بخشی از مقاله انگلیسی:
In semi-arid Mediterranean areas, the construction of small dams aimed at providing water for domestic supply, livestock, or irrigation has generated a need for information on sediment yields for the main river basins. In southern Italy, a long-term monitoring programme was initiated by the National Hydrographic Service during the first half of the last century to address this need. The information obtained for the rivers in Calabria during the 1960s and 1970s documented relatively low suspended sediment yields in this area. However, recent studies in this region have demonstrated that the low values of specific sediment yield derived from this monitoring programme obscure the existence of appreciable erosion rates in many areas of the catchments involved (Porto et al., 2009b). To better understand the relationship between the sediment yield at a catchment outlet, and rates of sediment mobilisation and transfer within the catchment, there is a need to employ alternative methods capable of providing information on soil redistribution rates for large areas. In recent years, the fallout radionuclide caesium-137 ( 137Cs) has been increasingly used to document rates of soil redistribution associated with sheet erosion both as an alternative to conventional measurements, and for calibrating physically-based soil erosion models (Di Stefano et al., 2000; Walling, 1998; Porto et al., 2001). This paper reports the results of a study where 137Cs measurements were employed within a medium-scale (41.3 km2 ) catchment in southern Italy, with the aim of assembling information on soil erosion and redistribution on the catchment slopes. Data available from suspended sediment monitoring undertaken at the catchment outlet during the 1960s and 1970s have been used to estimate the contemporary sediment yield. This estimate has been combined with the information provided by the 137Cs measurements to establish a sediment budget for the catchment. The results confirm that 137Cs measurements are valuable for quantifying both erosion and sediment redistribution within a catchment and therefore, for establishing its sediment.
THE STUDY AREA
The Melito catchment (Fig. 1) is located in Calabria (southern Italy) in the vicinity of the Sila National Park. The catchment has a drainage area of 41.3 km2 and ranges in altitude from 1300 m a.s.l. at its highest point (Colle San Domenico) to 324 m a.s.l. at the catchment outlet (Olivella) where the main channel flows into the larger River Corace. Geologically, the Melito catchment is underlain by granitoid sand and intermediate and high-grade metamorphic rocks, typical of the Aspromonte Mountains that are part of the Calabro-Peloritan arc, a region with the highest tectonic activity in Europe. Detailed soil surveys undertaken in this catchment have shown that the soils developed on these rock types are characterised by a range of textures, although sandy and silt-sandy soils are dominant. The catchment is mainly uncultivated and large areas are covered by pines (Pinus nigra ssp. laricio, P. sylvestris, P. leucodermis) beech (Fagus sylvatica L.) and different species of oak (Quercus cerris, Q. pubescens, Q. frainetto, Q. petrea, Q. robur). The rainy season extends from September to April, and the mean annual rainfall for the period 1962–۲۰۰۰ measured at Umbri (altitude 885 m a.s.l., 39°۰۱′۳۱″N, 16°۳۳′۲۴″E), is ~1127 mm (SIMI, 1920–۲۰۰۰). In 1983 the Melito catchment was identified as the preferred site for a proposed dam (with a reservoir storing more than 100 million m3 ) to provide water for domestic supply, livestock, and irrigation within the local area. To date, this dam has not been built, although construction is now in progress. To support the design of this and other dams in the region, the Italian Hydrographic Service (SIMI) undertook measurements of rainfall, runoff, and suspended sediment concentration at the catchment outlet during the period 1962–۱۹۷۷٫ During this monitoring period, the annual specific suspended sediment yield, derived from the sediment concentration measurements, ranged from 5.4 t km-2 year-1 in 1970 to 205 t km-2 year-1 in 1976, with a mean annual value of 40 t km-2 year -1 (Fig. 2). Porto et al. (2006) documented higher values of sediment yield (ranging from 760 to 2080 t km-2 year-1 ) for the coastal areas of the same region (see also Cinnirella et al., 1998; Porto et al., 2009a). However, the values reported in this work, although considerably lower, can be regarded as representative of the mountain areas of the Serre Massif (see Porto et al., 2009b).
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