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D H Vaughan - One of the best experts on this subject based on the ideXlab platform.
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changes in streambank erodibility and Critical Shear Stress due to subaerial processes along a headwater stream southwestern virginia usa
Geomorphology, 2008Co-Authors: Theresa Wynn, Marc Henderson, D H VaughanAbstract:Abstract Despite more than 40 yr of research attributing temporal changes in streambank erosion rates to subaerial processes, little quantitative information is available on the relationships between streambank erodibility (kd) and Critical Shear Stress (τc) and the environmental conditions and processes that enhance streambank erosion potential. The study goal was to evaluate temporal changes in kd and τc from soil desiccation and freeze–thaw cycling. Soil erodibility and τc were measured monthly in situ using a multiangle, submerged jet test device. Soil moisture, temperature, and bulk density as well as precipitation, air temperature, and stream stage were measured continuously to determine changes in soil moisture content and state. Pairwise Mann–Whitney tests indicted kd was 2.9 and 2.1 times higher (p
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changes in streambank erodibility and Critical Shear Stress due to subaerial processes along a headwater stream southwestern virginia usa
Geomorphology, 2008Co-Authors: T M Wynn, M B Henderson, D H VaughanAbstract:Despite more than 40 yr of research attributing temporal changes in streambank erosion rates to subaerial processes, little quantitative information is available on the relationships between streambank erodibility (kd) and Critical Shear Stress (τc) and the environmental conditions and processes that enhance streambank erosion potential. The study goal was to evaluate temporal changes in kd and τc from soil desiccation and freeze–thaw cycling. Soil erodibility and τc were measured monthly in situ using a multiangle, submerged jet test device. Soil moisture, temperature, and bulk density as well as precipitation, air temperature, and stream stage were measured continuously to determine changes in soil moisture content and state. Pairwise Mann–Whitney tests indicted kd was 2.9 and 2.1 times higher (p < 0.0065) during the winter (December–March) than in the spring/fall (April–May, October–November) and the summer (June–September), respectively. Regression analysis showed 80% of the variability in kd was explained by freeze–thaw cycling alone. Study results also indicated soil bulk density was highly influenced by winter weather conditions (r2 = 0.86): bulk density was inversely related to both soil water content and freeze–thaw cycling. Results showed that significant changes in the resistance of streambank soils to fluvial erosion can be attributed to subaerial processes. Water resource professionals should consider the implications of increased soil erodibility during the winter in the development of channel erosion models and stream restoration designs.
T M Wynn - One of the best experts on this subject based on the ideXlab platform.
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changes in streambank erodibility and Critical Shear Stress due to subaerial processes along a headwater stream southwestern virginia usa
Geomorphology, 2008Co-Authors: T M Wynn, M B Henderson, D H VaughanAbstract:Despite more than 40 yr of research attributing temporal changes in streambank erosion rates to subaerial processes, little quantitative information is available on the relationships between streambank erodibility (kd) and Critical Shear Stress (τc) and the environmental conditions and processes that enhance streambank erosion potential. The study goal was to evaluate temporal changes in kd and τc from soil desiccation and freeze–thaw cycling. Soil erodibility and τc were measured monthly in situ using a multiangle, submerged jet test device. Soil moisture, temperature, and bulk density as well as precipitation, air temperature, and stream stage were measured continuously to determine changes in soil moisture content and state. Pairwise Mann–Whitney tests indicted kd was 2.9 and 2.1 times higher (p < 0.0065) during the winter (December–March) than in the spring/fall (April–May, October–November) and the summer (June–September), respectively. Regression analysis showed 80% of the variability in kd was explained by freeze–thaw cycling alone. Study results also indicated soil bulk density was highly influenced by winter weather conditions (r2 = 0.86): bulk density was inversely related to both soil water content and freeze–thaw cycling. Results showed that significant changes in the resistance of streambank soils to fluvial erosion can be attributed to subaerial processes. Water resource professionals should consider the implications of increased soil erodibility during the winter in the development of channel erosion models and stream restoration designs.
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methods for determining streambank Critical Shear Stress and soil erodibility implications for erosion rate predictions
Transactions of the ASABE, 2007Co-Authors: L A Clark, T M WynnAbstract:According to the U.S. EPA, excess sediment is a significant cause of water quality impairment for rivers. The goal of this study was to compare different methods of determining two parameters used to estimate streambank erosion, soil Critical Shear Stress (t c) and soil erodibility (kd) and to determine the impact of those differences on predictions of streambank erosion. At 25 field sites, bank erosion tests were conducted using a submerged jet test device, and soil samples were collected. Critical Shear Stress was measured using a multi-angle submerged jet test device (JT) and estimated based on Shields' diagram (SD) and empirical relations based on the soil parameters, percent clay (Pc), plasticity index (Iw), particle size (D50) and percent silt-clay (SC). Additionally, using a single set of t c values, the kd measured by the jet test was compared to predictions from two empirical kd relations. Using these parameter values, streambank erosion rates were predicted for a local stream. The jet t c estimates were as much as four orders of magnitude greater than the SD, Pc, and D50 estimates, indicating the SD and empirical methods underestimate t c. The two empirical kd equations produced similar kd values that were generally two orders of magnitude less than the values from the jet test measurements. Erosion predictions followed the same trend as the kd data, with the jet test measurements resulting in higher predictions. Field validation of these methods over a wide range of soil types is recommended to develop methods of estimating kd and t c for fine-grained streambank soils.
Theresa Wynn - One of the best experts on this subject based on the ideXlab platform.
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changes in streambank erodibility and Critical Shear Stress due to subaerial processes along a headwater stream southwestern virginia usa
Geomorphology, 2008Co-Authors: Theresa Wynn, Marc Henderson, D H VaughanAbstract:Abstract Despite more than 40 yr of research attributing temporal changes in streambank erosion rates to subaerial processes, little quantitative information is available on the relationships between streambank erodibility (kd) and Critical Shear Stress (τc) and the environmental conditions and processes that enhance streambank erosion potential. The study goal was to evaluate temporal changes in kd and τc from soil desiccation and freeze–thaw cycling. Soil erodibility and τc were measured monthly in situ using a multiangle, submerged jet test device. Soil moisture, temperature, and bulk density as well as precipitation, air temperature, and stream stage were measured continuously to determine changes in soil moisture content and state. Pairwise Mann–Whitney tests indicted kd was 2.9 and 2.1 times higher (p
Jun Zhao - One of the best experts on this subject based on the ideXlab platform.
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A rational method for estimating erodibility and Critical Shear Stress of an eroding rill
Geoderma, 2008Co-Authors: Qingwen Zhang, Jun ZhaoAbstract:Abstract Soil erodibility and Critical Shear Stress are two of the most important parameters for physically-based soil erosion modeling. To aid in future soil erosion modeling, a rational method for determining the soil erodibility and Critical Shear Stress of rill erosion under concentrated flow is advanced in this paper. The method suggests that a well-defined rill be used for Shear Stress estimation while infinite short rill lengths be used for determination of detachment capacity. The derivative of the functional relationship between sediment yield and rill length at the inlet of rill flow, as opposed to average detachment rate of a long rill, was used for the determination of detachment capacity. Soil erodibility and Critical Shear Stress were then regressively estimated with detachment capacity data under different flow regimes. Laboratory data of rill erosion under well defined rill channels from a loess soil was used to estimate the soil erodibility and Critical Shear Stress. The results showed that no significant change in soil erodibility ( K r ) was observed for different slope gradients ranging from 5 to 25 while Critical Shear Stress increased slightly with the slope gradient. Soil erodibility of the loess soil was 0.3211 ± 0.001 s m − 1 . The soil erodibility and Critical Shear Stress calculations were then compared with data from other resources to verify the feasibility of the method. Data comparison showed that the method advanced is a physically logical and feasible method to calculate the soil erodibility and Critical Shear Stress for physically-based soil erosion models.
B W Ragan - One of the best experts on this subject based on the ideXlab platform.
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Critical Shear Stress for erosion of cohesive soils subjected to temperatures typical of wildfires
Journal of Geophysical Research, 2005Co-Authors: John A Moody, Dungan J Smith, B W RaganAbstract:Received 26 February 2004; revised 15 September 2004; accepted 5 November 2004; published 22 January 2005. [1] Increased erosion is a well-known response after wildfire. To predict and to model erosion on a landscape scale requires knowledge of the Critical Shear Stress for the initiation of motion of soil particles. As this soil property is temperature-dependent, a quantitative relation between Critical Shear Stress and the temperatures to which the soils have been subjected during a wildfire is required. In this study the Critical Shear Stress was measured in a recirculating flume using samples of forest soil exposed to different temperatures (40� –550� C) for 1 hour. Results were obtained for four replicates of soils derived from three different types of parent material (granitic bedrock, sandstone, and volcanic tuffs). In general, the relation between Critical Shear Stress and temperature can be separated into three different temperature ranges ( 275� C), which are similar to those for water repellency and temperature. The Critical Shear Stress was most variable (1.0–2.0 N m � 2 ) for temperatures 2.0 N m � 2 ) between 175� and 275� C, and was essentially constant (0.5–0.8 N m � 2 )f or temperatures >275� C. The changes in Critical Shear Stress with temperature were found to be essentially independent of soil type and suggest that erosion processes in burned watersheds can be modeled more simply than erosion processes in unburned watersheds. Wildfire reduces the spatial variability of soil erodibility associated with unburned watersheds by eliminating the complex effects of vegetation in protecting soils and by reducing the range of cohesion associated with different types of unburned soils. Our results indicate that modeling the erosional response after a wildfire depends primarily on determining the spatial distribution of the maximum soil temperatures that were reached during the wildfire.