ISSN:0435-3676    

DOI:10.1080/04353676.1992.11880349

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

ABSTRACTA brief review is given of research on soil erosion and conservation in central Tanzania during the period 1968–1992. The DUSER project studied land degradation and erosion control, for the first time within a multidisciplinary research project in Africa. Man's activities were found to be the prime factor influencing the rate and intensity of change in the physical landscape within a historical perspective. Partly on the basis of these results, a governmental decision was taken to promote soil conservation in Tanzania. Subsequently, the HADO soil conservation project was initiated in 1973. At present studies of land degradation are carried out within the“Man—Land Interrelations in Semi-arid Tanzania’programme which includes 12 separate studies of environmental change and resource conservation.

ISSN:0435-3676    

DOI:10.1080/04353676.1992.11880350

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

ABSTRACTThe north eastern Irangi Hills of the Kondoa District, Tanzania are severely affected by soil erosion with consequent land degradation caused by the loss of productive soil, gullying, sand deposition on lower slopes, and rapid siltation of lakes. Major changes in land surface morphology and soil characteristics have drastically altered the pattern of cultivation and settlement. A knowledge of soil and environmental conditions that existed prior to the phase of modern accelerated erosion is fundamental to the accurate assessment of land degradational processes, the extent of soil erosion and sedimentation, and the degree and sustainability of land recovery. This paper integrates the results of recent field-based geomorphological, pedological and sedimentological studies in the Haubi and Mwisanga catchments. Landforms, soil toposequences and recent colluvial and alluvial deposits are described in relation to erosion features, the dynamics of vegetation/land use changes and the development of Lake Haubi. Modification of the pre-existing soil landscape by accelerated erosional and depositional processes is discussed.

ISSN:0435-3676    

DOI:10.1080/04353676.1992.11880351

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

ABSTRACTBabati town was one of several areas in Tanzania that was flooded during the heavy rains in 1990. Lake Babati, situated to the south of the town, is a shallow fresh water lake rapidly responding to climatic fluctuations. The lake surged on April 6, 1990. The flood created a new outlet of the lake through the town centre. Street gutters were transformed into gullies and several buildings were destroyed.Analyses of climatic data, aerial photography and old records indicate that the floodings commenced in 1964 after a relatively long dry spell when the lake was reduced to about 1/4 of its present size. Subsequent floods occurred in 1979 and 1990 and can all be related to the building up of ground and surface water resources in the catchment after periods of increased rainfall amounts.The recent land use changes are discussed in relation to the natural causes of the floods.

ISSN:0435-3676    

DOI:10.1080/04353676.1992.11880352

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

ABSTRACTA mathematical process model is introduced, simulating the deposition of suspended material in lakes and reservoirs. The model is applied on the deposition processes in a reservoir within the Reventazon river basin in Costa Rica, Central America. The calculations show a trap efficiency of the reservoir of about 80 per cent. The influence is quantified of variations in grain size composition of the suspended material and of water discharge changes on the resulting grain size composition of bottom material in different parts of the reservoir. The significance of turbidity currents is elucidated. The methods seem to be useful for the interpretation of palaeohydrological changes with lake sediments as indicators.

ISSN:0435-3676    

DOI:10.1080/04353676.1992.11880353

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

ABSTRACTThe purpose of this paper is to describe the extent and intensity of interrili, rill and ephemeral gully erosion on arable land in southern Sweden. Measurements of rill and ephemeral gully erosion have been made in three agricultural districts (90 km2). Interrili erosion has been studied in six experimental fields. The measurements were carried out from October to April in the three years 1986/87, 1987/88 and 1988/89.Within the agricultural area studied (Scania - southern Sweden) about 7 per cent of the arable fields were affected each year by rill and ephemeral gully erosion at an average rate of about 825 kg ha-1year-1. The intensities showed a great spatial and temporal variation from 1 kg ha-1year-1to 120 t ha-1year-1. Some of the fields can be classified as having a land degradation problem of economic and environmental significance. Interrill erosion varied between 1 kg ha-1year-1and 16 t ha-1year-1.The observed erosion rates in this study are greater than the average erosion rate on arable land in Sweden, estimated by the Swedish Environmental Protection Board (SNV 1986). If the results are comparable it implies that earlier estimations are either too low or that the investigated region is more sensitive to erosion than other agricultural districts in Sweden.

ISSN:0435-3676    

DOI:10.1080/04353676.1992.11880354

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

ABSTRACTSnow avalanche landforms are identified at 22 sites in the Lairig Ghru based on morphology and distinctive surface sediment sorting patterns. Avalanche boulder tongues intermediate between fan and roadbank tongues occur at the Pools of Dee and larger, inactive roadbank tongues are described from Glen Luibeg. Two major recent debris flow events are identified in the valley and dated to 1961 and 1978. Contemporary morphological activity by avalanches is mainly associated with the reworking of debris flow deposits. Levées from one of the 1961 flows were completely bevelled over a 20 year period. These observations indicate snow avalanches are locally significant geomorphic agents in the Scottish mountains although the morphological evidence may be masked by more obvious debris flow or alluvial cone deposits which originate from similar source areas.

ISSN:0435-3676    

DOI:10.1080/04353676.1992.11880355

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

ABSTRACTDetailed geomorphological mapping, lichenometric dating of deposits, historical records and lacustrine sediment cores are used to reconstruct debris flow activity in the High Tatra Mountains of South Poland over the last 200 years. At the present time high energy geomorphic events are limited to the apex section of talus slopes and rarely affect the whole slope. During the Little Ice Age debris flows and rockfalls were both more frequent and of greater magnitude due to changes in both climatic factors and earthquake occurrence.

ISSN:0435-3676    

DOI:10.1080/04353676.1992.11880356

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

ABSTRACTThe Martinelli Snowpatch occupies a shallow hollow on the south side of Niwot Ridge, Colorado Front Range. A relatively long-term (up to 10 years) record of sediment movement onto and across its floor and of sediment yields from its catchment basin is reported here. This record shows sediment fluxes which are highly variable in time but which define a spatially consistent pattern involving high flux rates (up to 1500 g/m/yr) onto the basin floor at its head and slower rates of downslope movement from there. The small stream channels in the basin have been stable over the period of study and show an approximately balanced budget of silt and clay sized sediments. They, and the basin floor, are accumulating coarser sediment at a slow rate (<1 mm/yr) which suggests long-term landscape development by a decay model (Thornes and Brunsden 1977). This would require that the“nivation hollow”form tends to be removed under present conditions, though it does not take solutional processes into account.

ISSN:0435-3676    

DOI:10.1080/04353676.1992.11880357

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

ABSTRACTPediments in the Barn Mountains constitute lowlands which border upland massifs and surround isolated inselberg-like hills. They form gentle concave-up or planar slopes which terminate abruptly at steeper upper slopes. Field observations demonstrate that the surfaces truncate geological structure and are essentially slopes of transportation since they possess a negligible or thin (<2-5 m thick) veneer of locally-derived colluvium. A study of the soils and surficial materials upon one pediment in Anker Creek (lat: 68°37'N; long: 138°08'W) suggests that the pediments are largely inactive under today's climate. Current geomorphic activity appears largely limited to the formation and movement of earth hummocks in the seasonally thawed layer. The pediments are probably old landform features which have been re-activated episodically only during those periods of the Pleistocene when enhanced moisture levels promoted intense frost wedging of upper slopes and permitted enhanced debris waste transport (solifluction) across the pediment. The initial mechanism of pediment formation is still unclear.

ISSN:0435-3676    

DOI:10.1080/04353676.1992.11880358

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor