Scaling property of regional floods in New South Wales Australia

Regional flood frequency analysis (RFFA) is often used in hydrology to estimate flood quantiles when there is a limitation of at-site recorded flood data. One of the commonly used RFFA methods is the index flood method, which is based on the assumptions that a region satisfies criterion of simple scaling and it can be treated homogeneous. Another RFFA method is quantile regression technique where prediction equations are developed for flood quantiles of interest as function of catchment characteristics. In this paper, the scaling property of regional floods in New South Wales (NSW) State in Australia is investigated. The results indicate that the annual maximum floods in NSW satisfy a simple scaling assumption. The application of a heterogeneity test, however, reveals that NSW flood data set does not satisfy the criteria for a homogeneous region. Finally, a set of prediction equations are developed for NSW using quantile regression technique; an independent test shows that these equations can provide reasonably accurate design flood estimates with a median relative error of about 27%.     

水库调洪演算的随机数学模型

以介于微分方程和概率论之间的边缘数学分支随机微分方程的数学模型,对水库调洪过程中的随机现象和规律进行数学描述和分析,试图全面正确地综合各种不确定性因素对库水位随机过程的影响.根据水库蓄洪量具有Wiener过程特性的分析,推导了带有随机输入项和随机初始条件的调洪演算Ito方程.在此基础上,运用Fokker-Planck向前方程,求介了调洪过程库水位的概率密度分布.计算成果表明,运用随机微分方程进行水库的调洪演算,有利于正确分析水库调洪的随机过程和进一步开展水库泄洪风险分析.     

特小流域洪水计算概论

根据特小流域的雨洪特性，分别概论了特小流域设计洪峰流量计算、设计洪水过程线确定、方法（公式）选用与成果合理性分析等。特别提出了不管采用哪种方法（公式）计算设计洪峰流量，均需对特小流域进行水文查勘，并尽量利用实测资料，对各项参数进行分析和检验，使计算成果更符合实际情况。     

Effects of spatial data resolution on runoff predictions by the BASINS model

The BASINS model, developed by the United States EPA, is a popular simulation tool for predicting watershed responses, such as runoff, pollution exports, and water quality. It requires large amounts of data to set parameters. Many studies state that model input is a major source of model uncertainty. Thus, improvements to the quality and completeness of the data will improve the certainty of the model. The objective of this study is to discuss the effects of spatial data, including digital elevation models (DEMs) and spatial rainfall records, on predictions of runoff from the BASINS model. The result shows that both DEMs and rainfall data can significantly influence peak flow and runoff volume. Rainfall input has more influence on the curve shape of hydrograph than DEM resolution. DEM resolution can have more impact on peak flow predictions than rainfall input. Because the model uncertainties from DEMs and rainfall records influence each other, the prediction error does not always decrease when DEM resolution increases. The present results show that the BASINS model produces reliable answers in the case area when the grid size is less than 100 m × 100 m and the precipitation records from the Bihu Rainfall Station are correct and complete.     

Image acquisition for detection of vegetation change based on long-term rainfall in an arid rangeland in Western NSW, Australia

Research on vegetation change, rangeland assessment or desertification modelling in drylands using remotely sensed image acquisition normally ignores long-term rainfall as a key criterion in image acquisition. This article will present a novel procedure for image acquisition to investigate vegetation change in a degraded rangeland located in Western New South Wales (Western NSW) Australia. Western NSW experienced an unusually prolonged period of rainfall deficit during the 2000s compared to the 1970, 1980 and 1990s. For this purpose, vegetation changes were assessed using Landsat images supported by field survey. The long-term rainfall variability (42-year) was regarded as a key element in image acquisition. Within the timeframe of the 2000s, 2 years with 25 % lower than the 42-year mean annual rainfall were selected. These images were then compared to an image captured in a year (1988) with rainfall closer to the 42-year mean annual rainfall. Two change detection techniques were used, namely univariate image differencing and GIS approaches. Classification of the produced images was pursued based on the digital numbers (supervised) of ground-checked points within the reference image whilst considering the histogram (unsupervised) of each digital number of the produced image. This research emphasized rainfall as a key variable in image acquisition for vegetation change analysis in rangelands. Image acquisition based on long-term rainfall data allowed for the assessment of changes in perennial plant cover by eliminating the effects of extreme rainfall variation on annual grass dynamics and removing extreme reflections caused by their temporary high photosynthetic activity.     

Rainfall input of toxaphene to a South Carolina estuary

Toxaphene concentrations in rainfall over a South Carolina salt marsh were monitored from 1976–1978. This insecticide is toxic to some organisms in the low μg/kg range and causes sublethal effects in the very low ng/kg range. Rainfall was sampled by both continuously exposed collectors and by collectors which were exposed only during actual precipitation. Toxaphene concentrations in individual rainstorms showed a high day-to-day variation, and in general were 10–100 times higher than PCB and DDT levels. Washout ratios for toxaphene were higher than those reported for other chlorinated hydrocarbons, but lower than those of trace metals. During and immediately following the summer use season, toxaphene levels in rain exceeded by several times those concentrations reported to produce bone damage to young fish in laboratory experiments. The estimated aerial input of toxaphene to the 26 km² estuary was 1.2 kg over a 4-month period. Most of this input appeared to be due to rainfall rather than dry deposition. *** DIRECT SUPPORT *** A01BY010 00007     

Evaluating factors responsible for contrasting signature of wasteland development in northern and southern Ganga Plains (Bihar State,India) with focus on waterlogging

The present study provides assessment of wasteland development in Bihar State based on satellite data. Wasteland covers 6.90 % (6,501 km²) of the state area and exhibits dominance of waterlogged areas in North Bihar (25.28 %) and scrubland (26.61 %) in South Bihar. The waterlogged areas in the state are dominantly associated with northern Bihar plains (94 %) with minor development (6 %) in southern Bihar plains. Such unequal distribution of waterlogged land areas in northern and southern Bihar plains is largely governed by high cumulative discharge generated in the large catchment area in Himalayan mountain ranges in the upland areas of northern Bihar plains in contrast to low cumulative discharge generated within small catchments in the Chota Nagpur Plateau in the southern Bihar plains. It is evaluated that the relief and groundwater level define the primary controlling factors, whereas rainfall, watershed area, and upland/plain ratio exert secondary control. Lower relief areas with high rainfall exhibit high soil moisture thereby inducing conditions of waterlogging. The study signifies the potential of satellite image-based evaluation of waterlogging through the use of Digital Elevation Model, Tropical Rainfall Measuring Mission-based rainfall measurement, and temporal waterlogging assessment together with other terrain parameters for conceptual understanding of waterlogging in northern Bihar plains.     

Sheet flow in a salt-marsh basin,North Inlet,South Carolina

The magnitude of sheet flow in a small South Carolina salt marsh was evaluated by comparing the storage curve for the basin based on topographic data with that based on current measurements in the main channel. The results indicate that on spring tides more than 50% of the volume of water that enters the basin enters as sheet flow over the grassy flats of the marsh. The current data also suggest that the actual storage curve may be a hysteresis loop with separate flood and ebb segments.     

Rainfall threshold determination for flash flood warning in mountainous catchments with consideration of antecedent soil moisture and rainfall pattern

Flash flood disaster is a prominent issue threatening public safety and social development throughout the world, especially in mountainous regions. Rainfall threshold is a widely accepted alternative to hydrological forecasting for flash flood warning due to the short response time and limited observations of flash flood events. However, determination of rainfall threshold is still very complicated due to multiple impact factors, particular for antecedent soil moisture and rainfall patterns. In this study, hydrological simulation approach (i.e., China Flash Flood-Hydrological Modeling System: CNFF-HMS) was adopted to capture the flash flood processes. Multiple scenarios were further designed with consideration of antecedent soil moisture and rainfall temporal patterns to determine the possible assemble of rainfall thresholds by driving the CNFF-HMS. Moreover, their effects on rainfall thresholds were investigated. Three mountainous catchments (Zhong, Balisi and Yu villages) in southern China were selected for case study. Results showed that the model performance of CNFF-HMS was very satisfactory for flash flood simulations in all these catchments, especially for multimodal flood events. Specifically, the relative errors of runoff and peak flow were within?±?20%, the error of time to peak flow was within?±?2 h and the Nash–Sutcliffe efficiency was greater than 0.90 for over 90% of the flash flood events. The rainfall thresholds varied between 93 and 334 mm at Zhong village, between 77 and 246 mm at Balisi village and between 111 and 420 mm at Yu village. Both antecedent soil moistures and rainfall temporal pattern significantly affected the variations of rainfall threshold. Rainfall threshold decreased by 8–38 and 0–42% as soil saturation increased from 0.20 to 0.50 and from 0.20 to 0.80, respectively. The effect of rainfall threshold was the minimum for the decreasing hyetograph (advanced pattern) and the maximum for the increasing hyetograph (delayed pattern), while it was similar for the design hyetograph and triangular hyetograph (intermediate patterns). Moreover, rainfall thresholds with short time spans were more suitable for early flood warning, especially in small rural catchments with humid climatic characteristics. This study was expected to provide insights into flash flood disaster forecasting and early warning in mountainous regions, and scientific references for the implementation of flash flood disaster prevention in China.     

A cordierite-bearing granite suite from the New England Batholith,N.S.W., Australia

A suite of cordierite-bearing biotite-muscovite intrusive granites in the New England Batholith, New South Wales, outcrops over 3400 sq km and is the largest reported occurrence of granites of this type. Compositionally the granites are close to the low temperature minimum and display only limited chemical variation. The corundum-normative nature of the granites suggests a pelitic sedimentary parentage. Cordierite with an average 100 Mg/ Mg + Fe of 55 occurs as large tabular crystals and is considered to be a refractory phase brought up from the zone of partial melting. The presence of cordierite and the absence of garnet in these granites suggests a partial melting at a pressure maximum of 6 kb, equivalent to 22 km depth.     

Ebb-tidal fronts in Charleston Harbor,South Carolina: Physical and biological characteristics

Surface accumulations of foam and flotsam as well as sharp salinity, density, turbidity gradients and regions of acoustic scatter were characteristic of ebb-tidal fronts in Charleston Harbor, South Carolina. Surface convergence velocities at these fronts averaged 0.06 m s^?1 into the front at an angle of 30° to 60° with respect to the frontal axis, indicating along-front transport during the ebb. These fronts are tidally-induced, forming on the late flood and ebb along the interfaces of water masses. Horizontal and vertical measurements of density revealed that the upper harbor fronts form along the margin of a freshwater lens produced by riverine input. The hypothesis that these frontal zones have higher densities of phytoplankton and zooplankton than adjacent water masses was tested using chlorophylla measurements and net collections. The fronts did not demonstrate any significant accumulations of phytoplankton or zooplankton during the ebb tide. The results of this study suggest that the physical characteristics of ebb-tidal estuarine fronts in Charleston Harbor are periodic in nature and may indirectly affect plankton transport in this coastal plain estuary.     

Assessment of climate change impacts on rainfall using large scale climate variables and downscaling models – A case study

Many of the applied techniques in water resources management can be directly or indirectly influenced by hydro-climatology predictions. In recent decades, utilizing the large scale climate variables as predictors of hydrological phenomena and downscaling numerical weather ensemble forecasts has revolutionized the long-lead predictions. In this study, two types of rainfall prediction models are developed to predict the rainfall of the Zayandehrood dam basin located in the central part of Iran. The first seasonal model is based on large scale climate signals data around the world. In order to determine the inputs of the seasonal rainfall prediction model, the correlation coefficient analysis and the new Gamma Test (GT) method are utilized. Comparison of modelling results shows that the Gamma test method improves the Nash–Sutcliffe efficiency coefficient of modelling performance as 8% and 10% for dry and wet seasons, respectively. In this study, Support Vector Machine (SVM) model for predicting rainfall in the region has been used and its results are compared with the benchmark models such as K-nearest neighbours (KNN) and Artificial Neural Network (ANN). The results show better performance of the SVM model at testing stage. In the second model, statistical downscaling model (SDSM) as a popular downscaling tool has been used. In this model, using the outputs from GCM, the rainfall of Zayandehrood dam is projected under two climate change scenarios. Most effective variables have been identified among 26 predictor variables. Comparison of the results of the two models shows that the developed SVM model has lesser errors in monthly rainfall estimation. The results show that the rainfall in the future wet periods are more than historical values and it is lower than historical values in the dry periods. The highest monthly uncertainty of future rainfall occurs in March and the lowest in July.     

Mapping joint hurricane wind and surge hazards for Charleston,South Carolina

Combined effects of hurricane wind and surge can pose significant threats to coastal cities. Although current design codes consider the joint occurrence of wind and surge, information on site-specific joint distributions of hurricane wind and surge along the US Coast is still sparse and limited. In this study, joint hazard maps for combined hurricane wind and surge for Charleston, South Carolina (SC), were developed. A stochastic Markov chain hurricane simulation program was utilized to generate 50,000 years of full-track hurricane events. The surface wind speeds and surge heights from individual hurricanes were computed using the Georgiou’s wind field model and the Sea, Lake and Overland Surges from Hurricanes (SLOSH) model, respectively. To validate the accuracy of the SLOSH model, the simulated surge levels were compared to the surge levels calculated by another state-of-the-art storm surge model, ADCIRC (Advanced Circulation), and the actual observed water elevations from historical hurricane events. Good agreements were found between the simulated and observed water elevations. The model surface wind speeds were also compared with the design wind speeds in ASCE 7-10 and were found to agree well with the design values. Using the peak wind speeds and maximum surge heights, the joint hazard surfaces and the joint hazard maps for Charleston, SC, were developed. As part of this study, an interactive computer program, which can be used to obtain the joint wind speed and surge height distributions for any location in terms of latitude and longitude in Charleston area, was created. These joint hazard surfaces and hazard maps can be used in a multi-hazard design or risk assessment framework to consider the combined effects of hurricane wind and surge.     

Hydraulic routing of extreme floods in a large ungauged river and the estimation of associated uncertainties: a case study of the Damodar River, India

Many developing countries are very vulnerable to flood risk since they are located in climatic zones characterised by extreme precipitation events, such as cyclones and heavy monsoon rainfall. Adequate flood mitigation requires a routing mechanism that can predict the dynamics of flood waves as they travel from source to flood-prone areas, and thus allow for early warning and adequate flood defences. A number of cutting edge hydrodynamic models have been developed in industrialised countries that can predict the advance of flood waves efficiently. These models are not readily applicable to flood prediction in developing countries in Asia, Africa and Latin America, however, due to lack of data, particularly terrain and hydrological data. This paper explores the adaptations and adjustments that are essential to employ hydrodynamic models like LISFLOOD-FP to route very high-magnitude floods by utilising freely available Shuttle Radar Topographic Mission digital elevation model, available topographical maps and sparse network of river gauging stations. A 110 km reach of the lower Damodar River in eastern India was taken as the study area since it suffers from chronic floods caused by water release from upstream dams during intense monsoon storm events. The uncertainty in model outputs, which is likely to increase with coarse data inputs, was quantified in a generalised likelihood uncertainty estimation framework to demonstrate the level of confidence that one can have on such flood routing approaches. Validation results with an extreme flood event of 2009 reveal an encouraging index of agreement of 0.77 with observed records, while most of the observed time series records of a 2007 major flood were found to be within 95 % upper and lower uncertainty bounds of the modelled outcomes.     

Discharge of weathering products from acid sulfate soils after a rainfall event, Tweed River, eastern Australia

The oxidation of the iron sulfide, pyrite, in acid sulfate soil floodplains generate substantial acidity and this acid has caused further weathering of the soil profile. The movement of groundwater from these soils is an important geochemical control on surface water quality. The flux of acidified and metal-rich water during a wet season rainfall event has been examined at two study catchments on the Tweed River in eastern Australia. At the sites, 81 kg/ha and 60 kg/ha of oxidisable acidity are exported, along with Al, Fe and Zn during the flood event. The main contributors to the acid flux are H⁺, Fe and Al at the first site and whilst Fe and Al are present in the drainage waters at the second site, the main contributor is likely to be H⁺. The different flux characteristics at the sites may be caused by different surface soil hydraulic conductivities and oxidation history.     

Experimental duplication of a high-pressure megacryst/cumulate assemblage in a near-saturated hawaiite

The occurrence of corroded megacrysts and cumulates of olivine, clinopyroxene, orthopyroxene, plagioclase, ilmenite and apatite in near-saturated hawaiites from the mid-north coast of New South Wales point to the derivation of these hawaiites at elevated pressures. In an experimental study on one of these hawaiites under conditions ranging from 5–15 kb and 0–5% H₂O, orthopyroxene was identified in only one run with 2% H₂O at 1040° C and 6.5 kb. In this run it was associated with olivine, clinopyroxene and Fe-Ti oxide. The early appearance of plagioclase in the “dry” experimental runs and amphibole in runs with 5% H₂O, indicates that the water content in the natural hawaiite was intermediate to these values. The near-duplication of the natural megacryst-cumulate assemblage suggests that the hawaiite host precipitated these phases at a depth of approximately 20–24 km, prior to rapid eruption to higher crustal levels.     

Boninite primary magmas: Evidence from the Cape Vogel Peninsula,PNG

Boninites from Cape Vogel, PNG, are dominantly pyroxene-glass rocks, but many contain olivine, sometimes as refractory as Fo₉₄. We derive a parental magma for this suite (in equilibrium with Fo₉₄) which contains 20 wt.% MgO and is quartz-normative. This liquid is hydrous, and from petrographie evidence and whole rock H₂O⁺ values, we estimate it to contain 2–3 wt.% H₂O. These data suggest olivine fractionation and primary magmatic water are important in boninite genesis, but both are often obscured by later alteration. The derived parental magma has probably formed at 1,250–1,300° C and low pressures (< ?10kB) and is similar to those which gave rise to olivine-clinoenstatite phyric boninites from New Caledonia and from Howqua, Australia, and possibly to a proposed parental magma for the Bushveld Complex.     

Constraints on the origin of mafic alkaline volcanics and included xenoliths from Oberon,New South Wales,Australia

Basanites and alkali basalts from Oberon, NSW, Australia contain variable abundances of small Cr-diopside lherzolite xenoliths. Despite a limited range in (metamorphic) textures and modal mineralogy, there is significant variation in mineral chemistry. Mineral thermometric data applied to the geotherm of O'Reilly and Griffin (1985) suggests equilibration over a narrow pressure interval corresponding to depths of 30–45 km. These data show that significant compositional variations exist over a small depth interval in the subcontinental mantle.Basaltic host rocks show near-primary chemical characteristics. Mildly and strongly incompatible element (i.e. D< 1 and D1 respectively) concentrations have been used to constrain the modal amounts of clinopyroxene and garnet in a presumed garnet peridotite mantle source. Estimated proportions of (ol+opx)=73%; cpx=16%; gar= 11% closely resemble source compositions for other basaltic rocks of eastern Australia. Batch partial melting of this source in the range F=9.5–15% applied to the available REE data suggests the source is enriched relative to chondrite 8–10 × La, 2.1–2.4 × Tb and 2.5–3.7 × Yb.     

Sm-Nd,K-Ar and petrologic study of some kimberlites from eastern United States and their implication for mantle evolution

We provide new data on Sm-Nd systematics, K-Ar dating and the major element chemistry of kimberlites from the eastern United States (mostly from central New York State) and their constituent mineral phases of olivine, clinopyroxene, garnet, phlogopite and perovskite. In addition, we report Nd-isotopes in a few kimberlites from South Africa, Lesotho and from the eastern part of China. The major element compositions of the New York dike rocks and of their constituent minerals including a xenolith of eclogite are comparable with those from the Kimberley area in South Africa. The K-Ar age of emplacement of the New York dikes is further established to be 143 Ma.We have analyzed the Nd-isotopic composition of the following kimberlites and related rocks: Nine kimberlite pipes from South Africa and Lesotho, two from southern India; one from the U.S.S.R., fifteen kimberlite pipes and related dike rocks from eastern and central U.S. and two pipes from the Shandong Province of eastern China. The age of emplacement of these kimberlites ranges from 1300 million years to 90 million years. The initial Nd-isotopic compositions of these kimberlitic rocks expressed as _Nd ^I with respect to a chondritic bulk-earth growth-curve show a range between 0 and +4, with the majority of the kimberlites being in the range 0 to +2. This range is not matched by any other suite of mantle-derived igneous rocks. This result strengthens our earlier conclusion that kimberlitic liquids are derived from a relatively primeval and unique mantle reservoir with a nearly chondritic Sm/Nd ratio.     

Limitations of real-time models for forecasting river flooding from monsoon rainfall

Very intense rainfall during the southwest and northeast monsoons causes severe river flooding in India. Some traditional techniques used for real-time forecasting of flooding involve the relationship between effective rainfall and direct surface runoff, which simplifies the complex interactions between rainfall and runoff processes. There are, however, serious problems in deducing these variables in real time, so it is highly desirable to have a real-time flood forecasting model that would directly relate the observed discharge hydrograph to the observed rainfall. The storage routing model described by Baba and Hoshi (1997), Tanaka et al. (1997), and Baba et al. (2000), and a simplified version of this model, have been used to compute observed river discharge directly from observed hourly rainfall. This method has been used to study rainfall–runoff data of the Ajay River Basin in eastern India. Five intense rainfall events of this basin were studied. Our results showed that the Nash–Sutcliffe efficiency of discharge prediction for these five events was 98.6%, 94.3%, 86.9%, 85.6%, and 67%. The hindcast for the first two events is regarded as completely satisfactory whereas for the next two events it is deemed reasonable and for the fifth it is unsatisfactory. It seems the models will yield accurate hindcast if the rainfall is uniform over the drainage basin. When the rainfall is not uniform the performance of the model is unsatisfactory. In future this problem can, in principle, be corrected by using a weighted amount if rainfall is based upon multiple rain-gauge observations over the drainage basin. This would provide some measure of the dispersion in the rainfall. The model also seems unable to simulate flooding events with multiple peaks.