Analyse de la relation de puissance : débit solide - débit liquide à l'échelle du bassin versant de l'Oued Wahrane (Algérie)

Les flux de sédiments en suspension recueillis à l'exutoire d'un bassin versant sont étroitement liés aux débits liquides. Les modèles de relation liant ces deux paramètres reposent sur des concepts similaires faisant intervenir la loi de puissance Y=aXb. Bien que la validité d'une telle relation n'est pas à prouver, une analyse qualitative de la constante a et de l'exposant b a été effectuée pour un bassin versant situé en zone semi - aride : l'Oued Wahrane (Algérie). Les différentes échelles temporelles d'analyse utilisées ont permis d'expliquer le comportement des paramètres de l'équation en vue d'une meilleure compréhension de cette relation et de relier ces paramètres aux facteurs qui induisent le débit solide. L'objectif principal à trait aux aspects théoriques et pratiques du phénomène du transport solide en suspension. Les résultats ont permis d'identifier de manière assez concluante les modèles saisonniers. L'échelle saisonnière est très représentative du phénomène de transport solide dans le bassin versant. D'autres part, l'événement averse-crue s'est avéré l'unité hydrologique la plus adéquate pour les analyses en relation avec le transport solide.Fluxes of suspended materials collected at gauge stations are closely related to flow discharges. In the absence of continuous recorded suspended sediment concentration data, hydrologists have used rating sediment transport curves to define the water discharge/suspended sediment relationship and to estimate (predict) suspended sediment concentrations for use in flux calculations. Although there are many methods for developing rating curves, the most common is a power function Y=aXb that relates suspended sediment concentration to water discharge. The discharge measurement is composed of independent variables and a and b are the intercept and slope of the rating curve, respectively. These rating curves are usually generated by least squares regression. Although the accuracy of this approach has been questioned, the applicability appears to be adequate for many purposes. In order to better understand the relationship, this paper reports a qualitative analysis of parameters a and b.The average suspended sediment load for a cross-section of average stream discharge is the product of the average concentration of the suspended materials and the average flow discharge during the same period. The relation between sediment discharge and water discharge in Algeria rivers is unknown and difficult to assess. Some of these difficulties are related to sampling methods and a continuous record of suspended sediment concentrations is not available. This work will also be used to describe sedimentary dynamics specific to the basin during flood periods. The study was carried out on daily flow discharge data and the concentration of suspended materials collected from the gauging station on the Wahrane River (1972 to 1989). To determine the variation of the parameters a and b of the power relation, a methodology using regression models was used, based on an analysis on various scales of the parameters a and b of the equation of sediment transport in relation to the hydrological characteristics. The analysis reveals the evolution of the parameters a and b. Several temporal scales were used. An examination on an annual scale shows that it was possible to define a very strong relationship between a and the hydraulicity for the dry years and that indeed the factor a, indicating erodability, was well correlated with the hydraulicity during the dry period. The exponent b was correlated with hydraulicity only during the wet period. The relationship between a and mean rainfall was not significant. The seasonal scale revealed a very distinct effect.The production of sediments was very strong in autumn and winter when sediment transport approached the very typical power model. The seasonal rainfall strongly explained the variations of a while the exponent b was related to peak discharge. The analysis carried out on a monthly scale essentially produced the same conclusions as the analysis on a seasonal scale. It was found that the variation of a was more significant in winter and autumn than in the other seasons, presumably because of the hydrologic and sedimentology activity during this period, and the nature and surface quality of the soil. The relation between parameter a and the monthly average rainfall was very good. Given that the storm is the temporal unit most adequate for hydrological analyses in relation to sediment transport, analysis of single hydrologic events in the Wahrane River yields more details on the variation of a and b. The study was extended to the decomposition of the rising and falling limbs of the hydrograms. The floods of March and October showed the evolution of the parameters a and b. First, the range of variation of a and b, which was narrow during the preceding analyses, was broader for the analysis of the rising limb of the hydrograms. Secondly, the values of a and b showed opposite temporal trends. The high values of b were particularly characteristic of the risings associated with the autumn, during which flow discharges are strongest. The risings of winter floods were marked by low values of a. February and December were characterized by lower values of a in the falling limb than in the rising limb and stronger values of b in falling limb. Lastly, analysis of the values of a with respect to the antecedent precipitations index, IPA, suggested that the highest values of a were related to a weak IPA and a strong soil erodability in the catchment, whereas low values of a would reflect soil saturation (i.e. a strong IPA).The study showed that the power relationship between sediment load and stream flow was influenced by precipitation, runoff amount and soil moisture, and illustrated the complexity of solid transport

LA SEDIMENTATION DANS LES BARRAGES DE L’AFRIQUE DU NORD

La sédimentation des barrages dans les pays de l’Afrique du nord est très élevée et même spectaculaire. Elle est duedirectement aux forts taux d’érosion des bassins versants, dont les particules solides sont drainées directement par les coursd’eau et provoqueront à l’entrée des retenues des courants de densité. Cette sédimentation pose d’énormes problèmes à savoir;la réduction de la capacité, l’obturation des organes de vidange, la sécurité de l’ouvrage, la sédimentation des canauxd’irrigation et elle a même un impact sur la qualité de l’eau.Mots clés : Sédimentation - Afrique du nord - Barrage - Erosion - Courants de densité

The knowledges of traditional irrigation in the oasis of Kerzaz in southwest Algerian: Legacy and development

In the valley of Saoura, the demand for water for irrigation has increased significantly and rapidly, it requires mobilization and rational and intensive use of all existing water sources like the groundwater which are the only source of drinking water supply and irrigation in the region and the protection of the large vein that feeds the Saoura and bearing his name "oued Saoura". Oasis Kerzaz is amongst the the most celebrated oasis and the biggest of valley of Saoura , it now suffers from several impediments to their development as: the scarcity of irrigation water, land abandonment, the silting up, the chunking and the exiguity of agricultural land, the food nature of agricultural activity and incurable diseases of crops.Keywords: palm grove; well; Chadouf; Khottara; motorpump; Saoura

The fate of water in the oasis of Ouakda between traditional systems and modern (Region of Béchar, Southwest, Algeria)

One of the subjects that touch the field of environment is undoubtedly the traditional catchment systems and drainage divide in the oasis. The ancestral techniques such as wells chadouf, quanat, Khettara and foggaras have protected the oasis and the man in the past. These techniques were used in an arid middle by the oasis dwellers and resisted to a hostile climate for centuries. In spite of the low rainfall in the region of our oasis, the oasis dwellers of Ouakda through their intelligence, they were able to cultivate their land without disturbing a fragile ecosystem through exploitation of groundwater table thanks to the use of foggaras with the small distance which does not exceed 100 m. But the intervention of modern systems of water catchment like deep boreholes which overexploiting nonrenewable tablecloths and the pumps large capacity, the man has completely destroyed a clean environment. Today, thanks to these pumping, the groundwater level has dropped considerably; soil salinity is remarkable on all the parcels of the old palm grove and the Oued. We try in this Article to study the history of traditional techniques of water catchments in the oasis of Ouakda, to do a comparison between the ancestral systems used in the another oasis in this oasis, to study the impact of the motor pumps on the degradation of traditional systems and detrimental effects (Soil salinity and the phenomenon of lowering of the groundwater) after the use of modern techniques of water catchment.Keywords: Oasis, Ouakda, Foggara, Wells, Chadouf, motor pump

THE ORIGINALITY OF OASIS OF SAOURA IN SOUTH-WEST OF ALGERIA

For centuries the oases of the Saoura continue to manage critical situations of drought and the hostility of the Algerian Sahara through the rational exploitation of water, a rare and precious source of traditional irrigation techniques have proved their efficiency. The use of new groundwater drainage systems of drilling, and the lack of effective management of the Foggaras, has made this system lose its value, deteriorate and let the palm groves disappear. More than 80% of these systems have been abandoned in recent years. With increasing urbanization, population growth, climate change and the uncontrolled proliferation of motor pumps, the level of the water table is lowered and the quality of the water is degraded. The foggaras have gradually been abandoned, which leads to the degradation of the gardens and the old oasis

PROBLEMATIQUE DE SUREXPLOITATION DES EAUX SOUTERRAINES DANS LES ZONES ARIDES : CAS DE LA PLAINE DE GHRISS MASCARA –ALGERIE PROBLEMS OF OVEREXPLOITATION OF GROUNDWATER IN ARID AREAS: CASE OF THE PLAIN GHRISS MASCARA-ALGERIA.

La plaine de Ghriss couvre une vaste étendue d'une superficie d'environ 1185 Km2. Elle est située dans la wilaya de Mascara avec une altitude moyenne de 585,03 m. Avec un climat semi-aride et une sècheresse récurrente, cette région n'a enregistré qu'une pluie annuelle moyenne de 257,81 mm entre 1994 et 2004 alors qu'elle était située entre les isohyètes 400 et 500 mm. La plaine de Ghriss est une région à vocation agricole avec un maraîchage dominant. Le niveau moyen des eaux des puits ou forages dans cette plaine est estimé à 70 m et plusieurs puits d'observations du réseau piézométrique sont secs. Le volume d'eau extrait est estimé à 88 hm3/an alors que l'apport des nappes n'est que de 66 hm3/an soit un déficit de 32 hm3/an. Cette plaine souffre d'une surexploitation due à la pratique agricole et à la croissance démographique à travers l'AEP. En espérant un retour rapide des conditions météorologiques favorables, une politique de gestion de l'eau est inévitable pour sauver cette plaine qui est la plus riche de l'oranie du point de vue agricole. The plain of Ghriss covers vast wide of a surface of approximately 1185 km 2. It is located in the wilaya of Mascara with an average altitude of 585.03 m. With a semi-arid climate and a recurring secheress, this area recorded only one mean annual rain of 257.81 mm between 1994 and 2004 whereas it was located between isohyets 400 and 500 mm. The plain of Ghriss is an area with agricultural vocation with a truck farming dominating. The mean level of water of the wells or drillings in this plain is estimated at 70 m and several wells of observations of the piezometric network are dry. The volume of water extracted is estimated at 88 hm 3 / year whereas the contribution of the tablecloths is not that 66 hm 3 / year is a deficit of 32 hm 3 / year. This plain suffers from an overexploitation due to husbandry and the demographic growth through the AEP. By hoping for a fast return of the favorable weather conditions, a policy of management of water is inevitable to save this plain which is richest of the oranie from the agricultural point of view

Assessing the Effects of Personal Characteristics and Context on U.S. House Speakers’ Leadership Styles, 1789-2006

Research on congressional leadership has been dominated in recent decades by contextual interpretations that see leaders’ behavior as best explained by the environment in which they seek to exercise leadership—particularly, the preference homogeneity and size of their party caucus. The role of agency is thus discounted, and leaders’ personal characteristics and leadership styles are underplayed. Focusing specifically on the speakers of the U.S. House of Representatives from the first to the 110th Congress, we construct measures of each speaker’s commitment to comity and leadership assertiveness. We find the scores reliable and then test the extent to which a speaker’s style is the product of both political context and personal characteristics. Regression estimates on speakers’ personal assertiveness scores provide robust support for a context-plus-personal characteristics explanation, whereas estimates of their comity scores show that speakers’ personal backgrounds trump context