Natural Rainfall (natural + rainfall)

Distribution by Scientific Domains

Selected Abstracts

Infiltration, runoff and sediment production in blanket peat catchments: implications of field rainfall simulation experiments

J. Holden
Abstract Blanket peat covers the headwaters of many major European rivers. Runoff production in upland blanket peat catchments is flashy with large flood peaks and short lag times; there is minimal baseflow. Little is known about the exact processes of infiltration and runoff generation within these upland headwaters. This paper presents results from a set of rainfall simulation experiments performed on the blanket peat moorland of the North Pennines, UK. Rainfall was simulated at low intensities (3,12 mm h,1), typical of natural rainfall, on bare and vegetated peat surfaces. Runoff response shows that infiltration rate increases with rainfall intensity; the use of low-intensity rainfall therefore allows a more realistic evaluation of infiltration rates and flow processes than previous studies. Overland flow is shown to be common on both vegetated and bare peat surfaces although surface cover does exert some control. Most runoff is produced within the top few centimetres of the peat and runoff response decreases rapidly with depth. Little vertical percolation takes place to depths greater than 10 cm owing to the saturation of the peat mass. This study provides evidence that the quickflow response of upland blanket peat catchments is a result of saturation-excess overland flow generation. Rainfall,runoff response from small plots varies with season. Following warm, dry weather, rainfall tends to infiltrate more readily into blanket peat, not just initially but to the extent that steady-state surface runoff rates are reduced and more flow takes place within the peat, albeit at shallow depth. Sediment erosion from bare peat plots tends to be supply limited. Seasonal weather conditions may affect this in that after a warm, dry spell, surface desiccation allows sediment erosion to become transport limited. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Hydrological and erosional response to natural rainfall in a semi-arid area of south-east Spain

M. Martinez-Mena
Abstract A better knowledge of soil erosion by water is essential for planning effective soil and water conservation practices in semi-arid Mediterranean environments. The special climatic and hydrological characteristics of these areas, however, make accurate soil loss predictions difficult, particularly in the absence of minimal data. Two zero-order experimental microcatchments (328,759 m2), representative of an extensive semi-arid watershed with a high potential erosion risk in the south-east of Spain, were selected and monitored for 3 years (1991,93) in order to provide information on the hydrological and erosional response. A pluviogram and hydrograph recorded data at 1-min intervals during each storm, after which the soil loss was collected and the particle size of the sediment was analysed. Runoff coefficients of about 9% and soil losses of between 84·83 and 298·9 g m,2 year,1 were observed in the area. Rapid response times (geometric mean values lower than 2 h) and low runoff thresholds (mean values between 3·5 to 5·9 mm) were the norm in the experimental areas. A rain intensity of over 15 mm h,1 was considered as ,erosive rainfall' in these areas because of the total soil loss and the transport capacity of the overland flow. Differences in pore-size distribution explained the different hydrological responses observed between areas. The erosional response was more complex and basically seemed to be determined by soil aggregate stability and topographical properties. A greater proportion of finer particles in the eroded material than in the soil matrix indicated selective erosion and the transport of finer material. Copyright © 2001 John Wiley & Sons, Ltd. [source]


Daren Harmel
ABSTRACT: Measured field scale data are increasingly used to guide policy and management decisions based on comparative pollutant load information from various land management alternatives. The primary objective of this study was to compile measured annual nitrogen (N) and phosphorus (P) load data representing field scale transport from agricultural land uses. This effort expanded previous work that established an initial nutrient export coefficient dataset. Only measured annual N and P load data published in scientific peer-reviewed studies were included in the present compilation. Additional criteria for inclusion were: spatial scale (field scale or farm scale, minimum 0.009 ha); land use (homogeneous, either cultivated agriculture or pasture/rangeland/hay); natural rainfall (not rainfall simulation); and temporal scale (minimum one year). Annual N and P load data were obtained from 40 publications, resulting in a 163-record database with more than 1,100 watershed years of data. Basic descriptive statistics in relation to N and P loads were tabulated for tillage management, conservation practices, fertilizer application, soil texture, watershed size, and land use (crop type). The resulting Measured Annual Nutrient loads from A Circumlittoral Environments (MANAGE) database provides readily accessible, easily queried watershed characteristic and nutrient load data and establishes a platform suitable for input of additional project specific data. [source]

The impact of cotton geotextiles on soil and water losses from Mediterranean rainfed agricultural land

A. Giménez-Morera
Abstract High soil erosion risk of Mediterranean cultivated soils is due to steep slopes, high rainfall intensities and low vegetation cover. Traditional land management as ploughing and herbicides give rise to high soil erosion rates. This paper reports on the use of a cotton geotextiles to control soil and water losses on agricultural land under Mediterranean climatic conditions. Eight paired plots (1, 2, 4 and 16,m2) were studied during 1-year period under natural rainfall. Forty rainfall simulations under wet and dry climatic conditions, and water drop penetration time (WDPT) tests, were carried out in order to analyze the effect of a geotextile on soil and water losses on a typical rainfed orchard in Eastern Spain. Results showed that an 8,mm thick cotton geotextile reduced soil loss to negligible values (from 14 to 0·1,Mg,ha,1,y,1) due to the low sediment concentration as geotextile covered 100% of the soil. However, infiltration rates decreased and runoff increased due to the hydrophobic response of the cotton material. The runoff discharge increased from 8% to 16% for the 2004 period under natural rainfall and from 27% to 87% under simulated rainfall when summer dry conditions were reached. The cotton geotextile reduced local soil losses at plot-scale, but increased runoff. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Identification of a single dominant allele for resistance to blackleg in Brassica napus,Surpass 400'

PLANT BREEDING, Issue 6 2003
C.-X. Li
Abstract The inheritance of resistance to blackleg (caused by Leptosphaeria maculans) was examined in the F1 and F2 of a cross between highly resistant canola ,Surpass 400' and susceptible ,Westar' in the field. Blackleg-infected canola straw was collected from the field and scattered among plants to increase disease development with the aid of natural rainfall. Disease severity on seedlings was assessed as the average number of lesions on leaves 1 and 2, and on adult plants as the percentage necrosis on a cross-section of stems immediately above the crown. All ,Westar' plants were susceptible (S) and all ,Surpass 400' and F1 plants were resistant (R) at both growth stages. Disease severity on F2 plants segregated 3 : 1 (R : S) as expected for a single dominant resistance allele in both the seedling and adult plant stages. There was a high proportion (91.1%) of matching reactions (R-R and S-S) between seedling and adult plants. ,Surpass 400' is the source of a single dominant allele for blackleg resistance in Brassica napus that is expressed strongly in both seedlings and adult plants. [source]