Permeable Areas Research Articles

Fluid Circulations at Structural Intersections through the Toro-Bunyoro Fault System (Albertine Rift, Uganda): A Multidisciplinary Study of a Composite Hydrogeological System

Regional fault structures along rift basins play a crucial role in focusing fluid circulation in the upper crust. The major Toro-Bunyoro fault system, bounding to the east of the Albertine Rift in western Uganda, hosts local fluid outflow zones within the faulted basement rocks, one of which is the Kibiro geothermal prospect. This major fault system represents a reliable example to investigate the hydrogeological properties of such regional faults, including the local structural setting of the fluid outflow zones. This study investigated five sites, where current (i.e., geothermal springs, hydrocarbon seeps) and fossil (i.e., carbonate veins) fluid circulation is recognized. This work used a multidisciplinary approach (structural interpretation of remote sensing images, field work, and geochemistry) to determine the role of the different macroscale structural features that may control each studied fluid outflow zones, as well as the nature and the source of the different fluids. The local macroscale structural setting of each of these sites systematically corresponds to the intersection between the main Toro-Bunyoro fault system and subsidiary oblique structures. Inputs from three types of fluid reservoirs are recognized within this fault-hosted hydrogeological system, with “external basin fluids” (i.e., meteoric waters), “internal basin fluids” (i.e., hydrocarbons and sediment formation waters), and deep-seated crustal fluids. This study therefore documents the complexity of a composite hydrogeological system hosted by a major rift-bounding fault system. Structural intersections act as local relative permeable areas, in which significant economic amounts of fluids preferentially converge and show surface manifestations. The rift-bounding Toro-Bunyoro fault system represents a discontinuous barrier for fluids where intersections with subsidiary oblique structures control preferential outflow zones and channel fluid transfers from the rift shoulder to the basin, and vice versa. Finally, this work contributes to the recognition of structural intersections as prime targets for exploration of fault-controlled geothermal systems.

Investigation of gas condensate drop‐out effect on gas relative permeability by Lattice Boltzmann modelling

AbstractIn a gas condensate reservoir, a drastic pressure drop in the vicinity of the wellbore makes it subject to gas condensate drop‐out. This phenomenon can adversely affect the productivity of the well and reduce gas recovery. The objective of this paper is to conduct a two‐phase fluid flow simulation on two‐dimensional porous media to understand the effect of the gas condensate drop‐out on the gas relative permeability values. In order to do so, lattice Boltzmann (LB) modelling was applied as a computational fluid dynamics (CFD) approach to perform the simulations in homogeneous and heterogeneous porous structures. The developed model was constrained by periodic boundary conditions at inlet and outlet and bounce‐back boundary condition at fluid‐solid interfaces. It was shown that the model can appropriately monitor formation and movement of the condensate droplets as a result of the pressure drop as well as blockages due to the entrance of the droplets into the throats. A consistent decrease in gas relative permeability values with condensate saturation was observed. It was also indicated that the condensate droplets become mobile at higher critical saturations in the heterogeneous system due to the dominance of capillary forces over viscous forces in the less permeable areas. Such dominance results in more severe blockages in the heterogeneous systems, as the simulation results confirmed.

Adapting to urban flooding: a case of two cities in South Asia

Abstract Cities in South Asia are experiencing storm water drainage problems due to a combination of urban sprawl, structural, hydrological, socioeconomic and climatic factors. The frequency of short duration, high-intensity rainfall is expected to increase in the future due to climate change. Given the limited capacity of drainage systems in South Asian cities, urban flooding and waterlogging is expected to intensify. The problem gets worse when low-lying areas are filled up for infrastructure development due to unplanned urban growth, reducing permeable areas. Additionally, solid waste, when dumped in canals and open spaces, blocks urban drainage systems and worsens urban flooding and waterlogging. Using hydraulic models for two South Asian cities, Sylhet (in Bangladesh) and Bharatpur (in Nepal), we find that 22.3% of the land area in Sylhet and 12.7% in Bharatpur is under flooding risk, under the current scenario. The flood risk area can be reduced to 3.6% in Sylhet and 5.5% in Bharatpur with structural interventions in the drainage system. However, the area under flood risk could increase to 18.5% in Sylhet and 7.6% in Bharatpur in five years if the cities' solid waste is not managed properly, suggesting that the structural solution alone, without proper solid waste management, is almost ineffective in reducing the long-term flooding risk in these cities.

Parametric and numerical analysis of the estimation of groundwater recharge from water-table fluctuations in heterogeneous unconfined aquifers

The groundwater recharge produced by discrete precipitation events in unconfined aquifers is often estimated from water-table fluctuations (WTFs) recorded in shallow wells. This recharge estimate is prone to uncertainties when recharge is not instantaneous, when there is groundwater drainage, and when there are other processes producing WTFs. A numerical analysis of these uncertainties is presented, which accounts for noninstantaneous recharge and the changes in the stage of a river connected to the unconfined aquifer. This analysis is performed for idealized synthetic unconfined aquifers with one-dimensional (1-D) and 2-D numerical flow models which account for the anisotropy and the spatial heterogeneity of the hydraulic conductivity (K). The logarithm of K is assumed to be a Gaussian random field with a spherical semivariogram. Groundwater recharge may be grossly underestimated with the WTF data when the recharge is not instantaneous. Estimation errors are especially important near the river. On the other hand, the recharge may be largely overestimated when the river stage rises simultaneously during the recharge episode. The errors increase with the variance of the Ln K value and depend on the main direction of anisotropy and the spatial connectivity of the most permeable areas near the river. The errors are large along the most permeable zones connected to the river in the main direction of anisotropy. The recharge estimation errors are largest when the main direction of anisotropy is perpendicular to the river and are smallest when the main direction of anisotropy is parallel to the river.

Impactos ambientais pelo uso e ocupação do solo em sub bacias hidrográficas de Campinas, São Paulo, Brasil

As alterações promovidas por ações antrópicas em ecossistemas localizados em habitats urbanos vêm gerando a destruição de áreas com grande importância ambiental, como o que ocorre em pequenas bacias hidrográficas que vem sofrendo como consequência constantes episódios de enchentes. Essa pesquisa analisa e discute as consequências do uso e ocupação sobre os atributos de solo estudados permitindo dessa maneira ampliar a discussão sobre as relações entre a expansão urbana e a diminuição das áreas de vegetação e das áreas permeáveis em sub bacias hidrográficas urbanas. Assim, escolheu-se como área de estudo, as sub bacias Rio das Pedras e a do Baixo Anhumas, localizadas em Campinas, São Paulo. Foram analisados, em 2014, 37 pontos ao longo das sub bacias, a fim de caracteriza-los do ponto de vista ambiental, realizando também, coleta de amostras de solo (deformadas e indeformadas) para análises laboratoriais e realização de testes de resistência mecânica a penetração. Em geral, as sub bacias analisadas vêm sofrendo ao longo dos anos processos de fragilização de seus ecossistemas. Esse cenário de impactos antrópicos do solo em ambas as bacias, permite inferir que a ocupação urbana foi a responsável direta pelas alterações e perturbações ambientais sofridas na área.

Strata Movement and Fracture Propagation Characteristics due to Sequential Extraction of Multiseam Longwall Panels

Multiseam longwall mining-induced strata deformation and fracture propagation patterns are different from those of single-seam mining. This difference is due to interaction of the caved zones as a result of longwall mining activity at different coal seams, which severely impacts formation of subsidence and permeability of the strata after multiseam mining. Understanding this phenomenon is of great importance in order to predict the multiseam subsidence reliably, evaluate the risk of water inrush and take suitable preventive measures, and determine suitable locations for placing gas drainage boreholes. In this study, scaled physical modelling techniques are utilised to investigate strata deformation, fracture propagation characteristics, and vertical subsidence above multiseam longwall panels. The results show that magnitude of the incremental multiseam subsidence increases significantly after multiseam extraction in comparison with single-seam mining. This increase occurs to different extent depending on the multiseam mining configuration. In addition, interstrata fractures above the abutment areas of the overlapping panels propagate further towards the ground surface in multiseam extractions compared with single-seam extractions. These fractures increase the risk of water inrush in presence of underground/surface water and create highly permeable areas suitable for placing gas drainage boreholes.

Geophysical imaging of fluid circulation and its relation with the structural system of Cerritos Colorados geothermal field, La Primavera caldera (Mexico)

La Primavera volcanic caldera was formed 95 ky ago producing peralkaline volcanism. The intra-caldera faults are a consequence of the uplift as a result of the new magma accumulation. This accumulation below the caldera structure was responsible for the caldera floor uplift, post-caldera volcanism, and hydrothermal activity in the Cerritos Colorados geothermal field. Here, we present the results of geophysical investigations of shallow hydrothermal activity and its relation with the structural system in this geothermal field. We applied the self-potential method that combined with surface temperature measurements allowed to identify the main infiltration and ascending fluid zones in the area. Electrical resistivity tomography (ERT) was measured in two selected places. One ERT profile (1.2 km in length) was located in the P12 well area, and a 3D resistivity model was carried out on the Cerritos Colorados graben area. Combining these geophysical prospecting results with a detailed structural map, we identified the main degassing zones (i.e. fumaroles) that correspond to higher permeability areas located along normal and strike-slip faults described for the first time in this work. In addition, we recognized a large number of small convective zones at meter-scale with clear circulation paths (upflow and downflow) of hydrothermal fluids. Therefore, our data suggest that a strong structural control exists on the surface manifestations of the hydrothermal system limiting the lateral extension of fluids. This emphasizes the importance that old structural boundaries related to the intra-caldera tectonic structures have upon the way hydrothermal fluids move.

DCE-MRI based voxelized computational model for chemotherapeutic drug transport in human brain tumor

Understanding the distribution of chemotherapeutic drugs in tumor when administered systemically is important for assessing the efficiency of anticancer treatment. Despite numerous researches in this field, prediction of drug distribution within the tumors still remains a challenge due to wide heterogeneity of tumor vasculature. In this work, a voxelized computational fluid dynamics (CFD) model based on dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) has been employed to simulate the transport of chemotherapeutic drug (doxorubicin) in human brain tumors. The DCE-MRI data provide realistic heterogeneous vasculature of a tumor and help in determining the permeability of the tissue vascular wall to contrast agent and interstitial volume fraction (porosity) of the tissue. The permeability of the tissue to doxorubicin is calculated by correlating it with the permeability of the tissue to contrast agent. Patient-specific arterial input function (AIF) estimation has also been done to make the model patient-specific. The computational model provides steady-state interstitial fluid pressure and velocity values, which are further used to predict transient drug concentration in tumor tissue. Simulation results show that doxorubicin accumulates more in high permeability areas initially. However, drug accumulation increases in areas of higher interstitial volume fraction as time progresses. This observation implies that higher accumulation of chemotherapeutic drugs occurs in higher porosity areas, facilitating larger tumor cell killing in those areas.

Fine-scale analysis of urban flooding reduction from green infrastructure: An ecosystem services approach for the management of water flows

Climate change is expected to modify the timing and amount of precipitation in the future, increasing the demand for effective adaptation at the local scale, especially to mitigate the impacts of extreme events, expected to increase in frequency and magnitude. Green infrastructure (GI) can provide a crucial water regulating ecosystem service, helping communities to adapt to the increased stormwater runoff and associated flood risks expected from climate change. This paper presents a new planning tool that utilizes remote sensing and census data to model the supply and demand for urban flood reduction services through GI. A high-resolution urban digital model is used to distinguish between permeable and impermeable areas at fine (e.g. 25 cm) spatial scale. Flood reduction capacity was modeled using two indices: i) the amount of runoff reduced by existing GI, and ii) the runoff reduction coefficient. We also analyzed the flood reduction demand using a vulnerability index. The tool is demonstrated in a historical urban center of the Northern Italy, with different scenarios used to identify priority areas of intervention. The results show that the flood reduction capacity is unevenly distributed throughout the study area. Public and private surfaces contribute different amounts of runoff with different flood reduction potentials. In eight of nine urban study areas, private properties generate more runoff than public properties under the worst scenario conditions. The study identified two priority areas of intervention, based on their mismatch between supply and demand of GI’s water regulating services.

Evaluation of the open porosity of PVD coatings through electrochemical iron detection

This investigation analyses the use of the scanning electrochemical microscopy (SECM) to study the open porosity of PVD-coatings through electrochemical ion detection. CrN und TiN PVD coatings with artificially created permeable areas as well as without any mechanical damage were investigated. Furthermore, the thickness of the interlayers was also modified to increase the diffusion layer thickness. As a result, coatings with different protective effect were obtained and used for comparison purposes. The ion detection was done by means of a microelectrode located over the sample surface. It was used to oxidize ferrous Fe2+ ions coming from the substrate to ferric Fe3+ ions. The measurement of higher currents indicates higher anodic dissolution and consequently higher open porosity of the coating. The validity of the SECM measurements was supported by topographical analysis and optical evaluation of the samples after the measurements.

Mobile transect for identification of intra-urban heat islands in Uberlandia, Brazil

The “heat island” phenomenon is one of many serious problems caused by rapid urban growth. This study therefore sought to characterize and quantify heat islands in Uberlandia, to evaluate the seasonality of these islands (winter-summer) and to identify the effect of surface coverage on their intensity. To identify intra-urban heat islands in Uberlandia, air temperature data were collected in two seasons (winter and summer) using mobile and fixed transects seasons. Transition measurements were recorded automatically every 0.5 seconds using a car-mounted thermos-hygrometer moving at an average of 40 km h-1. GPS was used to select approximately ten data points every 500 meters of each transect. Fixed weather stations measured air temperature at three sites in the region. Transect data analysis showed that the intra-urban heat islands were more intense in winter (ΔT = 2.2ºC) than in summer (ΔT = 1.2ºC) mainly because by reduction in atmospheric vapor in winter (dry season) and by higher rate of radiative cooling that is favored in permeable areas. The methodology used in the present study proved to be a quick and efficient way to carry out this type of monitoring.

Experimental study on the effect of interfacial tension on the conformance control of oil-in-water emulsions in heterogeneous oil sands reservoirs

Reservoir heterogeneity is a serious problem for many mature oilfields. Due to heterogeneity, much of the displacing fluid may flow into the high permeability zones in the formation, leaving most of the low permeability areas un-swept, which leads to high water production and low oil recovery. In this work, oil-in-water (O/W) emulsions were used as conformance control agents to reduce fluid flow of the high permeability zones in heterogeneous oil sands reservoirs. As well, for the first time, interfacial tension (IFT) effect on emulsion conformance control performance was studied. Emulsification tests were first performed to screen suitable emulsifiers which could be used to prepare stable O/W emulsions with different IFTs. Physiochemical properties of the emulsions were investigated by characterization tests in terms of their stability behavior, droplet size distribution and rheological properties.A series of heterogeneous parallel, dual-sandpack flow experiments were carried out to evaluate the profile control ability of emulsions with different IFTs of 0.04, 0.15, 0.92 and 5.20 mN/m in heterogeneous oil sands reservoirs. The results show that for the dual-sandpack models used in this study, emulsion conformance control performance gets better as IFT decreases from 5.20 mN/m to 0.15 mN/m, but it becomes worse as IFT further decreases to 0.04 mN/m. The fractional flow of the heterogeneous dual-sandpack diverts only once when flooded by an emulsion with an IFT of 5.20 mN/m. Emulsion with an IFT of 0.92 mN/m causes several flow diversions in the emulsion injection process, but the profile control ability could be destroyed by the flood of water. Emulsion with an IFT of 0.15 mN/m has good conformance control performance both at the emulsion flooding and subsequent water flooding stages, while emulsion with the least IFT of 0.04 mN/m shows very little profile control effect. The effect of emulsion slug size and sandpack permeability ratio on emulsion conformance control ability are also discussed in this paper.

APLICAÇÃO DO MÉTODO WTF NO ESTUDO DA VARIAILIDADE DA RECARGA EM AQUÍFERO URBANO

A expansão dos espaços urbanos causa diversos impactos ao meio ambiente, sendo a alteração da recarga de aquíferos um dos componentes hidrológicos mais afetados. Apesar do aporte de recarga por fontes não contínuas, como vazamentos de águas de abastecimento e esgoto, a impermeabilização provoca diminuição das áreas permeáveis, dificultando a infiltração das águas pluviais. O presente trabalho visa estimar a recarga direta (reserva reguladora) de origem natural em área urbana e avaliar sua variabilidade espacial, utilizando como estudo de caso a cidade de Frederico Westphalen. A estimação da recarga foi realizada para o período de um ano, por meio da aplicação do método WTF, utilizando dados de monitoramento pluviométrico e o monitoramento hidrogeológico, realizado com periodicidade mensal em treze poços localizados em lotes urbanos. A recarga total estimada na área foi de aproximadamente 245,57 mm/ano, correspondendo a 9,46% da precipitação total (2.596,8 mm), sendo observado que, quanto maior a espessura da camada não saturada, maior a taxa de recarga quantificada. Os resultados apresentados fornecem subsídios para a gestão das águas pluviais urbanas, além de demostrarem a necessidade urgente de ampliação e preservação das áreas permeáveis em zonas urbanas.

Role of multi-seam interaction on gas drainage engineering design for mining safety and environmental benefits: Linking coal damage to permeability variation

Methane gas drainage is an effective method to ensure mining-process safety and deliver greater environmental benefits through reducing greenhouse gas (GHG) emissions. As most coal seams actually coexist with one or several other coal seams, i.e. the multi-layer coal seam group. A better understanding of the interaction between the adjacent coal seams could provide better guidance for the gas drainage engineering design to enhance its performance. Extensive studies on the multi-seam interaction have focused on the effect of mining the underlying coal seam on the overlying seam from perspectives of rock deformation, stress change and permeability variation. Meanwhile, as there is few coupled permeability models taking the coal-damage effect into account, previous permeability-variation analysis seldom commonly considered the mining-induced coal damage, coal mechanics changes and gas adsorption, which results in the permeability underestimation. Therefore, in this paper, a mathematical model which incorporates the coal permeability with coal damage, coal mechanical property and the gas adsorption was developed. Then this model was implemented into a finite-element numerical simulation, which was used to investigate the impact of the overlying coal seam mining on the underlying relieved seam from the perspective of damage-based permeability variation. Meanwhile, the effect of damage on gas-emission performance from the underlying seam was analyzed. Results show that there are four permeability areas under the mine-out panel, permeability increases greatly in areas I to III (the highest as over 650 times) while it increases slightly in the area IV. These permeability results are largely consistent with the stress-analysis conclusions obtained by other researchers. By taking the damage into account, the evaluation on gas-emission condition could become more reasonable. Above research outcomes could help to determine the favorable gas-drainage areas under the longwall mining panel and guide the drainage borehole design in the relieved coal seam, to deliver better drainage outcomes for the mining safety and GHG-emission reduction.

Influence of Thermal Marangoni convection on the recovery of bypassed oil during immiscible injection

Several phenomena could recover the bypassed oil in matrixes and low permeable areas, among them; Marangoni is the most unfamiliar one in fluid flow model. This mechanism triggers a convective flow from low interfacial tension point to a high interfacial tension point because of variation in solvent concentration, temperature or electrical charge.In this study, experimental and analytical tools have been utilized to investigate the effect of thermal Marangoni flux on the enhancement of oil recovery during immiscible injection in a matrix-fracture system. Results of non-isothermal experiments have been compared with isothermal (as the zero level of Marangoni) to study the presence of Marangoni flow and its direction respect to the fracture location. Results show that not only the Marangoni flux does exist and has significant impact on the recovery of bypassed oil but also, its magnitude is proportional to the absolute value of temperature gradient in phases interface.

Enhanced oil recovery ability of branched preformed particle gel in heterogeneous reservoirs

Reservoir heterogeneity is the main cause of high water production and low oil recovery in oilfields. Extreme heterogeneity results in a serious fingering phenomenon of the displacing fluid in high permeability channels. To enhance total oil recovery, the selective plugging of high permeability zones and the resulting improvement of sweep efficiency of the displacing fluids in low permeability areas are important. Recently, a Branched Preformed Particle Gel (B-PPG) was developed to improve reservoir heterogeneity and enhance oil recovery. In this work, conformance control performance and Enhanced Oil Recovery (EOR) ability of B-PPG in heterogeneous reservoirs were systematically investigated, using heterogeneous dual sandpack flooding experiments. The results show that B-PPG can effectively plug the high permeability sandpacks and cause displacing fluid to divert to the low permeability sandpacks. The water injection profile could be significantly improved by B-PPG treatment. B-PPG exhibits good performance in profile control when the high/low permeability ratio of the heterogeneous dual sandpacks is less than 7 and the injected B-PPG slug size is between 0.25 and 1.0 PV. The oil recovery increment enhanced by B-PPG after initial water flooding increases with the increase in temperature, sandpack heterogeneity and injected B-PPG slug size, and it decreases slightly with the increase of simulated formation brine salinity. Choosing an appropriate B-PPG concentration is important for B-PPG treatments in oilfield applications. B-PPG is an efficient flow diversion agent, it can significantly increase sweep efficiency of displacing fluid in low permeability areas, which is beneficial to enhanced oil recovery in heterogeneous reservoirs.

Experimental Study on Low Interfacial Tension Foam for Enhanced Oil Recovery in High-Temperature and High-Salinity Reservoirs

Foam flooding is an important method to enhance oil recovery after water flooding. In this paper, a novel low interfacial tension (LIFT) nitrogen foam was successfully prepared by an amphoteric surfactant and sodium formate. It has good foaming ability and can reduce interfacial tension to a low interfacial tension level (10–1 mN/m order of magnitude) in high-temperature (90 °C) and high-salinity (183 g/L salinity) reservoirs. The influence of surfactant concentration, organic bases concentration, and aging on the performances of the LIFT foam system has been systematically studied through the modified Ross-Miles experiment. Furthermore, the foam displacement in flat-panel sand model and etched-glass micromodels were conducted to investigate the foam displacement mechanisms for enhanced oil recovery. The results of flat-panel sand model experiment showed that the LIFT foam could block high permeability channels and divert following injection fluid to adjacent low permeability areas efficiently. Meanwhile, with the injection of the LIFT foam, the injection pressure of the whole model continued to increase, and the pressure distribution was more uniform. The etched-glass micromodels experiment results showed that the LIFT foam could block the high permeability channels and improve sweep efficiency. Furthermore, comparing with the common foam, the LIFT foam could emulsify oil and strip oil film from model surfaces more easily. So it could enhance the oil recovery more efficiently.

Application of Binary Permeability Fields for the Study of $${\hbox {CO}_{2}}$$ Leakage from Geological Carbon Storage in Saline Aquifers of the Michigan Basin

The feasibility of geological carbon storage (GCS) sites depends on their capacity to retain safely $${\hbox {CO}_{2}}$$ . While deep saline formations and depleted gas/oil reservoirs are good candidates to sequester $${\hbox {CO}_{2}}$$ , gas/oil reservoirs typically have a limited storage capacity compared to ideal targets ( $$\sim $$ 1 Mt/year) considered for $${\hbox {CO}_{2}}$$ disposal (Celia et al. in Water Resour Res 51(9):6846–6892, 2015. doi: 10.1002/2015WR017609 ). In this respect, deep saline aquifers are considered more appropriate formations for GCS, but present the disadvantage of having limited characterization data. In particular, information about the continuity of the overlying sealing formations (caprock) is often sparse if it exists at all. In this work, a study of $${\hbox {CO}_{2}}$$ leakage is conducted for a candidate GCS site located in the Michigan Basin, whose sealing properties of the caprock are practically unknown. Quantification of uncertainty on $${\hbox {CO}_{2}}$$ leakage from the storage formation is achieved through a Monte Carlo simulation approach, relying on the use of a computationally efficient semi-analytical leakage model based upon the solution derived by Nordbotten et al. (Environ Sci Technol 43(3):743–749, 2009), which assumes leakage occurs across “passive” wells intersecting caprock layers. A categorical indicator Kriging simulator is developed and implemented to represent the caprock sealing properties and model the permeability uncertainty. Binary fields of caprock permeability are generated and exhibit mostly low permeability, with sparsely-occurring local high permeability areas where brine and $${\hbox {CO}_{2}}$$ may leak out of the storage formation. In addition, the feasibility of extending the use of the semi-analytical model to large-area leakage pathways is studied. This work advances a methodology for preliminary uncertainty quantification of $${\hbox {CO}_{2}}$$ leakage at sites of GCS with little or no information on the sealing properties of the caprock. The implemented analysis shows that, for the considered site, $${\hbox {CO}_{2}}$$ leakage may not be negligible even for relatively low ( $$\sim $$ 1%) probabilities of finding permeable inclusions in the caprock and highlights the importance of being able to characterize caprock sealing properties over large areas.

Taking into Account the Role of the Weathering Profile in Determining Hydrodynamic Properties of Hard Rock Aquifers

The present study aims at understanding the role of the structure and the geometry of the weathering profile on the hydrodynamic behavior of hard rock aquifers. We first described 2D geophysical cross sections of weathering profiles realized and validated on an experimental site. Next, we implemented five long-term pumping tests in wells drilled at various locations of these cross sections. Finally, we chose the appropriate analytical solutions to determine the hydrodynamic parameters in consistence with the structure and the geometry of the weathering profile. Results reveal that land covers, weathering type and thickness, presence of no flow boundaries, etc. are all factors that explain the flow regime, which appears therefore much less unpredictable. In other words, the 2D geophysical data are enough to locate the best permeable areas, or the areas where the structure of the aquifer without impervious boundaries and with leakage favor a good long-term behavior of the well. The values of aquifer’s transmissivity vary between 5.10−3 and 4.10−5 m2/s. The storage varies between 0.06 and 7.10−7. The variability of these parameters from site to site reflects the high heterogeneity of hard rock aquifers.

The economic value of the flow regulation environmental service in a Brazilian urban watershed

Urban flood management have often focused either on the capacity expansion of drainage systems or on artificial detention storage. While flood control should take part early on urban planning, not enough is known to guide such plans and provide incentive to land use decisions that minimize the vulnerability to localized floods. In this paper, we offer a broader perspective on flood protection, by treating the original hydrologic flow regulation asan environmental service, and exploring how the value of this environmental service drives economic land use decisions that convert original (permeable) land into urbanized (impermeable). We investigate the relationship between land use decisions and their hydrologic consequences explicitly, and use this relationship to simulate resulting land use scenarios depending on the value attached to the environmental service of flow regulation. Rainfall-runoff simulation model results are combined to an optimization model based on two-stage stochastic programming approach to model economic land use decisions. The objective function maximizes the total expected land use benefit in an urban area, considering the opportunity cost of permeable areas in the first stage and the resulting loss of the environmental service of flow regulation on the second stage, under several probable hydrological events. A watershed in the city of Belo Horizonte, Brazil, is used to demonstrate the approach. Different values attached to the environmental service were tested, from zero to higher than the opportunity cost of land, and artificial detention infrastructure was included to calculate the resulting land use change and the loss in the environmental service value. Results indicate that by valuing the environmental service loss and discounting it from the economic benefits of land use, alternative solutions to land use are found, with decreased peak flows and lower flood frequency. Combined solutions including structural and non-structural techniques provide more cost effective results, avoiding both the depletion of the environmental service and the high opportunity cost associated to valuable commercial urban areas. Urban development under such premises will be more resilient and adapted to local flooding, instead of relying on increasingly expensive infrastructure.