ABRASION OF THE BOTTOM OUTLETS AND ITS REPAIR IN SANMENXIA PROJECT

The Sanmenxia Project completed in 1960 is a multi-purpose hydro project with emphasis on flood control. After the expounding, serious deposition occurs in the upstream part of the reservoir and the Weihe River. The project has to be rebuilt twice in the period from 1964 to 1978. Thus the discharge capacity is greatly enlarged by excavating two side tunnels on the left bank, converting three penstocks into sluice conduits and reopening & bottom outlets formerly used for di- version. By changing the operational mode from storing water year round to stor- ing clear water during the dry season and sluicing sediment during the flood season, the sediment problem of the reservoir is largely solved and multi-purpose benefits of the project are partially retained. But the heavy sediment load still caused serious abrasion on bottom outlets and turbines, particularly on the inlet gate slot, the service gate slot and the floor. Much effort has been made to clarify the mechanism of the damage and to choose abrasion-resistant material for repair. The repair of the bottom outlets has been going on since 1980. This paper describes the abrasion on the bottom outlets in details and the subsequent repair effected.     

MASS MOVEMENTS AND SEDIMENT TRANSPORT AS A NATURAL HAZARD

I.INTRODUCTIONFormillionsofyearswindandwaterhaveshapedtheearth,mountainshavebeenliftedanderodedaway,waterhasevaporatedfromtheoceansandfallenbackonland,rivershaveformedandcarriedwaterandsedanmentfromthemoufltainstotheseas.Someoftherivers--suchastheColoradoRiverintheGrandCanyonregionofNorthAJnerica-foundstablecoursesastheycarvedthemselvesintotheground,others--suchastheYellowhiverinChina-havechangedtheircoursesfrequentlyallthewayintorecenthistory.Itwasonlyafewthousandyearsagothatmanstarte…     

Efficacy of PIT tags and an autonomous antenna system to study the juvenile life stage of an estuarine-dependent fish

Many marine fishes use spatially distinct habitats as juveniles and adults. Determining which juvenile habitats are most important to sustaining adult populations (i.e., which habitats are nurseries) has proven difficult, in part due to challenges in estimating survival of juveniles in putative nursery habitats. Recent technological advances have made largescale tagging efforts a viable approach to estimating survival of juvenile fishes by increasing recapture rates and enabling the use of individual-identification tags. These techniques, using Passive Integrated transponder (PIT) tags and autonomous antenna detection systems (antenna), have been successfully applied in freshwater environments. This paper reports the adaptation of these techniques to estuarine mangrove creeks (salinity: 2–28‰) for research of the juvenile life stage on an estuarine-dependent marine fish,Centropomus undecimalis. Retention rate of PIT tags in juveniles >120 mm standard length was 100%, with no mortality. The antenna detection field covered 48% of the creek water column, and the antenna was experimentally determined to detect approximately 67% of tagged fish that swam through. Overall recapture rate of tagged fish by the antenna was >40%. This recapture rate is higher than the sparse data typical of traditional tag-recapture studies. A time-dependent Jolly-Seber model was fit to the data, providing estimates of capture probability (0.8) and weekly apparent survival (0.41) that will be invaluable in comparing juvenile habitats of different quality (e.g., natural versus anthropogenically degraded). This research demonstrates the viability of this approach to fish research in estuarine habitats.     

The response of the climate system to the indirect effects of anthropogenic sulfate aerosol

 The indirect effects of anthropogenic sulfate aerosols on the albedo and lifetime of clouds may produce a significant impact on the climate system. A `state of the art' general circulation model (GCM) which includes an interactive sulfur cycle and a physically based cloud microphysics scheme is coupled to a mixed-layer ocean model in order to study the impact of the indirect effects on the coupled climate system. The linearity of the two indirect effects on the model response is also investigated by including each effect separately in the model. The response of the sea surface temperatures (SSTs) and sea ice is found to provide an important feedback on the cooling at high latitudes and the change in meridional SST gradient results in a southward shift of the inter-tropical convergence zone (ITCZ). The sensitivity of the model to the forcing from the indirect effects of sulfate aerosol is found to be similar to, but slightly weaker than that obtained from a doubling of CO₂. Received: 30 August 2000 / Accepted: 3 January 2001     

皖南—浙西下古生界碳沥青成因及南方海相“有效烃源岩”问题探讨

赋存于皖南—浙西的固体碳沥青分为古油藏裂解碳沥青和古油藏破坏次生充填碳沥青两种类型 ,阐明了两类碳沥青的不同成因机制。重新认定了浙西“康山沥青脉”为碳沥青而不是泥岩。论证了皖南、浙西碳沥青的烃源为下寒武统、中—上奥陶统至下志留统、中—上寒武统等。认为加里东运动—广西事件期间是下扬子盆地相区以下寒武统黑页岩为烃源的油藏形成和部分破坏的主要时期。针对南方的油气勘探 ,提出了只有在晚期成藏中作出贡献的源岩才是“有效烃源岩”的新概念。     

A New Method of Surveying Underwater Parts of Self Elevating Drilling Platform

It is a new method of surveying leg spuds of self-elevating drilling platforms to lift them out of water with the help of additional middle guide blocks. Its main advantages in comparison with other methods normally used up to now are: less expensive, time saving, no need for specially designated water area, direct visual observation, good reliability and safety. The working principle has been presented with the example of two platforms "Bohai No. 8" and "Bohai No. 10", to which the method was used. Also a comprehensive comparison with other methods in technological and economical aspects is given in the paper.     

INFLUENCE OF THE UPSTREAM RESERVOIRS ON THE ADJUSTMENT OF DOWNSTREAM ALLUVIAL CHANNEL

I. INTRODUCTIONThe Yellow River is a heavily sediment--laden river. The sediment load of the Yellow River ranks the first in the world while its annual runoff is only of medium size. Toharness the river, it is necessary to build reservoirs for regulating runoff to meet the demands of economic development. Since the founding of PRC in 1949, I S4 large and medium--sized reservoirs have been constructed on the main stem and the tributaries with atotal storage capacity of 84.5 billion m3.…     

On dynamic and thermodynamic components of cloud changes

Clouds are sensitive to changes in both the large-scale circulation and the thermodynamic structure of the atmosphere. In the tropics, temperature changes that occur on seasonal to decadal time scales are often associated with circulation changes. Therefore, it is difficult to determine the part of cloud variations that results from a change in the dynamics from the part that may result from the temperature change itself. This study proposes a simple framework to unravel the dynamic and non-dynamic (referred to as thermodynamic) components of the cloud response to climate variations. It is used to analyze the contrasted response, to a prescribed ocean warming, of the tropically-averaged cloud radiative forcing (CRF) simulated by the ECMWF, LMD and UKMO climate models. In each model, the dynamic component largely dominates the CRF response at the regional scale, but this is the thermodynamic component that explains most of the average CRF response to the imposed perturbation. It is shown that this component strongly depends on the behaviour of the low-level clouds that occur in regions of moderate subsidence (e.g. in the trade wind regions). These clouds exhibit a moderate sensitivity to temperature changes, but this is mostly their huge statistical weight that explains their large influence on the tropical radiation budget. Several propositions are made for assessing the sensitivity of clouds to changes in temperature and in large-scale motions using satellite observations and meteorological analyses on the one hand, and mesoscale models on the other hand.     

A Whitecap Coverage Model Based on the Surface Slope For Criterion of Wave Breaking

Using the limit surface slope as a criterion of wave breaking,a simple model for estimatingthe spatial fraction of breaking surface of sea at an instant,which is regarded as the whitecap coverge inthis paper,is analytically derived from the probability density of surface slope based on Gaussianstatistics.The resulting fraction is found depending on the fourth moment of wave spectum,m_4,as well asthe critical threshold of surface slope.By expressing the fourth moment in terms of the Neumannspectrum,a formula linking the fraction and wind speed for fully developed sea states is obtianed.Anotherformula relating the fraction to both wind speed and fetch(or duration)is achieved by expressing m_4 interms of the Krylov spectrum and applying the empirical relationships used in the SMB ocean wave pre-dicting technique.A comparison between these results and the field data of whitecap coverage collected byMonahan and O＇Muircheartuigh shows an encouraging agreement.