This paper reports the results of a field investigation aiming at characterizing the morphology and hydraulics of both rills and ephemeral gullies (EGs) monitored at Sparacia experimental area, ...Sicily, Italy. The comparison between rill and interrill erosion measurements showed that sediment delivery processes occurred in some erosive events and that the rill erosion rate was dominant in many cases.
The measurements were used for testing both the empirical relationships between the channel (rill, EGs and gully) length and its eroded volume and among the morphological variables (length, width, depth and volume) describing the channelized process.
Finally, the rill and EGs hydraulic geometry was modelled by three well known power equations relating the discharge with the mean flow velocity, with the flow depth and with the width of each channel segment, respectively. The rill measurements also showed that the flow velocity was affected by the rill segment slope while the flow depth and width were controlled by the plot slope. Therefore, three equations, taking into account these slope effects, were proposed to estimate the hydraulic characteristics of the rills monitored at the Sparacia area.
► Rill and ephemeral gully erosion in Sicily, Italy. ► At event scale rill erosion is dominant in comparison with interrill erosion. ► The severity of the channelized erosion process can be estimated by channel length. ► A morphological similarity between rills and ephemeral gullies exists. ► Plot slope affects rill width and depth.
•Rill morphology evolution on 4 coarse-textured topsoils is studied by laser scanning.•Rill headward and downward erosion are two mutually reinforcing processes.•Soil erosion intensity can be ...indirectly evaluated by geomorphologic comentropy.
The sheet and rill erosion phases dominate the erosion process of the catchment area and up-slope of Benggang (a special gully) area, and its evolution has a vital impact on erosion characteristics in the erosion feedback loop. Here, the rill development processes, morphological characteristics and corresponding soil loss were investigated by laser scanning on the four coarse-textured granite topsoils defined as WH, TC, GX, and CT for the counties of Wuhua, Tongcheng, Ganxian, and Changting in China, respectively. A soil flume (3 × 0.8 m) at a slope gradient of 16.7% was treated with rainfall-inflow at the upslope inflow rate of 2 L min−1 and rainfall intensity of 90 mm h−1. Results showed that soil erosion rate increased with erosion evolution (sheet erosion, rill advance, and rill maturity phases). A comparison of the four different soils exhibited that the soil erosion rate showed a downtrend with the increase of soil clay and gravel contents. Specifically, the CT soil with high clay and gravel content showed the minimal soil erosion rate (0.024 kg m−2 min−1), rill density (0.95 m m−2), headward erosion rate (0.41 cm min−1), and surface evolution rate. The maximal soil erosion rate and rill depth were observed on the WH slope, with the rill headward erosion rate reaching the maximum of 20.59 cm min−1. Despite no significant difference in the geomorphologic comentropy of the four soils, their variation trend and rate could reflect dynamic changes in erosion. The total sediment transport efficiency was improved by rill formation and development, with rill erosion contributing to about 70% of total soil loss for the four soils. This study can enrich our understanding of the rill erosion process and surface morphology of coarse-textured topsoils.
Wildfires increased dramatically in frequency and extent in the European Mediterranean region from the 1960s, aided by a general warming and drying trend, but driven primarily by socio-economic ...changes, including rural depopulation, land abandonment and afforestation with flammable species. Published research into post-wildfire hydrology and soil erosion, beginning during the 1980s in Spain, has been followed by studies in other European Mediterranean countries together with Israel and has now attained a sufficiently large critical mass to warrant a major review. Although variations in climate, vegetation, soil, topography and fire severity cause differences in Mediterranean post-wildfire erosion, the long history of human landscape impact up to the present day is responsible for some its distinctive characteristics. This paper highlights these characteristics in reviewing wildfire impacts on hydrology, soil properties and soil erosion by water. The ‘mosaic’ nature of many Mediterranean landscapes (e.g. an intricate land-use pattern, abandoned terraces and tracks interrupting slopes) may explain sometimes conflicting post-fire hydrological and erosional responses at different sites and spatial scales. First-year post-wildfire soil losses at point- (average, 45–56
t
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in the first year) are similar to or even lower than those reported for fire-affected land elsewhere or other disturbed (e.g. cultivated) and natural poorly-vegetated (e.g. badlands, rangeland) land in the Mediterranean. The few published losses at larger-scales (hillslope and catchment) are variable. Thin soil and high stone content can explain supply-limited erosion preceding significant protection by recovering vegetation. Peak erosion can sometimes be delayed for years, largely through slow vegetation recovery and temporal variability of erosive storms. Preferential removal of organic matter and nutrients in the commonly thin, degraded soils is arguably just as if not more important than the total soil loss. Aspect is important, with more erosion reported for south- than north-facing slopes, which is attributed to greater fire frequency, slower vegetation recovery on the former and with soil characteristics more prone to erosion (e.g. lower aggregate stability). Post-fire wind erosion is a potentially important but largely neglected process. Gauging the degradational significance of wildfires has relied on comparison with unburnt land, but the focus for comparison should be switched to other agents of soil disturbance and/or currently poorly understood soil renewal rates. Human impact on land use and vegetation may alter expected effects (increased fire activity and post-wildfire erosion) arising from future climatic change. Different future wildfire mitigation responses and likely erosional consequences are outlined. Research gaps are identified, and more research effort is suggested to: (1) improve assessment of post-wildfire erosion impact on soil fertility, through further quantification of soil nutrient depletion resulting from single and multiple fire cycles, and on soil longevity; (2) investigate prescribed fire impacts on carbon release, air pollution and nutrient losses as well as on soil loss; (3) isolate hillslope- and catchment-scale impacts of soil water repellency under Mediterranean post-wildfire conditions; (4) test and refine application of cosmogenic radionuclides to post-wildfire hillslope-scale soil redistribution at different temporal scales; (5) use better temporal resolution of sedimentary sequences to understand palaeofire-erosion–sedimentation links; (6) quantify post-wildfire wind erosion; (7) improve the integration of wildfire into an overall assessment of the processes and impacts of land degradation in the Mediterranean; and (8) raise public awareness of wildfire impact on soil degradation.
This study challenges the paradigm that salt marsh plants prevent lateral wave-induced erosion along wetland edges by binding soil with live roots and clarifies the role of vegetation in protecting ...the coast. In both laboratory flume studies and controlled field experiments, we show that common salt marsh plants do not significantly mitigate the total amount of erosion along a wetland edge. We found that the soil type is the primary variable that influences the lateral erosion rate and although plants do not directly reduce wetland edge erosion, they may do so indirectly via modification of soil parameters. We conclude that coastal vegetation is best-suited to modify and control sedimentary dynamics in response to gradual phenomena like sea-level rise or tidal forces, but is less well-suited to resist punctuated disturbances at the seaward margin of salt marshes, specifically breaking waves.
Many embankment dams constructed with a core of nonplastic or very low plasticity silt–sand–gravel (typically of glacial, fluvioglacial or alluvial origin) have experienced internal erosion. This has ...often expressed itself with the development of sinkholes or with intermittent episodes of increased leakage, which then reduces. In this investigation 22 soil samples with gradations representing the range of the soils used in embankment dam cores have been tested in the laboratory. All 22 soils tested were shown to be internally unstable with particle movement within the soil after placement. Some soils exhibited global backward erosion (GBE), others suffusion, and some internal instability but with no erosion from the sample, indicating self-filtering. The internal erosion process was very rapid for suffusive soils, typically occurring within minutes of test commencement, and at a gradient of 1. For soils subject to GBE and no-erosion soils, the internal movement of particles continued for weeks and months, and re-activated when the overall gradient was increased. For GBE, the erosion process occurred over a range of gradients. A method for predicting the amount of erosion and the erosion mechanism based on the gradation of the soil has been developed that is related to the ability of the soil to self-filter.
Burrowing into riverbanks by animals transfers sediment directly into river channels and has been hypothesised to accelerate bank erosion and promote mass failure. A field monitoring study on two UK ...rivers invaded by signal crayfish (Pacifastacus leniusculus) assessed the impact of burrowing on bank erosion processes. Erosion pins were installed in 17 riverbanks across a gradient of crayfish burrow densities and monitored for 22 months. Bank retreat increased significantly with crayfish burrow density. At the bank scale (<6 m river length), high crayfish burrow densities were associated with accelerated bank retreat of up to 253% and more than a doubling of the area of bank collapse compared with banks without burrows. Direct sediment supply by burrowing activity contributed 0.2% and 0.6% of total sediment at the reach (1.1 km) and local bank (<6 m) scales. However, accelerated bank retreat caused by burrows contributed 12.2% and 29.8% of the total sediment supply at the reach and bank scales. Together, burrowing and the associated acceleration of retreat and collapse supplied an additional 25.4 t km−1 a−1 of floodplain sediments at one site, demonstrating the substantial impact that signal crayfish can have on fine sediment supply. For the first time, an empirical relation linking animal burrow characteristics to riverbank retreat is presented. The study adds to a small number of sediment budget studies that compare sediment fluxes driven by biotic and abiotic energy but is unique in isolating and measuring the substantial interactive effect of the acceleration of abiotic bank erosion facilitated by biotic activity. Biotic energy expended through burrowing represents an energy surcharge to the river system that can augment sediment erosion by geophysical mechanisms.
Riverbank burrowing by animals supplies sediment directly into river systems and has been hypothesised to increase bank erosion and promote mass failure. This field study of two rivers invaded by signal crayfish examines the rates and mechanisms of bank retreat under increasing densities of crayfish burrows and quantifies a sediment budget that partitions biotic, abiotic and interactive processes in driving fine sediment recruitment to river systems.
Soil erosion is expected to be affected by climate change. Climate changes in temperature and precipitation patterns will impact plant biomass production, infiltration rate, soil moisture, land use ...and crop management, and hence affect runoff and soil erosion. Close links between climate change and soil erosion have been observed in the past decades. This paper reviews the achievements regarding the impacts of climate change such as changed rainfall, vegetation cover, and land management on water erosion. More climate change models with climate scenarios and land use models should be coupled with hydrologic/erosion models to accurately predict climate change impacts. Soil erosion is expected to be affected adversely under future climate change in most case studies, although direct and indirect impacts can promote or suppress soil erosion. However, uncertainties are still involved with respect to specific influencing mechanisms and actual damages, and the impacts vary with different regions. The representation of extreme climate events should be improved in climate models. Relevant erosion processes including rill erosion, gully erosion or channel erosion need to be incorporated and differentiated in erosion models. Additionally, more research is needed to explore the impacts of crop management practices on soil erosion under future climate change. This review is intended to introduce the achievements and to point out the critical research needs to better understand and predict the responses of soil erosion to a changing climate in the future.
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