Belmatrik, S.

Chagdali, M.

El Kadi Abderrezzak, K.

Loudyi, D.

English

Hydraulic Engineering Repository

Article, Published VersionLoudyi, D.; Chagdali, M.; Belmatrik, S.; El Kadi Abderrezzak, K.Reservoir silting in MoroccoHydrolinkVerfügbar unter/Available at: https://hdl.handle.net/20.500.11970/109421Vorgeschlagene Zitierweise/Suggested citation:Loudyi, D.; Chagdali, M.; Belmatrik, S.; El Kadi Abderrezzak, K. (2018): Reservoir silting inMorocco. In: Hydrolink 2018/3. Madrid: International Association for Hydro-EnvironmentEngineering and Research (IAHR). S. 92-94. https://iahr.oss-accelerate.aliyuncs.com/library/HydroLink/HydroLink2018_03_Reservoir_Sedimentation.pdf.Standardnutzungsbedingungen/Terms of Use:Die Dokumente in HENRY stehen unter der Creative Commons Lizenz CC BY 4.0, sofern keine abweichendenNutzungsbedingungen getroffen wurden. Damit ist sowohl die kommerzielle Nutzung als auch das Teilen, dieWeiterbearbeitung und Speicherung erlaubt. Das Verwenden und das Bearbeiten stehen unter der Bedingung derNamensnennung. Im Einzelfall kann eine restriktivere Lizenz gelten; dann gelten abweichend von den obigenNutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte.Documents in HENRY are made available under the Creative Commons License CC BY 4.0, if no other license isapplicable. Under CC BY 4.0 commercial use and sharing, remixing, transforming, and building upon the materialof the work is permitted. In some cases a different, more restrictive license may apply; if applicable the terms ofthe restrictive license will be binding.92 hydrolink number 3/2018The Kingdom of Morocco is an arid country thatrelies heavily on water supplied by reservoirs(Figure 1). Long periods of drought, spreadingover several years, are common. In the 1960’sMorocco launched a vast dam building programto help solve the issues of water scarcity andrainfall variability which affected thousands offarmers and the agricultural based economy.Morocco now counts 140 large dams (meetingthe ICOLD definition) with an overall capacity ofabout 17,600 million cubic meters (Mm3), 13 hydraulic water transfer structures and morethan 100 small dams and hill reservoirs. Themain objective of reservoirs is to secureprimarily domestic water supply for large urbancenters, to store water for irrigation, to mitigateflood risk and finally to generate hydropower.Demand for domestic and industrial watersupply is increasing at a rate of 8% per year.Reservoirs supply 66% (as of 2016) of the waterdemand (80% in 2020)[1]. About 1,500,000 haare irrigated. The annual production ofhydropower is 2,527 GWh (10% of the totalproduction), out of a total potential capacityestimated at 5,100 GWh.Silting of Moroccan dams: factsThe latest monthly monitoring surveys forMoroccan reservoirs showed that, at the end ofJune 2018, the storage rate of the 55 largestreservoirs was 66% against 50% at the sameperiod in 2017 and 45% in 2016. These fluctua-tions are due to the variability of rainfall andtemperature, but also to the accumulatedsediment in the reservoirs. The siltingphenomenon has caused a loss of nearly 10%of the total storage capacity of reservoirs, whichrepresents a volume of 1,740 Mm3. Reservoirsedimentation translates into a storage capacityloss of nearly 75 Mm³ per year according to theMoroccan State Department in charge of water,which is equivalent to losing the average storagespace of one reservoir every year. The totalstorage capacity loss may reach 150 Mm³/yearin the near future if any mitigating measures arenot undertaken, depriving about 15,000 ha ofagricultural land of irrigation[2]. The rate of siltation varies between 0.03 Mm3/year in Dkhila reservoir to 14.3 Mm3/year in AlWahda reservoir (Table 1). It was noted that formost of Moroccan dams (older than 30 years)the dead storage has been already filled or willbe in very near future[3]. The accelerated pace ofwater development requires a thoroughknowledge of erosion, sediment transport andsiltation of dam and hill reservoirs. These naturalphenomena, which depend on climatic condi-tions, landform and vegetation cover, are accel-erated and intensified by human activities suchas land use, cultural practices, grazing anddeforestation. Most Moroccan basins are characterized by astrong erosion rate (» 2,000 t/km²/year, a peakvalue of 5,900 t/km²/year in the Nekor basin)[4,5].Among the nine river basins of Morocco (Figures2 to 5), the annual specific degradation indicesevaluated at the level of different watershedsshow that the country has seven geomorpho-logical regions whose erodibility decreases fromnorth to south. Dams built in the Moulouya basin(North of Morocco) are in a critical situationbecause of the siltation losing on average 39%of reservoirs’ storage capacity. They are followedby reservoirs in Tensift basin, Souss-Massa Draabasin and Loukkos basin. RESERVOIRS SILTING IN MOROCCOBY D. LOUDYI, M. CHAGDALI, S. BELMATRIK AND K. EL KADI ABDERREZZAKDam                          Basin                      Service year     Initial              Total                    Silting rate       Lost storage                                                                                         capacity           sedimentation      (Mm3/year)      capacity (%)                                                                                         (Mm3)              volume (Mm3)Oued El Malleh           Bouregrag-              1931                 18                    14.9                      0.2                    83%                                 Chaouia                   Sidi Driss                   Oum Er Rbia            1984                 7                      5.5                        0.35                  78%Al Khattabi                 Loukkos                  1981                 43.3                 31.7                      1.1                    73%Mohamed V               Moulouya                1967                 725.8               486.2                    11.5                  67%Dkhila                        Souss Massa          1986                 0.7                   0.46                      0.03                  67%                                 Draa                        Allal Al Fassi              Sebou                     1990                 81.5                 48.5                      2.4                    59%Nakhla                       Loukkos                  1961                 9                      4.8                        0.1                    53%Lalla Takerkoust         Tensift                     1979                 78.7                 26.1                      0.8                    33%Ibn Battouta               Loukkos                  1977                 43.6                 14.5                      0.4                    33%El Kansera                 Sebou                     1966                 294.4               77.9                      1.8                    26%Aoulouz                     Souss Massa          1991                 110                  21.0                      1.1                    19%                                 Draa                        Hassan Eddakhil        Ziz                           1971                 380                  69.7                      1.7                    18%Bin El Ouidane           Oum Er Rbia            1953                 1,484               292.0                    5.0                    18%Sidi Mohamed           Bouregrag-             1974                 508.6              76.9                      2.2                   15% Ben Abdellah             Chaouia                   (2007)               (974.8)            (55.3)                  (9.5)                 (6%)(after elevation)          Youssef Ben              Souss Massa          1972                 320                  21.1                      0.6                    7%Tachfine                     DraaAl Wahda                   Sebou                     1996                 3,730               208.2                    14.3                  6%Al Massira                 Oum Er Rbia            1979                 2,785               87.1                      2.3                    3%Table 1 Silting rates in a selection of Moroccan reservoirs[3]Figure 1. Map of Morocco and general information[1]RESERVOIRSEDIMENTATION93hydrolink number 3/2018western part of Casablanca, the industrial huband economical capital of Morocco. Dkhila(Souss Massa basin) and Sidi Driss (Oum ErRbia basin) dams are also in the same situation.In the absence of immediate interventions, AlKhattabi (Loukkos basin), Allal Al Fassi (Seboubasin) and Mohamed V (Moulouya basin) reser-voirs would be completely silted up by 2024,2027 and 2032, respectively.Solutions and mitigating measuresEighty-eight (88) large dams (64% of the totalnumber of dams) are now more than 20 yearsold[6]. Given that the economic life cycle of adam in Morocco is 50 years, fourteen majorhydraulic structures have exceeded theirlifetime. The situation is critical, which explainsthe launch of new dam projects to replace “endof life” ones. The Moroccan State Department incharge of water aims to build 59 dams by 2030.Since 2015, the construction of 35 dams ofThe situation of reservoirs in the North and Rif’smountains is very serious due to the high level oferosion and the hilly slopes. One such case isthe Oued El Malleh dam, constructed in 1931and now almost completely silted up. In theOum Er Rbia basin, Sidi Said Maâchou dam, theoldest modern dam in Morocco (completed in1929) is in a similar situation. This dam has lostits storage function to become exclusively acompensation dam for the turbines of Daouratplant which supplies drinking water to theIAHRFigure 2. Map showing the nine river basins andmain rivers in Morocco. Red circles: cities wherebasin agencies are located. Figure 7. National management program for the afforestation ofprimary twenty-two watersheds of large dams[11]Figure 6. Mohamed V dam (service year: 1967, height: 64 m, initial reservoir capacity: 728.5 Mm3,sedimentation rate: 11.5 M3/year) and, downstream, the Mechra Homadi dam (service year: 1955,height: 57 m, initial reservoir capacity: 42 Mm3, sedimentation rate: 1 Mm3/year), Moulouya River,Moulouya basin (adapted from Google earth)Figure 3. Dkhila dam (service year: 1986, height: 37 m, initial reservoir capacity: 0.7 Mm3,sedimentation rate: 0.03 Mm3/per year), Issen River, Souss Massa Draa basin (Google Earth)Figure 4. Al Massira dam (service year: 1979, height: 82 m, initial reservoir capacity: 2,785 Mm3, sedimentationrate: 2.3 Mm3/year), Oum Rbia River, Oum Rbia basinFigure 5. Bin El Ouidane dam (service year: 1953, height:133 m, initial reservoir capacity: 1,484 Mm3, sedimentationrate: 5 Mm3/year), Oum Er Rbia River, Oum Er Rbia basin RESERVOIRSEDIMENTATIONdifferent sizes, with an overall storage capacityof 3,064 Mm3, has been launched. These newdams will help ensure continued water supplyfor domestic and industrial uses in remote areaswhich suffer from water shortage, increase theirrigated area (the Green Morocco Plan has agoal of reaching 70% of irrigated arable lands by2030), mitigate the flood risk, and producehydropower energy.With the support of World Bank, a RESCONteam (see the paper by Efthymiou et al. in thisissue describing the RESCON tool) worked in2001 with Moroccan engineers and managers todetermine the needs for mitigation measures atseveral reservoirs. The RESCON approach wasapplied to ten existing reservoirs with theobjective of identifying optimal sedimentmanagement strategies that are both technicallyand economically feasible[7]. The selected damsranged from relatively small, with a reservoircapacity of 5.6 Mm3, to large, with a reservoircapacity of 1,500 Mm3. An interesting outcomeof this work was the sensitivity of the RESCONtool results to the assumed unit cost of dredging(cost provided by Moroccan engineers vs costcalculated by the RESCON program). Forinstance, when the default dredging costs calcu-lated by the RESCON program (which werehigher than US$ 4/m3), the optimal sustainablemanagement strategy shifted from dredging toflushing for three of the reservoirs. More detailsare given by Palmieri et al.[7].At present, solutions are being put in place,aiming to reduce the negative impact ofsedimentation on reservoir storage capacity.Apart from the construction of new dams, theDepartment of Water, in charge of the super-vision of dams, uses either technical or naturalmethods to mitigate against the silting process.The elevation of hydraulic structures is carriedout when technically feasible. This solution wasput in place for four dams: Lalla Takerkoust, ElKansera, Oued El Malleh and Sidi MohamedBen Abdellah. In addition to the sizing of deadstorage, flushing operations are carried outduring flood periods to remove part of thesediment through the bottom outlets. However,flushing operations remain limited because ofthe water scarcity and growing needs for watersupply and irrigation. Density current ventingunder low flow discharges is applied to only fewdams which are equipped with bottom outlets(e.g. Ibn Battouta, Youssef Ben Tachfine,Aoulouz, Hassan Eddakhil)[8]. Building ofupstream check structures (weirs and smalldams) has been initiated since 1980 to help totrap sediments upstream of large dam reservoirs. Sediment dredging is anothereffective solution for silting control. However, itscost remains very high and water andagroforestry operators do not reuse theextracted sediments. The removal of 1m3 ofsediment now costs 50 Moroccan Dirham(MAD), approximately US$ 5. This solution wasimplemented at the Sid Driss dam and theMechra Homadi dam (Figure 6). The latter wasconstructed in 1955 with an initial storagecapacity of 42 Mm3 that has been drasticallyreduced over time (silting rate of 1 Mm3/year).The dam reservoir was in a critical situation bythe end of 1990 (storage capacity of about 10Mm3), so that dredging operations wereconducted in 1994 (removing 3 Mm3) andbetween 2003 and 2009 (removing 5.4 Mm3),costing in total 120 million MAD (US$ 12million)[7]. The dam was also equipped withbottom outlets.The Department of Water is in favor ofafforestation, which remains an ecologicalmethod that both protects soils against erosionand preserves the efficiency of hydraulic infra-structures. A National Watershed ManagementPlan (PNABV)[9] was adopted in 1996 as astrategic framework setting priorities for interven-tions and proposing approaches as well asfinancial and institutional mechanisms for imple-menting erosion control for twenty-two high-priority watersheds. Morocco aims to reforestcatchments covering 1,500,000 ha at a rate of75,000 ha/year. Since 1996, 650,000 ha havebeen reforested in eighteen watersheds (Figure7). Morocco has also increased the rate ofbathymetric survey of reservoirs by a DifferentialGlobal Positioning System (DGPS) system.Twenty reservoirs are surveyed per yearcompared with only eight reservoirs per year inthe period from 1991 to 1998. Other methods tomeasure sedimentation include sedimentmonitoring at gaging stations (bed load andsuspended load), aerial surveys, radioisotopemethods and the use of degradation predictionrelationships for upstream basins[10]. Thesemeasures are undertaken by different depart-ments according to their legal jurisdiction andlocation. The main stakeholders involved insilting control of reservoirs are: the StateSecretary in charge of Water, the HighCommissioner for Waters, Forests andCombating Desertification, the Hydraulic BasinAgencies and the National Office for Electricityand Drinking Water ONEE - Water branch. nReferences[1] El Ghomari, K. (2017). La politique et les bienfaits des barragesau Maroc. Colloque national SolMaroc, Marrakech, Maroc. (Infrench).[2] El Mouden, A. (2017). Quantification de l’érosion hydrique vial’envasement des barrages - Autre approche pour cartographierl’érosion hydrique. Presses Académiques Francophones, 112 p.(in French).[3] Marzouki, T. Z., Ziyad, A., Abdani, M. (2018). State of Damssiltation in Morocco. Transactions of the 26th congress on LargeDams, Vienna, Austria.[4] Sadaoui, M., Ludwig, W., Bourrin, F., Le Bissonnais, Y., Romero, E.(2018). Anthropogenic reservoirs of various sizes trap most of theSediment in the Mediterranean Maghreb Basin. Water, 10, 927,doi: 10.3390/w10070927k.[5] Lahlou, A. (1988). Etude actualisée de l’envasement des barragesau Maroc. Revue des Sciences de l’Eau, 6, 337–356. (In french).[6] Amahdouk, A. (2017). Dam Safety Management in Morocco.World Hydropower Congress, Addis Ababa, Ethiopia.[7] Palmieri, A., Shah, F., Annandale, G. W., Dinar, A. (2003),Reservoir conservation: The RESCON approach. Vol. I,Washington DC, The World Bank. [8] Oualkacha, L. (2010). L’envasement des retenues de barrages auMaroc. Secrétariat d’Etat chargé d’eau. (In french).[9] Plan National d’Aménagement des Bassins Versants (PNABV)http://www.eauxetforets.gov.ma/fr/text.aspx?id=1070&uid=83.[10] Clark, M.L. (2015). Using GIS and the RUSLE model to create anIndex of Potential Soil Erosion at the large basin scale anddiscussing the implications for water planning and landmanagement in Morocco. Master of Global Policy Studies,University of Texas, Austin. [11] Haut Commissaire aux Eaux et Forêts et à la Lutte Contre laDésertification (HCEFLCD). (2008):http://www.eauxetforets.gov.ma.94 hydrolink number 3/2018Dalila Loudyi is Professor inhydrology and hydraulics at theDepartment of Water and Environ-mental Engineering at the Facultyof Sciences and Technics ofHassan II University of Casablanca.She is leading a research teamworking on water resourcesmanagement, numerical modelling, urban water andclimate change. She was selected by the MoroccanMinistry of Higher Education as a National Contact Pointin environment, in 2010, to promote the use of theSeventh European Framework Program (FP7) forresearch and development at a national level. She is amember of the Leadership Team of IAHR MENACommittee.Mohamed Chagdali is Professorin physics and fluid dynamics atBen Msik Faculty of Sciences ofHassan II University, Casablanca,Morocco. His research activitiescover fluid dynamics and sedimenttransport. Salah Bel Matrik is a ChiefEngineer and General Secretary ofthe river basin Agency ofBouregreg and Chaouia, Morocco.He is in charge of water resourcesplanning and management. He hasover thirty years of experience inlegal, administrative and technicalaspects of the public hydraulic domain.Kamal El kadi Abderrezzak isExpert at the National Laboratoryfor Hydraulics and Environment ofthe Research and Development(R&D) division of Electricité deFrance (EDF). His sphere ofresearch includes floodpropagation, dike breaching andsediment transport in open channels, with focus onprocesses and numerical modeling. He also teachesfluid mechanics, open channel flows and sedimenttransport at Ecole Polytechnique, Polytech Nice Sophia,and ESTP. He is member of the IAHR Europe Regional Division.RESERVOIRSEDIMENTATION

Reservoir silting in Morocco

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Reservoir silting in Morocco

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