Soil erosion and sediment yield modeling in watershed scale

Kulekhani watershed is a nationally important watershed because it is the catchment area of Kulekhani hydroelectric project; a power back up of electricity of Nepal. In recent years, it has reported that human accelerated soil erosion has increased in its Reservoir. Winrock-Nepal had facilitated for sharing hydropower royalty to initiate PES in 2003 for upstream conservation but present scenario shows that it could not achieve intended ecological and social outcomes. This study attempts to estimate soil erosion and carry feasibility study for payment for sediment retention in kulekhani watershed.
Experts view and literature review were done to find research problem and primary data were collected via household questionnaire survey, key informant survey, direct observation, group discussion and transect walk with stratified random sampling. Research reports, previous studies and online materials were used as secondary data.GIS/RS tools were used to analyze land use patterns.  Major sediment contributing sector were cultivated land 32.24%, riverbank erosions 41.64%, sediment production from rural roads 16.08% and other landslides 8%.Erosion in cultivated land in early monsoon was serious problem both  from sediment yield and productivity conservation perspective. About 10% of precipitation caused 60% of soil loss in pre-monsoon of1997. SALT-IV model tested in Tistung trail plot were found to be effective technology for reducing about 57% of erosion in a low cost technology. Communities were found interested in adapting this technology and considerable percentage (42%) of cost were willing to pay for it.
Problems of landslides, flash floods and debris flows were more severe in sub watershed of high drainage density & granite dominance sub watersheds such as Tasar, Kiniti-Rupse and Khaiti-Gharti. Gully erosions were more severe in alluvial deposited and cultivated areas. Land use over three and half decades shows that forest area was initially decreased  from 1978 to  1992 and then in increasing trend and stable in recent years whereas past records of cultivated land was vice versa. Original high rate of sediment deposition rate in reservoir were reduced correlating these phenomena but despite the fact rate of erosion is increasing recent years indicating that watershed management initiatives were effective in sediment reduction in past and recent years accelerated soil erosion is related to other factors such as unprotected development activities & farming etc.
It was estimated that soil erosion were 2-230(average84.86) t/ha/y, 0.2-4.3(average2) t/ha/y, 0.2-10.85(average4.87) t/ha/y from cultivated land, forest land and shrub land consequently. The total of 24, 92, 014.26 m3 soil erosion is taking place annually from the watershed area. If we managed the watershed area and introduced on farm conservation in cultivated land we can reduce it up to 50% (12, 98, 997.04m3/y). Average cost for on farm conservation using low cost technique (excluding external material) per unit hectare was found to be 91476.81 where communities are willing to pay average 42%.Soil erosion problems and management regime were categorized into pre-monsoon erosion, sheet rill erosion and gulley/landslide/bank erosion .The average extra cost/hectare for treatment of cultivated land suffered by pre-monsoon erosion, sheet rill erosion and gulley/landslide/bank erosion under low cost technique(excluding external material) was Nrs. 38,693.99, 72,885 and 40,747.97. It was also calculated that productive value of land per/ha was Nrs. 2, 40,263.38.
It was estimated that about 7, 79,398.20 M3  soil would be prevented from entering the reservoir and water saved from displacement would generate 15,18,000.0 kWh of energy which gives NRs. 1, 06, 26,000 revenue per hour (at discharge rate of 13.1m3/s and at an average price of NRs. 7 per kWh) if watershed is managed . Comparing investment needed for upstream cultivated land, it needs an estimated investment of 23, 26, 90,067/y in low cost method (excluding external material)which is approximately equal to possible revenue of one day of NEA.

Gandaki province has the good potentiality of hydroelectricity generation with existing twenty-nine hydroelectricity projects. Since the Province is rich in water resources, analysis of watersheds needs to be done for management, planning and identification of water as well as natural resources. GIS offers integration of spatial and no spatial data to understand and analyze the watershed processes and helps in drawing a plan for integrated watershed development and management. The Digital Elevation Model (DEM) available on the NASA-Earth data has been taken as a primary data for morphometric analysis of watershed in Gandaki Province using QGIS. Delineation of watershed was conducted from a DEM by computing the flow direction and using it in the Watershed tool. Necessary fill sink correction was made before proceeding to delineation. A raster representing the direction of flow was created using Flow Direction tool to determine contributing area. Flow accumulation raster was created f...

Upland erosion and reservoir sedimentation at Cameron Highlands are among the most important sedimentation problems in Malaysia. Uncontrolled deforestation and indiscriminate land clearing for agricultural, housing development and road construction resulted in widespread soil erosion over the land surface of Cameron Highlands leading to sedimentation of the rivers and of the Ringlet Reservoir. The increasing rate of sedimentation in the reservoir is adversely impacting the hydropower production scheme. The objective of this article is to present the results of a GIS-based analysis of the mean annual soil loss rate using the RUSLE model for the Upper Catchment of Cameron Highlands for the years 1997 and 2006. Data such as rainfall pattern, soil type, topography, cover management and support practice were integrated for soil erosion modeling using RUSLE and ArcGIS. The sub-catchments of Telom, Kial and Kodol, Upper Bertam, Middle Bertam, Lower Bertam, Habu, Ringlet and Reservoir catchments were studied. Sediments were detached and transported from the upper catchment and were eventually deposited in the Ringlet Reservoir. The soil loss of Cameron Highlands catchment was computed to be 282,465.5 m3/ year in 1997 and 334,853.5 m3/ year in 2006. The sediment yield for the Ringlet Reservoir was therefore computed to be 1564 m3/km2/yr or 15.64 tons/km2/yr for 1997 and 1854 m3/km2/yr or 18.54 tons/km2/yr in 2006 or an increase of 18.5% since 1997. Hence, the storage capacity of the reservoir is decreasing faster than anticipated because of the increasing sediment yield with time. Consequently, the reservoir life expectancy has also decreased considerable as compared to the design life expectancy.

Makalah ini membahas interaksi tanah dan air pada Daerah Aliran Sungai (DAS) Brantas dan Bengawan Solo di Pulau Jawa, yang merupakan wilayah kerja badan usaha milik negara (BUMN) pengelola sumber daya air, Perusahaan Umum (Perum) Jasa Tirta I. Berdasarkan kegiatan pengelolaan air yang selama ini dilakukan BUMN ini, interaksi kedua aspek ini telah dipengaruhi oleh aktifitas manusia (antrophogenic activities) yang menimbulkan dampak pada kualitas lahan dan keberadaan air permukaan. Degradasi lahan dan air di kedua DAS tersebut telah diamati sejak lama, dan dipastikan merupakan akibat perubahan tata guna lahan, pemakaian tanah secara intensif (misalnya dalam bentuk kegiatan pertanian yang menguras zat hara) atau perubahan fungsi lahan yang melampaui kapasitas daya dukungnya. Kondisi semacam ini menyebabkan kemampuan infiltrasi tanah menurun, meningkatkan limpasan permukaan, dan akhirnya menambah kelajuan erosi tanah. Peningkatan kelajuan ini akhirnya menekan ketersediaan air tawar akibat akumulasi sedimen yang mengendap di sungai maupun di waduk, sehingga mengancam keberlanjutan fungsi dan manfaat dari infrastruktur sumber daya air (SDA) di dalam DAS tersebut. Indikator penting dari degradasi lahan dan air yang ditemui pada daerah tangkapan air di bagian hulu dari kedua DAS ini adalah:

L’érosion du sol est un phénomène naturel qui rend compte de certains processus (détachement des particules, transport et dépôt) induits par différents agents érosifs. Dans les zones semi-arides, les précipitations sont souvent intenses sur les sols secs à végétation pauvre, ce qui peut entraîner une forte susceptibilité à l'érosion des sols. Par conséquent, une évaluation appropriée de l'érosivité des précipitations revêt une importance particulière en raison des effets négatifs causés par l'épuisement de la couche superficielle du sol et la charge excessive de sédiments dans les eaux réceptrices des réservoirs. La présente étude a été menée sur le bassin versant de l’Oued K'sob situé au Nord-Est de l'Algérie, dans le but d’étudier l’influence la variabilité climatique sur la production des sédiments. Le bassin draine une superficie de 1480 km² située entre les altitudes 585 et 1888 m. L’Oued principal s’écoule sur une longueur 73 km et alimente le barrage K’sob d’une capacité initiale de 29.5 Mm3, mis en service en 1940. La région d’étude présente un climat semi-aride à tendance continentale avec un hiver relativement pluvieux et un été sec et chaud, avec une pluie moyenne interannuelle est de 340 mm. La construction des courbes IDF a permis de déterminer un exposant climatique de la région, b=0.75. Pour l’érosivité des précipitations, le calcul d'un tel indice est basé sur les pluies dépassant un seuil spécifique et nécessite des données pluviométriques avec une fine résolution temporelle, qui, souvent, sont rares ou difficiles à acquérir. L'examen des pluies quotidiennes survenant avant une inondation portant une charge sédimentaire a montré une variabilité spatiale des seuils d'érosivité des précipitations. Les valeurs saisonnières des seuils sont faibles et se situent entre 2 mm en été et 6 mm en hiver, ce qui met en évidence un processus d'érosivité typiquement élevé dans les régions semi-arides. Des relations empiriques, établies à l'échelle saisonnière, ont été proposées comme solution alternative au calcul de l'indice R dérivé de l'équation révisée des pertes en sol. Les modèles déterminés ont permis de simuler l'érosivité des événements pluvieux en fonction de la pluie quotidienne. Entre 68 et 78 % de la variance de l'érosivité des précipitations s'explique par la pluie quotidienne donnant lieu à un événement pluvieux érosif. Ensuite, la moyenne spatiale de l'indice d'érosivité annuel a fluctué entre 228 et 386 MJ mm ha-1 h-1 an-1 avec une moyenne interannuelle de 302 MJ mm ha-1 h-1 an-1, ce qui a sous-estimé de 6% l'indice d'érosivité quantifié selon l'équation universelle révisée de perte de sol. L'érosivité des précipitations est le facteur déterminant du rendement en sédiments avec un degré de fixation différent au cours de l'année. En automne, 68 % de la variance de la production de sédiments s'explique par l'érosivité des pluies, contre seulement 42 % au printemps en raison des changements des conditions du sol, notamment la présence d'une couverture végétale qui protège le sol contre l'érosivité des pluies.

Conventional wastewater treatment technologies are deemed to be either ineffective or costly for developing countries such as Kenya. This has led to extensive research in phyto-remediation; the use of aquatic plants such as vetiver grass to reduce pollutant levels in wastewaters. This paper describes the comparative performance of vetiver grass systems in the treatment of domestic wastewater when the plant is established using three different techniques: in a soil medium (soil-based system), with roots suspended in water (hydroponic system) and as a hybrid of these two. Three experimental units of dimensions 1.0 x 0.6 x 0.4m (length x width x depth) fabricated from sheet metal and established with 120 vetiver plants using the three techniques were involved. They were administered with post-septic tank domestic wastewater whose levels of BOD 5 , TSS, TN and TP were measured prior to application, and five days after. The results indicated that generally, the soil-based vetiver system achieved the highest reduction in pollutant levels, followed by the hybrid and the hydroponic systems. For instance, in case of BOD 5, the soil-based, the hybrid, the hydroponic and the control units achieved 75.12, 68.44, 65.64 and 37.66 percentage reduction rates respectively. Analysis of variance at 5% significant level and the comparison of means by the least significance difference (LSD) test at P < 0.05 consistently indicated the existence of significant differences between the vetiver treatments and the control, and between the soil-based vetiver system and the others. The major findings were that both the soil medium and the vetiver plants play a major role in wastewater remediation. Based on these findings, it was concluded that constructed wetland vetiver systems should preferably involve a suitable solid growth medium.

Aam Talaab also known as Maavina Kere or mango beach is one of the major attractions of Raichur. It is located between Latitude 16º10′49.5′′ N to 16º11′27.8′′ N Latitude and 77º20′36′′ E to 77º23′26′′ E Longitude and an area of 4.77 km 2 , having maximum length of 3.98 km. The maximum and minimum elevation of the basin is 491 m and 404 m above MSL, respectively. The values of Stream frequency is 6.50, Form factor 0.30, Shape factor 3.32, Elongation Ratio 0.62, Circularity Ratio 0.39, Drainage density 2.66, Length of overland flow 0.19. The study of hypsometric properties of Aam Talab watershed using hypsometric integral (HI) and hypsometric curve retrieved in that, HI value is 0.52 and hence watershed falls under the Mature Stage. Rainfall was estimated by considering precipitation data from 1998 to 2016 it was found that maximum percentage of runoff took place in 2009 and minimum in the year 2012.

Various methods for erosion risk assessment are used by various countries in Europe. Generally, three types of approaches exist to identify areas at risk (Eckelmann et al., 2006): qualitative approach, quantitative approach, and model approach, All these methods vary in their characteristics and applicability. All already developed methods and approaches are improved in the recent period through use of geospatial databases developed using GIS technology.  The most spread erosion type in the East and Southeast Europe as well as in whole continent is water erosion.
Aim of this study is to evaluate applicability of these methods for various engineering purposes for water erosion control measures per sector. CORINE approach (EEA-1985); the RIVM  (1992); “the Hot Spots” approach (EEA - 2000, based on previous maps by Favis-Mortlock and  Boardman, 1999; de Ploey, 1989, and other data);  USLE method (Universal Soil Loss Equation - Wischmeier & Smith, 1978). The INRA,  PESERA approach (Gobin et al. -1999),  the European Soil Erosion Model – EUROSEM - (Morgan et al., 1998), Limburg Soil Erosion Model – LISEM - (De Roo et al., 1996a and 1996b; Takken et al., 1999), WEPP (Water Erosion Prediction Project), KINEROS and Erosion Potential Model (EPM) established by Gavrilovic (1972), CREAMS (Knisel,1980; Foster et al., 1981), etc.  After preliminary assessment, further analyses were aimed only to 6 methods: USLE, PESERA, KINEROS, WEP, WEPP and EPM.  The elements for evaluation were scale and outputs (maps and values) and qualitative research method was used. Evaluation was separated for purpose per task, scale, erosion type and sector: agro-engineering, bio-engineering and watershed management. The first output of these methods is map that is useful for preparation erosion control strategies. According to the numeric output and scale, applicability for engineering purposes vary from sector to sector. Some of the methods are developed in a very small scale and are interest only for general view of the state and general planning (CORINE, GLASOD, INRA..) and couldn’t be used for solving engineering problems.

The present study was planned to determine the effect of different levels of Nitrogen on the economic yield of wheat (Triticum aestivum L.) variety Aas-11. Thus, an experiment was carried out in the research area of Regional Agriculture Research Institute Bahawalpur (RARI) during 2013-14 to test the effect of various Nitrogen levels on the yield and yield component of wheat. The experiment was laid out in Randomized Complete Block Design (RCBD) with four replications. Nitrogen levels i.e, 0, 30, 60, 90, 120 and 150 kg/ha were tested in this study. The results revealed that 120 and 150 kg/ha levels of nitrogen fertilizer significantly increased the fertile tillers, plant height, spike length, number of spikelet per spike, number of grains per spike, 1000 grain weight, grain yield per plot and grain yield kg/ha. The application of nitrogen fertilizer was found to be most effective for enhancing the quantitative and qualitative growth of wheat.

Bu çalışmanın amacı Bakırçay Havzası'nda suya bağlı toprak kaybı miktarını belir-lemek ve erozyon risk durumu ortaya koyarak güncel arazi kullanımı/örtüsü ile ilişkisini değerlendirmektir. Araştırmada toprak kaybı miktarı (Revised Universal Soil Loss Equation-RUSLE) yöntemi kullanılarak hesaplanmıştır. RUSLE yöntemi kapsamında parametrelerin elde edilmesinde karelaj yöntemine göre belirlenen 108 noktadan temin edilen ve laboratuvar analizleri gerçekleştirilen toprak numuneleri, sayısal yükseklik modeli ve yağış verileri Coğ-rafi Bilgi Sistemi (CBS) teknikleri ile analiz edilmiştir. Arazi kullanımı/örtüsü durumunun tes-pitinde Temmuz 2013 tarihli 30m mekânsal çözünürlüğe sahip LANDSAT Operational Land Imager (OLI) uydu görüntüsü kullanılmıştır. Araştırma sonuçlarına göre Bakırçay Havza-sı'nda suya bağlı toprak kaybı miktarının, yüksek eğim değerlerine sahip, ormansızlaşmanın fazla olduğu havza tabanını çevreleyen dağlık kütleler üzerinde en yüksek değerlere ulaştığı görülmektedir. Ayrıca Soma çevresindeki açık ocak işletmeciliğine bağlı madencilik faali-yetlerinin gerçekleştirildiği sahalarda erozyon riskinin çok yüksek olduğu tespit edilmiştir. Mevcut arazi kullanımı/örtüsü faaliyetlerine göre toprak kaybının değerlendirilmesi ile eroz-yon miktarının ormanlık alanların tahribi ile meydana gelen ekili-dikili sahalar ve mera-çalı arazilerinde artmaya başladığı tespit edilmiştir. Araştırma sahasında, madencilik ve tarımsal faaliyetlerin yol açacağı arazi örtüsü değişiminin toprak kaybı riskinin artmasına neden ola-cağı olası görülmektedir. Bu bağlamda özellikle havza planlama ve yönetimi çalışmalarında toprak kaybı riski dikkate alınarak karar vericiler bu durumu göz önünde bulundurulmalıdır.

The estimation of soil loss and sediment transport is important for effective management of catchments. A model for semi-arid catchments in southern Africa has been developed; however, simplification of the model parameters and further testing are required. Soil loss is calculated through the Modified Universal Soil Loss Equation (MUSLE). The aims of the current study were to: (1) regionalise the MUSLE erodibility factors and; (2) perform a sensitivity analysis and validate the soil loss outputs against independently-estimated measures. The regionalisation was developed using Geographic Information Systems (GIS) coverages. The model was applied to a high erosion semi-arid region in the Eastern Cape, South Africa. Sensitivity analysis indicated model outputs to be more sensitive to the vegetation cover factor. The simulated soil loss estimates of 40 t ha −1 yr −1 were within the range of estimates by previous studies. The outcome of the present research is a framework for parameter estimation for the MUSLE through regionalisation. This is part of the ongoing development of a model which can estimate soil loss and sediment delivery at broad spatial and temporal scales.

The study of the hydrologic characters of a water course permits the correct management of the corresponding basin and a greater control over the water resources of the whole basin; therefore, a suitable planning and maintenance of the necessary interventions along the water course, especially in proximity of the outlet to sea, becomes necessary. An evaluation of the solid transport allows an estimation of the erosion to which the basin is subjected as a result of the river flow, and further helps to prevent hydrologic disasters in the possible risk zones. Among the various experimental techniques in use for measuring the suspended-solid transport, nuclear methods have been preferably used in this research, which are based on monitoring the concentration of the suspended sediments. The suspended-solid concentration is detected by the attenuation of radioactivity emitted by a source of 241Am dipped in the water. This attenuation, due to the presence of the sediments transported in great amounts during events of flood is measured using a scintillation detector made up of a crystal of NaI(Tl). With appropriate calibration curves built both in the laboratory and in the field, it is possible to trace the amount of suspended-solid transport in a certain river section that is located in the proximity of the river outlet. This methodology, applied to different equipped basins in Italy and Africa, is particularly useful for small and medium water courses (similar to those of the Apennine ranges in Italy), allowing an assessment of the erosion in the whole watershed. In this note, the techniques used are introduced in detail, with particular attention to the instrument calibration, and the numerical results obtained for some basins in the Marche region (Italy) are compared with some empirical formulae used in previous reports for the calculation of erosion.

Soil erosion by water is recognised as a worldwide land degradation issue, particularly in arid and semi-arid regions. The aim of this study is to apply the powerful capabilities of advanced remote sensing and geographic information system techniques to identify the areas at risk to water erosion. This study presents the assessment of water erosion in mountainous areas (eastern Aures, Algeria) based on three main factors: the friability of the bedrock, degree of slope and density of vegetation cover. Alsat1 image was used to produce land use and vegetation (NDVI) maps. Digital elevation model was used in constructing the slope gradient map. The erosion risk map was obtained by the combination of indices assigned to thematic layers following multicriteria decision rules. Water erosion was generally not concerning in the eastern Aures (slight risk = 33 %, moderate risk = 44 % of the area). This simple–qualitative approach gave good results for assessing soil erosion equally to quantitative methods since 89.55 % of field verifications were accurate. The non-alarming state and the low rate of severe and extremely severe risk to erosion are due to (1) the low steep slopes, (2) the good quality of vegetation (forests with thick undergrowth), and which are occurring on (3) resistant materials of the substratum, and (4) the low human pressure. Results of this study, which may be conducted with reasonable costs and accuracy over large areas, are of significant help in prioritising areas in decision making and sustainable planning.

Soil erosion is a major farming problem in any society, especially for the fact that food, which is chiefly grown on the soil, is the greatest human need. This study examined the impact of farmland erosion on agricultural development in Ibarapa Central Local Government Area of Oyo State. Data were collected using structural questionnaire, oral interview and personal observation. A total of 200 respondents comprising of farmers were given questionnaire to administer with the help of the researchers. Data collected were analyzed and presented in table. The study revealed that more males were involved in farming in Ibarapa Central Local Government Area. Erosion affected Alabi-illumo farmland than other farmlands. It was also revealed that erosion was wearing farm lands and roads in the study area, and caused low productivity, loss of farm product; loss of soil fertility; water pollution; and damaging of roads. Based on the finding, it was recommended that government and individuals should encourage to supports the control of erosion, transportation facilities should be improved upon; Government and individuals should search for effective and alternative means of improved agricultural development in order to curb low productivity and loss of soil fertility. Also alternative means of controlling erosion should be employed by individuals.

Conservation-oriented land practices have long been a strategy for mediating the environmental issues resulting from conventional agriculture. However, there is limited economic support and incentive for landowners to transition the sensitive marginal lands that need mitigation the most. To improve this approach, information tools built out of landowner preferences may help facilitate successful long-term adoption of diverse systems that achieve production and conservation goals, such as Multifunctional Perennial Cropping Systems (MPCs). Previous work has recognized MPCs to have the potential for providing both ecosystem services and perennial crops such as fruits, nuts, and grasses on land that landowners would otherwise consider marginal. To prioritize efforts for implementation of MPCs and provide tailored information to landowners, this study introduces a suitability model that identifies marginal land based on soil erosion, crop productivity, and other land traits that are important to landowners. Information provided by this tool can inform land management decisions. The land traits were spatially analyzed using a geographic information system (GIS) and parameterized to encode the magnitude of each variable's effect on MPCs suitability. Applied in the Upper Sangamon River watershed, central Illinois, we identified 18,685 ha of highly suitable cropland for MPCs. An 8.5 m spatial resolution allowed identification of subfield suitability areas, in addition to locating target regions of extensive occurrences of high suitability. The distribution of target areas was often located where crop productivity was low and topographic potential for erosion was high. For 26,743 ha of cropland, potential erosion was estimated to be greater than the soil loss standard, particularly in the northeastern section of the watershed where there was higher relief and peri-urban or riparian areas surrounding cropland. In a scenario in which landowners would implement MPCs on identified target regions, simulated soil erosion was reduced by 56% across the watershed. The model provides a simple and effective management tool for identifying priority areas for MPCs implementation, giving landowners and researchers actionable information to improve upon conservation strategies for marginal cropland.

Secondary minerals associated with acid mine drainage play an important role in metal cycling and may pose a geochemical hazard. The occurrence of secondary minerals indicates prevailing and past geochemical conditions. Detecting and characterising secondary minerals is necessary to the planning of remediation programmes. This paper investigates the mineralogical and heavy metal contents of mineral salts associated with acid mine drainage in the East Rand area of the Witwatersrand Basin. Powdered X-ray diffraction was used to identify and quantify mineralogical phases and a scanning electron microscope was used to determine the morphology of the identified minerals. Major cations and anions were determined using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Ion Chromatography (IC). Geochemical modelling was used to predict the saturation of the minerals. Efflorescent crusts contained high levels of trace metals. Enrichment of trace metals, electrical conductivity and sulphate were highest in white salts. A high metal content was associated with low pH values in mineral salts. The salts were dominated by quartz and clay minerals of the smectite group. Tamarugite, apjohnite and jarosite were the predominant sulphate minerals in the salts. These minerals are very acidic and will accelerate weathering in the surrounding soils. Geochemical modelling yielded precipitated hydrated sulphate, halite and goethite. The information gathered during this study will be useful in managing salinity and high metal contents in receiving waters and soils associated with gold mining activities.

Even with the flow of water over a soil surface in which roughness elements are well inundated, and in less erosive situations where erosional bed forms are not pronounced, the magnitude of resistance coefficients in equations such as those of Darcy±Weisbach, Chezy or Manning vary with flow velocity (at least). Using both original laboratory and field data, and data from the literature, the paper examines this question of the apparent variation of resistance coefficients in relation to flow velocity, even in the absence of interaction between hydraulics and resulting erosional bed forms. Resistance equations are first assessed as to their ability to describe overland flow velocity when tested against these data sources. The result is that Manning's equation received stronger support than the Darcy±Weisbach or Chezy equations, though all equations were useful.

La erosión del suelo por efecto de la escorrentía superficial es una de las principales preocupaciones ambientales en las cuencas hidrográficas ecuatorianas. Los modelos empíricos de erosión del suelo están basados en procesos que utilizan el factor R como índice de erosividad de la lluvia. Para obtener valores de los factores condicionantes de la erosión del suelo mediante el modelo Revised Universal Soil Loss Equation (RUSLE), se requieren mediciones de lluvia de alta resolución en un pequeño intervalo de tiempo; cuando estos datos no están disponibles, se utiliza información ráster satelital. El objetivo de este trabajo fue analizar las interrelaciones entre los factores condicionantes de la erosión del suelo en cuencas hidrográficas de Ecuador, como insumo para la construcción de un modelo espacial de pérdida del suelo. La metodología consistió en la delimitación de las cuencas y el cálculo de los factores de elevación y pendiente mediante un Modelo de Elevación Digital (DEM) de 1 km de resolución, que fue mejorado mediante los Softwares R y QGIS a una resolución de 4 km. La información de (a) cobertura del suelo se obtuvo desde Global Land Cover Database, a través del componente global del Servicio de Monitoreo Terrestre de Copernicus; el factor (b) Litología se recuperó desde la World Global Lithological Map Database; y los datos del (c) factor R (erosividad de la lluvia) se procesaron a partir del Global Rainfall Erosivity Database. Los resultados indicaron que el promedio de elevación de las cuencas ecuatorianas oscila entre 0 a 2200 msnm. El promedio de las pendientes va decreciendo conforme las cuencas se van alejando de las proximidades a la Cordillera de Los Andes, evidenciándose una mayor variación en las cuencas que drenan hacia el Pacífico. En cuanto a la cobertura vegetal del suelo, la mayor parte corresponde a bosques cerrados y vegetación herbácea. Desde el punto de vista geológico, hay una gran variedad de afloramientos litológicos correspondientes a rocas de distintas naturalezas, lo cual le confiere a cada unidad hidrográfica en particular, distintos niveles de erodabilidad. El factor R mostró un comportamiento regular en las áreas próximas a la Cordillera de Los Andes mientras que, en los sectores próximos al océano Pacífico, los valores se mostraron más irregulares. La información raster satelital recuperada y geoprocesada mediante herramientas y software propios de las Tecnologías de la Información Geográfica, permitieron reclasificarla para un mejor análisis de cada uno de los factores condicionantes de la pérdida del suelo por erosión en cuencas hidrográficas ecuatorianas, así como de las interrelaciones existentes entre ellos. Esto permitirá construir un modelo espacial de la erosión del suelo en Ecuador, herramienta de gran valor para la gestión y conservación de los recursos naturales que coexisten en sus cuencas hidrográficas.

Recent advances in hyperspectral remote sensing techniques and technologies allow us to more accurately identify
larger range of crop species from airborne measurements. This study employs hyperspectral AISA Eagle VNIR imagery
acquired with 9 nm spectral and 0.6 m spatial resolutions over a spectral range of 400 nm to 1000 nm. The area of study
is the Taita hills in Kenya. Various crops are grown in this region basically for food and as an economic activity. The crops
addressed are: maize, bananas, avocados, and sugarcane and mango trees. The main objectives of this study were
to study what crop species can be distinguished from the cultivated population crops in the agricultural landscape and
what feature space discriminates most effectively the spectral signatures of different species. Spectral Angle Mapper
(SAM) algorithm together with some dissimilarity concepts was applied in this work. The spectral signatures for crops
were collected using accurate field plot maps. Accuracy assessment was done using independent training vector data.
We achieved an overall accuracy of 77% with a kappa value of 0.67. Various crops in different locations were identified
and shown.

Soil erosion by water is recognised as a worldwide land degradation issue, particularly in arid and semiarid regions. The aim of this study is to apply the powerful capabilities of advanced remote sensing and geographic information system techniques to identify the areas at risk to water erosion. This study presents the assessment of water erosion in mountainous areas (eastern Aures, Algeria) based on three main factors: the friability of the bedrock, degree of slope and density of vegetation cover. Alsat1 image was used to produce land use and vegetation (NDVI) maps. Digital elevation model was used in constructing the slope gradient map. The erosion risk map was obtained by the combination of indices assigned to thematic layers following multicriteria decision rules. Water erosion was generally not concerning in the eastern Aures (slight risk 0 33 %, moderate risk 0 44 % of the area). This simple-qualitative approach gave good results for assessing soil erosion equally to quantitative methods since 89.55 % of field verifications were accurate. The nonalarming state and the low rate of severe and extremely severe risk to erosion are due to (1) the low steep slopes, (2) the good quality of vegetation (forests with thick undergrowth), and which are occurring on (3) resistant materials of the substratum, and (4) the low human pressure. Results of this study, which may be conducted with reasonable costs and accuracy over large areas, are of significant help in prioritising areas in decision making and sustainable planning.

Assessing the risk of soil erosion caused by water at the regional level is important for current and future planning of land use and environmental actions to combat land degradation. The gravity of the risk depends not only on the rate of soil erosion by water, but also on other factors, primarily soil depth and workability of the underlying rocks and sediments, which may be used to calculate the eroded soil. We estimate the rate of erosion by water (tons ha 21 year 21) applying the Universal Soil Loss Equation model. The map of soil content (tons ha 21) to the effective rooting depth was divided by the map of soil erosion rate to obtain the risk of erosion by water in Sicily, expressed in terms of years of complete loss of soil cover. This map was intersected with a map of workability of the underlying bedrock to give advice on where the cost of soil recovery by deep ripping and rock grinding are very high. 8382.9 km 2 (32.6% of the Sicilian territory) were rated as at high or very high risk (,100 years), of which 1230.9 km 2 developed on bedrock with low workability and so very costly to be recovered.

Landscape ecology is a relatively new science in the system of sciences. It has emerged from the need of accurate and precise characterisation and mapping of the ecosystem. Since the beginning of the 20th century landscape ecology has been developing its theory, so numerous landscape models were created. These models, however, are actually based on different data sources with different quality, scale, availability etc. The emergence of geo-informatics facilitates greatly data integration and management, as well as complex assessment of landscape. This study represents data integration methodologies using GIS and remote sensing techniques for designing a digital landscape model (DLM) of the territory of the Teyna River watershed. The data used is data for climatic features, such as temperature and precipitation; soil, geology and vegetation. These thematic layers were combined in a DLM with normalized attributive data to perform quick visualization, classification and assessment of the landscape structure of the study area. The resulting 98 secondary landscape units reflect the diversity in natural features and human impact on the study area and provide landscape ecology and land-use planners with a useful tool for decision making aimed at rational land use and nature resource management.

ABSTRACT The analysis of global soil erodibility data by Salvador Sanchis et al. (2008) showed that there is a significant climate effect on soil erodibility which allows for a split of the data into two subsets, one for prevailing cool conditions and another for prevailing warm conditions (defined using the Köppen climate classification). Despite the recognition of this new dichotomous variable, prediction of soil erodibility values remained very poor. This paper presents a new technique for dealing with such a variability by calculating probability density functions of soil erodibility K values when the user knows a set of textural parameters and the climatic classification of the site. Finally the user has the possibility to decide, on the basis of local knowledge, which K value to use. The procedure has been implemented in a freeware software named KUERY available for the scientific community. Finally, as an illustration, the methodology is applied to a catchment in south Italy.

The estimation of soil loss and sediment transport is important for effective management of catchments. A model for semi-arid catchments in southern Africa has been developed; however, simplification of the model parameters and further testing are required. Soil loss is calculated through the Modified Universal Soil Loss Equation (MUSLE). The aims of the current study were to: (1) regionalise the MUSLE erodibility factors and; (2) perform a sensitivity analysis and validate the soil loss outputs against independently-estimated measures. The regionalisation was developed using Geographic Information Systems (GIS) coverages. The model was applied to a high erosion semi-arid region in the Eastern Cape, South Africa. Sensitivity analysis indicated model outputs to be more sensitive to the vegetation cover factor. The simulated soil loss estimates of 40 t ha −1 yr −1 were within the range of estimates by previous studies. The outcome of the present research is a framework for parameter e...