Using the movability number to model local clear-water scour in rivers

Includes bibliographical references.Local scour is associated with a considerable number of bridge failures worldwide. It occurs at bridge piers and abutments as a result of interactions between complex flow features and the channel bed. The number of factors involved in the interactions makes it difficult to predict. A lot of research has therefore been performed by several investigators to gain insight into the scouring process and scour prediction. Currently, local scour is estimated using physical models, empirical formulae or numerical models. Of these methods, the use of numerical models appears to be more economical and ideal as it permits flexibility in the choice of flow parameters and allows different scenarios to be easily studied. The aim of this research was thus to investigation into the use of the commercial CFD code FLUENT 6.2 for scour prediction based on the Movability Number. The research, which focused exclusively on local clear-water scour at bridge piers, stemmed from previous works performed by Armitage & McGahey (2003) and Cunninghame (2005) in which the Movability Number approach was developed and assessed. Results from these studies indicated that there was considerable potential in the Movability Number approach and, also, there was a need for a completely automated procedure for scour prediction based on the approach. For the current research therefore, an 'equilibrium model' was developed in which the river bed was successively modified in response to computed bed Movability Numbers until the final result reflected an equilibrium clear-water scour hole. Unstructured grids were generated in GAMBIT 2.2 and imported into FLUENT for the simulations. The symmetry condition was applied and the grids were fined up in regions where large velocity gradients or changes in other fluid properties were expected. Before the clear-water scour evolution simulations were carried out, the performance of the standard k-& model was compared with that of the Reynolds Stress model, and standard wall functions with non-equilibrium wall functions for a flat bed. Both turbulence models predicted similar scour patterns. Results of the numerical simulations were compared with data from a physical model and it was found that the non-equilibrium wall functions predicted scouring in regions on the bed where scour was not observed in the physical model. The standard wall functions, on the other hand, appeared to give realistic results. Since the standard k-&model involved the solution of two transport equations whilst the Reynolds stress model involved the solution of seven, the former was used with the standard wall functions for the scour hole evolution simulations. It was believed that this would result in shorter simulation times. A scour potential was defined as the difference between a computed bed Movability Number and the critical Movability Number required for sediment movement. Scour was considered to occur at those locations where the scour potential values were greater than zero and the grid nodes were displaced in response. User-defined functions were written to perform the bed modifications and ensure the integrity of the mesh as the bed geometry changed. Five physical scour experiments were simulated numerically. These physical experiments were performed as part of the research and were carried out in a 0.6lm wide tilting flume in the Hydraulics laboratory of the Civil Engineering Department at the University of Cape Town. Results from the numerical simulations were compared with those from the physical models. Using the Movability Number to model local clear-water scour in rivers. Although, the numerically estimated equilibrium scour depths were relatively close to those from the physical models, the shapes of the scour holes were not that similar. This was attributed to numerical difficulties in accurately predicting the flow field (and hence the Movability Numbers) at the bed. It was recommended that ways of improving the accuracy of the flow field prediction be found in order to accurately predict the bed Movability Numbers. In general, however, the Movability Number approach showed considerable potential for use in the prediction of local clear-water scour

Capturing the role of the co-play of land use and rainfall on water and sediment flux dynamics across different spatiotemporal scales in intensively managed landscapes

Anthropogenic activities in intensively managed landscapes (IMLs) have significantly modified material travel times and delivery, and have led to more pronounced event-based dynamics compared to undisturbed conditions. Understanding and mitigating human impacts requires the use of both field-based observations and physically-based numerical models to tease out causal relationships and feedbacks between the relevant processes across the cascade of scales, from the plot to the watershed. Unfortunately, there are no event-based numerical models capable of adequately simulating sediment fluxes across scales in IMLs, thus hampering our ability to understand and mitigate anthropogenic impacts.The goal of this study was to develop a conceptual modeling framework for IMLs that considered all the connections and interactions between terrestrial and in-stream sources on an event basis, and to use the framework to identify a characteristic scale unit (CSU) representative of sediment flux laws within the drainage network. The CSU was considered to be a scale at which local-scale variability in landscape properties ceased to have an effect on mean trends in sediment fluxes and, thus, an appropriate scale for simulating/monitoring sediment fluxes for watershed management purposes.The framework was developed and tested in the South Amana sub-watershed (SASW), IA. An upland erosion model was coupled with an instream sediment transport model to simulate material fluxes along different pathways in SASW. A sediment fingerprinting model was also utilized to constrain the predicted contributions of terrestrial and instream sources. Modeling advances made included the incorporation of a surface roughness evolution threshold, space/time variant flow resistance representations of landscape attributes, and the stochastic representation of material origins, travel times, and delivery to the watershed outlet. The developed model was validated via an extensive field campaign performed at scales ranging from the plot to the sub-watershed.The study results revealed thresholds of influence of landscape roughness attributes, and highlighted important intra-seasonal trends in source contributions driven by the co-play of land use and rainfall. A CSU for sediment fluxes and the factors affecting it were identified. Future studies must examine the CSU as dictated by the interplay between event-based and seasonal dynamics, and the implications for watershed management

Understanding saturated hydraulic conductivity under seasonal changes in climate and land use

The goal of this study was to understand better the co-play of intrinsic soil properties and extrinsic factors of climate and management in the estimation of saturated hydraulic conductivity (Ksat) in intensively managed landscapes. For this purpose, a physically-based, modeling framework was developed using hydro-pedotransfer functions (PTFs) and watershed models integrated with Geographic Information System (GIS) modules. The integrated models were then used to develop Ksat maps for the Clear Creek, Iowa watershed and the state of Iowa. Four types of saturated hydraulic conductivity were considered, namely the baseline (Kb), the bare (Kbr), the effective with no-rain (Ke-nr) and the effective (Ke) in order to evaluate how management and seasonality affect Ksat spatiotemporal variability. Kb is dictated by soil texture and bulk density, whereas Kbr, Ke-nr, and Ke are driven by extrinsic factors, which vary on an event to seasonal time scale, such as vegetation cover, land use, management practices, and precipitation. Two seasons were selected to demonstrate Ksat dynamics in the Clear Creek watershed, IA and the state of Iowa; specifically, the months of October and April that corresponded to the before harvesting and before planting conditions, respectively. Statistical analysis of the Clear Creek data showed that intrinsic soil properties incorporated in Kb do not reflect the degree of soil surface disturbance due to tillage and raindrop impact. Additionally, vegetation cover affected the infiltration rate. It was found that the use of Kbinstead of Ke in water balance studies can lead to an overestimation of the amount of water infiltrated in agricultural watersheds by a factor of two. Therefore, we suggest herein that Keis both the most dynamic and representative saturated hydraulic conductivity for intensively managed landscapes because it accounts for the contributions of land cover and management, local hydropedology and climate condition, which all affect the soil porosity and structure and hence, Ksat

Scenario Planning for Restorative Justice in Lakeland

Final project for URSP708: Community Planning Studio (Fall 2022). University of Maryland, College Park.This report begins with a discussion of the concept of restorative justice and the three themes that guided and organized our work — community infrastructure, housing and land use, and climate change adaptation and mitigation. Following this introduction of the three guiding themes, the report contains a summary of our analysis of existing conditions, including a review of different planning sectors, a brief history of Lakeland, and a summary of plans and policies that have influenced the course of Lakeland. The next section of the report is a summary of the findings of our various community engagement approaches, including recommendations for future best practices for the city and the Restorative Justice Commission as they continue this work. Finally, we present the three planning scenarios — Status Quo, Reform, and Revolutionary — that envision various alternative futures for Lakeland.City of College Par

Two-Dimensional Numerical Modeling of Flow in Physical Models of Rock Vane and Bendway Weir Configurations

While there are a wide range of design recommendations for using rock vanes and bendway weirs as streambank protection measures, no comprehensive, standard approach is currently available for design engineers to evaluate their hydraulic performance before construction. This study investigates using 2D numerical modeling as an option for predicting the hydraulic performance of rock vane and bendway weir structure designs for streambank protection. We used the Sedimentation and River Hydraulics (SRH)-2D depth-averaged numerical model to simulate flows around rock vane and bendway weir installations that were previously examined as part of a physical model study and that had water surface elevation and velocity observations. Overall, SRH-2D predicted the same general flow patterns as the physical model, but over- and underpredicted the flow velocity in some areas. These over- and underpredictions could be primarily attributed to the assumption of negligible vertical velocities. Nonetheless, the point differences between the predicted and observed velocities generally ranged from 15 to 25%, with some exceptions. The results showed that 2D numerical models could provide adequate insight into the hydraulic performance of rock vanes and bendway weirs. Accordingly, design guidance and implications of the study results are presented for design engineers

Development of a Distributed Hydrologic Model for a Region with Fragipan Soils to Study Impacts of Climate on Soil Moisture: A Case Study on the Obion River Watershed in West Tennessee

Previous land surface modeling efforts to predict and understand water budgets in the U.S. Southeast for soil water management have struggled to characterize parts of the region due to an extensive presence of fragipan soils for which current calibration approaches are not adept at handling. This study presents a physically based approach for calibrating fragipan-dominated regions based on the “effective” soil moisture capacity concept, which accounts for the dynamic perched saturation zone effects created by the low hydraulic capacities of the fragipan layers. The approach is applied to the Variable Infiltration Capacity model to develop a hydrologic model of the Obion River Watershed (ORW), TN, which has extensive fragipan coverage. Model calibration was performed using observed streamflow data, as well as evapotranspiration and soil moisture data, to ensure correct partitioning of surface and subsurface fluxes. Estimated Nash-Sutcliffe coefficients for the various sub-drainage areas within ORW were all greater than 0.65, indicating good model performance. The model results suggest that ORW has a high responsivity and high resilience. Despite forecasted temperature increases, the simulation results suggest that water budget trends in the ORW are unlikely to change significantly in the near future up to 2050 due to sufficient precipitation amounts

Understanding saturated hydraulic conductivity under seasonal changes in climate and land use

The goal of this study was to understand better the co-play of intrinsic soil properties and extrinsic factors of climate and management in the estimation of saturated hydraulic conductivity (Ksat) in intensively managed landscapes. For this purpose, a physically-based, modeling framework was developed using hydro-pedotransfer functions (PTFs) and watershed models integrated with Geographic Information System (GIS) modules. The integrated models were then used to develop Ksat maps for the Clear Creek, Iowa watershed and the state of Iowa. Four types of saturated hydraulic conductivity were considered, namely the baseline (Kb), the bare (Kbr), the effective with no-rain (Ke-nr) and the effective (Ke) in order to evaluate how management and seasonality affect Ksat spatiotemporal variability. Kb is dictated by soil texture and bulk density, whereas Kbr, Ke-nr, and Ke are driven by extrinsic factors, which vary on an event to seasonal time scale, such as vegetation cover, land use, management practices, and precipitation. Two seasons were selected to demonstrate Ksat dynamics in the Clear Creek watershed, IA and the state of Iowa; specifically, the months of October and April that corresponded to the before harvesting and before planting conditions, respectively. Statistical analysis of the Clear Creek data showed that intrinsic soil properties incorporated in Kb do not reflect the degree of soil surface disturbance due to tillage and raindrop impact. Additionally, vegetation cover affected the infiltration rate. It was found that the use of Kbinstead of Ke in water balance studies can lead to an overestimation of the amount of water infiltrated in agricultural watersheds by a factor of two. Therefore, we suggest herein that Keis both the most dynamic and representative saturated hydraulic conductivity for intensively managed landscapes because it accounts for the contributions of land cover and management, local hydropedology and climate condition, which all affect the soil porosity and structure and hence, Ksat.This article is published as Elhakeem, Mohamed, AN Thanos Papanicolaou, Christopher G. Wilson, Yi-Jia Chang, Lee Burras, Benjamin Abban, Douglas A. Wysocki, and Skye Wills. "Understanding saturated hydraulic conductivity under seasonal changes in climate and land use." Geoderma 315 (2018): 75-87. doi: 10.1016/j.geoderma.2017.11.011.</p

The Role of Hydraulic Connectivity and Management on Soil Aggregate Size and Stability in the Clear Creek Watershed, Iowa

The role of tillage practices on soil aggregate properties has been mainly addressed at the pedon scale (i.e., soilscape scale) by treating landscape elements as disconnected. However, there is observed heterogeneity in aggregate properties along flowpaths, suggesting that landscape scale hydraulic processes are also important. This study examines this supposition using field, laboratory and modeling analysis to assess aggregate size and stability along flowpaths under different management conditions: (1) tillage-induced abrasion effects on aggregate size were evaluated with the dry mean weight diameter (DMWD); (2) raindrop impact effects were evaluated with small macroaggregate stability (SMAGGSTAB) using rainfall simulators; and (3) these aggregate proxies were studied in the context of connectivity through the excess bed shear stress (&#948;), quantified using a physically-based landscape model. DMWD and SMAGGSTAB decreased along the flowpaths for all managements, and a negative correspondence between the proxies and &#948; was observed. &#948; captured roughness effects on connectivity along the flowpaths: highest connectivity was noted for parallel-ridge-till flowpaths, where &#948; ranged from 0&#8315;8.2 Pa, and lowest connectivity for contour-ridge-till flowpaths, where &#948; ranged from 0&#8315;1.1 Pa. High tillage intensity likely led to an increase in aggregate susceptibility to hydraulic forcing, reflected in the higher gradients of aggregate size and stability trendlines with respect to &#948;. Finally, a linear relationship between DMWD and SMAGGSTAB was established