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Formación, cursos, eventos y seminarios

How do new development activities affect coastal groundwater systems in Africa? The case of Kwale, Kenya

SEMINARIO GRUPO DE HIDROLOGÍA SUBTERRANEA

UNIDAD ASOCIADA (UPC-CSIC)

 

PONENTE: Nuria Ferrer Ramos. Estudiante de doctorado

How do new development activities affect coastal groundwater systems in Africa? The case of Kwale, Kenya

ABSTRACT:

Industrialisation and free markets are powering African growth in the 21st century. The African continent has huge potential for wealth generation from its extensive mineral resources; the scale of resource exploitation has grown rapidly in recent years following discoveries of hitherto unknown and economically viable mineral deposits. However, these new development activities, including not only mineral extraction but also industrial agriculture, are associated with an increase in water use and potentially reduced water quality, thereby affecting the availability of safe water resources for local communities. 

Even though our understanding of Africa’s sustainable growth and development has improved during the last decade, Africa’s critically important groundwater systems are still poorly understood in the socio-ecological context. Some of the most vulnerable groundwater systems are located in the coastal zones of Africa.  Groundwater systems in these densely populated areas are at high risk of saline intrusion, a risk which is exacerbated by a lack of knowledge of aquifer behavior.

In this study, we evaluate the potential impacts of diverse economic activities on the coastal aquifer system in Kwale County (Kenya) by means of kilometric geophysical profiles, hydrochemical and isotopic data across both dry and wet seasons, and groundwater level hydrographs. This area encapsulates the evolving situation in many parts of Africa: two multi-national companies have become established in Kwale County since 2012, augmenting the existing tourist industry.  Base Titanium Ltd. is conducting the country’s largest mining operation and KISCOL is developing 5,500 hectares of irrigated sugarcane. These companies and the communities living nearby exploit groundwater from a multi-layered aquifer composed of sand and limestone close to the surface and a fractured semi-confined sandstone and limestone aquifer at depth. Results indicate that geological structure plays an important role in determining the effect of these new development activities on water resources. They also suggest that, in this system, climate variation may have a greater influence on water resource quality and availability than new large-scale extractive use.

 

LUGAR: UPC-Departamento de Ing. Civil. Modulo D2 Aula Hidrologia

Fecha: JUEVES 7 SEPTIEMBRE A LAS 12:15H

Characterization across scales of reactive solute transport in porous media

 

SEMINARIO GRUPO DE HIDROLOGIA SUBTERRÁNEA
(UPC-CSIC)

 

Giovanni Porta (Politecnico di Milano)


Título: Characterization across scales of reactive solute transport in porous media

Abstract:
Recent studies have shown that traditional reactive transport models are grounded on assumptions which are often violated in real applications. This has a definite impact on the ability of such models to properly 
interpret laboratory and field scale data. At the same time, advancements in digital rock physics techniques has pushed forward our ability to model pore scale processes and to characterize porous media at the pore level.

In this talk we focus on a simple reactive setting, characterized by an irreversible bimolecular reaction. A key element which controls the investigated reactive process is incomplete mixing of the reactants at 
pore-scale, which can considerably affect the effective reaction parameters associated with continuum-scale models. We compare two classes of modeling options: (i) available models which require 
calibration through parameter estimation and (ii) models which rely solely on information related to pore-scale geometry and velocity field. 

We assess the performance of the selected models by comparison against pore-scale simulation of bimolecular reactive transport in a disordered porous medium. Through this comparison we discuss the impact of 
incorporating pore-scale information into continuum-scale effective parameters.


Lugar: Departamento de Ing. Civil, Aula de CIHS, Planta Baja
Jueves 21 de Septiembre a las 12:15 h 

Groundwater studies in Mongolia

SEMINARIO GRUPO DE HIDROLOGIA SUBTERRÁNEA
(UPC-CSIC)
Groundwater studies in Mongolia
a cargo de
Buyankhishig Nemer 
(School of Geology and Mining Engineering, Ulaanbaatar)

Jueves 22 de Junio a las 12:15 h
en
Departamento de Ingeniería del Terreno, Aula CIHS, Planta Baja


Abstract:
The seminar will give general information about groundwater conditions in Mongolia

Lectura de Tesis: Water resources assessment in cold regions: the Upper Tuul River basin, Mongolia

LECTURA DE TESIS

GRUPO DE HIDROLOGIA SUBTERRÁNEA

(UPC-CSIC)

 


Water resources assessment in cold regions: the Upper Tuul River basin, Mongolia

 
Enkhbayar Dandar

Thesis advisors: 
Dr. Jesús Carrera (CSIC)  
Dr. Maarten Saaltink (UPC) 

Dr. Buyankhishig Nemer (MUST)   

 

DATE: Wednesday, June 21th 2017
Hour: 11:00 

 

Place: UPC, Campus Nord. Building C1. Classroom: 002.


ABSTRACT

Groundwater withdrawals are growing in most developing countries, including Mongolia, where freshwater resources are limited and unevenly distributed, and most surface waters are frozen during winter. Groundwater represents some 80% of the water supply in the country. Computation of recharge is important, but is complicated in cold regions, because of phase change and permafrost, which is found on 63 percent of the country, and causes conventional physically-based land surface models to be inaccurate.

 

We have developed a two-compartment water and energy balance model that accounts for freezing and melting and includes vapor diffusion as a water and energy transfer mechanism. It also accounts for the effect of slope orientation on radiation, which may be important for mountain areas. We applied this model to the Upper Tuul River Basin to evaluate recharge under different soil and vegetation types. The basin is divided into 12 zones (models) based on elevation ranges, orientation and slope. Due to the limited number of observation data in this area, precipitation, air temperature and relative humidity were corrected as a function of elevation by means of lapse rates. Results show that recharge is relatively high and delayed with respect to snowmelt during spring, because it is mainly associated to thawing at depth, which may occur much later. Most importantly, we find that vapor diffusion plays an important quantitative role in the energy balance and a relevant qualitative role in the water balance. Except for a few large precipitation events, most of the continuous recharge is driven by vapor diffusion fluxes. Large vapor fluxes occur during spring and early summer, when surface temperatures are moderate, but the subsoil remains cold, creating large downwards vapor pressure gradients. Temperature gradients reverse in fall and early winter, but the vapor diffusion fluxes do not, because of the exponential shape of the saturated vapor pressure as a function of temperature giving smaller vapor pressure differences at lower temperature. The computed sensible heat flux is higher than the latent heat flux, which reflects the dry climate of the region. The downward latent heat flux associated to vapor diffusion is largely compensated by an upward heat conduction, which is much larger than in temperate regions.

The alluvial aquifer around Ulaanbaatar supplies water to the city and is under pressure because of the growing water demand. To address this concern, we built a numerical model, which is challenging, not only because of the lack of data, but also because the river freezes during winter. River flow under the ice is sustained by groundwater, which provides the energy to prevent full freezing of the whole river thickness, but which may not occur where groundwater levels are depleted by pumping. At present, the river still flows under the ice during winter at both ends of the Ulaanbaatar alluvial aquifer. The downstream end, to the West, receives aquifer discharge, whereas the river is fed by discharge from adjacent alluvial aquifers upstream of the east end. But, in the central portion, the river is fully frozen. In fact, the river bed in this portion becomes dry in April most years, probably because of sublimation and because melted water immediately infiltrates into the aquifer. If groundwater pumping increases, either at the Ulaanbaatar alluvial aquifer or at the alluvial

aquifer near Gachuurt village, it is likely that the currently winter flowing portion of the river will also dry or, rather, become fully frozen during winter. This will not be a major problem from a quantitative point of view because aquifer storage is sufficient to support winter pumping, even if pumping is increased. However, it may have other environmental and cultural implications. Therefore, further study is needed to monitor at both the upper and downstream stream parts of the aquifer.

Towards quantification of mixing-relevant quantities from geophysics

SEMINARIO GRUPO DE HIDROLOGIA SUBTERRÁNEA

UPC-CSIC

Towards quantification of mixing-relevant quantities from geophysics


Niklas Linde (University of Lausanne)

Día: 15 de Junio a las 12.15 h
Lugar: Aula CIHS. Departamento de Ing. Terreno


Abstract:
Geophysics provides non-invasive field-scale imaging of spatially- and temporally-variable upscaled physical properties. Among those, electrical conductivity is closely linked to salinity. Because of non-linear averaging, these upscaled properties are oftentimes unrepresentative of (arithmetic) mean properties. Sub-resolution effects (impacts of property distributions below the resolution of geophysical tomograms) are seldom accounted for when using geophysics to infer hydrogeologically relevant information. In this talk, I will first illustrate sub-resolution effect with an example of fracture-aperture estimation using ground penetrating radar data. I will then present two
laboratory-scale examples that use electrical resistivity measurements to monitor tracer test experiments: one concerns the effect of two distinct fluid conductivities with application to dual-domain mass transfer, the other concerns the effect of small-scale salinity fluctuations below the averaging scale of the measurements. We hypothesise that sub-resolution effects carry information that is relevant to characterise mixing of solutes in groundwater systems, with implications for the characterisation of saline intrusion processes and interpretations of tracer tests using geophysics.

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