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Connectivity analysis between overland flow generation and erosion under Mediterranean semiarid conditions (Porta-Coeli experimental micro-basin, Valencia, Spain)

AuthorsPascual, Juan Antonio ; Andreu Pérez, V. ; Rubio, José Luis
Issue DateNov-2011
PublisherUniversidad Politécnica de Madrid
CSIC - Instituto de Diagnóstico Ambiental y Estudios del Agua (IDAEA)
Consejo Superior de Investigaciones Científicas (España)
Citation2nd SCARCE Annual Conference (2011)
AbstractOverland flow generation within the same basin is dependent on different factors that facilitate sectors connectivity and flow concentration. Dominant factors (climatic, topographic, ecologic, etc.) may not be the same according to the area size and hence their interaction is dependent on scale (drainage area size) and dimensions (rainfall intensity and duration). Hydrological connectivity is also behind of the subsequent process of erosion, which is understood as a major threat in Mediterranean semiarid ecosystems due to vegetation scarcity. Surface water connection will determine the existence of erosion production, transport and accumulation inside and outside the basin. If hydrological connectivity may produce also erosion connectivity, soil depletion and loss of soil capacity to sustain plants will be undesirable consequences producing the final degradation of soils and increasing the risk of desertification. In this work a methodology to study overland flow generation and sediment (erosion) yield has been developed in the Portacoeli experimental micro-basin nested in the greater Barranc the Carraixet watershed in the proximity of the city of Valencia, Spain. Hydrological connectivity and response to rainfall events has been analysed at three scales: (1) The greater Barranc the Carraixet watershed, (2) the micro-basin (both instrumented with automatic flow records) and (3) seven experimental plots, four under controlled conditions with different vegetation cover and three under natural conditions. Erosion response related to rainfall events and overland flow was studied in all experimental plots. The analysis has been applied to a one year records of rainfall, overland flow and sediment data, from April 2008 to March 2009. Results show that scale is a key element to establish flows concentration and hence connectivity. There is an exponential relationship between the size of the draining area and flow production, regardless of the type of cover. Nonetheless, at plot scale the type of vegetation cover has influence on overland flow production where open spaces with bare soil spaces may be crucial to organized water connections through some slope sectors. Other factor as topography and lithology (e.g. areas of rock outcrops) may result relevant to micro-basin scale where slope sectors connectivity has to be overcome. To greater scale, major landscape or land cover units together with anthropogenic and meteorological characteristics have to be considered to produce concentrated flow. In fact no record has been registered at the watershed (Barranc de Carraixet) scales during more than ten years. At plot scale erosion has been scarcely produced. Of the total 26 rainfall events recorded very few were identified as erosive, and in all cases with very small amounts mainly obtained under natural conditions. Such results suggest that erosion connectivity, when exists, may be produced at slope scale and further incorporated to concentrated flow at the micro-basin scale. The absence of flow registers to the watershed scale suggests that the small proportion of sediments conveyed at micro-basin scale may not abandon such scale unit being redistributed internally without further connections.
DescriptionPoster presentado en el 2nd SCARCE Annual Conference celebrado en Madrid el 28 y 29 de noviembre de 2011
Appears in Collections:(CIDE) Comunicaciones congresos
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