A systematic approach to the input determination for neural network rainfall–runoff models

Input determination has a great influence on the performance of artificial neural network (ANN) rainfall–runoff models. To improve the performance of ANN models, a systematic approach to the input determination for ANN models is proposed. In the proposed approach, the irrelevant inputs are removed. Then an adequate ANN model, which only includes highly relevant inputs, is constructed. Unlike the trial‐and‐error procedure, the proposed approach is more systematic and avoids unnecessary trials. To demonstrate the effectiveness of the proposed approach, an application to actual typhoon events is presented. The results show that the proposed ANN model, which is constructed by the proposed approach, has advantages over those obtained by the trial‐and‐error procedure. The proposed ANN model has a simpler architecture, needs less training time, and performs better. The proposed ANN model is recommended as an alternative to existing rainfall–runoff ANN models. Copyright © 2007 John Wiley & Sons, Ltd.     

Population structure of antarctic krill (Euphausia superba Dana) in the waters north and west of Antarctic Peninsula

Antarctic krill (Euphasia superba Dana) is a key organism of the Antarctic marine ecosystem and a potential fishery resoure. Its ecology was the major biological project in the First Chinese Antarctic Expedition (1985). Acoustic observations and IKMT tows were madecin waters north and west of Antarctic Peninsula. Environmental factors were also observed. Analyses of the population structure, i.e. the sex percentage distribution and other data obtained show that among the 3,640 individuals of determinable sex, only 38.1% were males and that the larger the body length the smaller the percentage of males, for example, male percentage dropped to 8.3% for size group >55 mm. The population's relations to environmental factors are also discussed. Contribution No. 1711 from the Institute of Oceanology, Academia Sinica.     

Application of integrated back‐propagation network and self organizing map for flood forecasting

Much of the nonlinearity and uncertainty regarding the flood process is because hydrologic data required for estimation are often tremendously difficult to obtain. This study employed a back‐propagation network (BPN) as the main structure in flood forecasting to learn and to demonstrate the sophisticated nonlinear mapping relationship. However, a deterministic BPN model implies high uncertainty and poor consistency for verification work even when the learning performance is satisfactory for flood forecasting. Therefore, a novel procedure was proposed in this investigation which integrates linear transfer function (LTF) and self‐organizing map (SOM) to efficiently determine the intervals of weights and biases of a flood forecasting neural network to avoid the above problems. A SOM network with classification ability was applied to the solutions and parameters of the BPN model in the learning stage, to classify the network parameter rules and to obtain the winning parameters. The outcomes from the previous stage were then used as the ranges of the parameters in the recall stage. Finally, a case study was carried out in Wu‐Shi basin to demonstrate the effectiveness of the proposal. Copyright © 2009 John Wiley & Sons, Ltd.     

Effects of land‐use changes on hydrological processes in the middle basin of the Heihe River,northwest China

The effects of land‐use changes on the runoff process in the midstream plain of this arid inland river basin are a key factor in the rational allocation of water resources to the middle and lower reaches. The question is whether and by how much increasingly heavy land use impacts the hydrological processes in such an arid inland river basin. The catchment of the Heihe River, one of the largest inland rivers in the arid region of northwest China, was chosen to investigate the hydrological responses to land‐use change. Flow duration curves were used to detect trends and variations in runoff between the upper and lower reaches. Relationships among precipitation, upstream runoff, and hydrological variables were identified to distinguish the effects of climatic changes and upstream runoff changes on middle and downstream runoff processes. The quantitative relation between midstream cultivated land use and various parameters of downstream runoff processes were analysed using the four periods of land‐use data since 1956. The Volterra numerical function relation of the hydrological non‐linear system response was utilized to develop a multifactor hydrological response simulation model based on the three factors of precipitation, upstream runoff, and cultivated land area. The results showed that, since 1967, the medium‐ and high‐coverage natural grassland area in the midstream region has decreased by 80·1%, and the downstream runoff has declined by 27·32% due to the continuous expansion of the cultivated land area. The contribution of cultivated land expansion to the impact on the annual total runoff is 14–31%, on the annual, spring and winter base flow it is 44–75%, and on spring and winter discharge it is 23–64%. Once the water conservation plan dominated by land‐use structural adjustments is implemented over the next 5 years, the mean annual discharge in the lower reach could increase by 8·98% and the spring discharge by 26·28%. This will significantly alleviate the imbalance between water supply and demand in both its quantity and temporal distribution in the middle and lower reaches. Copyright © 2006 John Wiley & Sons, Ltd.     

Composite analytical solutions for a soil vapour extraction system

Soil vapour extraction (SVE) is a common remediation technique for cleaning up unsaturated soils contaminated by volatile organic compounds (VOCs). Analytical solutions, which result from simple mathematical models, can allow the fast approximation of the time‐dependent effluent concentration and the gaining of insight into the processes that take place during soil remediation. Deriving the analytical solutions to advection–dispersion equations that simultaneously take into account the mechanical dispersion and molecular diffusion is very difficult because of the variable dependence of governing equations' coefficients. In this study, we first present two simplified analytical solutions that only consider mechanical dispersion or molecular diffusion. The two developed analytical solutions are compared with the numerical solution that simultaneously considers both mechanical dispersion and molecular diffusion to examine the applicability of the two simplified analytical solutions and distinguishes the individual contribution of the mechanical dispersion and molecular diffusion to total VOCs transport in an SVE system. Results show that dispersion plays an important role during SVE decontamination and neither the diffusion‐dominated solution nor the dispersion‐dominated solution can agree well with the numerical solution when both mechanical dispersion and molecular diffusion have significant contributions to the total VOCs transport flux. A composite analytical solution that linearly couples the diffusion‐ and dispersion‐dominated analytical solutions, which is proposed herein to eliminate the discrepancy between the analytical solutions and the numerical solution. Results indicate that the proposed composite analytical solution agrees well with the numerical solution and is an effective tool for quickly and accurately evaluating the time‐dependent effluent concentration for parameters of the different ranges of interest in an SVE remedial system. Copyright © 2006 John Wiley & Sons, Ltd.     

Evaluating the stress intensity factors of anisotropic bimaterials using boundary element method

This paper presents a boundary element method (BEM) procedure for a linear elastic fracture mechanics analysis in two‐dimensional anisotropic bimaterials. In this formulation, a displacement integral equation is only collocated on the uncracked boundary, and a traction integral equation is only collocated on one side of the crack surface. A fundamental solution (Green's function) for anisotropic bimaterials is also derived and implemented into the boundary integral formulation so that except for the interfacial crack part, the discretization along the interface can be avoided. A special crack‐tip element is introduced to capture the exact crack‐tip behavior. A computer program using FORTRAN has been developed to effectively calculate the stress intensity factors of an anisotropic bimaterial. This BEM program has been verified to have a good accuracy with previous studies. In addition, a central cracked bimaterial Brazilian specimen constituting cement and gypsum is prepared to conduct the Brazilian test under diametral loading. The result shows that the numerical analysis can predict relatively well the direction of crack initiation and the path of crack propagation. Copyright © 2007 John Wiley & Sons, Ltd.     

Storm‐event rainfall–runoff modelling approach for ungauged sites in Taiwan

This work develops a top‐down modelling approach for storm‐event rainfall–runoff model calibration at unmeasured sites in Taiwan. Twenty‐six storm events occurring in seven sub‐catchments in the Kao‐Ping River provided the analytical data set. Regional formulas for three important features of a streamflow hydrograph, i.e. time to peak, peak flow, and total runoff volume, were developed via the characteristics of storm event and catchment using multivariate regression analysis. Validation of the regional formulas demonstrates that they reasonably predict the three features of a streamflow hydrograph at ungauged sites. All of the sub‐catchments in the study area were then adopted as ungauged areas, and the three streamflow hydrograph features were calculated by the regional formulas and substituted into the fuzzy multi‐objective function for rainfall–runoff model calibration. Calibration results show that the proposed approach can effectively simulate the streamflow hydrographs at the ungauged sites. The simulated hydrographs more closely resemble observed hydrographs than hydrographs synthesized using the Soil Conservation Service (SCS) dimensionless unit hydrograph method, a conventional method for hydrograph estimation at ungauged sites in Taiwan. Copyright © 2008 John Wiley & Sons, Ltd.     

Potential impacts of invasive Spartina alterniflora on spring bird communities at Chongming Dongtan,a Chinese wetland of international importance

Invasive smooth cordgrass (Spartina alterniflora, hereafter Spartina) has been expanding rapidly in the estuarine wetlands at Chongming Dongtan (East China) at the expense of native sea-bulrush (Scirpus mariqueter, hereafter Scirpus) and common reed (Phragmites australis, hereafter Phragmites). To examine the potential impacts of the Spartina invasion on bird diversity, we compared the abundance and species richness of birds in habitats created by Spartina, Phragmites, Spartina mixed with Phragmites, Scirpus, and the bare intertidal zone at Chongming Dongtan in spring 2008. Most birds were recorded in the native habitats, with songbirds and breeding birds being most abundant in the Phragmites habitats, and waterbirds and migrants being most abundant in the Scirpus habitats and bare intertidal zone. Both species number and population densities of birds were lower in the exotic Spartina habitats than in the other four habitats. Although some songbirds and breeding birds used the Spartina-invaded habitats, and even preferred Spartina-invaded habitats to Scirpus habitats and bare intertidal zone, their densities were lower in the Spartina-invaded habitats than in the native Phragmites habitats. This might have resulted from the dense Spartina stands restricting bird movement and providing insufficient useable food for most birds. We conclude that the spread of exotic Spartina has negative impacts on local bird communities. Because Chongming Dongtan is an important stopover site for energy replenishment of shorebirds in the East Asian–Australasian Flyway, urgent measures are needed to control further spread of Spartina and to restore the native habitats for birds.     

DSQ型水管倾斜仪安装中的一些技术问题

讨论了DSQ型水管倾斜仪安装中洞体安装条件、密封保温设施、水管气泡排除、IP标定等应注意的一些技术问题.