Low Flow Regime Research Articles

The Influence of Urban Development Patterns on Streamflow Characteristics in the Charlanta Megaregion

AbstractAlthough it is widely recognized that urbanization has a notable impact on streamflow characteristics, the relative influence of the extent, spatial configuration, and positioning of urban development on low, high, and peak flow regimes is still not fully understood. The overarching research objective of this study was to clarify these relationships by analyzing 119 watersheds throughout the Charlanta megaregion, which stretches from Charlotte, NC to Atlanta, GA. Spatial metrics were derived from land use/land cover data sets to quantify the urban development patterns of each watershed while the streamflow characteristics were evaluated using mean daily discharge and annual peak streamflow data. Analysis of variance tests, bivariate correlations, and multivariate regression models were used to identify intraregional variability and quantify the impact of urban development patterns on streamflow characteristics while controlling for the physical differences between watersheds. The statistical analysis revealed that increasing the extent of urban development enhanced high and low flow frequency as well as annual peak unit discharge. Therefore, urbanization within Charlanta generally produced a more extreme streamflow regime. In terms of the spatial configuration of urban development, the models indicated that more contiguous developed open space increased high and low flow frequency. Finally, the positional analysis suggested that clustering impervious surfaces in source areas distant from streams increased the frequency of high flows. The study highlights the overall importance of considering the extent, configuration, and positioning of urban development when devising land use policies aimed at minimizing streamflow alteration due to urbanization.

Hydrograph separation using tracers and digital filters to quantify runoff components in a semi‐arid mesoscale catchment

AbstractChemical hydrograph separation using electrical conductivity and digital filters is applied to quantify runoff components in the 1,640 km2 semi‐arid Kaap River catchment and its subcatchments in South Africa. A rich data set of weekly to monthly water quality data ranging from 1978 to 2012 (450 to 940 samples per site) was analysed at 4 sampling locations in the catchment. The data were routinely collected by South Africa's national Department of Water and Sanitation, using standard sampling procedures. Chemical hydrograph separation using electrical conductivity (EC) as a tracer was used as reference and a recursive digital filter was then calibrated for the catchment. Results of the two‐component hydrograph separation indicate the dominance of baseflow in the low flow regime, with a contribution of about 90% of total flow; however, during the wet season, baseflow accounts for 50% of total flow. The digital filter parameters were very sensitive and required calibration, using chemical hydrograph separation as a reference. Calibrated baseflow estimates ranged from 40% of total flow at the catchment outlet to 70% in the tributaries. The study demonstrates that routinely monitored water quality data, especially EC, can be used as a meaningful tracer, which could also aid in the calibration of a digital filter method and reduce uncertainty of estimated flow components. This information enhances our understanding of how baseflow is generated and contributed to streamflow throughout the year, which can aid in quantification of environmental flows, as well as to better parameterize hydrological models used for water resources planning and management. Baseflow estimates can also be useful for groundwater and water quality management.

Low Flow Regimes of the Tarim River Basin, China: Probabilistic Behavior, Causes and Implications

Droughts are a frequent occurrence in Xinjiang, China, and therefore fundamental to determining their hydrologic characteristics is low flow analysis. To that end, 11 probability distribution functions and 26 copulas functions were employed to analyze the changing characteristics of low flow regime (defined as seven-day low flow) of the Tarim River Basin. Results indicated that: (1) The Wakeby distribution satisfactorily described the probabilistic behavior of the low flow regime. According to Akaike Information Criterion (AIC), Bayesian Information Criterions (BIC), maximum likelihood, and other residual-based metrics, Tawn copula, Farlie–Gumbel–Morgenstern copula and Frank copula were the best choice and used in this current study. (2) After 1987, hydrological droughts of longer return periods were prone to higher occurrence frequency. (3) The low flow volume has been increasing in recent years due to the temperature-induced increase of snowmelt and increasing precipitation. However, hydrological droughts can be expected to occur due to the massive increase in water demand from the development of irrigated agriculture, increasing arable land and livestock farming. As a result, the water shortage in the lower Tarim River Basin will be increasingly severe under the influence of climate change and human activities. To alleviate the shortage would call for the development of water-saving agricultural irrigation, water-saving technology, conservation of eco-environment and sustainable development of local socio-economy.

Modeling fine particle dynamics in gravel-bedded streams: Storage and re-suspension of fine particles

Fine particles or sediments have various effects on water quality and aquatic ecosystems. Thus, understanding the dynamics of these fine particles between water body and stream bed is an important issue in sediment research. Previous studies and analysis of empirical data suggest that fine particles are stored in the sediment bed in the low flow regime, where flow rate is smaller than the critical flow rate that mobilizes the sediment bed. These fine particles are re-suspended during flood events when the flow rate becomes larger than the critical flow rate that mobilizes bed material. The transition from pattern recognition to process analysis required incorporation of the dominant processes controlling fine particle dynamics within gravel-bedded streams into a model. The process analysis was performed using continuous flow and turbidity data at two locations on the Russian River in California to test process descriptions and then calibrate a quantitative model to represent those processes. The resulting process model coupled fine particle retention within the sediment bed by filtration and sedimentation with the release of accumulated fine particles in response to flood events. Model parameters, such as the critical flow rate required for initiating sediment bed fluidization, the maximum fine particle storage capacity within the sediment bed, and background particle concentration for the watershed, were estimated from the monitoring data. Model calibration optimized the filtration and the sediment bed fluidization parameters over two or three years of data. Overall, the difference between modeled and observed fine particle mass released from the sediment bed was within 20% of the measured mass.

A modification of the Regional Nutrient Management model (ReNuMa) to identify long-term changes in riverine nitrogen sources

Source apportionment is critical for guiding development of efficient watershed nitrogen (N) pollution control measures. The ReNuMa (Regional Nutrient Management) model, a semi-empirical, semi-process-oriented model with modest data requirements, has been widely used for riverine N source apportionment. However, the ReNuMa model contains limitations for addressing long-term N dynamics by ignoring temporal changes in atmospheric N deposition rates and N-leaching lag effects. This work modified the ReNuMa model by revising the source code to allow yearly changes in atmospheric N deposition and incorporation of N-leaching lag effects into N transport processes. The appropriate N-leaching lag time was determined from cross-correlation analysis between annual watershed individual N source inputs and riverine N export. Accuracy of the modified ReNuMa model was demonstrated through analysis of a 31-year water quality record (1980–2010) from the Yongan watershed in eastern China. The revisions considerably improved the accuracy (Nash-Sutcliff coefficient increased by ∼0.2) of the modified ReNuMa model for predicting riverine N loads. The modified model explicitly identified annual and seasonal changes in contributions of various N sources (i.e., point vs. nonpoint source, surface runoff vs. groundwater) to riverine N loads as well as the fate of watershed anthropogenic N inputs. Model results were consistent with previously modeled or observed lag time length as well as changes in riverine chloride and nitrate concentrations during the low-flow regime and available N levels in agricultural soils of this watershed. The modified ReNuMa model is applicable for addressing long-term changes in riverine N sources, providing decision-makers with critical information for guiding watershed N pollution control strategies.

Investigation on different discrete velocity quadrature rules in gas-kinetic unified algorithm solving Boltzmann model equation

Different discrete velocity quadrature rules are analyzed and applied in gas-kinetic unified algorithm (GKUA) for rarefied free-molecule transition to continuum flows, including the original and modified Gauss–Hermite quadrature rules, the composite Newton–Cotes integration methods, the multi-subinterval Gauss–Legendre numerical quadrature rule and the Gauss–Chebyshev integral rule. Mathematical description and basic procedures of GKUA are presented briefly in solving the gas flow problems covering various flow regimes on the basis of the direction solution to the unified kinetic model of the Boltzmann equation. The numerical analyses and the application conditions of these quadrature rules are given in detail, as well as the evaluating method for the discretized velocity ordinate (DVO) points and their corresponding weights of each rule. According to the comparisons for some Gauss-type function integrations, the original and modified Gauss–Hermite quadrature rules can obtain the integration results with enough accuracy by using least DVO points among these rules, while the impossibility of more nodes limits the application scope of these two quadrature rules. Other four rules can conduct the problems with a needful wide integral interval, even if they use more DVO points than the Gauss–Hermite rules. Besides, the multi-subinterval Gauss–Legendre and the Gauss–Chebyshev rules can use less DVO points to obtain accurate integration results than the other two rules, which demonstrate their advantage and are recommended to be applied in GKUA to solve the Boltzmann model equation efficiently.Numerical simulations for the Sod and Lax shock-tube problems and the shock-density wave disturbing interaction problems are conducted by using GKUA with the above quadrature rules to make comparison. All quadrature rules can obtain nice accurate results with different number of the DVO points. The original and modified Gauss–Hermite quadrature rules, using the least DVO nodes to obtain results with enough computed precision, are the best options for GKUA to simulate low mach number flow regimes, while the Gauss–Chebyshev quadrature rule, which can obtain results with adequate and controllable precision for a wide integral interval using little DVO nodes, is the most appropriate quadrature rule for GKUA solving some complex and high mach number flows covering various flow regimes.

Ecohydrological effects of water reservoirs with consideration of asynchronous and synchronous concurrences of high- and low-flow regimes

ABSTRACTInflow of nine reservoirs in the Liao River basin, China, is used to analyse the concurrence of high/low flows, and also the ecological instream flow. The results indicate that the general extreme value distribution model performs well in describing the probabilistic behaviour of high/low flows in the basin. Specifically, the Gumbel and Frank copula functions perform better than other functions. Reservoir inflow encounter series are subject to high synchronous concurrence, at greater than 27% for low flow vs low flow. Thus, the water supply system of the basin is not steady. The ecological instream flow can be analysed by a monthly frequency computation method, with 90% guarantee rate. The low-flow periods are January, February and May, and water transfers are not feasible in these periods. Thus, external sources of water are urgently needed to guarantee sufficient water supply to provide critical water resources and to protect important aquatic environments.

TRACE METALS IN WATER AND SEDIMENTS OF THE PRUT RIVER, ROMANIA

A 120 kilometers reach of the Prut River, Romania was surveyed and the concentrations of four trace metals (copper, cadmium, lead and zinc) were determined in water and sediments. These elements are the main pollutants expected in the region, as a steel-producing factory in Romania is located in the close neighborhood of an area under protection, the Lower Prut Floodplain Natural Park. Samples were collected in 2010 and 2011 from the water-sediment interface at six locations along the lower sector of the Prut River. Sediments were sampled only once whereas water samples were collected during four campaigns organized at the end of the summer and beginning of the autumn in order to include both high and low flow regimes of the river. Toxic metals (Pb and Cd) were not found to reach notable levels. The resulted concentrations for all trace metals were lower than the values determined in other Romanian rivers (e.g. Danube) and within the values range imposed by the Romanian regulations for water and sediments quality.

Low Flow Trends and Frequency Analysis in the Blue Nile Basin, Ethiopia

Low flow analysis provides crucial information for the planning and design water resource development, risk assessment and environmental flow management. Understanding the low flow regimes and evaluating the magnitudes for incorporating in water resources management is vital for the countries like Ethiopia where demand for water is increasing. However, there were hardly enough studies in understanding the trends of low flow and frequency analysis. Therefore, this study focuses on evaluation of the trends in low flows and regional low flow analysis in the Blue Nile Basin, Ethiopia. In order to carry out the study, 15 river sub-basins in the Blue Nile Basin were selected based on the long term data availability and presence of quality of data. The 3-day sustained low flow (3d-slf), the 7-day sustained low flow (7d-slf) and the 14-day sustained low flow (14d-slf) models were used to extract the data from the daily time series stream data obtained from MoWIE. Trends in low flow were analyzed separately by using Mann-Kendall (MK) trend test. Low flow frequency analysis was used to estimate the long term low flow quantiles. In addition, regional analysis for estimating the quantiles for ungaged catchments was also developed based on the regional growth curve and catchment characteristic of drainage basins. The results indicated that 3d-slf, 7d-slf and 14d-slf models of low flow series indicated no significant difference for each station at 95% CI. Out of the 15 selected stations, 12 of stations have indicated decreasing; two stations indicated increasing and remaining one station with no trend. Mainly decreasing trend was associated with the land cover and climate change which results in increasing runoff and evapotranspiration respectively. Weibull distribution—GEV and LGN was found best fit based on the L-Moment Ratio Diagram (L-MRD). Hence quantile estimations have indicated diminishing magnitudes of low flow quintiles for 2 - 500 years return periods. Regional low frequency analysis has provided a very good relationship between discharge and catchment characteristics with an R2 of 0.72. Where area (A) and rainfall (R) followed by slope were found sensitive to compute in developing the regional region equations between mean low flows and the physiographic data. This study indicated that there needs to be a new water management scenario and adaptation mechanism of climate change and land use land cover dynamics for utilizing water resource in the Blue Nile Basin.

Evolução da contribuição do Sistema Aquífero Urucuia para o Rio São Francisco, Brasil

O Sistema Aquífero Urucuia (SAU) é o mais importante da bacia hidrográfica do Rio São Francisco; possui produtividade elevada, mantém uma vasta área de irrigação e representa aproximadamente 41% da disponibilidade hídrica subterrânea de toda a bacia. Seu escoamento de base é o principal responsável por manter as vazões do Rio São Francisco nas estações secas, de maneira que o conhecimento da variação dessa contribuição ao longo do tempo é de suma importância. O objetivo deste trabalho é analisar o comportamento temporal e estimar a contribuição do SAU em todas as sub-bacias tributárias do Rio São Francisco. Foram utilizadas informações de 45 estações fluviométricas distribuídas em todo o SAU, analisadas pelo método de mínimos locais para separação de escoamentos superficial e subterrâneo em hidrogramas. A média do fluxo de base é de aproximadamente 200 mm/ano (570 m³/s). Dentre os ciclos presentes no último século, o mais marcante e presente em toda a extensão do aquífero teve seu pico em 1980, com 280 mm/ano (792 m³/s) de contribuição para o Rio São Francisco; desde então apresenta padrão de queda contínua, totalizando uma diminuição de 49% (390 m³/s). Independente dos efeitos causadores desta queda, naturais e/ou antrópicos, é preponderante a tomada de medidas para garantir a sustentabilidade destes recursos, visto que a diminuição sistemática de água potável acarreta em grandes estresses socioeconômicos.

Effects of deposition temperature and ammonia flow on metal-organic chemical vapor deposition of hexagonal boron nitride

The use of metal-organic chemical vapor deposition at high temperature is investigated as a means to produce epitaxial hexagonal boron nitride (hBN) at the wafer scale. Several categories of hBN films were found to exist based upon precursor flows and deposition temperature. Low, intermediate, and high NH3 flow regimes were found to lead to fundamentally different deposition behaviors. The low NH3 flow regimes yielded discolored films of boron sub-nitride. The intermediate NH3 flow regime yielded stoichiometric films that could be deposited as thick films. The high NH3 flow regime yielded self-limited deposition with thicknesses limited to a few mono-layers. A Langmuir-Hinshelwood mechanism is proposed to explain the onset of self-limited behavior for the high NH3 flow regime. Photoluminescence characterization determined that the intermediate and high NH3 flow regimes could be further divided into low and high temperature behaviors with a boundary at 1500 °C. Films deposited with both high NH3 flow and high temperature exhibited room temperature free exciton emission at 210 nm and 215.9 nm.

Spatial and seasonal variations of surface and groundwater quality in a fast-growing city: Lubango, Angola

Lubango is a fast-growing city of Angola, with a very deficient water distribution public system. The majority of the population uses groundwater from shallow, rudimentary dug wells and also surface water from the Mapunda River, which crosses the city. The city has very poor systems for collecting domestic sewage and household wastes. The majority of domestic sewage is dumped directly into the Mapunda River or in pit latrines. In this study, the surface water quality and groundwater quality were assessed. In surface water, the low oxygen contents are related to the high temperature (T) in the warm rainy season and with high contents of oxygen-consuming organic pollution and nutrients, as shown by PCA, in both seasons. Anoxic conditions, with negative ORP values (− 55.7 mV), are caused by oxygen-consuming organic pollution, added with low flow regime during the dry, cold season. The very low ecological quality of the surface water is also indicated by the high contents of PO4 and Clt (up to 2.00 and 0.44 mg L−1, respectively). The phosphate contamination is higher in the warm rainy season, due to higher run-off and higher T, as expressed by PCA, both in river water and groundwater. Most groundwater sampling points are contaminated with nitrate (contents up to 132 mg L−1). The pH, total dissolved solids (TDS), alkalinity, Clt and K, determined in the surface water reflect the anthropic contribution to the river water. The variations in water bulk parameters (T, TDS, alkalinity, ORP, DO) and chemical species are indicative of pollution by diffuse sources (N-species, phosphates). The PCA shows that non-point sources such as the free discharge of household wastewater, intense laundering in the river, agriculture and animal grazing are the main contributors to low water quality, associated with seasonality and low contents of dissolved oxygen due to its consumption by organic matter. The multivariate analysis allows the evaluation of the changes in water quality, in fast-growing cities where the climate has a clear seasonality.

Early Triassic environmental dynamics and microbial development during the Smithian–Spathian transition (Lower Weber Canyon, Utah, USA)

The Early Triassic biotic recovery following the end-Permian mass extinction is well documented in the Smithian–Spathian Thaynes Group of the western USA basin. This sedimentary succession is commonly interpreted as recording harsh conditions of various shallow marine environments where microbial structures flourished. However, recent studies questioned the relevance of the classical view of long-lasting deleterious post-crisis conditions and suggested a rapid diversification of some marine ecosystems during the Early Triassic. Using field and microfacies analyses, we investigate a well-preserved Early Triassic marine sedimentary succession in Lower Weber Canyon (Utah, USA). The identification of microbial structures and their depositional settings provide insights on factors controlling their morphologies and distribution. The Lower Weber Canyon sediments record the vertical evolution of depositional environments from a middle Smithian microbial and dolosiliciclastic peritidal system to a late Smithian-early Spathian bioclastic, muddy mid ramp. The microbial deposits are interpreted as Microbially Induced Sedimentary Structures (MISS) that developed either (1) in a subtidal mid ramp where microbial wrinkles and chips are associated with megaripples characterizing hydrodynamic conditions of lower flow regime, or (2) in protected areas of inter- to subtidal inner ramp where they formed laminae and domal structures. Integrated with other published data, our investigations highlight that the distribution of these microbial structures was influenced by the combined effects of bathymetry, hydrodynamic conditions, lithology of the substrat physico-chemical characteristics of the depositional environment and by the regional relative sea-level fluctuations. Thus, we suggest that local environmental factors and basin dynamics primarily controlled the modalities of microbial development and preservation during the Early Triassic in the western USA basin.

Interpretation of massive sandstones in ephemeral fluvial settings: A case study from the Upper Candelária Sequence (Upper Triassic, Paraná Basin, Brazil)

Ephemeral rivers display a wide range of upper- and lower-flow regime structures due to great flow-velocity changes during the floods. The development of flow structures in these setting is yet to be understood, especially in the formation of thick, massive sandstones. The Upper Triassic of Southern Gondwana was marked by a climate with great seasonal changes, yet there is no description of river systems with seasonal characteristics in Southern Gondwana. This work aims to characterize a ephemeral alluvial system of the Upper Triassic of the Paraná Basin. The characteristics of the deposits are discussed in terms of depositional processes through comparison with similar deposits from literature, flow characteristics and depositional signatures compared to flume experiments. The alluvial system is divided in four facies associations: (1) channels with wanning fill, characterized by low width/thickness ratio, tabular bodies, scour-and-fill structures with upper- and lower-flow regime bedforms; (2) channels with massive fill, characterized by low w/t ratio, sheet-like bodies, scour-and-fill structures with massive sandstones; (3) proximal sheetfloods, characterized by moderate w/t ratio, sheet-like bodies with upper- and lower-flow regime bedforms and (4) distal sheetfloods, characterized by high w/t ratio, sheet-like bodies with lower-flow regime bedforms. Evidence for the seasonal reactivation of the riverine system includes the scarcity of well-developed macroforms and presence of in-channel mudstones, thick intraformational conglomerates, and the occurrence of well- and poorly-preserved vertebrate bones in the same beds. The predominantly massive sandstones indicate deposition from a hyperconcentrated flow during abrupt changes in flow speed, caused by de-confinement or channel avulsion, whereas turbulent portions of the flow formed the upper- and lower-flow regime bedforms after the deposition of the massive layers. The upper portion of the Candelária Sequence records a good example of strongly ephemeral alluvial systems, where the predominance of massive sandstones is a particular characteristic.

Aromatic interactions in aryl-capped polylactides: A thermorheological investigation

A series of aryl-capped poly(lactide)s (PLAs) were synthesized by living ring-opening polymerization with a chain transfer agent (also referred to as immortal polymerization, iROP) using a previously reported dinuclear indium catalyst, [(NNO)InCl]2(μ-Cl)(μ-OEt) (A). For understanding the extent and strength of association caused by the arylated chain ends, end-functionalized PLAs were analysed using thermal, rheological, and mechanical techniques. We show that the end-group has a greater effect on the properties of low molecular weight PLAs due to the larger number density of the aryl end groups; significant interactions can be induced under oscillatory shear conditions in the low frequency flow regime (terminal zone). The effects of associations on the extensional properties are also discussed.

Experimental correlations on critical Reynolds numbers and friction factor in tubes with wire-coil inserts in laminar, transitional and low turbulent flow regimes

This paper analyses 23 circular helicoidal wire-coils with different geometric characteristics ranging from: dimensionless pitch p/d=[0.25–3.37], dimensionless thickness e/d=[0.071–0.286] and a Reynolds number interval from 50 to 8000. This interval widely includes the Reynolds number range in which rigid wire-coil inserts present better performance as passive enhancement technique for tubular heat exchanger applications Re=[200–2000]. Based on their hydraulic performance, the wire-coil inserts are categorized according to a new dimensionless parameter: the Transition Shape Parameter (TSP). A new set of correlations are obtained to predict the Fanning friction factor coefficient as a function of Reynolds number and geometrical characteristics of the insert within the three flow regimes: laminar, transitional and low turbulent. Additional correlations are proposed to estimate the critical Reynolds number at the beginning and ending of the transition region, which allows to select the most adequate friction factor correlation as a function of the operational Reynolds number for a heat exchanger design application. Finally, a comparative between the proposed and the published correlations in the open literature for laminar and turbulent regimes is presented. This brings to light the need and interest of having the suitable and reliable set of correlations presented in this paper to compute the friction coefficient covering all the wire-coil applicability range as an enhancement technique.

Finding land cover change impacts on low flow regimes

Abstract Climate changes, as well as land cover changes, affect the flow regimes in streams. Understanding the contributions of climate variables and land cover changes on low flows will help planners and decision makers to improve water resources management. An approach which uses data driven artificial neural networks (ANNs) is proposed in this study. Land cover, rainfall, snow and temperature were used as inputs to the ANN model. In this approach, an index called relative strength effect was used to assess the contribution of each input used in ANN. The proposed approach was experimented in three contrasting watersheds in northwest Indiana, USA. The study indicates that the changes in low flow regime for a less urbanized watershed were explained by land cover changes up to 30% while the remaining 70% variations were explained by meteorological inputs. In the watershed with a more developed area, the low flow variations were influenced up to 80% by meteorological inputs.

Use of stable isotopes to understand run‐off generation processes in theRedRiverDelta

AbstractThis paper presents the use of stable isotopes of water for hydrological characterization and flow component partitioning in the Red River Delta (RRD), the downstream section of the Red River. Water samples were collected monthly during 2015 from the mainstream section of the river and its right bank tributaries flowing through the RRD. In general, δ18O and δ2H river signatures were depleted in summer–autumn (May–October) and elevated in winter–spring (November–April), displaying seasonal variation in response to regional monsoon air mass contest. The Pacific equatorial–maritime air mass dominates in summer and the northern Asia continental air mass controls in winter. Results show that water of the RRD tributaries stems solely from local sources and is completely separated from water arriving from upstream subbasins. This separation is due to the extensive management of the RRD (e.g., dykes and dams) for the purposes of irrigation and inundation prevention. Mainstream river section δ18O and δ2H compositions range from −10.58 and −73.74‰ to −6.80 and −43.40‰, respectively, and the corresponding ranges inside the RRD were from −9.35 and −64.27‰ to −2.09 and −15.80‰. A combination of data analysis and hydrological simulation confirms the role of upstream hydropower reservoirs in retaining and mixing upstream water. River water inside the RRD experienced strong evaporation characterized by depleted d‐excess values, becoming negative in summer. On the other hand, the main stream of the Red River has d‐excess values around 10‰, indicating moderate evaporation. Hydrograph separation shows that in upstream subbasins, the groundwater fraction dominates the river flow composition, especially during low flow regimes. Inside the RRD, the river receives groundwater during the dry season, whereas groundwater replenishment occurs in the rainy season. Annual evaporation obtained from this hydrograph separation computation was about 6.3% of catchment discharge, the same order as deduced from the difference between subbasin precipitation and discharge values. This study shows the necessity to re‐evaluate empirical approaches in large river hydrology assessment schemes, especially in the context of climate change.

High-energy flood events recorded in the Mesoproterozoic Meall Dearg Formation, NW Scotland; their recognition and implications for the study of pre-vegetation alluvium

The Mesoproterozoic–Neoproterozoic Torridonian Sandstone of NW Scotland has renewed sedimentological significance following recent advances in the understanding of pre-vegetation alluvium, as it is one of the most extensive and easily accessible successions of such strata worldwide. This paper presents the first modern sedimentological analysis of the unit's constituent Meall Dearg Formation (late Mesoproterozoic), recognizing a dominance of alluvial facies, with subordinate aeolian facies. Alluvial strata within the Meall Dearg Formation contain direct evidence for event deposition by high-energy floods, including the following: (1) widespread upper and transitional upper flow regime elements; (2) frequent stacking of successively lower flow regime elements; (3) common subcritical subaqueous dune fields with superimposed ripple marks; (4) occasional thin, desiccated mudstones; (5) evidence that microbial mats colonized substrates during intervals of sedimentary stasis. Together these strands of primary sedimentary geological evidence indicate that the alluvial deposition of the Meall Dearg Formation was typified by supercritical flows during high-energy floods, punctuated by prolonged intervals of sedimentary stasis. The preservation potential of all of the features was boosted by highly aggradational sedimentary conditions. These primary observations have implications for the ‘norm’ in pre-vegetation alluvium and confirm that, despite increasing recognition of diversity within Precambrian fluvial systems, classical pre-vegetation motifs of high-energy alluvial flood deposits preserved as ‘sheet-braided’ alluvium are still an archetypal sedimentary signature in some instances. Using supportive evidence from the Meall Dearg Formation, we recommend that the term ‘sheet-braided’ be used in inverted commas in future studies; this emphasizes the polygenetic depositional nature of the 20:1 width:thickness fluvial style, while maintaining the value of the term in the isolation of a key characteristic of pre-vegetation sedimentary architecture.

Changes in High- and Low-Flow Regimes: a Diagnostic Analysis of Tropical Cyclones in the Western North Pacific

This study aims to determine the characteristics of hydrological behaviors in the basins of the representative multipurpose dams in the Korean Peninsula that depend on typhoon conditions for sustainable water management and restoration of the water ecosystem. Based on the annual maximum flow and seven-day low-flow results, trend analyses were conducted on hydrological changes, such as magnitude, timing, duration, and frequency of the extreme flows. Among the eight selected multipurpose dams in South Korea, the Chungju and Soyang dams have been subject to dramatic reduction of inflow during the spring and early summer. The Sumjin Dam was indicated the most sensitive to the severity and magnitude of typhoons and it showed a statistically significant increase in the frequency and duration of peak inflows resulting from such typhoons. As regards low flow, the Chungju and Andong dams showed a distinct reduction in this flow in the winter, but the changes resulting from typhoons were relatively subtle. This diagnostic study is expected to provide foundational data to examine the causalities related to the streamflow patterns of Korean basins. In addition, the study could aid in establishing basin-customized mid- and long-term measures for supplying of water resources in the environmental system and for managing the effects of natural disasters by analyzing various hydrological changes related to extreme events.