Mohammed Zaidi

Nasre-Dine Ahfir
email: ahfirn@univ-lehavre.fr

Bouabid Abdellah Alem

El Mansouri

Huaqing Wang

Said Taibi

Benoît Duchemin

Abdesselam Merzouk

Bouabid El Mansouri

Assessment of clogging of managed aquifer recharge in a semi-arid region

Keywords: semi-arid region, Managed Aquifer Recharge, particles transfer, hydraulic conductivity, clogging, soil cracks

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

In water-limited environments, population growth has led to amplified water demand stressing aquifers and streams [START_REF] Treese | Clogging of an Effluent Dominated Semiarid River: A Conceptual Model of Stream-Aquifer Interactions1[END_REF]. Arid and semi-arid climates are particularly susceptible, often relying on groundwater to support the needs of large urban centres or irrigated agriculture in the absence of sufficient surface water resources [START_REF] Famiglietti | The global groundwater crisis[END_REF]. Also, natural recharge is intrinsically limited in these climates, and the predicted effects of climate change on recharge in these regions are highly uncertain [START_REF] Taylor | Ground water and climate change[END_REF]. In order to increase the security of groundwater resources, managed aquifer recharge (MAR) programs have been developed and implemented globally [START_REF] Stefan | Web-based global inventory of managed aquifer recharge applications[END_REF]. MAR is an engineering system that aims to increase groundwater supplies by water injection (well) into aquifers and also by infiltration being carried out from large and accessible surface structures (constructed basins, and perfectly dimensioned or natural wadi beds) [START_REF] Bouwer | Artificial recharge of groundwater: hydrogeology and engineering[END_REF][START_REF] Missimer | Enhancement of wadi recharge using dams coupled with aquifer storage and recovery wells[END_REF]. Other objectives of this technique include reducing marine intrusions, storing water and improving surface water quality [START_REF] Dillon | Future management of aquifer recharge[END_REF][START_REF] Dillon | Managed aquifer recharge: An Introduction[END_REF]. Managed aquifer recharge was the subject of several research studies that addressed its various technical and economic aspects [START_REF] Marino | Artificial groundwater recharge, I. Circular recharging area[END_REF][START_REF] Detay | Rational Ground Water Reservoir Management: The Role of Artificial Recharge[END_REF].

The soil infiltration rate decreased due to the high rate of sedimentation during flow periods. The study of [START_REF] Hatch | Spatial and temporal variations in streambed hydraulic conductivity quantified with time-series thermal methods[END_REF] of Pajaro River in California, showed that the hydraulic conductivity of the streambed ranged from 10 -6 to 10 -4 m/s within the experimental site, with lower hydraulic conductivity determined later in the dry season, as deposits were accumulated on the streambed during periods of low flow. For the Danube River (Vienna), [START_REF] Blaschke | Clogging processes in hyporheic interstices of an impounded river, the Danube at Vienna, Austria[END_REF] reported a reduction of the seepage rate by about 40% to 60% over a period of 4.5 years. The experiment conducted by [START_REF] Pholkern | Riverbed clogging experiments at potential river bank filtration sites along the Ping River, Chiang Mai, Thailand[END_REF] at the Mae Rim site (Thailand) indicates that during the 22-day period of the experiment, with channel flow (0.05 m/s) and turbidity , vertical hydraulic conductivity decreased significantly from 5.6 ×10 -6 to 7.3 ×10 -7 m/s between 0 and 0.03 m in depth.

Clogging has long been an issue in managed aquifer recharge [START_REF] Dillon | Analysis of ASR Clogging Investigations at Three Australian ASR Sites in a Bayesian Context[END_REF]. The main operational challenge of infiltration systems is usually management of clogging, which causes a decrease in permeability. As a consequence, the recharge rate decreases, leading to the failure of managed recharge system [START_REF] Jeong | A review on clogging mechanisms and managements in aquifer storage and recovery (ASR) applications[END_REF]. A study conducted by [START_REF] Pavelic | Review of international experience in injecting natural and reclaimed waters into aquifiers for storage and reuse[END_REF] found that clogging was the dominant reason for abandonment of Aquifer Storage and Recovery projects. Clogging of surface infiltration has multiple impacts, counting: i) decreasing infiltration rates [START_REF] Schubert | Hydraulic aspects of riverbank filtration-field studies[END_REF] and ii) reducing soil infiltrability efficiency, which involves a regular maintenance [START_REF] Siegrist | Soil Clogging During Subsurface Wastewater Infiltration as Affected by Effluent Composition and Loading Rate 1[END_REF]. In porous media, the clogging layer (cake) is the part of the medium over which a sharp drop in hydraulic head occurs as water infiltrates a sedimentary profile [START_REF] Houston | Infiltration Considerations for Ground-Water Recharge with Waste Effluent[END_REF]. There are two distinct kinds of clogging layers that can be formed in the infiltration surface: i) a top layer consisting of suspended particles material, algae and/or microbes accumulating above native material and ii) a lower layer containing the autochthon sediment with organic and inorganic solids trapped in the pore space [START_REF] Hutchison | Clogging Issues Associated with Managed Aquifer Recharge Methods[END_REF].

Clogging can be the result of chemical, biological or physical mechanisms or some combination of the three: (i) chemical clogging, which depends on chemical factors that control the colloidal stability of the particles and minerals precipitated from water [START_REF] Mays | Hydrodynamic and Chemical Factors in Clogging by Montmorillonite in Porous Media[END_REF]; (ii) biological by the growth of microorganisms (algae, biofilm and bacteria) at the infiltration surface or on a thin layer [START_REF] Nie | Analysis of the bacterial community changes in soil for septic tank effluent treatment in response to bio-clogging[END_REF] and (iii) physical or mechanical related to solid particles inputs [START_REF] Rinck-Pfeiffer | Interrelationships between biological, chemical, and physical processes as an analog to clogging in aquifer storage and recovery (ASR) wells[END_REF][START_REF] Siriwardene | Clogging of stormwater gravel infiltration systems and filters: Insights from a laboratory study[END_REF] and environmental compaction related to basin activities, water loads when the basin is filled and settling of sediment deposits themselves [START_REF] Gonzalez-Merchan | Monitoring of clogging evolution in the stormwater infiltration system and determinant factors[END_REF]. In nature, sediments carried by flows can have several origins but mainly erosion of crumbly geological formations [START_REF] Gaskin | Erosion of undisturbed clay samples from the banks of the St[END_REF] or by human activities, such as the extractive industry (gravel and clay extraction), agricultural activities and construction projects [START_REF] Ryan | Environmental effects of sediment on New Zealand streams: A review[END_REF]. Hydraulic conductivity is one of the most significant soil properties that controls water infiltration from the surface to subsurface. The hydraulic conductivity is largely dependent on the soil proprieties and can therefore vary considerably in space and time [START_REF] Viviani | Wastewater Reuse Effects on Soil Hydraulic Conductivity[END_REF][START_REF] Sepaskhah | Effects of wastewater application on saturated hydraulic conductivity of different soil textures[END_REF]). For clayey soils, desiccation cracking is a phenomenon that may considerably increase the hydraulic conductivity. However, as shown by [START_REF] Rayhani | Physical modeling of desiccation cracking in plastic soils[END_REF], under cyclic drying and wetting, for some highly plastic soils, hydraulic conductivity decreased with an increase in permeation time, which is attributed to the cracks self-healing.

Many studies have been undertaken to study the clogging phenomenon in situ. [START_REF] Skolasińska | Clogging microstructures in the vadose zone-laboratory and field studies[END_REF] identified the post-depositional changes that have occurred in river deposits affected by forced infiltration of river water and concluded that the decomposition of organic matter present in deposits or in infiltrating water is a very important factor controlling clogging. [START_REF] Casas-Mulet | Key hydraulic drivers and patterns of fine sediment accumulation in gravel streambeds: A conceptual framework illustrated with a case study from the Kiewa River, Australia[END_REF] studied the main hydraulic factors and trends in fine sediment accumulation on a river by installing sediment collectors in a lateral gravel bar subject to irregular flow fluctuations in the river. They estimated that an important horizontal inter-gravel transport contributed to a significant accumulation of fine sediments. [START_REF] Fetzer | Clogging of an Alpine streambed by silt-sized particles -Insights from laboratory and field experiments[END_REF] investigated the dynamics of clogging by comparing infiltration of silty fine particles and sandy fine particles and by comparing the results between laboratory and field experiments. They showed that clogging is rather pronounced in the field due to a highly fluctuating water regime, a polydispersed suspension and a high concentration of suspended particles in comparison to laboratory conditions.

In Morocco, the techniques of artificial recharge started since 1958 [START_REF] Sadiki | Improvement of groundwater resources potential by artificial recharge technique: A case study of Charf El Akab aquifer in the Tangier region, Morocco[END_REF]. The first experiments were carried out on the Charf El Akab aquifer in the North-Western area. Then these techniques were generalised to all unconfined aquifers that suffer from excessive exploitation of groundwater resources. There were 40 projects carried out, of which 96% are on the embankments constructed on streams, alimented by rainwater and dam releases. The clogging of recharge areas represents the common issue between these projects, induced by sediments mobilised during flows.

Until now and to our knowledge, there have been no studies on the clogging processes in artificial recharge facilities in Morocco (semi-arid region) according to hydrometeorological conditions of the field. Thus, an investigation in that optic was carried out.

The aim of this study was to evaluate the extent of clogging in the field by measuring the amount of fine particles infiltrating in depth and the thickness of sediments deposited on the bed surface in recharge sites. This was accomplished by using an original approach that consists of implanting pickets and sand-filled columns in recharge sites for assessing particle deposition on the soil surface and subsurface. Saturated hydraulic conductivity measurements were made, in situ and in the laboratory, to evaluate the effect of deposit accumulation on infiltration. Deposited particles, in the surface and subsurface, characteristics (particles size and composition of the organic and inorganic matter) were determined.

Materials and Methods

Description of study area

Berrechid Plain is located in the centre of Morocco (Fig. 1). It extends to 1,500 km². This region is characterised by an arid to semi-arid climate, with an average temperature of 18°C. The annual average rainfall varies from 280 to 310 mm/year [START_REF] El Assaoui | Modeling of Climate Changes Impact on Groundwater Resources of Berrechid Aquifer[END_REF].

The plain is marked by intense industrial activity, particularly the ceramics industry and the development of agriculture based on the exploitation of groundwater resources. According to the Bouregregreg and Chaouia Hydraulic Basin Agency (ABHBC), the water balance deficit increased from 20 Mm 3 in 2010 to 30 Mm 3 /year in 2016, which was linked to withdrawals from about 3,000 wells and boreholes, where 96% of the total volume pumped is for agricultural use [START_REF] Ouassissou | Rivalités et arrangements coopératifs pour l'accès à l'eau souterraine dans la plaine de Berrechid au Maroc[END_REF]. For many years, this aquifer has been the subject of many geological and hydrogeological studies [START_REF] Hazan | Notice hydrogéologique de la plaine de Berrechid[END_REF][START_REF] Ruhard | Chaouia et la plaine de Berrechid (Tome 1)[END_REF][START_REF] El Mansouri | Structure et modélisation quantitative de l'aquifère de Berrechid (Maroc) : Validation par l'approche géostatistique[END_REF]. Berrechid Plain takes the form of a subsidence basin in which Triassic, Cretaceous, Pliocene and Quaternary geologic formations have been deposited on the Paleozoic basement [START_REF] Hazan | Notice hydrogéologique de la plaine de Berrechid[END_REF]. The aquifer is supplied mainly by lateral flows from the Phosphate Plateau in the southern part of the basin, mainly Boumoussa, Tamedrost, Mazer and El Himmer (27 km length) wadies (Fig. 1) and by direct infiltration from rainfall and the return of irrigation flow [START_REF] Eldridge | Geochemical and isotopic characterization of groundwater and identification of hydrogeochemical processes in the Berrechid aquifer of central Morocco[END_REF].

Fig.1

The surface deposits in the study area are generally dominated by aggregates topped with silty red clay, gravel and cobble [START_REF] El Mansouri | Structure et modélisation quantitative de l'aquifère de Berrechid (Maroc) : Validation par l'approche géostatistique[END_REF]. In the southern section of the aquifer, El Himmer wadi has been equipped since 2008 by a managed aquifer recharge (MAR) system: two percolation tanks (S1 and S3), which retard flood water to facilitate infiltration of the underlying aquifer during runoff, as well as two recharge releases (S2 and S4), which are used to retain dam's releases inducing slow drainage of water into the streambed to ameliorate the infiltration rate (Cf. Fig. 1; photos a and b). Note that outside the rainy period and dam's releases, El Himmer wadi remains dry. After more than ten years of use and despite some curing operations carried out by the authorities to remove sediments carried by the flows, a high volume of fine soils transported by flows each year settles along the wadi, particularly in percolation basins, thereby limiting groundwater recharge.

Rainfall

The daily rainfall time series, provided by ABHBC, covering a period of eight months (from August, 2018 to March 2019) is depicted in Fig. 2. Rainfall data was collected from El Mers climate station (x=320,050 m; y=279,150 m) located at 10 km from the study area (Cf.

Fig. 1). The observation of the daily rainfall histogram (Fig. 2) distinguishes two typical periods: one was from October to November with 151.8 mm, and another was relatively dry between December and January with rainfall about 25.4 mm. During the study period (from October 20 th , 2018 to January 19 th , 2019), the total rainfall was less than 122.6 mm, with an average of 1.34 mm/day. The mean daily temperature was around 18°C (Fig. 2).

Field investigations

As mentioned above, the objective of this study was to assess the physical clogging in MAR sites (S1, S2, S3, and S4) located along the El Himmer Wadi (Fig. 1). To achieve this objective, at each studied site and over an area of 750 m² (15*50), pickets and sand-filled columns were implanted in different positions (Fig. 3c). The implantation of these pickets and columns was done on October 20th, 2018. More than 60 pickets have been implanted. The top of each picket remained uncovered by 10 cm, which makes it possible to measure the thickness of the deposits after 91 days of exposure to hydro-meteorological conditions (until January 19th, 2019). The implanted PVC columns were 7.5 cm in inner diameter and 30 cm in length. The sand filling the columns was sieved and cleaned to remove all organic matter and fine particles attached to the grains. The grain-size distribution of the sieved sand ranged from 140 to 1,200 µm, with a mean diameter of 520 μm and a uniformity coefficient of 2.1. The average porosity and saturated hydraulic conductivity of the sand filling columns were 0.38 (±0.01) and k =2.2×10 -3 m/s (± 2×10 -4 ), respectively. A total of 24 columns were buried (Figs. 3b andc) in the four recharge sites. The top of each column was on the same level of the wadi bed. The positions of the pickets and the columns were recorded by GPS. After 91 days of exposure to natural conditions of the field (from October 20, 2018 to January 19 th , 2019), 12 columns and 43 pickets were recovered successfully, while the others were found damaged. Notice that all implanted columns and pickets in site S4 were damaged. The columns were dig up and carefully transported to the laboratory for treatment and analysed.

Each column was divided into 1 cm layers. For each layer, the quantity of fine particles retained was determined by washing, drying and weighing [START_REF] Alem | Filtration of kaolinite particles in a saturated porous medium: hydrodynamic effects[END_REF]. The particles deposition profile along the length of each column was determined. The deposited particles collected from sand during the washing process were stored in vials for granulometric analysis in order to determine the particle size distribution, using a laser diffraction particle size analyser.

Fig.3

In this study, saturated hydraulic conductivity measurements were performed in recharge sites using the double-ring infiltrometer test (NF X 30-418, 2012). It's a classic method that is widely used [START_REF] Sidiras | Infiltration measurements with double-ring infiltrometers and a rainfall simulator under different surface conditions on an Oxisol[END_REF][START_REF] Archie | A method for automating data collection from a double-ring infiltrometer under falling head conditions[END_REF][START_REF] Fatehnia | Automating double ring infiltrometer with an Arduino microcontroller[END_REF]. Thus, 30 measurements were carried out. It should be noted that, as shown in Fig. 4a, the soil surface constituting the first centimetres (from 5 to 10 cm depth) of the wadi bed is completely cracked. That is why during field measurements, and to prevent preferential flow paths, the part of the cracked soil is completely cleared. Thus, the soil surface hydraulic conductivity was measured at a depth between 5 and 10 cm. It is assumed that, at these depths, the hydraulic conductivity measured is that of the older deposits induced by the dam's release and/or rainfall. There were 30 other measurements that were made in the same positions, by digging holes around 100 cm in depth, in order to evaluate the water infiltration in the subsurface without surface deposits. As shown in Fig. 4b, even at depths beyond 50 cm, cracks persist. In addition, 30 turbid water samples were taken from the retained water in percolation tanks S1 and S3 for measuring their suspended solids concentrations.

Fig.4 1.4. Laboratory investigations

Laboratory analyses were performed on samples collected in the field. Among the analyses carried out were i) measurement of the saturated hydraulic conductivity of the layers formed on soil surface (cake) using a triaxial permeameter according to ASTM D5084-10 (2010);

ii) percentage of organic matter (OM) in the cake. To evaluate this, the loss-on-ignition (LOI) method was used. The LOI method consists of a known soil mass being placed in a ceramic crucible (≤10g), which is then heated at 440°C overnight (ASTM D2974-14, 2014). Then they are cooled in a desiccator and weighed. The OM content is determined as the difference between the initial mass and the final mass of the sample divided by the initial mass of the sample multiplied by 100%. A dozen of samples were tested;

iii) particle size distribution (PSD) of the deposited particles in the surface and subsurface (columns depth); the PSD is measured using laser granulometer (Mastersizer, 2000); iv) Atterberg limits. The liquid limit wL and plastic limit wP of the soil covering the surface of the recharge sites, before and after the studied period, were measured according to NF EN ISO 17892-12 (E), 2018 and v) mineralogical characterisation of the deposited particles using X-ray diffraction (XRD). XRD was performed on a PANalytical X'Pert powder diffractometer equipped with a CoKα anode (λ = 1.7903 Å) powered at 40 kV and 40 mA.

The detector was a linear PIXcel 1D detector equipped with 0.04 rad Soller slits. A powder scan was performed on a sample that was back-loaded in a specific sample holder.

Programmable anti-scatter slits had a fixed aperture of 1/2°, whereas the anti-diffusion slits had an aperture of 1°. A 15 mm mask was selected. The scans were performed in the 5-100° range in steps of 0.0131° (399 s/step). The samples were also continually rotated at 8 sec/turn in order to minimise preferred orientation. In order to characterise the clay fraction, oriented mounts were also prepared from the supernatant of a clay/ultrapure water fraction. The supernatant was dropped on microscope glass slides and allowed to dry. These mounts were then measured by XRD as prepared, after exposure to ethylene glycol or after heating to 550°C for 5 h in a furnace. Measurements were performed in duplicates. The weight fractions were estimated using the Relative Intensity Ratio (RIR) method implemented in software PANalytical high score (v.3.0.5).

Hydraulic conductivity estimation

To display the clogging of the sand filled columns, the saturated hydraulic conductivity drop as a consequence of the particles deposition is estimated on the basis of the Kozeny-Carman equation as follows:

= ∅ ∅ ∅ ∅ 0 (1)
k0 and k are the initial and reduced hydraulic conductivity values, respectively. S0 and S are the specific surface area of the clean sand and the clogged sand, respectively. T0 and T are, respectively, the tortuosity of the clean and clogged sand.

The specific surface area S of the clogged sand is estimated as follows [START_REF] Alem | Filtration of kaolinite particles in a saturated porous medium: hydrodynamic effects[END_REF]:

= ∅ 1 -∅ + 1 -∅ (2)
ϕd, ρp and Sp are the porosity, the particles specific density and the specific surface area of the deposited particles. σ is the retention defined as the volume of deposited particles per unit of porous-medium volume. The deposit porosity ϕd is derived from the average density of deposited particles as follows [START_REF] Boller | Particle characteristics and headloss increase in granular media filtration[END_REF]:

∅ = 1 -= 1 - + !1 -" # $ % (3)
ρd is the average deposit density, ρw is the fluid density, N is the number of particles in a deposit layer and a and b are constants, taken as equal to 1 and 1.3, respectively.

& = '∅ (4)
where F= ϕ -m is the formation factor [START_REF] Archie | A method for automating data collection from a double-ring infiltrometer under falling head conditions[END_REF] given empirically as a function of porosity, with m=1.3 for a sandy medium.

Results and Discussion

Assessment of columns clogging

Subsurface clogging

At the end of the study period (91 days), the implanted columns were recovered (January 19, 2019). The results observed accumulation of fine particles in all columns filled sand. As mentioned above (Section 1.3), each column was divided into 1 cm layers in order to determine the mass of the particles deposited as a function of depth. Clogging that occurred in columns could be divided into two types: superficial and internal clogging. The superficial (surface) deposit (cake) on each column is discussed below in section 2.1.2.

Fig. 5a shows the particles deposition profiles in three columns (C1, C2 and C5) implanted in recharge site S1. For clarity, only three profiles are represented for this site (S1).

Profiles illustrate that the amount of infiltrated particles is important in the column inlet and decreases with depth. It means that suspended particles were trapped largely in the nearsurface layer that corresponds to the first 3 cm thick (internal clogging). In the study presented by [START_REF] Page | Determining treatment requirements for turbid river water to avoid clogging of aquifer storage and recovery wells in siliceous alluvium[END_REF], a similar result was obtained. They showed that clogging was concentrated in the top 3 cm of the columns.

Table 1 summarises the masses of the deposited particles in the first 3 centimetres and those in the rest of the columns (from 3 to 30 cm). The average masses of the retained particles in the first 3 cm thick layer of the columns implanted in sites S1, S2 and S3 equal 21 g, 15 g and 9g, respectively. Beyond 3 cm depth, the amount of retained particles (by sand) ranges between 0 to 3 g/cm (Fig. 5a). It can be seen that the deposits in the first 3 centimetres can reach over 30% of the total deposit measured in the columns.

Table 1

The damage to the porous medium, after 91 days of exposure to hydro-meteorological conditions, as a result of particle deposition, was assessed by observing declines in either the porosity or the hydraulic conductivity. Knowing the mass of the deposited particles in each layer, the current porosity ϕ of the porous medium (sand + deposited particles) was estimated.

Porosity variation of the porous medium as a consequence of the particles deposition is depicted in Fig. 5b, c andd. ϕ0 is the initial porosity of the clean sand (ϕ0=0.38). The results

show that the porosity declines, on average, by 10 to 30% in the first 3 centimetres from the top of the sand filled columns. Beyond this depth, the decrease in porosity varies between 2 and 8%. The results plotted in Fig. 6 show variation of (k/k0) predicted by equation (1) as a function of the columns depth. For clarity, only three profiles are presented. Fig. 6 shows clearly that the damage is not uniform in the sand-filled columns. Damage is important at the inlet to the column and decreases with depth. In the first centimetres of the sand-filled columns, k/k0 reduced drastically, which is owed to the high amount of deposited particles in the entrance of the columns and clogged up pores. This reduction can exceed 95% in the immediate entrance of the columns. Beyond the first 10 centimetres, hydraulic conductivity reduction varies between 10 and 40%. The same order of magnitude of hydraulic conductivity reduction has been observed by [START_REF] Pavelic | Laboratory assessment of factors affecting soil clogging of soil aquifer treatment systems[END_REF]. They showed that physical clogging was more significant than other forms of clogging and that the relative hydraulic conductivity (k/k0) declined to around 90% in some columns.

Surface clogging

Surface clogging (or external clogging) occurs when the suspended particles with size larger than the pore diameters are intercepted in the surface. On the surface of the columns implanted in the wadi bed, a layer due the particles deposition was developed. The measurement of the solid particles concentration was done in the Percolation tanks (S1 and S3) for the turbid water before it cross the embankment were ranged from 1.1 to 1.4 g/L.

The thickness and the mass of the deposited particles (cake) on surface of each column are presented in Table 2. The thickness of the cake formed above each column filled with sand ranged from 0 to 7 cm. Indeed, an average cake thickness of 2.2 cm can be retained.

Notice that when the thicknesses of the formed cake were measured, their average water content was about 29%. The results show that the cake thickness depends on the position of the implanted columns. Thus, columns C1, C6, C7 and C10, implanted near the embankments facilities, receive a high deposit volume, caused by embankments-break flows charged by suspended particles.

Table 2

This important deposit generates a total clogging of the implanted columns. As shown above (section 2.1.1), the deposition in the first 3 centimetres of the sand-filled columns drastically reduces its hydraulic conductivity (a drop more than 50%, on average, was measured). Thus, one can assume that the cake completely controls the hydraulic conductivity of the sand, which can be considered as totally clogged.

Characterisation of the cake's particles

In this section, the percentage of organic matter (OM) and the mineralogical characterisation of the particles constituting the cake formed on the surface are presented.

Results indicate an average percentage of OM around 3%. Thus, it can be considered that the amount of total organic carbon in the total mass analysed is low.

Analysis of cake particles by X-ray diffraction (XRD) was used to achieve two main objectives: i) obtaining a general idea of the mineralogical composition of the particles constituting the cake and ii) evaluating the presence of certain clay minerals, which are highly reactive in the presence of water, such as smectite and montmorillonite. Their clogging potential is prejudicial for water infiltration [START_REF] Mays | Hydrodynamic and Chemical Factors in Clogging by Montmorillonite in Porous Media[END_REF].

The results are shown in Fig. 7. The sample contained several minerals including quartz (50%), calcite (20%) and dolomite (10%). The remaining sample fraction was attributed to the presence of various clays, namely vermiculite, an interstratified illitevermiculite and two kaolinite polytypes (halloysite 7Å and dickite). The halloysite:dickite ratio was estimated using the RIR method at 15:2. It is noted that the results show the absence of smectite and montmorillonite, two clay minerals that swell quickly in the presence of water, leading to a rapid clogging of the pores. The PSD of the retained particles in columns show a very slight differences in the particle size distribution as a function of the depth. However, there is a slight tendency towards decreasing the size of the particles retained with the depth. 90% of particles that infiltrated the sand-filled columns were less than 25 µm. An average median diameter around 6 µm was measured (Table 3).

The PSD of the particles constituting the cake (surface deposits) indicate a wider distribution up to 600 μm. The PSD presented in Fig. 8 is representative of all that measured for the different analysed samples. The average median diametre measured for the particles retained in surface was 25 µm. Also, as indicated in Table 3, more than 34% of the particles constituting the cake are greater than 63 µm. More than 50% of the particles deposited on MAR surface ranged between 30 and 400 μm. These results confirm what was expected, i.e.

the largest particles are mainly retained at the columns' surfaces.

In this study, among the mechanism involved in the retention of the suspended particles in the subsurface, straining dominates; however, on the surface, straining and sedimentation are the two mechanisms that affect particle retention.

Straining of the particles in porous media depends on the ratio of dp50/dg50, where dp50

is the median diameter of the suspended particles and dg50 is the median diameter of the grains constituting the porous medium. As reported by [START_REF] Bradford | Modeling Colloid Attachment, Straining, and Exclusion in Saturated Porous Media[END_REF], straining occurs when the dp50/dg50 ratio is greater than approximately 0.005. The median grain diameter of the used sand in this study was dg50 = 520 µm, and the median diameter of suspended particles infiltrated in the sand filled columns was dp50 = 6 µm (Table 3). The ratio of dp50/dg50 equals 0.011, which leads to significant particles retention by strainning in sand.

As discussed above, for surface deposition, larger particles were retained, and then the ratio of dp50/dg50 equalled 0.048. Retention of larger particles by straining in the surface of the sand has actively participated in the filtration of particles of all sizes, including the finest, thus preventing their transport in deep, favouring surface clogging.

These results clearly show the extent of the low rainfall (during 91 days) to promote the mobilisation and transport of suspended particles carried by runoffs. They reveal that despite the high grain size distribution of the sand used, unlike the natural soil of the recharge sites, there is a significant clogging on the surface.

Fig.8

Table 3 2.2. Assessment of sites clogging

Distribution of surface clogging on the studied sites

To quantify the thickness of the deposited particles on natural soil of the wadi bed, many pickets were placed at different positions of the recharge sites over a large area (~750 m²). As shown in Fig. 9, deposits accumulation varied significantly according to the distance to the embankment. Investigations undertaken over 91 days indicate that, even with the low rainfall, the thickness of the accumulated deposits is important and ranges between 0 and 12 cm, with an average of 2.5 cm. For site S1, the accumulated deposit reaches thicknesses greater than 2 cm, at a distance of 40 metres from the embankment. However, this thickness is reached in site S3 at a distance of 20 m from the embankment. This observation can be justified by the position of the recharge sites; thus, site S1, which is upstream of sites S2 and S3, retains more particles transported by the flows. Also, many factors can affect the cake thickness such as wadi bed topography, presence of surface preferential flow and vegetation density. In some picket positions, the cake thickness reached up to 6 cm (Fig. 9b), which is owed to topographical depressions (bowl-shaped) where a significant volume of water stagnates and favours more particles deposition. In contrast, suspended particles deposition was distributed fairly evenly throughout site S1 (Fig. 9a), except on the right bank where more deposits were observed. Among possible interpretation of the latter observation, the lack of vegetation on the right bank favoured surface erosion from the bank during rainfall. As a consequence, high accumulations were observed compared to the left bank which is covered with vegetation.

Note that it has been observed that some large cracks (aperture of 3 or 4 cm) do not close completely even if after several days of rain accompanying high water level (20 to 30 cm) in the recharge site. However, their depth has decreased, which is owed to the suspended particles deposition.

Fig. 9

Hydraulic conductivity

In this part, we discuss the hydraulic conductivity of the soil that controls the water infiltration from the recharge sites surface to the subsurface soil and therefore to the aquifer.

For this purpose, as discussed above, in situ saturated hydraulic conductivity measurements at the surface and subsurface (around 100 cm depth) have been carried out using the double rings infiltrometer (Cf. section 1.3).

For all sites and for surface and subsurface measurements, saturated hydraulic conductivity varies from 8.33×10 -5 to 1.67 ×10 -6 , with an average value of 4.25×10 -5 m/s. For example, in site S3, an average value of 3×10 -5 (±2×10 -6 ) m/s and 6×10 -5 (±3×10 -6 ) were obtained for k measurements in the surface and subsurface, respectively. These measured k values are low for silty-clayey soil but can be explained by the presence of micro cracks. As discussed above (section 1.3), cracks exist in the surface and the subsurface (Fig. 4) of the tested soils, and their presence increases water infiltration rate.

The measurement of the hydraulic conductivity of the cake represents a main element for assessing clogging. To evaluate the hydraulic conductivity of the formed cake without cracks, measurements were made on cake samples taken after the 91 days investigation, either on the columns surfaces or around the pickets. Hydraulic conductivity of the cake was determined by using a triaxial permeameter system. An example of measurements of the hydraulic conductivity of the cake, under different confining pressure ranging from the greatest pressure (300 kPa) to the smallest (20 kPa), is presented in Fig. 10. The hydraulic conductivity of the cake under zero confining pressure is obtained by extrapolation of the curve (Fig. 10), and an average value of 4×10 -8 m/s was retained.

Fig.10

Clayey soils tend to crack when drying [START_REF] Morris | Cracking in drying soils[END_REF]. The resulting cracking causes crucial problems in geo-environmental engineering and dramatically affects hydraulic conductivity [START_REF] Peron | Fundamentals of desiccation cracking of finegrained soils: experimental characterisation and mechanisms identification[END_REF]. Silty-clayey soil of El Himmer wadi bed has been submitted

to several wetting and drying (W-D) cycles due to seasonal variations, including temperatures and rainfall. As a result of soil desiccation, cracks are created at the surface and in depth (Cf.

Fig. 4). As mentioned above, the measured hydraulic conductivity in laboratory by triaxial permeameter is in the range of 10 -8 m/s. However, measurements undertaken in the field using the double rings infiltrometer revealed a hydraulic conductivity that varies between 10 -5 and 10 -6 m/s. The ratio between the hydraulic conductivity measured in field and that obtained in laboratory (kfield/klab) can reach 10 3 . Despite the difference between the two techniques of measurement and the difference in observation scale, the difference between the measured values in laboratory and in the field remains significant. It is very low for non-cracked samples and very high for cracked soils. Based on the experimental studies in laboratory, several studies have been conducted on the effect of a cracks network on hydraulic conductivity in clayey soil. [START_REF] Louati | Impact of wetting-drying cycles and cracks on the permeability of compacted clayey soil[END_REF] showed that after three W-D cycles and for all tested samples with different initial densities, the hydraulic conductivity increased in the presence of cracks. [START_REF] Lu | Heat Transport and Water Permeability during Cracking of the Landfill Compacted Clay Cover[END_REF] also concluded that after a four W-D cycles; the conductivity increased from 8.3×10 -9 to 1.5× 10 -7 m/s for compacted clay.

However, as reported by [START_REF] Rayhani | Physical modeling of desiccation cracking in plastic soils[END_REF], during the periods of rainfall (wetting cycles) that follow periods of evaporation (drying cycles), water fills cracked soil. The hydrostatic forces increased, and the water is slowly absorbed by the clay. The effect of the absorption is to increase the unit weight of the clay as well as to reduce the unit weight of its shear strength. As a result of these processes, the driving forces (sliding) increase at the same time as the resistance forces (shear strength) decrease. During water filling, cracks tend to disappear and hydraulic conductivity decreases. This process can be carried out rapidly in clayey soil with high plasticity index [START_REF] Rayhani | Physical modeling of desiccation cracking in plastic soils[END_REF]. This phenomenon is known as the "self-healing".

In this study, before and after the studied period, the liquid limit wL and plastic limit wP of the soil covering the surface of the recharge sites were measured. The obtained results

indicate that wL = 66% and wP = 32%. Thus, the plasticity index Ip equals 34%.

After water infiltration in the studied sites, a slight reduction of the cracks opening in some locations was observed, which can be attributed to the self-healing due to the high plasticity index of the silty-clayey soil. In other locations, the cracks were filled entirely or partially by the particles transported by flows. Indeed, in the periods of high precipitations and, therefore, with a large contribution to the suspended particles deposition (sediment supply) in the recharge sites, deposits that form the cake could reduce the saturated hydraulic conductivity by 1,000 orders of magnitude in comparison to those measured during dry period. Thus, the hydraulic conductivity reduction generates less infiltration towards the subsurface, which is owed to evaporation.

Recommendations for monitoring clogging sites

Various factors can reduce infiltration rates in recharge sites. Physical clogging, predominantly related to a filter cake forming, is usually the most important factor.

Management approaches were developed to reduce clogging effects and renovate recharge rates. To manage site clogging, recommendations exist such as deposits removal and scraping [START_REF] Mousavi | Evaluation of scraping treatments to restore initial infiltration capacity of three artificial recharge projects in central Iran[END_REF][START_REF] Gale | Strategies for Managed Aquifer Recharge (MAR) in Semiarid Areas[END_REF], use of gravel filters [START_REF] Hatt | Treatment performance of gravel filter media: implications for design and application of stormwater infiltration systems[END_REF] and vegetation cultivation [START_REF] Woo | The role of vegetation in the retardation of rill erosion[END_REF][START_REF] Gonzalez-Merchan | Influence of spontaneous vegetation in stormwater infiltration system clogging[END_REF][START_REF] Al-Maktoumi | Experimental study of clogging of subsurface pores in the vicinity of dams in arid zones: groundwater recharge efficiency and potential solution[END_REF].

To extend bed life of recharge sites in wadi El Himmer, there are three recommendations: i) a regular scraping of clogged layers. Due to the cake thickness measured in this study, it is thought that at least one scraping per year is necessary for a depth of 10 to 20 cm. The scraping technique must be recurrent as long as these sites are exploitable. ii) The second recommendation, with lasting effects, is planting shrubs in the upstream of MAR sites and on the wadi banks, which could reduce fine particles transport and their deposition in MAR sites. Also, as discussed above, as infiltration is controlled by cracks [START_REF] Römkens | Rain infiltration into swelling/shrinking/cracking soils[END_REF][START_REF] Dunkerley | Bank permeability in an Australian ephemeral dry-land stream: variation with stage resulting from mud deposition and sediment clogging[END_REF][START_REF] Greve | Investigations of soil cracking and preferential flow in a weighing lysimeter filled with cracking clay soil[END_REF], the reduction of particles contribution towards these sites will make it possible to exploit the presence of theses cracks systems to maximise recharge. This last technique (vegetation) would reduce the number of scraping intervention on the sites. Thus, it is thought that the cultivation of the Stipa tenacissima upstream of the MAR sits can be a good solution. As reported by [START_REF] Eldridge | Geochemical and isotopic characterization of groundwater and identification of hydrogeochemical processes in the Berrechid aquifer of central Morocco[END_REF], the shrub Stipa tenacissima can enhance the sorptivity and infiltration 2-3 times higher than in intact on soil crusts. In addition, this shrub is adapted to the silty soil and to arid and semi-arid climates [START_REF] Ghiloufi | Assessment of species diversity and state of Stipa tenacissima steppes[END_REF], which makes it suitable for cultivation in an environment characterised by increasing degradation of water resources (Ramı´rez et al., 2007). Cultivation of the shrub Stipa tenacissima in wadi El Himmer represents a hydro-ecological solution; it is clean, less expensive and more efficient for limiting particles transfer and renovating infiltration through the wadi bed. iii) The third recommendation consists of the construction of a settling basin upstream of the recharge sites, supplied by rainwater during floods and dam releases; this may be useful for reducing flow rates and the sedimentation rate of downstream recharge sites.

Therefore, an experimental model should be developed even before the construction of the recharge facilities, in order to predict or estimate the impact of clogging in MAR sites.

Moreover, the data generated by the model can be easily integrated into the cost-benefit ratio of the models, making it possible to predict the most cost-effective cleaning strategies [START_REF] Phipps | Development of a percolation decay model to guide future optimization of surface water recharge basins[END_REF], in order to improve the percolation efficiency of the MAR and minimise the operating costs.

Conclusions

This study was undertaken to investigate the extent of clogging in Managed Aquifer Recharge (MAR) sites in wadi El Himmer (Berrechid, Morocco) over 91 days. To evaluate the in situ clogging, sand-filled columns and pickets were implanted in the wadi bed. Results

indicate that, although the low rainfall during the studied period, clogging that occurred in wadi bed is significant. The thickness of the deposited particles forming a cake (surface clogging) is important and drastically reduces the hydraulic conductivity of the wadi bed soil.

A 1,000 order of magnitude can be reached during the wetting cycles when the cake formed is cracks free. The obtained results from the columns show damage to the sand medium that is owed to surface and subsurface clogging. The main mechanism involved in the sand clogging, either in the surface or subsurface, is straining. Because of the large particle size distribution of the particles carried by the flow, more than 50% of the particles deposited on MAR surface ranged between 30 and 400 μm. Hydraulic conductivities measured in situ during the drying period are in the order of 10 -5 m/s and are affected by the presence of cracks that promote infiltration. However, due to the high plasticity index of the MAR soil, a slight reduction of the cracks opening during wetting cycles is observed. In addition, contribution of fine particles deposited in these cracks would participate actively in the reduction of hydraulic conductivity.

Despite the low rainfall (an average of 1.34 mm/day) and the short period (91 days) of this investigation, MAR sites clogging is effective; the thickness of the deposits exceeds 3 cm in a large part of the MAR. However, a long-term study is necessary to more precisely evaluate the role of cracks under cyclic drying and wetting.

Fig. 2

 2 Fig.2

  Fig.5

  Fig.7

FIGURES

  FIGURES

Fig. 1 .

 1 Fig.1. The study sites (S1, S2, S3, and S4) are located along the El Himmer Wadi. Inset photos indicate a (A) Percolation Tank and (B) a Recharge releases located at the studied sites (S1 and S2)

Fig. 5 .

 5 Fig.5. (a) Mass of the retained particles in the sand filled columns C1, C2, and C5 implanted in site S1. Profiles of porosity decline of the clogged sand filled columns implanted in sites (b) S1, (c) S2, and (d) S3

Table 1 .

 1 Mass of deposits in sand filled columns in the first 3 cm and between 3 and 30 cm depth

	Tables

Table 3 .

 3 Size of the particles retained in depth and in surface (cake)

		(≤ 63 µm) (%)	(> 63 µm)(%)	dP10 (µm)	dP50 (µm)	dP90 (µm)
	Particles retained in surface	66.0	34.0	2.1	24.7	409.0
	Particles retained in depth	100.0	0.0	1.5	6.0	25.0

Acknowledgements

This study is supported by PHC TOUBKAL project (18/74): Campus France N° 38951NJ.

The authors wish to thank the Bouregregreg and Chaouia Hydraulic Basin Agency (ABHBC) for the providing the climate data.


Dr Marie-Christine Rousseau
email: marie-christine.rousseau@ssl.aphp.fr

Karine Baumstarck

Sherezad Khaldi-Cherif

Thierry Billette De Villemeur

Nafissa Khaldi-Cherif

Agnés Felce

Maria Valkov

Catherine Brisse

Anderson Loundou

Pascal Auquier

Agnès Felce

Tanguy Leroy

Souhali Haddadou

Cécile Freihuber

Sofiane Amalou

Julie Bonheur

Stéphanie Valence

Marie-Christine Nougues

Laurent Luciani

Jean-Pierre Nouet

Catherine Coiffier

Philippe Sellier

P Julien

J C Grasset

S Delvert

A Belorgey

; Hasni

Si Abdelkader

Sophie Mathieu

Ustafa Ardati

; Kammache

Delphine Héron

Arnaud Isapof

Alexandra Afenjar

K Maincent

Diana Rodriguez

Diana Doummar

Marie- Laure Moutard

Daniel Willocq

Julie Teulade

; Stéphane

Stéphane Lenormand

Etorre Laracca

Valérie Aynie

Elizabeth Grimont

Health issues in polyhandicapped patients according to age: Results of a large French cross-sectional study

Keywords: Health status, polyhandicap, disability, comorbidity, mental retardation

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Polyhandicap (PLH), as a recently defined French concept [START_REF] Rousseau | Adequacy of care management of patients with polyhandicap in the French health system: A study of 782 patients[END_REF][START_REF] Rousseau | Le parcours de santé de la personne en situation de polyhandicap[END_REF][START_REF] Rousseau | Impact of caring for patients with severe and complex disabilities on health care workers' quality of life: determinants and specificities[END_REF], the PLH concept refers to a complex disability condition corresponding to a chronic affliction occurring in an immature brain, leading to the combination of severe/profound mental retardation and serious motor deficit, resulting in an extreme restriction of autonomy and communication. This term is close to the notion of profound intellectual and multiple disabilities, which is used in other countries, and does not systematically refer to a disorder affecting an immature brain. Polyhandicap is a syndromic entity and meets several progressive and non-progressive etiologies. The scarce data available in France enable an estimation of the prevalence of polyhandicap as between 0.7 and 1.3 per thousand, i.e. [START_REF] Rumeau-Rouquette | Definition and prevalence of school-age multi-handicaps[END_REF]. Due to the combination of severe motor deficit and profound mental retardation, the patients, completely dependent on human and technical aid, develop with aging, various comorbidities and -impairments [START_REF] De Villemeur | Comment la loi Leonetti s'applique t'elle à l'enfant polyhandicapé?[END_REF], which can lead to premature death [START_REF] Rousseau | Aetiologies, comorbidities and causes of death in a population of 133 patients with polyhandicaps cared for at specialist rehabilitation centres[END_REF]. Few data examined the evolution of the health status, kinetic occurrence of comorbidities/impairments, and adaptation of care management during the life of the individual, including childhood, adolescence, and adulthood. However, it allows a better understanding of the natural course of life of these patients and consequently optimizing the preventive and curative care management strategies.

Previous studies concerning the description of the health status of patients with polyhandicap have some limitations: performed on a small-and intermediate-sized sample (less than 200 patients), including heterogeneous samples (mixture of severe and less severe patients, such as cerebral palsy and intellectual disability patients), restricting younger children, based on retrospective design, and focusing on very specific issues (such as sensory perception, respiratory disorders, digestive disorders, etc.) [START_REF] Vlaskamp | Reliability of assessing the sensory perception of children with profound intellectual and multiple disabilities: a case study[END_REF][START_REF] Yoshikawa | Acute respiratory distress syndrome in children with severe motor and intellectual disabilities[END_REF][START_REF] Idaira | Factors affecting the oral condition of patients with severe motor and intellectual disabilities[END_REF][START_REF] Calis | Dysphagia in children with severe generalized cerebral palsy and intellectual disability[END_REF][START_REF] Lee | Long-term percutaneous endoscopic gastrostomy feeding in young adults with multiple disabilities[END_REF][START_REF] Poppes | Frequency and severity of challenging behaviour in people with profound intellectual and multiple disabilities[END_REF][START_REF] Ohtsuka | Pathological study of bronchospasms/tracheomalasia in patients with severe motor and intellectual disabilities[END_REF][START_REF] Veugelers | Prevalence and clinical presentation of constipation in children with severe generalized cerebral palsy[END_REF][START_REF] Yoshikawa | The difficulties of diagnosing VPA-induced pancreatitis in children with severe motor and intellectual disabilities[END_REF]. For the first time, we reported from a large sample of young polyhandicapped patients aged 3 to 25 years, according to the age-related developmental periods of the children (early childhood 3 to 5, childhood 6 to 11, adolescence 12 to 17, and early adulthood 18 to 25 years old): i) the description of their health status (including severity, comorbidities and impairments, neurodevelopmental status) and ii) the description of the devices and the rehabilitation procedures they benefit.

Methods

Design and settings

This

General organization of the PLH cohort

The French national PLH cohort was implemented in various French centers spread over different territories: specialized rehabilitation centers, residential facility, and a university hospital center (Paris, France). The general aim of the cohort was to identify the effect of (socioeconomic, environmental, epidemiologic) determinants on the health status of the patients and the daily life of their (natural and institutional) caregivers (clinical trial registration number NCT02400528). Three different populations were eligible: i. Patients with polyhandicap; ii. Familial referents of the included patients (French legal mention for this type of patients, represented by parents in the majority of cases); and iii. Institutional health care workers of the included patients. The present study focused on patients.

Selection criteria

The patient selection criteria were as follows: aged from 3 to 25 years; with a polyhandicap defined by the combination of motor deficiency (quadriplegia, hemiparesis as a predominant hemibody motor impairment, diplegia, extra pyramidal syndrome, cerebellar syndrome, and/or neuromuscular problems) and severe/profound mental impairment (intelligence quotient <40; for patients older than 5 years old: IQ= developmental age below 2 years old; for children from 3 to 5 years old: IQ= developmental quotient<40%) associated with everyday life dependence (Functional Independence Measure <55), and restricted mobility (Gross Motor Function Scale (GMFCS and GMFCS-ER), III, IV and V [START_REF] Palisano | Development and reliability of a system to classify gross motor function in children with cerebral palsy[END_REF]); age at onset of cerebral lesion below 3 years old. A written parental / legal guardian consent form was obtained for each participant.

Data collection

Data were collected from medical records obtained by a dedicated clinical research assistant and was supported by the referent physician of the patient (a referent physician is designated for each patient). The data included the following items:

1) Socio demographic data: age category based on age at inclusion (4 age classes were defined in accordance with the age-related development periods of children [START_REF] Rousseau | Impact of caring for patients with severe and complex disabilities on health care workers' quality of life: determinants and specificities[END_REF][START_REF] Rumeau-Rouquette | Definition and prevalence of school-age multi-handicaps[END_REF][START_REF] De Villemeur | Comment la loi Leonetti s'applique t'elle à l'enfant polyhandicapé?[END_REF], [START_REF] Rousseau | Aetiologies, comorbidities and causes of death in a population of 133 patients with polyhandicaps cared for at specialist rehabilitation centres[END_REF][START_REF] Vlaskamp | Reliability of assessing the sensory perception of children with profound intellectual and multiple disabilities: a case study[END_REF][START_REF] Yoshikawa | Acute respiratory distress syndrome in children with severe motor and intellectual disabilities[END_REF][START_REF] Idaira | Factors affecting the oral condition of patients with severe motor and intellectual disabilities[END_REF][START_REF] Calis | Dysphagia in children with severe generalized cerebral palsy and intellectual disability[END_REF][START_REF] Lee | Long-term percutaneous endoscopic gastrostomy feeding in young adults with multiple disabilities[END_REF], [START_REF] Poppes | Frequency and severity of challenging behaviour in people with profound intellectual and multiple disabilities[END_REF][START_REF] Ohtsuka | Pathological study of bronchospasms/tracheomalasia in patients with severe motor and intellectual disabilities[END_REF][START_REF] Veugelers | Prevalence and clinical presentation of constipation in children with severe generalized cerebral palsy[END_REF][START_REF] Yoshikawa | The difficulties of diagnosing VPA-induced pancreatitis in children with severe motor and intellectual disabilities[END_REF][START_REF] Palisano | Development and reliability of a system to classify gross motor function in children with cerebral palsy[END_REF][START_REF] Kurihara | Prognosis in severe motor and intellectual disabilities syndrome complicated by epilepsy[END_REF], [START_REF] Motawaj | Le Décès Des Patients Polyhandicapés: L'expérience Du Service de Pédiatrie Spécialisée Pour Polyhandicapés de La Roche-Guyon[END_REF][START_REF] Srivastava | Clinical whole exome sequencing in child neurology practice[END_REF][START_REF] Germany | Trends in prevalence and characteristics of postneonatal cerebral palsy cases: a European registry-based study[END_REF][START_REF] Nordli | Epileptic encephalopathies in infants and children[END_REF][START_REF] Sasmal | Ocular manifestations in children with cerebral palsy[END_REF][START_REF] Van Den Broek | A Systematic Review of the Literature on Parenting of Young Children with Visual Impairments and the Adaptions for Video-Feedback Intervention to Promote Positive Parenting (VIPP)[END_REF][START_REF] Van Timmeren | Physical health issues in adults with severe or profound intellectual and motor disabilities: a systematic review of crosssectional studies[END_REF][START_REF] Guyard | Family adaptation to cerebral palsy in adolescents: A European multicenter study[END_REF] years, gender, and structure of care management (specialized rehabilitation center, residential facility, at home), 2) Etiologies of polyhandicap: unknown etiology, known etiology (central nervous system malformations, neurometabolic and neurogenetic encephalopathy, epileptic encephalopathy, pre/perinatal and post-natal causes).

3) Health status:

-Global health severity: i. severe for patients who meet all the following criteria: motor handicap (diplegia or quadriplegia and/or extrapyramidal syndrome and/or severe general hypotonia), IQ <25, FIM <=20, and GMFCS IV and V; ii. less severefor patients who do not meet these criteria, -Global health stability: i. unstable for patients who meet at least one of the following criteria: recurrent pulmonary infections (>=5/yrs), drug-resistant epilepsia (>=4 seizures/month); ii. stable for patients who do not meet any of these criteria, -Motor deficiency: quadriplegia, diplegia; movement disorders, severe dystonia, severe hypotonia, extrapyramidal syndrome, ataxia; -Associated handicaps: i) neuro-sensorial handicaps: visual impairment (partial/complete blindness) and hearing impairment (partial/complete deafness); ii) behavioral disorders (including intermittent screaming, and/or agitation and/or stereotypies and/or intermittent crying and/or self-aggressivity and/or hetero-aggressivity), iii) sleep disturbance (short sleep, night wake up, and difficulties falling asleep).

-Co-morbidities: epilepsia (yes/no, previous status epilepticus, drug-resistant disease), orthopedic (scoliosis, limb deformations, limb fractures, hip luxation, previous arthrodesis and/or other previous orthopedic surgery), pulmonary (pulmonary recurrent infections, aspiration syndrome), digestive (fecal impaction, gastro esophageal reflux, and drooling), urinary (recurrent urinary tract infections-at least once a year and urinal retention), cutaneous (bedsores, pressure sore), chronic pain, chronic diseases (at least one of the following diseases: vascular stroke, myocardial infarction, diabetes, and/or cancer), antibiotic resistant bacteria.

-Neurodevelopmental patterns: i. autonomy: seven facets of autonomy were scored by the referent physician from 1 (worse) to 7 (best autonomy/developmental degree) for the following domains: visual contact, oral language, postural ability, grasping ability, moving ability, cleanliness, and feeding ability; ii. general neuro-developmental status was assessed using the Brunet-Lézine scale, a developmental quotient assessment tool available for infants up to 24month old. This developmental quotient cannot be used in patients over 2 years old therefore in the present study, only the 4 developmental domains (language, posture-motor abilities, coordination, and sociability) were used. All scores ranged from 0 to 24 months.

4) Medical devices and rehabilitation procedures management:

-Medical devices: at least one, number, and type (invasive mechanical ventilation, non-invasive mechanical ventilation, tracheotomia, nasogastric tube, gastrostomy, permanent urinary probe, cerebrospinal fluid derivation, and central venous catheter).

-Rehabilitation procedures: bed without orthesis, limb orthesis, verticalization device. first age classes (from 3 to 17 years) while only one-quarter of the individuals aged 18-25 years were unstable.All details are shown in Table 1.

Etiologies

Etiologies of polyhandicap were unknown for 11.5% of the cases. Among the known etiologies, 39% (n=183) of the patients presented central nervous system malformations, 5% (n=25) neurometabolic diseases, 4% (n=19) neurogenetic diseases, 2% (n=10) epileptic encephalopathies, and 163 (34%) patients presented an acquired disease, including pre-perinatal (N=129) and post-natal (N=34) etiologies, and 15% (n=70) other causes. All of the details are provided in Table 2.

Associated impairments

Eighty to 85% of the patients presented quadriplegia. The proportion of movement disorders was lower (12%) for the oldest individuals (18-25 years) compared with the other age classes (16% for the 3 youngest age classes). Severe dystonia was reported for 18% of the youngest age class 3.

Comorbidities

Approximately 60% of the sample, independent of the age class, presented epilepsy. Drug-resistant epilepsy was less frequent for the oldest individuals (18% for the [18-25 y 4.

Neurodevelopmental status:

All autonomy scores were low (1 to 4/7); scores tended to decrease or to be stable in the oldest age classes. From Brunet-Lezine, the developmental level of polyhandicap patients was very low (4 to 7 months) for all domains and patients did not demonstrate any progression with age in none of the four domains of the Brunet-Lézine scale. All details are shown in Figure 1.

Medical devices and rehabilitation procedures:

The proportion of patients with at least one medical device increased with age: 32% for the [3-5 y] class and over 40% for the 3 other age classes. Gastrostomy was the most frequent device that patients needed (30 to 40%). Very few patients required permanent urinary probe, central venous catheter, or tracheotomy. Rehabilitation procedures such as daily installation of patients in sitting device (wheelchair sitting and positioning devices such as contoured seat intended to increase postural stability), limb orthesis (ankle-foot orthesis, or knee ankle-foot orthesis, wrist-hand splint, ..) and daily installation in verticalization devices did not differ across the 4 age classes. All medical devices and rehabilitation procedures are shown in supplemental file.

Discussion

The present study provides for the first time a substantial description of the health status and the care management of a large sample of French young patients with polyhandicap according to four age classes, from 3 to 25 years. This description of the 4 age classes presents interesting proposals of the evolution over time as key elements for health care workers to optimize the preventive and curative care management of these patients.

A higher proportion of the youngest children were managed in home care. It is probable that families succeed in keeping their child at home during the first years of life, even those who presented with severe health status and a higher level of dysautonomy. However, the families were most likely no longer able to take care of them when the child grows or becomes an adult (due to their own aging, psycho-social, and organizational reasons). The instability of health status and the progressive nature of the disease, more frequently reported for patients cared for at home, can result in important difficulties to face in these singular situations at their own home and induce parents and families to orientate the patient, after some years, towards a structure offering continuous medical monitoring.

The proportion of patients with an unknown etiology of the polyhandicap (11.5%) was relatively lower than the proportion provided in previous studies, which ranged from 15 to 60% [START_REF] Kurihara | Prognosis in severe motor and intellectual disabilities syndrome complicated by epilepsy[END_REF][START_REF] Motawaj | Le Décès Des Patients Polyhandicapés: L'expérience Du Service de Pédiatrie Spécialisée Pour Polyhandicapés de La Roche-Guyon[END_REF]. This finding may be partially explained by the fact that we focused on a population including young individuals while other studies included mixed (children and adult) populations. The spreading of etiological investigation and genetic counseling during the last years contribute to the decrease in the part of unknown etiologies [START_REF] Srivastava | Clinical whole exome sequencing in child neurology practice[END_REF]. Nearly 50% of the known etiologies were constitutional diseases (including malformations of the central nervous system and genetic disorders), while acquired etiologies constituted a third of the total cases. The acquired etiologies had more likely prenatal or perinatal origins, as previously highlighted in a European study showing a decline in post-natal cerebral palsy cases [START_REF] Germany | Trends in prevalence and characteristics of postneonatal cerebral palsy cases: a European registry-based study[END_REF]. Approximately 6% of the etiologies were the consequences of rare diseases, as progressive encephalopathies well-known diseases leading to premature death. A (very) low proportion of our patients presented epileptic encephalopathy, a well-known disease with severe cognitive deficiency and difficulty to control the seizures [START_REF] Nordli | Epileptic encephalopathies in infants and children[END_REF]. We are convinced that this proportion was underestimated due to the difficulty to rebuild the entire medical history of these patients since birth.

As an informative finding, we found that the global severity of the patients remains stable over the age classes. This stability over time may be due to the definition of the global severity, which we have based on non-or few-progressive clinical aspects (including motor impairment and/or cognitive deficiency). Developing a severity index comprising both fixed and progressive clinical aspects as comorbidities and associated impairments may better reflect the global severity of the patients.

However, the stability notion varied throughout growth: older age classes were less unstable. In this study, the stability notion was partially based on drug-resistant epilepsy. Two explanations may concur: first, drug-resistant epilepsy is known to be less frequent when the child is growing (particularly for children with epileptic encephalopathy) and second, children with progressive etiologies, such as neurometabolic etiologies frequently associated with resistant epilepsy, usually die before adulthood [START_REF] Nordli | Epileptic encephalopathies in infants and children[END_REF].

Not surprisingly, a large majority of our patients presented a heavy motor impairment (quadriplegia 85%), which is consistent with the pre-defined selection criteria of our cohort. For other neurological impairments, movement disorders, severe dystonia, and global hypotonia were more frequent in younger. Movement disorders and dystonia are often linked to progressive diseases leading to premature death. And it is known that early cerebellar lesions were associated to hypotonia which decreased throughout growth.

Expectedly, sensorial (visual and hearing) deficiencies remained stable throughout aging because the deficiencies directly result from the etiology of polyhandicap. Nevertheless, the proportion of patients presenting visual impairment was lower than in other studies performed on children with intellectual disability and motor impairment, and children with cerebral palsy [START_REF] Sasmal | Ocular manifestations in children with cerebral palsy[END_REF][START_REF] Van Den Broek | A Systematic Review of the Literature on Parenting of Young Children with Visual Impairments and the Adaptions for Video-Feedback Intervention to Promote Positive Parenting (VIPP)[END_REF][START_REF] Van Timmeren | Physical health issues in adults with severe or profound intellectual and motor disabilities: a systematic review of crosssectional studies[END_REF], which can be explained by an under/misdiagnosis of sensorial deficiency due to the very little communication ability of the patients. Systematic detection and diagnosis of these deficiencies may improve the wellbeing of the patients. Similar to cerebral palsy patients, behavioral disorders (40-72%) were very frequent in polyhandicapped children and largely increased during adolescence [START_REF] Guyard | Family adaptation to cerebral palsy in adolescents: A European multicenter study[END_REF]. The presence of noisy behavioral disorders may have an important consequence for the patient, prompting the family to select a non-familial care structure when the patient is growing and aging.

People with severe or profound intellectual and motor disabilities experience multi-comorbidities that complicate health needs [START_REF] Rousseau | Aetiologies, comorbidities and causes of death in a population of 133 patients with polyhandicaps cared for at specialist rehabilitation centres[END_REF][START_REF] Van Timmeren | Physical health issues in adults with severe or profound intellectual and motor disabilities: a systematic review of crosssectional studies[END_REF]. As one of the most frequent comorbidity of polyhandicap, epilepsy (particularly uncontrolled epilepsy) contributes to an increase in brain damage. In our study, epilepsy (55-60%) and drug-resistant epilepsy (18-31%) were a little less frequently reported than in previous studies (70-80% for epilepsy, 66% for drug-resistant epilepsy) [START_REF] Kurihara | Prognosis in severe motor and intellectual disabilities syndrome complicated by epilepsy[END_REF][START_REF] Van Timmeren | Physical health issues in adults with severe or profound intellectual and motor disabilities: a systematic review of crosssectional studies[END_REF][START_REF] Matsumoto | Epilepsy in severe motor and intellectual disabilities syndrome (SMIDS)--a clinical and electroencephalographic study of epileptic syndromes[END_REF], and nearly one quarter of patients already presented previous status epilepticus. The availability of recent antiepileptic drugs, allowing for a better control of epilepsy, may be an explanation. Although the proportion of epilepsies remained stable through the age classes, the proportion of drug-resistant epilepsy was lower for the oldest class, and thus this finding is most likely linked with progressive neurometabolic etiologies before adulthood and frequent stabilization of epilepsy after adolescence.

Not surprisingly, as a consequence of the neurological damage and tone disorders, orthopedic comorbidities were very frequent and increased during growth, in particular during the pubertal period. Detection and taking care of these comorbidities, source of chronic pain and mobility deterioration, may limit their health consequences. Dislocations of the hips and scoliosis associated with thoracic deformity may benefit from curative and preventive measures [START_REF] Saito | Natural history of scoliosis in spastic cerebral palsy[END_REF][START_REF] Majd | Natural history of scoliosis in the institutionalized adult cerebral palsy population[END_REF], such as spasticity treatment, arthrodesis, and reduction of scoliosis before adolescence.

The proportion of recurrent pulmonary infections was around 10-15% over age as a probable consequence of aspiration syndrome (32%) [START_REF] Yoshikawa | Acute respiratory distress syndrome in children with severe motor and intellectual disabilities[END_REF]. The deterioration of the respiratory function probably occurs later due to aggravation of scoliosis and subsequent repeated episodes of pulmonary infections caused by chronic bronchial congestion, associated with aspiration syndrome is the leading cause of death in patients with polyhandicap [START_REF] Rousseau | Aetiologies, comorbidities and causes of death in a population of 133 patients with polyhandicaps cared for at specialist rehabilitation centres[END_REF][START_REF] Hanaoka | Survival prognosis of Japanese with severe motor and intellectual disabilities living in public and private institutions between 1961 and 2003[END_REF][START_REF] Hogg | Policy, service pathways and mortality: a 10-year longitudinal study of people with profound intellectual and multiple disabilities[END_REF].

Other comorbidities, such as fecal impaction, recurrent urinary tract infections, renal failure, cutaneous defects, thyroid disorders, chronic anemia increased with age inducing discomfort and chronic pain, potentially lead to premature death. Strategies of detection, prevention, and treatment previously showed interesting efficacy to improve well-being of the patients and should more systematically be implemented.

One key point should draw specific attention. While a large proportion of the patients received antalgic medication, chronic pain was still sub-controlled. It is well-known that polyhandicapped patients are a high-risk pain-related medical condition (spasticity, joint dislocation, and pressure sores) [START_REF] Van Timmeren | Physical health issues in adults with severe or profound intellectual and motor disabilities: a systematic review of crosssectional studies[END_REF][START_REF] Van Der Putten | Pain assessment in people with profound intellectual and multiple disabilities; a pilot study into the use of the Pain Behaviour Checklist in everyday practice[END_REF]. We have to promote systematic assessment and management of pain using specific methods developed for these patients with communication difficulties. It is remains difficult to totally control pain due to the need to be careful and cautious with the use of level III opioids.

The low proportion of chronic diseases may partially be explained by the young age of the individuals and the absence of exposure to some cardiovascular risk factors (tobacco and alcohol, overeating).

Patja et al. have previously reported a similar finding, demonstrating a reduced mortality from chronic pathology, specifically from neoplasm, in patients with intellectual disability [START_REF] Patja | Life expectancy of people with intellectual disability: a 35-year follow-up study[END_REF]. As previously reported in cerebral palsy children, sleep disorders were more frequent for youngest patients, particularly in difficulties initiating and maintaining sleep [START_REF] Newman | Sleep: the other life of children with cerebral palsy[END_REF][START_REF] Atmawidjaja | Sleep disturbances in Malaysian children with cerebral palsy[END_REF].

Concerning the neurodevelopmental aspects, patients aged from 3 to 5 years hardly reached the level of development from 5 to 7 months of normal development, both in motor (posture, coordination) and cognitive domains (language, socialization), and the developmental process no longer evolved during adolescence and adulthood. Tonus disorders result in a delay or an impossibility of acquisition of the movements, and consequent development of praxis and gnosis; heavy motor impairment leads to poor sensorimotor experimentations that reduce the development of spatial somatognosic and temporal references and the construction of these representations. The general benefit of poor and inappropriate educational management aggravated motor and cognitive deficits while individualized and intensive educative care should be promising of interesting progression [START_REF] Kozulin | Cognitive modifiability of children with developmental disabilities: a multicentre study using Feuerstein's Instrumental Enrichment--Basic program[END_REF][START_REF] Nilsson | Driving to learn: a new concept for training children with profound cognitive disabilities in a powered wheelchair[END_REF].

Expectedly, administered treatments and medical devices were more frequent in the highest age classes according to the various comorbidities that the patients developed. The most common medical device was gastrostomy (30%), a well-known device useful for preventing recurrent pulmonary infections and gastroesophageal reflux [START_REF] Lee | Long-term percutaneous endoscopic gastrostomy feeding in young adults with multiple disabilities[END_REF][START_REF] Strauss | Survival in cerebral palsy in the last 20 years: signs of improvement?[END_REF] and for treatment of swallowing disorders.

Strengths and limitations

Our study provides health characteristics across ages from a large and homogeneous population PLH children and young adults as previous studies focusing on this population of patients are smaller with inhomogeneous sample. The results of this cross-sectional study have to be considered with caution and should be confirmed by future researches using longitudinale design (Appendix 1 and 2).

Conclusion

In the polyhandicap, heavy cerebral damage occurring on an immature brain explains the severe health condition of the patients, resulting in the entanglement of multiple impairments and comorbidities. Early detection and management of impairments and comorbidities may improve the disease course of the patients.

The authors declare that they have no vested interests.

  study was a cross-sectional study including patients from March 2015 to September 2016. The recruitment of patients was performed from 4 specialized rehabilitation centers, from 9 residential facilities of the 17 centers of the French Comité d'Études, d'Education et de Soins Auprès des Personnes Polyhandicapées Association (CESAP), and from a specialized pediatric/neurological department of a university hospital (Service de Neuropédiatrie, UPMC, Hôpital Trousseau, Assistance Publique Hôpitaux de Paris, France) during a routine visit. This study was included in the French national PoLyHandicap (PLH) cohort.

  (3-5 years) and decreased with aging (10-11% for the oldest classes). Global hypotonia decreased with aging: 49, 38, 33, and 25%, respectively, for [3-5 y], [6-11 y], [12-17 y], [18-25 y] classes. Ataxia was reported at a similar proportion for the 4 age classes. Twenty-four to 36% of the children presented with visual impairment, and 4 to 8% presented with hearing impairment with no evident change over time. Behavioral disorders were less frequent in younger children (40%) compared with older individuals (more than 70% for the children older than 12 years). Sleep disorders were more frequently observed in younger children ([3-5 y] and [6-11 y] age classes) compared with older patients. All details are shown in Table

----- 20 ----

 20 Lysosomal diseases N=6 (Metachromatic leucodystrophia N=2, Gangliosidosis N=1, Tay Sacks N=1, Glucocerebrosidasis (Type III Gaucher disease) N=1, Sandhoff disease N=1) Neuronal ceroid lipofushinosis N=8 -Mucopolysaccharidosis II and III N=3 Peroxysomal diseases N=1 -Adrenoleucodystrophy N=1 Other metabolic syndroms N=3 (Aicardi Gouttiéres N=1, Sjogren Larsson syndrom N=1, CDG syndrom N=1) Rett syndrome N=5 -Angelman syndrome N=3 Demyelinisating affection of central nervous system N=1 Progressive degenerative encephalopathy N=1 Sensitive neuropathy type 2 N=1 -Dygue-Melchior-Clausen syndrome N=1

  ] class) compared with the youngest classes (31% for[3-5 y] and[6-11 y] classes). Although orthopedic comorbidities consequently increased with aging, pulmonary comorbidities (recurrent pulmonary infections and aspiration syndrome) remained stable. Although the proportion of gastro esophageal reflux was stable over age, the proportion of fecal impaction regularly increased with the age of the patients (29, 33, 41, and 47% in the 4 successive age classes). The proportion of drooling was stable across ages. Recurrent urinary tract infections were more frequent in the older age. The proportion of urinal retention was lower for the youngest age class (3%) compared to the 3 oldest age classes (approximately 4-5%). Cutaneous comorbidities (pressure fragility and bedsores) regularly increased with age. Chronic pain proportions differed between age classes. Antibiotic resistant bacteria occurrence did not change across the 4 age classes. All details are shown in Table

Table 1 . Sociodemographics and health status of polyhandicapped patients (N=545) 3-5 years N=80 6-11 years N=166 12-17 years N=155 18-25 years N=144 p 1) Sociodemographics

 1

	Gender	Boys/Men	41 (52.2)	80 (48.2)	86 (55.5)	83 (57.6)	0.134
		Girls/Women	39 (48.8)	86 (51.8)	69 (44.5)	61 (42.4)
	Care modality structure	Spec. Reeduc.center	18 (23)	59 (36)	56 (37)	65 (45)	<0.001
		Residential facility	14 (17)	85 (52)	81 (54)	75 (52)
		Home care	47 (60)	20 (12)	12 (8)	4 (3)
	2) Etiologies	Unknown	7 (9)	23 (14)	13 (9)	23 (14)	0.653
		Known	72 (91)	138 (86)	138 (91)	122 (86)
	3) Health status
	Severity	Less severe	40 (52)	86 (51.8)	77 (50.7)	74 (51.4)	0.896
		Severe	37 (48)	80 (48.2)	75 (49.3)	70 (48.6)
	Stability	Stable	49 (63.6)	104 (62.7)	96 (63.6)	106 (75.2)	0.041
		Unstable	28 (36.4)	62 (37.3)	55 (36.4)	35 (24.8)

Table 2 . Main etiologies of polyhandicapped patients Unknown etiologies N=63

 2

Table 3 . Associated impairments of polyhandicapped patients (N=545)

 3 behaviorial disorders including intermittent screaming, and/or agitation and/or stereotypies and/or intermittent crying and/or self-aggressivity and/or

	3-5 years	6-11 years	12-17 years	18-25 years	p
	N=80	N=166	N=155	N=144

*

Table 4 . Comorbidities of polyhandicapped patients (N=545)

 4

	3-5 years	6-11 years	12-17 years	18-25 years
	N=80	N=166	N=155	N=144

* chronic diseases: at least one of the following diseases: vascular stroke, myocardial infarction, diabetes, and/or cancer

Figure captions Figure 1. Neurodevelopmental status of polyhandicappedpatients according to age classes

Acknowledgements

The authors are grateful to Claire Morando for her logistical support.The French Polyhandicap Group includes the following individuals: Tanguy Leroy;Souhali Haddadou;Cécile Freihuber; Sofiane Amalou; Julie Bonheur; Stéphanie Valence; Marie-Christine Nougues;Laurent Luciani;Jean-Pierre Nouet;Catherine Coiffier; PhilippeSellier;P Julien; JC Grasset; S Delvert; M Gaulard; A Belorgey; Sophie Mathieu ;Mustafa Ardati ; Kammache I ;Delphine Héron ;Arnaud Isapof ; Alexandra Afenjar; K Maincent; Diana Rodriguez ;Diana Doummar;Marie-Laure Moutard;Daniel Willocq ; Maria Valkov ; Julie Teulade;Stéphane Pietra ; Stéphane Lenormand;Etorre Laracca;Valérie Aynie;Elizabeth Grimont.

Fundings

This work is financially supported by French PREPS (Programme de recherche sur la performance du système de soins, year 2013) and the French Institute National de la Santé et de la Recherche Médicale (INSERM, year 2013): Grant DGOS and INSERM. The sponsor was represented by Assistance Publique, Hôpitaux de Marseille, France; and its role was to control the appropriateness of ethical and legal considerations.

Authors' contributions

Conception and design: MCR, TBV, PA.

Study coordination: MCR, TBV, KB, PA.

Acquisition of data: MCR, MV, TBV, AF, CB, NK.

Analysis of data: MCR, KB, AL.

Interpretation of data: MCR, TBV, KB, PA.

Drafting and writing of manuscript: MCR, KB.

Ethics

Regulatory monitoring was performed according to the French law that requires the approval of the French ethics committee (Comité de Protection des Personnes Sud Méditerranée V, 20/10/2014, reference number 2014-A00953-44). A written consent form was obtained for each participant.

Clinical trial registration number NCT02400528.

Statistics

Results

General characteristics of the sample

During the 18-month study period, a total of 545 patients (participation rate 90%) were included: 80 predominantly care managed at home (60%), whereas the oldest age classes were shared between specialized care centers and residential facilities. All of the details are provided in Table 1.

Health status

Less than half of the individuals were defined as severe according to the definition described above independent of the age classes. Thirty-six to 37% of the individuals were defined as unstable for the 3