Contribution of Soil Physical Propreties in The Assessment of Flood Risks in Tropical Areas. Case of The Mbo Plain

Flooding occurs when water is in excess and can no longer be evacuated normally. The nature of the soil has been identified as one of the major causes of flooding, hence this study aimed is to show the influence of the physico-chemical properties of the soil on the recurrence of flooding in the Mbo plain. Four soil profiles were carried out on the alluviums according to the altitudes. These profiles were described and undisturbed soil samples were taken. Then, measurements of the infiltration rate of water in the soil by the Porchet method were carried out in sixteen sites. Finally, soil samples taken by auger and core sampling were studied in the laboratory. Physico-chemical parameters such as grain size, porosity, moisture, pH, compactness and organic matter were determined. Infiltration tests carried out in situ using the Porchet method revealed a hydraulic conductivity between 10−5 and 10−7 m/s, characteristic of a semi-permeable soil. This low value of permeability results from the morpho-structural arrangement and the chemical composition of the soils of the plain. These soils are hydromorphic, which means that they are constantly flooded and temporarily waterlogged. They are more or less sandy-clay on the surface, and very clayey at depth, generally from 25 cm. The very clayey soils at the base considerably slow down infiltration and act as a real barrier layer that prevents water from infiltrating, resulting to intense runoff. These soils are very porous and compact with a fairly high water content of up to 71%. This work allows us to conclude on the role of intrinsic soil properties on the genesis of floods in lowland areas. As in many plains in Africa and in the world, the nature of the soil in the Mbo plain is a natural predisposing factor to flood risks. The methods used can be applied in areas with the same characteristics as the Mbo Plain.

Framework to Study the Effects of Climate Change on Vulnerability of Ecosystems and Societies: Case Study of Nitrates in Drinking Water in Southern Finland

Climate change may alter the services ecosystems provide by changing ecosystem functioning. As ecosystems can also resist environmental perturbations, it is crucial to consider the different processes that influence resilience. Our case study considered increased NO3− concentration in drinking water due to the climate change. We analyzed changes in ecosystem services connected to water purification at a catchment scale in southern Finland. We combined climate change scenarios with process-based forest growth (PREBAS) and eco-hydrological (PERSiST and INCA) models. We improved traditional model calibration by timing of forest phenology and snow-covered period from network of cameras and satellite data. We upscaled the combined modelling results with scenarios of population growth to form vulnerability maps. The boreal ecosystems seemed to be strongly buffered against NO3- leaching by increase in evapotranspiration and vegetation NO3- uptake. Societal vulnerability varied greatly between scenarios and municipalities. The most vulnerable were agricultural areas on permeable soil types.

Estimation of Bearing Capacity Dropping Due to Cavities from Gypseous Soils Melting

The presence of gypsum in the soil will cause problems if the source of freshwater is available and permeable soil permitting significant movement of water is to take place. The solubility of gypsum by excess water from irrigation or localized leak into the gypseous soil may cause cavity formation. In this research, a model was developed for governing the mass-transport to assess the variation of gypsum content of the soil during dissolution. A general three-dimensional finite element program (PLAXIS tunnel) was selected for the numerical analysis method to generate the solution. Parameters that affect the bearing capacity of a square footing represented by the gypsum content, the cavity volume, and the location of the cavity which represent by three offset distances from the footing center to the cavity center (x, y, and z), where (X) represents the horizontal distance, (Y) represents the vertical (depth) distance, and (Z) represents the diagonal distance. The main results show that the cavity location found to be the most parameter that affects the bearing capacity ratio (BCR). The minimum values are found when the cavity locates at the center of the footing base, and the lowest one (0.211) when the gypsum dissolved equal to 40%, also there is no effect of the cavity location when the ratio of (X/B) and (Z/B) exceed (3.0) for any depth and when the gypsum dissolved less than 10%. For high gypsum dissolution (more than 30%), the dimensionless ratios (X/B), (Z/B), and (Y/B) of the cavity must be more than 5.0.

Researches on the use of textile materials for protection against soil erosion

Erosion of sandy soil due to wind action is a global ecological problem with major implications both in the field of agriculture and in the socio-economic sphere. Erosion and sand transport have a negative effect both in the “active area” in which it occurs and outside it, not being a strictly defined phenomenon. The present paper deals with the problems due to the erosion of soils by wind, and the way of diminishing this phenomenon by using some protective textile screens placed transversely to the wind direction. The aim of the paper is to provide numerical contributions on wind interaction with permeable soil protection obstacles. For concrete data, a number of numerical simulations of the air flow in the atmospheric boundary layer area was carried out, in the presence of a wind barrier having different degrees of permeability, depending on the textile used, for the determination of the speed upstream and downstream of the obstacle. The program used for the numerical simulation is ANSYS FluentTM, a computational fluid dynamics software that uses a variety of equations for the modelling of fluid flow. The results obtained will be used as a basis for further research, based on scaled textile barriers models for physical experiments in the aerodynamic tunnel.

A Mathematical Model of Gas and Water Flow in a Swelling Geomaterial—Part 2. Process Simulation

Gases can potentially generate in a deep geological repository (DGR) for the long-term containment of radioactive waste. Natural and engineered barriers provide containment of the waste by mitigating contaminant migration. However, if gas pressures exceed the mechanical strength of these barriers, preferential flow pathways for both the gases and the porewater could form, providing a source of potential exposure to people and the environment. Expansive soils, such as bentonite-based materials, are widely considered as sealing materials. Understanding the long-term performance of these seals as barriers against gas migration is an important component in the design and the long-term safety assessment of a DGR. This study proposes a hydro-mechanical mathematical model for migration of gas through a low-permeable swelling geomaterial based on the theoretical framework of poromechanics. Using the finite element method, the model is used to simulate 1D flow through a confined cylindrical sample of near-saturated low-permeable soil under a constant volume boundary stress condition. The study expands upon previous work by the authors by assessing the influence of heterogeneity, the Klinkenberg “slip flow” effect, and a swelling stress on flow behavior. Based on the results, this study provides fundamental insight into a number of factors that may influence two-phase flow.

Using Water Stable Isotopes for Identifying Groundwater Recharge Sources of the Unconfined Alluvial Zagreb Aquifer (Croatia)

The main purpose of this study was to understand the interactions between precipitation, surface water, and groundwater in the Zagreb aquifer system using water stable isotopes. The Zagreb aquifer is of the unconfined type and strongly hydraulically connected to the Sava River. As the groundwater is the main source of drinking water for one million inhabitants, it is essential to investigate each detail of the recharge processes of the aquifer to ensure adequate protection of the groundwater. Measuring the content of water stable isotopes in surface waters and groundwater enabled the creation of two- and three-component mixing models based on the isotopic mass balance for the purpose of the quantification of each recharge component. The mixing models gave ambiguous results. Observation wells equally distant from the Sava River did not have the same recharge component ratio. This indicated that there were more factors (in addition to the distance from the river) that were affecting groundwater recharge, and the properties of the unsaturated zone and surface cover data were therefore also taken into consideration. The thickness of the unsaturated zone and the characteristics of different soil types were identified as important factors in the recharge of the Zagreb aquifer. The areas with high thickness of the unsaturated zone and well-permeable soil had a very similar recharge component ratio to the areas with small thickness of the unsaturated zone but low-permeable soil.

Analysis of the effect of impermeability of urban soils on the infiltration of rainwater in the city of Recife, PE

The process of urbanization interferes in the elements of the hydrological cycle, altering the infiltration, flow, and evaporation of rainwater. Several methods and tests exist for analyzing this hydrological cycle that aim to hydrodynamically characterize the soil of a locality. However, the collection and field trials can be expensive and time consuming. Because of these high costs, it is important to look for methods that save time and money. One such method is to perform simulations of water flow in the soil, using computational models such as Hydrus 1-D, in order to explain the water balance of a region. The results of these simulations showed that 355.18 mm.m-2 of the total 385.02 mm.m-2 of precipitation was able to infiltrate, indicating that the soil of the region has a high infiltration capacity, due to its high sand content. However, of the 228,000 m2 studied, only 38,760 m2 are unpaved soil. This shows that the soil at the location studied would be able to infiltrate most rainwater without the occurrence of flooding, if more than only 17% of the land area were permeable soil. This conclusion can be extrapolated to other areas surrounding this neighborhood and to other large urban centers, which have similar characteristics.