The onsite cost of gully erosion and cost‐benefit of gully rehabilitation: A case study in Ethiopia

Gully erosion often indicates extreme land degradation. In the highlands of Ethiopia, wide and deep gullies are common features, significantly affecting land used for agriculture. However, little action is being taken to address the problem. Where rehabilitation actions in Ethiopia are taking place, they are rarely studied by financially quantifying their costs and benefits. Therefore, this study developed methods of quantifying gully erosion costs and rehabilitation costs and benefits by considering the soil components of four model rehabilitated gullies in Ethiopia. Data were obtained from a physical survey supported by secondary information from relevant agricultural offices. Quantification was achieved by monetizing gully erosion cost through yield loss and gully rehabilitation calculations according to expenditure, while rehabilitation benefits were obtained by monetizing estimated deposited soil nutrients using fertilizer prices. Cost‐benefit values show that investment in gully rehabilitation can be an economically viable proposition in some instances. Stakeholders involved in gully rehabilitation should continue to invest in appropriate techniques of gully rehabilitation and management to ensure continued benefits from rehabilitated gullies and use of surrounding farmlands. Copyright © 2010 John Wiley & Sons, Ltd.     

Prediction of existing gully erosion in vineyard parcels of the NE Spain: a logistic modelling approach

This paper presents a study of determining factors and a method to predict the existence of gully erosion in vineyard parcels. The Alt Penedès-Anoia region (Catalonia, NE Spain), mainly dedicated to the cropping of vineyards for high quality wine production, was selected as the case study area. Single factors related to the existence of gully erosion were determined by means of statistical tests (Student's t-test and chi-square). The existence of gully erosion was predicted by means of a multivariate procedure. A stepwise selection of variables (relief, soil, land use/management characteristics) was performed, which allowed the identification of factors that present a significant relationship with the existence of gully erosion. The selected factors, slope degree and planar slope form, were considered as independent variables in a logistic regression of binary response. The model computes the probability that gullies exist in given vineyard parcels, and it can be implemented in a raster-based geographical information system (GIS). The assessment of the model in 52 parcels, different from the training data set, yielded an overall accuracy of 84.6%. The predictive model can be applied for areas with similar conditions, but the modelling approach can be applied in other different areas.     

Wind-splash erosion of bare peat on UK upland moorlands

Peat is a common land surface material in many countries of the world and is particularly important in upland regions of the UK. Peat landscapes represent an important land use for hill farming, water management, and shooting, and are a globally scarce resource. Wind is a fundamental characteristic of upland environments in the UK and has long been recognised as a significant factor in peat erosion. This paper presents the first results of a project that aims to determine the significance of wind action in the erosion of upland peat. Wind erosion monitoring is being undertaken at Moor House in the North Pennines on a 3-ha area of relatively flat, sparsely vegetated peat. Measurements using arrays of passive horizontal mass flux gauges (fixed orientation vertical slot gauges), together with a vertical array of mass flux samplers (directional), provide estimates of sediment flux. A micrometeorological station records local wind speed (four heights), wind direction, rainfall, soil moisture, and temperature conditions. For 1999 and 2000, the annual horizontal net erosion flux is 0.46 and 0.48 t ha⁻¹, respectively. Results of detailed monitoring over a 10-month period demonstrate that the peat sediment flux collected in windward- and leeward-oriented sediment traps on 10 separate occasions is between 3 and 12 times greater in the windward-facing traps. The concentration of peat with height decays rapidly and the majority of the peat is transported close to the ground surface. Above 0.3 m, very little peat is found. Significant horizontal fluxes of peat occur in both wet and dry periods. This is evaluated using the local micrometeorological data to try and predict sediment yields. Correlations among time-averaged friction velocity measurements, surface conditions, and sediment flux are complex. Event-based measurements, as opposed to cumulative sediment yields, are required to resolve this. These results quantify for the first time the significance of wind action in the erosion of peat in a UK upland environment.     

Trends in relief design and construction in opencast mining reclamation

This paper examines trends in topography design and construction in opencast mining restoration. The greatest geomorphological focus is the protection of aquatic ecosystems downstream of reclaimed sites through the construction of topographies and structures that not only reduce sediments and contaminants to a minimum, but which soften the impact of maximum water flows. From the ecological point of view, the most important focus is the integration of the geomorphological component with those of the soil and vegetation, and the formation of a functional ecosystem with the capacity to maintain itself. The conceptual models of relief that have been used in practice are discussed and criticized: these include the platform‐bank model (geotechnically but not ecologically stable), faithful reproduction of the original topography (inadequate in steep areas), and understanding the hydrological basin as a restoration unit (now considered the most appropriate). Finally, erosion models are reviewed as tools for relief design. The practicality of ‘RUSLE 1.06 for Mined Lands, Construction Sites and Reclaimed Lands’ is underlined owing to its ease of use. Copyright © 2003 John Wiley & Sons, Ltd.     

Factors influencing adoption of soil and water conservation measures in southern Mali

A soil and water conservation (SWC) extension programme, promoting erosion control measures and soil fertility measures, has been going on in southern Mali since 1986. Five factors that influence farmer adoption of SWC measures were analysed: land pressure, cotton‐growing area, possession of ploughing equipment, possession of a donkey cart and farmer training in SWC. Interviews were carried out with 298 farmers and two to three fields per farmer were visited, in 30 representative villages and 30 villages with high SWC adoption. Correlation, regression and factor analysis led to the following conclusions:

• (1) Farmers in the high land‐pressure area adopt more soil fertility measures.
• (2) Farmers in the cotton‐growing area adopt less SWC measures.
• (3) Farmers with more ploughing equipment adopt more SWC measures.
• (4) Farmers with a donkey cart adopt more soil fertility measures.
• (5) Trained farmers adopt more erosion control measures.

There is a strong correlation between the adoption of erosion control measures and soil fertility measures that could not be explained by these five factors only. This suggests that there are additional factors that trigger the adoption of SWC measures. Copyright © 2003 John Wiley & Sons, Ltd.     

喀斯特高原山地土壤抗冲性与土壤物理性质的关系

为探究喀斯特高原山地不同土地利用类型土壤抗冲性及其与土壤物理性质的关系,以马尾松人工林地(PMP)、桂花人工林地(OFP)、天然乔灌混交林地(ASL)、天然草地(NGL)、撂荒地(AL)、农地(CL)为研究对象,采用原状土水槽冲刷试验法,根据研究区地形及气候特点,设置3个坡度(5°,15°,25°),3个冲刷流量(3.2,4.8,6.4 L/min),冲刷时间均为15 min,结合土壤物理性质(容重、孔隙度、水稳性团聚体、机械组成等),定量分析不同土地利用类型下土壤抗冲性及其与土壤物理性质的关系。结果表明:(1)在原状土冲刷试验过程中,各地类初始径流含沙量较高,但随着冲刷时间的延长,径流含沙量呈先降低后趋于稳定趋势,且随着坡度和冲刷流量的增大,径流含沙量趋于稳定的时间有所提前;(2)土壤抗冲系数随坡度和冲刷流量的增大而减小,且坡度对土壤抗冲性的影响比冲刷流量更明显。在同等条件下,各地类土壤抗冲系数依次为NGL＞PMP＞ASL＞AL＞OFP＞CL,土壤抗冲系数分别为13.44~87.84,[JP]8.14~93.15,2.93~45.36,1.21~10.01,1.25~5.48,0.17~1.27(L·min)/g;(3)土壤抗冲性与土壤容重、砂粒含量、水稳性团聚体含量呈极显著正相关(P＜0.01),与总孔隙度、黏粒含量呈显著负相关(P＜0.05),其关系均可用幂函数表示(R²＞0.78)。研究结果可为喀斯特区土壤侵蚀研究和水土保持防治提供科学依据。     

径流泥沙实时自动监测仪的研制

针对径流泥沙过程监测仪缺乏和监测误差大的状况,研制了一种具有野外复杂条件下普遍适用的径流泥沙高精度实时自动监测仪,并建立了数据/站点管理云平台。该仪器从径流泥沙过程中提取驱动仪器运转的物理量并将其转换为测控信号,实现径流泥沙过程的实时自动监测;通过对仪器总体结构及各功能部件的优化设计,消减泥沙粘附和沉积,提高监测精度。通过标准泥沙样品验证了该仪器的适用性,结果表明该仪器监测的含沙量相对误差均值为3.67%,决定系数为0.997。土槽试验获取了径流过程中变幅较宽的径流量和含沙量的动态过程曲线。可见,该仪器不仅可以准确地监测径流泥沙过程,而且创新了水土流失监测技术和方法,推动了水土流失监测的自动化和信息化。     

不同覆盖措施对褐土养分流失的影响

为探究不同覆盖措施对养分流失及其粒径分布的影响,采用人工模拟降雨试验的方法,模拟了不同雨强(30,60mm/h)和不同覆盖物(枯落物、砾石)下,不同覆盖度对褐土坡面养分流失的影响,并对侵蚀土壤的粒径分布、养分流失浓度进行了分析。研究表明:(1)不同覆盖措施均能有效减少土壤流失,250g/m~2的枯落物和盖度为50%的砾石覆盖可减少91%~98%和68%~91%的土壤流失。(2)褐土坡面下,被侵蚀土壤中有机质、速效氮、速效磷的浓度基本不随覆盖条件的变化而变化,而速效钾的浓度随坡面覆盖度的增加可增至裸地对照组的144%~325%。(3)土壤中养分流失随坡面覆盖度增加而减少,250g/m~2的枯落物和盖度为50%的砾石覆盖可减少64%~96%和43.29%~94.39%的养分流失。(4)被侵蚀土壤的粒径显著小于侵蚀前土壤,并且侵蚀模数越大,被侵蚀土壤的粒径组成越接近于原状土。     

Applying the USLE Family of Models at the Sparacia (South Italy) Experimental Site

Soil erosion is a key process to understand the land degradation, and modelling of soil erosion will help to understand the process and to foresee its impacts. The applicability of the Universal Soil Loss Equation (USLE) at event scale is affected by the fact that USLE rainfall erosivity factor does not take into account runoff explicitly. USLE‐M and USLE‐MM, including the effect of runoff in the event rainfall–runoff erosivity factor, are characterized by a better capacity to predict event soil loss. The specific objectives of this paper were (i) to determine the suitable parameterization of USLE, USLE‐M and USLE‐MM by using the dataseries of Sparacia experimental site and (ii) to evaluate their performances at both event and annual scale. The measurements allowed to establish the relationships for calculating the factors of USLE, USLE‐M and USLE‐MM usable at the Sparacia experimental area. At first, for slope‐length values greater than 33 m, the calibration of USLE model at event scale pointed out that sediment delivery processes, that is processes involving deposition of the transported eroded soil particles, occur. The analysis showed that USLE and USLE‐M tend to overestimate low event soil losses, while for USLE‐MM, this tendency is less pronounced. However, the USLE‐MM performed better than USLE and USLE‐M and was able to reproduce better than other two models the highest soil loss values that are the most interesting from a practical point of view. The results obtained at annual scale were generally consistent with those obtained at event scale. Copyright © 2016 John Wiley & Sons, Ltd.     

Final Analysis of the Accuracy and Precision of Methods to Calculate the Sediment Retained by Check Dams

Knowing how much sediment check dams have trapped during their lifespan is essential to estimate their effectiveness or the sediment yields of their basins. Methods to calculate the volume of sediment trapped by check dams play an important role in the understanding of these issues. Several authors have proposed different methods to measure the volume of retained sediment, but their accuracy has, as yet, not been precisely determined and is currently a subject of debate. We compare the most frequently used methods (geometric: prism, pyramid and geometric; topographic: Digital Terrain Models (DTMs), trapezoids and sections methods) to evaluate their accuracy and precision in determining the volume of sediment retained by check dams. Our calculations are based on ten virtual check dams simulated in several gullies of Saldaña (Spain), where we determine their volumetric capacity for trapping sediment (real volume). This was made by means of an intensive topographic survey of these gullies, employing a terrestrial laser scanning system to obtain a high‐resolution digital elevation model (5 × 5 cm, ±2 mm). The results showed that topographic methods provided a very good fit to real volume with a difference of around 8%, being the sections method the most accurate. Geometric methods were less accurate, showing differences of up to 28%. Thus, the results obtained until now by geometric methods should be considered with caution. Although topographic methods were more accurate, they require many field data and much time than the others. So geometric methods can still be useful by correcting their results using our obtained percentage of variation. Knowing the accuracy of the methods before measuring is essential to obtain the most reliable results to analyse the role of check dams in controlling sediment, erosion processes and land degradation. Copyright © 2017 John Wiley & Sons, Ltd.