Laboratoire De Modélisation Hydraulique Et Environnement

ABSTRACT
Drip irrigation is frequently used as a mean to improve irrigation efficiency. Recent research, however, has shown that unsaturated solute transport may be strongly affected by
preferential flow, especially due to hydrophobic conditions in dry soil. The degree of preferential flow using typical drip irrigation with moderately saline water for two typical soil types was investigated using multiple tracers (dye and bromide). The experiments were carried out in two
different types of dry soil, clayey and sandy soil. Three plots at each site were chosen. An amount of solution containing dye and bromide, equal to a typical daily irrigation volume was discharged through a single irrigation dripper at each plot. On the following day, horizontal 5-cm trenches were dug and dye pattern and bromide concentrations were recorded. The effects of hydrophobicity and preferential flow appeared not to be significant for the soil down to tillage depth. For the clayey soil preferential flow was not significant in spite of clay aggregates. Cracks below tillage depth were the main cause for preferential flow. For the dry sandy soil preferential flow effects were also not significant. The infiltrated solute wetted twice the soil volume for the sandy soil as compared to the clayey soil.
Keywords: Drip irrigation; bromide; dye; sigma probe; preferential flow.

Coastal aquifers are at threat of salinization in most
parts of the world. This study was carried out in coastal
shallow aquifers of Aousja-Ghar El Melh and Kalâat el
Andalous, northeastern of Tunisiawith an objective to identify
sources and processes of groundwater salinization. Groundwater
samples were collected from 42 shallow dug wells
during July and September 2007. Chemical parameters such
as Na+, Ca2+, Mg2+, K+, Cl−, SO4
2−, HCO3
−, NO3
−, Br−, and
F− were analyzed. The combination of hydrogeochemical,
statistical, and GIS approaches was used to understand and
to identify the main sources of salinization and contamination
of these shallow coastal aquifers as follows: (i) water-rock
interaction, (ii) evapotranspiration, (iii) saltwater is started to
intrude before 1972 and it is still intruding continuously, (iv)
irrigation return flow, (v) sea aerosol spray, and finally, (vi)
agricultural fertilizers. During 2005/2006, the overexploitation
of the renewable water resources of aquifers caused saline
water intrusion. In 2007, the freshening of a brackish-saline
groundwater occurred under natural recharge conditions by
Ca-HCO3 meteoric freshwater. The cationic exchange processes
are occurred at fresh-saline interfaces of mixtures along
the hydraulic gradient. The sulfate reduction process and the
neo-formation of clays minerals characterize the hypersaline
coastal Sebkha environments. Evaporation tends to increase
the concentrations of solutes in groundwater from the recharge
areas to the discharge areas and leads to precipitate carbonate
and sulfate minerals.

Drip irrigation is frequently used as a mean to improve irrigation efficiency. Recent research, however, has shown that unsaturated solute transport may be strongly affected by preferential flow, especially due to hydrophobic conditions in dry soil. The degree of preferential flow using typical drip irrigation with moderately saline water for two typical soil types was investigated using multiple tracers (dye and bromide). The experiments were carried out in two different types of dry soil, clayey and sandy soil. Three plots at each site were chosen. An amount of solution containing dye and bromide, equal to a typical daily irrigation volume was discharged through a single irrigation dripper at each plot. On the following day, horizontal 5-cm trenches were dug and dye pattern and bromide concentrations were recorded. The effects of hydrophobicity and preferential flow appeared not to be significant for the soil down to tillage depth. For the clayey soil preferential flow was not sig...

Central Tunisia is characterized by a semi arid to arid climate where groundwater is the primary source of water supply. Oum
Ali-Thelepte aquifer, located in Kasserine (Central Tunisia) with an arid climate, is among the most available water resources in the
region. Natural recharge quantification is thus a crucial issue for a better evaluation of this resource.
The present work aims to estimate and study groundwater recharge processes at the long term in an arid context. Chloride Mass
Balance (CMB) and variably saturated numerical modeling are the retained methods to fulfill these objectives.
Potential recharge areas of the aquifer were already identified using hydrogeological, geochemical and isotopic methods. Selected
sites (in the recharge areas) were then retained to perform soil sampling. In the present study we are presenting investigations carried
out in one representative site located near the North West of the Algerian border. 18 interstitial water samples have been obtained
from the unsaturated zone using a dry drilled soil profile of 8m depth (reaching groundwater level). Soil texture, bulk density, gypsum
content, water content and physico-chemical analyses (pH, Temperature, Electrical Condictivity, Na, Ca, Mg, K, HCO3, Cl, SO4, F
and NO3) were performed.
CMB was applied for both groundwater and the unsaturated zone (chloride profile method). Hydrus-1D was calibrated using field and
climate data at a daily scale and for a long time period to reach a nearly steady state regime.
The mean annual recharge calculated was 7.13 mm/year (2.34% of the mean annual rain) using the chloride profile method and 3.81
mm/year (1.26% of the annual rain) using the CMB for groundwater. Model calculations showed that the average annual recharge
was about 11.28 mm/year (3.7% of the mean annual rain). The recharge rate obtained from these different methods is relatively of similar range values. Calculations are to be continued for the remaining selected sites in order to attribute recharge rates for each
recharge area.

The  paper  factory  located  in  Kasserine  (west-central  Tunisia)  is  the  main  industrial  activity  in  the  region.  It  has
been releasing, over decades, several contaminants in the nature rejected within the effluents and the leakages. Thus, an
important  amount  of  mercury  was  reported  to  have  been  regularly  loaded  at  the  level  of  the  factory  site  and  Wadi
Andlou.
The  main  objective  of  the  present  paper  is  to  study  the  transport  of  mercury  in  soil  and  groundwater  and  to  test
numerically the excavation technique efficiency as a remediation solution proposed in former studies.
A review of former studies dealing with the subject and the site has been performed. The collected data was treated
and analyzed using GIS and geochemical diagrams.
Filed investigations, conducted in 2005, showed a variable degree of contamination with mercury for sediments and
water  samples  collected  from  Wadi  Andlou,  the  factory  site  and  the  Arish  shallow  aquifer.  In  some  cases  mercury
concentrations exceeded the CCME standards.
Simulations  of  unsaturated  transport  of  mercury  have  also  been  carried  out  using  Hydrus1D  for  9  boreholes.
Concentrations issued from the unsaturated modeling study were used to perform isoconcentration maps of mercury in
groundwater  at  different  dates.  The  adsorption  coefficient  Kd  was  calibrated  using  the  measured  mercury
concentrations for soil and groundwater.
Prediction scenarios based on the excavation of 50 cm of the upper layer were performed using Hydrus1D. They
showed  that  this  technique  provides  decontamination  of  the  first  layers,  however,  the  mercury  remains  in  the  lower
horizons of the soil column.

Acknowledgement:  The  authors  would  like  to  thank  the  Tunisian  Ministry  of  the  environment  especially  Mrs
Dhekra Gharbi for assisting with documentation.

Groundwater sampling and piezometric measurements were carried out along two flow paths (corresponding to two transects) in Korba coastal plain (Northeast of Tunisia). The study aims to identify hydrochemical processes occurring when seawater and freshwater mix. Those processes can be used as indicators of seawater intrusion progression and freshwater flushing into seawater accompanying Submarine Groundwater Discharge (SGD). Seawater fractions in the groundwater were calculated using the chloride concentration. Hierarchical cluster analysis (HCA) was applied to isolate wells potentially affected by seawater. In addition, PHREEQC was used to simulate the theoretical mixing between two end members: seawater and a fresh-brackish groundwater sample. Geochemical conventional diagrams showed that the groundwater chemistry is explained by a mixing process between two end members. Results also revealed the presence of other geochemical processes, correlated to the hydrodynamic flow paths. Direct cation exchange was linked to seawater intrusion, and reverse cation exchange was associated to the freshwater flushing into seawater. The presence of these processes indicated that seawater intrusion was in progress. An excess of Ca, that could not be explained by only cation exchange processes, was observed in both transects. Dedolomitization combined to gypsum leaching is the possible explanation of the groundwater Ca enrichment. Finally, redox processes were also found to contribute to the groundwater composition along flow paths.

With  the  rapid  growth  of  industrialization  and  urbanization,  the  subsurface  media  is  increasingly  exposed  to
contamination.  Therefore,  a  serious  solution  for  remediation  is  required.  Nanotechnology,  a  recently  developed
technology and largely applied in different fields, could be helpful for this objective.
Two sand columns (Diameter=4.8 cm; length=20 cm), saturated with textile wastewater, with varying physical and
chemical properties were injected with two pore volumes of a sonicated solution containing 0.5 g NZVI (Nanosized
Zero-Valent  Iron)  L
-1
and  eluted  at  two  different  flow  rates  of  5  ml/min  and  10  ml/min.  These  experiments  were
conducted to investigate the influence of physicochemical factors on the transport and retention of surfactant stabilized
NZVI  nanoparticles.  The  concentration  of  the  nanoparticles  in  the  effluent  was  determined  using  a  UV
spectrophotometer. Breakthrough of NZVI was analyzed using filtration theory and a Hydrus 1-D transport model that
incorporated two-site kinetic attachment-detachment.
The  research  of  this  project  proves  that  an  increase  in  pH  leads  to  a  slight  increase  in  mobility  of  NZVI  in  the
saturated  porous  media.  A  decrease  in  grain  size  leads  to  more  trapping  of  nanoparticles  due  to  the  increase  in
maximum  capacity  of  attachment.  A  higher  retention  is  noticed  with  a  decrease  in  pore  water  velocity.  The  break
through curves simulated with Hydrus-1D showed that, while considering both attachment and detachment with first
order and second order attachment coefficients, the first order detachment coefficient fitted the experimental data better
than considering only the attachment, irrespective of pH or flow velocity. Thus the simulation study proves that both
attachment/detachment processes are the important mechanisms affecting NZVI transport in saturated porous media.

Acknowledgement: The study was carried out as a part of project under Department of Science and Technology,
India.

Drip irrigation is frequently used as a mean to improve irrigation efficiency. Recent research, however, has shown that unsaturated solute transport may be strongly affected by preferential flow, especially due to hydrophobic conditions in dry soil. The degree of preferential flow using typical drip irrigation with moderately saline water for two typical soil types was investigated using multiple tracers (dye and bromide). The experiments were carried out in two different types of dry soil, clayey and sandy soil. Three plots at each site were chosen. An amount of solution containing dye and bromide, equal to a typical daily irrigation volume was discharged through a single irrigation dripper at each plot. On the following day, horizontal 5-cm trenches were dug and dye pattern and bromide concentrations were recorded. The effects of hydrophobicity and preferential flow appeared not to be significant for the soil down to tillage depth. For the clayey soil preferential flow was not significant in spite of clay aggregates. Cracks below tillage depth were the main cause for preferential flow. For the dry sandy soil preferential flow effects were also not significant. The infiltrated solute wetted twice the soil volume for the sandy soil as compared to the clayey soil.

Infiltrated water may originate from rainfall; irrigation; water bodies such as ponds, rivers, and lakes; or other anthropogenic activities. The terms infiltration and percolation are frequently interchangeably used even though they represent two different processes. Infiltration describes the entry from the surface to the subsurface, whereas percolation focuses on the flow of water through soil and porous media. The amount of water percolation that reaches the groundwater represents the groundwater recharge. When the soil surface is exposed to rainfall or submersion, infiltrated water fills the interstices between soil grains of the upper layers of the soil. The soil profile may contain a saturated horizon that extends a few millimeters in depth, called the saturated zone. Water continues to penetrate into the subsurface forming a...

Infiltration is defined as the entry of water from the surface into the subsurface.
Introduction
Infiltrated water may originate from rainfall; irrigation; water bodies such as ponds, rivers, and lakes; or other anthropogenic activities. The terms infiltration and percolation are frequently interchangeably used even though they represent two different processes. Infiltration describes the entry from the surface to the subsurface, whereas percolation focuses on the flow of water through soil and porous media. Theamountofwaterpercolationthatreachesthegroundwater represents the groundwater recharge. When the soil surface is
exposed to rainfall or submersion, infiltrated water fills the interstices between soil grains of the upper layers of the soil. The soil profile may contain a saturated horizon that extends a few millimeters in depth, called the saturated zone. Water continues to penetrate into the subsurface forming a transmission zone. The water content in this zone varies with depth, and the water flow is essentially vertical and driven by gravitational forces. For the wetting zone, located below the transmission zone, the water content decreases sharply to reach the initial water content of the soil. The limit between dry and wet compartments of the soil profile is called wetting front (Fig. 1). It is characterized by a steep hydraulic gradient and presents a sharp limit between dry and wet horizons of soil. Over the infiltration process, the wetting front progresses vertically, and the transmission zone expands (Hendriks 2010). Infiltration rate is variable with time. It demonstrates a steep decline from the beginning of the infiltration episode and reaches a steady state when the soil becomes saturated. At this stage, the infiltration rate is approximately equal to percolation rate. Infiltration rate depends also on infiltration capacity of each soil type expressed in mm/h and the presence of macropores (Wilson 1990). Soil water infiltration is controlled by soil physical properties, slope, vegetation, surface roughness, and the rate and duration of water application. Infiltration capacity is commonly determined by hydrograph analysis and infiltrometer experiments. Infiltrometers are classified into two types: rainfall simulators or flooding devices. Rainfall simulators producedropsofwaterfalling ontothesoilsurfaceatameasured rate providing a method of investigating the infiltration process. They are used to give assessment of the time needed to ponding when a uniform rainfall rate occurs on the soil surface. The rainfall can be simulated by sprinkling water from an array of capillaries or by using a rotating swirl plate device. Flooding devices are typically rings or tubes inserted