LANDSLIDE POTENTIALITY OF THE TSENGWEN RESERVOIR WATERSHED,TAIWAN,CHINA

To recognize the geographical characteristics of the landslide areas will be helpful for the watershed management in the reservoir watershed.According to the quantitative analysis,we'll take different scores and weighting for the potential parameters of the landslide areas in the Tsengwen reservoir watershed,and in the meanwhile,we'll extract the different factors,including the slope,aspect,altitude,soil and geological textures etc.,and the results shown as maximum one-day rainfall,ratio of forests and average relief is the most affecting parameters on the potential risk map of landslide areas.     

The determination of erosion rates from exposed tree roots in the piceance basin,colorado

Tree roots, exposed by hillslope erosion in the Piceance basin of Colorado, were inspected to determine average net erosion rates during the last four centuries. Twenty pinyon pine and juniper root sections were obtained from each of five sites in this region. The date when a root was first exposed by erosion was determined, for 83 of the sections collected, by one of three methods: 1. time of initial cambium dieback; 2. interpretation of annual ring growth pattern; and 3. the earliest occurrence of reaction wood. Analysis indicated no significant difference in erosion rates between the five study sites. However, a strong difference in erosion rates was noted between north-facing (0–56 mm/yr) and south-facing (1.18 mm/yr) slopes. No significant difference in erosion rates were found between various south-facing aspects and local steepness of slopes. Significant differences were noted between erosion rate and the length of time the root was exposed to erosion. Rates of erosion on south-facing slopes in the pinyon-juniper community during the last four centuries are as follows: period (years ago) 0-99 100-199 200-299 300-399 erosion rate (mm/yr) 1-79 0-49 0-33 0-22. Although there appears to be a slow increase in erosion rates during the three earliest centuries the dramatic increase during the last century may have been substantially augmented by the introduction of cattle into this region approximately one hundred years ago.     

Patterns and rates of slopewash on the badlands of Hong Kong

Slopewash measurements were made at 449 sites on the badlands of Hong Kong over a 15-month period. The mean amount of ground retreat was 2.17 cm and the spread of data was large (coefficient of variation = 36.6 per cent). This demonstrates a large variation in rates of slopewash in the study area. A large sample size is suggested for any future work to narrow the limits of the sampling error. It is also shown that ground retreat, as conventionally measured in the field, is different and should be distinguished from vertical lowering. In the study of erosion rates and slope evolution, different conclusions are likely to be drawn unless the distinction is realized. Various attempts have been made to account for the observed variations in slopewash rates on the badlands of the study area. It was found that the site to site variations in slopewash rate could not be attributed to the conventional soil, microtopographic and distance parameters. This absence of relationship is probably due to the fact that the sites on the slope profiles are not isolated systems, but are components of a larger functional entity, in which all sites are in some form of adjustment and equilibrium with the others.     

Predicting stream channel erosion in the lacustrine core of the upper Nemadji River, Minnesota (USA) using stream geomorphology metrics

The USA Clean Water Act requires the development of a total maximum daily load (TMDL) when Minnesota’s water quality standard for turbidity is exceeded; however, regions underlain with fine-grained lacustrine deposits yield large natural background loads of suspended inorganic sediment. A review of hydrogeologic pathways was conducted along with the statistical analysis of geomorphic metrics, collected at 15 sites with varying drainage areas in the upper Nemadji River basin, northeastern Minnesota. Regression analysis indicated a strong linkage between bankfull cross-sectional area and drainage area. Dimensionless geomorphic metric ratios were developed to predict channel evolution potential and associated channel erosion risk. Sites located in drainage areas less than 2 km² had low erosion risk and showed a correlation between channel slope and relative roughness (D ₈₄/mean bankfull channel depth, 88%). A principal components analysis explained over 98% of the variance between sites and indicated five important channel shape metrics to predict channel erosion: bankfull width, bankfull depth, maximum depth, cross-sectional area, and valley beltwidth. Mass wasting of cohesive stream channel sediment was influenced by groundwater discharge and produced turbid waters in the upper Nemadji River.     

A study of erosion rates on salt diapir surfaces in the Zagros Mountains, SE Iran

Salt exposures and weathering residuum on several salt diapirs in different geographic/climatic settings were studied. Anhydrite, gypsum, hematite, calcite, dolomite, quartz, and clay minerals are the main constituents of the weathering residuum covering the salt diapirs in various thicknesses. Erosion rates of residuum as well as of rock salt exposures were measured at selected sites for a period of 5 years by plastic pegs as benchmarks. Recorded data were standardized to a horizontal surface and to long-term mean precipitation. For the rock salt exposures the following long-term denudation rates were determined of 30–40 mm a⁻¹ for coastal diapirs and up to 120 mm a⁻¹ for mountain salt diapirs. Long-term mean superficial denudation rate measured on weathering residuum of low thickness reached 3.5 mm a⁻¹ on coastal diapirs. The total denudation rate estimated for the thin residuum is close to 4–7 mm a⁻¹ based on apparent correlation with the uplift rate on Hormoz and Namakdan diapirs. Denudation of rock salt exposures is much faster compared to parts of diapirs covered by weathering residuum. The extent of salt exposures is an important factor in the morphological evolution of salt diapirs as it can inhibit further expansion of the diapir. Salt exposures produce huge amounts of dissolved and clastic load, thus affecting the surrounding of the diapir.     

RUNOFF-ENERGY FACTORS FORMUSLE SEDIMENT-YIELD MODEL FOR SURFACE MINES

1INTRODUCTIONSediment-yieldestimatesarerequiredforsurfacec0al-minepermitsunderFederalandStatelaws-Estimatesareneededfordeterminingtheimpactsofminingandreclamationduringmine0Peration,fordiversi0nandsmallimpoundmentdesigns,andforsizingsedimentpondstocontrolsedimenttransporteddownstfeam0faproposedminesite.Technologiesavailablef0rsediment-yieldestimationsincludetheUniversalSoilLossEquati0n(USLE,WischmierandSmith,l978);theWaterErosionPredictionPr0ject(WEPP,FlanaganandLivingst0n,l995),…     

鄂西渝东地区晚燕山-喜马拉雅期剥蚀量

鄂西渝东地区是中国南方海相油气勘探的重要区块,又是目前页岩气勘探的热门地区,该地区晚燕山-喜马拉雅期以来长期遭受隆升剥蚀.剥蚀量是烃源岩热演化、油气藏形成与演化、资源量计算和盆地模拟中不可缺少的基础参数.考虑到剥蚀量恢复方法固有的局限性和适用条件,本文在分析了古温标镜质体反射率Ro剖面特征之后,采用古地温梯度反演法进行钻井剥蚀量恢复,然后分析钻井剥蚀量与钻井开孔层位之间的相关性,再与地质图相结合编制剥蚀量平面分布图.结果表明：鄂西渝东地区古温标Ro剖面不存在明显的“错断”、“跳跃”现象,记录的古地温为达到最大埋深时的古地温;钻井剥蚀量与钻井开孔层位之间具有明显的相关性,开孔层位越老,剥蚀量越大,反之亦然;晚燕山-喜马拉雅期剥蚀量总体上从东往西逐渐变小.东部的利川复向斜剥蚀量为2000~4000 m,中部的石柱复向斜为1500~2500 m,方斗山以西为1000~1500 m.     

REVIEW ON LOCAL SCOUR DUE TO JETS

The safety of an apron of the energy dissipator is threatened by the large-scale scour in the downstream of the apron due to the erosive action of a horizontal jet issuing from a sluice opening. Also, large-scale deposition of the scoured sediments due to an impinging jet in a plunging pool type energy dissipator affects the passage of flow adversely in the downstream channels. Owing to the significant practical importance, the problem of local scour due to jets has been studied by many investigators, In this paper, a comprehensive review of the up-to-date investigations on local scour due to horizontal and impinging jets is presented including all possible aspects, such as scouring process, parameters affecting scour, time variation of scour velocity distribution on the apron and within the scour hole, development of boundary layer thickness, bed shear stress, scour estimation formulas and protection works.     

EVALUATION OF EROSION PRODUCTIVITY IMPACT CALCULATOR （EPIC） MODEL FOR MIDDLE MOUNTAIN REGION OF NEPAL

This study verifies the applicability of EPIC model for an erosion plot (61 .2 m~2) and an uplandterraced watershed (72 ha) using a total of 94 rainfall events over a study period of two years. Inorder to analyze the effect of storm size on runoff and soil loss processes, rainfall events aredivided into three groups: small (<25mm), moderate (25--50mm) and large (>50mm). Resultsindicate that the model could predict reasonably well the runoff and soil loss from the erosion plotand the watershed for the moderate and large rainfall events. However, the runoff and soil lossprediction for the small rainfall events is found to be poor. On annual basis, both surface runoff andsoil loss predictions match well the observations. In ligh of the importance of the moderate andlarge rainfall events in producing most of the annual runoff and soil loss in the study area, the EPICmodel is applied to assess the impacts of erosion on agricultural productivity and to evaluatemanagement practices to protect watersheds in the     

ASSESSMENT OF SOIL LOSS ON UNCULTIVATED SLOPE LAND BY USING 137CS TECHNIQUE IN THE UPPER YANGTZE RIVER BASIN OF CHINA

Radionuclides are used as tracers of sediments in areas where no plot data or field monitoring data are not available. Caesium-137 can provide important information on both soil loss rates and sediment sources. The 137Cs technique is employed to assess soil erosion rates in forest and grass lands in the Upper Yangtze River Basin, China. The study area includes 6 forestlands and 4 grasslands in 8 counties and cities over the eastern part of the basin. The ^137Cs reference inventories ranged from 620.9 Bq m-2 to 2560.3 Bq m^-2. For the 6 forestlands, the average 137Cs inventory over a field ranges from 960.8 Bq m^-2 to 2560.3 Bq m^-2. The average erosion rate is estimated from the ^137Cs measurements between 0 to 588 t km^-2yr^-1. For the 4 grasslands, the average ^137Cs inventory ranges from 119.0 Bq m2 to 869.7 Bq m^-2. The average rate of erosion from grassland varies from 0 to 4435 t km^-2 yrl. Where the erosion was more severe, the ^137Cs inventory was lower. The results showed that there is no clear relationship between ^137Cs inventory, slope length and slope gradient on uncultivated land. The erosion rates for uncultivated land and cultivated land is compared. The result indicates that the erosion rates on uncultivated land is much lower than those on cultivated slopes and the severity of the soil erosion is closely related to vegetation cover.