Magnitude of soil erosion on the northern slope of the Uluguru Mountains,Tanzania: Interrill and rill erosion

The magnitude of interrill and rill erosion was determined on the northern slopes of the Uluguru Mountains, Tanzania which is representative for larger areas of East African Arch Mountains, where population pressure is high and land degradation is severe. The aim of the study was to develop a database to support soil conservation in the area. The study was done on two distinct geomorphic units with respect to altitude and hence rainfall distribution pattern: mountain ridges with an altitude ranging from 1000 to 1500 masl and mean annual rainfall of 2300 mm and mountain foothills whose altitude and mean annual rainfall are 550 to 900 masl and 900 mm, respectively. Total soil loss was measured on 36 individual bounded plots measuring 1.2 m × 20 m using Gerlarch troughs on each day with rain from July 2000 to June 2001. The plots were located on six different geopedologic units, nine on mountain ridges and the rest on the mountain foothills. The slope gradient on the terrain ranged from 30% to 70%. The plots were put under maize cultivation as the main crop. Soil loss through rill erosion was estimated by volumetric measurements of rills on each soil erosion plot. The soil loss due to interrill erosion was obtained by subtracting soil loss through rill erosion from the total soil loss measured in the Gerlarch troughs. The results indicate that soil loss due to both interrill and rill erosion was very high with mean soil loss of 69 and 163 t/ha/year, respectively. Rill erosion accounted for about 58% of the total soil loss while interrill erosion contributed to the remaining 42%. Both interrill and rill erosion were higher in the mountain ridges with mean soil loss of 88 t/ha/year and 210 t/ha/year compared to 49 and 116 t/ha/year in the mountain foothills, respectively. Rill erosion was significantly higher (P ≤ 0.001) in all geopedologic units with slope gradient above 40% (mean soil loss ranged between 91 and 258 t/ha/year) compared to interrill erosion with mean soil loss varying from 41 to 115 t/ha/year. In geopedologic units with slope gradient above 60% both interrill and rill erosion were highly active while in geopedologic units with slope gradient below 40% the two processes were less active. The results demonstrate that rill erosion is more important than interrill erosion in the study area particularly where the slope gradient exceeds 40%. The results further show that the major part of the studied area has moderate interrill erosion (10–50 t/ha/year) and severe to very severe (> 100 t/ha/year) rill erosion. This study clarifies the magnitude of interrill and rill erosion which is important for designing soil conservation on agricultural fields.     

Rill formation and evolution caused by upslope inflow and sediment deposition on freshly tilled loose surfaces

Rill erosion easily occurs on tilled surfaces because the soil shear resistance is less than the runoff shear stress. However, rill erosion formation and evolution on tilled surfaces under upslope inflow conditions remain unclear. The objective of this study was to investigate the rill formation process and rill erosion amount on tilled surfaces via flow scouring under different inflow rates (4, 6, and 8 L min⁻¹) at a 15° slope. Close-range photogrammetric technology was applied to measure the rill morphology during the experiments. The results suggested that the rill formation process due to inflow could be divided into two distinct stages, namely, before and after runoff reached the downslope end, i.e., stages I and II, respectively. At stage I, runoff washed soil particles along the downslope direction. In this process, due to limited transport capacity of runoff, washed soil particles were deposited at the runoff head and formed a soil mound, which blocked the flow path, after which the runoff direction changed within the 6.7°− 50.6° range with an average moving distance of 0.62 m. As a result, a curved rill and a series of soil mounds were left on the surface. The inflow rate affected rill morphology by influencing the runoff direction change angle and runoff moving distance between the mounds on the surface. Herein, the rill formation process is referred to as downslope-trending erosion by inflow (DTEI). At stage II, runoff reached the downslope end, and a rill channel was formed throughout the slope. Thereafter, DTEI was largely reduced, and headward erosion was strengthened. As a result, the rill morphology quickly changed, such as the rill depth and rill width, which gradually increased with ongoing headward erosion. During DTEI, the rill paths were curved due to sediment deposition, and the sediment deposition conditions varied under the different inflow rates. Therefore, the rill curvature (RC) differed (1.039 ± 0.014). The RC decreased with headward erosion progression at stage II. The total sediment yield (TSY) increased with increasing inflow rate. Under inflow rates ranging from 4 to 6 L min⁻¹ and 6–8 L min⁻¹, the TSY increased 2.1–2.4 times. Consequently, DTEI on tilled surfaces significantly affects the initial rill morphology and evolution at the later stage. Hence, on slopes, its role should be considered in rill erosion assessment.     

Experimental determination of sediment transport capacity of rill flow over sandified loess slope

Rill erosion is affected by the sand particle content in soil, especially in the wind and water erosion transition region of the Loess Plateau. The sediment transport capacity (STC) is a key parameter in rill erosion research, assessing the impact of aeolian sand intrusion on the STC of rill flow is of importance for a better understanding of rill erosion. This study aimed to assess the effect of aeolian sand intrusion on the STC on sandified loess slopes, with typical slopes and flow discharges, using a flume system which consisting of a sediment-feeding and a sediment-supply/settlement flume. The sediment feeding flume was jointed by 10° higher than that of the sediment measurement flume section. Three flow discharges (2, 4, and 8 L min⁻¹) and four slope gradients (5°, 10°, 15°, and 25°) were used to represent the natural hydrological conditions under three intrusion rates (SIR) of aeolian sands (10%, 20%, and 50%). The results show that STC increased with slope gradient and flow discharge, and the relationship between the STC and the SIR was significantly affected by the slope gradient; the STCs decreased with the SIR on a slope of 5° but increased with the SIR on steep slopes of 15°–25°, implying a significant impact of slope gradient on the relationship between SIR and STC. The SIR of 50% resulted in the highest sediment concentration nearly 1200 kg m⁻³ on slopes of 25°. On sandified loess slopes of 10%, 20%, and 50% SIR, the STC were about 30%, 46%, and 57% higher than on loess slopes, indicating an increased erosion rate by sand particle intrusion into loess soil. These results highlight the impact of sand intrusion on STC of rill flow and provide deeper insights into the soil loss process on the sandified loess slope.     

Laboratory Studies on the Influence of Rainfall Pattern on Rill Erosion and Its Runoff and Sediment Characteristics

Rill is a major type of erosion on upland slopes. Continuous rainfall is commonly used in laboratory studies on rill erosion despite the fact the rainfall was often discontinuous in the field; this is particularly true in the Chinese Loess Plateau. This study compares rill erosion under continuous and intermittent rainfalls by using laboratory experiments. The experiments include two rainfall‐intensity treatments (90 and 120 mm h⁻¹) and two rainfall‐pattern treatments (continuous and intermittent). The results indicate that rill formation had a significant effect on runoff and sediment concentration. For continuous and intermittent rainfall at the rainfall intensity of 90 mm h⁻¹, the mean sediment concentrations were 1·91 and 1·73 times after rill initiation than those before rill initiation, respectively, and the rill erosion accounted for 75·5% and 77·7% of runoff duration, respectively. For continuous and intermittent rainfall at the rainfall intensity of 120 mm h⁻¹, the mean sediment concentrations after rill initiation were 1·38 and 1·32 times that those before rill initiation, respectively, and the rill erosion represented 88·7% and 78·8% of the total runoff duration, respectively. We observed sediment sorting under all treatments; however, the low rainfall intensity boosted but the high rainfall intensity lowered the clay fraction; in contrast, the sorting remained roughly the same between the rainfall‐pattern treatments. The runoff velocity also affected the sediment sorting. Our empirical results indicated the important significance of the rainfall intermittence in predicting rill erosion. Copyright © 2017 John Wiley & Sons, Ltd.     

冻融条件下土壤侵蚀阻力影响因素

为揭示季节性冻融区土壤侵蚀阻力的变化机制，确定影响土壤侵蚀阻力主控因子，通过室内冻融模拟、水槽冲刷和土壤抗剪试验，对黄绵土(SM粉质壤土)、风沙土(WS砂壤土)和黑土(KS黏壤土)侵蚀阻力影响因素进行研究。结果表明：(1)随着冻融循环次数增加，细沟可蚀性值逐渐升高，而临界剪切力降低。经历10次冻融循环后，SM粉质壤土、WS砂壤土和KS黏壤土的细沟可蚀性分别增加76%,63%,11%,临界剪切力分别减小37%,13%,91%。(2)细沟可蚀性随土壤抗剪强度、黏聚力和内摩擦角增大而减小，临界剪切力则呈相反趋势。与内摩擦角相比，黏聚力更适合用来表征土壤侵蚀阻力。采用黏聚力对SM粉质壤土、WS砂壤土和KS黏壤土的细沟可蚀性进行预测，决定系数(R²)分别为0.42,0.78,0.50,平均为0.57;对临界剪切力的预测效果较差，决定系数(R²)分别为0.16,0.14,0.18,平均仅为0.16。(3)根据皮尔逊相关分析结果，基于土壤的初始含水率、冻融循环次数、力学特性以及土壤参数等分别建立细沟可蚀性(R²=0.85)和临界剪切力...     

Quantifying spatial distribution of interrill and rill erosion in a loess at different slopes using structure from motion (SfM) photogrammetry

The spatial distribution of interrill and rill erosion is essential for unravelling soil erosion principles and the application of soil and water conservation practices. To quantify interrill and rill erosion and their spatial development, four 30-min rainfalls at 90 mm h^?1 intensity were consecutively simulated on runoff plots packed with a loess at six slopes of 10°, 15°, 20°, 25°, 30° and 35°. The soil surface was measured using the structure from motion (SfM) photogrammetry upon each simulation run, and the runoff and sediment samples were collected and measured at every 10 min. Rills did not develop until the third simulation run. During the initial two runs, the lower third section was more severely eroded than the upper and middle thirds along the slope direction, yet the interrill erosion was statistically uniform from left to right. Rills tended to emerge by both sidewalls and in the lower portion in the third run. The corresponding rill erosion increased with slope from 10° to 20° and then decreased for the slopes steeper, which was consistent with the slope trend of the sediment yield directly measured. The rills expanded substantially primarily via head retreat and to a lesser extent via sideward erosion after receiving another 30-min rainfall. Rill erosion contributed 69.3% of the total erosion loss, and shifted the critical slope corresponding to the maximum loss from 20° to 25°. These findings demonstrate the significance of rill erosion not only in total soil loss but also in its relation to slope, as well as the effectiveness of SfM photogrammetry in quantifying interrill and rill erosion.     

7Be示踪坡耕地次降雨细沟与细沟间侵蚀

对于坡面细沟与细沟间侵蚀过程的了解是建立侵蚀预报模型的基础,但传统方法难以对其进行深入研究。利用7Be示踪技术并结合人工模拟降雨,考虑坡脚沉积作用,研究了25°坡耕地径流小区次降雨过程中细沟与细沟间侵蚀动态。结果表明：根据流出径流小区泥沙7Be含量变化计算坡面明显细沟出现时间,由于坡脚沉积作用使得A、B两试验小区这一时间比实际细沟出现分别延迟了45 min和11 min;根据坡面-侵蚀泥沙中7Be总量守恒和泥沙质量平衡原理,坡面细沟间侵蚀及细沟侵蚀在坡面总侵蚀、坡脚沉积区泥沙及流出径流小区泥沙中的比例被定量区分开;总体上,细沟间侵蚀量在径流泥沙中的比例逐渐减少,而细沟侵蚀量逐渐增加。两试验小区中7Be示踪计算坡面细沟侵蚀量和坡脚沉积量与实测值相比相对误差均较小,因此7Be示踪技术可以对土壤侵蚀进行较为准确地定量研究。     

黄土高原水蚀风蚀交错区风沙土细沟分离能力探究

细沟侵蚀产沙是黄土高原水蚀风蚀交错区坡面侵蚀产沙的主要来源,明确该区细沟侵蚀过程特征及其影响因素,对有效防控入黄泥沙和维护流域安全具有重要的科学意义和实践价值。选取水蚀风蚀交错区下垫面典型风沙土为研究对象,通过不同流量(3,5,7,9,11 L/min)、不同坡度(9°,12°,15°,18°,21°)组合下的室内水槽冲刷试验定量揭示风沙土细沟分离过程对坡度、流量以及流速的响应关系,并建立分离能力方程。结果表明:(1)分离能力对坡度和流量的响应均呈线性正相关关系,且相关性极显著。流量对风沙土分离能力的影响大于坡度。除了受到坡度、流量的影响,分离能力还受到坡度和流量叠合作用的影响,这3种因子对分离能力影响由强到弱依次为流量、坡度和流量的叠合作用、坡度,且分离能力与这3种因子的关系可用线性正相关关系表示。(2)流速可作为反映坡度和流量之间叠合作用的关键因子。细沟分离能力对流速的响应呈显著线性正相关关系,试验条件下,临界流速为0.607 m/s。(3)坡度与流量组合下,坡度、流量与坡度和流量叠合作用组合下,单个流速因子下以及坡度、流量与流速因子组合下的4个分离能力方程均能较好地预测和模拟风沙土的分离能力,其中考虑坡度、流量以及坡度和流量叠合作用的方程拟合效果最佳。该研究结果可为完善水蚀风蚀交错区细沟水蚀过程模型提供一定的理论基础。     

Modeling Interrill Erosion on Unpaved Roads in the Loess Plateau of China

Unpaved roads play an important role in soil loss in small watersheds. In order to assess the impact of these unpaved roads in the Loess Plateau of China, runoff and sediment yields from road‐related sources must be quantified. Field rainfall simulation experiments were conducted under three slope gradients and five rainfall intensities on unpaved loess roads in a small watershed. Results showed that the runoff generation was very fast in loess road surface (time to runoff < 1 min) and produced a high runoff coefficient (mean value > 0·8). Soil loss rates were decreased as surface loose materials were washed away during a rainstorm. Rainfall intensity, initial soil moisture, and slope gradient are key factors to model surface runoff and sediment yield. Soil loss on loess road surface could be estimated by a linear function of stream power (R² = 0·907). Four commonly interrill erosion models were evaluated and compared, and the interrill erodibility adopted in the Water Erosion Prediction Project model was determined as 1·34 × 10⁶ (kg s m⁻⁴). A new equation taking into account different parameters like rainfall intensity, surface flow discharge, and slope gradient was established. Copyright © 2013 John Wiley & Sons, Ltd.     

黄土区坡耕地细沟间侵蚀和细沟侵蚀的研究

利用人工模拟降雨试验,通过在径流小区上覆盖纱网消除雨滴动能和增加雨滴除落高度来增加雨滴功能,并采用翻耕裸露作对照的试验处理,对黄土区坡耕地细沟间侵蚀和细沟侵蚀过程及其机理进行了研究。结果表明,坡面侵蚀产沙过程可明显的分为四个阶段,即溅蚀,细沟间侵蚀、细沟侵蚀和雨后径流侵蚀阶段。     

坡面细沟发生临界水动力条件初探

通过玻璃水槽试验和土槽放水冲刷试验对坡面细沟侵蚀发生的临界水动力条件进行了初步研究。结果表明 ,坡面径流在顺坡向下流动过程中以滚波形式运动并发生叠加是造成侵蚀方式发生变化的主要原因。由于径流流动过程中发生滚波叠加 ,造成在径流流路上出现局部水深增加 ,导致侵蚀切应力激增 ,当切应力大于该处的土壤抗蚀力时便发生侵蚀 ,并最终造成细沟沟头的出现。通过对土槽冲刷试验的结果分析 ,运用能量守恒原理建立了径流能耗和径流侵蚀产沙率之间的关系 ,给出了给定土壤条件下坡面细沟侵蚀率估算模型。结果表明 ,坡面土壤侵蚀的发生具有一定的临界条件 ,当径流能耗大于 7 3 8(J)时坡面开始有细沟侵蚀发生     

估算细沟含沙水流剥蚀率的改进方法

为了得到更接近实际的细沟侵蚀模拟数据,改进了前人研究细沟含沙水流剥蚀率的方法。选取黄土高原的典型土壤(安塞黄绵土),采用12 m长土槽在5个坡度(5°,10°,15°,20°,25°)和3个流量(2、4、8 L/min)条件下进行细沟侵蚀过程模拟试验。估算各水力工况下沿细沟含沙水流剥蚀率,探究含沙量,沟长,坡度及流量对于剥蚀率的影响并验证该试验方法的准确性。结果表明:剥蚀率随含沙量的增加呈线性递减,在陡坡(15°,20°,25°)上,随细沟长度的递增呈指数下降,该变化规律在陡坡和大流量下更为显著;并与前人数据进行对比分析,相关系数为0.917,说明与前人结果吻合度高,验证了该研究试验方法的准确性。研究结果将为更好地描述黄土细沟侵蚀过程及土壤侵蚀预测预报提供参考依据。     

紫色土细沟水流输沙能力对近地表水流作用的响应

地表径流与近地表水流耦合作用会引发强烈的土壤侵蚀。输沙能力作为土壤侵蚀的关键参数之一,对完善近地表水流作用下的土壤侵蚀过程具有重要的理论意义。通过限定性细沟模拟试验,采用从底部供水的方式构建近地表水流,在此基础上测定了距弱透水层不同饱和深度(5、10、15 cm)与水力条件(3个流量2、4、8 L·min–1,3个坡度5°、10°、15°)下细沟水流的输沙能力,进一步采用多变量非线性方程分析流量、坡度、近地表水流饱和深度及其交互作用对细沟水流输沙能力的影响。结果表明,输沙能力随近地表水流饱和深度的增加而增大,且增大的速率逐渐减小,最终输沙能力趋于稳定。细沟水流输沙能力与流量、坡度及近地表水流饱和深度呈正相关关系,与坡度相比流量对输沙能力的影响作用更大。试验结果为明确地表径流与近地表水流耦合作用的土壤侵蚀机制提供了一定的理论基础与科学依据。     

Efficiency of wheat straw mulching in reducing soil and water losses from three typical soils of the Loess Plateau,China

Mulching the soil surface with a layer of plant residue is considered an effective method of conserving water and soil because it increases water infiltration into the soil, reduces surface runoff and the soil erosion, and reduces flow velocity and the sediment carrying capacity of overland flow. However, application of plant residues increases operational costs and so optimal levels of mulch in order to prevent soil and/or water losses should be used according to the soil type and rainfall and slope conditions. In this study, the effect of wheat straw mulch rate on the total runoff and total soil losses from 60-mm simulated rainstorms was assessed for two intensive rainfalls (90 and 180 mm h⁻¹) on three slope gradients typical conditions on the Loess Plateau of China and elsewhere. For short slopes (1 m), the optimal mulch rate to save water for a silt loam and a loam soil was 0.4 kg m⁻². However, for a clay loam soil the mulch rate of 0.4 kg m⁻² would be optimal only under the 90 mm h⁻¹ rainfall; 0.8 kg m⁻² was required for the 180 mm h⁻¹. In order to save soil, a mulch rate of 0.2 kg m⁻² on the silt loam slopes prevented 60%–80% of the soil losses. For the loam soil, mulch at the rate of 0.4 kg m⁻² was essential in most cases in order to reduce soil losses substantially. For the clay loam, 0.4 kg m⁻² may be optimal under the 90 mm h⁻¹ rain, but 0.8 kg m⁻² may be required for the 180 mm h⁻¹ rainstorm. These optimal values would also need to be considered alongside other factors since the mulch may have value if used elsewhere. Hence doubling the optimal mulch rate for the silt loam soil from 0.2 kg m⁻² or the clay loam soil under 90 mm h⁻¹ rainfall from 0.4 kg m⁻² in order to achieve a further 10% reduction in soil loss needs to be assessed in that context. Therefore, Optimal mulch rate can be an effective approach to virtually reduce costs or to maximize the area that can be treated. Meantime, soil conservationist should be aware that levels of mulch for short slopes might not be suitable for long slopes.     

Impacts of soil tilth on the effectiveness of biological geotextiles in reducing runoff and interrill erosion

The effectiveness of a surface cover material (e.g. geotextiles, rock fragments, mulches, vegetation) in reducing runoff and soil erosion rates is often only assessed by the fraction of the soil surface covered. However, there are indications that soil structure has important effects on the runoff and erosion-reducing effectiveness of the cover materials. This study investigates the impact of soil pre-treatment (i.e. fine tilth versus sealed soil surface) on the effectiveness of biological geotextiles in increasing infiltration rates and in reducing runoff and interrill erosion rates on a medium and steep slope gradient. Rainfall was simulated during 60 min with an intensity of 67 mm h⁻¹ on an interrill erosion plot having two slope gradients (i.e. 15 and 45%) and filled with an erodible sandy loam. Five biological and three simulated geotextiles with different cover percentage were tested on two simulated initial soil conditions (i.e. fine tilth and sealed soil surface). Final infiltration rates on a sealed soil surface (7.5–18.5 mm h⁻¹) are observed after ca. 10 min of rainfall compared to ca. 50 min of rainfall on an initial seedbed (16.4–56.7 mm h⁻¹). On the two tested slope gradients, significantly (α = 0.05) smaller runoff coefficients (RC) are observed on an initial seedbed (8.2% < RC < 59.8%) compared to a sealed soil surface (75.7% < RC < 87.0%). On an initial seedbed, decreasing RC are observed with an increasing simulated geotextile cover. However, on an initial sealed soil surface no significant effect of simulated geotextile cover on RC is observed. On a 15% slope gradient, calculated b-values from the mulch factor equation equalled 0.054 for an initial fine tilth and 0.022 for a sealed soil surface, indicating a higher effectiveness of geotextiles in reducing interrill erosion on a fine tilth compared to a sealed soil surface. Therefore, this study demonstrates the importance of applying geotextiles on the soil surface before the surface tilth is sealed due to rainfall. The effect of soil structure on the effectiveness of a surface cover in reducing runoff and interrill erosion rates, as indicated by the results of this study, needs to be incorporated in soil erosion prediction models.     

陡坡细沟含沙水流剥蚀率的试验研究及其计算方法

细沟剥蚀土粒随着细沟股流中含沙量的增加而减少，这一概念已在一些侵蚀模型（如WEPP）中得到应用。用黄土高原一种典型的粉壤土，在5种坡度（5°，10°，15°，20°，25°），3种流量（2，4，8 L/min）条件下进行了细沟侵蚀模拟试验，试验沟长0.5～8 m。通过405次试验，确定了不同坡度、入流量条件下，侵蚀产沙量与细沟长度的定量函数关系。在假定细沟径流和土壤侵蚀沿细沟的行为相同条件下，提出了一种计算含沙水剥蚀率的方法，并进一步表达了细沟剥蚀率随含沙量以及沟长变化的函数关系。实验结果在15°，20°，25°时表现出很好的显著性。     

Relative Contribution of Rill/Interrill and Gully/Channel Erosion to Small Reservoir Siltation in Mediterranean Environments

Reservoir siltation because of water erosion is an important environmental issue in Mediterranean countries where storage of clear surface water is crucial for their economic and agricultural development. The high density of gully systems observed in Mediterranean regions raises the question of their contribution to reservoir siltation. In this context, this study quantified the absolute and relative contributions of rill/interrill and gully/channel erosion in sediment accumulation at the outlet of small Tunisian catchments (0·1–10 km²) during the last 15 years (1995–2010). To this end, a fingerprinting method based on measurements of caesium‐137 and total organic carbon combined with long‐term field monitoring of catchment sediment yield was applied to five catchments in order to cover the diversity of environmental conditions found along the Tunisian Ridge and in the Cape Bon region. Results showed the very large variability of erosion processes among the selected catchments, with rill/interrill erosion contributions to sediment accumulated in outlet reservoirs ranging from 20 to 80%. Overall, rill/interrill erosion was the dominant process controlling reservoir siltation in three catchments whereas gully/channel erosion dominated in the other two catchments. We identified the presence of marly gypsum substrates and the proportion of catchment surface covered by soil management/conservation measures as the main drivers of erosion process variability at the catchment scale. These results provided a sound basis to propose guidelines for erosion mitigation in these Mediterranean environments and suggested to apply models simulating both rill/interrill and gully/channel erosion in catchments of the region. Copyright © 2015 John Wiley & Sons, Ltd.     

Quantitative assessment of rill and interrill soil erosion in Romania

Soil erosion is an important geomorphological process with potential negative consequences especially on land agricultural potential. Unsuitable agricultural practices may increase soil erosion, leading to rapid loss of soil fertility and decrease of crop production. It is therefore important to correctly quantify soil erosion rates in order to adapt agricultural practices and implement proper conservation measures. This study attempts to assess the rill and interrill erosion in Romania, using the Romanian soil erosion model and GIS techniques. The database includes the digital terrain model, the soil map of Romania, the land use map of Romania and the rainfall erosivity regions. The results show that the high and very high erosion risk classes include 4.1% of the Romanian territory (9,627 km²). Most of this land is present in the hilly and plateau areas (Subcarpathians, Moldavian Plateau, Getic Plateau, Western Hills, Dobrogea Plateau). The model was validated by comparison of its predictions with long‐term erosion measurements from different locations in the country. Comparison with previous non‐GIS assessments of soil erosion at national level shows that the total estimated rill and interrill erosion in our study was very close to previous estimates. Comparison with the RUSLE 2015 model computed for Europe as a whole reveals that the two models assign almost 54% of their shared area to the same erosion class, while for 39% of the territory there is one class difference between the models. The results can be used for evaluations of erosion risk at national and regional scales.     

The effect of slope on interrill erosion at short slopes

Slope gradient is an important factor that affects soil erosion. This study was conducted to investigate the effect of slope gradient on soil erosion and determine the splash contribution to interrill erosion at short steep slopes. An experimental device was used to make simultaneous measurements of interrill splash and wash at 9, 18, 27, 36, 47, 58, 70, 84, and 100% slopes under a constant rainfall intensity of 67 mm h^? 1 in a laboratory setting. The specially designed runoff and sediment collection system provided a means of partitioning total splash into four directional components and interrill sediment transport into wash and splash components. The results revealed that the total splash loss, net downslope splash loss and wash loss all increased with slope, and then decreased after a maximum value was reached. The slope factor equation of short slopes in RUSLE matched the wash loss from this study very well when the slope gradient was less than or equal to 58%. The ratio of net downslope splash loss to wash loss increased from 0.21 to 1.33 as the slope gradient increased from 9% to 100%. Taken together, these results indicate that upslope splash loss was a very important component of the total splash loss on gentle slopes and may be neglected on slopes greater than 36%. Splash transport was a significant part of interrill sediment delivery at short steep slopes.     

Developing a magnetic tracer to study soil erosion

Soil erosion is commonly measured as the quantity of sediment leaving a plot or watershed. The techniques for measuring soil erosion patterns and sediment redistribution within plots or watersheds by direct monitoring are very limited. The objective of this study was to develop a direct and non-intrusive tracer method to study the sources, patterns and rates of erosion and deposition of sediments in erosion plots. The magnetic tracer developed in this study consisted of polystyrene plastic beads embedded with a magnetic powder (magnetite). The “magnetized” beads, with a mean weight diameter of 3.2 mm and particle density of about 1.2 g cm⁻³, were uniformly mixed with soil and tested in the laboratory using simulated rainfall and inflow studies to simulate the interrill and rill components of soil erosion, respectively. In the interrill and rill experiments, the tracer was transported in the same proportion it was initially mixed with the soil. Given this fact, a magnetometer, which measures the soil's magnetic susceptibility, could be used to identify areas of deposition or detachment. The magnetic susceptibility would be increased or reduced depending on whether deposition or detachment occurs. To simulate detachment and deposition, a magnetometer was tested for different tracer concentrations and different thickness of soil containing the tracer. The magnetometer promises to be a sensitive, accurate, and useful tool to study the spatial variation of soil erosion when magnetic tracers are used.