M. Isabel P. de Lima

The influence of storm movement on water erosion: storm direction and velocity effects

Abstract Although the problem of storm movement affecting flows (shape of the hydrograph and peak discharges) has been recognised for a long time, most overland flow and water erosion studies do not take into account the effect on the runoff response caused by the movement of the storm across the catchment. Ignoring of the storm movement can result in considerable over- and underestimation of runoff volumes and peaks, and associated soil loss by sheet erosion. This work shows the results of laboratory experiments that were undertaken to study the effect of moving storms on the water erosion process. The experiments were carried out using a soil flume adjustable to different slopes and a movable sprinkling-type rainfall simulator. Both the effects of storm velocity and direction, and surface slope were studied. To simulate moving rainstorms, the rainfall simulator was moved upstream and downstream over the soil surface. The results show that the storm direction and velocity strongly affect the water erosion process. The soil loss caused by the downstream moving rainstorms is higher than that caused by the identical upstream moving rainfall storms.

Mapping Soil Surface Macropores Using Infrared Thermography: An Exploratory Laboratory Study

Macropores and water flow in soils and substrates are complex and are related to topics like preferential flow, nonequilibrium flow, and dual-continuum. Hence, the quantification of the number of macropores and the determination of their geometry are expected to provide a better understanding on the effects of pores on the soils physical and hydraulic properties. This exploratory study aimed at evaluating the potential of using infrared thermography for mapping macroporosity at the soil surface and estimating the number and size of such macropores. The presented technique was applied to a small scale study (laboratory soil flume).

Using thermal tracers to estimate flow velocities of shallow flows: laboratory and field experiments

Abstract Accurate measurement of shallow flows is important for hydraulics, hydrology and water resources management. The objective of this paper is to discuss a technique for shallow flow and overland flow velocity estimation that uses infrared thermography. Laboratory flumes and different bare, vegetated and paved field surfaces were used to test the technique. Results show that shallow flow surface velocities estimated using thermal tracers and infrared technology are similar to estimates obtained using the Acoustic Doppler Velocimeter; similar results were also obtained for overland flow velocity estimates using thermography, here comparing with the dye tracer technique. The thermographic approach revealed some potential as a flow visualization technique, and leaves space for future studies and research.

Hydrological research in small catchments – an approach to improve knowledge on hydrological processes and global change impacts

1 Institute of Hydrology, Slovak Academy of Sciences, Ondrašovská 16, 031 05 Liptovský Mikuláš, Slovakia. 2 Institut für Wasserwirtschaft, Hydrologie und konstruktiver Wasserbau (IWHW), University of Natural Resources and Life Sciences, (Boku), Muthgasse 18, 1190 Vienna, Austria. 3 Department of Civil Engineering, Faculty of Science and Technology of the University of Coimbra, Rua Luís Reis Santos, Campus II – University of Coimbra, 3030-788 Coimbra, Portugal. 4 MARE Marine and Environmental Sciences Centre and IMAR Institute of Marine Research, Coimbra, Portugal.

Análise de tendência da precipitação anual e mensal no período 1900-2000, em Portugal Continental

EnglishThis work investigates the presence of trends in the temporal structure of precipitation in Mainland Portugal. The study uses annual and monthly precipitation data from 1900 to 2000, recorded in 9 locations scattered over the territory. The data are analyzed using statistical methods (e.g. Mann-Kendall trend test). In order to take into account seasonality and serial correlation, the different months of the year were analyzed separately. The analyses of monthly data lead to a characterization of changes in the distribution of precipitation within the year over Mainland Portugal. portuguesEste trabalho debruca-se sobre o estudo da precipitacao em Portugal Continental, com base em nove series temporais de observacoes udometricas, abrangendo todo o seculo XX. Os dados analisados tem uma distribuicao geografica que cobre varias regioes do Pais. As series sao analisadas por metodos estatistic9s com o objectivo de testar se existe uma alteracao, ao longo do tempo, da grandeza climatica em estudo. E feita a analise de tendencia da precipitacao anual e da precipitacao mensal, o que permite caracterizar, neste ultimo caso, as alteracoes da distribuicao da precipitacao durante o ano, no territorio nacional

Revisiting simple methods to estimate drop size distributions: a novel approach based on infrared thermography

Abstract The infrared thermography has been successfully applied as a tool for high resolution imaging in different hydrological studies. This exploratory experimental study aimed at evaluating the possibility of using infrared thermography to determine the diameter of raindrops. Rain samples are collected on a pre-heated acrylic board, which is exposed to rain during an instant, and thermograms are recorded. The area of the thermal stains (“signatures” of the raindrops) emerging on the board is measured and converted to drop diameters, applying a calibration equation. Diameters of natural raindrops estimated using this technique were compared with laser disdrometer measurements; the Nash-Sutcliffe efficiency coefficient was used for evaluating the match between the resulting histograms of drop size distribution. Results confirm the usefulness of this simple technique for sizing and counting raindrops, although it is unsatisfactory in light rain or drizzle.

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...