Abstract:Taking the typical tributaries in the sediment-rich area with more coarse ones inthe middle reaches of the Yellow River as an example, this paper analysed the causeof reduction of incoming sediments in the 1980s. The authors hold that the reductionof rainfall and intensity of rainfall was the main cause of sediment reduction in the1980s, whose effects upon sediment reduction were about 70%, while the effects of thecomprehensive control over the watershed upon the degree of sediment reduction accounted for 30% of total sediment reduction.

Abstract:This paper deals with the process of sediment production by erosion and sever-ity of its damages in Huangfuchuan watershed. Also,this paper analysed the effects ofTianchao hydraulic power station in Fugu upon the sedimentation of the downstreamriver bed in this watershed, and the effects of Huangfuchuan watershed upon Tianchaohydraulic power station and sediment deposition of each river section of trunkstreamsof the Yellow River in Fugu. At the same time, the authors analysed the sedimentproduction by erosion, and causes of intensified soil erosion, and further pointed outthat land reclamation by human beings is the important cause to intensify soil ero-sion. Also. less rainfall with more rainstorms and strong weathering special bedrocksare the main links in the strongly-eroded areas in the middle reaches of the Yellow-River.Therefore,conserving the existing loess, increasing grass and shrub coverage, andstrengthening protection engineering structures in gullies can be the fundamentalmeasures at present-for comprehensive control over Huangfuchuan watershed.

Abstract:Basde on the analysis of the existing conditions and damages caused by soil and water loss, this paper deals with the position and role of soil and water conservation in the construction of commercial grain producing bases in the black eartharea,Eventually, the authors presented the approaches and measures of prevent-ing and controlling water and soil loss in the black earth area,

Abstract:Dongting Lake area in Hunan.Province is one of severe flood hit in 1991. After the serious floods, there are some questions worthregions in China thinking about,Based on the detailed field surveys, the authors discussed the genesis of flood disaster an strategi cal measures for permanent control over floods in Dongting Lake

Abstract:In the summer of 1991,Anhui province suffered from severe disasters caused by verystrong rainstorms with one hundred year's frenquency, floods and water loggings. Ne-vertheless, Huangbang small watershed in Jinzhai county located in the Huaihe Rivervalley has bronght about the remarkable benefits in reducing floods and disastersbecause of the complete water and soil conservation protective system in carrying outthe comprehensive control over water and soil loss in accordance with local conditionsand adopting the combination of biological measures with engineering structures. Theauthor summarized the experience gained in Huangbang small watershed, thusgiving people a deep enlightenment and a deep thought about the past, work onwater and soil conservation is a matter of vital and lasting importance in developingagricultural production and ensuring the economic construction and safety ef the peopleand their properties.

Abstract:Baiquan county in Heilongjiang Province suffered the rainstorms with seriouslosses from June to August in 1991 after the flooding disasters, the authors immedi-ately made a field survey of 1.88 million mu of farmlands under better comprehensivecontrol over water and soil loss. It is estimated in accordance with the measureddata from the experimental plots that there is an average reduction of 37% of surfacerunoff and 56% of soil loss in the controlled area in comparison with those in theuncontrolled area, of which 11 pilot small wetersheds have shown a better effect upon the reduction of runoff and sediments. At the same time, the authors made adeep thought about water and soil conservation work in the county through fieldsurveys and analysis, and pointed out some existing problems and the measures totackle them in water and soil conservation.

Abstract:The author studied the effects of slope gradient of land surface, vegetation coverpercentage, rainfall intensity upon infiltration rate into soil under the conditionsof artificial rainfall with high intensity. The results showed that the accumulatedinfiltration water was in inverse proportion to slope gradient, and also, there exist-ed an apparent critical slope gradient affectimg the depth of accumulated runoffwater. In the case of this test, the critical slope gradient of different time sectionsand different vegetation, types varied between 23.6°-30.4°. The vegetation coverpercentage increased, and the accumulated infiltration water went up exponentiallyThe steady infiltration rate has an increasent trend with the increasing rain intenasity.

Abstract:Based on the analysis of ancient natural vegetation landscape and present-day vegetation zonifications as well as artificial vegetation growing situations, it is con-sidered that the zones with rainfall of over 550 mm are suitable for forests to grow so that forests are growing much better and these zones can be classified as the artificial tree belts,while the zones with rainfall of 400-550 mm where trees are evi-dently dwarfed can be classified as the dwarfed trees and shrub belts, The better vegetation can be constructed over most of places on the Loess Plateau, Meanwhile，based on the well -preserved natural vegetation cover and extension of artificial vegetation cover percentage in close combination with Chikugo method and the estimation from the regression equation with field surveying data, it is suggested that thevegetation percentage in forest belt on the Loess Plateau reach 90%一100% under the natural conditions (without any damagss caused by human activities)while that cover the forest and grassland belts (with rainfall of 400-500 mm) reach over 80%.

Abstract:Soil water evaporation is affected by many factors, but the main factors are soilwater and litter thickness. A mathematical model on soil water evaporation under littercover of 5 cm in thickness is: Q_t = (652.5e~(0.0166)t -660.5)/e~(0.0166)t. It has been foundthrough testings that this mathematical model can be used to describe the rule of soilwater evaporation, and its parameters are easy to be fixed and convenient to be used