Artur Paiva Coutinho

Combined effect of capillary barrier and layered slope on water, solute and nanoparticle transfer in an unsaturated soil at lysimeter scale

It is well recognized that colloidal nanoparticles are highly mobile in soils and can facilitate the transport of contaminants through the vadose zone. This work presents the combined effect of the capillary barrier and soil layer slope on the transport of water, bromide and nanoparticles through an unsaturated soil. Experiments were performed in a lysimeter (1×1×1.6m(3)) called LUGH (Lysimeter for Urban Groundwater Hydrology). The LUGH has 15 outputs that identify the temporal and spatial evolution of water flow, solute flux and nanoparticles in relation to the soil surface conditions and the 3D system configuration. Two different soil structures were set up in the lysimeter. The first structure comprises a layer of sand (0-0.2cm, in diameter) 35cm thick placed horizontally above a layer of bimodal mixture also 35cm thick to create a capillary barrier at the interface between the sand and bimodal material. The bimodal material is composed of a mixture 50% by weight of sand and gravel (0.4-1.1cm, in diameter). The second structure, using the same amount of sand and bimodal mixture as the first structure represents an interface with a 25% slope. A 3D numerical model based on Richards equation for flow and the convection dispersion equations coupled with a mechanical module for nanoparticle trapping was developed. The results showed that under the effect of the capillary barrier, water accumulated at the interface of the two materials. The sloped structure deflects flow in contrast to the structure with zero slope. Approximately 80% of nanoparticles are retained in the lysimeter, with a greater retention at the interface of two materials. Finally, the model makes a good reproduction of physical mechanisms observed and appears to be a useful tool for identifying key processes leading to a better understanding of the effect of capillary barrier on nanoparticle transfer in an unsaturated heterogeneous soil.

Telhado verde: desempenho do sistema construtivo na redução do escoamento superficial

Na atualidade, metade da populacao mundial reside em centros urbanos, e os impactos negativos decorrentes de eventos hidrologicos tem sido recorrentes, visto que, com o aumento da impermeabilizacao, ha reducao nas taxas de infiltracao, levando a diminuicao da recarga dos aquiferos e a diminuicao do escoamento de base. Consequentemente, o escoamento superficial e intensificado, aumentando a frequencia e a magnitude dos picos de cheia, o que pode resultar na ocorrencia de inundacoes, especialmente nos centros urbanos. Por outro lado, verifica-se ja ha algum tempo o emprego de telhados verdes em varias partes do mundo para contribuicao arquitetonica estetica e melhoria do conforto ambiental. Alem desses enfoques, esta solucao vem sendo tratada, tambem, como uma estrutura de controle do escoamento pluvial. Considerando caracteristicas reais e os dados obtidos em campo, foi realizada a simulacao da dinâmica da agua em dois telhados verdes, com o emprego do codigo computacional Hydrus-1D, para diferentes intensidades de precipitacao, visando verificar o desempenho desse sistema construtivo na reducao do escoamento superficial. Os hidrogramas de saida mostraram-se qualitativamente adequados e quantitativamente coerentes e pode-se concluir que os telhados verdes constituem importantes dispositivos no amortecimento do escoamento superficial oriundo dos telhados, para as condicoes climaticas da area investigada.

Characterization of the Capibaribe River Dry Bed with Ground Penetrating Radar (GPR)

For an adequate hydrogeological study of alluvial layers in the semi-arid zone, it is important to know well its geometry and its hydraulics characteristics. Alluvial formations are generally constituted by erosion, transport and sedimentation processes, causing considerable heterogeneity in soil hydraulic parameters and water flow. The present research had as objective to perform a geophysical characterization using the Ground Penetrating Radar – GPR in the dry bed of the Capibaribe river. To the extent that depositional layers exhibit changes in water content, granularity, sediment type and layer orientation, the water table as well as sedimentary structures and lithological contacts tend to be identified, making the method effective for hydrogeology research. The study area comprises alluvial dry river bed of upper Capibaribe river in the municipality of Santa Cruz do Capibaribe. The results showed that GPR was efficient in the imaging of the subsurface contributing to the knowledge of the geometry and the stratigraphy of the aquifer of the dry bed of the river. In the dry bed of the river, with 400 MHz antenna the signal reached a depth of 2.65 m, and with the antenna of 200 MHz, the signal reached a depth of 6.00 m. The capillary fringe was identified at a depth of 3.0m with the use of 200MHz and 400MHz antennas.