Search results for "feature"

Channel forms and vegetation adjustment to damming in a Mediterranean gravel‐bed river (Serpis River, Spain)

2018

Contribution of the largest events to suspended sediment transport across the USA

2010

This work analyses the contribution of the largest events to suspended sediment transport on the continental scale. The analysis is based on the United States Geological Survey (USGS) Suspended Sediment and Ancillary database. Data were obtained from 1314 catchments, comprising more than 2 500 000 daily events. The total number of days in the dataset amounts to 10 000 years. Catchments are of different sizes and belong to distinct climatic environments; they are distributed for the analysis according to USA hydrological divisions (HDs). The main objective of the research is to examine the effect of the n-largest event on the total suspended sediment load over recorded periods, and to discus…

Flood events in Mediterranean ephemeral streams (ramblas) in Valencia region, Spain

2001

This article deals with flood events in Mediterranean ephemeral streams typical of the Valencia region. The combination of the basin physical characteristics steep slopes, sparse vegetation, thin soils and permeable rock. and intense, heavy and irregularly distributed rain, generates flash floods. Runoff generation is sudden, giving rise to flash floods with sharp, narrow hydrographs with short time lags. The high amount of runoff is, nevertheless, only a small fraction of the total rainfall, since the characteristics of the river basins are such that infiltration of large amounts of water occurs. Using daily hydrological data from the Rambla de la Viuda basin and 5-min data from both the B…

Reliability and effectiveness of Ellenberg’s indices in checking flora and vegetation changes induced by climatic variations

2001

Two methods are proposed to assess the significance of time-spanned local variations of Ellenberg’s indicator values in floristic and phytosociological data sets respectively. Both methods are based on frequencies and averages of the indicator values within and among data sets. Main goal of proposed methods is to determine the threshold above which the observed variations are to be considered significant. In order to relate the observed floristic variations to recent climatic changes, attention was focused on the Ellenberg’s indices dealing with the main climatic variables: heliophany, temperature and precipitation. Study-cases from Zannone Island (Pontine Archipelago, Mediterranean region)…

Shrubland as a soil and water conservation agent in Mediterranean-type ecosystems

2015

John Thornes found that shrubland was a key factor in the control of soil erosion on Mediterranean hillsides. His research inspired many scientists to investigate the impact of shrubland changes and management in semi-arid ecosystems. An example of Professor Thornes’ scientific influence is the experiment carried out on the El Teularet–Sierra de Enguera experimental station since 2003 which showed erosion rates on a 30-year-old abandoned orchard with dense vegetation cover of Ulex parviflorus and Cistus albidus and a 20-year-old fire-affected maquia with Quercus coccifera, Pistacia lentiscus and Juniperus oxycedrus. The measurements demonstrated that the shrubs help create more stable soil …

Groundwater nitrate risk assessment using intrinsic vulnerability methods: A comparative study of environmental impact by intensive farming in the Me…

2015

Abstract Groundwater contamination by nitrate and other nutrients is a major problem throughout the world, often occurring as the result of anthropogenic activities, lack of management, and over-exploitation of groundwater resources. In the last few decades in the majority of the Italian regions, the nitrate concentrations in groundwater have dramatically increased, mainly as a consequence of the large-scale agricultural application of manure and fertilizers. This excessive use of chemicals and fertilizers increases the risk of surface and groundwater pollution from diffuse sources, which have an important impact on human health and the environment. Sicily is located in the central Mediterr…

Hydrochemical evolution and environmental features of Salso River catchment, central Sicily (Italy)

2000

A hydrogeochemical study of the Salso River highlighted the chemical and isotopic space-time evolution along its flow path and the main contamination processes. Within the basin, three different hydrogeochemical facies have been individuated: (1) Ca-Mg-HCO3, (2) Ca-Mg-SO4 and (3) Na-Cl. The first facies reflects the chemical composition of the groundwaters hosted in the carbonate reliefs that belong to the Madonie Mountains. The second and the third facies are the result of the interaction processes between surface waters and the gypsum and salty clays, respectively. Two pollution sources have been also located in the basin downstream from the salt mine and downstream from a discharge area …

A diachronic analysis of estuarine turbidity due to a flood following an extreme rainfall event

2011

During floods following rainfall events characterized by long return period, rivers bring to their mouths the higher concentration of sediments. This paper deals with a qualitative assessment of coastal water and turbidity load in estuarine waters as a consequence of an intense rainfall event occurred on the 16t h and 17 th September 2003 in the eastern part of Sicily. Although empirical relationships to estimate turbidity using remote sensing can be found in literature, however models parameters need to be calibrated through in situ measures acquired via intensive field campaigns. The algorithm used within this research was calibrated using field data acquired during three periods in 2008 …

Analysis of rill step–pool morphology and its comparison with stream case

2021

In this paper, the morphology of step–pool features is analysed using rill measurements and literature data for streams. Close-range photogrammetry was used to carry out ground measurements on rills with step–pool units, shaped on a plot having slope equal to 14, 15, 22, 24 and 26%. Data were used to compare the relationships between H/L, in which H is the step height and L is the step length, and the mean gradient of the step–pool sequence, Sm, for streams or the slope of the step–pool unit, S, for rills. The relationship of H/L against Sm is widely used to test the occurrence of the maximum flow resistance condition in streams, which is associated with the range 1 ≤ (H/L)/Sm ≤ 2. Further …

Extraordinary sediment delivery and rapid geomorphic response following the 2008-2009 eruption of Chaitén Volcano, Chile

2016

U.S. Geological Survey Volcano Science Center SERNAGEOMIN's Programa de Riesgos Volcanicos Conicyt Fondecyt grants 1110609 1141064 11130671 Conicyt Fondap 15090013 Vamos Research Centre