Anne-Lyse Ravon
email: al.ravon@hotmail.fr

Claire Gaillard

Jean-Laurent Monnier

Menez-Dregan (Plouhinec, Far Western Europe): the lithic industry from layer 7 and its Acheulean components

Keywords: Colombanian, Acheulean, Cleavers, Menez-Dregan, Cobble tools

; sometimes flakes are produced by percussion on anvil; they are never Levallois. The small tool kit mainly includes denticulates and notches with a few scrapers. The heavy-duty tools mostly comprised of various types of choppers are shaped on larger cobbles selected for their rather flat, often elongated shape and for their homogenous nature (sandstone or microgranite). This paper presents some specimens noticeably yielded by layer 7; although few they are typical and definitely akin to the Acheulean techno-typological facies, especially two cleavers made on flakes (quartzite and microgranite), and two bifacial tools roughly shaped on cobbles (sandstone and quartzite), with a third one from the top of the underlying layer 8. These findings revive the question of the relationship between the Acheulean and the Colombanian. Moreover the position of the site in a setting where the natural rocks are available in the form of pebbles/cobbles, flint only as small pebbles, questions the influence of raw material on technical traditions. This provides arguments for understanding the Lower Palaeolithic variability and contributes to the debate on the definition of Acheulean.

Introduction

The Lower Palaeolithic site of Menez-Dregan I (Plouhinec, Finistère), located in Brittany at the very tip of western Europe, has been under excavation since 1991 (fig. 1). It is an ancient marine cave where the roof has gradually collapsed partly protecting the archaeological living floors from erosion (fig. 2). The fauna has not been preserved due to the acidic environment at the site, leaving only the lithic industry as evidence of the living style of the human groups who settled there and, notably, mastered the very early lighting/control of fire in late MIS 13 or early MIS 12 (Monnier et al., 1996, p.63).

In the current state of research the stratigraphy preserved at Menez-Dregan displays an alternating sequence of levels of human occupation and marine deposits (fig. 3) between ca. 465 and 113 ky [START_REF] Mercier | Nouvelles données chronologiques pour le site de Menez-Dregan 1 (Bretagne) : l'apport de la thermoluminescence[END_REF], and the excavation has yielded more than 200,000 lithics artefacts and millions of knapping fragments. This paper presents the lithic industry of layer 7, notable for its Acheulean components [START_REF] Gaillard | Menez-Dregan I, des Prénéandertaliens aux Néandertaliens à l'extrême ouest de l'Europe[END_REF].

Regional setting: the Lower Palaeolithic in Brittany

The Lower Palaeolithic in the Armorican Massif consists of two different groups, which are Acheulean sensu stricto on one side, and "archaic" lithic industries characterised by cobble tools on the other side. The name "Colombanian" was given to this second group whose type site is Saint-Colomban (Carnac, Morbihan, Brittany) by J.-L. Monnier in the late 1980's [START_REF] Monnier | Le gisement paléolithique inférieur de la Pointe de Saint-Colomban, Carnac, Morbihan[END_REF][START_REF] Monnier | Acheuléen et industries archaïques dans le Nord-Ouest de la France[END_REF].

The lithic industry of the site of Menez-Dregan has been attributed to this "Colombanian group" by J.-L. [START_REF] Monnier | Acheuléen et industries archaïques dans le Nord-Ouest de la France[END_REF] on the basis of its composition: predominance of cobble tools among the heavy-duty tools, retouched light-duty tools on flake-blanks comprising mostly notches and denticulates, and knapping method akin to the "SSDA -Clactonian" [START_REF] Forestier | Le Clactonien : Mise en application d'une nouvelle méthode de débitage s'inscrivant dans la variabilité des systèmes de production lithique du Paléolithique ancien[END_REF]. The flakes have prominent bulbs, wide butts rarely faceted and wide open flaking angles, resulting from an alternate flaking of the cores (SSDA -"système par surface de débitage alternée", [START_REF] Forestier | Le Clactonien : Mise en application d'une nouvelle méthode de débitage s'inscrivant dans la variabilité des systèmes de production lithique du Paléolithique ancien[END_REF]. The Levallois method is lacking, handaxes are absent or extremely rare, and there are very few scrapers. Thus the Colombanian proves to be an industry of the Lower Paleolithic, essentially localised on the south Armorican shoreline, between Crozon and Noirmoutier, contemporary with classic European Acheulean but typologically distinct [START_REF] Monnier | Acheuléen et industries archaïques dans le Nord-Ouest de la France[END_REF][START_REF] Monnier | Le Colombanien: un faciès régional du Paléolithique inférieur sur le littoral armoricano-atlantique[END_REF][START_REF] Molines | Les industries à galets aménagés du littoral sud-armoricain (France) au Paléolithique inférieur[END_REF][START_REF] Molines | L'Acheuléen de l'Ouest de la France : apports du site de Menez-Dregan 1 (Plouhinec, Finistère, France)[END_REF]. The "Colombanian group" is composed of the sites of St Colomban, la Croix Audran, the island of Groix, Menez-Dregan, Primelin, and Le Bois-de-la-Chaize, plus a large number of isolated finds all along the shoreline (fig . 1), and is the subject of a new study that focuses mainly on the Lower Palaeolithic site of Menez-Dregan I (Ravon, in prep.;[START_REF] Ravon | La transition Paléolithique inférieur-moyen dans l'Ouest armoricain : l'exemple de la couche 4 du site de Menez-Dregan1 (Plouhinec, Finistère)[END_REF][START_REF] Monnier | Menez-Dregan I, layer 4: a transitional layer between Lower and Middle Palaeolithic in Brittany[END_REF].

A c c e p t e d m a n u s c r i p t

All the Colombanian sites are located on the current shoreline, their deposits sheltered in corridors of marine erosion or in collapsed marine caves. Settlements are always found on ancient marine beaches, this position seems to indicate that the human occupation occurred at the transition between interglacial and glacial periods, in rather mild climatic conditions [START_REF] Monnier | Acheuléen et industries archaïques dans le Nord-Ouest de la France[END_REF].

The site of Menez-Dregan I has been undergoing excavation since 1991 as part of a multidisciplinary project [START_REF] Monnier | Rapport de fin d'opération pluri-annuelle sur la fouille du gisement paléolithique inférieur de Menez-Dregan I à Plouhinec[END_REF][START_REF] Monnier | Rapport intermédiaire sur la fouille du gisement paléolithique inférieur de Menez-Dregan I, campagne[END_REF]. The deposit is located within the cliff above the current sea level. In Menez-Dregan the sedimentological evidence is strongly reduced because of multiple episodes of marine erosion in the cave (low sedimentary preservation in terms of sedimentation and erosion process). However, the proximity of a section with a longer sedimentary record (Gwendrez cliff) has allowed for an attempt at correlation between the different deposits by means of a sedimentological study applied to sandy marker beds (dunes). The resulting new data allowed a more precise chronostratigraphy of this site to be drawn up and contributed to further validation of dating [START_REF] Monnier | Application of sedimentological analysis to the correlation of eroded layers under beaches with local and regional Pleistocene stratigraphy. A contribution to geological dating of Palaeolithic sites on Northern coast of Brittany (France)[END_REF][START_REF] Laforge | Contribution à la chronostratigraphie du gisement Paléolithique inférieur de Menez-Dregan 1 (Plouhinec, Finistère, France). Corrélations avec les dépôts de la falaise de Gwendrez[END_REF]. On the basis of the comparison with the stratigraphy on site and on the Pleistocene deposits preserved at the Gwendrez beach nearby, layer 7 of the site of Menez-Dregan I can be geologically correlated to stage 11 (fig. 4; [START_REF] Laforge | Contribution à la chronostratigraphie du gisement Paléolithique inférieur de Menez-Dregan 1 (Plouhinec, Finistère, France). Corrélations avec les dépôts de la falaise de Gwendrez[END_REF][START_REF] Laforge | Le cadre chronostratigraphique des peuplements pléistocènes de l'Ouest de la France[END_REF].

Presentation of layer 7

Layer 7 is a thick humic black layer, that has recorded a dense human occupation. It is composed of an alternation of argillaceous horizons and beds of gravels and sand, rich in humiferous organic materials. The sandy argillaceous sediment is poorly sorted, as shown by the straight aspect of the granulometric curve (Monnier et al., 1996, p.25). The micromorphology shows an abundant presence of phosphatic organic materials, with a variable amount of granitic sand and ashen beds including charcoals of bones and wood, besides small organic debris and poorly humic mycelium (Monnier et al., 1996, p. 25). Some very rolled blocks occur at the base and at the top of the layer, disturbing the stratigraphy. At least three different sublevels of human occupation can be distinguished on the basis of the spacial distribution of the artefacts and remains of hearths. Numerous charcoals were found in layer 7, sometimes quite large (5 cm) and including several taxa in a single sample; they provide interesting information about the different types of wood burnt at the site (N. Marcoux, pers. com.).

The lithic industry from layer 7

Since the beginning of the excavation, 15377 artefacts bigger than 3 cm have been recorded in layer 7; their composition is shown in table 1. All the different stages of the chaîne opératoire are represented in this layer, as in all the other layers of the site, from the cores to the smallest knapping fragments. Two distinct chaînes opératoires are used in coexistance and are evident right from the stage of raw material selection: the debitage is preferentially made on flint (ca. 80%), then quartz (ca. 15%) and quartzite or glossy sandstone. By contrast the cobble tools are made on sandstone (ca. 80%) or microgranite. All these raw materials are available in the form of cobbles on the beaches near the site, except the glossy sandstone, of which outcrops are known some 20 km away.

A c c e p t e d m a n u s c r i p t

In layer 7, the lithic assemblage is composed of 77.3% of flakes and flake fragments, resulting from the débitage of flint (63.3%) or quartz (16.9%) and from the façonnage of cobble tools in sandstone (10.2%) or microgranite (6.5%).

Only 4.6% of the light-duty tools are retouched, the majority on flint (82.1%) and glossy sandstone (7.2%). They comprise mostly of denticulates, scrapers and notches.

The cores represent 9.5% of the assemblage, and are mainly made on flint (81.6%) or on quartz (16.1%). They are very rarely reduced to exhaustion, and they most frequently result from alternate flaking (fig. 5).

The heavy duty tools (4.5% of the assemblage) are mainly composed of choppers (28%), pebble fragments (23%), cobbles with single removals (17%), chopping-tools (5%), and some few bifacial pieces (1.7%). These bifacial artefacts, rare but typical, are indicative of the Acheulean technical tradition. In layer 7, 3 handaxes, 4 cleavers and 3 unifaces were found during the recent excavations [START_REF] Gaillard | Menez-Dregan I, des Prénéandertaliens aux Néandertaliens à l'extrême ouest de l'Europe[END_REF]. Some biface thinning flakes in flint were noticed recently too, and attest to the shaping of handaxes at the site in this layer, although handaxes made in flint are totally absent in the lithic collection.

Presentation of the Acheulean artefacts

Some artefacts from the layer 7 at Menez-Dregan I are considered as Acheulean on the basis of their typology and underlying technology: they correspond to handaxes and cleavers. Handaxes, also called bifacial pieces, are tools showing a bilateral symmetry, with rather elongated shape, convergent edges, a bifacially shaped edge exceeding 50% of the perimeter, and a façonnage covering more than 50% of the surface of the blank. These bifacial pieces are considered as belonging to the Acheulean technical tradition for they are worked on both faces, but they do not always result from typical bifacial façonnage. However the cleavers are very characteristic of this technical tradition. Cleavers are large cutting tools made on flakes, with a transversal edge kept unmodified while the lateral edges are shaped either unifacially or bifacially. It is to be noted that the direction of the transversal edge varies from strictly perpendicular to the long axis of the tool to notably diagonal, thus forming a point at one of the distal corners. This variability blurs the typological limit between handaxe and cleaver and therefore the type cleaver has to be understood sensu lato (cf. [START_REF] Tixier | Le hachereau dans l'Acheuléen nord-africain -Notes typologiques[END_REF][START_REF] Fiedler | Conception of Lower Acheulian Tools. A Comparison of Three Sites of the Early Handaxe Culture and its Aspect of Behaviour[END_REF][START_REF] Mourre | Implications culturelles de la technologie des hachereaux[END_REF][START_REF] Chevrier | Les assemblages à pièces bifaciales au Pléistocène inférieur et moyen ancien en Afrique de l'Est et au Proche-Orient. Nouvelle approche du phénomène bifacial appliquée aux problématiques de migrations, de diffusion et d'évolution locale[END_REF].

The raw materials used at Menez-Dregan I to make these Acheulean artefacts are the same as the ones used for the cobble tools: quartzite, quartz, microgranite and sandstone, from cobbles or boulders available on the local beaches. Their blanks are large flakes, split cobbles, broken cobbles if not undetermined.

In order to complement the illustrations (figs. 6 to 8), the bifacial pieces yielded by the layer 7 at Menez-Dregan 1 are described here in terms of raw material, blank, overall shape, shaping sequence and finally interpretation, indicating what are the "transformative" and the "prehensive" parts [START_REF] Lepot | Approche techno fonctionnelle de l'outillage lithique moustérien : essai de classification des parties actives en termes d'efficacité technique[END_REF] and whether the artefact can be considered as "bifacial piece as a tool" or as "bifacial piece as a blank for a tool" [START_REF] Boëda | Approche de la variabilité des systèmes de production lithique des industries du Paléolithique inférieur et moyen : chronique d'une variabilité attendue[END_REF][START_REF] Boëda | Technogenèse de systèmes de production lithique au Paléolithique inférieur et moyen en Europe occidentale et au Proche-Orient[END_REF][START_REF] Boëda | Identification des chaînes opératoires du Paléolithique ancien et moyen[END_REF] A c c e p t e d m a n u s c r i p t 1990) with alternative terminology: "shaped piece as a tool" or "shaped piece as a matrix" [START_REF] Chevrier | Les assemblages à pièces bifaciales au Pléistocène inférieur et moyen ancien en Afrique de l'Est et au Proche-Orient. Nouvelle approche du phénomène bifacial appliquée aux problématiques de migrations, de diffusion et d'évolution locale[END_REF].

The bifacial pieces in layer 7

-MDI.2011.7.115085: Handaxe or pick (fig. 6). Raw material: Fine grained sandstone. Blank: Cobble with an irregular fracture perpendicular to its main plane, forming a medioproximal back / steep side, and with a large preliminary removal. Cortex remaining on both faces.

Overall shape: Triangular in front view; trihedral section with a median ridge on the upper face; two adjacent converging cutting edges forming an acute point at the tip. Dimensions: 148 x 73 x 58 mm. Façonnage: Lower face (= flattest face) shaped first: three transverse removals, struck from the cortical sector of the upper face, the distal one crossing the entire breadth of the tool; from the distal end of this invasive removal one direct removal shapes the trihedral point. Then at least one removal is struck from the lateral fracture and reduces the median ridge. The base of the tool is then shaped by a series of small inverse removals used as striking platform for a large direct removal that thins the upper face, and for five smaller removals of which two on the left of the proximal part create the only bifacial shaping of the tool. Interpretation: "Bifacial piece as a tool". The transformative part comprises the trihedral point and both the adjacent lateral edges, total on the right side but only distal on the left side. The prehensive part corresponds to the back in medio-proximal left position and to the base (bevel-edge) of the tool, clearly opposed to its tip.

-MDI.2011.7.115337: handaxe (fig. 6). Raw material: microgranite Blank: split cobble. Overall shape: Oval front view, plano-convex profile, trapezoidal section; the apex is convex, not pointed, and quite sharp. Dimensions: 116 x 86 x 43 mm. Façonnage: First, four invasive flakes remove half of the cortex on the upper face, then one abrupt removal is made on each side of the lower face. Some direct retouches occur on the convex distal edge without modifying its already acute angle (about 30°). Interpretation: "Bifacial piece as a blank for a tool". The transformative part is the apical sharp convex edge with both adjacent convergent edges on the distal half of the tool. The proximal half is the prehensive part, with cortex on the upper face and proximal side, and with abrupt removals on both sides. MDI.2013.7.125555: handaxe (fig. 6). Raw material: Quartzite Blank: Undetermined, but probably from a quartzite cobble although no neocortex is visible. Overall shape: Globally oval in front view with slightly concave lateral sides; biconvex profile; upper face hardly more convex than lower face; apex convex and sharp. Dimensions: 108 x 67 x 33 mm. Façonnage: The distal facet on the lower face is not easy to locate in the processing sequence: it probably the earliest. Transversal removals on the upper face are prior to those on the lower face: one on the left side, two on the right side, covering the entire width of the A c c e p t e d m a n u s c r i p t tool. They are used as striking platforms for two inverse invading removals that create the lateral convexities, and four smaller removals on the distal part of the left edge. The lower face is further shaped by a few proximal removals, especially on the left corner. Finally a large removal thins the proximal part on the upper face. Finer shaping occurs in the form of direct thin retouches on distal convex cutting edge, which is quite sharp (30° to 45°). Interpretation: "Bifacial piece as a blank for a tool" or "shaped tool as matrix", the preferentially active part being the end scraper-like distal edge. The lateral edges may also be considered as transformative: the right edge is completely shaped to be cutting, unlike the left side, yet more concave and possibly meant to have a special function (cf. notch). The prehensive part is the proximal third of the tool; it has been thinned and turned convex by a series of removals that are longer than those of the active part.

The cleavers in layer 7 MDI.2013.7.125568: cleaver (fig. 7). Raw material: Quartzite Blank: Large flake, technically short ("side stuck") with a width almost twice the length. Dihedral butt, making a medium angle with the upper face; point of percussion slightly out from the ridge of the dihedron. Three dorsal removals including two longitudinal-unipolar and one undetermined. Overall shape of the tool: Trapezoidal front view, plano-convex profile; double edge, diagonal in distal position, perpendicular in proximal position. Dimensions: 73 x 126 x 33 mm. Façonnage: On the left edge (striking platform), unsymmetrical bifacial removals, thick on the upper face, thin and marginal on the lower face, the latter also extending on the distal cutting edge. These are followed by a large invading direct removal thinning the proximal part of the tool but not encroaching on the proximal cutting edge. The left edge (distal side of the flake) is bifacially shaped by thick marginal removals, the direct ones also extending on the proximal cutting edge. Interpretation: Double cleaver with both cutting edges partly retouched on the upper face. These are considered as the transformative parts of the tool. The acute distal left angle probably contributed to enhance the efficiency of the distal cutting edge by forming the classical functional unit "edge-point" [START_REF] Boëda | Technogenèse de systèmes de production lithique au Paléolithique inférieur et moyen en Europe occidentale et au Proche-Orient[END_REF]. The prehensive parts are supposed to be both lateral edges of the tool, but the left edge shows some crushing marks and might have been used too. MDI.2011.7.116167: Cleaver (fig. 7). Raw material: Quartz (saccharoid). Blank: Large, technically short flake. Dihedral, open angled butt, with striking point on one facet, not on the ridge of the dihedron. The upper face shows 4 longitudinal-unipolar removals and remaining cortex on the left side and distal left corner. Overall shape of the tool: Rounded rectangle in frontal view, biconvex in sagital view. Two transversal edges, the distal one being broader and sharper than the proximal one and thus considered as the main active part of the tool. Dimensions: 111 x 79 x 41 mm. Façonnage: Two direct removals and four inverse thin invading removals shape the left side into an abrupt back. The right side is rather steep (striking platform of the flake) and bears A c c e p t e d m a n u s c r i p t bifacial marginal removals further extending, but on the upper face only, on the right proximal corner. Interpretation: Double cleaver with the main transformative edge, in distal position, showing damage in the form of chip and flake removals on both faces. The proximal edge, cortical on the upper face, shows crushing marks. The prehensive part corresponds to both lateral sides of the tool. MD1.2011.7.115638: Cleaver (fig. 7). Raw material: Fine grained quartzite Blank: Technically short quartzite flake, with upper face almost entirely cortical, apart from two incomplete flake negatives. Butt missing due to shaping. Overall shape of the tool: Rounded diverging triangle in front view, biconvex, slightly asymmetrical in profile view. The ventral face of the flake being more convex (and more worked) it becomes the upper face of the tool. The distal edge is slightly diagonal. Dimensions:142 x 89 x 48 mm. Façonnage: For the two removals on the cortical face, it is difficult to know whether they were made before the detachment of the flake-blank or after, as part of the shaping process. Anyway, these are used as striking platforms for the shaping of the other face by a series of removals and retouch along the left edge of the tool (proximal side of the flake). These removals are invasive in the middle sector and gradually turn to marginal in the proximal and distal parts. The opposite edge is similarly worked by marginal unifacial removals on the median and proximal parts. The proximal end is a convex bevel-edge (medium angled), entirely cortical on the lower face. The distal cutting edge is unworked but shows small accidental removals on both faces. The shaping of this tool is almost strictly unifacial. Interpretation: Cleaver belonging to the type 0 of [START_REF] Tixier | Le hachereau dans l'Acheuléen nord-africain -Notes typologiques[END_REF]. The main transformative part is the large distal cutting edge. Presented upside down, the same tool can be seen as a large cutting tool with convergent edges and rounded tip. Is there any prehensive part on this tool which cannot be also transformative part? MD1.2014.7.129366: Cleaver (fig. 7). Raw material: Sandstone Blank: Large cortical flake, technically long ("end-struck"). Overall shape of the tool: Rounded rectangle with a cut corner in front view, plano-convex profile. The distal edge is broader than the proximal side, which is steep. Dimensions: 153 x 101 x 28 mm Façonnage: The right side alone is shaped, bifacially, by two direct abrupt removals and then two inverse thin removals. The other sides are blank and the upper face is almost completely cortical. Interpretation: Cleaver of Tixier's type 0 [START_REF] Tixier | Le hachereau dans l'Acheuléen nord-africain -Notes typologiques[END_REF]. The transformative part is the distal edge and possibly the lateral left edge which is almost as sharp. The prehensive parts must be the steep sides, unmodified and cortical in proximal position, partly shaped, partly cortical in lateral right position. These Acheulean artefacts do not occur only in layer 7. Some handaxes were also found in the immediately underlying layer 8b, especially in the top of it, which can be interpreted as the beginning of the human occupation recorded in layer 7 [START_REF] Gaillard | Menez-Dregan I, des Prénéandertaliens aux Néandertaliens à l'extrême ouest de l'Europe[END_REF].

The bifaces in layer 8b

A c c e p t e d m a n u s c r i p t -MDI.2013.8b.125302: Handaxe (fig. 8) Raw material: Microgranite Blank: Technically short flake with a cortical butt (at least the remaining part of it) probably knapped from the split face of a cobble/boulder or from the flat ventral face of a large flake ending with an S-fracture. This forms the upper face of the flake-blank, without any dorsal removal.

Overall shape of the tool: Oval, almost rhombic in front view, plano-convex in profile. The upper face of the flake is the flattest and therefore the lower face of the tool. Dimensions: 111 x 67 x 27 mm Façonnage: Lateral edges are shaped in the sector where they are converging, i.e. the distal 2/3 of the tool, by thin to large removals, bifacial on the right and distal left edges, otherwise direct only. These contribute to shape the apex into a very convex cutting edge. The proximal part is unmodified: blank cutting edge on the left and cortical (upper face) bevel-edge on the right, both converging in a very convex but not pointed proximal end. Interpretation: "Bifacial piece as a blank for a tool". The active part may be the converging edges, as they are shaped and as they are adjacent to a nearly pointed tip (edge + point), but the unretouched edges in the proximal part of the tool also show the same morphological features.

- MDI.2014.8b.128886: Handaxe (fig. 8). Raw material: Quartz Blank: Undetermined; irregular fracture planes; no cortex visible. Overall shape of the tool: Oval with a straight base in front view; thick profile suddenly thinner in the distal fifth of the tool. Dimensions: 119x71x44 mm Façonnage: The shaping nearly extends on the whole perimeter, starting with a few large removals on each face, and continuing with a second generation of smaller removals all around except on most of the right steep side (back). The left side is a bevel-edge (medium angled) in proximal and median position, a cutting edge in distal position. The distal cutting edge forms an angle but not a proper point. The opposite base is abrupt. Interpretation: "Bifacial piece as a blank for a tool" as the cutting edge can be retouched or transformed without modifying the general shape. The distal, sharper edge is obviously the main transformative part, opposite to the comfortable prehensive base of the tool, but the left edge is probably transformative too, especially as it is opposed to a back on the right side.

These large cutting tools are rather simple as far as their façonnage is concerned. Handaxes are not really bifacial, except n° 125555, shaped by very few large removals, possibly belonging to the blank itself. The cleavers are more characteristic of the Acheulian tradition, although this type is rare in the European Acheulian and much more common in Africa or in western and southern Asia. Compared with the choppers, the configuration of these large cutting tools suggests that they are less specialized, not only in the manner of being handled but probably also in the manner of being used: transformative parts often appear as multiple with their corresponding prehensive parts. On the contrary the choppers usually offer one transformative part only, associated to a wide prehensive (and receptive?) cortical area.

Menez-Dregan: between Colombanian and Acheulean

A c c e p t e d m a n u s c r i p t

In the past few years, the Lower Palaeolithic site of Menez-Dregan I has been attributed to the Colombanian by J.-L. Monnier and N. Molines, on the basis of the composition of the lithic industry and environmental conditions. The Levallois method is lacking, handaxes are absent or extremely rare, and there are very few scrapers. The Colombanian was known to be a facies of the Lower Paleolithic, essentially localised on the south Armorican shoreline, between Crozon and Noirmoutier, contemporary with classic European Acheulean but typologically distinct [START_REF] Monnier | Acheuléen et industries archaïques dans le Nord-Ouest de la France[END_REF][START_REF] Monnier | Le Colombanien: un faciès régional du Paléolithique inférieur sur le littoral armoricano-atlantique[END_REF][START_REF] Molines | Les industries à galets aménagés du littoral sud-armoricain (France) au Paléolithique inférieur[END_REF][START_REF] Molines | L'Acheuléen de l'Ouest de la France : apports du site de Menez-Dregan 1 (Plouhinec, Finistère, France)[END_REF]. However, recent finds on the site reveal that the lithic industry always includes some Acheulean components; they are few but they occur in all the layers of human occupation, except in layer 9, the first archaeological level of the site. Some bifacial artefacts were found in layers 4, 5, 6, 7, and 8, showing that the lack of bifaces was not a criterion to define the Colombanian. This lead [START_REF] Monnier | L'Acheuléen armoricain et la variabilité des industries du Paléolithique inférieur[END_REF] to propose the concept of "Acheulean of Saint-Colomban type". In this respect it is to be noted that the layer 7 of Menez-Dregan 1, with 1.7 % of large cutting tools among the heavy-duty tools, is typologically not far from Terra Amata, where this proportion of large cutting tools varies from 3 to 5 % and whose status of Acheulian site was never questioned (de Lumley (dir.), 2015), although the cleavers do not fit into the strict definition of cleavers (on flake; Tixier 1956). The only common features between all the Colombanian sites are their position on the south Armorican shoreline, the high proportion of cobble-tools within the assemblage, and the occurrence of two distinct chaînes opératoires in all the sites, one for the débitage and the other one for the façonnage, with two distinct uses of the local raw materials [START_REF] Monnier | Menez-Dregan I, layer 4: a transitional layer between Lower and Middle Palaeolithic in Brittany[END_REF]. The high proportion of cobble-tools on sandstone and microgranite can be explained by the total absence of flint in the geological ground in the Armorican Massif (fig. 9). The closest cretaceous outcrop is located 40 km offshore in the Audierne bay [START_REF] Lefort | Apport de la géologie marine à la détermination des sources de matières premières au Paléolithique dans le Massif armoricain : Origine possible du silex utilisé sur les stations paléolithique inférieur de Menez-Dregan (Plouhinec, Finistère, France). Implications paléoclimatiques et paléoenvironnementales[END_REF], providing flint only in the form of small marine pebbles and small cobbles. These were used by the Paleolithic populations to make their débitage products, but they were too small to produce heavy-duty tools. On the contrary, sandstone, quartzite and microgranite are naturally available around the site in the form of much larger cobbles, regularly oval in front view and rather thin in profile view, especially those in sandstone. This can be seen as an adaptation to the environment, explaining in some way that Palaeolithic craftsmen used to take advantage of the natural shape of the cobbles to make their heavy-duty tools by shaping one edge only, with a minimal number of unifacial removals. In this context the handaxes and cleavers witness more technical investment, at least in obtaining the blanks of the tools. Besides they may be multi-functional tools while the cobble tools look more specialized.

Regional perspective: isolated finds

The Acheulean in Brittany is mostly characterized by the presence of isolated finds, often without context, except for the site of La Ville-Mein, in Planguenoual (Côtes-d'Armor) where some handaxes made on glossy sandstone were found in ploughed fields [START_REF] Lamotte | Le gisement acheuléen de la Ville-Mein à Planguenoual (Côtes d'Armor)[END_REF]. However, in all the Colombanian sites, at least one Acheulean component is present, such as in St Colomban where a quartzite handaxe was found, in La Croix Audran which displayed an armorican sandstone handaxe, in Groix where some cleavers were noticed, and of course in Menez-Dregan (Ravon, in progress). However, the Acheulean elements in Brittany are mostly found out of context, without any stratigraphy [START_REF] Monnier | Le Paléolithique de la Bretagne dans son cadre géologique[END_REF]. In Menez-Dregan II, located further west from the site of Menez-Dregan I, a bifacial piece has been recently found (Summer 2015). Furthermore, just near the site, a quartz cleaver A c c e p t e d m a n u s c r i p t was found within the Pleistocene deposits preserved in the Gwendrez cliff (fig. 10), and is typologically very similar to the cleavers found in Menez-Dregan. These finds show that the Acheulean elements, although rare, are present in the region, and contemporary with the Colombanian records.

Conclusion

Although the definition of the Colombanian suggests that the large cutting tools or bifaces are absent in the lithic assemblages, some bifacial pieces and moreover some typical cleavers are found in all the Colombanian sites. The Colombanian does not seem to be typologically distinct from the Acheulean anymore, and appears to be an adaptation to an environmental constraint where flint is only available in the form of small size nodules, leading the Palaeolithic knappers to select other raw materials on the fossil beaches surrounding the site for the manufacture of their heavy-duty tools. The Colombanian proves to be a regional facies where all the sites are sheltered in corridors of marine erosion, along the current shoreline, but from a typological point of view there are no clear differences with the Acheulean in the region. The site of Menez-Dregan I is an example of the variability of the lithic industries in the Lower Palaeolithic, and highlights the importance of the environment on technical traditions. Hinguant, in Monnier et al., 1996, modified). 0: present-day soil; 1: coarse head which filled up the deep (this is the last cold period recorded at the site); 2a: large blocks and flagstones, from the final collapse of the marine cave; 2b: arenaceous head; 3a: flaky and argillaceous sand (littoral dune); 3b: Set sandy crust; 4a to 4c: flaky head mixing marine sand and pebbles, with palaeolithic tools (mainly 4b) and strained black layers at its base (4c); 5a to 5e: anthropic soils alternating black (presence of charcoals) and brown layers, very rich with lithic industry, with the presence, at the top of 5c, of a structure of combustion; 5e-d: disturbed ash-bearing layer with structure of combustion arranged at the top of the underlying pebble beach; 6: pebble beach; 7: alternation of Paleolithic layers and dark organic layers, with rounded and smoothed blocks from the collapsed cave, and presence of pebbles at its basis; 8b: raised beach with rocks from the collapsed roof; 8a: sandy layer from the raised beach (8b); 9: sandy-loamy layer, with lithic tools, bones and charcoals, presence of a structure of combustion in a pit; 10: raised beach; 11: raised beach; gneiss: bedrock. Waelbroeck et al., 2012;Shackelton, 1987;[START_REF] Lisiecki | A Pliocene-Pleistocene stack of 57 globally distributed benthic D 18 O records[END_REF]Raymo, 2005. (In Laforge, 2012, p. 94, modified).

Fig. 1 :

 1 Fig. 1: Geographic location of the Lower Palaeolithic site of Menez-Dregan I (CAD: L. Quesnel).

Fig. 2 :

 2 Fig. 2: The site of Menez-Dregan I, view from the south (Photo A.-L. Ravon).

Fig. 3 :

 3 Fig. 3: Stratigraphy of the Lower Palaeolithic site of Menez-Dregan I. Drawings: T. Paterson, CAD: A.-L. Ravon. (After S.Hinguant, in Monnier et al., 1996, modified). 0: present-day soil; 1: coarse head which filled up the deep (this is the last cold period recorded at the site); 2a: large blocks and flagstones, from the final collapse of the marine cave; 2b: arenaceous head; 3a: flaky and argillaceous sand (littoral dune); 3b: Set sandy crust; 4a to 4c: flaky head mixing marine sand and pebbles, with palaeolithic tools (mainly 4b) and strained black layers at its base (4c); 5a to 5e: anthropic soils alternating black (presence of charcoals) and brown layers, very rich with lithic industry, with the presence, at the top of 5c, of a structure of combustion; 5e-d: disturbed ash-bearing layer with structure of combustion arranged at the top of the underlying pebble beach; 6: pebble beach; 7: alternation of Paleolithic layers and dark organic layers, with rounded and smoothed blocks from the collapsed cave, and presence of pebbles at its basis; 8b: raised beach with rocks from the collapsed roof; 8a: sandy layer from the raised beach (8b); 9: sandy-loamy layer, with lithic tools, bones and charcoals, presence of a structure of combustion in a pit; 10: raised beach; 11: raised beach; gneiss: bedrock.

Fig. 4 :

 4 Fig.4: Relative sea levels and chronological distribution of the isotopic stages for the last 450 ky, after the work ofWaelbroeck et al., 2012; Shackelton, 1987;[START_REF] Lisiecki | A Pliocene-Pleistocene stack of 57 globally distributed benthic D 18 O records[END_REF] Raymo, 2005. (In Laforge, 2012, p. 94, modified).

Fig. 5 :

 5 Fig. 5: Lithic industry from Menez-Dregan I, cores in layer 7 (Photos & CAD: A.-L. Ravon).

Fig. 6 :

 6 Fig. 6: Lithic industry from Menez-Dregan I, bifacial elements in layer 7 (Photos C. Gaillard & A.-L. Ravon, CAD: A.-L. Ravon).

Fig. 7 :

 7 Fig. 7: Lithic industry from Menez-Dregan I, cleavers in layer 7 (Photos R. Cheruel, C. Gaillard & A.-L. Ravon, CAD: A.-L. Ravon).

Fig. 8 :

 8 Fig. 8: Lithic industry from Menez-Dregan I, handaxes in layer 8 (Photos: R. Cheruel & A.-L. Ravon, CAD: A.-L. Ravon).

Fig. 9 :

 9 Fig. 9: Geological map of North Western France, showing the location of the site of Menez-Dregan I (white star) and the location of the nearest cretaceous flint outcrop (in black circle). Extrait de la carte géologique de France au 1/1 000 000ème, éd. B.R.G.M., Orléans. CAD: A.-L. Ravon.

Fig. 10 :

 10 Fig. 10: Quartz cleaver found in the Gwendrez cliff (Photo & CAD: A.-L. Ravon).

Acknowledgments

The authors would like to thank Josephine Mills and Tabitha Paterson for their proofreadings of the manuscript, and Nick Ashton for his review and helpful comments on this document.


Jérôme Le Coz
email: jerome.lecoz@irstea.fr

Antoine Patalano

Daniel Collins

N F Guillen

C M Garcia

Graeme M Smart

Jochen Bind

Antoine Chiaverini

Raphaël Le Boursicaud

Guillaume Dramais

Nicolás Federico Guillén

Carlos Marcelo García

Isabelle Braud

Lessons learnt from recent citizen science initiatives to

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

Introduction

New communication and digital image technologies have enabled the public to produce and share large quantities of flood observations. Valuable hydraulic data such as water levels, flow rate estimates, inundated areas, etc., can be extracted from photos and movies taken by citizens and help improve the analysis and modelling of flood. As for other research fields, citizen science initiatives on flood hydrology have emerged in the recent years (cf. e.g. [START_REF] Lowry | CrowdHydrology: Crowdsourcing Hydrologic Data and Engaging Citizen Scientists[END_REF]).

We introduce three recent citizen science initiatives which have been launched independently by research organisations to document floods in some catchments and urban areas of Argentina, France and New Zealand. While the three projects differ in their objectives, methods and hydrological situations, they provide convergent feedback on the potential and limitations of such initiatives for flood hydrology.

The three projects 2.1 The Flood Chasers Project

The researchers of the National University of Córdoba have developed and implemented the Flood Chasers Project ("Cazadores de crecidas" in Spanish, [START_REF] Patalano | Desarrollo e implementación del proyecto "Cazadores de crecidas" en ríos de la provincia de Córdoba [Development and implementation of the Cazadores de crecidas project in rivers of the Córdoba province, in Spanish], IV Simposio sobre métodos en hidráulica[END_REF]) to populate a database of videos and digital photos of flash floods in rivers of the province of Córdoba recorded and shared by citizens using advanced digital technology. Flood movies recorded by citizens are then processed to estimate river discharges using image velocimetry techniques such as Large Scale Particle Image Velocimetry (LSPIV, [START_REF] Patalano | Evaluación experimental de la técnica de velocimetría por seguimiento de partículas a gran escala para la determinación de caudales en ríos serranos [Experimental evaluation of large scale particle tracking velocimetry technique for flow discharge measurements in mountains rivers[END_REF]). During the last rainy season (2014-2015), extreme hydrological events occurred and in some cases the data obtained with this technique is the only information available to characterise the observed hydrological events. The first step was to create a website a with domain of the University, performing then an intensive dissemination of the existence of this webpage in major newspapers and some television channels. On the project website people can upload their flood videos along with metadata (recording date and time, location of the river a http://www.cazadoresdecrecidas.unc.edu.ar/ section, etc.). The website provides guidelines about the best way to make contributions that are useful for quantifying flood discharges. Users who are interested in participating in the Flood Chasers Project can send or upload their videos using different platforms (i.e. Dropbox, Mega and WeTransfer) through basic tutorials generated by the scientists. A webpage also lists all the recorded floods and include the flow results if the video has been suitable for analysis (Figure 1). In turn, there is a YouTube channel called "Cazadores de Crecidas" in which the project leaders upload their own collection of videos, also published on the website.

Image sequences of recorded videos are processed using Matlab tool PIVlab [START_REF] Patalano | RIVeR -Towards affordable, practical and user-friendly toolbox for Large Scale PIV and PTV techniques[END_REF] for calculating the velocity field from each pair of images. Each of these instantaneous velocity fields is processed and the average displacement field in pixels per image pair is calculated. The results are exported to the RIVeR (Rectification of Image Velocity Results) toolbox, another Matlab toolbox [START_REF] Thielicke | PIVlab -Towards Userfriendly, Affordable and Accurate Digital Particle Image Velocimetry in MATLAB[END_REF] where the displacement data are transformed into velocity data in m/s after rectification of perspective effects due to the oblique capture of the videos with respect to the flow surface.

The methodology was notably applied to a video recorded by the witness of a flood that occurred in the Los Chorrillos Creek, in the city of Carlos Paz, Córdoba, Argentina, after an extraordinary flood event occurred on the morning of 14 March 2014. The recurrence period of the rainfall event generating this flood was estimated to be 56 years with a duration of 160 minutes. The witness uploaded this video to a website of a newspaper in the province of Córdoba (cf. Figure 2). The scientists recognised the house from which the video was captured and proceeded to contact the author. Subsequently, the scientists went to the place and surveyed the cross-section bathymetry using an Acoustic Doppler Current Profiler (ADCP) mounted on a mobile platform (cf. Figure 3). The camera movement due to the videographer holding the camera by hand without a tripod was preliminarily corrected. Such movement creates significant errors in the processing of the images. Then, the surface velocity profile was computed (cf. Figure 3) and integrated throughout the transect using a depth-average to surface flow velocity ratio of 0.85, the default value generally used for uniform flow of average roughness [START_REF] Coz | Performance of image-based velocimetry (LSPIV) applied to flash-flood discharge measurements in Mediterranean rivers[END_REF][START_REF] Welber | Field assessment of non-contact stream gauging using portable surface velocity radars (SVR)[END_REF]. The estimated flow rate was 984 m 3 /s.

Figure 3. Bathymetry of the cross-section of interest and crossprofile of surface velocities obtained by LSPIV

The relationship of the Flood Chasers Project leaders with government authorities is more than optimal. The minister of water, environment and energy of the Córdoba province is actually a professor at Universidad Nacional de Córdoba (at leave) who is interested in the implementation of the technique. The results obtained in the project have been used by the government to hydrologically evaluate some of the recorded events. Due to this interest the project has received support from the government including logistics for conducting the required surveys (topography survey, field work, etc.). For the next rainy season, the researchers are looking for training groups of people who can be great partners, for example the civil defence workers and advanced students (16 to 17 years old) from high schools that are located near rivers. A strong message of safety is also transmitted. It is very important to avoid any life in danger and be sure there is no risk in recording a video.

The FloodScale Project

As part of the ANR b FloodScale project (France) on Mediterranean flash floods [START_REF] Braud | Multi-scale hydrometeorological observation and modelling for flash flood understanding[END_REF], a similar action was independently launched throughout the Ardèche river catchment, South-East France. The FloodScale project, a contribution to the HyMeX c project (Hydrological cycle in the Mediterranean Experiment) was designed to make progress in the understanding and modelling of flash floods. Specific communication actions focussed on the determination of flood discharges throughout the Ardèche b Agence Nationale pour la Recherche (National Research Agency, France) c www.hymex.org river catchment (France) using home movies shared by observers and volunteers. Safety instructions and a simplified field procedure (cf. poster in Figure 4) were shared through local media and were made available in French and English on the project website d .

The processing of flood movies to extract surface flow velocities and discharges is based on the LSPIV technique originally proposed by Fujita et al. [START_REF] Fujita | Large-scale particle image velocimetry for flow analysis in hydraulic engineering applications[END_REF] and also used in the Flood Chasers project. The applicability of the LSPIV technique to flood home movies was investigated by Le Boursicaud et al. [START_REF] Boursicaud | Gauging extreme floods on YouTube: Application of LSPIV to home movies for the post-event determination of stream discharges[END_REF]. Using flood movies recorded by non-professional witnesses usually raises specific issues and requires some image pre-processing before the LSPIV analysis. LSPIV analysis was conducted using Fudaa-LSPIV [START_REF] Coz | Image-based velocity and discharge measurements in field and laboratory river engineering studies using the free Fudaa-LSPIV software[END_REF], a free, user-friendly software available online e . Image pre-processing was conducted using Hugin, another free software available online. The complete procedure to collect and pre-process home movies for further LSPIV analysis comes as a short methodological guide [START_REF] Boursicaud | Guide méthodologique -Collecte et préparation de film amateur en vue d'une exploitation par analyse d'image [Methodological Guide -Collection and preprocessing of home movies for operations by image analysis[END_REF].

Simple procedures for taking useful flood movies, highlighting safety warning (cf. Figure 4) have been disseminated to the public through various media including the project website f and local media (newspapers, radio). Legal aspects including a copyright transfer form have been settled with the help of Irstea's legal services. Communication campaign was well received by locals and municipalities, but jeopardised by local issues (concurrent update of official flood risk mapping) and lack of coordination with and support from local authorities due to safety concerns. After long discussions, the communication campaign had to be postponed.

Partly due to communication restrictions, few videos were received by the scientists, even after the series of significant floods which occurred during the 2014 autumn. And none of those was actually usable because they generally did not follow the recommendations. However, some useful movies were harvested by scientists after each flood of interest, especially drone videos (cf. Figure 5) shared on YouTube g by a local company h specialising in UAV-borne image recording. As often, the water stage estimation appears to be the main source of uncertainty (cf. Table 1). However, discharge estimates were found to be consistent with the rated flows at the upstream gauging station. d https://floodscale.irstea.fr/donnees-en/videosamateurs-de-rivieres-en-crue/videos-amateurs-derivieres-en-crue e https://forge.irstea.fr/projects/fudaa-lspiv/files f https://floodscale.irstea.fr g https://www.youtube.com/watch?v=4lgws8pvFyg h http://www.ardechevideo.com/ Table 1. Discharge results and comparison with records from upstream gauging station

The RiskScape Project

The New Zealand national institute NIWA has called citizens to contribute to floodmapping during the May 2014 inundation events in the city of Christchurch, as part of the RiskScape i project. Two days after the flood peak, members of the public were invited, via press releases to mainstream media, a scientific blog j and outreach via social media (Facebook, Twitter), to send photos of maximum flood levels to NIWA, indicating when and where each photo was taken. When applicable, water surface levels were derived from the photos in conjunction with LiDAR scans of the city. The resulting point data were interpolated, along with additional survey i www.riskscape.org.nz j http://sciblogs.co.nz/waiology/2014/03/07/calling-forchristchurch-flood-photos/ data, to derive a flood hazard model to calculate flood risk and potential losses across the city.

Over 600 photos were received (Figure 6). Ultimately, 300 photos were used to get a fix on 289 water levels around the city. Combined with field surveys, the resulting inundation map (Figure 7) indicates flooding along the Avon and Heathcote Rivers as well as various residential suburbs throughout Christchurch, including the severely impacted Flockton Basin. High media and public interest suggested that, in addition to providing useful data, the public engagement fostered a greater appreciation of flood hydrology and its scientific study. The resultant information has been invaluable in understanding the changed flood risk for post-earthquake Christchurch, was used to validate hydrodynamic models and is being used to plan mitigation, response and evacuation plans and to calculate human and economic costs of flooding.

Lessons learnt 3.1 A clear and simple procedure

The three projects have produced procedures in the form of simple instructions for recording the images and sending the data in good agreement with their distinct objectives. The type of images and metadata, the protocols to send them to the scientists and the safety and copyright aspects were dealt with in a concise and precise manner. However, for the capture of valuable movies, a written procedure may not be sufficient and additional training should be provided as tutorials and short movies, e.g. on collaborative websites like WikHydro in France k .

Suitable data collecting and processing

It is necessary to develop platforms able to collect large quantities of data coming with contrasted formats and quality levels. Website forms and uploads, as well as smart (apps) or basic (textos) phones, are efficient tools to collect crowdsourced data, as long as the effort required from the user is kept minimal. However, it sometimes remains more efficient for scientists to harvest adequate image materials from sharing platforms and social networks.

The processing of the collected data generally requires specific techniques and tools that are not previously available off the shelf. It is important to carefully review the quality of the crowdsourced data, in particular through post-event field investigation and cross-checking of the results with other sources of information. The use of crowdsourced hydrologic data in models and scientific studies also requires suitable techniques that are able to assimilate data coming with contrasted and possibly large uncertainties.

An efficient communication plan

Communication is key to efficiently mobilise flood observers, make them aware of flood-related dangers (and discourage them from risking their lives), avoid conflicts with local authorities, and provide feedback on the use of collected data. Simple and direct explanations are essential, even when it comes to science or legal terms. Such initiatives are usually well received by locals and the media. Communication efforts should be directed at both the general public and specific community groups.

The reported experience highlights the necessity to adapt the communication vectors to each project. Communicating through radio and TV allows reaching a wide audience. Local newspapers and scientific blogs can probably reach a more specific audience but can be efficient to release punctual and periodic reminders of the projects. Distributing flyers and displaying posters at key k http://wikhydro.developpement-durable.gouv.fr/ observation points and at places attended by the public may dramatically increase the quantity of image materials at particularly strategic sites. Social networks like Twitter and Facebook are essential as they allow to reach a wide audience and to do it at any time. Being constantly active in the whole range of available media is key.

Support from local stakeholders

As consistently illustrated in the polarised French and Argentinian experiences, getting the support of local authorities or not can significantly enhance or jeopardise your citizen science project. In the specific context of the FloodScale project, calling for images before rather than during or just after the flood appeared to be the main source of concerns for the administration. However, the support of local stakeholders and authorities should still be sought actively. There is always a chance that they realise the potential of citizen science initiatives for the success and acceptance of flood risk policies.

Public engagement

The call is much more successful when the public and the media are prepared and aware of natural hazards, as was the case in Christchurch, New Zealand, after the earthquakes of 2010 and 2011. Social studies could also profit from such crowdsourced feedback from people on how they have been affected by the flood and how they have reacted, as done through calls and interviews in social science projects as done in HyMex l . Provided there is sufficient expert oversight during project design and data analysis, such citizen science seems a viable means of improving our understanding of flood risk. However, in some cases the value of the obtained data is much less than the impact and engagement of the citizen community [START_REF] Lowry | CrowdHydrology: Crowdsourcing Hydrologic Data and Engaging Citizen Scientists[END_REF]. Feedback to the public is absolutely essential, through any available means: project website, online database, publication of results, follow-ups on scientific blogs mn and communication through the media.

Conclusions

The reported three projects are typical of emerging citizen science initiatives for crowdsourcing flood hydrology data. They illustrate their great potential for improving flood risk assessment in interaction with the local communities. Beyond the technical and communication challenges, this is an efficient way to enhance the culture of flood risk and make people more engaged collectively. We hope that our feedback may help such initiatives emerge and develop successful strategies.

l www.hymex.org and web form: http://goo.gl/forms/q80gfQbPNN m http://sciblogs.co.nz/waiology/2014/06/16/citizenscientists-help-map-christchurch-flooding/ n http://sciblogs.co.nz/waiology/2014/09/04/full-citizenscience-flood-map-for-christchurch-march-2014/

Figure 1 .

 1 Figure 1. The page of the website of the Flood Chasers Project which lists recent flood movies of interest

Figure 2 .

 2 Figure 2. Image of the flood in the Los Chorrillos Creek in the city of Carlos Paz, Córdoba, Argentina on 14 March 2014 and grid points for correcting the computed velocities.

Figure 4 .

 4 Figure 4. Instructions provided to the public for the intended poster campaign of the FloodScale Project

Figure 5 .

 5 Figure 5. Applying LSPIV to a drone video of the Ardèche River at Sampzon Bridge, France, shared on YouTube after 2014 floods. Water Level (m)

Figure 6 .

 6 Figure 6. Photos of the May 2014 inundation in Christchurch received from the public: (a) Slater St, Richmond; (b) Francis Ave, Mairehau; (c) Buxton Tce flow gauging site, St Martins; (d) Intersection of Oxford Tce and Barbadoes St.

Figure 7 .

 7 Figure 7. Inundation extent and depth across Christchurch, 5 th May 2014, based on photos received from the public. The Flockton basin is in the foreground. Where houses are shown there is no modelled surface flooding on the property; where there are no houses shown surface flooding is indicated by the shade of blue (darker = deeper).

Acknowledgements

The Flood Chasers project acknowledges the support of the Government of the Córdoba Province, Argentina, through the PROTRI project. The FloodScale project was funded by the French National Research Agency (ANR) under Contract No ANR 2011 BS56 027, which contributes to the HyMeX program. Catherine Ambroise-Rendu and Thierry Fournier (Irstea) contributed to the FloodScale communication campaign. Collaboration between NIWA and Irstea was enhanced by the PHC Dumont D'Urville project 34185SH (2015-2016) and the Irstea grant and NIWA support for the scientific visit of J. Le Coz at NIWA. All the citizens who have provided images for the three projects are gratefully thanked.