Jorge Isidoro

Influence of wind-driven rain on the rainfall-runoff process for urban areas: Scale model of high-rise buildings

The hydrological response of impervious urban areas with varying building densities to the combined action of wind and rain is not well understood. Exploratory laboratory simulations were conducted using a scale model of a hypothetical high density urbanized area with high-rise buildings. Seventy two runs were conducted for static and moving storms in upstream and downstream directions, with and without wind, for different building densities and for an average rainfall intensity of 120 mm/h. The laboratory experiments show that building density and the spatial and temporal distribution of rainfall that results from wind and storm movement have a clear influence on the hydrological response to rainstorms. Increased urbanization promotes a higher peak discharge, a longer base time and reduces the slope of the hydrographs rising limbs, while wind-driven rain attenuates these effects. Downhill storm movement promotes a faster hydrological response and a higher discharge peak than uphill movement.

Classification of landforms in Southern Portugal (Ria Formosa Basin)

A Geographic Information Systems-based tool is used for macro-landform classification following the Hammond procedure, based upon a Digital Terrain Model (DTM) created from ordinary Kriging. Gentle slopes, surface curvature, highlands and lowlands areas are derived from the DTM. Combining this information allows the classification of terrain units (landforms). The procedure is applied to the Ria Formosa basin (Southern Portugal), with five different terrain types classified (plains, tablelands, plains with hills, open hills and hills).

Analytical Closed-Form Solution for 1D Linear Kinematic Overland Flow under Moving Rainstorms

AbstractAn analytical solution for overland flow under (upstream and downstream) moving storms that uses Laplace transformation to solve the one-dimensional (1D) linear kinematic wave equation is presented. This solution, which corresponds to a single continuous function for the total space-time domain of the overland hydrograph, enables evaluation of the discharge over time for the total drainage plane surface. The result was compared with another analytical solution, a numerical simulation, and experimental runs using a laboratory flume. The comparison showed very good fit, and the proposed analytical solution was thus regarded as validated. By applying the model to hypothetical catchments and storm patterns, distinct hydrologic responses for upstream and downstream moving storms were identified.

Incorporating the Effect of Moving Storms into Hillslope Hydrology: Results from a Multiple-Slope Soil Flume

The importance of storm movement on surface flow has long been acknowledged at varying scales ranging from headwater scales to drainage basins. Different studies have shown that moving rainstorms substantially affect surface flow hydrographs, although some of the results reported need further discussion. The main objective of this study is to quantify at the hillslope scale the hydrologic response to both non-moving and moving rainstorms in terms of discharge and soil loss. Controlled laboratory experiments were carried out using a multiple-slope soil flume subjected to a movable sprinkling-type rainfall simulator. To simulate moving rainstorms, the rainfall simulator was moved upstream and downstream over the soil surface at different speeds. Results show that the direction of storm movement, especially for very high intensity rainfall events, significantly affected runoff and water erosion with downstream-moving storms, causing higher peak runoff and erosion than did upstream-moving storms.

Infiltration of Portuguese cobblestone pavements – An exploratory assessment using a double-ring infiltrometer

Abstract The present study aims to evaluate small-scale infiltration losses of Portuguese cobblestone pavements. This type of pavement consists of rectangular hand-cut natural stones, mainly limestone, with different sizes and it is the most usual type of pavement for sidewalks and squares in Portuguese villages and cities. Portuguese cobblestone pavement can also be seen in several urban environments worldwide. A double-ring infiltrometer under constant and falling head was used for the field research work. Portuguese cobblestone pavements with small and coarse blocks were studied. The latter yield lower infiltration rates when compared to the former. The results show that, despite the block size, Portuguese cobblestone pavement contribute to reduce runoff, when compared with other impervious urban pavements.

Enhancing the spatial rainfall uniformity of pressurized nozzle simulators

Purpose Rainfall simulators are used on experimental hydrology, in areas such as, e.g., urban drainage and soil erosion, with important timesaving when compared to real scale hydrological monitoring. The purpose of this paper is to contribute to increase the quality of rainfall simulation, namely, for its use with scaled physical models. Design/methodology/approach Two pressurized rainfall simulators are considered. M1 uses three HH-W 1/4 FullJet nozzles under an operating pressure of 166.76 kPa and was tested over a 4.00 m length by 2.00 m width V-shaped surface. M2 was prepared to produce artificial rainfall over an area of 10.00 m length by 10.00 m width. The spatial distribution of rainfall produced from a single nozzle was characterized in order to theoretically find the best positioning for nozzles to cover the full 100 m2 area with the best possible rainfall uniformity. Findings Experiments with M1 led to an average rainfall intensity of 76.77-82.25 mm h−1 with a 24.88 per cent variation coefficient and a Christiansen Uniformity Coefficient (CUC) of 78.86 per cent. The best result with M2 was an average rainfall intensity of 75.12-76.83 mm h−1 with a 21.23 per cent variation coefficient and a CUC of 83.05 per cent. Practical implications This study contributes to increase the quality of artificial rainfall produced by pressurized rainfall simulators. Originality/value M2 is the largest rainfall simulator known by the authors worldwide. Its use on rainfall-runoff studies (e.g. urban areas, erosion, pollutant transport) will allow for a better understanding of complex surface hydrology processes.

Soil erosion, Serra de Grândola (Portugal)

ABSTRACT Soil erosion has long been the subject of attention for environmental management researchers because it implies the loss of a key natural resource for sustaining life. Several methodologies for soil erosion assessment have been developed; many of these are supported by Geographic Information Systems. This study aims to classify the susceptibility of rainfall-induced erosion at the Serra de Grândola (Portugal), based on the Priority Actions Programme/Regional Activity Centre guidelines for mapping soil erosion on the Mediterranean coast. Results show a low-to-moderate susceptibility to rainfall-induced erosion in the lowlands, becoming moderate to high in the highlands of the Serra de Grândola.

Longitudinal Hillslope Shape Effects on Runoff and Sediment Loss: Laboratory Flume Experiments

AbstractCatchment geomorphology is one of the most important factors governing runoff and erosion. However, its complexity is difficult to describe accurately; thus, for simplicity, many studies as...

GIS-Based Models as Tools for Environmental Issues: Applications in the South of Portugal

© 2012 Isidoro et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. GIS-Based Models as Tools for Environmental Issues: Applications in the South of Portugal

Brain Perfusion SPECT in patients with Mild Cognitive Impairment: comparison with visual function assessment

Background: There is a great interest in Mild Cognitive Impairment (MCI) characterization and in proposing new biomarkers that predict the conversion to Alzheimer’s Disease (AD). We are especially interested in hypo-perfusion profiles as measured by single photon emission computed tomography (SPECT), and in the use of psychophysical visual measures, since motion perception seems to be impaired in mild-AD. We aimed to investigate whether such deficits are already present at the stage of MCI and correlate these results with multi-regional cerebral blood flow (rCBF). Methods: A group of amnestic MCI (N 1⁄4 38), mild-AD (N 1⁄4 35) and matched controls (N 1⁄4 20), were recruited using standard criteria. A sub-group of participants without retinal pathology underwent visual function assessment using psychophysical tests: Structure-From-Motion (SFM) perception, Cambridge Colour Test (CCT), Frequency-Doubling Test (FDT). rCBF was measured using [99mTc-HMP] and images were analysed using Neurogam-software. Results: MCI group presented a significant hypo-perfusion (<1.5 SD) comparatively to an internal-software control group, in posterior cingulate cortex (A23 and A24) and left entorhinal cortex (A28). As a group, mild-AD subjects had more extensive areas of hypo-perfusion in neocortex with significant differences to MCI in internal temporal areas, Wernicke’s area, parietal lobes, pre-frontal and cingulate cortex. Post-hoc comparisons between groups revealed significant impairment of mild-AD patients relative to controls in all visual tests, while MCI patients were impaired only in SFM discrimination. In these patients, weobserveda significant correlation between SFM and hypo-perfusion of occipital areas (V2). CCT was significantly correlated with one of the major hypo-perfusion areas (A24) and also with angular gyrus. The FDT test presented a broader correlation with frontal-eye-field areas, associative visual cortex and both fusiform and superior temporal gyri. There was also a strong correlation between all tasks and Thalamus perfusion. Conclusions: MCI group presented hypo-perfusion in cingulate cortex, medial temporal and pre-frontal regions, the typical profile of pre-clinical histological AD. Visual function assessment indicated dissociation between dorsal and ventral visual stream deficits in amnestic types of dementia, suggesting that occipital and parietal networks involved in motion perception may be affected early in the course of the disease. The emergence of correlation between visual tasks and hypo-perfusion corroborates the early occipital network involvement.