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 (SMAGG_STAB) using rainfall simulators; and (3) these aggregate proxies were studied in the context of connectivity through the excess bed shear stress (δ), quantified using a physically-based landscape model. DMWD and SMAGG_STAB decreased along the flowpaths for all managements, and a negative correspondence between the proxies and δ was observed. δ captured roughness effects on connectivity along the flowpaths: highest connectivity was noted for parallel-ridge-till flowpaths, where δ ranged from 0–8.2 Pa, and lowest connectivity for contour-ridge-till flowpaths, where δ ranged from 0–1.1 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 δ. Finally, a linear relationship between DMWD and SMAGG_STAB was established.

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.

This paper presents a system simulation technique that combines the capabilities of two defacto standard tools. The SPICE tool that accounts for electronic device characteristics is seamlessly incorporated with SIMULINK, which is a more general purpose dynamic system simulation environment. The result is a simulation technique that has the general flexibility of SIMULINK while accounting for electronic device level characteristics. The proposed technique also gives greater flexibility to the SPICE tool by simplifying the description of nonlinear circuit effects. The technique is demonstrated on a magnetic levitation system. The simultation results are in closer agreement to experimental data than the original SIMULINK model used on the project.

This paper examines the coevolutionary roles of variable flow features and heterogeneous substrates on knickpoint migration. A conceptual model is used to depict distinct migration mechanisms in a channelized headwater system of a representative intensively managed watershed in the Deep Loess Region of the U.S. Midwest. Throughout this region, entrenched streams have eroded into alluvial‐based strata that are horizontally consistent but vertically heterogeneous. Variable flow in these streams switches between vented conditions, where water shoots from the knickpoint face as an aerated plunging jet, and unvented conditions, where water clings close to its face through suction. These switches affect hydrodynamic mechanisms controlling migration but cannot explain fully observed alternating slow‐fast migration rates. It is hypothesized that vertically heterogeneous strata in entrenched streams, specifically strong‐over‐weak layers, facilitate observed changes in knickpoint migration rates. Preferential erosion of weaker sublayers is thought to trigger other erosional mechanisms to accelerate migration even at low flows. Herein, a migration “diary” documents a representative knickpoint's displacement over time with flow measurements and site stratigraphy. Slower migration occurred from 2006 to 2009 through fluvial erosion of a resistant silt loam cap. From 2009 to 2012, migration accelerated as the knickpoint face reached a critical height through scour. A flow back roller formed, which preferentially eroded a weaker sand sublayer. Undercutting/cantilever failure cycles persisted, causing 30 m of retreat within 2 months (i.e., 62.5% of the total migration over 78 months). Comparisons with established fluvial hydraulics‐based and undercutting/cantilever‐based migration models confirm the hypothesis and importance of both stratified substrates and hydrodynamic controls on knickpoint migration.