Aleksey Sidorchuk

Dynamic and static models of gully erosion

Abstract The main causes of gully formation are anthropogenic factors: the clearing of native forests, tilling of fallow lands and associated change of the hydrological conditions in the rainfall–runoff system. Gully channels formation is very rapid during the period of gully initiation, when morphological characteristics of a gully (length, depth, width, area, and volume) are far from stable. This period is relatively short, about 5% of a gullys lifetime. For the most part of a gullys lifetime, its size is near stable, maximum value. These two stages of gully development led to two types of gully erosion models: (1) dynamic models to predict rapid changes of gully morphology at the first period of gully development; (2) static models to calculate final morphometric parameters of stable gullies. The dynamic gully model is based on the solution of the equations of mass conservation and gully bed deformation. The model of straight slope stability was used for prediction of gully side walls inclination. The static gully model is based on the assumption of final morphological equilibrium of a gully; when averaged for several years, elevations and width of gully bottom do not change. This stability is associated with a negligible rate both of erosion and sedimentation at the gully bottom. It means that flow velocity is less than the threshold value for erosion initiation, but is more than the critical velocity of wash load sedimentation. The dynamic and static gully models were verified on the data on gullies morphology and dynamics from Yamal peninsula (Russia) and New South Wales (Australia).

Gully erosion modelling and landscape response in the Mbuluzi River catchment of Swaziland

Abstract In southern African countries soil erosion and the related problems, such as water quality issues or decreasing soil productivity, are the main topics affecting the inhabitants of both rural and urban areas. Therefore, the attention has been recently placed on those problems related to soil erosion. This can also be documented by an increasing number of studies carried out on erosion and by the development and application of erosion models. Nevertheless, gully erosion phenomena have been widely neglected in erosion modelling. This is because the development of erosion models was focused on those regions with an intense agriculture typical of developed countries on the one hand, and because of the spatial and temporal heterogeneity of gully erosion processes on the other hand. This study regards the identification of gully erosion forms and processes in the Mbuluzi River catchment (Kingdom of Swaziland) by using the Erosion Response Units (ERU) concept. The following modelling of gully erosion was done through the stable gully model [Catena 37 (1999) 401]. The input data were obtained through the application of remote sensing techniques (API method) and GIS-analyses. The example from Swaziland shows that the applied methods are able to identify areas affected by gully erosion. Furthermore, it is possible to estimate the amount of soil loss due to gully erosion, which, for example, is not taken into consideration by the USLE-type models.

Fluvial response to the Late Valdai/Holocene environmental change on the East European Plain

Abstract The relicts of large meandering paleochannels are found throughout the territory of the periglacial zone of the last (Valdai=Weichselian) glaciation on the Russian Plain, on the lower levels of river terraces and on the floodplains. Channel widths of so-called macromeanders can be 15 times larger than the recent meanders on the same rivers. Paleolandscape and paleohydrological reconstructions show that such periglacial river channels were formed under the conditions of high spring water flow, up to eight times greater than modern discharges, when the flow coefficient was close to 0.9–1.0 due to the existence of permafrost. Also, summers were dry and streams lacked ground water supply. Permafrost degradation increased soil permeability in the spring and increased ground water flow during summer, causing a decrease of annual flow 12,000–14,000 years BP in the southern periglacial zone, and up to 8500 years BP in the northern periglacial zone. In the taiga zone, an annual flow in the recent river basins is about 80–85% of that found in the periglacial zone in the east, and 30–60% of that in the west. In the east of the broad-leaved forest zone, it is about 40–50% of that of the periglacial zone, and 20–25% in the western part of the broad-leaved forest zone. In the eastern steppe and forest steppe, the modern annual flow is about 40–60% of that of the periglacial zone and about 10% in the western part of steppe and forest steppe zones. As a result, large periglacial channels were abandoned and transformed into floodplain lakes and bogs. The Holocene channels have much smaller channel widths and meander lengths, formed under conditions of lower annual flows and much steadier flow regime.

Floodplain sedimentation: inherited memories

Abstract Swampy inherited floodplains are found throughout the steppe and forest steppe over the Russian Plain. These floodplains were formed during the Late Glacial/Holocene transition on the relicts of large meandering palaeochannels in the former periglacial zone as a result of dramatic decrease in river channel widths (up to 1/15). Inherited floodplains were only partly reworked by the activity of the Holocene rivers. The remnants of the ancient fluvial relief control the flow hydraulics and sediment transport delivery to the river channels on the wide floodplains, causing sediment discontinuity. Such discontinuity reaches its maximum in the chain-of-lakes channels, and decreases with the evolution of the inherited floodplain into a typical floodplain with developed continuous channels.

A LUCIFS Strategy: Modelling the Sediment Budgets of Fluvial Systems

Cumulative Global Change is occurring through the removal of forests, conversion of marginal land to cultivation, and intensification of cultivation. Systemic Global Change, in the form of changes in climate and atmospheric chemistry, is likely to alter land use patterns during the next century. All of these changes will affect rivers and their catchments, altering the fluxes of water, sediment, nutrients, carbon and pollutants. The effects of past changes of land use and climate are still being felt in many catchments, and are difficult to understand without an historical perspective. Future changes, when superimposed on changes triggered in the past, will produce complex responses, which may be difficult to anticipate.