João L. M. 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.

Role of physical fragmentation and invertebrate activity in the breakdown rate of leaves

We evaluated the relative importance of current velocity and invertebrate activities in the breakdown rate of alder (Alnus glutinosa (L.) Gaertner) leaves. Decomposition experiments were carried out in artificial channels, where current velo- city and shredder presence were manipulated, and in a 4 th order stream, in both summer and autumn, where litter bags were incubated in several reaches differing in both depth and current velocity. Alder leaves incubated in artificial channels decomposed signifi- cantly faster in the presence of shredders than in their absence (k = 0.0368/d vs. k = 0.0210/d in low current and k = 0.0472/d vs. k = 0.0219/d in high current). However, cur- rent (up to 2.35 m/s) had no significant effect on decomposition rates. In channels with- out invertebrates, no significant differences in k values were found between coarse and fine mesh bags in high (0.20 m/s) and low (0.05 m/s) current. Leaves incubated in the stream during summer, in reaches with current velocity ranging from 0.003 to 1.185 m/s, did not differ in their decomposition rates (k = 0.0489/d to k = 0.0645/d). In autumn, leaves exposed to high current (1.228 m/s) had faster decomposition rate (k = 0.0417/d vs. k = 0.0136/d), which may be related to sediment transport during this time of the year or to the tendency for higher number of shredders in high current-shallow reaches.

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.

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).

Prediction of skin surface soil permeability by infrared thermography: a soil flume experiment

This study presents a new technique to map soil surface permeability using infrared thermography, and to identify preferential flow. Laboratory tests were carried out using a soil flume where different scenarios were tested. Heated water was used to create a temperature gradient on the soil surface and high-resolution soil surface thermal imaging were obtained using a portable infrared camera. The technique was tested using soils with different permeability. The proposed technique successfully allows us to identify different soil surface permeability and to visualise preferential flows.

Impact of severe rain storms on soil erosion: Experimental evaluation of wind-driven rain and its implications for natural hazard management

Abstract Prediction and risk assessment of hydrological extremes are great challenges. Following climate predictions, frequent and violent rainstorms will become a new hazard to several regions in the medium term. Particularly agricultural soils will be severely threatened due to the combined action of heavy rainfall and accompanying winds on bare soil surfaces. Based on the general underestimation of the effect of wind on water erosion, conventional soil erosion measurements and modeling approaches lack related information to adequately calculate its impact. The presented experimental-empirical approach shows the strong impact of wind on the erosive potential of rain. The tested soils had properties that characterize three environments 1. Silty loam of semi-arid Mediterranean dryfarming and fallow, 2. clayey loam of humid agricultural sites and 3. cohesionless sandy substrates as found at coasts, dune fields and drift-sand areas. Total erosion was found to increase by a factor of 1.3 to 7.1, depending on site characteristics. A complementary laboratory procedure was applied to quantify explicitly the effect of wind on raindrop erosion as well as the influence of substrate, surface structure and slope on particle displacement. These tests confirmed the impact of wind-driven rain on total erosion rates to be of great importance when compared to all other tested factors. To successfully adapt soil erosion models to near-future challenges of climate change induced rain storms, wind-driven rain should be included into the hazard management agenda.

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.

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.

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