SSS2.7

Predicting ephemeral gully (EG) location is essential for erosion modeling because it helps confine portions of the hillslope segment above locations that gully and channel soil loss processes dominate. In the Water Erosion Prediction Project (WEPP), the prediction of EG occurrence location influences the model results by shorting or expanding the flow path, which the hillslope erosion modeling relies on. This research aimed to analyze the sensitivity of EG locations prediction accuracy on WEPP model output within the framework of the Daily Erosion Project (DEP) at the regional scale. DEP is a near real-time estimator of precipitation, soil detachment, hillslope soil loss, and water runoff using WEPP as the erosion model. The above estimations are conducted on randomly selected and spatially distributed flowpaths, and the means are reported at the HUC12 watershed level. The flowpaths are identified based on Digital Elevation Model (DEM) grid cell and D8 connectivity to adjacent cells. A flow path starts at a cell such that all adjacent cells are at a lower elevation, that is, no other adjacent cell directs flow into it and ends when sufficient flow concentration and soil conditions occur that channel erosion processes dominate soil loss where usually EGs occurrence. In this research, the DEP flowpaths, down to and including ephemeral gully heads, were surveyed in 8 HUC12 watersheds distributed in 8 different Iowa MLRAs using high-resolution imagery in-field measurement. A grid order model was used as a method for EG location prediction. The sensitivity of accuracy of EG location prediction on WEPP/DEP soil detachment, hillslope soil loss, and water runoff model output was explored at hillslope, watershed, and regional spatial scale with both extreme rainfall events and yearly average erosion modeling. This research will allow a more clear understanding of EG prediction influence on erosion modeling and help improve the accuracy of erosion modeling by using WEPP / DEP.

How to cite: Wang, C., Cruse, R., Brian, G., Daryl, H., Kelly, T., and David, J.: Influence of Ephemeral Gully Location Prediction on Soil Erosion Estimation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1478, https://doi.org/10.5194/egusphere-egu21-1478, 2021.

The spreading use of remote techniques is in our daily life benefits to ease and/or speed up the acquisition and analysis of geographical data that can be meaningful for risk assessment or for taking decisions for prevention measures.

Here is presented one of the possible applications for the Unmanned Aerial Vehicle (UAV) acquisition, to evaluate the volume of eroded soils in a crop field due to washout after heavy rains. The case study is located North of Lausanne (Switzerland), in the village of Savigny. It is a crop field with a gentle slope where we can clearly see washout gullies appearing after rainfalls. A great number of small water streams disappeared for more intense agriculture which is the case here : According to topographical maps, a small stream was flowing in the past but disappeared  after 2004. It is interesting to see that after important rainfalls, gullies appear that could correspond to old small stream patterns. 

The data acquisition survey of October 30th, 2020 was done by means of a DJI Phantom 4 RTK flying at an altitude of about 20m and the Pix4d Capture planning mission application. To process the obtained 800 images, the new Pix4D Matic software was tested to get a fast dense point cloud with GSD ~1 cm accuracy, a DEM and an orthophoto. The dense point cloud was then analyzed with two compared methods to estimate the washout volumes, which are (1) inverse Sloping Local Base Level; and (2) Point cloud segmentation based on normal vectors and curvatures.

As a result, these two methods gave a first estimation of the eroded volume of around 15m3 over a surface of 9 hectares which corresponds to an erosion rate of 1,7m3/hectare. These remote and non-destructive techniques are fast and easy compared to conventional field surveys, and the data acquisition and processing could be automated. In conclusion, these techniques provide a relatively low-cost time-series datasets processing to monitor and quantify the ongoing gully erosion. 

Further investigation would be to keep recording the volume and erosion rate estimations after important rainfalls, when clear new gullies appear and to record in the meanwhile the rainfall intensity. This could help assess in a second step the relationship between the erosion rate and the rainfall intensity and control if this relation follows a power-law function. Such a study could also give some clues about the possible impact of climate changes on erosions in crop fields. 

How to cite: Charlotte, W., Tiggi, C., Marc-Henri, D., Li, F., and Michel, J.: Quantification of erosion rate in crop field gullies from point clouds with two different methods  : the case study of Savigny crop field (North of Lausanne, Switzerland), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2613, https://doi.org/10.5194/egusphere-egu21-2613, 2021.

Soil erosion is an important threat in the high-quality development of the Loess Plateau of China, and Ephemeral Gully (EG) erosion is an important erosion type. Answering the distribution characteristics of EG at the regional scale is an important basis for EG control. The regional distribution of EG and the areas that still at high risk of EG development after the 'Grain for Green Project' since more than 20 years ago remain poorly understood. This study aimed to solve the above problems by using visual interpretation based on sub-meter Google Earth images in 137 systematically selected small watersheds in the Loess Plateau. The EG density, length, land use of the hillslope where each EG existed, and other parameters were obtained and analyzed using the GIS method. The spatial distribution of EG density, average length, and spatial correlation in the Loess Plateau was explored. The current EG distribution and key prevention areas in the Loess Plateau were identified. The results showed that: (1) EGs were found in 46 surveyed watersheds accounting for 33.6% of the total watershed number, with an EG density average value of 3.41km/km² and maximum value of 21.92 km/km². The average number of EG was 60.32/km². EG length was mainly distributed in 20 ~ 60 m, with an average length of 63.31 m; The critical slope length of EGs was mainly 40 ~ 60 m, with an average 56.20 m. (2) The watersheds with EGs were mainly located in the north-central, the west, and northwest of the Loess Plateau. EG erosion is extremely strong in loess hilly and gully region, and moderate in loess plateau gully region.(3) 38.3% of EG was distributed in cropland; 35.3% distributed in grassland; 22.8% distributed in forest land. After the 'Grain for Green Project', the EGs that were still distributed on cropland were a more important threat to soil erosion and need better prevention efforts. EGs located on cropland were still widely distributed in many areas of Loess Plateau, such as the northwest of Yan 'an City in the middle and upper reaches of Beiluo River, Suide and Luliang in the lower reaches of Wuding River, at the junction of Dingxi and Huining and in Qingyang area. This research would help in a more reasonable distribution of erosion control practices in the Loess Plateau.

How to cite: Zhong, Y., Wang, C., Pang, G., Yang, Q., Guo, Z., Liu, X., and Su, J.: Spatial Distribution and Key Prevention Areas of Ephemeral Gully under the 'Grain for Green Project' in Loess Plateau, China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3676, https://doi.org/10.5194/egusphere-egu21-3676, 2021.

Gully rehabilitation is often applied as part of catchment management aimed at reducing downstream sediment yields, yet the observed responses globally are variable. In the semi-arid tropics, there is limited data available to evaluate the performance of individual rehabilitation measures. This study investigated the effects of several low-cost gully rehabilitation strategies on sediment yields and vegetation establishment, in a savanna rangeland, north-east Queensland, Australia, over an eight-year period. Four gullies were monitored as untreated control gullies. Two gullies were subject to treatments aimed at: (i) reducing runoff to gully head cuts; (ii) increasing sediment trapping on gully floors; and (iii) increasing vegetation cover on gully walls and floors. Vegetation was monitored in nine gullies under long-term grazing exclosure as an additional reference to measure vegetation recovery. A runoff diversion structure reduced headcut erosion from 4.3 m² y^-1 to 1.2 m² y^-1. Total sediment yields were substantially lower in gullies treated with small porous check dams and cattle exclusion fencing, with mean total sediment yields reduced by 0.3-2.4 t ha y^-1. These treatments, however, had negligible effect on gully fine sediment (silt and clay) yields. While sediment deposited behind porous check dams was found to contain much less fine silt and clay than parent material, it contained several times that measured in untreated gullies. Organic matter and fine material deposited behind porous check dams were sufficient to trap seeds and initiate vegetation re-establishment on the gully floor, including native perennial tussock grasses and woody trees and shrubs. In this water-limited landscape, long-term rehabilitation will be strongly influenced by prevailing climatic conditions, with periods of recovery following wetter periods, and regression during extended dry periods. Understanding linkages between rehabilitation measures, their hydrologic, hydraulic and vegetation effects and gully sediment yields is important to defining the conditions for their success.

How to cite: Koci, J., Wilkinson, S., Hawdon, A., Kinsey-Henderson, A., Bartley, R., and Goodwin, N.: Effects of low-cost rehabilitation measures on gully sediment yields and vegetation in a savanna rangeland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3742, https://doi.org/10.5194/egusphere-egu21-3742, 2021.

Soil erosion by water is a frequent soil degradation process in rangelands of SW Spain. The two main erosive processes in these areas are sheetwash erosion in hillslopes and gully erosion due to concentrated flow in valley bottoms. Land use changes and overgrazing play a key role in the genesis and development of gullies and gully erosion is a frequent process with negative consequences at the valley bottoms of these landscapes.

The development of new techniques allows monitoring of gully dynamics with an increase at spatial and temporal resolutions. Here we present a detailed study of a valley-bottom gully in a Mediterranean rangeland with a savannah-like vegetation cover that was partially restored in February 2017. Restoration activities included check dams (gabion weirs and fascines) and livestock exclosure by fencing. The objectives of this study were: (1) to analyze the effectiveness of the restoration measures, (2) to study erosion and deposition dynamics before and after the restoration activities, (3) to examine the role of micro-morphology on the observed topographic changes and (4) to compare the current and recent channel dynamics with previous studies conducted in the same study area through different methods and spatio-temporal scales, quantifying medium-term changes. Topographic changes were estimated using multi-temporal high-resolution DEMs produced using Structure-from-Motion (SfM) photogrammetry and aerial images acquired by a fixed-wing Unmanned Aerial Vehicle (UAV). DEMs and orthophotographs with a Ground Sampling Distance of 0.02 m were produced by means of SfM photogrammetric techniques. The average Root Mean Square Error (RMSE) estimated during the SfM processing was 0.03 m.

The performance of the restoration activities was satisfactory to control gully erosion. Check dams were effective favoring sediment deposition and reducing lateral bank erosion. Nevertheless, erosion was observed immediately downstream in 9% of the check dams. Livestock exclosure in the most degraded area promoted the stabilization of bank headcuts and revegetation. The sediments retained behind check dams reduced the longitudinal slope gradient of the channel bed and established a positive feedback mechanism for channel revegetation.

Keywords: gully erosion, restoration, topographic change, UAV+SfM, rangeland.

How to cite: Alfonso-Torreño, A., Gómez-Gutiérrez, Á., and Schnabel, S.: Spatio-temporal dynamics of erosion and deposition in a partially restored valley-bottom gully, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6378, https://doi.org/10.5194/egusphere-egu21-6378, 2021.

Lake Abaya and Lake Chamo are located within the rift valley that cuts across eastern Ethiopia. Severe soil erosion, predominantly gully erosion in the midlands and highlands, and flash flooding along rivers in the lowlands resulted in sediment and nutrient accumulation in the rift lakes. In this study, conducted in four river catchments on the Western border of the Abaya-Chamo rift, an inventory of gully channels is made and factors controlling the location of gullies are analysed. The inventory, which was prepared using Google Earth imagery and field surveys, consists of 7336 gullies over a study area of 1050 km², resulting in a high average gully density (1.56 km.km^-²) with specifically high densities (3.74 km.km^-²)  in the Northern Shafé river catchment. Of all mapped gullies, 56% show signs of active erosion (i.e. mostly bare gully walls and bed, and/or fresh sediments deposited in the lower parts of the gully). In order to reduce the effects of gully erosion, it is vital to understand the factors controlling gully initiation and locations most susceptible to develop new gullies. Instead of using gully head, which due to head cut retreat might not be representative of the characteristics of the gully initiation point, a slope-area threshold (SA) is used to identify the most probable gully initiation point along existing gullies. The spatial susceptibility of these sites to gully initiation is then modelled using the frequency ratio and logistic regression methods using a set of 15 geo-environmental variables related to topography, soil texture, geology, rivers, knickpoints and land cover, as potential controlling factors. Active and inactive gullies are modelled separately. Slope, type of lithology, location of knickpoint rejuvenating the landscape through channel incision, distance from roads and mean annual rainfall are identified as very important controlling factors of gully initiation sites. The most susceptible gully erosion areas are observed in the steep midland, where limited population is living, and bare land and rangeland is dominant. The results show that the models are reliable and have a good prediction performance of gully initiation when using an independent validation dataset. The produced gully susceptibility maps highlight locations where soil and water conservation or other sustainable planning actions are required. Such maps are also needed to estimate the long-term contribution of gullies to the sediments delivered to the Abaya-Chamo Lakes.

How to cite: Belayneh, L., Dewitte, O., Gulie, G., Poesen, J., and Kervyn, M.: Spatial modelling of gully initiation in the Abaya-Chamo lakes catchments, southern Ethiopia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13060, https://doi.org/10.5194/egusphere-egu21-13060, 2021.

Land degradation is a global concern posing significant threat to sustainable development. One of its major aspects is soil erosion, which is recognised as one of the critical geomorphic processes controlling sediment budget and landscape evolution. Natural rate of soil erosion is exacerbated due to anthropogenic activities that may lead to soil infertility. Therefore, assessment of soil erosion at basin scale is needed to understand its spatial pattern so as to effectively plan for soil conservation. This study focuses on Parbati river basin, a major north flowing cratonic river and a tributary of river Chambal to identify erosion prone areas using RUSLE model. Soil erodibility (K), Rainfall erosivity (R), and Topographic (LS) factors were derived from National Bureau of Soil Survey and Land Use Planning, Nagpur (NBSS-LUP) soil maps, India Meteorological Department (IMD) datasets, and SRTM30m DEM, respectively in GIS environment. The crop management (C) and support practice (P) factors were calculated by assigning appropriate values to Land use /land cover (LULC) classes derived by random forest based supervised classification of Sentinel-2 level-1C satellite remote sensing data in Google Earth Engine platform. High and very high soil erosion were observed in NE and NW parts of the basin, respectively, which may be attributed to the presence of barren land, fallow areas and rugged topography. The result reveals that annual rate of soil loss for the Parbati river basin is ~319 tons/ha/yr (with the mean of 1.2 tons/ha/yr). Lowest rate of soil loss (i.e. ~36 tons/ha/yr with mean of 0.22 tons/ha/yr) has been observed in the open forest class whereas highest rate of soil loss (i.e. ~316 tons/ha/yr with mean of 32.08 tons/ha/yr) have been observed in gullied area class. The study indicates that gullied areas are contributing most to the high soil erosion rate in the basin. Further, the rate of soil loss in the gullied areas is much higher than the permissible value of 4.5–11 tons/ha/yr recognized for India. The study helps in understanding spatial pattern of soil loss in the study area and is therefore useful in identifying and prioritising erosion prone areas so as to plan for their conservation.

How to cite: Kumar, R., Deshmukh, B., and Sathunuri, K.: RUSLE Model based Assessment of Soil Erosion in Parbati River Basin, Central India using Google Earth Engine and GIS, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1524, https://doi.org/10.5194/egusphere-egu21-1524, 2021.

【Objective】Rock fragments (>2mm diameter) are an important component of soil, and its presence has a significant impact on soil erosion and sediment yield. So it is essential to take into full account content of the rock fragments for accurate calculation of soil erodibility factor (K). 【Method】In this paper, based on the data available of the content of rock fragments and classes of soil texture with a resolution of 30 arc-second, influence of the content of rock fragments, including rock fragments in the soil profile (RFP) and gravels on the surface of the soil (SC), on K was assessed at a global scale, using the equation (Brakensiek, 1986) of the relationship between saturated hydraulic conductivity and grade of soil permeability, and the equation (Poesen) of soil erodibility attenuation under a rock fragment cover. 【Result】Results show: (1) The existence of rock fragments in the soil increased K by 4.43% and soil permeability by 5.68% on average in grade and lowering soil saturated hydraulic conductivity by 11.57% by reducing water infiltration rate of the soil and increasing surface runoff. The gravels on the surface of the mountain land and desert/gobi reduced K by 18.7% by protecting the soil from splashing of rain drops and scrubbing of runoff; so once the content of rock fragments in the soil profile and gravels on the surface of the land are taken into account in calculation, soil K may be 5.52% lower; (2)In the areas dominated with the effect of rock fragments, about 62.7% of the global land area, soil K decreased by 0.0091( t•hm²•h)•( hm^-2•MJ^-1•mm^-1) on average, while in the area affected mainly by rock fragments in profile, about 31.1% of the global land area, soil K increased by 0.0019( t•hm²•h)•( hm^-2•MJ^-1•mm^-1); and (3)The joint effect of rock fragments in profile and gravels on the surface reduced the soil erosion rate by 11.8% in the 6 sample areas. 【Conclusion】 The presence of RFP increases soil K while the presence of SC does reversely. The joint effect of the two leads to decrease in soil erosion. In plotting regional soil erosion maps, it is essential to take both of the two into account so as to improve accuracy of the mapping.

How to cite: Yang, M., Yang, Q., Zhang, K., Li, Y., Wang, C., and Pang, G.: Effects of Content of Soil Rock Fragments on Calculating of Soil Erodibility, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1976, https://doi.org/10.5194/egusphere-egu21-1976, 2021.

Steep-slope agricultural landscapes often show a mosaic of diverse terraced and non-terraced hillslope configurations. The use and specific design of Soil and Water Conservation (SWC) measures such as earth bank or dry-stone wall terraces is often the result of agro-landscape evolution, and is shaped by various factors such as culture-historical values (e.g. traditional cultivation methods), agronomic development (e.g. mechanisation), site-specific conditions (e.g. local rainfall regime and construction materials), as well as environmental concerns (e.g. runoff and erosion control). Concerning the latter, the effectiveness of SWC measures is becoming increasingly urgent in the face of climate change expressed as extreme rainfall interspersed with drought periods, as commonly found in Mediterranean Europe.

While past research has provided unique insights in the impact of several terracing practices on runoff and erosion control (doi.org/10.1016/j.catena.2020.104604), this mostly focussed on descriptive analysis of detailed soil degradation patterns in a limited number of study areas. In this study, we expand this research by a comprehensive and massive evaluation of 50 vineyards cultivated by 5 different terracing and non-terracing techniques in the cultural landscape of Soave, northern Italy. This provides a grand comparison of SWC impacts based on a systematic workflow of high-resolution topographic analysis, physical erosion modelling, and statistical evaluation. Analysis is performed on a preselected set of 50 representative vineyards (10 sites for each practice) with homogeneous soil type and properties, geometric shape and size, slope positioning and steepness (calculated from 1-m LiDAR data). A set of SWC indicators is determined (e.g. average rates of soil erosion, deposition, and runoff), and are computed for each vineyard using spatially-distributed physical simulations by the Simulated Water Erosion (SIMWE) model. Simulated processes are quantified by zonal statistics, while differentiating between potential detachment and deposition hotspots (i.e. pre-determined uphill and downhill zones inside each vineyard). This allows a first indication of SWC impacts by the different hillslope configurations. Furthermore, we provide a comparison of the actual cultivated study sites and an assumed “natural scenario” (i.e. smoothed terrain, natural vegetation), in order to quantify the impacts of the 5 different terrace configurations on SWC.

Our findings provide relevant insights in the SWC effectiveness of terraced and non-terraced cultivation practices commonly found in the steep-slope agricultural landscapes of Italy. The unique experimental scale of our systematic comparison offers reliable and novel findings, which support sustainable landscape planning and management, e.g. as in our case by rural development plan Soilution System “Innovative solutions for soil erosion risk mitigation and better management of vineyards in hilly and mountain landscapes” (www.soilutionsystem.com). Future research along the same lines are encouraged in order to improve the general understanding of SWC in steep cultivation systems across diverse geographical settings.

How to cite: Pijl, A., Straffelini, E., Wang, W., and Tarolli, P.: A grand comparison of soil & water conservation in 50 vineyards under 5 different terracing systems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2272, https://doi.org/10.5194/egusphere-egu21-2272, 2021.

The impact of climate change on future soil loss is commonly assessed with soil erosion models, which are potentially an important source of uncertainty. Here we propose a soil erosion model ensemble, with the aim to reduce the model uncertainty in climate change impact assessments. The model ensemble consisted of five continuous process-based soil erosion models that run at a daily time step, i.e. DHSVM, HSPF, INCA, MMF and SHETRAN. All models simulate detachment by raindrop impact (interrill erosion), detachment by runoff (rill erosion) and immediate deposition of sediment within the cell of its origin. The models were implemented in the SPHY hydrological model. The soil erosion model ensemble was applied in a semi-arid catchment in the southeast of Spain. We applied three future climate scenarios based on global mean temperature rise (+1.5, +2 and +3 ºC). Data from two contrasting regional climate models were used to assess how an increase and a decrease in extreme precipitation affect model uncertainty. Soil loss is projected to increase and decrease under climate change, mostly reflecting the change in extreme precipitation. Model uncertainty is found to increase with increasing slope, extreme precipitation and runoff, which reveals some inherent differences in model assumptions among the five models. Moreover, the model uncertainty increases in all climate change scenarios, independent on the projected change in annual precipitation and extreme precipitation. This supports the importance to consider model uncertainty through model ensembles of climate, hydrology, and soil erosion in climate change impact assessments.

This research was funded by ERDF/Spanish Ministry of Science, Innovation and Universities - State Research Agency (AEI) /Project CGL2017-84625-C2-1-R; State Program for Research, Development and Innovation Focused on the Challenges of Society.

How to cite: Eekhout, J., Millares-Valenzuela, A., Martínez-Salvador, A., García-Lorenzo, R., Pérez-Cutillas, P., Conesa-García, C., and de Vente, J.: A process-based soil erosion model ensemble to reduce model uncertainty in climate change impact assessments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2464, https://doi.org/10.5194/egusphere-egu21-2464, 2021.

Gully erosion is an important land degradation process, threatening soil and water resources worldwide. However, in contrast to sheet and rill erosion, our ability to simulate and predict gully erosion remains limited, especially at the continental scale. Nevertheless, such models are essential for the development of suitable land management strategies, but also to better quantify the role of gully erosion in continental sediment budgets. We aim to bridge this gap by developing a first spatially explicit and process-oriented model that simulates average gully erosion rates at the continental scale of Africa.

We are developing a model that predicts the likelihood of gully head occurrence by means of the Curve Number (CN) method. This model will allow to simulate the spatial patterns of gully density at high resolution (30m) based on the physical principles that control the gully erosion process by using GIS and spatial data sources that are available at the continental scale. To calibrate and validate this model, we make use of an extensive database of 44 000 gully heads mapped over 1680 sites that are randomly distributed across Africa. The exact location of all gully heads was manually mapped by trained experts, using high resolution optical imagery available in Google Earth. This allows to extract very detailed information at the level of the gully head, such as the local slope and the area draining to the gully.

Based on an explorative analysis on a subset of this dataset we found that the CN method does not directly allow to make reliable predictions on gully head occurrence within a pixel. Although land use and land cover seem to play an important role (with gully heads being clearly located in erosion-prone land use classes), the hydrological soil groups (HSGs) based on soil texture do not provide a clear relation between soils with high runoff risk and gully occurrence. A potential cause for this is likely that compensating soil effects occur: i.e. HSGs that produce low runoff volumes may be characterized by a lower soil cohesion, making them nonetheless prone to gullying. This may then cause the combination of HSG and land use to be an insignificant predictor of gully occurrence. Also uncertainties on the input data likely play an important role in this.

Overall, our results indicate that modelling gully densities using a process-oriented and spatially explicit method offers opportunities to better quantify this important land degradation process at the global scale. Nevertheless, a key challenge lies in accurately quantifying the importance of soil characteristics and especially in better understanding their relative contribution to runoff production and soil cohesion.

How to cite: De Geeter, S., Vanmaercke, M., Verstraeten, G., and Poesen, J.: Can we use the Curve Number approach to predict gully head occurrence at the continental scale of Africa?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2666, https://doi.org/10.5194/egusphere-egu21-2666, 2021.

In the Mediterranean semi-arid environment (e.g., in Southern Italy and Spain), headwaters are characterized by local factors, such as steep slopes, low drainage areas and heavy and short-duration rainstorms, which make the torrents prone to flash floods, soil erosion and landslides. The construction of check dams has contributed to mitigate the runoff and erosion rates, but the effectiveness of these structures has been rarely assessed. In these contexts, the availability of studies monitoring the mitigation effect of check dams on the hydrological response of torrents at the watershed scale over a long time could help developing new management strategies. To this aim, this study proposes an assessment of the multi-decadal runoff and erosion rates in two headwaters of torrents in Southern Italy, using a modeling approach. The first torrent (Vacale, 12.5 sq. km) is regulated by check dams built in ‘1950-1960, while the second torrent (Serra, 13.7 sq. km) is not regulated. Both catchments experienced an increase in forest cover up to the 70%, while the agricultural land decreased by about 30% of the total area after the construction of the control works until now. The hydrological response of the two headwaters has been simulated using the widely applied Hydrologic Modeling System (HEC-HMS) model for runoff and peak flow, coupled with the Modified Universal Soil Loss Equation (MUSLE) to model sediment yield. To this purpose, 10 heavy rainfall-runoff events occurred between 1956 and 1971 were modeled. The peak flows and sediment yields of the regulated watershed were compared with the corresponding simulations at the undisturbed torrent. To summarize the results of this modeling experience, the changes in land cover resulted in a noticeable decrease in flood peak discharge (on average -53%) in both torrents, while the torrent with check dams showed a significant reduction of eroded sediment for each event (on average -9%) compared to the unregulated headwater. These findings help supporting a better understanding on the impact of control works and land use changes on the hydrological responses of Mediterranean torrents, indicating the most effective strategy to mitigate flash flood hazards and heavy erosion risks in similar environmental contexts.

Acknowledgement: This research was funded by ERDF/Spanish Ministry of Science, Innovation and Universities-State Research Agency (AEI) /Project CGL2017-84625-C2-1-R; State Program for Research, Development and Innovation Focused on the Challenges of Society.

How to cite: Bombino, G., D'Agostino, D., Denisi, P., Labate, A., Perez Cutillas, P., Martinez Salvador, A., Zema, D. A., Zimbone, S. M., and Conesa Garcia, C.: Comparing the hydrological response of regulated vs. not regulated mountain torrents in the Mediterranean semi-arid environment: a case study in Southern Italy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2707, https://doi.org/10.5194/egusphere-egu21-2707, 2021.

Rainfall-induced shallow landslides characterize most of the geomorphological phenomena occurred in Liguria (North West Italy) in the last decades: high frequency is observed between the beginning of October and the end of April, reasonably correlated with the seasonal rainfall regime.Over the years, in national and international scientific papers, the thickness of the debris cover, the poor geotechnical characteristics of the soil, the sparse forest and shrub areas, the runoff water erosion along the slope surface were identified as landslide causal factors.However, an aspect that does not seem to be considered in Liguria Region is the causal relationship between wildfires and surface landslides.The wildfire determines a series of physical and chemical changes on the slope surface, first of all the wood and shrub cover reduction. The rapid change in land use determines an increase in the run-off and a consequent soil erosion evolving into landslides.This research aims to create a first basic statistics at regional scale among landslides and wildfire, crossing different databases and inventories, estimating a trend line both in the spatial and in the temporal domain.

How to cite: Terrone, M., Faccini, F., Paliaga, G., and Solimano, M.: Wildfire and shallows landslides: a first statistical description in Liguria (North-West Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3149, https://doi.org/10.5194/egusphere-egu21-3149, 2021.

Gully erosion is one of the most important erosion gully types in the Loess Plateau. Its generation and development seriously affect and destroy the ecological environment. Therefore, it is the premise of scientific management to make clear the spatial distribution of gully region scale. At present, scholars at home and abroad mainly focus on the spatial distribution of gully in a specific small watershed, and there are few reports on the regional scale. In view of this, this study, based on Google Earth sub meter image combined with GIS method, uses the means of manual visual interpretation to conduct sampling survey of gully in the Loess Plateau. A total of 137 sampling units were set up, and the area of each sampling unit was about 0.2 square kilometers. The results showed that: (1) there were 75 gullies in 54.7% of the survey units, with a total of 712 gullies. The sampling units with gullies were mainly located in the northeast of the Loess Plateau (yan'an-dongsheng area on both sides of the Shanxi Shaanxi Yellow River) and the middle of the Loess Plateau (the border area of Guyuan, Ningxia and Huining, Dingxi, Gansu), with an average gulley density of 3.32km/km² and a maximum of 19.94km/km²; (2) the grassland was the most gullied area The main land use types of gully development accounted for 40.03%, followed by cultivated land and forest land, accounting for 30.06% and 20.08% respectively, and 9.83% of gully development was in bare land, orchard and residential land, collectively referred to as other land; (3) the average values of gully width, length and distance from watershed were 7.76m, 69.81m and 79.19m, respectively, and the gully width was mainly distributed in 3-5M, accounting for 50% 39.6％。 The length of gully was mainly distributed in 30-70m, accounting for 46.3%. The distance between  and watershed was mainly 25-50m, accounting for 41.6%; (4)  existed most in sub region I of Loess Plateau (22.7%), followed by sub region III of Loess Plateau (20.0%), sub region V of Loess Plateau (12.0%) and sub region II of Loess Plateau (9.3%); (5) according to the existing erosion classification standards,  erosion intensity of Loess Plateau reached strong level No. The gully density and gully length show obvious spatial differentiation characteristics. The highest density area is in yan'an-dongsheng area on both sides of Shanxi Shaanxi Yellow River, and the gully length in this area is about 100m. This study will help to better understand the spatial distribution characteristics of  in the Loess Plateau, support  management in the Loess Plateau, and promote scientific decision-making of  control in the Loess Plateau.

How to cite: Su, J., Wang, C., Pang, G., Yang, Q., Liu, X., Guo, Z., and Zhong, Y.: Regional Scale Distribution of Gully in Loess Plateau Based on High Resolution Google Earth Satellite Imagery, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3698, https://doi.org/10.5194/egusphere-egu21-3698, 2021.

Introduction

Accelerated erosion by human activities leads to degradation of soil ecosystem services and aquatic environment. It is unavoidable issue in Japan because it holds many sloped agricultural lands. Tokoro river watershed, TRW, in eastern Hokkaido, Japan has unique climate characterized with the least precipitation in Japan and cold winter with little snow which induces soil freezing. Frozen subsoil forms impermeable layers to increase surface runoff in early spring. The objectives of this study were i) to understand the spatial and seasonal variation of water and sediment movement in TRW using Soil and Water Assessment Tool, SWAT which is a process-based hydrological model and ii) to evaluate the impact of agricultural activities, topography of agricultural lands, and runoff characteristics on soil erosion through identification of highly erosive areas and seasons based on the simulation output.

Materials and methods

Water and sediment movement in TRW was simulated from 2011/1/1 to 2015/12/31. SWAT calculates water and sediment movement processes using spatial and temporal information of topography, land use, soil, weather, and land management in watershed. TRW was delineated into 17 subbasins based on topographic information and further divided into 764 HRUs which had homogenous combination of slope class, soil type, and land use in each subbasin. On-land processes were calculated in each HRU. After water and sediment yield from HRUs were summed in each subbasin, stream routing processes were calculated. Model parameters were calibrated so that the estimated stream flow and sediment load at the outlet would fit the measurements. From the simulation by the calibrated model, outputs were extracted as follows: 1) Contribution to the gross sediment yield and erosion rate of each land use; 2) Erosion rate of each subbasin; 3) Erosion rate of whole watershed on each month; and 4) Surface runoff and percentage of surface runoff in water yield in each month.

Results and Discussions

Calibrated SWAT reproduced well the fluctuation of stream flow and sediment load at the outlet of TRW. Although the model underestimated sediment load during large flood events with the average estimation error of -16.1±5.4% on peak-discharge months, it showed satisfactory performance with coefficient of determination: R²=0.88, Nash-Sutcliffe efficiency coefficient: Ens=0.86, and percentage of bias: PBIAS=0.34% for monthly sediment load estimation. Agricultural lands which covered 17.6% of the watershed were considered as the primary sediment sources contributing to 68.5% of estimated gross sediment yield of the watershed. Spatial variation of estimated erosion rate showed high sediment yield in the middle- and down-stream area of TRW where agricultural activities were intensive, and higher sediment yield particularly in the area where more agricultural lands had steep slopes (more than 51 t km^-2 yr^-1). Monthly erosion rate estimation indicated that the most severe erosion occurred on March and April (6.9±1.4 and 7.3±1.9 t km^-2 mon^-1 respectively). On March, average percentage of surface runoff was estimated as 90.5±6.5%. Therefore, surface runoff in early snowmelt season when the frozen subsoil prevented infiltration was considered as an important driver of soil erosion.

How to cite: Mihara, K., Kuramochi, K., and Hatano, R.: Spatio-temporal analysis of soil erosion in Tokoro river watershed in eastern Hokkaido, Japan, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4036, https://doi.org/10.5194/egusphere-egu21-4036, 2021.

Wind erosion of arable soil is considered a risk factor for Austrian fields, but direct measurements of soil loss are not available until now. Despite this uncertainty, vegetated windbreaks have been established to minimize adverse wind impacts on arable land. The study addresses these questions: i) How relevant is wind erosion as a factor of soil degradation? ii) How important is the protective effect of vegetated windbreaks? iii) Are systematic patterns of spatial and temporal variability of wind erosion rates detectable in response to weather conditions? 

Two experimental fields adjacent to windbreaks were equipped with sediment traps, soil moisture sensors, and meteorological measurement equipment for microclimatic patterns. Sediment traps were arranged in high spatial resolution from next to the windbreak to a distance of ten times the windbreak height. Beginning in January 2020, the amount of trapped sediment was analyzed every three weeks. The highest wind erosion rates on bare soil were observed in June and July. For unprotected fields with bare soil, upscaled annual erosion rates were as high as 0.8 tons per hectare, and sediment trapped increased in a linear fashion with distance from the windbreak. Soil water content near the surface (5 cm depth) was three percent higher at a distance of two times the height of the windbreak than at a distance of six times the height. For the same respective distances from the windbreak, we observed 29 days of soil water contents below the wilting point compared with 60 days.

The preliminary outcomes confirmed the expected effects of windbreaks on soil erosion and microclimate in agricultural fields. Prospective results from multiple vegetation periods will be used in an upscaling approach to gain informations for the whole basin. That is meant to be done by a combination with a soil wind erosion model which was so far used for regional modelling of wind erosion susceptibility.

How to cite: Weninger, T., Scheper, S., King, N., Gartner, K., Kitzler, B., Lackoova, L., Strauss, P., and Michel, K.: Spatio-temporal effects of vegetated windbreaks on wind erosion and microclimate as basis for model development, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9182, https://doi.org/10.5194/egusphere-egu21-9182, 2021.

Piping is an erosion process in which cracks and macropores extend into channels with a diameter of cm or more. The study of loess erosion is important because loess covers about ten percent of the continents surface and is susceptible to piping, formation of gullies and intense erosion of agricultural soil. Study was done in Střeleč quarry (Czech Republic), where a several meters thick loess cover occurs in the upper part, sometimes with cracks and macropores. Rill erosion and piping conduits are formed in the loess cover and this makes it an ideal place for field experiments and observations. The erosion rate of the loess by water trickle at quarry face, erosion of the drill hole and erosion under the impact of the droplets were studied. The erosion rate of the rills was measured using long screws screwed directly into the rill. Rapid erosion occurred within first tens of centimeters from original ground surface in the zone where the loess structure was disintegrated by frost or wetting-drying cycles. Below this zone, the erosion rate was much lower, and it ceased with time as rill deepened. Small piping conduits developed rapidly by pouring water into small desiccation cracks on the loess surface. On the other hand, the dril hole did not expand into piping conduit in deeper zone of loess. Moisture content of small loess blocks have strong impact on final degree of erosion. While dry blocks began to disintegrate relatively quickly into incoherent material, the pre-wetted samples did not disintegrated and more or less kept their initial shape. This shows that slaking is responsible for disintegration of small dry blocks on loess surface. While the surface zone of the loess is highly erodible by flowing water, probably due to the loss of its original structure, the loess in the deeper zone is far less erodible in the quarry and even pre-formed conduit (dril hole) do not develop into larger conduit.

Many thanks to the management of Střeleč Quarry for enabling of the field documentation and experiments. The research was supported by Charles University Grant Agency (GAUK #1292119).

How to cite: Vojtisek, J. and Bruthans, J.: Erodibility of loess depending on its weathering: field experiments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9717, https://doi.org/10.5194/egusphere-egu21-9717, 2021.

The characteristics (magnitude and timing) of individual rainfall erosivity (RE) events in Europe strongly control soil loss at timescales from the individual event to long term annual average. While annual averages of soil erosion encompass the long-term variability of the event-based drivers of soil erosion (soil condition, water kinetic energy, vegetation properties), they provide both little direct information on the timing of soil loss or capacity to fully understand future erosion. Across the spectrum of empirical to physically based process models, event-scale estimates of rainfall energy are vital. The (R)USLE EI₃₀ index is a popular description of the combined effect of rainfall kinetic energy and the maximum 30-minute intensity of a rainfall event on soil loss. Modelling RE from daily or event rainfall accumulation seeks to capture the intra-annual meteorological controls on the EI30 index, with the goal of utilising rainfall data with higher abundance (eg daily) than conventional but less common hyetograph data. To date, no systematic study has provided model parameter surfaces for Europe’s climatic regions and investigated their spatial configuration. For each of 74 relevant environmental strata (EnS) within 13 broader environmental zones, we calibrate and validate 5 power-law based models with monthly and annual parameter sets using the REDES dataset, composed of over 300,000 RE events from national gauge networks.

We demonstrate the applicability of delineated environmental strata for subsampling and modelling event rainfall erosivity with heterogeneous national gauge data coverage and extent. Power-law model fits with 12 individual monthly parameter sets outperformed annual models with periodic cosine functions. The power-law α and β parameters are generally correlated through space (r = 0.66) and follow the general European trend of long-term annual average RE, increasing from North-West to South-East. The average annual Nash-Sutcliffe model efficiency for all strata increased from 0.427 (max: 0.76, min: 0.21) to 0.437 when the top 1 percentile of events were removed, which contribute between 8 and 27% of the total RE per stratum. The prediction capacity was higher in autumn and winter than in spring and summer when rainfall holds generally higher unit kinetic energy. Average model efficiency per environmental zone depended on both the rainfall stochasticity and size of the national data sample within each stratum, highlighting the importance of ample data extents for predicting event rainfall erosivity in Europe.

How to cite: Matthews, F., Panagos, P., and Verstraeten, G.: Modelling event scale rainfall erosivity across European climate regions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10087, https://doi.org/10.5194/egusphere-egu21-10087, 2021.

Fuzzy logic is often used for calculation and simulation of real environmental situations. Wind erosion can often be complex, and from various erosion situations it is one of the hardest to be calculated and exactly described. In our research, we based the structure of the fuzzy system on the soil loss of six soils with different mechanical compositions measured in wind channels. Measurement of soil loss in four wind speed ranges during soil channel testing of soils. During the wind tunnel analysis of the soils, the topsoil loss was measured in four wind speed ranges (I. 11,2-11,6 m/s; II. 12.5-13.3 m/s, III. 14.4-14.7 m/s, IV. 15.5-15.7 m/s) on six soils with different mechanical compositions (four sand and two clayey sand soil). The mathematical model programmed and built up in MATLAB, this mamdani type fuzzy evaluation system uses two input parameters wind speed and ErosionFactor. The mathematical model requests the soils mechanical composition and identifies it based on the USDA triangle diagram. Many mathematical methods applicable to fine tune a fuzzy system. We have chosen the method of exhaustive design to cover the whole parameter space. The mathematical model calculated the soil loss. Model runs were also performed with the SWEEP model according to the soils examined in the wind tunnel. Based on our results, we found that using our fuzzy mathematical model, we obtained estimated soil loss values similar to the SWEEP model compared to the soil loss measured in the wind tunnel. However, it should be noted that the USDA SWEEP model requires a much larger amount of data to estimate the extent of soil loss caused by a wind erosion damage event.

How to cite: Tatárvári, K. and Piros, A.: Fuzzy mathematical model for estimating wind erosion based on wind tunnel data, comparison of results with laboratory measured and SWEEP model results, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13701, https://doi.org/10.5194/egusphere-egu21-13701, 2021.

In erosion studies the behavior of rainfall is primordial, since rain is responsible for the first stage of the erosion process: the detachment of soil particles. The erosive potential of rainfall, erosivity, is considered in the universal soil loss equations (R)USLE family through the parameter R, or R factor. This factor is calculated from the rainfall erosivity index, which is the product of kinetic energy of the rain by the maximum intensity of the rain of 30 minutes of duration. As sub-hour rainfall data is not always available, there are in the literature a series of equations obtained from regression, which use monthly and annual rainfall and present a good estimate of erosivity for your study site. In Brazil, in addition to limitations regarding the temporal resolution of rainfall data, there are also spatial limitations. Monitoring stations are concentrated mostly in urbanized areas, usually near the coast. The other regions, such as agricultural and forest areas, are poorly monitored, and these areas are of great interest for monitoring erosion, not only because they are periodically exposed soil areas, but also because of the high rainfall rates that humid forests like Amazon have. MSWEP is a rainfall database that combines observed, satellite and reanalysis data. It has global coverage, temporal resolution of 3 hours, spatial 0.1º and data from 1979 to 2016. Databases like this have great potential to be used in areas such as Brazil, due to its spatial and temporal resolution. In this context, considering the relevance that the soil loss equations still present today, this work developed a rainfall erosivity database entitled REDB-BR (Rainfall Erosivity Database for Brazil). It provides the R factor in a 0.1º resolution grid, developed with 37 years of rainfall data from the MSWEP dataset. The R factor was calculated trough 73 erosivity index regression equations, which mostly uses the Modified Fournier Index (MFI), a relation between monthly precipitation and annual precipitation. Thiessen polygons were used in order to spatialize and define the areas of each equation. Over the Brazilian territory, the R factor ranges from 1.200 to 20.000 MJ mm ha-1 h-1 year-1, with the higher values in the North region, and the lowest values in the Northeast. The spatial patterns of erosivity are very similar to the climatic zones of Brazil. The R factor map takes advantage of MSWEP dataset and presents a spatial resolution very detailed to a country with continental scale such as Brazil. The database includes the equations shapefile and table, Thiessen Polygons shapefile and the R factor map in raster format, which allows more possibilities of application. The database can be accessed at <https://zenodo.org/record/4428308#.X_hxsOhKiUk>. We identified sudden changes in behavior between the delimited areas, which suggests a need for more regression equations in order to better represent the behavior of the erosivity in the Brazilian territory.

How to cite: Petry, I. and Mainardi Fan, F.: A Rainfall Erosivity database for Brazil from MSWEP rainfall dataset, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1432, https://doi.org/10.5194/egusphere-egu21-1432, 2021.

The soil splash phenomenon is the initial stage of the water erosion process. It occurs when a rain drop hits the soil surface and causes a few processes e.g. i) detachment of soil particles and their transport over different distances, ii) breakdown of soil aggregates, iii) surface runoff or iv) formation of a crusted surface.

The aim of the study was to carry out an analysis of the splash erosion in mineral soil in 4 variants of sample preparation: a) dry natural soil, b) wet natural soil, c) dry burnt soil, d) wet burnt soil.

In both cases (natural soil and soil modified with high temperature), full moistening was achieved by capillary rise. Fire simulation was carried out in several variants at varying temperature and duration. Variant that affected soil wettability to the greatest extent was selected for the splash analyses. "Natural" and "modified" wettability were measured using the water drop penetration time (WDPT) method. "Natural" wettability classified soil into the "wettable" group (WDPT < 5s), while the modification of the surface properties by high temperature changed the wettability group of the analyzed soil into "slightly to moderately repellent" (5 s > WDPT < 60s).

Each time, the soil material was placed in aluminum rings with an internal diameter of 36mm and a height of 10mm, and the surface was leveled without excessive compaction of the sample.

A single drop of distilled water with a diameter of 4.2 mm fell on the sample prepared in this way from a height of 1.5m. The drops were dosed with a peristaltic pump and reached the final velocity of 4.98 m/s.

Three synchronized Phantom Miro M310 cameras (Vision Research, USA) were used to register the splash phenomenon. The recorded films were used to analyze the splash phenomenon through measurements of the velocity, angle and distance of ejected particles.

A Scan3D UNIVERSE 10 MPiX structural light scanner (Smarttech 3d, Poland) was used to determine the magnitude of the surface deformation caused by the drops. The analyses made it possible to determine e.g. the depth, diameter, and volume of craters and the height of surrounding rims.

The analysis of the results showed significant differences in the size and dynamics of the emerging splash depending on the degree of soil wettability.

The study was partially funded by the National Science Centre, Poland, as part of project no. 2017/26/D/ST10/01026.

How to cite: Sochan, A., Mazur, R., Beczek, M., Ryżak, M., Polakowski, C., and Bieganowski, A.: The analysis of splash erosion depending on the degree of soil wettability - a preliminary study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14186, https://doi.org/10.5194/egusphere-egu21-14186, 2021.