Splash Erosion on Terraces, Does It Make a Difference If the Terracing Is Done before or after a Fire?

Terraces are a common Mediterranean feature influencing soils, slopes and subsurface hydrology; however, little is known about their impact on erosion processes, especially in humid regions. The purpose of this study was to assess how terracing after a fire affected erosion processes such as splash erosion. For 8 months, the study monitored splash erosion in three terraced plots, one plot under pre-fire conditions and the other two under post-fire conditions. Assessment of the impact of the terracing treatment in such plots was carried out by the installation of two different splash erosion quantitative systems: cups and funnels. An analysis of the splash data obtained in 17 rainfall events and meteorological data collected during each one of those periods was then performed. A significant positive correlation between the amount of rainfall and the splash erosion was observed. The two splash sampling systems show a high degree of concordance; however, the funnel-type model seems to be the most appropriate when it comes to preventing loss of splashed soil samples. The post-fire treatment with terracing leads to a smaller stability of surface soil aggregates, causing higher splash erosion rates. Sampling using the funnel system collects three times the amount of splashed soil than that collected by the cup system, although both systems correlate appropriately with the meteorological parameters.

Inferring Sediment Transport Capacity from Soil Microtopography Changes on a Laboratory Hillslope

In hillslope erosion modeling, the Transport Capacity (Tc) concept describes an upper limit to the flux of sediment transportable by a flow of given hydraulic characteristics. This widely used concept in process-based erosion modeling faces challenges due to scarcity of experimental data to strengthen its validity. In this paper, we test a methodology that infers the exceedance of transport capacity by concentrated flow from changes to soil surface microtopography sustained during rainfall-runoff events. Digital Elevation Models (DEMs) corresponding to pre- and post-rainfall events were used to compute elevation change maps and estimate spatially-varying flow hydraulics ω taken as the product of flow accumulation and local slope. These spatial data were used to calculate a probability of erosion PE at regular flow hydraulics intervals. The exceedance of Tc was inferred from the crossing of the PE = 0.5 line. The proposed methodology was applied to experimental data collected to study the impact of soil subsurface hydrology on soil erosion and sediment transport processes. Sustained net deposition occurred under drainage condition while PE for seepage conditions mostly stayed in the net erosion regime. Results from this study suggest pulsating erosion patterns along concentrated flow networks with intermittent increases in PE to local maxima followed by declines to local minima. These short-range erosion patterns could not be explained by current Tc-based erosion models. Nevertheless, Tc-based erosion models adequately capture observed decline in local PE maxima as ω increased. Applying the proposed approach suggests a dependence of Tc on subsurface hydrology with net deposition more likely under drainage conditions compared to seepage conditions.

Deployment, calibration, and efficiency of SHUD model in cold and arid watersheds

<p>The hydrologic model is ideal for experimenting and understanding the water movement and storage in a watershed from the upper mountain to the river outlet. Nevertheless, the model's performance, suitability, and data availability are the primary challenge for a modeler. This study introduces the Simulator for Hydrologic Unstructured Domains (SHUD), a surface-subsurface integrated hydrological model using the semi-discrete Finite Volume Method. Though the SHUD applies a fine time-step (in minutes) and flexible spatial domain decomposition (m to km) to simulate the fully coupled surface-subsurface hydrology, the model can solve the watershed-scale problem efficiently and dependably. Plenty of applications in the USA proved the SHUD model's performance and suitability in the humid and data-rich watersheds.  </p><p>In this research, we demonstrate the SHUD model deployment in two data-scarce watersheds in the northwest of China with global datasets, validate the simulations against local observational data, and assess the SHUD model's efficiency and suitability.  The one is the Upstream Heihe River (UHR), which is a typical semi-arid mountainous watershed.  The other is Yellow River Source (YRS), the upstream of Yellow River, contributing more than 50% of total discharge. The results, figures, and analysis based on SHUD simulations under global datasets highlight the model's suitability and efficiency in data-limited watersheds, even ungaged ones. The SHUD model is a useful modeling platform for hydrology and water-related coupling studies.</p>

The impacts of peat slides on upland blanket peatland hydrology, ecology and soil structure. A paired catchment approach.

<p>Rainfall-induced landslides are difficult to forecast and often evolve into highly destructive flows, as such, they are one of the most dangerous natural hazards globally. While our understanding of peatland hydrology has improved greatly in the past two decades, there has been less focus on the response of peat hydrology following perturbations such as wildfires and landslides.  Here we report on a new paired catchment experiment in Ireland. Our focus is to quantify the hydrological changes following peat landslides and further, to establish the short-term and longer-term impacts on local peatland hydrology, ecology and recovery.</p><p>The two paired sites are located in Co. Leitrim, Ireland, in two adjacent, small upland blanket bog catchments. The first peat catchment (0.2km<sup>2</sup>) is an area of a recent (June 2020) slope failure. According to preliminary estimates ~178,000 – 188,000 tonnes of peat were transported downstream during the peat slide event, resulting in a large landslide scar section (~0.059 km<sup>2</sup>) in a special area of conservation [SAC]. Preliminary impacts are assessed to include: habitat loss, decreased slope stability, impacts on hydrology and water quality, as well as increased local erosion.</p><p>This catchment is paired with an adjacent upland blanket peat catchment (0.11 km<sup>2</sup>) which is deemed to have been under the same anthropogenic pressures (grazing, upslope forestry plantation).</p><p>A hydrometric suite, including weather station, piezometers, and water level recorders to evaluate the surface and subsurface hydrology has been installed at both sites. In addition, we are monitoring the response of landslide deposits (e.g. rafted peat, some with still-standing sika spruce), ecology, soil structure, permeability and shear strength in both catchments.</p><p>Here we will report on the initial results of our monitoring.</p>

Hydrologic characterization of an alpine valley infill through integration of ERT, active seismic and active/passive surface wave interferometry (Unaweep Canyon, US)

<p>Unaweep Canyon (Western Colorado, US) is an enigmatic alpine landform and hypothesized to represent a partially exhumed paleo valley which was glacially over-deepened in the late Paleozoic. Processing and interpretation of recently acquired 2D seismic reflection and refraction data support the concept of glacial over-deepening and indicate maximum bedrock depths of about 550 meters. Additionally, pronounced reflectors are observed within the sedimentary infill. The seismic data have also been subjected to surface wave analysis revealing a significant increase of the Vp/Vs ratio below a shallow (50 – 150 m depth) intra-sedimentary reflector. A large Vp/Vs ratio can be caused by both saturation and poor consolidation of dry low-porosity materials (e.g. dry sands).</p><p>To investigate the potential occurrence of an aquifer associated with this interface, a high-density/long-offset electrical resistivity survey was conducted in fall 2019 along the seismic line. The maximum offset is 915 m at an electrode spacing of 5 meters, aiming at reaching depths of investigations between 150 and 200 meters. Inversion of the ERT data was initially conducted by means of smoothness-constrained algorithms. The imaging results revealed consistent structures with those resolved through seismic methods, at least within the required depth of investigation between 150 – 200 m. Furthermore, improvements in the resolution of the ERT imaging results was investigated after the inclusion of seismic interfaces as structural constraints in the inversion of the data. The comparison of the two approaches permitted to improve the interpretation of the ERT imaging results, which indicate low resistivities in the zone of high Vp/Vs ratios and thus strengthen the aquifer hypothesis. We present an integrated interpretation based on seismic structure, resistivity distribution, Vp and Vs velocities, and a distant well core. In a larger context, the results provide new insights on the subsurface hydrology in this arid part of the continental US as well as on the significance of multi-valued datasets for the interpretation and characterization of aquifers.   </p>