Production et transport des matières solides en suspension dans le bassin versant de la Haute-Tafna (Nord-Ouest Algérien)

Dans ce travail on s'intéresse aux sédiments transportés en suspension par le cours d'eau Oued Tafna à Beni-Bahdel. Une analyse de la variabilité de la charge en suspension de l'eau quant aux fluctuations des régimes hydro-climatiques, pour la période allant de septembre 1988 à août 1993, montre que la production des sédiments est très forte en automne mais de faible ampleur au printemps. En été, des crues éphémères fortement chargées sont parfois observées. En automne, le flux des matières solides en suspension représente 44% du flux annuel estimé à 286000 tonnes, alors que les apports en eaux ne représentent que 17% de l'apport annuel moyen évalué à 30,9 millions de m3. Au printemps, malgré l'augmentation des débits (60% de l'apport total annuel), la charge en suspension diminue de façon significative.Cependant, les sédiments ramenés par le cours d'eau sont produits soit par ruissellement superficiel sur les versants soit arrachés du lit et des berges du cours d'eau. On montre alors que la contribution de ces deux mécanismes d'érosion reste remarquablement constante d'une année à une autre. La production du ruissellement superficiel en matières solides représente alors 62% du flux annuel alors que l'érosion du cours d'eau contribue par 38%.Knowledge of suspended sediment loads carried by rivers provides insight into the underlying erosion mechanisms. In Maghreb rivers there are few data available on suspended sediment transport (PROBST and SUCHET, 1992). In this context knowledge of suspended sediment loads in the Oued Sebdou River (Mediterranean Algeria), which is a main stream in the Upper-Tafna basin, is of interest. The purpose of this study was to determine periods of active erosion and estimate the contributions of slope erosion and channel erosion in this basin.Situated in northwest Algeria, the Upper-Tafna basin covers an area of 256 km2 (Fig.1). Rising in Ouled Ouriach, the upper reaches of the river flow through Jurassic soils at altitudes up to 1400 m. These tributary streams join on the Sebdou plain (900 m), which is composed of Plio-quaternary alluviums. The soil is composed of calcareous-marnes, calcareous and Jurassic dolomites (BENEST, 1972; BENEST et al., 1999) until the Beni-Bahdel dam.The study zone is characterized by a semi-arid climate. Analysis of the rainfall data at the Beni-Bahdel station (X=34°42'33"; Y=01°29'48"; Z=660 m) from 1939-1940 to 1997-1998 (Fig. 2) demonstrates that the rain supply has decreased greatly since 1975, with more than an 18% decrease in rainfall amounts.Hydrological data and methodology The study used instantaneous water discharge and suspended sediment load values (1257 values) measured and supplied by the National Agency of Hydrologic Resources [ANRH]. Five annual water years have been investigated during the period from September 1988 to August 1993. The discharge values (QL, in m3/s) were determined from the rating curve for the measured heights of the water at the gauging station. The suspended load (g/l) was determined on water samples taken from the stream channel banks. The number of samples taken was adapted to the hydrological regime (i.e. every other day or during flood periods) and samples were collected as frequently as increments of 10 cm.The suspended sediments were carried from the slopes into the river by surface runoff or by stream channel erosion caused by flowing water. In order to express the contribution of these two mechanisms, we applied hydrograph separation methods used by ETCHANCHU (1988), ETCHANCHU and PROBST (1986), KATTAN et al. (1987) and PROBST and BAZERBACH (1986).Balance sheet of solid and liquid contributionsThe annual liquid contributions from 1988 to 1993 were evaluated to be 30.9 million m3. The abrupt slopes of the basin cause water to move quickly with a lot of force. In turn a large amount of suspended sediments (estimated at 286,000 tons) is generated, which corresponds to a soil erosion rate of 1120 tons/km2/year. This value is comparable to those estimated by WALLING (1984) where the erosion rates ranged between 1000 and 5000 tons/km2 /year.As seen in Table 1, the annual suspended sediment load varies dramatically. In 1990/91, the soil erosion rate was estimated to be 4283 tons per km2 ; this amount was 180 times higher than the sediment load in 1992/93 (24 tons per km2). Furthermore, there is no relationship between annual suspended sediment load and water discharge or annual rainfall. The annual precipitation (355 mm) was recorded during the year 1988/1989, and generated a soil erosion rate evaluated at 1072 tons per km2. For a similar rainfall, 345 mm recorded during the year 1992/93, the erosion rate was only about 24 tons/km2 /year.Autumn liquid contributions represent only about 17% of the mean annual supply (Fig. 4). Furthermore the heavy rains produce higher peak flows as the rain encounters dry soil with less vegetation cover and produces large quantities of solid by heavy rain splash erosion. The mean seasonal suspended sediment concentration was higher representing approximately 44% of total annual production. Spring corresponds to a dilution in sediment concentration caused by a large groundwater contribution. The volume discharged by spring flow is about 60% of total annual river discharge. The solids transported during this period are mainly eroded from the stream banks and represent 36% of total annual sediment load.Calculated values of monthly suspended sediment load and water supply are reported in Table 3. The monthly suspended sediment load carried by the river was very irregular. The majority (94%) of the total sediment load was transported in only three months, 45% in September, 30% in March and 19% in July. The monthly amounts varied from year to year, and this can be explained by the occurrence of floods (Table 4).The river suspended sediments were carried from the slopes into the river by surface runoff water or by stream channel erosion. Using a hydrograph separation method, the contributions of these two mechanisms are summarized in Table 4. According to these values we observed that : - The contribution of slope erosion processes represents an average of 62% of the total river-suspended sediment transport. - The second contribution from channel erosion represents at least 38% of the total river transport. This percentage is comparable with those obtained by ETCHANCHU and PROBST (1986) for the Garonne River basin (30%). This contribution is higher than those estimated by KATTAN et al. (1987) (22% for the Senegal River basin) and by ROBINSON (1977) for some American rivers. - This contribution was far less than those estimated by DUYSING (1985) for a forest stream in Luxemburg, where sediment produced by surface runoff was about 62% of annual suspended sediment loads. - This estimate is comparable to those estimated by where the erosion rates range between 1000 and 5000 tons/km2/year. - Although the annual amount of suspended sediment was variable, the relative contributions of the slope and channel erosion were less variable from year to year

Etude du transport solide en suspension dans l'Oued Mouilah (Nord Ouest Algérien)

Les résultats d'analyse graphique des valeurs instantanées des débits solides en suspension dans le cours d'eau de l'Oued Mouilah et leurs relations avec les débits liquides, durant les compagnes de prélèvements de 1977 à 1993, ont permis de montrer l'existence de deux périodes d'érosion actives. Le flux des matières solides en suspension dans le cours d'eau est très variable d'une année à une autre et la dégradation spécifique moyenne annuelle sur les 16 années d'étude est estimée à 126 tonnes par km2. Cette valeur est relativement faible par rapport à celles trouvées pour d'autres régions à régime hydrologique similaire.The extent and rates of alluvial deposit and dam siltation caused by sediment deposition from Maghreb streams have prompted a number of attempts to quantify and explain the complex mechanisms of suspended sediment transport. In Algeria, a country with scarce water resources, deposition of sediments in dams is estimated to average 20 million m3 /year, which contributes to a 0.3 % yearly loss of storage capacity from a total capacity estimated at 6.2 billion m3.Of interest in this context are suspended sediment loads in Mediterranean Algeria's Mouilah River, on which is built the Hammam Boughrara, a 117 million-m3 capacity dam put into service in 1998.The Mouilah River basin, situated in northwest Algeria, covers a 2650-km2 area and has a 230-km perimeter (Table I).The Mouilah runs along 124 km, rising at an altitude of 1250 m in Algeria then flowing into Morocco. It is ephemeral; perennial flow sets in near Oujda (Morocco), below which it re-enters Algeria near Maghnia (Figure 1).The study zone is characterized by a semi-arid climate. From 1977 to 1993, annual mean temperature was 16.7 °C. Rainfall was relatively scarce and unequally distributed throughout the year, with an inter-annual average of 300 mm over the same period (Figure 2).Analysis of hydrological dataThe study used instantaneous water discharge values (m3/s) measured at the mouth of the Mouilah from September 1977 to August 1993 (results calculated and furnished by the National Agency of Hydric Resources [ANRH]). For measured values, suspended loads (g/l) were evaluated using samples taken from the river: total suspended loads were calculated as the product of these concentrations and water discharge. The number of samples was adapted to the hydrological regime: They were taken every other day or, during flood periods, as frequently as quarter-hourly.Analysis of the instantaneous discharges showed that suspended loads were related to discharge by a power law (Figure 3).To study the responses of the basin over the hydrological year, we grouped the results - 16 years' worth of data - according to season, and analysed the relationship between liquid discharge and suspended sediment load (Table II). Graphical analysis of Figure 4 reveals that autumn and the spring are distinguished by strong river discharges leading to important transport of solids. The maximum flow of solids was about 104 000 kg/s, resulting from a water discharge of 1880 m3/s in November 1986. By contrast, winter and summer discharges were much smaller; values did not exceed 220 m3/s in winter and 83 m3/s in summer.After the dry season, the first rains of autumn encounter dry, hard and barely erodible soil. The response of the basin in terms of suspended-solids generation is therefore very small. It is the heavy rains of October and November that remove large quantities of solids transportable by streams.After the very dry and cool winter and a succession of freezes and thaws, spring rains fall on poorer soil, leading to relatively high loads, though still lesser than those of autumn.Summer is marked by very dispersed values encompassing the smallest discharges of the year and some relatively high suspended loads associated with low discharges, the latter arising from seasonal storms.In summary, stream discharge is very variable throughout the hydrological year. Suspended sediment transport in the Mouilah River basin occurs principally during flood periods. We distinguished two periods of active erosion, one in autumn and another, lesser period in spring.Annual contributions An annual balance sheet of solid and liquid contributions shows that these two parameters vary regularly and as a function of rainfall (Figure 5). Annual liquid contributions from 1977 to 1993 were evaluated at 48.7 million m3, which corresponds to a mean flood depth of 18.4 mm, and a low flow coefficient of 6 %. Due to very dispersed and extreme values and variability, rainfall-discharge relations are varied. This leads to inter-annual irregularity for flood depths: consequently, a relationship with annual rainfalls (Figure 6) was difficult to establish. However, we noted a tendency of the form: LE=0.0009P1.69 (R=0.74).The annual mean contribution of suspended sediment at the mouth of the river was estimated at 335 000 tons, which corresponds to a soil erosion rate of 126 tons/km2/year. This value is moderate compared to other basins of the region, such as the Mazafran (Algiers) and Isser (Lakhdaria) river basins, where erosion rates are about 1610 and 2300 tons/km2/year, respectively (Table III).The inter-annual solid and liquid contributions contrast markedly. Indeed, for liquid contributions, the first and third quartiles are 21.8 and 64.7 million m3, respectively, which shows that 25 % of the annual moduli representing humid years were three times more important than those representing dry years (Figure 7). Furthermore, in annual loads expressed as stream turbidity, variation between the temperate and arid reaches of the stream is apparent.Figure 8 shows that the highest annual liquid contribution, 117.8 million m3, was recorded during the year 1979-80, and generated a solid contribution of 670 000 tons. This liquid contribution is higher than that of 1986-87, evaluated at 106.4 million m3, which carried 2.69 million tons - an erosion rate of more than 1000 tons/km2/year

Hydrological modeling in semi-arid region using HEC-HMS model. case study in Ain Sefra watershed, Ksour Mountains (SW-Algeria)

Ain Sefra is one of the Algerian cities that had been experienced several devastating floods during the past 100 years. The purpose of this study is to simulate rainfall-runoff in the semi-arid region of Ain Sefra watershed through the employing of HEC-HMS model. In this paper, the frequency storm is used for the meteorological model, the SCS curve number is selected to calculate the loss rate and SCS unit hydrograph method have been applied to simulate the runoff rate. After calibration and validation, the simulated peak discharges were very closed with observed values.The Nash-Sutcliffe efficiency coefficient was 0.95 which indicated that the hydrological modeling results are satisfactory and accepted for simulation of rainfall-runoff. The peak discharges obtained for the 10, 50, 100 and 1000 years storms were respectively 425.8m3/s, 750.5m3/s, 904.3m3/s and 1328.3m3/s.Keywords: Ain Sefra, Floods, HEC-HMS, Frequency storm, Hydrological Modeling,Semi-ari

Hydrogeological caracterization and modeling of the aquifer of oued in amguel. (Tamanrasset, Central Hoggar - South Algeria)

The region of In Amguel takes its water from a single groundwater resource known in the Hoggar by "the inferoflux water table", captured by an underground dams with a  capacity of 4 Hm3 realised in 2000. This aquifer is highly exploited for supply drinking water and agriculture which create big deficit of water demand. Also, for better  management of this inféroflux, we realized its hydrogeological model by using the computer code ASMWIN, allowing us to better understand the hydrodynamic   functioning, refine the distribution of spatial characteristics governing groundwater flow in steady state and transient and conduct simulations of the behavior of the system for different operating scenarios.Keywords: Tamanrasset, Hoggar, In Amguel, inferoflux, modeling, ASMWIN, simulatio

Climate change: assessment and monitoring of meteorological and hydrological drought of Wadi El Hammam Basin (NW- Algeria)

During the last century, Algeria experienced a rainfall deficit was recorded in 1944, then successive drought periods since 1975 to the present day in Northen and Eastern. The most recent has repercussions on water resources and on agriculture. In this paper, we focus on the meteorological and hydrological drought. For describing and monitoring drought severity periods, we used meteorological and hydrological drought indices: Standardized Precipitation Index (SPI), effective Drought Index (EDI) and the standardized Runoff Index (SRI). Data was recording for the period of 30 years at Wadi Louza catchment (NW- Algeria). The best correlation between meteorological drought indices was found for 9-month time step. The results show that severe meteorological identified in March-1983 till the end of August-1984 in Sid Ahmed region and extreme hydrological drought during 1993.Keywords: Rainfall deficit; EDI; SPI; SRI; Wadi El Hamma

Characterization of q-Dunkl Appell symmetric orthogonal q-polynomials

AbstractWe introduce a q-Dunkl operator T(θ,q)≔Hq+θH−1 where Hq is the q-derivative one and we determine all symmetric T(θ,q)-Appell classical orthogonal q-polynomials. Up to a dilatation, the solution is a q2-analogue of generalized Hermite polynomials orthogonal with respect to the form H(μ,q2). Integral representation and discrete measure of H(μ,q2) are given for some values of parameters

Contribution of G.I.S. for the survey and the management of water resources in the basin “Benhandjir – Tirkount” (Ain Sefra) – mounts of Ksour - Saharian Atlas – Algeria

This work relates to the space numerical data processing, containing information having a relationship with the study and the management of the water resources of the basin of « Benhandjir – Tirkount » (Ain Sefra) characterized by his principal aquifer system of the lower Cretaceous sandstone. The study aims to geographical information system (GIS). The adopted methodology is based on two steps. The first approach practical was to reconstitute the aquifer geometry and study of the hydrodynamic and hydrochemical parameters. Analysis of an important variation of the flow and mineralization helped highlight the leading role hydrogeological fault “Ras Touil-Ain Sefra”. The second approach methodological, elaboration from the thematic analyses the synthetic map will serve as a support to a better approach for the management and to identify the zones that are most favourable to wells for the drinkable water, and the agriculture.Keywords: Ain Sefra – G.I.S. - water resources - lower cretaceous sandstone - fault “Ras Touil-Ain Sefra

Le comportement d'un système hydrologique en climat méditerranéen par l'analyse corrélatoire et spectrale des débits et des pluies. Cas de trois sous bassins sud-méditerranéens : (oued Sebdou, Moulah et Isser - Tafna - NW Algérie)

Les analyses corrélatoire et spectrale des chroniques de la pluie (entrée) et de débits (sortie) journaliers enregistrés au niveau des trois bassins sud méditerranéens Sebdou, Mouilah et Isser durant un seul cycle hydrologique nous ont permis d’obtenir des informations sur le fonctionnement de ces systèmes hydrologiques. Bien que la structure du signal « pluie » semble présenter les mêmes caractéristiques pour les trois bassins, le signal de sortie « débit » indique que l’oued Sebdou réagit différemment par rapport aux oueds Mouilah et Isser.The aim of this work was to show that correlation and spectral analyses can be used to understand the functioning of hydrological systems. Accordingly, a study was carried out on three southern Mediterranean basins: Sebdou; Mouilah and Isser; located in the north western of Algeria. (Figure 1). Correlation and spectral analyses of daily rainfall and discharge rates for one hydrological cycle were carried out.Simple analysisSimple analysis of rainfall showed that the correlograms (Figure 2) decreased rapidly for the three basins, reaching a value of 0.2 within 1-2 days. This result indicated that rainfall was a quasi-random phenomenon. The variance density spectrum (Figure 3) showed that the rainfall distribution was not monotonous and presented a “Leigh” signal structure.The simple analysis of discharge rates indicated that the Sebdou system was different. The correlogram (Figure 4a) decreased quickly, characterising independent events without memory and with non-significant amounts of water. However, the Mouilah and Isser correlograms (Figure 4 b,c) decreased slowly. They represent important memory effects with regulation of significant amounts of water. The spectral band (Figure 5) confirmed that the Sebdou system did not modify the input information. The regulation time was about 5 d for Sebdou, 21 and 43 d respectively for Mouilah and Isser.Cross analysisThe correlograms (Figure 6) show that the Mouilah and Isser rivers have a great buffering ability. The Sebdou River was characterised by a composite response of the surface flow and an important groundwater flow. The amplitude function (Figure 7) indicated that the Sebdou system had good inertia. The lag time (Figure 8) was 9, 2 and 5 days respectively for the Sebdou, Mouilah and Isser rivers. The amplification and attenuation of the input signal (Figure 10) show that the Sebdou basin is the most karstified system. The non-linearity of the relationship between rainfall and discharge was expressed by the coherence coefficient (Figure 9), which was lower than 1

Performance Analysis of Intelligent Reflecting Surface Aided Wireless Networks with Wireless Power Transfer

The low efficiency of wireless power transfer (WPT) poses a key challenge for energy-constrained wireless networks. To address this issue, in this letter, the integration of intelligent reflecting surface (IRS) into a WPT network is investigated. To this end, an accurate approximation for the probability density function of the end-to-end cascaded fading channel is presented. By leveraging the derived result, accurate closed-form expressions of the outage probability (OP) and average symbol error probability (ASER) are derived for the proposed IRS-aided WPT system. To gain further insight into the system performance, asymptotic closed-form expressions for the ASER and OP are further derived and interesting observations are reported. Particularly, our asymptotic analysis reveals that the achievable diversity in the underlying scenario is independent of the reflective elements of the IRS. The analytical derivations, corroborated by simulation results, demonstrate that IRSs can be promising candidates for the realization of a highly efficient power transfer enabled wireless network.acceptedVersionPeer reviewe