ahlem gara | Agronomic National Institute Of Tunisia (original) (raw)

Papers by ahlem gara

2015 6th International Conference on Modeling, Simulation, and Applied Optimization (ICMSAO), 2015

Tunisia presents a large spatio-temporal variability of rainfall which was largely observed in th... more Tunisia presents a large spatio-temporal variability of rainfall which was largely observed in the last years. This variability is influenced by several local and regional factors. The objective of this paper is to study the characteristics of the space and temporal variability of maximum daily rainfall in the state of Bizerte, located in the low valley of the medjerda basin and to seek the factors (topography, latitude, longitude, proximity of the sea, the speed direction of the wind …) who influence this variability to introduce them in the rainfall cartography. In order to study the space-time variability of the maximum daily rainfall, we used the frequential analyses, the principal component analysis (PCA) and the variography. Results show an important spatio-temporal variability caused by the effect of the several factors such as the topography, the depressions and the effect of the sea whose behavior of the rains differs from the South to the North of the state. These Observations are introduced into the cartography which is carried out by various methods of interpolation, the deterministic methods and geostatistics in aim to establish the maps of isohyets. Keywords—Space-time variability, maximum daily rainfall, frequential analyses, PCA, variography, medjerda basin.

Hydrological Sciences Journal

Predicting the impacts of climate change on water resources remains a challenging task and requir... more Predicting the impacts of climate change on water resources remains a challenging task and requires a good understanding of the dynamics of the forcing terms in the past. In this study, the variability of precipitation and drought patterns is studied over the Mediterranean catchment of the Medjerda in Tunisia based on an observed rainfall dataset collected at 41 raingauges during the period 1973–2012. The standardized precipitation index and the aridity index were used to characterize drought variability. Multivariate and geostatistical techniques were further employed to identify the spatial variability of annual rainfall. The results show that the Medjerda is marked by a significant spatio-temporal variability of drought, with varying extreme wet and dry events. Four regions with distinct rainfall regimes are identified by utilizing the K-means cluster analysis. A principal component analysis identifies the variables that are responsible for the relationships between precipitation...

This paper aims to protect against floods of the area of Sidi Thabet, which is located in the Low... more This paper aims to protect against floods of the area of Sidi Thabet, which is located in the Lower valley of Medjerda catchment in the North of Tunisia and known by its wide variability of runoff between dry and wet seasons, with a diffuse distribution of urban and rural areas and the abundance of undeveloped water courses often causing flooding annoying to people and infrastructure. To identify the area of intervention and to propose the suitable accommodations in these ones, we was based on a refined cartography by using GIS tool, on a detailed hydrological study of the zone of the project, on a statistical analysis of the rainfall data using the statistical software HYFRAN, besides the application of the CAQUOT model to obtain the dimensioning flows of the projected hydraulic equipments. The protection primarily consists on establishing different collectors in the five sub-catchments responsible for channeling and routing the storm water to its natural discharge point and replac...

La Medjerda est le seul cours d’eau perenne en Tunisie. Le bassin versant est le plus important d... more La Medjerda est le seul cours d’eau perenne en Tunisie. Le bassin versant est le plus important de la Tunisie en termes de ressources hydriques et contribue a pres de 25% de l’ensemble des ressources mobilisables du pays. La comprehension fine de l’hydrologie de ce bassin versant anthropise, dans un milieu fortement perturbe par des amenagements dont les objectifs sont parfois antagonistes (conservation, production, mobilisation,…), couple a la problematique des changements climatiques dont plusieurs scenarios plaident en faveur d’une baisse significative des precipitations associee a un accroissement des temperatures, indiquant des ressources hydriques moins importantes pour des besoins plus eleves, reste donc un pre-requis a sa gestion durable.

This paper presents an integrated and a trans-disciplinary analysis from a case study in Northwes... more This paper presents an integrated and a trans-disciplinary analysis from a case study in Northwest of Tunisia in order to release a decision for upscaling sustainable land management practices in the national level. The integrated, trans-disciplinary approach aims at initiating a process of co-production of knowledge and joint learning between relevant stakeholders from the local to the (sub-) national level. Thus, a range of different stakeholders – from land users, civil society organisations, and local authorities to industry and government representatives must actively be engaged in this process. This study is conducted using a range of workshops, which are a cornerstone of stakeholder participation and aim at enabling transdisciplinary-learning processes, between scientific and non-scientific actors. Thus, the workshops provide opportunities to initiate, promote and deepen a mutual learning process between the researchers and a range of relevant stakeholders (e.g. land managers...

Hydrological Sciences Journal , 2020

Research Article-Hydrology, 2019

The purpose of this paper was to demonstrate the added value of the spatial distribution of rainf... more The purpose of this paper was to demonstrate the added value of the spatial distribution of rainfall and potential evapotranspiration (PE) in the prediction of the discharge for a small Mediterranean catchment located in the Medjerda basin in Tunisia, i.e. the Raghay. We compare therefore the performance of a conceptual hydrological model available in the ATHYS platform, using global and spatial distributed input data. The model was implemented in two different ways. The first implementation was in a spatially distributed mode, and the second one was in a non-distributed lumped mode by using spatially averaged data weighed with a Thiessen-interpolated factor. The performance of the model was analysed for the distributed mode and for the lumped mode with a cross-validation test and through several modelling evaluation criteria. Simultaneously, the impact of the spatial distribution of meteorological data was assessed for the two cases when estimating the model parameters, the flow and water amounts, and the flow duration curves. The cross-validation of the split-sample test shows a preference for the spatially distributed model based on accuracy criteria and graphical comparison. The distributed mode required, however, more simulation time. Finally, the results reported for the Raghay indicated that the added value of the spatial distribution of rainfall and PE is not constant for the whole series of data, depending on the spatial and temporal variability of climate data over the catchment that should be assessed prior to the modelling implementations.

Olive mill wastewater (OMW) is occurred from the production of olive oil in olive mills. Many oli... more Olive mill wastewater (OMW) is occurred from the production of olive oil in olive mills. Many olive mills are scattered in most Mediterranean countries which produce it seasonally. This led to an environmental problem in these olive oil-producing countries, due to the elevated level of salinity, polyphenols, and the pollution burden. However, OMW is also characterized by richness in organic and mineral compounds. Consequently, OMW spreading can be an alternative for a low cost soil organic amendment. This work aimed to study the effect of OMW spreading on the chemical properties of soils in arid regions. Amendments with OMW were applied on two different soils in arid regions from Southern Tunisia with a quantity of 300 L per 100 m 2 (per plot), in a completely randomized experimental setup. The main objective of this work is to identify the short-term effect of OMW on fertility of sandy soil, for the supply of soil on organic carbon, inorganic nitrogen, available phosphorus and exchangeable potassium during 2010 as well as assessment of its effect on pH, salinity of soils in arid regions. Obtained results show that under the conditions of our experiment, applying of this organic effluent has changed significantly the content of exchangeable potassium (197% and 221%, respectively, for Dar Dhaoui (A) and El Fje (B) soil), mineral nitrogen, phosphorus (370% and 445%, respectively for (A) and (B) soil), and organic matter in soil (from 0.92% to 1.51% and from 0.87% to 1.95%, respectively, for (A) and (B) soil). Consequently, OMW is considered as a rich organic material and may constitute a potential potassic amendment for dryland soils poor in this element, which has the tendency to increase the content of major elements and the soil organic matters. OMW application did not cause a significant change in soil pH, due to the low quantity of OMW used in the soil. However, we highlighted the value of OMW as an organic amendment that requires further study on optimizing

Land degradation is intrinsically complex and involves decisions by many agencies and individuals... more Land degradation is intrinsically complex and involves decisions by many agencies and individuals, land degradation mapping
should be used as a learning tool through which managers, experts and stakeholders can re-examine their views within
a wider semantic context. In this paper, we introduce an analytical framework for mapping land degradation, developed
by World Overview for Conservation Approaches and technologies (WOCAT) programmes, which aims to develop some
thematic maps that serve as an useful tool and including effective information on land degradation and conservation status.
Consequently, this methodology would provide an important background for decision-making in order to launch rehabilitation/
remediation actions in high-priority intervention areas. As land degradation mapping is a problem-solving task that
aims to provide clear information, this study entails the implementation of WOCAT mapping tool, which integrate a set
of indicators to appraise the severity of land degradation across a representative watershed. So this work focuses on the
use of the most relevant indicators for measuring impacts of different degradation processes in El Mkhachbiya catchment,
situated in Northwest of Tunisia and those actions taken to deal with them based on the analysis of operating modes and
issues of degradation in different land use systems. This study aims to provide a database for surveillance and monitoring of
land degradation, in order to support stakeholders in making appropriate choices and judge guidelines and possible suitable
recommendations to remedy the situation in order to promote sustainable development. The approach is illustrated through
a case study of an urban watershed in Northwest of Tunisia. Results showed that the main land degradation drivers in the
study area were related to natural processes, which were exacerbated by human activities. So the output of this analytical
framework enabled a better communication of land degradation issues and concerns in a way relevant for policymakers.

Tunisia presents a large spatio-temporal variability of rainfall which was largely observed in th... more Tunisia presents a large spatio-temporal variability of rainfall which was largely observed in the last years. This variability is influenced by several local and regional factors.
The objective of this paper is to study the characteristics of the
space and temporal variability of maximum daily rainfall in the state of Bizerte, located in the low valley of the medjerda basin and to seek the factors (topography, latitude, longitude, proximity of the sea, the speed direction of the wind …) who influence this variability to introduce them in the rainfall cartography. In order to study the space-time variability of the maximum daily rainfall, we used the frequential analyses, the principal component analysis (PCA) and the variography.
Results show an important spatio-temporal variability caused by the effect of the several factors such as the topography, the
depressions and the effect of the sea whose behavior of the rains differs from the South to the North of the state.
These Observations are introduced into the cartography which is carried out by various methods of interpolation, the deterministic methods and geostatistics in aim to establish the maps of isohyets.

Flash floods are the most destructive natural hazards that occur in the Mediterranean region at s... more Flash floods are the most destructive natural hazards that occur in the Mediterranean region at short time scales usually in small basins. Rainfall–runoff models can be very useful for flash flood forecasting and prediction. The Medjerda Wadi represents the only permanent hydro-system in Tunisia that; unfortunately the latter is at the same time threatened and threatening. This work consists on the application of the physical-spatialized model MERCEDES in the case of a catchment area situated in the left bank of the high valley of Medjerda, the catchment area of the Raghay wadi of surface of approximately 322 km². This basin is characterized by a very important morphological, climatic and physical variability in time and space, often presenting very important floods because of flow not measured which comes from the Algerian frontier part. The flow arriving thus at the discharge system is added with the flow coming from the principal waterway on the level from the junction with Medjerda, often causing very important damage on the level of the cities which are year downstream. The choice is fixed on six events distributed over three different seasons, recorded on the level of two pluviograph stations for an hour time-step and which control the flow in the discharge system of the catchment area. The parameters of entry of the GREEN and AMPT production function are maps having the variability of the physics parameters of the soil as well as the variation of altitude and of the directions of drainage. The advantage of this function is related on its physical base, and the theoretical possibility to estimate the parameters starting from data of grounds or ―in situ‖ measurements. The results of simulations show that, in general, the selected model simulates volume well and underestimates the maximum flow for the validation phase, but in general the model is validated for the Raghay catchment.

Le présent rapport vise à la protection contre les inondations ( PCI) de la régi on ... more Le présent rapport vise à la protection contre les inondations ( PCI) de la régi on de Sidi Thabet qui est située à la Basse vallée de la Medjerda.
Cette zone est connue par sa large variabilité des apports entre les saisons sèches et humides, par une répartition diffuse des zones urbaines et celles rurales et par l’abondance des cours d’eau non aménagés provoquant souvent des inondations gênant à la population et à l ’infrastructure. La PCI des bassins d'étude est assurée par la proposition des aménagements convenables dans chaque zone. Ces aménagements consistent essentiellement à implanter des collecteurs enterrés à l ’intérieur de la ville pour résoudre les problèmes de stagnation de l ’eau et de respecter la largeur des rues en évitant d’implanter des collecteurs dans les rues étroites. Cette proposition
d’aménagements est le résultat d’une cartographie raffinée en employant l’outil SIG, d’une étude hydrologique détaillée de la zone du projet, d’une analyse statistique des données pluviométriques à l ’aide du logiciel d’ajustement statistique HYFRAN, en plus de l’application du modèle de Caquot pour obtenir les débits de dimensionnements des ouvrages hydrauliques projetés.

Ce travail concerne le bassin versant de Sidi Thabet qui est une région de la ba... more Ce travail concerne le bassin versant de Sidi Thabet qui est une région de la basse vallée de la Medjerda_Tunisie. Son but est de quantifier l’érosion hydrique des sols et d’élaborer un plan d’aménagement. L ’élaboration de la carte de sensibilité au ruissellement a conduit à
estimer les coefficients de ruissellement. Les volumes des crues sont estimés par l ’application du modèle de Sokolovsky . L ’érosion spécifique au ni veau de tout les sous bassins versant est la même de l’ordre de
2669,5 t/km²/an. L’apport responsable du risque d’érosion dans cette régi on est le maximum mensuel qui est de 227,3 mm de période de retour 26 ans. Les aménagements proposés sont définis en s’appuyant sur la carte de risque d’érosion et les aménagements existants. La carte
d’aménagement établie a pour but de planifier l ’installation des techniques qui assureront l e maintien et l ’amélioration de la fertilité des sols, la stabilisation et la réhabilitation des zones érodées. Les techniques proposées vont emprisonner une grande partie des eaux de ruissellement et assurer une bonne protection des sols contre l ’érosion

This work concerns the catchment area of Sidi Thabet which is a region of the lower valley of the... more This work concerns the catchment area of Sidi Thabet which is a region of the lower valley of the Medjerda basin in Tunisia.
Our aim in this study is to quantify the water erosion of the soil and to develop a management plan. The development of the
sensitivity map to runoff has led us to estimate the coefficients of runoff, the volumes of the floods(of period of return 26
years) are estimated by the application of the Sokolovsky model. The specific erosion "Es" at all sub-watersheds is the same.
Specific erosion is in equal to 2669,5 t/km²/year. The responsible factor of the risk of erosion in the study area is the maximum
monthly rainfall which is 227.3 mm. This value has a return period equal at 26 years. The proposed andplanified installations
are defined based on the map of risk of erosion andexisting structures hydraulic.

This research study consists on the validation of the physically and distributed hydrological mo... more This research study consists on the validation of the
physically and distributed hydrological model, throw the application
of the ATHYS platform for hydrological modeling, for the case study
of a catchment area situated in the left bank of the high valley of the
Medjerda basin, the catchment area of the Raghay wadi having an
area of approximately 322 km². This watershed is characterized by a
very important morphological, climatic and physical variability in
time and space, often presenting very important floods because of the
not measured flow coming from the Algerian frontier part instead of
the large difference of atitude from 165 to 1180 in the Tunisian part.
The choice is fixed on six events distributed over three different
seasons, recorded on the level of two pluviographic stations for an
hour time-step and which control the flow in the discharge system of
the catchment area. The parameters of entry of the GREEN and
AMPT production function are maps having the variability of the
physical parameters of the soil as well as the variation of altitude and
of the directions of drainage. The advantage of this function is
related on its physical base, and the theoretical possibility to estimate
and optimize the parameters starting from data of grounds or “in
situ” measurements. The evaluated criteria for optimization are the
Nash criteria which is varying between 0.73 and 0.98 for the
calibration phase, and between 0.62 and 0.75 for the validation for
the three seasons, instead of the Arithmetic Mean Error for the
volume and the peak flow giving very good errors for the Wintry
season, good errors for the Autumnal season and medium errors for
the Springer season. The results of simulations show that the selected
model is well validated for the Raghay catchment than, its
performance in the comprehension of the hydrological answer of a
Mediterranean watershed, which provide important information for
decision makers in order of protection against floods of the area

2015 6th International Conference on Modeling, Simulation, and Applied Optimization (ICMSAO), 2015

Hydrological Sciences Journal

Hydrological Sciences Journal , 2020

Research Article-Hydrology, 2019

Tunisia presents a large spatio-temporal variability of rainfall which was largely observed in th... more Tunisia presents a large spatio-temporal variability of rainfall which was largely observed in the last years. This variability is influenced by several local and regional factors.
The objective of this paper is to study the characteristics of the
space and temporal variability of maximum daily rainfall in the state of Bizerte, located in the low valley of the medjerda basin and to seek the factors (topography, latitude, longitude, proximity of the sea, the speed direction of the wind …) who influence this variability to introduce them in the rainfall cartography. In order to study the space-time variability of the maximum daily rainfall, we used the frequential analyses, the principal component analysis (PCA) and the variography.
Results show an important spatio-temporal variability caused by the effect of the several factors such as the topography, the
depressions and the effect of the sea whose behavior of the rains differs from the South to the North of the state.
These Observations are introduced into the cartography which is carried out by various methods of interpolation, the deterministic methods and geostatistics in aim to establish the maps of isohyets.