Página 1 dos resultados de 2403 itens digitais encontrados em 0.009 segundos

Runoff and soil loss from steep sloping vineyards in the Douro Valley, Portugal: rates and factors

Figueiredo, Tomás de; Poesen, Jean; Ferreira, Alfredo Gonçalves; Gonçalves, Dionísio
Fonte: University of Athens Publicador: University of Athens
Tipo: Parte de Livro
ENG
Relevância na Pesquisa
37.25%
The Douro Region,, NE Portugal, where the grapes for Port Wine are produced, faces a high potential erosion risk due to its natural setting, for long tackled with heavy labour inputs. These allowed the stabilization of steep vineyard covered hill-slopes by means of traditional terracing, manually built and following models that changed through time. Alternative vineyard installation and cultivation techniques were tested and progressively adopted, namely row plantation perpendicular to the contour, nowadays an integral yet small part of the plantation schemes accepted under the rules of the World Heritage status, granted by UNESCO in 2001. This paper investigates the effects of vine plantation schemes on long-term (10 years) runoff and soil loss data recorded in the Douro Region using a set of meso-scale erosion plots installed in vineyards planted in rows perpendicular to the contour. It also aims at identifying, and quantitatively deriving the significance of erosion factors helping to interpret the results obtained. Runoff and soil loss were measured between 1978 and 1988 using five runoff plots, 32.1 m long and 5.2 m wide, on a 45 % slope, over a silt loam soil containing 60 % rock fragments by mass, under Mediterranean climatic regime with less than 600 mm mean annual rainfall. Vine plantation schemes tested correspond to three different plant densities (3571...

Runoff erosion

Evelpidou, Niki; Cordier, Stephane; Merino, Agustin; Figueiredo, Tomás de; Centeri, Csaba
Fonte: University of Athens Publicador: University of Athens
Tipo: Livro
ENG
Relevância na Pesquisa
37.3%
Table of Contents PART I – THEORY OF RUNOFF EROSION CHAPTER 1 - RUNOFF EROSION – THE MECHANISMS CHAPTER 2 - LARGE SCALE APPROACHES OF RUNOFF EROSION CHAPTER 3 - MEASURING PRESENT RUNOFF EROSION CHAPTER 4 - MODELLING RUNOFF EROSION CHAPTER 5 - RUNOFF EROSION AND HUMAN SOCIETIES: THE INFLUENCE OF LAND USE AND MANAGEMENT PRACTICES ON SOIL EROSION PART II - CASE STUDIES CASE STUDIES – INTRODUCTION: RUNOFF EROSION IN MEDITERRANEAN AREA CASE STUDY 1: Soil Erosion Risk And Sediment Transport Within Paros Island, Greece CASE STUDY 2: The Soil Erosion In The Greater Urban Areas (Athens - Budapest) CASE STUDY 3: Site Preparation Impacts On Physical And Chemical Forest Soil Quality Indicators CASE STUDY 4: Integrated Farm-Scale Approach For Controlling Soil Degradation And Combating Desertification In Alentejo, South Portugal - An Example Of Good Farming Practices Towards A Sustainable Land Use In A High Desertification Risk Territory CASE STUDY 5: The Role Of No-Till And Crop Residues On Sustainable Arable Crops Production In Southern Portugal CASE STUDY 6: Runoff And Soil Loss From Steep Sloping Vineyards In The Douro Valley, Portugal: Rates And Fsactyors CASE STUDY 7: Runoff Erosion In Portugal: A Broad Overview CASE STUDY 8: Extraction Of Biomass From Forest Soils - The Main Aspects To Take Into Account To Prevent Soil Degradation

Transporte de fósforo na enxurrada superficial em função do tipo de fonte de P e intensidade das chuvas: Relevância à gerência ambiental em sistemas de produção brasileiros; Phosphorus transport in surface runoff as a function of P source type and rainfall intensity: Relevance to environmental management of Brazilian production systems

Shigaki, Francirose
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 01/09/2006 PT
Relevância na Pesquisa
37.25%
Estima-se que a água potável no futuro será limitada devido a: (1) problemas ambientais, (2) aumento na demanda (a população mundial deve atingir 10,5 bilhões de habitantes em 2050); e (3) 60% do consumo mundial é baseado em recursos não renováveis. Conseqüentemente, é imperativo que os recursos de águas doces sejam cuidadosamente manejados para assegurar seu uso para as gerações futuras. Um dos principais problemas ambientais que limita o uso da água é a eutrofização, que pode ser acelerada por entradas de nitrogênio (N) e fósforo (P). Como resultado, a minimização das perdas de P para as águas é essencial para diminuição da incidência e severidade da eutrofização. Entretanto, suplementos adequados de P são necessários para produção de culturas de interesse econômico na maioria das vezes dependentes de suplementação adequada de P do solo. Sendo assim, o P é adicionado rotineiramente para melhores rendimentos de todas as culturas. A maioria dos fertilizantes fosfatados utilizados na agricultura são altamente solúveis em água, afim de fornecer P prontamente disponível para absorção das plantas. Entretanto, uma alta proporção desse fósforo aplicado torna-se indisponível devido as reações químicas dos constituintes do solo (fixação). Fertilizantes fosfatados com alta solubilidade em água tendem a dissolver-se rapidamente...

Parâmetros relacionados com a erosão hídrica sob taxa constante da enxurada, em diferentes métodos de preparo do solo; Water-erosion related parameters under steady runoff-rate for different soil tillage methods

Bertol, Ildegardis; Mello, Eloy Lemos de; Cogo, Neroli Pedro; Vidal Vázquez, Eva; Paz González, Antônio
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
POR
Relevância na Pesquisa
37.28%
O preparo do solo altera as suas condições físicas de superfície e subsuperfície e, conseqüentemente, influencia os valores dos fatores que se relacionam com a erosão hídrica. Considerando estes aspectos, realizou-se um experimento de erosão em campo, sob a ação de chuva simulada, entre outubro de 1999 e maio de 2000, na região do Planalto Sul Catarinense, tendo por objetivo a avaliação de alguns fatores relacionados com a erosão hídrica do solo na condição de equilíbrio do escoamento superficial, em três métodos de preparo do solo. No estudo, utilizou-se Nitossolo Háplico alumínico de textura argilosa, apresentando, no local do experimento, 0,14 m m-1 de declividade. Os tratamentos avaliados foram: (a) preparo reduzido (escarificação + gradagem); (b) preparo convencional tradicional (aração + duas gradagens), e (c) preparo convencional alterado (aração + duas gradagens + duas rastelagens), os dois primeiros em solo continuamente cultivado e o último em solo mantido continuamente sem cultivo (tratamento-testemunha). Os tratamentos foram caracterizados em termos de rugosidade ao acaso e cobertura superficiais do solo, as quais foram avaliadas imediatamente antes e depois do preparo, no dia anterior à aplicação da chuva simulada. O teste de chuva foi realizado por ocasião da semeadura da soja...

RUNOFF UNDER SPRINKLER IRRIGATION. AFFECTING FACTORS AND CONTROL PRACTICES.

Silva, Luis Leopoldo
Fonte: Nova Science Publishers Publicador: Nova Science Publishers
Tipo: Livro Formato: 8954 bytes; application/pdf
ENG
Relevância na Pesquisa
37.32%
The need to reduce energy costs associated with the use of sprinkler irrigation systems has led farmers towards the use of low pressure operating systems. The characteristics of water applied by these systems, with high water application rates usually exceeding soil infiltration capacity, has increased surface runoff problems under sprinkler irrigation. Surface runoff can cause different problems: (i) reduction of irrigation efficiency and uniformity, increasing energy and water consumption; (ii) soil erosion; (iii) crop yield spatial variability; and (iv) environmental problems, by transporting sediments and applied fertilizers or other agrochemicals washed-out from the field causing the contamination of surface waters. To minimize surface runoff it is required a good knowledge of all factors that directly or indirectly can affect it. The irrigation process, from water application by the irrigation system to its infiltration or runoff, is very complex. This complexity is essentially due to the great number of factors that can influence infiltration and surface runoff and the interactions between them. In this chapter, major surface runoff affecting factors under sprinkler irrigation are identified and their effects on surface runoff analyzed. In order to minimize surface runoff...

The effects of cover crops and conventional tillage on soil and runoff loss in vineyards and olive groves in several Mediterranean countries

Gómez, J.A.; Llewellyn, C.; Basch, G.; Sutton, P.B.; Dyson, J.S.; Jones, C.A.
Fonte: John Wiley & Sons Publicador: John Wiley & Sons
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
37.32%
Cover crops (CC) in vineyards and olive groves provide an alternative to conventional tillage (CT) for land management. Runoff, sediment and nutrient loss from six sites in France, Spain and Portugal were compared over 3–4 yr. In general, runoff loss was not significantly reduced by the CC alternatives: average annual runoff coefficients ranged from 4.9 to 22.8% in CT compared with 1.9– 25% in the CC alternatives. However, at two sites, reductions in average annual runoff coefficients were greater for CC: 17.2 and 10.4% in CT, 6.1 and 1.9% in CC. Nutrient loss in runoff followed a similar pattern to runoff, as did pesticide loss on the one site; reductions occurred when runoff losses were significantly reduced by CC. The lack of differences at the other sites is thought to be due to a combination of soil conditions at the surface (compaction and capping) and sub-surface (lowpermeability horizons close to the surface). In contrast, CC always resulted in reductions in soil erosion loss, plus similar reductions in nutrients and organic matter (OM) associated with sediment. Soil erosion loss ranged from 1.4 to 90 t ⁄ ha ⁄ yr in CT compared with 0.04–42.7 t ⁄ ha ⁄ yr in CC. Overall, reductions in runoff and associated nutrient and pesticide loss from vineyards and olives occurred with the introduction of CCs only when soil permeability was sufficiently high to reduce runoff. In contrast...

Runoff under sprinkler irrigation. Affecting factors and control practices.

Silva, Luis Leopoldo
Fonte: Nova Science Publishers Publicador: Nova Science Publishers
Tipo: Parte de Livro
POR
Relevância na Pesquisa
37.32%
The need to reduce energy costs associated with the use of sprinkler irrigation systems has led farmers towards the use of low pressure operating systems. The characteristics of water applied by these systems, with high water application rates usually exceeding soil infiltration capacity, has increased surface runoff problems under sprinkler irrigation. Surface runoff can cause different problems: (i) reduction of irrigation efficiency and uniformity, increasing energy and water consumption; (ii) soil erosion; (iii) crop yield spatial variability; and (iv) environmental problems, by transporting sediments and applied fertilizers or other agrochemicals washed-out from the field causing the contamination of surface waters. To minimize surface runoff it is required a good knowledge of all factors that directly or indirectly can affect it. The irrigation process, from water application by the irrigation system to its infiltration or runoff, is very complex. This complexity is essentially due to the great number of factors that can influence infiltration and surface runoff and the interactions between them. In this chapter, major surface runoff affecting factors under sprinkler irrigation are identified and their effects on surface runoff analyzed. In order to minimize surface runoff...

Comparative assessment of infiltration, runoff and erosion sprinkler irrigated soils

Santos, Francisco Lúcio; Reis, João; Martins, Olga; Castanheira, Nádia; Serralheiro, Ricardo
Fonte: Biosystems Engineering Publicador: Biosystems Engineering
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
37.28%
Abstract The impacts of sprinkler irrigation on infiltration, runoff and sediment loss of ten representative soils of Southern Portugal were assessed by laboratory sprinkler irrigation simulation tests. All soils showed very low permeability to applied water. The mechanical impact of water droplets enhanced soil dispersion and further lowered their infiltration capacity, particularly for high clay plus silt content soils that showed the poorest results. As a consequence, high runoff and sediment losses were also measured, primarily with the first irrigation. More moderate losses were observed thereafter. Soils with higher sand particle size fractions better absorbed the energy impact of droplets and showed higher infiltration rates and lower runoff and sediment losses. Polyacrylamide (PAM) applied to the soils through the irrigation water acted as a binding and settling agent to increase soils aggregate stability and infiltration and reduce runoff and sediment losses. Slope increase, from 2·5 to 5%, decreased overall soils infiltration by 7% and increased runoff and sediment losses by 10 and 27%, respectively. Exposed to the same change in slope, PAM application boosted overall infiltration of treated soils to a 24% difference and increased runoff by only 10%. It had a less positive effect on sediment loss...

Rainfall simulation underestimates runoff phosphorus concentrations from dairy pastures

Dougherty, W.; Fleming, N.; Cox, J.; Chittleborough, D.
Fonte: The Regional Institute Ltd; CD-ROM Publicador: The Regional Institute Ltd; CD-ROM
Tipo: Conference paper
Publicado em //2004 EN
Relevância na Pesquisa
37.33%
Concentrations of phosphorus (P) in runoff from intensively managed pastures such as those used for dairying are high. Soil P has a large influence on runoff P concentrations. The most common technique used to derive soil P–runoff P relationships is rainfall simulation. A project is underway to test the utility of combining soil P-runoff P relationships with landscape hydrological models to assist in identifying areas for priority remedial action to reduce runoff P losses. However, there have been conflicting reports on the reliability of rainfall simulation to predict runoff P concentrations under natural rainfall at broader scales, e.g. hill-slope or sub-catchment. This paper reports a comparison of two methods of measuring runoff P concentrations, a) large plots (1250 m2) with low intensity simulated rainfall (8 mm/hr) and, b) small plots (1.5 m2) with high intensity simulated rainfall (80 mm/hr). Measurements were made on two occasions and over a range of soil P concentrations. There was a highly significant (P<0.01) effect of the method of measuring runoff P concentration. Runoff P concentrations from the small plots were approximately half of those derived from large plots. We hypothesize that these differences are the result of differences in contact times between the P source and runoff. However...

Small-scale, high-intensity rainfall simulation under-estimates natural runoff P concentrations from pastures on hill-slopes

Dougherty, W.; Nash, D.; Cox, J.; Chittleborough, D.; Fleming, N.
Fonte: C S I R O Publishing Publicador: C S I R O Publishing
Tipo: Artigo de Revista Científica
Publicado em //2008 EN
Relevância na Pesquisa
37.33%
Rainfall simulation is a widely used technique for studying the processes, and quantifying the mobilisation, of phosphorus (P) from soil/pasture systems into surface runoff. There are conflicting reports in the literature of the effects of rainfall simulation on runoff P concentrations and forms of P compared to those under natural rainfall runoff conditions. Furthermore, there is a dearth of information on how rainfall simulation studies relate to hill-slope and landscape scale processes and measures. In this study we compare P mobilisation by examining P forms and concentrations in runoff from small-scale, high-intensity (SH, 1.5 m2, 80 mm/h) rainfall simulation and large-scale, low-intensity (LL, 1250 m2, 8 mm/h) simulations that have previously been shown to approximate natural runoff on hill-slopes. We also examined the effect of soil P status on this comparison. The SH methodology resulted in lower (average 56%) runoff P concentrations than those measured under the LL methodology. The interaction method × soil P status was highly significant (P < 0.001). There was no significant effect of method (SH v. LL) and soil P status on P forms (%).The hydrological characteristics were very different between the 2 methods, runoff rates being c. 42 and 3 mm/h for the SH and LL methods...

Runoff measurement and prediction for a watershed under natural vegetation in central Brazil

Silva,C. L.; Oliveira,C. A. S.
Fonte: Sociedade Brasileira de Ciência do Solo Publicador: Sociedade Brasileira de Ciência do Solo
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/1999 EN
Relevância na Pesquisa
37.25%
This work aimed to measure and analyze total rainfall (P), rainfall intensity and five-day antecedent rainfall effects on runoff (R); to compare measured and simulated R values using the Soil Conservation Service Curve Number method (CN) for each rainfall event; and to establish average R/P ratios for observed R values. A one-year (07/01/96 to 06/30/97) rainfall-runoff data study was carried out in the Capetinga watershed (962.4 ha), located at the Federal District of Brazil, 47° 52' longitude West and 15° 52' latitude South. Soils of the watershed were predominantly covered by natural vegetation. Total rainfall and runoff for the period were 1,744 and 52.5 mm, respectively, providing R/P of 3% and suggesting that watershed physical characteristics favored water infiltration into the soil. A multivariate regression analysis for 31 main rainfall-runoff events totaling 781.9 and 51.0 mm, respectively, indicated that the amount of runoff was only dependent upon rainfall volume. Simulated values of total runoff were underestimated about 15% when using CN method and an area-weighted average of the CN based on published values. On the other hand, when average values of CN were calculated for the watershed, total runoff was overestimated about 39%...

Analysis of soil surface component patterns affecting runoff generation. An example of methods applied to Mediterranean hillslopes in Alicante (Spain)

Arnau Rosalén, Eva; Calvo-Cases, Adolfo; Boix-Fayos, Carolina; Lavee, H.; Sarah, P.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 579917 bytes; image/jpeg
ENG
Relevância na Pesquisa
37.32%
Spatial patterns of soil surface components (vegetation, rock fragments, crusts, bedrock outcrops, etc.) are a key factor determining hydrological functioning of hillslopes. A methodological approach to analyse the patterns of soil surface components at a detailed scale is proposed in this paper. The methods proposed are applied to two contrasting semi-arid Mediterranean hillslopes, and the influence of soil surface component patterns on the runoff response of the slopes was analysed. A soil surface components map was derived from a high resolution photo-mosaic obtained in the field by means of a digital camera. Rainfall simulation experimental data were used to characterise the hydrological behaviour of areas with a specific pattern of soil surface components by means of the parameters of the Horton equation. Plot runoff data were extrapolated at the hillslope scale based on the soil surface component maps and their hydrological characterisation. The results show that in both slopes runoff generation is concentrated up- and downslope, with a water accepting area in the centre of both slopes disrupting the hydrological connectivity at the slope scale. This reinfiltration patch at the centre of the slope is related to the type of soil surface component and its spatial pattern. Herbaceous vegetation and ‘on top rock fragments’ increase the infiltration capacity of soils at the centre of the slope. In contrast...

Effects of soil tillage on runoff generation in a Mediterranean apricot orchard

Abrisqueta Villena, Isabel; Plana, V.; Mounzer, Oussama; Ruiz Sánchez, Mª Carmen
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 579917 bytes; image/jpeg
ENG
Relevância na Pesquisa
37.22%
Two different soil tillage practices (perforated topsoil and mini-catchments) were compared with no tillage (control) in an assay to reduce runoff, promote infiltration and take advantage of rainfall in a drip irrigated, hillside apricot orchard under semi-arid Mediterranean conditions. In addition, the efficiency of water harvesting was quantified for the purpose of saving irrigation water. To predict runoff generation in the three treatments, the best fit was obtained with a two-parameter exponential model, which included the product of rainfall amount and rainfall intensity as independent variable. The model explains, on average, 92% of runoff generation for three soil tillage treatments. The antecedent soil moisture content may account for part of the unexplained runoff generation. More than 30% of the rainfall was lost by runoff in the control treatment, underlining the potential risk of sloping plantations for water and soil conservation. Both soil tillage treatments (mini-catchments and perforated topsoil) decreased the runoff by an 80% compared to the control treatment. During the experimental period, the mini-catchment treatment collected 86% and the perforated topsoil 57% more than the control, providing mean irrigation water saving of about 11 and 9%...

The role of antecedent soil water content in the runoff response of semiarid catchments: a simulation approach

Castillo Sánchez, Victor Manuel; Gomez-Plaza, A.; Martínez-Mena García, M. Dolores
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 579917 bytes; image/jpeg
ENG
Relevância na Pesquisa
37.3%
The soil water content is recognized as one of many runoff controlling factors in semiarid environments. A simple, physically based distributed model has been developed to study the role of antecedent soil water content in runoff generation in three small catchments in semiarid southeast Spain. The catchments were set up in two different zones: a burnt area with scarce vegetation and unburnt area with a denser plant cover. The infiltration process is determined by the Green–Ampt equation and the initial soil water content is taken into account by means of maps obtained by Conditional Gaussian simulation. The model was run 2700 times with different soil moisture scenarios and design storms. Stochastic sensitivity analysis was used to examine the role of antecedent soil water content in the runoff response. The results showed that the hydrological response after high intensity, low frequency storms is independent of the initial soil water content. On the other hand, the antecedent soil water content is an important factor controlling runoff during medium and low intensity storms, a type of rainstorm that is relatively frequent in semiarid areas. The sensitivity of the runoff response to soil moisture depended on the predominant runoff mechanisms. When infiltration excess overland flow is predominant...

Establishing Volume Reduction Goals and Reducing Stormwater Runoff Using Low Impact Development to Improve Coastal Water Quality

Fouts, Shannon
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Masters' project
Publicado em 25/04/2014
Relevância na Pesquisa
37.36%
Despite the Clean Water Act (CWA), passed by Congress in 1972, coastal water quality has continued to decline. The primary reason is the Act’s failure to adequately deal with stormwater runoff, the leading source of water pollution in coastal areas. Coastal development causes the velocity and volume of rainwater running off the land to increase, picking up pollutants in the process. Traditional stormwater systems convey that runoff directly into watersheds and coastal waters. Alternatives to the tradition stormwater systems exist that prevent runoff, instead of conveying it off the land as fast as possible. Low impact development (LID) is one option that uses a variety of techniques to mimic the lands natural hydrology by holding rainwater on the land and allowing it to infiltrate the soil. LID incorporate fairly simple measures, such as disconnecting downspouts from impervious surfaces, using rain barrels to capture runoff, and installing rain gardens, to reduce the runoff from development. Reducing stormwater runoff can be an effective way to improve water quality in areas where waters are not meeting their designated uses established under the CWA. This can be done by bringing runoff levels back to historically acceptable volumes. This analysis uses the methods in the NC Coastal Federation’s Watershed Restoration Planning Guidebook to establish a stormwater runoff volume reduction goal by calculating the increase in runoff between 2004 and 2013 in Beaufort...

An Economic approach to the ecological issues of urban stormwater runoff: A Case study of the Allen Creek Watershed in Monroe County, New York

Hellman, Kelly
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
37.3%
Urban stormwater runoff is excess runoff created by increased imperviousness in an urbanized watershed and can have significant impacts on both water quantity and quality. Natural communities and human communities are faced with damages that occur as a result of the change in the type and magnitude of stormwater runoff flows, including but not limited to increased flooding and degradation of natural aquatic systems. Therefore, from both an economic and ecological perspective, it is important that urban planners effectively manage excess stormwater runoff. This paper details the development of an ecological-economic model that can be used to guide urban planners in the implementation of cost-effective abatement solutions for a given watershed. The model can be used on a large-scale to guide stormwater management policies in entire counties, watersheds, etc., but can also be applied on a smaller scale, which is demonstrated by a case study in a sub-section of the Allen Creek watershed located primarily in the Town of Brighton, NY. The case study is focused on the impact of a potential development project in Brighton on the downstream residential properties and uses a hedonic price model to estimate the marginal damage cost of additional average annual stormwater runoff as a result of the new development project. This marginal damage cost is compared to the marginal cost of residential abatement technologies to determine the optimal volume of abatement in the Town of Brighton. Though focused primarily on the cost of increased water quantity...

TOPMODEL CAPABILITY FOR RAINFALL-RUNOFF MODELING OF THE AMMAMEH WATERSHED AT DIFFERENT TIME SCALES USING DIFFERENT TERRAIN ALGORITHMS (doi: 10.4090/juee.2011.v5n1.001014)

Nourani, Vahid; Roughani, Arash; Gebremichael, Mekonnen
Fonte: JUEE Press Publicador: JUEE Press
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; Formato: application/pdf
Publicado em 17/09/2011 ENG
Relevância na Pesquisa
37.25%
In this study the rainfall- runoff response of the Ammameh watershed located in Tehran, Iran was studied using TOPMODEL, a semi-distributed and geomorphologic model that simulates runoff at the watershed outlet based on the concepts of the saturation excess runoff and subsurface flow. Topographic index as an indicator of the spatial distribution of excess runoff generation in the catchment was calculated using Dinf and D8 methods which compute the flow direction from each cell using two different algorithms. The analysis was done at three time scales: event, daily, and monthly. The modeling performance of TOPMODEL in simulating runoff process for each of three types of time series was analyzed and compared visually and statistically. Also, the effects of D8 and Dinf methods on rainfall- runoff modeling were validated and compared and it was realized that modeling result of Dinf algorithm, especially in event- based rainfall- runoff modeling was more accurate than the D8 algorithm; whereas, the difference between the results were not notable in the daily modeling. Although the obtained results demonstrate the capability of the TOPMODEL in both event-based and daily simulations, the model could lead to the more reliable results in daily modeling because of considering the watershed soil moisture conditions...

Effects of tillage on runoff from a bare clayey soil on a semi-arid ecotope in the Limpopo Province of South Africa

Mzezewa,Jestinos; van Rensburg,Leon D
Fonte: Water SA Publicador: Water SA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2011 EN
Relevância na Pesquisa
37.32%
Runoff constitutes one of the major water losses from agricultural fields in semi-arid areas. However, by adopting appropriate soil management practices, the runoff can be harnessed for improving crop yields. The main objective of this study was to quantify rainfall-runoff relationships under in-field rainwater harvesting (IRWH) using simulated rainfall, and to compare these results to those obtained with annually tilled conventional tillage (CON) (control). IRWH is a special type of no-till (NT) crop production practice that promotes runoff from a crusted runoff strip into basins where the water infiltrates beyond evaporation but is available for crop use. Runoff was related to time to runoff, total runoff, final runoff rate and runoff coefficient. This experiment demonstrated that by adopting IRWH production technique smallholder farmers could harness an additional 45.54 m³·ha-1 of water compared to the CON system. The extra water harvested could meet about 1% of maize water requirements.

Quantifying rainfall-runoff relationships on the Melkassa Hypo Calcic Regosol ecotope in Ethiopia

Welderufael,WA; le Roux,PAL; Hensley,M
Fonte: Water SA Publicador: Water SA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2009 EN
Relevância na Pesquisa
37.25%
Droughts, resulting in low crop yields, are common in the semi-arid areas of Ethiopia and adversely influence the well-being of many people. The introduction of any strategy that could increase yields would therefore be advantageous. The objective of this study was to attempt to assess the influence of in-field rainwater harvesting (IRWH), compared to conventional tillage, on increasing the amount of water available to a crop like maize on a semi-arid ecotope at Melkassa situated in the eastern part of the Rift Valley. To achieve the objective of the study rainfall-runoff measurements were made during 2003 and 2004 on 2 m x 2 m plots provided with a runoff measuring system and replicated 3 times for each treatment. There were 2 treatments: conventional tillage (CT) on which hand cultivation was practised in a way that simulated the normal local CT; and a flat surface simulating the no-till, undisturbed surface of the IRWH technique (NT). Rainfall-runoff measurements were made over 2 rainy seasons during which there were 25 storms with > 9 mm of rain. From the 25 storms, only the 2nd season storms (8 storms) had runoff measurements. These storms were used for calibration and validation of the Morin and Cluff (1980) runoff model (MC Model). Appropriate values for final infiltration rate (If)...

Projected future runoff of the Breede River under climate change

Steynor,AC; Hewitson,BC; Tadross,MA
Fonte: Water SA Publicador: Water SA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/07/2009 EN
Relevância na Pesquisa
37.25%
The Breede River is the largest river in the Western Cape Province of South Africa, and as such, is a key resource for a variety of activities within the region. It is this significance of the river that prompted a study into the impact of climate change on future runoff in the river and hence, the potential impacts a projected change in catchment runoff may have on the future use of the river. Due to the complexities of the catchment only specialised hydrological models can capture the system dynamics of the river adequately. This limitation prompted the use of an alternative approach (self-organising maps (SOMs)) to hydrological modelling and, at the same time, performed an assessment of the appropriateness of this alternative approach for use in such applications. SOMs are a powerful tool in synoptic climatology as they can be used to objectively classify a large number of daily synoptic states into a predetermined number of groups. Each archetypal synoptic pattern is linked to an observed associated runoff in the catchment. With an assessment of the change in frequency of each atmospheric state from control to future comes an assessment of the change in frequency of the associated runoff from control to future. The end result of this is a quantified assessment of the projected change in both high-frequency runoff events and in the projected change in mean annual runoff (MAR) in the catchment from the present to the future under 3 climate models. Not only does this information assist in the process of long-term policy decisions made in relation to water-transfer schemes...