Impact of Anthropogenic Facilities on the Morphodynamic Evolution of an Estuarine System: the Case of Oum Er-Rbia Estuary (Azemmour, Morocco)

Journal of Marine Science and Engineering

Article Impact of Anthropogenic Facilities on the Morphodynamic Evolution of an Estuarine System: The Case of Oum Er-Rbia Estuary (Azemmour, Morocco)

Mustapha El Jakani 1,2,3,* , Said Ettazarini 1,4 , Hassan Rhinane 5, Mohammed Raji 2,3, Mohamed Radid 3 and Mohamed Talbi 3 1 Regional Center of the Trades of Education and Training (CRMEF) of Casablanca-Settat, Casablanca PC 20340, Morocco 2 Laboratory of Applied Geology, Geomatic and Environment, Faculty of Sciences Ben M’Sik, Hassan II University, Casablanca PC 20670, Morocco 3 Research Observatory in Didactics and University Pedagogy, Faculty of Sciences Ben M’Sik, Hassan II University, Casablanca PC 20670, Morocco 4 Laboratory of Natural Resources and Environment, Multidisciplinary Faculty of Taza, Sidi Mohamed Ben Abdellah University, Taza PC 35000, Morocco 5 Laboratory of Geosciences, Faculty of Sciences Ain Chock, Hassan II University, Casablanca PC 20100, Morocco * Correspondence: [email protected] or [email protected]

Received: 2 June 2019; Accepted: 24 July 2019; Published: 29 July 2019

Abstract: The Oum Er-Rbia estuary is located on the Atlantic littoral of Morocco. It undergoes severe clogging due to the sand deposition in its outlet. The current study examined the indicators of the morphodynamic evolution in the littoral system including the Oum Er-Rbia estuary and the neighboring beaches over 1970–2017. The methodology adopted was based on the analysis and the interpretation of aerial photographs and Google Earth images under a GIS environment and field work. The morphodynamic evolution was discussed by taking into account the evolution of hydraulic facilities installed in the watershed area, especially the construction of dams, as well as the dredging works in the Oum Er-Rbia estuary. The results highlight the morphologic evolution estimated in terms of surface units observed in the estuary and the neighboring beaches. The evolution of the littoral system was mainly influenced by the closest dam location and by the dredging works, in addition to the regulation of the river flow by the installation of hydraulic facilities upstream.

Keywords: littoral degradation; hydrologic engineering; dredging impact; estuarine system; sustainability; remote sensing

1. Introduction The design of any sustainable development strategy should necessarily incorporate the concepts of environmental preservation and the rational management of natural resources. However, this expectation is not always easy to achieve because it is often hampered by compelling socio-economic requirements. According to many researches aiming at the digital modelization of estuaries and the prediction of their behavior, it has been demonstrated that their functioning is complex in most estuaries of the world due to the action of many factors controlling the equilibrium in these environmental systems [1–5]. Indeed, the factors controlling the morphodynamics of estuaries and deltas are variable, including natural factors such as sea level change, swell and tide actions, storm event, ﬂuvial hydrology, etc., and

J. Mar. Sci. Eng. 2019, 7, 248; doi:10.3390/jmse7080248 www.mdpi.com/journal/jmse J. Mar. Sci. Eng. 2019, 7, 248 2 of 19 anthropogenic factors such as hydraulic facilities, engineering works of protection and rehabilitation, dredging, etc. [6–10]. The bathymetry and the morphology of an intertidal plain and transversal section of a shallow bottom estuary cause a tide asymmetry that affects the flow duration, compared to the ebb time, and the celerity of the tide current [1,2,10–12]. In coastal environments, the waves generate coastal currents that interact with incident waves and lead to the sediment transportation and the process is favored when the angle between the waves and the coastal line is significant [13–16]. As a response to coastal hydrodynamics, the alternation of sedimentation and erosion processes in the estuary can generate net sedimentary balances through a tide cycle [17,18]. The installation of hydraulic reservoirs in upstream areas affects the hydrodynamic equilibrium and sedimentary balances downstream, due to the flood water regulation and the decrease of the solid sediments supply [19–25]. Blott) [26] concluded that the morphodynamic evolution of Mersey estuary in England through a period of 150 years was mainly controlled by engineering and rehabilitation works, such as the construction of training walls and dredging. Besides, the importance of other factors, notably sea level change, tide amplitude, wave current, and supply of fresh water was relatively reduced [26]. The perturbation of estuarine hydrodynamics is permanently regulated by morphologic transformations through sedimentation and erosion processes mobilized to re-establish the hydrodynamic equilibrium [21,22,27]. The morphodynamic change concerns the estuary outlet, the main channel, and the intertidal plains [19,20,28]. In addition, the morphodynamic change in the estuary affects the morphology of neighboring littoral areas and, consequently, causes the shoreline fluctuation [3,29–31]. Numerous works have analyzed the morphologic evolution of coastal systems through multi-temporal photographs [30,32–40]. This study is an attempt to provide elements to aid in understanding the Oum Er-Rbia coastal system’s behavior by analyzing the estuarine morphodynamic evolution and comparing it with the evolution of the hydraulic facilities installed in the catchment area, as well as the shoreline changes observed in the neighboring marine beaches.

2. Materials and Methods

2.1. Study Area The study area is situated in the northern part of Morocco, where a Mediterranean climate is dominant and is characterized by a significant contrast between a brief pluvial period and an elongated dry period [41–47]. Indeed, drought periods affected the hydrodynamics of the surface waters [48] and a dam construction program has been running since the 1960s in Morocco to combat the effects of drought by the management of surface water mobilization in all watersheds throughout the country, especially in the Oum Er-Rbia catchment area. The decrease in rainfall observed during the 1980s was accompanied by a sharp decrease in the annual availability of surface water at the Oum Er-Rbia catchment area, with a rate of 30% to 40%, and an interannual average volume dropping from 3930 Mm3 between 1941 and 1981 to 2345 Mm3 between 1981 and 2009 [49]. The hydrological infrastructures installed on the basin make it possible to mobilize up to 93% of available resources [50–53]. The principal dams constructed downstream of Oum Er-Rbia are the Massira, put into service in 1980 with a capacity of 2760 Mm3, in addition to compensation dams, notably: Imfout in 1944 with 18.2 Mm3, Daourat in 1950 with 9.5 Mm3, Sidi Said Maachou in 1929 with 5.5 Mm3 and Sidi Daoui in 1985 with 5 Mm3. The location of these facilities is shown in Figure1c. The studied coastal system includes the bay beaches of El Haouzia and Lalla Aicha El Bahria as well as the Oum Er-Rbia estuary. It is located near the Azemmour city, between the longitudes 8.16◦ W and 8.22◦ W and the latitudes 33.15◦ N and 33.21◦ N (Figure1). It constitutes the downstream zone of the Oum Er-Rbia watershed area that is 34,000 km2. The main watercourse is 550 km long and constitutes the longer stream system and the most regular in Morocco. The channel in the study area J. Mar. Sci. Eng. 2019, 7, x FOR PEER REVIEW 3 of 20 J. Mar. Sci. Eng. 2019, 7, 248 3 of 19 and constitutes the longer stream system and the most regular in Morocco. The channel in the study area represents less than 3% of the main watercourse, but its situation downstream makes its importantrepresents as less a thanzone 3%sensible of the to main hydrodynamic watercourse, changes but its situation in both downstreamupstream and makes littoral its areas. important The hydraulicas a zone infrastructure sensible to hydrodynamic is composed of changes fifteen indam both reservoirs, upstream installed and littoral on the areas. Oum TheEr-Rbia hydraulic main streaminfrastructure and its istributaries composed [51,54,55], of fifteen damwhere reservoirs, the closest installed construction on the Oumis the Er-Rbia Sidi Daoui main dam stream at and15 km its upstream.tributaries [51,54,55], where the closest construction is the Sidi Daoui dam at 15 km upstream.

FigureFigure 1. ((aa)) Location Location map map of of the the Oum Oum Er-Rbia Er-Rbia watershed; watershed; ( (bb)) investigation investigation area area showing showing the the Oum Oum Er-RbiaEr-Rbia estuary estuary and and the the neighboring neighboring beaches beaches as as well well as as the the Sidi Sidi Daoui dam dam location, and and ( (cc)) the the OumOum Er-Rbia Er-Rbia watershed, watershed, drainage drainage network, network, and and wa waterter bodies bodies including including the the Massira Massira dam dam (MD) (MD) and and compensationcompensation dams dams situated situated downstream: downstream: Sidi Sidi Daoui Daoui (SDD), (SDD), Sidi Sidi Said Said Maachou Maachou (SSMD), (SSMD), Daourat (DD),(DD), and and Imfout Imfout (IMD). (IMD).

FigureThe geomorphology 2 shows the location in the studyof Sidi area Daoui is dominated dam installed by the 15 eoliankm upstream dune ridges of the edified estuary by outlet. the NW and ENE winds characterizing the Moroccan littoral zone [56]. Pebble deposits are well developed on both El Haouzia and Lalla Aicha El Bahria beaches and are of a sedimentary and eruptive nature. Their sources are the outcrops crossed by the Oum Er-Rbia river. The sedimentary bodies of the estuary and neighboring beaches are part of recent formations of Quaternary age. Upstream, the channel of the estuary is meandering and is approximately 200 m wide. The shores are usually steep and tree-covered cliffs. Downstream, the channel is straighter and the banks are plain, bare or planted with shrubs. The estuarine hydrodynamics are mainly controlled by the river flow and tidal currents. The highest monthly mean flow of the Oum Er-Rbia River is generally observed in March and the lowest in August with 40 m3/s. According to the “Conseil Supérieur de l’Eau” (CSE), the absolute minimum was recorded at the Imfout check station in August 1984 and was about 14 m3/s [57]. In the Oum Er-Rbia

J. Mar. Sci. Eng. 2019, 7, 248 4 of 19 estuary, most of the water flow corresponds to the release of water from dams situated upstream [58]. The tide is semi-diurnal on the Atlantic Moroccan side and its amplitude at the estuary alternates between approximately 1.5 m and 4 m, according to the Casablanca Port maritime services. The swell dynamics have a WNW to NW dominant direction during 78% of the time and its effect is generally important along the Moroccan Atlantic coast in autumn and winter [59]. The most efficient swells have a period T 11 s which represents 59% of the time [59,60]. Figure2 shows the location of Sidi ≥ J.Daoui Mar. Sci. dam Eng. installed 2019, 7, x FOR 15 km PEER upstream REVIEW of the estuary outlet. 4 of 20

Figure 2. Overview of thethe SidiSidi DaouiDaoui damdam in in the the Oum Oum Er-Rbia Er-Rbia estuary estuary showing showing ﬂow flow over over the the wall wall of ofthe the dam. dam.

2.2. DataThe Usedgeomorphology in the study area is dominated by the eolian dune ridges edified by the NW Thisand studyENE waswinds based characterizing on the analysis the ofMoroccan two types littoral of data: zone (1) the[56]. hydrologic Pebble deposits data provided are well by developedcollected from on both the Moroccan El Haouzia Direction and Lalla of HydraulicsAicha El Bahria (DH), beaches including and historical are of a data sedimentary for the period and eruptivebetween nature. 1926 and Their 2017. sources The information are the outc concernsrops crossed the monthly by the Oum mean Er-Rbia flow of river. the Oum Er-Rbia River collectedThe sedimentary from the Sidi bodies Said Maachou of the estuary station and for theneighb periodsoring of beaches 1926–1928 are andpart 1930–1939, of recent formations the Imfout ofobservation Quaternary station age. Upstream, that provided the channel the data of for the the estuary period is of meandering 1941–1970, and and is the approximately Massira station 200 for m wide.the period The shores of 1979–2017, are usually in addition steep and to data tree-covere on the capacityd cliffs. Downstream, of dam reservoirs the channel installed is in straighter the river andcatchment the banks area are [50 plain,,51,54 bare]. The or planted dataset with was completedshrubs. with information provided by the “Office NationalThe deestuarine l’Eau Potable” hydrodynamics (ONEP) [are52, 55mainly], the CSEcontroll [57,61ed], by as wellthe river as data flow from and studies tidal currents. by Loup [The41]. highestHydrologic monthly data concern mean flow equally of informationthe Oum Er-Rbia on the swellRiver dynamics is generally and itsobserved impact onin theMarch Haouzia and baythe lowestfrom the in works August of Chaibiwith 40 [36 m,593/s.,60 According]. (2) Cartographic to the “Conseil data were Supéri extractedeur de from l’Eau” two (CSE), aerial photographsthe absolute minimumcovering the was estuary recorded area at for the each Imfout one check of dates station 1970 in and August 1988. 1984 The photographsand was about were 14 producedm3/s [57]. In at 1the/40000 Oum scale Er-Rbia and estuary, with a 10.5 most km of the11.5 water km sceneflow corresponds size. Two other to the photographs release of water corresponding from dams to × 1982situated were upstream used. They [58]. areThe attide the is1 semi-diurnal/7500 scale and on athe 1.75 Atlantic km Moroccan1.75 km scene side and size, its but amplitude they cover at × the estuaryestuary outletalternates and abetween part of Elapproximately Haouzia beach 1.5 only. m and The 4 aerialm, according photographs to the are Casablanca available at Port the “Agencemaritime Nationale services. The de la swell Conservation dynamics Fonci haveè re,a WN du CadastreW to NW et dominant de la Cartographie” direction during (ANCFCC, 78% Rabat,of the timeMorocco). and its Information effect is generally was equally important taken along out from the GoogleMoroccan Earth Atlantic imagery, coast through in autumn images and provided winter [59].by DigitalGlobe, The most efficient CNES swells/Airbus, have and a Landsatperiod T/ Copernicus.≥ 11 s which Sevenrepresents images 59% were of the used time for [59,60]. the years of 2004, 2009, 2011, 2012, 2014, 2016, and 2017. The topographic map of Azemmour at the 1/50000 scale was2.2. Data used Used as a reference for rectifying and geo-referencing the used images. This study was based on the analysis of two types of data: (1) the hydrologic data provided by 2.3. Methods collected from the Moroccan Direction of Hydraulics (DH), including historical data for the period betweenThe 1926 methodology and 2017. adopted The information in this study concerns is summarized the monthly in the mean flowchart flow of of the Figure Oum3. TheEr-Rbia statistical River processingcollected from of hydrological the Sidi Said data Maachou was performed station for using the periods Excel software. of 1926–1928 It was and used 1930–1939, to estimate the the Imfout water observationflow downstream station of that the provided Oum Er-Rbia the data River for and the to period compare of 1941–1970, it with the evolutionand the Massira of the cumulative station for thecapacity period managed, of 1979–2017, the rate in ofaddition evolution to data relative on th toe thecapacity total cumulativeof dam reservoirs capacity, installed and the in di thefference river valuecatchment expressed area in[50,51,54]. percentage The of thedataset entire was capacity. completed The monthly with information volume of water provided expected by the to reach “Office the National de l’Eau Potable” (ONEP) [52,55], the CSE [57,61], as well as data from studies by Loup [41]. Hydrologic data concern equally information on the swell dynamics and its impact on the Haouzia bay from the works of Chaibi [36,59,60]. (2) Cartographic data were extracted from two aerial photographs covering the estuary area for each one of dates 1970 and 1988. The photographs were produced at 1/40000 scale and with a 10.5 km × 11.5 km scene size. Two other photographs corresponding to 1982 were used. They are at the 1/7500 scale and a 1.75 km × 1.75 km scene size, but they cover the estuary outlet and a part of El Haouzia beach only. The aerial photographs are available at the “Agence Nationale de la Conservation Foncière, du Cadastre et de la Cartographie” (ANCFCC, Rabat, Morocco). Information was equally taken out from Google Earth imagery, through images provided by DigitalGlobe, CNES/Airbus, and Landsat/Copernicus. Seven images

J. Mar. Sci. Eng. 2019, 7, x FOR PEER REVIEW 5 of 20

were used for the years of 2004, 2009, 2011, 2012, 2014, 2016, and 2017. The topographic map of Azemmour at the 1/50000 scale was used as a reference for rectifying and geo-referencing the used images.

2.3. Methods The methodology adopted in this study is summarized in the flowchart of Figure 3. The statistical processing of hydrological data was performed using Excel software. It was used to J.estimate Mar. Sci. Eng. the2019 water, 7, 248flow downstream of the Oum Er-Rbia River and to compare it with the evolution5 of 19 of the cumulative capacity managed, the rate of evolution relative to the total cumulative capacity, and the difference value expressed in percentage of the entire capacity. The monthly volume of estuarywater wasexpected estimated to reach by subtracting the estuary the was allocations estimated reserved by subtracting for irrigation the ofallocations the Doukkala reserved perimeter, for andirrigation for industrial of theand Doukkala urban uses perimeter, in the Casablanca-Saﬁ and for industrial coastal and zone, urban from uses the totalin the volume Casablanca-Safi of available watercoastal released zone, from by the the Massira total volume dam. of The available calculation water of released the added by the value Massira in % ofdam. capacity The calculation was based onof thethe volumeadded value of managed in % of capacity reservoirs was in based the Oum on the Er-Rbia volume catchment of managed area, reservoirs relative in to the each Oum period Er- 3 expressedRbia catchment in % of area, a total relative capacity to each of 5301.7 period Mm ex.pressed These variablesin % of a reﬂecttotal capacity the impact of 5301.7 of the Mm construction3. These ofvariables hydraulic reflect facilities the inimpact the catchment of the construction area on the of hydrodynamic hydraulic facilities evolution in the downstream catchment area of the on Oum the Er-Rbiahydrodynamic River. evolution downstream of the Oum Er-Rbia River.

FigureFigure 3. 3.Flowchart Flowchart showing showing thethe methodologymethodology adopted to analyze the morphodynamic morphodynamic evolution evolution of of thethe coastal coastal system system of of Oum Oum Er-Rbia. Er-Rbia.

TheThe mapping mapping ofof thethe morphologicmorphologic evolutionevolution of the coastal system including including the the Oum Oum Er-Rbia Er-Rbia estuaryestuary and and its its neighboring neighboring beachesbeaches waswas basedbased onon the interpretation of of the the aerial aerial photographs photographs and and GoogleGoogle Earth Earth images. images. TheThe preprocessingpreprocessing ofof aerialaerial images was performed under under the the ArcGis ArcGis software software environmentenvironment and and consisted consisted of of geo-referencing geo-referencing and and ortho-rectification ortho-rectification by applyingby applying an image an image to image to methodimage method that uses that common uses common fix points. fix points. The Lambert The Lambert conformal conformal conic conic projection projection “Nord-Maroc” “Nord-Maroc” was usedwas toused display to display the images. the images. The target The target line features line feat wereures extractedwere extracted directly directly from Google from Google Earth imagesEarth throughimages thethrough Google the Earth Google server Earth and server exported and under exported Keyhole under Markup Keyhole language Markup Zipped language (KMZ) Zipped format. The(KMZ) extracted format. lines The were extracted then displayed lines were in then ArcGis displa byyed transforming in ArcGis themby transforming to shape files. them A coordinate to shape systemfiles. A transformation coordinate system was done transformation from WGS84 was to nationaldone from coordinate WGS84 system:to national Lambert coordinate “Nord-Maroc”. system: FletcherLambert et “Nord-Maroc”. al. [62] consider Fletcher that the lowet al water. [62] consider position isthat useful the low to reveal water changes position related is useful to alongshore to reveal changes related to alongshore rather than cross-shore profile adjustment. In addition, low water rather than cross-shore profile adjustment. In addition, low water position allows for the following of position allows for the following of the geomorphic evolution of sand bars within the estuary. the geomorphic evolution of sand bars within the estuary. Indeed, the limits of the river banks and the Indeed, the limits of the river banks and the boundaries of the sand bars along the channel were boundaries of the sand bars along the channel were targeted in the estuary. For the shoreline detection, targeted in the estuary. For the shoreline detection, many researchers consider that what is often many researchers consider that what is often referred to as the upper limit of the tidal level [30,31,33,34]. referred to as the upper limit of the tidal level [30,31,33,34]. This is a wet and dark area that can be This is a wet and dark area that can be followed and mapped less difficultly. The selected images met followed and mapped less difficultly. The selected images met best the objective, when the date and best the objective, when the date and time of the acquisition coincided with the low-tide phase and the time of the acquisition coincided with the low-tide phase and the upper limit of the tide was still upper limit of the tide was still detectable. The target limits were then identified by the contrast of gray scale for aerial photographs [33–35]. The same extraction method, based on color contrast, was used for Google Earth images [30,31,36,37]. The morphological state of 1988 was compared to that of 1970, while each image of the Google Earth series was compared to the previous image, starting from 2004 as a reference situation. The superposition of lines corresponding to two successive periods, using GIS techniques in ArcGis, made it possible to draw zones of accretion and erosion and calculate surface budgets of erosion/accretion reflecting the morphodynamic evolution of the coastal system. The morphological analysis was completed by the processing of the digital terrain model DEM (Source: United States Geological Survey USGS) using the U.S. Hydrologic Engineering Center - J. Mar. Sci. Eng. 2019, 7, 248 6 of 19

River Analysis System (HEC-RAS) application and ArcGis software. The treatment provided the opportunity to generate a 3D perspective view of the watercourse between the Sidi Daoui dam and the estuary outlet. The data collected in the ﬁeld include, on the one hand, bathymetric measurements taken in March and July 1997 along the central line of the watercourse and useful for following the evolution of its topography, and, on the other hand, the sampling of sediments for particle size and organic matter content analyses. The granulometric characterization of the conserved sediments was based on the “Association française de normalisation” (AFNOR) sieving method to determine the sand and mud fractions. Samples from the stations S4, S7, and S9 were selected and processed by the laser-based microgranulometric method, using a Mastersizer 2000 for more precision. The same samples were analyzed to estimate the organic matter content by using the calcination method at 450 ◦C.

3. Results

3.1. Hydrologic Evolution of the Oum Er-Rbia River The evolution of the hydrological regime, downstream of the Oum Er-Rbia catchment area, is expressed in terms of monthly water ﬂow volumes recorded at the Sidi Said Maachou, Imfout, and Al Massira dams (Figure4). These records cover a period of 92 years through which the evolution reﬂects two distinct periods separated by the construction of the Massira dam in 1979 that contributes more than 75% to water mobilization in the Oum Er-Rbia watershed (Figure4, Table1). Indeed, from 1926 to 1970, the volumes of water reaching the Atlantic Ocean were very dispersed with monthly peaks ranging between 1000 Mm3 and 2100 Mm3. The monthly average volume calculated for this period was 271 Mm3. In the second period, from 1980, the total potential volume managed in dam reservoirs over the entire Oum Er-Rbia watershed increased to 5301.7 Mm3 and allowed the improvement of the waterJ. Mar. mobilizationSci. Eng. 2019, 7, ratex FOR in PEER the REVIEW basin at more than 93%. 7 of 20

2500 6000 3 3

5301,7 2123 5000 2000 4548,7

1768 1781 4000 1500 Water inputs in Mm 1410 1342

3000 Managed capacity in Mm

1000 Drain of 2000 1511,2 1334,2 Al Massira Dam 500 506 351 1000 271 Mm3

29 Mm3 20,7 0 0 Jul-34 Jul-43 Jul-50 Jul-57 Jul-64 Jan-31 Jan-38 Jan-47 Jan-54 Jan-61 Jan-68 Jun-80 Jun-87 Jun-94 Jun-01 Jun-08 Jun-15 Oct-82 Oct-89 Oct-96 Oct-03 Oct-10 Oct-17 Apr-86 Apr-93 Apr-00 Apr-07 Apr-14 Sep-26 Sep-35 Sep-44 Sep-51 Sep-58 Sep-65 Feb-85 Feb-92 Feb-99 Feb-06 Feb-13 Dec-83 Dec-90 Dec-97 Dec-04 Dec-11 Aug-81 Aug-88 Aug-95 Aug-02 Aug-09 Aug-16 Nov-27 Nov-36 Nov-45 Nov-52 Nov-59 Nov-66 Mar-32 Mar-39 Mar-48 Mar-55 Mar-62 Mar-69 May-33 May-42 May-49 May-56 May-63 May-70 Month Water volume downstream of Oum Er-Rbia Average volume per period Cumulative capacity in reservoirs of managed dams

FigureFigure 4. 4.Monthly Monthly evolution evolution of theof hydrologicalthe hydrological regime re downstreamgime downstream of Oum of Er-Rbia Oum RiverEr-Rbia compared River tocompared the cumulative to the cumulative capacity in capacity reservoirs in ofreservoirs managed of dams. managed dams Figure4 shows that the average monthly volume for the period 1980–2017 was sharply reduced Figure 4 shows that the average monthly volume for the period 1980–2017 was sharply by 89% with only 29 Mm3. The maximum values recorded in 2010 and 2013, which were, respectively, reduced by 89% with only 29 Mm3. The maximum values recorded in 2010 and 2013, which were, respectively, 506 Mm3 in March and 351 Mm3 in April, corresponded to the controlled drain events of the Massira dam. These volumes are recuperated and regulated downstream by the compensation dams, notably Imfout, Daourat, Sidi Said Maachou, and Sidi Daoui. Exceptionally, water surpluses reached the estuary by flowing over the wall of Sidi Daoui dam (Figure 2). Under the conditions of climate change in the 1980s, the water available in the watershed was often less than what is needed [63]. Thus, their management in terms of allocations at the beginning of each agricultural year depends on the availability in reservoirs upstream of the basin.

Table 1. Evolution of cumulative capacity managed in dam reservoirs of Oum Er-Rbia catchment area, showing the contrast between the periods before and after 1979.

Cumulative Rate Relative to Added Value Average Volume of Water Period Capacity Total Capacity in % of Supply to the Estuary ± Managed (Mm3) (%) Capacity Standard Deviation (Mm3) 1926–1953 30.2 0.6 +0.6 251 ± 280 1954–1970 1511.2 28.5 +27.9 298 ± 295 1979–2001 4548.7 85.8 +57.3 33 ± 25 2002–2017 5301.7 100.0 +14.2 24 ± 54

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506 Mm3 in March and 351 Mm3 in April, corresponded to the controlled drain events of the Massira dam. These volumes are recuperated and regulated downstream by the compensation dams, notably Imfout, Daourat, Sidi Said Maachou, and Sidi Daoui. Exceptionally, water surpluses reached the estuary by ﬂowing over the wall of Sidi Daoui dam (Figure2). Under the conditions of climate change in the 1980s, the water available in the watershed was often less than what is needed [63]. Thus, their management in terms of allocations at the beginning of each agricultural year depends on the availability in reservoirs upstream of the basin.

Table 1. Evolution of cumulative capacity managed in dam reservoirs of Oum Er-Rbia catchment area, showing the contrast between the periods before and after 1979.

Cumulative Rate Relative Added Average Volume of Water Period Capacity Managed to Total Value in % Supply to the Estuary (Mm3) Capacity (%) of Capacity Standard Deviation (Mm±3) 1926–1953 30.2 0.6 +0.6 251 280 ± 1954–1970 1511.2 28.5 +27.9 298 295 ± 1979–2001 4548.7 85.8 +57.3 33 25 ± 2002–2017 5301.7 100.0 +14.2 24 54 ±

3.2. Drought Evolution in the Oum Er-Rbia Watershed Area Many studies, in the available literature, on the evolution of drought in Morocco are based essentially on the calculation of the Standardized Precipitation Index (SPI) of McKee et al. (1993) [64], which is largely used and recommended [47,65–68]. This index is exploited by referring to the McKee (1995) [69] classiﬁcation that deﬁnes six classes of drought according to its values, namely, extreme drought (SPI < 2), severe drought ( 2 to 1), moderate drought ( 1 to 0), moderately wet (0 to 1), − − − − very wet (1 to 2), and extremely wet (SPI > 2). SPI is calculated on the basis of precipitation data as shown in the Equation (1). SPI = P P /σ (1) i − where Pi total rainfall of the year i, P mean annual rainfall of the time series, and σ rainfall standard deviation of the time series. The results reveal the alternation at an irregular rhythm of short wet periods with long dry periods. Severe drought periods were 1980–1985, 1990–1995, 1997–2002, and 2005–2008 without reaching the extreme conditions [47,67,68], while wet seasons were recorded in the 1970s, 1989, 1996 as the wettest year, and 2009–2010 [47]. By considering the period of 1970–2010, dry years accounted for 61.3% and wet years 38.7% [47,48].

3.3. Morphological Evolution of the Oum Er-Rbia Estuary To assess the geomorphological processes occurring in the Oum Er-Rbia estuary, aerial photographs and Google Earth images, covering the period of 1970–2017, were selected, analyzed, and then compared. Nine shoreline positions were, thus, extracted according to the methodology adopted. Principal indicators of morpho-sedimentary evolution of the Oum Er-Rbia estuary are summarized in Table2. The observed variations in the estuary were mainly related to the width of the river outlet, ranging from 28 m to 127 m, and its direction, relatively stable between 1970 and 1982 (5◦ NNE) but moving since 1988. The evolution trends are expressed in terms of clogging/unclogging deducted from the surface balance of the morphological units as a result of the deposition/erosion processes into the estuary. The corresponding results are mapped and shown in Table2 and Figure5. Figure6 represents an instantaneous state of the Oum Er-Rbia mouth in 1982 that shows the ﬁrst accretion spit on its left side and the reduction of the mouth width after the construction of the Massira dam. J. Mar. Sci. Eng. 2019, 7, 248 8 of 19

Table 2. Indicators of morpho-sedimentary evolution of the Oum Er-Rbia estuary.

Axis Direction Surface Estuary Outlet Year Image Source of the Estuary Sedimentary Tendency Width (m) Outlet Balance (m2)

1970 ANCFCC 125 5◦ NNE Reference position - 1982 ANCFCC 82 5◦ NNE +6644 Clogging 1988 ANCFCC 49 7◦ NNW +153,108 Clogging 1 2004 Google Earth 61 35◦ NNW Reference position - 1 2009 Google Earth 49 46◦ NNW 189,383 Unclogging 1 − 2011 Google Earth 127 32◦ NNW 18,630 Unclogging 1 − 2012 Google Earth 59 44◦ NNW +68,763 Clogging 1 2014 Google Earth 45 54◦ NNW +28,383 Clogging 2016 Google Earth 1 28 49 NNW 26,390 Unclogging ◦ − 2017 Google Earth 1 96 30 NNW 37,115 Unclogging ◦ − J. Mar. Sci. Eng. 2019, 7, x1 FORImages PEER provided REVIEW by DigitalGlobe, CNES/Airbus, and Landsat/Copernicus. 9 of 20

FigureFigure 5. 5. (a(a) )Assessment Assessment of of the the processes processes of ofclogging/u cloggingnclogging/unclogging in inthe the Oum Oum Er-Rbia Er-Rbia estuary estuary and and its outlet;its outlet; (b) field (b) ﬁeld photographs photographs showing showing the estuary the estuary clogging clogging (up) (up)and andaccretion accretion on the on left the side left sideof the of outletthe outlet (down); (down); (c) aerial (c) aerial photographs photographs and and Google Google Earth Earth im imagesages of ofthe the Oum Oum Er-Rbia Er-Rbia estuary estuary in in the the differentdiﬀerent times times of of spatial spatial observation.

FigureFigure 76 showsrepresents the locationan instantaneous of stations state and of a 3Dthe perspective Oum Er-Rbia view mouth generated in 1982 by that the HEC-RASshows the firstapplication, accretion showing spit on its the left watercourse side and the located reduction between of the themouth Sidi width Daoui after dam the and construction the outlet of the the Massirariver. It dam. is a channel with a sinuous shape which was dug into a plateau area. The follow-up of longitudinalFigure 7 morphologicalshows the location evolution of stations was and based a 3D on perspective a succession view of thirty-six generated cross-sections. by the HEC-RAS The application, showing the watercourse located between the Sidi Daoui dam and the outlet of the river. It is a channel with a sinuous shape which was dug into a plateau area. The follow-up of longitudinal morphological evolution was based on a succession of thirty-six cross-sections. The resulting topographic profile of the center line was then adjusted using the bathymetric data for the months of May and July in 1996 (Figure 7C). The figure shows the longitudinal topographic evolution of the watercourse bottom, with more frequent undulations downstream than upstream. It reflects that the estuary morphology has been mainly stable since 1988.

J. Mar. Sci. Eng. 2019, 7, 248 9 of 19 resulting topographic profile of the center line was then adjusted using the bathymetric data for the months of May and July in 1996 (Figure7C). The figure shows the longitudinal topographic evolution of the watercourse bottom, with more frequent undulations downstream than upstream. It reflects that J. Mar. Sci. Eng. 2019, 7, x FOR PEER REVIEW 10 of 20 theJ. Mar. estuary Sci. Eng. morphology 2019, 7, x FOR hasPEER been REVIEW mainly stable since 1988. 10 of 20

Figure 6. The first accretion form recorded in the estuary outlet in 1982 after the construction of the Figure 6.6. The ﬁrstfirst accretionaccretion form recorded in thethe estuaryestuary outletoutlet in 19821982 afterafter thethe constructionconstruction of the Massira dam. Massira dam.

Figure 7.7. ((A)) 3D3D viewview ofof thethe estuaryestuary betweenbetween thethe SidiSidi DaouiDaoui damdam andand thethe riverriver outlet.outlet. ((BB)) HEC-RASHEC-RAS Figure 7. (A) 3D view of the estuary between the Sidi Daoui dam and the river outlet. (B) HEC-RAS generated 3D3D model model of theof the estuary estuary studied. studied. (C) Longitudinal (C) Longitudinal section section with exaggerated with exaggerated slope showing slope generated 3D model of the estuary studied. (C) Longitudinal section with exaggerated slope theshowing topographic the topographic evolution ofevolution the river of centerline the river between centerline the outletbetween and the the outlet Sidi Daoui and dam.the Sidi S1 toDaoui S10: showing the topographic evolution of the river centerline between the outlet and the Sidi Daoui Locationsdam. S1 to of S10: the Locations sediment sampling,of the sediment S1, S2, sampling, and S3, are S1, taken S2, and from S3, the are littoral taken sidefrom as the shown littoral in side (A). as dam. S1 to S10: Locations of the sediment sampling, S1, S2, and S3, are taken from the littoral side as shown in (A). Theshown sieving-based in (A). granulometric characterization of sediments collected from the nine stations revealed the dominance of sand downstream (82–99.6% of sand), on the undulated bottom of the The sieving-based granulometric characterization of sediments collected from the nine stations estuaryThe and sieving-based on the neighboring granulometric beaches, characterization while the muddy of sediments sediments collected were dominant from the (94.1–99.6% nine stations of revealed the dominance of sand downstream (82–99.6% of sand), on the undulated bottom of the mud)revealed in thethe upstreamdominance part of ofsand the downstream estuary and on(82–99.6% both sides of sand), of the on Sidi the Daoui undulated dam (Figure bottom8). of The the estuary and on the neighboring beaches, while the muddy sediments were dominant (94.1–99.6% of estuary and on the neighboring beaches, while the muddy sediments were dominant (94.1–99.6% of mud) in the upstream part of the estuary and on both sides of the Sidi Daoui dam (Figure 8). The mud) in the upstream part of the estuary and on both sides of the Sidi Daoui dam (Figure 8). The cumulative curves resulting from the laser-based analysis of the samples S4, S7, and S9 helped to cumulative curves resulting from the laser-based analysis of the samples S4, S7, and S9 helped to calculate the average particle sizes d50 between March and July, estimated to 253 µm for S4, 17.5 µm calculate the average particle sizes d50 between March and July, estimated to 253 µm for S4, 17.5 µm for S7, and 6.3 µm for S9 (Figure 9). This confirms the results obtained by the AFNOR sieving for S7, and 6.3 µm for S9 (Figure 9). This confirms the results obtained by the AFNOR sieving method. In addition, the sand samples showed the same mineralogical composition and the method. In addition, the sand samples showed the same mineralogical composition and the amounts of organic matter were less than 2% in sands downstream and beaches but increased up to amounts of organic matter were less than 2% in sands downstream and beaches but increased up to

J. Mar. Sci. Eng. 2019, 7, 248 10 of 19 cumulative curves resulting from the laser-based analysis of the samples S4, S7, and S9 helped to calculate the average particle sizes d50 between March and July, estimated to 253 µm for S4, 17.5 µm for S7, and 6.3 µm for S9 (Figure9). This conﬁrms the results obtained by the AFNOR sieving method. In addition, the sand samples showed the same mineralogical composition and the amounts of organic J.J. Mar.Mar. Sci.Sci. Eng.Eng. 2019,, 7,, xx FORFOR PEERPEER REVIEWREVIEW 11 11 ofof 2020 matter were less than 2% in sands downstream and beaches but increased up to 6.7% in muddy 6.7%sediments in muddy upstream. sediments These upstream. remarks areThese favorable remarks for are a marinefavorable origin for a of marine the sands origin collected of the insands the collectedestuary downstream. in the estuary The downstream. estuary clogging The estuary by marine clogging sands by covered marine a sands distance covered of 5 km a distance downstream of 5 wherekm downstream depth was where between depth 1 m andwas 3 between m, while 1 the m remainingand 3 m, while part (10 the km) remaining was characterized part (10 km) by mudwas characterizeddeposits and depths by mud between deposits 5 and m and depths 10 m. between 5 m and 10 m.

100% 8 90% 7 80% 6 70% 60% 5 50% 4 40% 3 Particle size Particle Particle size Particle 30% 2 Organic matter % matter Organic 20% % matter Organic 10% 1 0% 0 123456789 Stations

D < 63µm 2 mm > D > 63µm Organic matter %

Figure 8.8. Sieving-based granulometric characterization and and organic matter content in the sedimentsediment samples collected from thethe estuaryestuary andand coastalcoastal sides.sides.

16 5 5 14 S4 4,5 S7 4,5 S9 4 4 12 4 3,5 3,5 10

10 % Frequency Frequency % Frequency Frequency % Frequency 3 % Frequency

Frequency % Frequency 3 Frequency % Frequency 3 8 8 2,5 2,5 6 2 2 4 1,5 1,5 1 1 2 1 0,5 0,5 0 0 0

0 0 0 0 0 0 0 0 100 200 300 400 500 600 700 800 900 100 200 300 400 500 600 700 800 900 100 200 300 400 500 600 700 800 900 100 200 300 400 500 600 700 800 900 100 200 300 400 500 600 700 800 900 100 200 300 400 500 600 700 800 900 SizeSize inin µmµm SizeSize inin µmµm SizeSize inin µmµm JulyJuly March JulyJuly March JulyJuly March

100 100 100 90 S4 90 S7 90 S9 80 80 80 70 70 70 60 60 60 50 50 50 40 40 40 Cumulative percentCumulative Cumulative percentCumulative Cumulative percentCumulative Cumulative percentCumulative Cumulative percentCumulative 30 30 percentCumulative 30 20 20 20 10 10 10 0 0 0 1000 100 10 1 0,1 1000 100 10 1 0,1 1000 100 10 1 0,1 d Size in μm d5050 Size in m d5050 SizeSize inin μm d5050 SizeSize inin μm JulyJuly March JulyJuly March JulyJuly March Figure 9.9. Laser-basedLaser-based granulometricgranulometric characterization characterization of of sediments sediments taken taken from from the the stations stations S4, S7,S4, andS7, andS9, showing S9, showing frequency frequency curves curves and cumulativeand cumulative curves. curves.

3.4. Morphological Morphological Evolution of the Neighboring Beaches The evolution in the neighboring beaches is expr expressedessed in terms of advance/retreat advance/retreat trends as summarized in Table 3 3 and and Figure Figure 10 10.. AlongAlong thethe beachbeach ofof ElEl Haouzia,Haouzia, thethe evolutionevolution ofof shorelineshoreline position over the period of 1970–2017 indicates a global advance, resulting in an extension of the beach over an area of 57,855 m22 (Table(Table 3).3). FromFrom 19701970 toto 1988,1988, thethe evolutionevolution ofof thethe shorelineshoreline showsshows aa clear advance of the beach of El Haouzia on a considerable surface of 94,700 m22.. Locally,Locally, aa retreatretreat surface was detected near the river outlet, whereas the advance was observed into the outlet, with a north-facing and arrow-shaped sandy body, and hook-shaped sandy bodies insideinside thethe estuaryestuary (Figure 10). Since 2004, the shoreline profiles show a perceptible lateral redistribution of sands between multiple alternating zones of accretion and erosion (Figure 10). The exception was noted

J. Mar. Sci. Eng. 2019, 7, x FOR PEER REVIEW 12 of 20 J. Mar. Sci. Eng. 2019, 7, 248 11 of 19 for the time span of 2009–2011, which showed a clear retreat trend of the Haouzia beach on a surface of 73,462 m2. positionIn the over Lalla the Aicha period El of Bahria 1970–2017 beach, indicates the evolut a globalion of advance,the shoreline resulting position inan showed extension an overall of the 2 beachtendency over to an erosion area of between 57,855 m1970(Table and 32017,). From marked 1970 by to 1988,a shoreline the evolution retreat on of an the area shoreline of 333,285 shows m2 2 a(Table clear advance3). Short-term of the beachevolution of El of Haouzia the shoreline on a considerable revealed a surfacefirst linear of 94,700 retreat m .of Locally, 57 m near a retreat the surfaceestuary wasoutlet detected between near 1970 the riverand outlet,1988 (Figure whereas 10 the). Since advance 2004, was two observed new erosion into the phases outlet, were with adetected, north-facing linear and retreats arrow-shaped estimated at sandy 40 m body, and 31 and m hook-shapedwere revealed sandy in the bodies2009–2011 inside and the 2012–2016 estuary (Figureperiods, 10 ).respectively. Since 2004, theTheses shoreline erosion proﬁles phases show aresult perceptible in a lateralloss of redistribution beach width of sandsestimated between at multipleapproximately alternating 2.7 m zones as annual of accretion mean value. and erosion (Figure 10). The exception was noted for the time span of 2009–2011, which showed a clear retreat trend of the Haouzia beach on a surface of 73,462 m2. Table 3. Morpho-sedimentary surface balance in m2 of units through the neighboring beaches of 2 TableOum 3.Er-RbiaMorpho-sedimentary estuary. Positive surfacevalues balancesignify inshor melineof unitsadvance, through while the negative neighboring values beaches indicate of Oumshoreline Er-Rbia retreat. estuary. Positive values signify shoreline advance, while negative values indicate shoreline retreat. Surface balance in m2 Period 2 El Haouzia SurfaceBeach balance L.A. El in Bahria m Beach Period 1970–1988 El Haouzia+94,700 Beach L.A. El− Bahria1373 Beach 1970–19882004–2009 +10,149+94,700 +19,8241373 − 2004–20092009–2011 −+73,46210,149 −175,148+19,824 2009–2011 73,462 175,148 2011–2012 +59,819− −−13,820 2011–2012 +59,819 13,820 2012–2014 −3109 −−37,087 2012–2014 3109 37,087 − − 2014–2016 −19,30119,301 −139,076139,076 − − 2016–2017 −10,94110,941 +13,395+13,395 − Overall Balance +57,855 333,285 Overall Balance +57,855 −−333,285

Figure 10. Evolution of the shoreline in the beachesbeaches neighboring the Oum Er-Rbia estuary.

J. Mar. Sci. Eng. 2019, 7, 248 12 of 19

In the Lalla Aicha El Bahria beach, the evolution of the shoreline position showed an overall tendency to erosion between 1970 and 2017, marked by a shoreline retreat on an area of 333,285 m2 (Table3). Short-term evolution of the shoreline revealed a ﬁrst linear retreat of 57 m near the estuary outlet between 1970 and 1988 (Figure 10). Since 2004, two new erosion phases were detected, linear retreats estimated at 40 m and 31 m were revealed in the 2009–2011 and 2012–2016 periods, respectively. Theses erosion phases result in a loss of beach width estimated at approximately 2.7 m as annual mean value.

4. Discussion The morpho-sedimentary equilibria in estuaries are established and maintained by the nature of hydrodynamic relationships between fluvial and marine dynamics and local anthropogenic activities [19–22,70–74]. Indeed, the morpho-sedimentary changes revealed in the Oum Er-Rbia River outlet, over time, are a direct result of local and successive hydrodynamic imbalances caused by two principal events that are the construction of Al Massira dam in 1979 and Sidi Daoui dam in 1985. These dams, and others, were installed in the watershed area to minimize the impact of prolonged periods of drought that have characterized the Moroccan climate since 1980. Indeed, the main feature of the climatic evolution is the increase in dry year frequency over time, unlike wet years which are becoming rare. Fifteen dams were constructed along the main course of the Oum Er-Rbia, which allowed for regulation of the surface waters in the Oum Er-Rbia watershed and, thus, disabled flood waters from reaching the ocean. During the drought period of 1980–1985, an annual volume of fresh water estimated at 200 Mm3 was lost at sea [75]. In this context, the Sidi Daoui dam was constructed in 1985 to stop the rise of the saline water and to save 5.5 Mm3 of fresh water needed for drinking and irrigation purposes in Azemmour city and the surrounding agricultural areas [75]. The monthly evolution of the hydrological regime downstream of the Oum Er-Rbia basin shows a drop in water input volume estimated at 89% over time, with an average monthly input of 271 Mm3 − before 1970, but limited to 29 Mm3 after that date. This change can be attributed, on the one hand, to climatic changes resulting in a rainfall reduced by 30% to 40% on the watershed, and on the other hand, to the important hydrological facilities constructed in the watershed and which allowed for the mobilization and the regulation of the totality of the annual water inputs into the watershed. Also, the continental sediments reaching the ocean were also reduced by 90% [57,61,76]. Fluviatile deposits were mainly silty-clay, with total suspended solids limited to between 0.002 g/L and 0.20 g/L depending on the season [77]. Consequently, the hydrological influence of the Oum Er-Rbia River at the estuary level, in terms of fluvial energy and solid inputs, is considered irrelevant. The main morphological changes observed in the downstream part of the river, between the Sidi Daoui dam and the sea, are the result of the interaction between the marine and estuarine dynamics influenced by the dredging works downstream. Between 1970 and 1988, the most significant morphological disturbances were observed in this period. They are mainly guided by the dam construction events resulting in a significant decrease of the impact of the upstream fluvial hydrodynamics. In 1970, the morphodynamic situation reflected a state of equilibrium among a normal fluvial hydrodynamics in humid periods, with frequent flood events able to maintain the estuary completely unclogged and a width mouth close to 125 m. After the installation of the Massira dam and under the effect of the drought of the 80s, the estuary showed the first sandy accretions at its mouth in 1982 leading to the reduction of the width of its mouth to 82 m. This proves that the equilibrium was broken due to the significant reduction of the fluvial flows reaching the estuary. The impact of the upstream Oum Er-Rbia hydrodynamics on the estuary was therefore very limited. In 1985 and after the construction of the Sidi Daoui dam, the estuary of the Oum Er-Rbia experienced a massive clogging of its mouth reduced to 49 m in 1988 instead of 125 m in 1970. These rapid changes were guided by marine processes on both sides of the mouth. Indeed, the normal and inverse littoral drifts converging towards the mouth of the estuary favored the confluence of the sediments and J. Mar. Sci. Eng. 2019, 7, 248 13 of 19 their transportation into the estuary by the high tide currents [30,78]. Similar observations were also evidenced in El Haouzia bay by Chaibi [36,59,60] and in other similar environments [29,30,79–82]. The clogging of the estuary was accelerated after the construction of the Sidi Daoui dam in 1985, thus, suggesting a significant influence on the tidal dynamics, as observed in similar situations elsewhere [20,21,26]. According to many local fishermen, the clogging process was significantly activated after the building of the Sidi Daoui dam [77]. Migniot [73] and Nahon [83] explained this evolution, observed in many estuaries, as a process of equilibrium recovery by a readjustment of the energy distribution scheme in relation with the hydraulic efficiency of the estuary [75,83]. In addition, the sandy sedimentation caused the rapid clogging between 1985 and 1988 of the estuary, leading to the installation of an unhealthy and anoxic environment evoked by Idrissi et al. [84] and El Jakani [77]. The estuary clogging observed in 1988 was maintained until 2004, thus, reflecting a new state of hydrodynamic equilibrium of the estuary system [19,77]. Between 2004 and 2011, considering the continuity of prolonged drought periods and the weak effect of the upstream part of the river, the expected situation was the continuation of the estuary clogging triggered since 1982, as observed in similar situations [85]. But the observed state between 2004 and 2011 was different from the expected. The explanation for this change was attributed to human intervention by the sand dredging in two separate stages. Indeed, between 2004 and 2009, the interior of the estuary was unclogged while the mouth was always reduced. This was the result of the dredging leading to the deepening of the inner estuary of about 4 m at low tide. After 2009, the dredging at the mouth level allowed the widening of the mouth that reaches 127 m width, leading to free communication between the downstream estuary and the sea. An event characterizing this period is the breaking of the Sidi Daoui dam (Figure 11) and the appearance of accretion zones inside the estuary (Figure 10). Benzekri [75] reported that the marine hydrodynamics effects could be sensed upstream at a location as far as 20 km at least from the river mouth [75]. The construction of the Sidi Daoui dam at 15 km only constituted an amputation of a large part of the estuary’s original volume and directly caused a disturbance in the daily circulation of the high tide that can explain the dam rupture in 2011. The coastal sides of Lalla Aicha El Bahria, mainly, and El Haouzia, secondarily, show areas of erosion that could be the source of the sediments transported inside the estuary after 2009 by the currents of high tide and by the effects of hydrodynamic resonance, as suggested by previous researches [7,86,87]. Thus, the morpho-sedimentary evolution of the estuary was the result of the interaction between the downstream estuary and the sea, while human intervention by dredging was an action that masked the expected natural consequences of accelerated clogging. Between 2011 and 2014, a relatively immediate restart of sedimentation of sands within the estuary was observed. It was marked mainly by the extension of the sandy spits on both sides of the river mouth where the width was reduced between 2011 (127 m) and 2014 (45 m). The return of accelerated clogging was explained by the re-establishment of the Sidi Daoui dam and the temporary stoppage of the dredging works, thus favoring an accretion trend. The erosion of the coastline observed during this period in the neighboring beach of El Bahria on an estimated area of 50,907 m2 was the probable origin of the sands obstructing the river mouth. This natural tendency of clogging is a manifestation of the migration towards a new state of hydrodynamic equilibrium under conditions of moderate works of dredging and continuous marine contribution. The sources of sediment supply into the estuary were probably the erosion zones revealed on the nearby beaches. Four exceptional swell events along the Moroccan Atlantic coast were recorded during the investigation period. They were seen in 1978, 2005, 2008, and 2014 [88]. However, there was no significant change that can be linked to these exceptional swells. Between 2014 and 2017, the main character of the morpho-sedimentary evolution of the estuary was the alternation between clogging and unclogging tendencies and the fluctuations of the river mouth width and the direction of its axis. Considering the absence of the hydrodynamic effect of the upstream river on the estuary and the intermittent restart of dredging, the morphological evolution J. Mar. Sci. Eng. 2019, 7, x FOR PEER REVIEW 14 of 20

In addition, the sandy sedimentation caused the rapid clogging between 1985 and 1988 of the estuary, leading to the installation of an unhealthy and anoxic environment evoked by Idrissi et al. [84] and El Jakani [77]. The estuary clogging observed in 1988 was maintained until 2004, thus, reflecting a new state of hydrodynamic equilibrium of the estuary system [19,77]. Between 2004 and 2011, considering the continuity of prolonged drought periods and the weak effect of the upstream part of the river, the expected situation was the continuation of the estuary clogging triggered since 1982, as observed in similar situations [85]. But the observed state between 2004 and 2011 was different from the expected. The explanation for this change was attributed to human intervention by the sand dredging in two separate stages. Indeed, between 2004 and 2009, the interior of the estuary was unclogged while the mouth was always reduced. This was the result of the dredging leading to the deepening of the inner estuary of about 4 m at low tide. After 2009, the dredging at the mouth level allowed the widening of the mouth that reaches 127 m width, leading to free communication between the downstream estuary and the sea. An event characterizing this period is the breaking of the Sidi Daoui dam (Figure 11) and the appearance of accretion zones inside the estuary (Figure 10). Benzekri [75] reported that the marine hydrodynamics effects could be sensed upstream at a location as far as 20 km at least from the river mouth [75]. The construction of the Sidi Daoui dam at 15 km only constituted an amputation of a large part of the estuary’s original volume and directly caused a disturbance in the daily circulation of the high tide that can explain the dam rupture in 2011. J. Mar.The Sci. Eng.coastal2019 ,sides7, 248 of Lalla Aicha El Bahria, mainly, and El Haouzia, secondarily, show areas14 of of 19 erosion that could be the source of the sediments transported inside the estuary after 2009 by the currents of high tide and by the effects of hydrodynamic resonance, as suggested by previous researchesof the estuarine [7,86,87]. environment Thus, the wasmorpho-sedimentary the result of two antagonisticevolution of processes:the estuary the was sand the dredging result of andthe interactionthe natural between contribution the downstream of marine sands estuary testiﬁed and bythe the sea, appearance while human of erosion intervention zones by on dredging the coast, wasespecially an action Lalla that Aicha masked El Bahria the expected (Figure 10natu). ral consequences of accelerated clogging.

Figure 11. Illustrations of the Sidi Daoui dam through the watercourse of Oum Er-Rbia showing its rupture in 2011 and restitution in 2012.

5. Conclusions The results presented in this paper on the evolution of a coast-estuary system are based on non-expensive methods of analysis of governmental hydrological data, spatial images, and ﬁeld data. They have provided useful information on the coastal system of Oum Er-Rbia River on the Atlantic coast of Morocco, a region where data and similar studies are scarce. For several decades, Morocco has overcome the hazards of prolonged drought periods by the mobilization and management of surface water resources. Important hydraulic infrastructures of dams were, thus, built in the catchment area of the Oum Er-Rbia River. Over time, the Oum Er-Rbia estuary was deeply clogged by marine sands, with the existence of unclogging features. Retreat and advance phases were revealed on the neighboring coastal sides, indicating alternating erosion and sedimentation processes. By analyzing the interactions over time between the upstream part of the river, the estuary, and the neighboring beaches, it was demonstrated that the natural functioning of the estuary, where the river freely communicates with the sea, was interrupted by the construction of dams, especially the Massira in 1979 and Sidi Daoui in 1985. The new situation was favorable to the clogging of the estuary by marine sands, but the human intervention by the dredging works was a process which masked this situation and which became the main factor of morphological change and an antagonist to the clogging process. J. Mar. Sci. Eng. 2019, 7, 248 15 of 19

Finally, two principal suggestions are proposed for the rehabilitation of the Oum Er-Rbia coastal system and similar environments: (1) The compensation of the hydrodynamic anomaly caused by the location of the Sidi Daoui dam is required. In the future, a study on the resonance phenomenon’s impact on the hydrodynamics downstream of the estuary will be helpful to understand the mechanisms controlling the drop in energy that favors the sand accumulation and causes the estuary clogging. (2) The beaches of Lalla Aicha El Bahria, principally, and El Haouzia, secondarily, were revealed as the potential origin of the marine sands mobilized in the coastal system. Their stabilization is, thus, necessary for maintaining the coastal system’s equilibrium.

Author Contributions: Conceptualization, M.E. and S.E.; methodology, M.E. and S.E.; software, S.E.; validation, M.E.; S.E.; H.R.; M.R. (Mohammed Raji); M.R. (Mohamed Radid); and M.T.; formal analysis, M.E. and S.E.; investigation, M.E. and S.E.; data curation, M.E.; writing—original draft preparation, M.E.; writing—review and editing, M.E. and S.E.; visualization, M.E.; S.E.; H.R.; M.R. (Mohammed Raji); M.R. (Mohamed Radid); and M.T. Funding: This research received no external funding. Acknowledgments: The authors would like to thank the “Agence du Bassin Hydraulique de l’Oum Er-Rbia” (ABHOER) for providing the necessary hydrological data for this work, the “Office National de l’Electricité et de l’Eau potable” (ONEE) for providing the authors with data on water intake for urban and industrial use downstream of the Massira dam, and the “Office Régional de Mise en Valeur Agricole des Doukkala” (ORMVAD) for providing data on allocations and water transfers for irrigation. Conflicts of Interest: The authors declare no conflict of interest.

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