with highly variable flow regimes. The eflows are largely (96%) within the central range of previous implementations, and the outcomes reveal an overall good and acceptable level of the method’s performance (for 83% of the cases R 2 ≥ 0.84, slope = 1 ± ≤ 0.2), consistent with supporting indices of flow variability.