Contribution à la gestion de la retenue d'un barrage réservoir sur la rivièreSebou (Maroc) à l'aide d'un modèle hydraulique

Dans cette étude, on propose un modèle hydraulique capable de contribuer à la gestion des eaux de la rivière Sebou au niveau de la retenue d'un barrage de garde situé à l'intérieur de la plaine agricole du Gharb. Le modèle hydraulique élaboré (MHS.1) est du type filaire et utilise un schéma de différences finies. L'écoulement est influencé par la présence du barrage à l'aval et de nombreuses grandes stations de pompage utilisées pour l'irrigation le long du tronçon étudié. Cependant, les données relatives à la quantité d'eau pompée au niveau de ces stations ainsi que par les particuliers sont rarement disponibles. Ainsi, une attention particulière a été attribuée à l'estimation du pompage vue son importance quantitative. Les résultats du calibrage et de la validation du modèle pour des périodes de basses eaux de l'année 1997 sont très satisfaisants. Le modèle donne les valeurs du niveau d'eau aux stations de pompage et permet de suivre l'évolution de la réserve de la retenue du barrage. Ce code regroupe dans un seul outil des données provenant de différentes sources et utilisées pour la première fois dans un modèle hydraulique. Il représente un atout considérable pour les organismes publics gestionnaires des ressources hydriques.The studied reachThe Sebou River (600 km) is an important river in Morocco and its waters are solicited for several different uses. The Sebou has an average bottom slope of 10-4, variable geometry and many meanders. The flow is characterised by considerable annual and seasonal variations (Figure 2). The studied reach is situated between the town of Belksiri and the Lalla Aïcha dam. Flow is influenced by the presence of two dams, the Al Wahda upstream and the Lalla Aïcha in the downstream reach. The first dam was constructed on the Ouergha River, which has a torrential regime. The second dam comprises five principal and two secondary radial floodgates and these gates are opened from the bottom. This dam is completely opened during the period of high flows. The maximum flow during this season is 1800 m3/ s. The dam has a catchment area of 2700 km2. The maximum volume of the dam reservoir is 37 Mm3. Its length of influence is about 120 km.During the dry season, the floodgates are partially closed in order to increase the water level upstream. The maximum level upstream of the dam is 6.5 m NGM (the bottom is at -1 m). This situation facilitates the pumping of water for agriculture, allowing the irrigation of 15,600 hectares of rice. A volume of 200 Mm3 of water is mobilised annually, which, before the construction of the dam, was lost to the Atlantic Ocean.The hydraulic model MHS.1The hydraulic model MHS.1 is based on a modification (essentially the representation of the topography and the outputs) of the DYNHYD5 model. It solves the one dimensional Saint-Venant equations of continuity and momentum (equations 1 and 2). The Manning coefficient used in the momentum equation is evaluated initially by the empirical formula (Formula No. 3) proposed by Chow. The factor n0 is evaluated from granulometric measurements that were carried out from upstream to downstream in the studied reach. The others coefficients were evaluated from observations of the river in aerial photos, from the cross sectional areas and available photos, and from field visits. MHS.1 uses a network called ''Link-Node''. The equations of continuity and momentum, expressed in a finite difference manner, give respectively equations 4 and 5. These equations are solved using a Runge-Kutta procedure.Discretisation of the studied reachThe discretisation of the studied reach was performed using aerial photos achieved by the ORMVAG (L'Office Régionale de la Mise en Valeur Agricole du Gharb) in 1983. These photos were taking in a dry period where the river was nearly dry. This situation permitted a good stereoscopic visualisation of the river morphology. The river reach was divided into 529 grids with a length varying between 50 and 900 m. Data on cross sectional areas from the ORMVAG and other sources were used. Near the town of Souk Tlat (Figure 1), we exploited a new technique called ''Numeral photogrammetry'', which allowed us to reconstitute many cross sectional areas. This technique uses principally stereoscopic pairs of aerial photographs and photogrammetry software. The remaining cross sectional areas were evaluated from observations on aerial photos and from field visits.Evaluation of the pumped waterOne of the important factors that affect flow in the studied reach is the intensive pumping of waters along the river. The pumped water was divided into two types. The first type corresponded to the ten central stations managed by the ORMVAG (Fig. 1). The data of this first type were neither centralised nor easily available. Only the data at the important S2 station were readily available. The second type corresponded to water pumped by individuals and is less quantified than the first type.Two major hypotheses were adopted. First, the pumped flow at the S2 station was assumed to be equal to 25% of the total flow pumped by all the ORMVAG stations. The stations were classified into three classes according to their theoretical capacity (Table 1). This hypothesis allowed the estimation of the unknown pumped flow at the nine other stations. We further assumed that in the neighbourhood of each station, the flow pumped by individuals was equal to the flow pumped by the station. This latter hypothesis was adopted on the basis of a field investigation in a 7 km characteristic reach. Figure 3 shows the evolution of the overall pumped flow evaluated for the months of June and July 1997. These two months were used respectively for the validation and calibration of the model.Calibration and validation of MHS.1The Manning coefficient, estimated initially by the Chow formula (3), varied along the studied reach. It ranged from 0.02 to 0.04 s/m1 /3, with a mean value of 0.037 s/m1 /3. In the calibration procedure, the Manning coefficient was modified to the same degree along the studied reach because we assumed that the sources of errors involved in its evaluation are identical for all the grids.Along the studied reach, the only available measured data are the water levels at the S2 station and upstream of the dam. The period chosen for the calibration was from 07/01/1997 to 07/30/1997. The upstream boundary (at the Belksiri hydrological station) was given as values of the water level as a function of time (Figure 4). The downstream boundary was given as values of the discharge (flow through the dam gates) as a function of time (Figure 5). Figures 6 and 7 give the results of the calibration (month of July). The Manning coefficient decreased for all the reaches by 0.008 s/m1 /3. These figures show good agreement between the calculated and the observed water level at the S2 station and near the dam. In order to confirm the results of the calibration test, we proceeded with a validation test of the model for the period from 06/04/1997 to 06/30/1997. The results are also satisfactory (Figure 6 and 7, month of June).Figure 8 shows the evolution of the water level on 12/06/1997. The water level profile remains parallel to the bed profile for the zones situated very far from the dam (the downstream end). From the 45th kilometre (between stations S7 and S8, see Figure 1), we begin to detect the effect of the dam, characterised by an increase in the water level (and therefore an increase in depth). Figure 9 show the evolution of stream velocity from the upstream to downstream regions on 12/06/1977. Great variations in velocity can be seen due to the changes in river geometry. Also, these variations tend to decrease downstream, reflecting the effect of the dam.Figure 10 represents the evolution of the water reserve available for the whole reach during the months of June and July. It shows a series of decreases in this variable due to the pumping of water. The reserve reaches very low levels (15 Mm3) compared to its maximal capacity, which is 37 Mm3. Also, there is an interrelationship between the evolution of the reserve, and pumped water and the flow differences between upstream and downstream. The reserve increases when the upstream-downstream flow difference is greater than the pumped flow. Inversely, when the pumped water is greater, the water reserve decreases.Finally, in this study we proposed a mathematical model that can provide the stages at all locations of the studied reach, specifically at the pumping stations. Water reserve availability can also be provided at any moment, allowing rapid interventions when this variable begins to decrease dramatically. However, more measured water levels at different stations could improve the present results. Also, other considerations must be included such as hydroelectric energy production in dams upstream and river characteristics. Thus, a multipurpose model of the river must be used. More hydraulic data can improve the accuracy of the present model

Simultaneous estimation of hydro-dipersive parameters using a new modified levenberg-marquardt algorithm

Determination of soil hydrodynamic parameters at field scale is of great importance for modeling soil water dynamics and for agricultural water management. The direct estimation of those parameters is time-consuming and afflicted with serious uncertainties. Inverse modeling is known to get efficient technique for solving non-linear problems in hydrology. Levenberg–Marquardt (LM) algorithm is a gradient-based method, which has been widely used for solving inverse soil water flow problems. In the LM algorithm, sensitivity coefficients are mainly evaluated by numerical differentiation methods. However, sensitivity coefficients are difficult to be precisely calculated by numerical differentiation methods, if transient states and non-linearities are involved. In this paper, a new approach is proposed for sensitivity analysis using the complex variabledifferentiation method (CVDM) to estimate simultaneously the hydraulic and dispersive properties of unsaturated soil from in-situ experiments. In this approach, the sensitivity coefficients can be determined in a more accurate way than the traditional finite difference method. The results show that the new inverse analysis method in the present work has high accuracy, validity, uniqueness and higher inversion efficiency, compared with the previous least-squares method. The simulated and measured water contents and tracer concentration were generally close. Overall, it was concluded that the CVDM is a promising method to estimate hydro-dispersive parameters in the unsaturated zone

Analytical and numerical study of the salinity intrusion in the Sebou river estuary (Morocco) – effect of the “Super Blood Moon” (total lunar eclipse) of 2015

The longitudinal variation of salinity and the maximum salinity intrusion length in an alluvial estuary are important environmental concerns for policy makers and managers since they influence water quality, water utilization and agricultural development in estuarine environments and the potential use of water resources in general. The supermoon total lunar eclipse is a rare event. According to NASA, they have only occurred 5 times in the 1900s – in 1910, 1928, 1946, 1964 and 1982. After the 28 September 2015 total lunar eclipse, a Super Blood Moon eclipse will not recur before 8 October 2033. In this paper, for the first time, the impact of the combination of a supermoon and a total lunar eclipse on the salinity intrusion along an estuary is studied. The 28 September 2015 supermoon total lunar eclipse is the focus of this study and the Sebou river estuary (Morocco) is used as an application area. The Sebou estuary is an area with high agricultural potential, is becoming one of the most important industrial zones in Morocco and it is experiencing a salt intrusion problem. Hydrodynamic equations for tidal wave propagation coupled with the Savenije theory and a numerical salinity transport model (HEC-RAS software "Hydrologic Engineering Center River Analysis System") are applied to study the impact of the supermoon total lunar eclipse on the salinity intrusion. Intensive salinity measurements during this extreme event were recorded along the Sebou estuary. Measurements showed a modification of the shape of axial salinity profiles and a notable water elevation rise, compared with normal situations. The two optimization parameters (Van der Burgh's and dispersion coefficients) of the analytical model are estimated based on the Levenberg–Marquardt's algorithm (i.e., solving nonlinear least-squares problems). The salinity transport model was calibrated and validated using field data. The results show that the two models described very well the salt intrusion during the supermoon total lunar eclipse day. A good fit between computed salinity and measurements is obtained, as verified by statistical performance tests. These two models can give a rapid assessment of salinity distribution and consequently help to ensure the safety of the water supply, even during such infrequent astronomical phenomenon

Karst groundwater vulnerability mapping to the pollution: Case of Dir springs located between EL KSIBA and Ouaoumana (High Atlas, Morocco)

The study area is located in the north of the province of Beni Mellal, it covers the Piedmont of the high Atlas between El Ksiba and Ouaoumana. It is characterized by a poorly developed hydrographic network and the presence of very important karstic forms. These forms condition the rapid infiltration to the karstic springs are the subject of this study. In this work we presented a method of mapping the vulnerability to pollution of Karstic springs located between El Ksiba and Ouaoumana. To do this, we have introduced a vulnerability index called F which takes into account four parameters (EPIK): Development of the Epikarst, importance of the protective cover, infiltration conditions and development of the Karst network. The overlay of the thematic maps of these parameters through a GIS software (ArcGIS) gave us a map of the vulnerability to contamination on the whole hydrogeological basin of the springs

Investigational methods for the modeling of infiltration process in the soil and the estimating the soil hydrodynamic parameters

Unsaturated zone in the soil generally plays an important role in the transfer of water and pollutants in the underground environment. In this context, the determination of the hydrodynamic parameters constitutes an essential step for any study of transfers of water and solutes in the unsaturated zone. The purpose of this article is the estimation the soil hydrodynamic parameters by the direct method and the inverse method, from the infiltration data by using the disc infiltrometer in the soil the basin Loukkos located in northern Morocco. Our results the numerical modeling reproduced correctly the experimental measurements. These results show that the inverse method remains a robust and accurate method for determining the soil hydrodynamic parameters compared to other conventional methods

Karst groundwater vulnerability mapping to the pollution: Case of Dir springs located between EL KSIBA and Ouaoumana (High Atlas, Morocco)

The study area is located in the north of the province of Beni Mellal, it covers the Piedmont of the high Atlas between El Ksiba and Ouaoumana. It is characterized by a poorly developed hydrographic network and the presence of very important karstic forms. These forms condition the rapid infiltration to the karstic springs are the subject of this study. In this work we presented a method of mapping the vulnerability to pollution of Karstic springs located between El Ksiba and Ouaoumana. To do this, we have introduced a vulnerability index called F which takes into account four parameters (EPIK): Development of the Epikarst, importance of the protective cover, infiltration conditions and development of the Karst network. The overlay of the thematic maps of these parameters through a GIS software (ArcGIS) gave us a map of the vulnerability to contamination on the whole hydrogeological basin of the springs