Subsurface flow can be an important process in gully erosion through its impact on decreasing soil cohesion and erosion resistance as soil water content or pressure increases and more directly by the effects of seepage forces on particle detachment and piping. The development of perched water tables fosters lateral flow that can result in seepage at the surface and/or formation of soil pipes by internal erosion of preferential flow paths. Continued internal erosion of soil pipes can lead to gullies, dam and levee failures. However, the processes involved in particle and aggregate detachment from soil pipe walls and transport processes within soil pipes have not been well studied or documented. This paper reviews the limited research on sediment detachment and transport in macropores and soil pipes and applies the knowledge learned from the much more extensive studies conducted on streams and industrial pipes to hydrogeologic conditions of soil pipes. Knowledge gaps are identified and recommendations are made for future research on sediment detachment and transport in soil pipes. Copyright © 2017 John Wiley & Sons, Ltd.

No abstract

In agricultural regions, gully erosion is now recognized as a dominant source of soil loss, and the development and upstream migration of headcuts is critical to the initiation, incision, and dissection of these upland areas. This study examined the effect of soil texture on headcut development and migration using four common soils from the southeastern United States, tested on bed surface slopes ranging from 1 to 5% and overland fl ow rates ranging from 45 to 71 L min −1 . In response to this fl ow, actively migrating headcuts developed with migration rates ranging from 0.00001 to 0.0025 m s −1 , maximum scour depths ranging from 0.042 to 0.148 m, and sediment discharge rates ranging from 0.00017 to 0.0356 kg s −1 depending on the soil and boundary conditions imposed. Nearly all experimental runs resulted in steady-state soil erosion, wherein the headcut developed attained a constant rate of migration, shape, and sediment discharge as a function of time. These experimental observations were successfully compared with predictive equations for mass conservation, jet entry angle, maximum scour depth, and migration rate developed for actively migrating headcuts in upland concentrated fl ows. These results further demonstrate that systematic headcut development can occur in a range of soils, slopes, and fl ow rates, and that modifi ed jet impingement theory can be used to predict the erosional characteristics of these headcuts, thus providing the necessary analytical framework for improving soil erosion prediction technology.

No abstract

Rill and gully erosion in upland and agricultural areas can result in signifi cant soil degradation worldwide, and headcuts are the primary mechanism by which this landscape dissection occurs. Experiments were conducted to further examine the morphodynamic behavior of actively migrating headcuts in upland concentrated fl ows with varying boundary conditions. The effect of soil texture greatly modifi ed the erodibility of the select soils, and headcut migration rates, scour depths, and sediment discharges were correlated to the critical shear stress and erodibility of the select soils. The effect of increasing tailwater height greatly reduced the nappe entry angle at the brink of the headcut, completely arresting the soil erosion processes. Altering subsurface pore-water pressures markedly changed the erodibility coeffi cients of the select soil, which caused greater headcut migration rates and sediment discharges, yet shallower scour holes, in the presence of a subsurface water table. Current analytic formulations based on jet impingement theory successfully predicted these experimental observations, further demonstrating the utility of such analytic formulations in advancing watershed management technology.

rangement and distribution of the cracks. Moreover, White (1972) explained the energy implications that The theory of water movement in high shrink/swell soils has expericause the cracks to reappear in the same position from enced consistent revision since Haines first presented the topic in 1923. Several aspects of the infiltration process in cracking soils have event to event. Johnston and Hill (1944) observed that proven to be difficult to measure; seal/crust formation and properties, cracks develop between crop rows where the water concrack network patterns, preferential flow zones and contributions, tent was higher (due to less uptake by plants) and, thus, and soil moisture determinations within the profile (near crack and the strength of the soil was lower. Since dry clay soils near center of prismatic column) to name a few. Here, we used simutend to moisten more rapidly to a greater depth along lated rainstorms, laser measurements of surface elevation, needlea crack than at a distance from a crack, cracks transmit penetrometer measurements, and mass measurements of infiltrating more water deeper under heavy precipitation events, water over a 206-and 145-d period to examine water movement and making the soil wetter in this area. cracking patterns in a large sample box filled with a swelling clay soil.

The development and evolution of gullies on soil‐mantled hillslopes can devastate agricultural regions and cause widespread soil and landscape degradation. Since 2000, international symposia have been organized to address gully erosion processes, and this paper and special issue provide additional context for the 7th International Symposium on Gully Erosion held at Purdue University in 2016. Several important themes of gully erosion emerged during this symposium that warranted additional discussion here. These topics include the importance and impact of technology transfer, disciplinary fragmentation as an impediment for research advancement, the difficulty in defining the erodibility of sediment within gullies, and the opportunities afforded by remote sensing technology. It is envisioned that such symposia will continue to enhance the capabilities of researchers and practitioners to monitor, model, and manage these important geomorphic processes and to mitigate landscape degradation. © 2018 John Wiley & Sons, Ltd.

Core Ideas Photogrammetric techniques for spatiotemporal measure of topographic data Physical data for validation and development of soil erosion modeling technology Automated analysis presentation package Rill and ephemeral gully monitoring at high spatial and temporal resolution When flowing water concentrates on hillslopes, the erosivity of the water may only be limited by the erodibility of the soil. Over time, concentrated flow paths may become permanent drainage channels, and such rills and ephemeral gullies often have negative impacts on crop yield and downstream sedimentation. Spatiotemporal topographic assessments of rill and gully dimensions compliment hydraulic erosion estimates, and they can elucidate soil erosion processes and provide data for model validation. Accurate and detailed topographic assessments, however, can be cost prohibitive. The objectives of this study are to describe and evaluate a topographic assessment method with relatively high spatial and temporal resolution, to discuss its costs and limitations, and to provide an assessment procedure for erosion characterization and data optimization. Three locations are evaluated that are pertinent to soil erosion research on the field, plot, and laboratory scale. In each setting, the sites are monumented and monitored using photogrammetric techniques. Photogrammetry is a simple, robust means to track landscape evolution and morphodynamic changes in rills and ephemeral gullies. The assessment procedure describes study site attributes at a variety of spatial and temporal scales, it is cost‐effective, workforce empowering, and reliable, and the analysis and presentation can be automated. Capturing this type of information is critical to an improved understanding of the fundamental principles necessary to enhance modeling technology to estimate erosion potential at various scales and to assess the efficacy of conservation practices.