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Relationship between tectonic activity, fluvial system and river morphology in the Dohuk catchment, Iraqi Kurdistan

Relations entre l’activité tectonique, le système fluvial et la morphologie fluviale dans le bassin-versant du Dohuk, Kurdistan iraquien
Elias R. Ziyad
p. 91-100

Résumés

La zone d'étude se situe le long de la rivière Dohuk, qui s'écoule du lac de Dohuk jusqu'au lac de Mosul (Kurdistan iraquien), dans la partie plissée des Monts Zagros au nord de l'Irak. Les caractéristiques géomorphologiques de la zone d'étude tels que l'altitude, la pente moyenne du cours d'eau, la longueur du cours d'eau principal sont issues d'un Modèle Numérique de Terrain. Les indices utilisés incluent un paramètre de pente (Stream Length Gradient Index, SL), qui est plus élevé dans la section amont de la zone d'étude que dans la section aval. La variabilité topographique concerne la section aval de la zone d'étude, ce qui n'est pas seulement imputé au soulèvement du piémont des Zainiyat mais aussi à l'activité du réseau hydrographique s'écoulant vers le cours principal de la rivière Dohuk. L'indice d'asymétrie du réseau hydrographique (Drainage basin asymetry, Af) indique un soulèvement de la partie ouest de la zone d'étude et un abaissement à l'est. L'indice de symétrie (Transverse Topographic Symmetry Factor, T) indique que le bassin versant est presque symétrique et cela a un impact sur son drainage dans l'aire d'étude. L'indice de sinuosité de front montagneux (Mountain Front Sinuosity index, Smf) présente des valeurs relativement élevées. Les études de terrain montrent qu'il y a une accumulation de trois ensembles de dépôts alluviaux dans la section supérieure et cinq dans la section inférieure. L'augmentation des dépôts vers l'aval est reliée au volume de l'écoulement dans le chenal principal de la section inférieure de la vallée, la faible résistance des roches à l'érosion et le relèvement des pentes dans le piémont des Zainiyat.

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Notes de la rédaction

Article soumis le 14 mai 2013, accepté le 22 août 2013.

Texte intégral

The author would like to thank the anonymous reviewers for their constructive comments on earlier version of this paper.

Introduction

1There are many previous studies of tectonic activity in the arid zone (Bull and McFadden 1977; Rockwell et al., 1985; Wells et al., 1988; Silva, 1994; Keller and Pinter, 1996; Azor et al., 2002; Keller and Pinter, 2002; Silva et al., 2003; Molin et al., 2004; El Hamdouni et al., 2008) and on the Zagros Mountain Range in Iran (Khavari et al., 2009; Dehbozorgi et al, 2010; Alipoor et al., 2011; Mumipour and Najad, 2011; Toudeshki and Arian, 2011). The review of the literature presented here shows that our knowledge of the effects of tectonic movements on river valley forms, fluvial processes and deposits is still insufficient. The Zagros Mountains in Iraq are an area where these problems have not been subject to detailed investigation. The impact of the geological structure in determining the shape of the river valleys and types of deposits has been recognised in studies of the beds of the rivers Tigris (Al-Dabbagh and Al-Naqib 1991), Euphrates (Demir et al., 2007) and Khazir (Al-Daghistany and Salih, 1993). This study looks at the relationship between tectonic activity and the morphology of the Dohuk river valley in Iraqi Kurdistan. It investigates how tectonic activity impacts on the relief and morphology of the valley and then as a result impacts on the fluvial processes and the layers of deposits.

2C.M.G. Bolton (1958) classified the Zagros Mountains in northern Iraq into three zones of folding. There are the high competent folded mountains, the low competent folded mountains, and the foothill belt. Most of the rivers originate in the high mountains in northern Iraq, as this is an active neotectonic zone. Even at the present time, mountains are being uplifted and rivers, in an effort to counteract this, are eroding down more strongly and forming deep gorges. Tectonically driven changes can involve both uplift and subsidence. The Dohuk River was chosen for a case study from the Dohuk Lake in the Bekhair Mountains, through a plain area to the south of this lake, crossing the west limb of Dohuk Mountain and flowing south into Mosul Lake after having crossed the slope of the Zainiyat foothills (fig. 1). The aim of this paper is find out how tectonic activity has an impact on the morphology of the Dohuk River and then produces changes in the fluvial processes and in the layers of deposits.

Fig. 1 – SRTM (level 2) shown the relief and the location of the study area.
Fig. 1 – Fond SRTM (niveau 2) montrant le relief et la localisation de la zone d’étude.

Fig. 1 – SRTM (level 2) shown the relief and the location of the study area. Fig. 1 – Fond SRTM (niveau 2) montrant le relief et la localisation de la zone d’étude.

1: metamorphic suture zone; 2: imbricated and simple folded zone; 3: foothill zone; 4: study site.
1 : zone de suture métamorphique ; 2 : zone plissée et à chevauchements imbriqués ; 3 : piémont ; 4 : zone d'étude.

Geological background of the Zagros in the Kurdistan region of Iraq

3The geological formations in the study area are called Aqra-Bekhma, Shiranish, Kholosh, Khurmala, Gercus, Pilaspi, Lower and Upper Fars, Lower and Upper Bakhtiari, and Quaternary (fig. 2). The lithology of the rocks from the Dohuk Lake to the Mosul Lake is classified into two rock types, medium hard and soft rocks (fig. 3). Medium hard rocks are bonded with clay whereas soft rocks are clayey and chalky (Buday, 1980).

Fig. 2 – Geological map of the study area.
Fig. 2 – Carte géologique de la zone étudiée.

Fig. 2 – Geological map of the study area. Fig. 2 – Carte géologique de la zone étudiée.

1: Aqra-Bekhma formation (upper cretacous); 2: Shiranish formation (upper cretacous); 3: Kolosh formation (upper and lower Paleocene) ; 4: Khurmala formation (upper and lower Paleocene) ; 5: Gercus formation (upper and lower Paleocene); 6: Pilaspi formation (Upper Eocene); 7: Lower Fars (Middle Eocene); 8: Upper Fars (Upper Eocene); 9: Lower Bakhtiari (Upper Eocene); 10: Upper Bakhtiari (Upper Eocene); 11: Quaternary (Pleistocene and Holocene); 12: river.
1 : Formation d'Aqra-Bekhma (Crétacé supérieur) ; 2 : Formation de Shiranish (Crétacé supérieur) ; 3 : formation de Kolosh (Paléocène) ; 4 : formation de Khurmala (Paléocène) ; 5 : Formation de Gercus (Paléocène) ; 6 : Formation de Pilaspi (Eocène supérieur) ; 7 : Lower Fars (Eocène moyen) ; 8 : Upper fars (Eocène supérieur) ; 9 : Lower Bakhtiari (Eocène supérieur) ; 10 : Upper Bakhtiari (Eocène supérieur) ; 11 : Quaternaire (Pléistocène et Holocène) ; 12 : cours d'eau.

Fig. 3 – Longitudinal profile of the Dohuk channel.
Fig. 3 – Profil en long du chenal du Dohuk.

Fig. 3 – Longitudinal profile of the Dohuk channel. Fig. 3 – Profil en long du chenal du Dohuk.

1: Middle Hard Rock; 2: Soft Rock; 3:Out crop rock; 4: Terraces.
1 : Roche moyennement résistante ; 2 : roche tendre ; 3 : affleurement rocheux ; 4 : terrasses.

Regional tectonic setting

4Zagros Mountains building started in Late Cretaceous time, due to the collision between the Arabian and Eurasian plates (Berberian, 1995; Talbot and Alavi, 1996). The shortening between the Arabian and Eurasian plates, whose horizontal velocity still reaches 2-2.5 cm/a, is partitioned into S-SW directed folding and thrusting and NW-SE to N-S trending dextral strike-slip faulting (e.g., Dewey et al., 1973; Dercourt et al., 1986; Talbot and Alavi, 1996; Talebian and Jackson, 2002; Blanc et al., 2003; McQuarrie, 2004). In the Kurdistan region of Iraq, the Zagros Orogeny is divided into four NW-SE striking tectonic units by (Numan, 1997): Thrust zone, Imbricate Zones, High Folded Zone, and Low folded zone (fig. 4). The boundary between the High Folded Zone and the Foothill Zone is marked by a regional morphotectonic feature, the Mountain Front Fault, delineated by a clustering of seismic events, which causes a sudden change in the level of exposed sedimentary layers. The Mountain Front Fault is trending parallel to the Zagros Belt and is interpreted as a result of the reactivation of Zagros basement structures (Berberian, 1995; McQuarrie, 2004; Jassim and Goff, 2006). The fold-and-thrust belt in the Kurdistan Region of Iraq is dominated by open to gentle folds, with a characteristic wavelength of 5-10 km (Reilf et al., 2012), therefore considerably lower than the average values of 15-25km in the SE parts of the Zagros fold-and-thrust belt (Mouthereau et al., 2007), and amplitudes of less than 2.5 km. The two main reasons for this difference in the fold-wavelength are the absence of major faults and thick salt horizons serving as detachments. For example, the Neo-Proterozoic Hormuz salt overlying the crystalline basement in the SE part of the Iranian Zagros, which acts as a ductile detachment during deformation (Mouthereau et al., 2007), is absent in the NW part of the Zagros (Bahroudi and Koyi, 2003), where study area is located.

Fig. 4 – Tectonic subdivision of Iraqi Kurdistan by N.M.S. Numan (1997), modified.
Fig. 4 – Subdivision tectonique du Kurdistan iraquien, d’après N.M.S. Numan (1997), modifié.

Fig. 4 – Tectonic subdivision of Iraqi Kurdistan by N.M.S. Numan (1997), modified.Fig. 4 – Subdivision tectonique du Kurdistan iraquien, d’après N.M.S. Numan (1997), modifié.

Neotectonic setting

5D. Reilf et al. (2012) have divided the earthquakes in three groups according to their focal point depths. The data extracted from the USGS/NIEC, PDE database, 2011 (state to 6.7.2011) show results from years 1973 to 2011 (fig. 5). The shallowest and most common group recorded are earthquakes with hypocentre depth of 0-30 km, the second, deeper and less common group with from 30 up to 150 km hypocentre depth. Only one earthquake with hypocentre deeper than 150 km was recorded. The most earthquake magnitudes are ranging between 4 and 5. The bulk thickness of the sediments is about 8 km in the High Folded Zone (study area) and about 12 km in the Foothill Zone, which means that the most of the hypocentres lie probably in the crystalline basement.

Fig. 5 – The study area (denoted by a black rectangle) is situated in the High Folded Zone of Zagros, characterised by simple folding and further to the NE by increasing occurrence of thrust faulting (imbricated zones).
Fig. 5 – La zone d’étude (délimitée par rectangle noir) est située dans la zone hautement plissée de Zagros, caractérisée par des plis simples et plus vers le NE, par une augmentation des failles compressives.

Fig. 5 – The study area (denoted by a black rectangle) is situated in the High Folded Zone of Zagros, characterised by simple folding and further to the NE by increasing occurrence of thrust faulting (imbricated zones). Fig. 5 – La zone d’étude (délimitée par rectangle noir) est située dans la zone hautement plissée de Zagros, caractérisée par des plis simples et plus vers le NE, par une augmentation des failles compressives.

B corresponds to the depth of the earthquake hypocentres (values in km, dark gray to white circles, USGS/ NIEC, PDE database, 2011 (state to 6.7.2011) within the study area, combined with the σ Hmax data from World Stress Map (Heidbach et al., 2008) with plotted focal mechanism regimes (NF-normal faulting, SS-strike-slip, TF-thrust faulting) and GPS velocities of plate movement (Walpersdorf et al., 2006). The plate boundaries (in dark-grey) originally from the World Stress Map are modified after A.M. Ziegler (2001).
B correspond à la profondeur des hypocentres des séismes (valeurs en km, cercles gris-noir à blancs, USGS/ NIEC, base de données PDE, 2011 (état le 6.7.2011) dans la zone d’étude, combinée avec les données de σ Hmax provenant de World Stress Map (Heidbach et al., 2008) avec régimes de faille au foyer (NF-faille normale, SS-strike-slip, TF faille inverse) et vitesses GPS des mouvements de plaque (Walpersdorf et al., 2006). Les limites de plaque (en gris foncé) proviennent de World Stress Map, modifié par M.A. Ziegler (2001).

Data used

Digital Elevation Model

6A Digital Elevation Model (DEM) was used to define the characteristic morphology of the river through the catchment modelling system software program. A relief map of the study area was derived by ArcGIS. A profile of the mountain front sinuosity was drawn by Global Mapper and from a topographic map. Field trials and GPS measurements were carried out from the Dohuk Lake to the Mosul Lake in August 2010 and 2011. A digital camera was used to take photos around the valley and in the valley bottom. The catchment modelling system helped to measure more detailed information about the Dohuk catchment such as area, basin slope, mean elevation, sinuosity, and average overland flow. Arc GIS was useful for obtaining three dimension images to get more information about relief of the study area. A topographic map and geological map contain information about the index of tectonic activity and the lithology of the rock. A field trip was made to measure the layer of the deposits in both the upper and lower sections of the valley.

Indices of tectonic activity

7An understanding of the relationship between the tectonics and fluvial system was obtained using geomorphology index tools. One of the most significant impacts is that the river is very sensitive to tectonic movement especially uplift and tilting. So the best analysis was obtained using a geomorphic index of active tectonic deformation of the basin (Toudeshki and Arian, 2011). The tectonic activity indices may detect anomalies in the fluvial system or along the mountain fronts. These anomalies may be produced by local changes in tectonic activity and the results of this are seen in uplift and subsidence (El Hamdouni et al., 2008).

8The Stream Length-Gradient Index (SL) is defined as:
SL = (ΔH / ΔL) x L (1)
where SL denotes the Stream Length Gradient Index, ΔH / ΔL denotes the channel slope or gradient of the reach (ΔH is the change in elevation of the reach and ΔL is the length of the reach), and L denotes the total channel length from the point of interest.

9The Asymmetry Factor (Af) is defined as:
Af = 100 x (Ar/At) (2)
where Ar is the area of the basin to the right (facing downstream) of the trunk stream and At is the total area of the drainage basin (Hare and Gardner, 1985; Cox, 1994; Pinter, 1996).

10The Transverse Topographic Symmetry factory (T) is:
T = Da/Dd (3)
where Da is the distance from the midline of the drainage basin to the midline of the active channel or meander belt and Dd is the distance from the basin midline to the basin divide (Hare and Gardner, 1985; Cox, 1994; Pinter, 1996).

11The Mountain Front Sinuosity (Smf) is:
Smf = Lmf / Ls (4)
where Smf denotes the mountain front sinuosity, Lmf is the length of the mountain front along the foot of the mountain at the pronounced break in slope, and L denotes the straight-line length of the mountain front. The sinuosity of highly active mountain fronts generally ranges from 1.0 to 1.5, that of moderately active fronts ranges from 1.5 to 3, and that of inactive fronts ranges from 3 to more than 10. A sinuosity greater than 3 describes a highly embayed front (Bull and McFadden, 1977).

Results

12SL is 76.8 in the upper section and 67.2 in the lower section (fig. 3) of the study area, Af is 42, and T values measured in the upper section and lower section of the study area are 0.6 and 0.5, respectively. The mountain front sinuosity is shown in table 1 and in fig. 6. The longitudinal profile of the Dohuk channel is shown in fig. 3. In this profile, there is an outcrop of rock and terraces along the channel. The outcropping rock lies in the Bekhair and Dohuk Mountains and the terraces are between the lowland and these mountains. Longitudinal profile of the Dohuk River illustrates the shape of the channel from the source to the mouth. Profile of the river is concave in the Dohuk Mountain and Zainiyat foothills and convex in the upper section and between Dohuk Mountain and Zainiyat foothills. The stream has built terraces in both the upper section and lower section of the valley (fig. 7A and B). In the upper section, there are three layers of deposits and there are five layers of deposits in the lower section of the valley. The number of layers of deposits increases in the lower section, which demonstrates how the fluvial processes and deposits change. The layers of deposits include gravel, clay and gravel with sand (fig. 7C) in the upper section and clay, silt, clay, silt and gravels with sand (fig. 7D) in the lower section. The gravels are big in both sections and may be it is deposits during the uplift of the mountains.

13The study area lies in the higher folded zone. Indexes of tectonic activity show that the SL index is sensitive to change along the river case study and this change connected with tectonic activity, channel slope, rock resistance, and topography. Higher value of SL index is in the upper section of the valley and lower is in the lower section. The result obtained in this study is concordant with previous studies (Keller and Pinter, 2002; El Hamdouni et al., 2008). Af shows that area is being uplifted in the west and tilted in the east of the Dohuk valley (fig. 8). T indicates that the valley is roughly asymmetrical in the upper section and almost symmetrical in the lower section. The result obtained in this study is concordant with the previous studies (Arian and Pourkermani, 2001; Toudeshki and Arian, 2011). Smf is in the range from 1.0 to 1.5, i.e. high active (tab. 1). The obtained data show that south range of Bekhair Mountain and north and south ranges of Dohuk Mountain are the most active segments of the Dohuk catchment. The Dohuk channel adjusts to this tectonic activity by meandering between these two mountains and the valley is deep in this part. The gorges are deep close to mountain fronts that dissect fluvial presses emerging from those fronts. Also, the tectonic activity has gradually increased in the north and south ranges of Zainiyat foothills. The Dohuk channel in the lower section is wider and shallower than in the upper section.

14Smf (fig. 6) shows well-development triangular facets of the mountains. These facets suggest active folding triangular facet at different elevation that indicates several stages of uplift and reactivation of tectonic processes (Riley and Moore, 1993). Thickness of the deposits developed at the base of the front suggests different movements and displacements along the fold. The morphology of the valley is shown in tab. 2. The basin slope of the valley is 0.232 m/m and the average overland flow length is 892.79 m. The total sinuosity of the basin is 2.4, indicating strong sinuosity, and the stream has numerous closely spaced bunds and very few straight sections. This is the result obtained with the stream classification of D.L. Rosgen (1994). In the upper and lower sections, there are fluvial deposits recognised by changes in slope. These deposits have been tilted by active tectonics along the study area. In the upper section more than in the lower section of the valley bottom, deposits of various thicknesses arose for three reasons: first is the tectonic movement activity, second the lithology of the formations and third is the shape of the drainage pattern. Tectonic movements influence the shape of rivers, fluvial processes, forms and deposits. Tectonic traces are visible along all the rivers but the most effective impact is connected with uplifted zones of the Dohuk Mountains and the Zainiyat foothills. Tectonic signatures are observed in the forms of the drainage pattern in the both sections. A dendritic drainage pattern is located in upper section and connected with the gentle regional slope. The lithology of rocks is medium or soft in this section. The number and length of tributaries is lower in the upper section than in the lower section (fig. 8). In the lower section, the hydrographical network is parallel; there is a pronounced slope to the surface. A parallel pattern also develops in the regions of parallel, elongate landforms like outcropping resistant rock bands. Lithology of rocks is soft in this section. The length of tributaries is longer and the fluvial processes are more active in this section.

Fig. 6 – Topographic profiles of the front sinuosity.
Fig. 6 – Profils topographiques du front de sinuosité.

Fig. 6 – Topographic profiles of the front sinuosity. Fig. 6 – Profils topographiques du front de sinuosité.

In the south range of Bekhair Mountain (A), in the north range of Dohuk Mountain (B), in the south range of Dohuk Mountain (C), in the north range of Zainiyat Hillslopes (D), and in the south range of Zainiyat Hillslopes (E).
Dans la partie méridionale de Bekhair Mountain (A), dans la partie septentrionale de Dohuk Mountain (B), dans la partie méridionale de Dohuk Mountain (C), dans la partie septentrionale de Zainiyat Hillslopes (D) et dans la partie méridionale de Zainiyat Hillslopes (E).

Fig. 7 – Photographs of the Dohuk valley.
Fig. 7 – Photographies de la vallée du Dohuk.

Fig. 7 – Photographs of the Dohuk valley. Fig. 7 – Photographies de la vallée du Dohuk.

A: Upper section of the valley. B: Lower section of the valley. C: Profile of the terrace deposits in the upper section of the valley. D: Profile of the terrace deposits in the lower section of the valley.
A : Section amont de la valley. B : Section aval de la valley. C : Dépôts de terrasse dans la partie amont de la vallée. D : Dépôts de terrasse dans la partie amont de la vallée.

Fig. 8 – Subdivision of the study area in upper and lower zones.
Fig. 8 – Subdivision de la zone d’étude en zones amont et aval.

Fig. 8 – Subdivision of the study area in upper and lower zones. Fig. 8 – Subdivision de la zone d’étude en zones amont et aval.

Tab. 1 – Mountain front sinuosity.
Tab. 1 – Front de sinuosité du massif.

Mountain range

Front sinuosity

South range of Bekhair

1.17

North range of Dohuk

1.07

South range of Dohuk

1.02

North range of Zainiyat

1.51

South range of Zainiyat

1.87

Tab. 2 – Morphology of the Dohuk catchment.
Tab. 2 – Morphologie du bassin-versant du Dohuk.

Morphology

Dohuk

catchment

Area (in km2)

197.79

Basin slope (in m/m)

0.232

Average overland flow length (in m)

892.79

Mean basin elevation (in m asl)

1125.12

Maximum flow distance (in m)

42702.7

Sinuosity

2.4

Conclusions

15The river valley was divided into an upper section and a lower section. SL is higher in the upper section than in the lower section. Af shows that point where the tectonic activity changes lies in the east of the study area. The tilting of the valley is much less intense because T is often lower than 0.50, thus it can be concluded that the majority of the drainage basin is almost symmetrical. The variability of land surfaces is in the lower section of the study area and this is not only due to the uplift of the Zainiyat foothills but also to the activity of the drainage pattern flowing into the trunk stream of the Dohuk River. The activity of fluvial processes increases because of the uplift and the tectonic movement activity in the lower section. Increasing numbers of layers of deposits are found in the lower section because of the tectonic activity and soft rock lithology, and because tributes joint with the trunk channel.

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Annexe

Version abrégée en français

La zone d'étude se situe le long de la rivière Dohuk, qui s'écoule du lac de Dohuk jusqu'au lac de Mosul (Kurdistan iraquien), dans la partie plissée des Monts Zagros au nord de l'Irak. Cette étude s'intéresse à la relation entre l'activité tectonique et la morphologie de la vallée de la rivière Dohuk. Elle montre en quoi l'activité tectonique impacte le relief et la morphologie de la vallée et en conséquence influence les processus fluviatiles et l'alluvionnement.

La variabilité topographique que l'on observe sur la section aval de la zone d'étude n'est pas seulement imputée au soulèvement du piémont des Zainiyat mais aussi à l'activité du réseau hydrographique s'écoulant vers le cours principal de la rivière Dohuk. L'indice d'asymétrie du réseau hydrographique (Drainage basin asymetry, Af) indique un soulèvement de la partie ouest de la zone d'étude et un abaissement à l'est. L'indice de symétrie (Transverse Topographic Symmetry Factor, T) indique que le bassin versant est presque symétrique et cela a un impact sur son drainage dans l'aire d'étude. L'indice de sinuosité de front montagneux (Mountain Front Sinuosity index, Smf) présente des valeurs relativement élevées, de 1 à 1,5, indiquant une forte activité tectonique (tab. 1). La figure 6 montre le développement de facettes triangulaires en front de montagne. Ces facettes suggèrent une déformation active à différentes altitudes qui indique plusieurs épisodes de soulèvement et de réactivation des processus liés à la tectonique.

La morphologie de la vallée est décrite dans la table 2. La pente moyenne du bassin est de 0,232 m/m et la distance moyenne de l'écoulement de surface est de 892,79 m. La sinuosité totale du cours d'eau est forte (2,4), il présente de nombreuses boucles très resserrées et très peu de sections rectilignes.

Le profil en long du chenal de la Dohuk est présenté sur la figure 3. Il est accidenté par un affleurement rocheux, qui s'étend dans les montagnes de Bekhair et de Dohuk, et, tout au long de la vallée, des terrasses se développent entre ces montagnes et les zones basses. Le profil de la rivière est concave dans la montagne de Dohuk et le piémont des Zainiyat, il est convexe dans la partie supérieure du bassin versant et entre la montagne de Dohuk et le piémont des Zainiyat. Les terrasses fluviatiles se disposent aussi bien dans la partie supérieure que dans la partie inférieure de la vallée. Les études de terrain montrent que les terrasses de la section supérieure sont composées d'une accumulation de trois ensembles de dépôts alluviaux et de cinq dans la section inférieure. L'augmentation des dépôts vers l'aval est reliée au volume de l'écoulement dans le chenal principal de la section inférieure de la vallée, la faible résistance des roches à l'érosion et le relèvement des pentes dans le piémont des Zainiyat qui favorise l'incision et les apports sédimentaires. Cet alluvionnement croissant vers l'aval démontre l'évolution des processus fluviatiles et de la nature des dépôts. Dans la partie amont, l'accumulation se manifeste par le dépôt successif de niveaux incluant des graviers, des argiles puis des graviers et des sables (fig. 7C). Dans la partie aval, ces dépôts sont successivement argileux, limoneux, argileux, limoneux et enfin constitués d'un mélange de limons, de graviers et de sables (fig. 7D). Les graviers sont grossiers dans les deux sections et peut-être leur dépôt est-il en lien avec le soulèvement du massif montagneux. L'épaisseur des dépôts accumulés à la base du front montagneux suggère différents mouvements et déplacements le long de la zone d'activité tectonique.

L'indice de pente SL ( Stream Length Gradient Index) est très changeant le long de la rivière et cette sensibilité est corrélée avec l'activité tectonique, la pente du chenal, la lithologie et la topographie. Les valeurs élevées de l'indice SL sont observées dans la partie amont de la vallée et elles sont plus basses dans la partie aval. L'indice d'asymétrie (Af) indique que le secteur où l'activité tectonique change se situe dans la partie orientale de la zone d'étude. L'indice de symétrie T, souvent inférieur à 0,50, montre que la subsidence de la vallée y est bien moins intense, et ainsi une grande partie du réseau hydrographique est presque symétrique. L'activité des processus fluviatiles augmente dans la section inférieure de la rivière en raison des mouvements liés à l'activité tectonique et en particulier au soulèvement, mais aussi en raison de la conjonction des affluents vers le cours d'eau principal.

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Table des illustrations

Titre Fig. 1 – SRTM (level 2) shown the relief and the location of the study area. Fig. 1 – Fond SRTM (niveau 2) montrant le relief et la localisation de la zone d’étude.
Légende 1: metamorphic suture zone; 2: imbricated and simple folded zone; 3: foothill zone; 4: study site.1 : zone de suture métamorphique ; 2 : zone plissée et à chevauchements imbriqués ; 3 : piémont ; 4 : zone d'étude.
URL http://geomorphologie.revues.org/docannexe/image/10539/img-1.png
Fichier image/png, 714k
Titre Fig. 2 – Geological map of the study area. Fig. 2 – Carte géologique de la zone étudiée.
Légende 1: Aqra-Bekhma formation (upper cretacous); 2: Shiranish formation (upper cretacous); 3: Kolosh formation (upper and lower Paleocene) ; 4: Khurmala formation (upper and lower Paleocene) ; 5: Gercus formation (upper and lower Paleocene); 6: Pilaspi formation (Upper Eocene); 7: Lower Fars (Middle Eocene); 8: Upper Fars (Upper Eocene); 9: Lower Bakhtiari (Upper Eocene); 10: Upper Bakhtiari (Upper Eocene); 11: Quaternary (Pleistocene and Holocene); 12: river. 1 : Formation d'Aqra-Bekhma (Crétacé supérieur) ; 2 : Formation de Shiranish (Crétacé supérieur) ; 3 : formation de Kolosh (Paléocène) ; 4 : formation de Khurmala (Paléocène) ; 5 : Formation de Gercus (Paléocène) ; 6 : Formation de Pilaspi (Eocène supérieur) ; 7 : Lower Fars (Eocène moyen) ; 8 : Upper fars (Eocène supérieur) ; 9 : Lower Bakhtiari (Eocène supérieur) ; 10 : Upper Bakhtiari (Eocène supérieur) ; 11 : Quaternaire (Pléistocène et Holocène) ; 12 : cours d'eau.
URL http://geomorphologie.revues.org/docannexe/image/10539/img-2.png
Fichier image/png, 576k
Titre Fig. 3 – Longitudinal profile of the Dohuk channel. Fig. 3 – Profil en long du chenal du Dohuk.
Légende 1: Middle Hard Rock; 2: Soft Rock; 3:Out crop rock; 4: Terraces.1 : Roche moyennement résistante ; 2 : roche tendre ; 3 : affleurement rocheux ; 4 : terrasses.
URL http://geomorphologie.revues.org/docannexe/image/10539/img-3.png
Fichier image/png, 200k
Titre Fig. 4 – Tectonic subdivision of Iraqi Kurdistan by N.M.S. Numan (1997), modified.Fig. 4 – Subdivision tectonique du Kurdistan iraquien, d’après N.M.S. Numan (1997), modifié.
URL http://geomorphologie.revues.org/docannexe/image/10539/img-4.png
Fichier image/png, 459k
Titre Fig. 5 – The study area (denoted by a black rectangle) is situated in the High Folded Zone of Zagros, characterised by simple folding and further to the NE by increasing occurrence of thrust faulting (imbricated zones). Fig. 5 – La zone d’étude (délimitée par rectangle noir) est située dans la zone hautement plissée de Zagros, caractérisée par des plis simples et plus vers le NE, par une augmentation des failles compressives.
Légende B corresponds to the depth of the earthquake hypocentres (values in km, dark gray to white circles, USGS/ NIEC, PDE database, 2011 (state to 6.7.2011) within the study area, combined with the σ Hmax data from World Stress Map (Heidbach et al., 2008) with plotted focal mechanism regimes (NF-normal faulting, SS-strike-slip, TF-thrust faulting) and GPS velocities of plate movement (Walpersdorf et al., 2006). The plate boundaries (in dark-grey) originally from the World Stress Map are modified after A.M. Ziegler (2001).B correspond à la profondeur des hypocentres des séismes (valeurs en km, cercles gris-noir à blancs, USGS/ NIEC, base de données PDE, 2011 (état le 6.7.2011) dans la zone d’étude, combinée avec les données de σ Hmax provenant de World Stress Map (Heidbach et al., 2008) avec régimes de faille au foyer (NF-faille normale, SS-strike-slip, TF faille inverse) et vitesses GPS des mouvements de plaque (Walpersdorf et al., 2006). Les limites de plaque (en gris foncé) proviennent de World Stress Map, modifié par M.A. Ziegler (2001).
URL http://geomorphologie.revues.org/docannexe/image/10539/img-5.png
Fichier image/png, 685k
Titre Fig. 6 – Topographic profiles of the front sinuosity. Fig. 6 – Profils topographiques du front de sinuosité.
Légende In the south range of Bekhair Mountain (A), in the north range of Dohuk Mountain (B), in the south range of Dohuk Mountain (C), in the north range of Zainiyat Hillslopes (D), and in the south range of Zainiyat Hillslopes (E).Dans la partie méridionale de Bekhair Mountain (A), dans la partie septentrionale de Dohuk Mountain (B), dans la partie méridionale de Dohuk Mountain (C), dans la partie septentrionale de Zainiyat Hillslopes (D) et dans la partie méridionale de Zainiyat Hillslopes (E).
URL http://geomorphologie.revues.org/docannexe/image/10539/img-6.png
Fichier image/png, 447k
Titre Fig. 7 – Photographs of the Dohuk valley. Fig. 7 – Photographies de la vallée du Dohuk.
Légende A: Upper section of the valley. B: Lower section of the valley. C: Profile of the terrace deposits in the upper section of the valley. D: Profile of the terrace deposits in the lower section of the valley. A : Section amont de la valley. B : Section aval de la valley. C : Dépôts de terrasse dans la partie amont de la vallée. D : Dépôts de terrasse dans la partie amont de la vallée.
URL http://geomorphologie.revues.org/docannexe/image/10539/img-7.png
Fichier image/png, 1,9M
Titre Fig. 8 – Subdivision of the study area in upper and lower zones. Fig. 8 – Subdivision de la zone d’étude en zones amont et aval.
URL http://geomorphologie.revues.org/docannexe/image/10539/img-8.png
Fichier image/png, 2,3M
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Référence papier

Elias R. Ziyad, « Relationship between tectonic activity, fluvial system and river morphology in the Dohuk catchment, Iraqi Kurdistan », Géomorphologie : relief, processus, environnement, vol. 20 - n° 1 | 2014, 91-100.

Référence électronique

Elias R. Ziyad, « Relationship between tectonic activity, fluvial system and river morphology in the Dohuk catchment, Iraqi Kurdistan », Géomorphologie : relief, processus, environnement [En ligne], vol. 20 - n° 1 | 2014, mis en ligne le 01 janvier 2016, consulté le 24 septembre 2017. URL : http://geomorphologie.revues.org/10539 ; DOI : 10.4000/geomorphologie.10539

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Auteur

Elias R. Ziyad

Salahaddin University – Iraqi Kurdistan (ziyadelias@yahoo.com).

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