This thesis summarizes the efforts of two years of field investigation and water quality data analysis. With a focus on construction sites, background monitoring was carried out at two sites and data from a third, active site was also included for analysis. The water quality data was used to estimate event-based sediment yield from each location, and continuously-collected rainfall, water level and turbidity data was used to calibrate an event-based hydrologic model (SEDCAD). Based on the results of this research and the outputs of the calibrated model, an event-based sediment yield equation calibrated for Southern Ontario conditions is presented in conjunction with an IDF design tool. The IDF design tool can be used to effectively size and site construction-phase erosion and sediment controls before shovels break ground. The regulatory framework by which such controls are assessed is also discussed, and improvements to existing stormwater management guidelines are proposed.

Subsurface erosion forms has been regarded as a unique exception to the more common surficial erosion forms such as rills and gullies, and have therefore been viewed as being of little consequence consequence for the total annual soil loss within any given region. A total of 148 subsurface erosion system occurring at 66 sites in Southern KwaZulu-Natal and Transkei were analysed morphologically to determine the significance of subsurface erosion within this region, to assess the extent to which the observed phenomena may be explained by current theories. Based on morphological criteria related to the dimensions of the subsurface erosion phenomena, it has been shown that there are five distinct -subsurface erosion systems namely scree slope systems; gully- sidewall systems; anthropogenically induced systems; system associated dispersive soils, seepage systems. It was further found that, under certain circumstances, the sediment lost through surficial erosion can be increased 77% by subsurface erosion and the subsurface erosion is spacially to particular slope units which are defined on the basis of the dominant geomorphic processes. Although soil chemistry, in particular dispersion related to the exchangeable Sodium percentage and the Sodium Absorption Ratio, is an important factor in facilitating subsurface erosion, other factors are also important as scree slope systems for example occur in soils which are completely non-dispersive. It has been possible to demonstrate that there is a statistically' significant correspondence between the spatial orientation of inter-ped surfaces the orientation of bedrock joints. This correspondence has enabled the explanation of how the well documented phenomenon of structurally controlled drainage basins may develop._ This correspondence has enabled the explanation of how well documented phenomenon of structurally controlled drainage basins may develop. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1996.

This thesis describes a comparative study of actual and potential soil erosion in the Wilderness area of the Umfolozi Game Reserve, and a biophysiographically comparable adjacent traditional KwaZulu landuse area. Estimates of temporal and spatial variations in eroded surfaces, sparsely vegetated surfaces susceptible to erosion, and active gullies were obtained from five sets of sequential aerial photographs taken between 1937 and 1983. Estimates of the potential influence of rainfall erosivity, soil erodibility, topography, and changes in vegetation communities and landuse practices on these variations, were extrapolated from these aerial photographs as well as from maps, field surveys, records and other studies. Interrelationships between these potential influences, and the extent to which they actually contributed to the temporal and spatial variations in the three 'erosion' surfaces, were assessed visually using a geographic information systems thematic overlay technique, and computationally using a forward stepwise multiple regression procedure. / Thesis (Ph.D.)-University of Durban-Westville, 1990.

No description available.

No description available.

Agricultural land in China is being degraded, with soil erosion becoming an increasing problem. In Yunnan Province, south-west China, there is a long history of soil erosion due to soil type, climate, anthropogenic influence and because 95% of the Province is mountainous. Population pressure and lack of flat land necessitate cultivation of steep slopes. The Yunnan Government prohibits cultivation of slopes >25°, however policy enforcement would result in food shortages in the Province, due to a lack of suitable land <25°. Therefore, the most appropriate way to curb soil erosion in Yunnan is to devise affordable agronomic means of reducing soil loss, which do not decrease crop productivity on sloping land currently under cultivation. At present, very little research has addressed these issues. A research project, building on existing work from 1993-1996, was initiated in 1998. The aim was to test the hypothesis that contour cultivation and contour cultivation plus straw mulch decrease runoff and soil erosion rates on sloping land in Yunnan Province under maize cultivation and to assess the impact of these conservation measures on maize productivity and soil nutrient status. Thirty runoff plots, located on three different slope angles (I 3°, II 10° and III 27°), in three groups of 10, were used to examine three cropping treatments in a replicated plot design in 1998 and 1999. Treatments were downslope cultivation (control), contour cultivation and contour cultivation plus straw mulch. In addition, there was an unreplicated bare plot in each group. Runoff and soil loss were measured on a storm-by-storm basis. Soil nutrient status was measured at the beginning and end of each cropping season. Crop growth parameters and soil physical properties were measured throughout the cropping seasons (21/05–7/10 in 1998 and 22/05–2/10 in 1999). In 1998, seasonal rainfall was 1024 mm, ~28% greater than the 30-year mean. Soil loss was significantly reduced by contour cultivation on Slopes I and II. On Slope I, downslope cultivation produced 3.07 t ha-1 soil loss and contour cultivation reduced this by 81.4 %. On Slope II, downslope cultivation produced 19.11 t ha-1 and contour cultivation reduced this by 58.0%. The addition of straw mulch gave a further, nonsignificant, reduction on both slopes. On Slope III, downslope cultivation and contour cultivation produced 6.92 and 6.29 t ha-1 of soil loss, respectively, with contour cultivation plus straw mulch having 99.4% less erosion than downslope cultivation. In the much drier 1999 season, no treatment significantly reduced soil loss on Slope I. Contour cultivation significantly reduced soil loss on Slopes II and III. On Slope II, downslope and contour cultivation produced 11.52 t ha-1 of soil loss and contour cultivation reduced this by 85.8%. On Slope III, downslope and contour cultivation produced 8.62 and 0.23 t ha-1, respectively; a reduction of 97.3% by contour cultivation. The addition of straw mulch did not further decrease soil loss. Treatment effects on soil nutrient status varied between the two years. At the end of the 1998 season, there was significantly higher soil available N under contour cultivation plus straw mulch on all three slopes (Slopes I and II P <0.001, Slope III P <0.05), an effect that was not found in 1999. At the end of the 1999 season, soil available K was significantly (P <0.001) higher under contour cultivation plus straw mulch on Slope III. In both years, contour cultivation plus straw mulch significantly reduced soil temperature. However, this did not result in yield reductions in comparison with the control. There was an increase in soil moisture content under contour cultivation plus straw mulch during dry periods, which was particularly noticeable in 1999. In 1998, there were no significant treatment effects on grain or shoot yield. In 1999, on Slope II, contour cultivation plus straw mulch significantly increased grain yield by 50.3% compared with the downslope treatment (P <0.05). In 1999, contour cultivation plus straw mulch also significantly increased leaf plus stem yield on Slopes I and II by 12.4 and 36.8%, respectively. It is concluded that on ≤10° slopes, contour cultivation alone is a suitable soil conservation measure. However, use of straw mulch would benefit soil moisture and nutrient status and could, therefore, increase crop yield. On ≥27° slopes, it is recommended that contour cultivation plus straw mulch be used as a soil conservation measure to ensure maximum soil conservation, even in extreme rainfall conditions.

The delivery of suspended sediment from drainage basins has frequently been quantified in mass terms by use of the suspended sediment budget approach, which identifies sources, storage and output of mobilised sediment. This thesis investigates the particle size characteristics of the sediment associated with the key components of the suspended sediment budgets of four drainage basins in Devon, U. K. to determine whether particle size selectivity occurs in the delivery of suspended sediment from the hillslopes to the basin outlet. Attention focused on pasture land because previous studies had indicated that this was the dominant source of suspended sediment and that arable fields and channel banks were relatively insignificant in these catchments. Samples of sediment were mobilised from pasture hillslopes using a field-portable rainfall simulator; samples of suspended sediment were collected from the river channel during storm events either manually, by automatic pump samplers or by using rising limb siphon samplers; suspended sediment deposited on the channel bed was sampled using bed traps and by resuspending sediment deposited on the river bed during low flows; and sediment deposited on the floodplain during overbank flooding was collected using Astroturf mat traps or by sampling surface material. Samples were collected to investigate both temporal and spatial variability in grain size behaviour. All sediment samples were pretreated to remove organic matter and their chemically dispersed (absolute) particle size composition was measured using a Coulter LS 130 laser granulometer. The particle size composition of transported/deposited sediment was compared with that of the samples from potential sources to determine whether particle size selectivity had occurred. Where possible, measurements of the natural in situ particle size distribution (effective particle size) were also undertaken by quick return of samples to the laboratory for immediate measurement without pre-treatment using the laser granulometer. Particle size selectivity was found to have occurred in the mobilisation of sediment from the hillslope pasture land sources. Seasonal variations were identified in the particle size characteristics of both sediment mobilised from the hillslopes and suspended sediment samples. Spatial variations were identified in the particle size composition of sediment deposited on the floodplain. These seasonal and spatial variations reflect the particle size selectivity of detachment, transport and deposition processes which is in turn influenced by the aggregation or flocculation (effective particle size) of the sediment.

No description available.

Thesis (Ph. D. - Renewable Natural Resources)--University of Arizona, 1991. / Includes bibliographical references (leaves 287-296).

Thesis (Ph.D.) -- University of Western Sydney, Hawkesbury, 1998. / Thesis submitted for the degree of doctor of philosophy. Erratum sheets in back pocket. Includes bibliographical references.