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Anthropogenic impacts on the morphology of the Haora River, Tripura, India

Impacts anthropiques sur la morphologie de la rivière Haora, Tripura, Inde
Shreya Bandyopadhyay et Sunil Kumar De
p. 151-166

Résumés

Depuis le début du XXe siècle, la rivière Haora, ligne de vie de la ville indienne d'Agartala (Etat de Tripura), a été intensément utilisée par les citadins pour satisfaire leurs propres besoins. Les habitants, directement ou indirectement, polluent non seulement l'eau de la rivière mais altèrent également sa morphologie et sa dynamique. La rivière Haora prend sa source dans l'Etat de Tripura et conflue avec la rivière Titas au Bangladesh. Elle a une longueur totale de 61,2 km dont 52 km sur le territoire indien. Sur cette longueur de 52 km, trois longues sections ont été identifiées, sur lesquelles le cours de la rivière ainsi que son débit ont été modifiés en raison des activités anthropiques. Partant de la frontière internationale, ces tronçons couvrent respectivement 5,35 km, 4,74 km et 5,47 km de longueur. L'identification des changements du tracé de la rivière Haora sur la période 1932-2005 a été réalisée en fonction de la disponibilité des cartes et des images (photographies aériennes). Les principales activités, responsables de ces changements, sont la construction de canaux de dérivation pour dévier les eaux de crue, le déversement d'énormes quantités de gravats de brique dans les champs le long de la rivière et le déversement de déchets ménagers sur les berges. En dehors de ces trois tronçons, on a identifié d'autres secteurs où des changements mineurs dans la dynamique fluviale (formation de barres, changement de cours, érosion des berges, etc.) se sont produits. Ils sont initiés par la construction de routes, piles de ponts et autres activités anthropiques.

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Notes de la rédaction

Article soumis le 08 mars 2017, reçu sous sa forme révisée le 11 décembre 2017 et définitivement accepté le 27 février 2018.

Texte intégral

The authors are thankful to Prof. Sunanado Bandyopadhyay, Department of Geography, University of Calcutta, Kolkata, India and Prof. Aurobindo Ghosh, Department of Geological Science, Jadavpur University, Kolkata, India for their help and suggestion in carrying out the study. The authors are also grateful to the reviewers and the Editor of the journal Géomorphologie: Relief, Processus, Environnement for their valuable and meticulous suggestions for upgrading the paper.

1. Introduction

1Since the beginning of human civilization, like Indus, and Harappa man is trying to modify or have already modified several fluvial landforms (Ollero, 2010). In the late 20th century, rivers of India play a vital role in modern civilization and also raise the environmental concern. Growing urbanization (Douglas, 1974, 1978; Ebisemiju, 1989a, 1989b; Hammer, 1972; Hollis, 1976; Klein, 1979; Laronne and Shulker, 2002) and associated human activities are of major problem to the river system (Ebisemiju, 1991). Though those human activities such as bridge, artificial levees are important for development and welfare of human being but they have adverse impact on river morphology (Gregory, 2006; James and Marcus, 2006; Jeje and Ikeazota, 2002; May et al., 1997) and on its natural characteristics (Khan and Islam, 2015). The Tripura state of India is also a riverine state. Among the ten major rivers of Tripura, the Haora River is flowing through the capital city of this state. This river basin was almost uninhabitated before 1900. After the partition of India and East Pakistan (presently Bangladesh) huge numbers of Hindu immigrants entered into adjacent Tripura and settled down along the Haora River in the Agartala city (capital city). Since then the dwellers have been using the Haora River for fulfilling their own needs and also for economic benefits (Kharas, 2010). The dwellers, directly or indirectly are not only polluting the river water but also altering the morphology of the river. But in most of the published papers, researchers are more concerned about the human impacts on the river like pollution status (Hynes, 1960; Baskaran and De Britto, 2010; Pitchammal et al., 2009; Reddy and Baghel, 2010; Subin and Husna, 2013), damage of ecosystem (Duda et al., 1982; Ellis and Marsalek, 1996; Porcella and Sorenson, 1980; Suren, 2000) and there are only few published work concerning about the changes in physical configuration of the river Haora due to human activities. Some of the published works on human’s impacts on different rivers of the world have been given in Table 1.

Tab. 1 – List of some published works on human’s impacts on different rivers of the world.
Tab. 1 – Liste de quelques références bibliographiques traitant des impacts de l'homme sur différentes rivières du monde.

Tab. 1 – List of some published works on human’s impacts on different rivers of the world.   Tab. 1 – Liste de quelques références bibliographiques traitant des impacts de l'homme sur différentes rivières du monde.

2Since the beginning of twentieth century, channel of the main Haora River has been modifying, firstly by the “then king” (Maharaja Birendra Kishore Manikko) and after that Government agencies and local people. To meet the increasing demand of water of the city, Government as well as the local people has been constructing several obstructions along (roads and embankments in some places) and across the river (bridge piers, causeways, sand bag filling for collecting water and so on), for which the river is being compelled to change its natural flow. Other human activities like, land-use change, sand mining, water collection, solid waste disposal, agriculture and cutting of tilla land (Tillas are the low elevated denudational uplands which is bifurcated by narrow dry up channels, called lunga. The elevation variations between tilla and adjacent lunga is only a few meter) for supplying raw materials to the brick industries (Bandyopadhyay et al., 2013a) are also causing the change of the river course, modifying the natural dynamics and gradually making the Haora River sick. Thus, to analyze such an important issue of the Haroa river, the following objectives have been taken into consideration (i) to identify the stretch-wise course changes and the causes behind such individual changes (in terms of artificial channel modification, solid waste disposal, brick waste dumping, sand extraction, etc.) and (ii) to analyze channel rugosity of the Haora River and other changes like bank erosion, land use change, etc., within the river basin, due to the said human activities and probable consequences of them.

2. Location of the study area

3The Haora River is one of the major rivers of the West Tripura District in India located at latitudinal extension of 23˚37΄ and 23˚53΄N, and longitudinal extension of 91˚15΄ and 91˚37΄E (fig. 1). The river basin is covers an area of 405.8 km² (in India and Bangladesh) and is located in the southern part of West Tripura District bordering by the Khowai and the Shipahijola Districts in eastern and southern sides and by the Bangladesh from north and northwestern sides. After originating from the western flank of the Baramura range, the river flows through the hilly tracts for a distance of 6.6 km and debouches onto the foothill zone near Chandrasadhubari (83 m). The river is exhibiting its characteristics of the middle course up to a distance of 21.8 km (up to Jirania, 32 m) from the debouching point. From Jirania onwards, the Haora River flows through the plain, with an elevation below 30 m, until the confluence point with Titas River in Bangladesh (10 m). This river has a total length of about 61.2 km among which 52 km is flowing in Indian Territory. Physiographically, the major part of the Haora River flows through moderately low undulating denudational topography i.e. tilla lands, having elevation between 6 m to 201 m. All the tilla land in Haora River Basin possess Dupitila group (Pleistocene period) of rock in their top layer. The composition of Dupitila group is sandy clay, clayey sandstone; ferruginous sandstone with pockets of plastic clay, silica, and laterite (Menon, 1975). Most of these rocks of Dupitila group are so soft and fragile that they can be very easily excavated even through axe. The Haora River is mainly a rain fed river and having a sinuous drainage pattern. From the analysis of 21 years hydrological data obtained from Central Water Commission (CWC) it is revealed that the total annual discharge of the Haora River is about 180 m³.s¹, but the monthly rate of discharge is widely fluctuating. At least two peaks are noticed in every year that indicates the number of months having high discharge. Maximum monthly discharges are noticed in 2004 followed by 2006 (about 140-165 m³.s¹) which are considered as intense flood years.

Fig. 1 – Location map of the Haora River Basin.
Fig. 1 – Carte de localisation du bassin versant de la rivière Haora.

Fig. 1 – Location map of the Haora River Basin. Fig. 1 – Carte de localisation du bassin versant de la rivière Haora.

A. Map of India indicting NE India; B. State wise division of NE India highlighting Tripura and Tripura map locating the Haora River Basin; C. Entire drainage basin map of the Haora River; 1. Perennial rivers; 2. Non perennial rivers; 3. National Highway; 4. International border between India-Bangladesh.
A. Carte de l'Inde ; B. Carte des États du Nord-Est de l'Inde localisant le district de Tripura et le bassin versant de la rivière Haora ; C. Réseau hydrographique du bassin de la rivière Haora ; 1. Cours d'eau pérenne ; 2. Cours d'eau non pérenne ; 3. Autoroute ; 4. Frontière internationale entre l'Inde et le Bangladesh.

3. Methodology

4In classical approach in geomorphology diachronic analysis of is an important technique of the evolution and changes of any topography (Piégay and Schumm, 2003; Michalkova, 2009; Bălteanu et al., 2012; Gomez et al., 2015; Grecu et al., 2017). Detection of course change of the main Haora between the years 1932-2005 has been considered based on the availability of maps. This temporal changes of the Haora River have been identified from the 1932 Survey of India (SOI) topographical maps (scale 1:63,360), 1956 USGS Army topographical map (scale 1:250,000) and from the Google images of 2009, 2011 and 2014. The course of 1956 is taken into consideration for detecting such changes because there was a great earthquake (magnitude-8.6) in North-East India on 15 December 1950 (Seeber and Armbruster, 1981; Molnar, 1990). That earthquake led to the change of many river courses in the region including the Brahmaputra River, the longest river in NE India. Google images are used for detecting the nature and amount of changes of the tilla (denudational upland) and agricultural lands. The vertical lowering (reduction of relief) of the said land is identified from field survey.

5Location of major anthropogenic activities like brick fields (sites for brick construction), bridges and causeways along the Haora River have initially been identified from the Google image and thereafter verified with the help of GPS during field survey.

6Cross profiles for three consecutive years (2010-2012) have been taken from several sections along the Haora River with the help of Dumpy Level for detecting the changes and to assess the probable causes behind it. To standardize those cross-profiles of different years, the starting points and the finishing points were remain fixed and some other fixed intermediate points were also taken into consideration. Fixed bench marks were set for all the cross sections of different time periods.

7Sediments are collected from the mid channel bed of the river from 2 km upstream side of the brick fields, near the brick fields and 2 km downstream from the brick fields area, for understanding the artificial textural changes of the sediments. Finally, the extents of the anthropogenic activities in all the upstream and downstream stretches along the Haora River have been identified from the field survey.

4. Results and discussion

4.1. Course change of the Haora River

8From the superimposed courses of the River Haora (fig. 2A), no major change along the course has been observed between 1932 and 1956. The river course remained unaltered even after the 1950 earthquake. Between 1956‑2005 four sections along the Haora River have been detected, where major changes occurred along the course and they are marked as a, b, c and d in Figure 2A. In the stretch a, about 9.89 km long courses of the Haora River as well as the course of one of its earlier tributary (the Katakhal River) have changed drastically (fig. 2A). Still in the 1956 SOI topographical maps it was found that, after crossing the international border, the Haora River used to take a sharp northward bend to meet with the River Titas. The same topographical map showed the connection of the Katakhal River with Haora River (fig. 3A); but from a recent satellite image (Google, 2005) it is observed that the Haora River has left its northward course and is flowing westward to meet with the River Titas. In the case of the Katakhal River, the connection between the Haora and Katakhal Rivers is completely abandoned, and now it is flowing separately. Such change occurred due to neo-tectonic activities i.e. upliftment of the interfluvial zone between the Haora River and the Katakhal river (fig. 3B) near their confluence due to folding (Bandyopadhyay et al., 2013a). But in rest of the stretches (i.e. b, c and d) changes occurred due to anthropogenic impacts.

Fig. 2 – Superimposed courses of the Haora River with the location of cross-sections across the river.
Fig. 2 – Cartographie diachronique des tracés de la rivière Haora avec l'emplacement des transects recoupant la rivière.

Fig. 2 – Superimposed courses of the Haora River with the location of cross-sections across the river.   Fig. 2 – Cartographie diachronique des tracés de la rivière Haora avec l'emplacement des transects recoupant la rivière.

A. Super-imposed map of the Haora River courses for the period 1932-2005. a. 1st stretch of course change in Bangladesh; b. 2nd stretch of course change between the College-Tilla to the Bangladesh Border; c. 3rd stretch of course change along the major market disposal sites; d. 4th stretch of course change between the Jirania and Ranir Bazar Blocks; 1. River course for the year 1932; 2. River course for the year 1956; 3. River course for the year 2005; 4. India-Bangladesh Border. B. Locations of cross-sections along the Haora River. 4. India-Bangladesh Border; 5. Cross sections.
A. Carte des cours de la rivière Haora sur la période 1932-2005. a. 1er secteur au Bangladesh ; b. 2ème secteur entre College-Tilla et la frontière du Bangladesh ; c. 3ème secteur le long des principaux sites de dépôt d'ordures des marchés ; d. 4ème secteur entre les blocks de Jirania et Ranir Bazar ; 1. Tracé de la rivière en 1932 ; 2. Tracé de la rivière en 1956 ; 3. Tracé de la rivière en 2005 ; 4. Frontière Inde-Bangladesh. B. Localisation des transects réalisés le long de la rivière Haora. 4. Frontière Inde-Bangladesh ; 5. Transects.

Fig. 3 – Diagrammatic representation of tectonic changes that lead to the changes in courses and the confluence of the Haora River and the Katakhal River (after Bandyopadhyay et al., 2013A).
Fig. 3 – Représentation schématique des changements tectoniques qui entraînent des changements dans le tracé des cours et de la confluence de la rivière Haora et de la rivière Katakhal (d'après Bandyopadhyay et al., 2013A).

Fig. 3 – Diagrammatic representation of tectonic changes that lead to the changes in courses and the confluence of the Haora River and the Katakhal River (after Bandyopadhyay et al., 2013A).   Fig. 3 – Représentation schématique des changements tectoniques qui entraînent des changements dans le tracé des cours et de la confluence de la rivière Haora et de la rivière Katakhal (d'après Bandyopadhyay et al., 2013A).

A. Condition of the Katakhal River and the Haora River confluence zone during 1932; B. Condition of the Katakhal River and the Haora River confluence zone after detachment; 1. Traces of the oscillations of the Titas River meander; 2. The directions of shifting of both the rivers.
A. État de la zone de confluence de la rivière Katakhal et de la rivière Haora en 1932 ; B. État de la zone de confluence de la rivière Katakhal et de la rivière Haora après leur séparation ; 1. Localisation des tracés du méandre de la rivière Titas ; 2. Directions de migration des deux rivières.

4.1.1. Channel planform in Portion B (from the College-Tilla up to the Bangladesh Border)

9The 2nd stretch, marked as b in Figure 2A, is located near the Agartala city between College‑Tilla up to Bangladesh Border (fig. 4A). In this stretch the change (6.06 km long in 2005) occurred in two parts (fig. 4B). In the first part, from College-Tilla to Rajnagar, the course has been shifted towards south. Again from Rajnagar to Bangladesh Border the shifted course is located Northward of the earlier course (fig. 4). The sinuosity index (SI) of this stretch has been reduced from 1.31 to 1.10. From the field survey it is revealed that the shifting occurred due to human activity. During the regime of Maharaja Birendra Kishore Manikko (1909-1923), a canal (the present course) from the Haora River was dug (fig. 4) in order to save Agartala Town from flood. But the canal gradient and the channel bed was lower than the original Haora River. As a result the Haora River diverts its flow through the canal and the mouth of the original course near the connection was getting sedimented.

10The cut-off of the 2nd segment still can be traced from the ground which is still flowing as a narrow canal through agricultural land and River (fig. 4C). The left off course of the 1st segment is still existing and the area has been modified by the expanding town area.

Fig. 4 – Changing course of the Haora River between the College-Tilla to the Bangladesh Border.
Fig. 4 – Changement de tracé de la rivière Haora entre le Collège-Tilla et la frontière du Bangladesh.

Fig. 4 – Changing course of the Haora River between the College-Tilla to the Bangladesh Border.   Fig. 4 – Changement de tracé de la rivière Haora entre le Collège-Tilla et la frontière du Bangladesh.

A. Latitudinal and longitudinal extension of the area; B. Google Image depicting the river course change between College-Tilla to Bangladesh Border; C. Inset depicting the trace of earlier abandoned channel as elongated water bodies; 1. River course for the year 1932; 2. River course for the year 2005; 3. India-Bangladesh Border.
A. Extension latitudinale et longitudinale de la zone ; B. Image Google illustrant le changement de tracé de la rivière entre le Collège-Tilla à la frontière du Bangladesh ; C. Encart représentant le tracé d'un ancien chenal abandonné occupé par des plans d'eau allongés ; 1. Tracé de la rivière en 1932 ; 2. Tracé de la rivière en 2005 ; 3. Frontière entre l'Inde et le Bangladesh.

4.1.2. Channel planform in portion C (near the major garbage disposal sites)

11The third stretch (8.47 km long in 2005) of course change (marked as c in Figure 2A) is located near the major markets sites in Ranir Bazar Block (such as Bridhhanagar market and Ranir Bazar Market). Although from the comparison of sinuosity index (SI) for the year 1932 (SI = 1.43) and 2005 (SI = 1.42) no major morphological changes has been found on map, from the analysis of cross-section (Cross-section 18 in Figure 2B) for 3 consecutive years (2010-2012), the change in the river morphology is clearly evidenced. These cross-sections have been taken near the Bridhhanagar market site (fig. 5D). From that cross-sectional analysis it was found that in the year 2010 the width - width has been detected based on the water level along the both banks during survey in the month of February-March each year - of the Haora River was 42 m but in 2012 the width has come down to 10 m. This is because all these markets dump their waste materials along the right bank of the Haora River (fig. 5A-C). Since these dumping materials contain plastic and other artificial components, these get mixed with the suspended sediment very quickly and act as binding nuclei to force the sediment to be clod and deposited. Within the 3 years survey periods, the Haora River catchment experienced two heavy discharge but those materials can still be traced within the deposition during the post monsoon season. This prevailed strong adhesive characteristic of those materials, got mixed with the sediment and make that so hard, cannot be eroded entirely by the monsoon water. This type of depositions continued downstream up to a distance of 1.8 km from the Ranir Bazar.

Fig. 5 – Changing course of the Haora River along the major market disposal sites.
Fig. 5 – Changement de tracé de la rivière Haora le long des principaux sites de dépôt d'ordures des marchés.

Fig. 5 – Changing course of the Haora River along the major market disposal sites.   Fig. 5 – Changement de tracé de la rivière Haora le long des principaux sites de dépôt d'ordures des marchés.

A. Picture of the market site taken in the year 2010; B. Picture of the market site of 2011; C. Market site picture of 2012; D. 3 years consecutive cross sections of the Haora River along the market site; 1. Cross section of 2010; 2. Cross section of 2011; 3. Cross section of 2012.
A. Photo du site du marché prise en 2010 ; B. Image du site du marché en 2011 ; C. Photo du site du marché en 2012 ; D. Trois ans consécutifs de coupes transversales de la rivière Haora le long du site du marché ; 1. Coupe transversale de 2010 ; 2. Coupe transversale de 2011 ; 3. Coupe transversale de 2012.

4.1.3. Channel planform in portion D (between the Jirania and Ranir Bazar Blocks)

12The 4th stretch (8.90 km long in 2005) of course change is taking place between the confluence zone of the Donaiganjand GhoramaraChara with the Haora River (fig. 6). The stretch is located in the Jirania and Ranir Bazar blocks. The Sinuosity Index in this small stretch was changed from 1.27 to 1.22 within 1932-2005.The changes in this stretch have been occurred due to the establishment of brick fields cluster (50 fields) (Bandyopadhyay et al., 2013b).

Fig. 6 – Changing course of the Haora River between the Jirania and Ranir Bazar Blocks.
Fig. 6 – Changement de tracé de la rivière Haora entre les blocks de Jirania et de Ranir Bazar.

Fig. 6 – Changing course of the Haora River between the Jirania and Ranir Bazar Blocks.   Fig. 6 – Changement de tracé de la rivière Haora entre les blocks de Jirania et de Ranir Bazar.

1. Haora River course of 1932; 2. Haora River course of 2005; 3. Brick fields.
1. Cours de la rivière Haora en 1932 ; 2. Cours de la rivière Haora en 2005 ; 3. Champ de briques.

13During field survey between the years 2010-2014, an interesting feature was found in the Haora River near the brick field clusters in Debendranagar area (Cross-section 9 in Figure 2B). Since this stretch of the Haora River belongs to upper portion of its middle course, the depositional material of this area is mainly of sandy-silty composition. In the year 2010, a point bar of silty composition was found along the left bank of the river (fig. 7A). In the year 2011 the earlier bar was getting eroded and a new bar of purely clay deposit has been formed in its frontal part (fig. 7B).

14Formation of this bar was leading to the reduction of the channel width (from 9 m to 6.4 m in Figure 7E). In the year 2012 this newly formed bar has further been enlarged (fig. 7C) and the width of the channel has further been narrowed by 0.6 m (fig. 7E). The narrow channel has been failing to carry its water and during high discharge period it has started to form a new course through the left side of the earlier silty point bar. In 2014 it is found that this newly formed channel has become the main flow of the river because of excessive left bank erosion but that clayey bar is still enlarging (fig. 7D). This phenomenon has occurred in several places up to 1.5 km downstream from Debendranagar.

Fig. 7 – Evidence of river course changes and sequential cross sections (2010-12) of the Haora River near Debendranagar.
Fig. 7 – Indices des changements de tracé de la rivière Haora et transects séquentiels (2010-12) près de Debendranagar.

Fig. 7 – Evidence of river course changes and sequential cross sections (2010-12) of the Haora River near Debendranagar.   Fig. 7 – Indices des changements de tracé de la rivière Haora et transects séquentiels (2010-12) près de Debendranagar.

A. Photograph showing the condition of the Haora River near Debendranagar in the year 2010; B. River course of 2011; C. River course of 2012; D. River course for the year 2014; E. Superimposed cross sections of 3 consecutive years (2010-12); 1. Direction of flow; 2. Location of the cross section; 3. Cross section of the year 2010; 4. Course section of 2011; 5. Cross section of 2012; 6. Wetted part, line joining two extreme points of the wetted part of a particular year is considered the water level during the time of survey of that particular year.
A. Photo montrant l'état de la rivière Haora près de Debendranagar en 2010 ; B. Cours de la rivière en 2011 ; C. Cours de la rivière en 2012 ; D. Cours de la rivière en 2014 ; E. Transects superposés de trois années consécutives (2010-2012) ; 1. Direction de l'écoulement ; 2. Emplacement de la section transversale ; 3. Transect de 2010 ; 4. Transect de 2011 ; 5. Transect de 2012 ; 6. Section mouillée, la ligne joignant deux points extrêmes de la section en eau d'une année donnée est considérée comme le niveau de l'eau au moment de l'étude.

15To find out the cause behind such deposition a survey has been carried out in the upstream site along the river up to a distance of 2 km. It is found that two brick fields, namely R.B.I and Ramthakur, situated along the right bank of the river are dumping all its wastes along the river bank (fig. 8A). To find out the impact of such deposits, 3 sediment samples have been collected from upstream side of the brick fields, near the R.B.I brick field (fig. 8B) and also from the downstream part of the brick fields (from the clay bar in Debendranagar, fig. 7B).

16The 1st sample has been collected from 2 km upstream side from the R.B.I brick field, composed of structure-less clay (fig. 8C). This type of sediment is usually found in suspended form in water, transported up to a long distance and finally deposited in the lower course of the river where the velocity becomes very low. The 2nd sample has been collected near the R.B.I. brick field area (fig. 8D). In the river it was found in lump form, but when it was crushed in the laboratory, some tiny brick particles were detected. Finally in the 3rd sample, collected from the bar near Debendranagar, tiny particles of brick were found in metamorphosed form (fig. 8E). From the structural characteristics of the samples it can be stated that although the textural composition of the aforesaid sample are same, intrusion of tiny brick particles within this clay is making the structure different. These brick particles are acting as the lumping nuclei and leading to the deposition of clay in the form of bars which cannot be eroded by the river. And as this lumps being deposited randomly in the channel are also increasing the rugosity of the river and channel migration.

Fig. 8 – Location of the brick fields, the places and photographs of sediment samples collected along the course of Haora River.
Fig. 8 – Emplacement des champs de briques, des sites et des photographies des échantillons de sédiments recueillis le long de la rivière Haora.

Fig. 8 – Location of the brick fields, the places and photographs of sediment samples collected along the course of Haora River.   Fig. 8 – Emplacement des champs de briques, des sites et des photographies des échantillons de sédiments recueillis le long de la rivière Haora.

A. Location of the brick fields; B. Photo of R.B.I Brick field located just along the right bank of the Haora River; C. Photo of sediment sample collected from upstream part of the river; D. Condition of sediment sample collected near R.B.I. brick field; E. Sediment sample collected from Debendranagar; 1. Brick fields; 2. Traces of tiny brick particles within the sediment sample.
A. Emplacement des champs de brique. B. Photo du champ de brique R.B.I situé le long de la rive droite de la rivière Haora ; C. Photo d'un échantillon de sédiments prélevé dans la partie amont de la rivière ; D. État de l'échantillon de sédiment recueilli près du champ de brique R.B.I. ; E. Échantillon de sédiment prélevé à Debendranagar ; 1. Champs de briques ; 2. Traces de minuscules particules de brique dans l'échantillon de sédiment.

4.2. Tilla land degradation

17Most of the brick fields within this river basin collect mud by degrading the surrounding tilla lands haphazardly (by axing here and there randomly along the tillas resulting in reduction of their heights and change in their structure) (fig. 9A). The left out loose particles are transported to the Haora River and create excessive sedimentation (Davinroy et al., 2003; Arohunsoro et al., 2014). The brick fields (pink spots) and degraded tilla lands (yellow spots) have been mapped by a GPS. Both of these two maps have then been superimposed on the 3D terrain model of the area. From the figure it is clearly noticed that the brick fields are located either in low lying areas between the tillas or at the foot of the tillas (fig. 9B). It suggests that the brick fields collect their raw materials from the surrounding tilla lands. From the satellite image, a total of 1.45 km² of tilla lands affected by these brick fields were mapped.

Fig. 9 – Location of brick fields and cut off lands in 3D model.
Fig. 9 – Emplacement des champs de briques et des terres incisées dans le modèle 3D.

Fig. 9 – Location of brick fields and cut off lands in 3D model.   Fig. 9 – Emplacement des champs de briques et des terres incisées dans le modèle 3D.

A. Location of the brick fields; B. Superimposition of brick fields and tilla cut off in 3D DEM; 1. Brick fields; 2. Tilla cut off.
A. Emplacement des champs de brique ; B. Superposition de champs de brique et de tilla incisés dans le modèle 3D ; 1. Champ de briques ; 2. Tilla incisé.

18In most cases it is found that tilla lands are degrading at an alarming rate (Eswaran et al., 1993; Eswaran, 1999). During the field survey one such tilla land has been taken as a case study. Firstly, areal degradation of the tilla land is measured from Google image. The area of that particular tilla was reduced from 11,290 m² to 8,760 m² and 5,490 m² in the years 2009 (fig. 10A), 2011 (fig. 10B) and 2014 (fig. 10C) respectively. In 2010 the tilla land was cut to collect the raw materials in two different tiers. The 1st tier, having an area of 5,521.8 m² was cut up to the level of NH44 (National Highway No-44) and the next tier having an area of 3,594.1 m² was excavated further downward up to a depth of 8.06 m from the 1st tier. It indicates that a total volume of 33,682.98 m³ material from the 1st tier and 28,968.446 m³ materials from the 2nd tier has been removed (fig. 10D). The height of the tilla land has also been estimated from the field survey. In 2010 the tilla was still maintaining its height about 6.1 m (from the level of NH44) but in 2012 the height of that tilla was reduced to 1.6 m (fig. 10E).

Fig. 10 – Evidences of areal reduction and step by step sequential degradation of tilla lands (Near National Brick Industry - N.B.I).
Fig. 10 – Évidences de la réduction de surface et de la dégradation séquentielle progressive des terres à tilla (Near National Brick Industry - N.B.I).

Fig. 10 – Evidences of areal reduction and step by step sequential degradation of tilla lands (Near National Brick Industry - N.B.I).   Fig. 10 – Évidences de la réduction de surface et de la dégradation séquentielle progressive des terres à tilla (Near National Brick Industry - N.B.I).

A. Google image of 2009 showing the N.B.I. Brick field and surrounding tilla land; B. Google image of 2011 of N.B.I Brick field; C. Google image of the year 2014; D. Photograph showing condition of the N.B.I. surrounding tilla land in 2010; E. Photo of vertical reduction of the tilla in 2012; 1. Area coverage of the tilla in 2009; 2. Tilla land areal coverage in 2011; 3. Areal coverage in 2014.
A. Image Google de 2009 montrant le champ de brique N.B.I. et les tilla environnantes ; B. Image Google de 2011 du champ de brique N.B.I ; C. Image Google de l'année 2014 ; D. Photographie montrant l'état de la N.B.I. dans le secteur des tilla en 2010 ; E. Photographie du décapage vertical du tilla en 2012 ; 1. Couverture de la zone des tilla en 2009 ; 2. Couverture du secteur des tilla en 2011 ; 3. Couverture géographique en 2014.

4.3. Agricultural land degradation

19Apart from the tilla lands, brick fields also collect raw material (soil) from the agricultural land (Rahman and Khan, 2001; Khan et al., 2007). Most of these brick fields in the Haora River Basin are surrounded by agricultural land (fig. 11A). Soil texture within the basin varies from loamy to clayey with slight acidity and high compactness. Thus, they are considered as very rich raw material for the brick fields. For quantifying the rate of cutting of agricultural land, one affected agricultural land is taken into consideration, located in the opposite bank of the river of LNBI brick field (fig. 11A). The outline of that selected agricultural plot was digitized to delineate spatio-temporal changes and verified from the field photographs. In the 2009 image the agricultural land appears unaffected (fig. 11B). In the 2011 image it is found that excavation had started and within this 2 year period a total of 0.0184 km² of agricultural land was damaged (fig. 11C). In 2014 the amount of land cutting has further increased to 0.0306 km² and land quarrying has been extended further inside (south-east ward) from the river (fig. 11D). From the field it is estimated that the brick fields are excavating that agricultural land at an average depth of 0.6-2.5 m (noticed during field survey in 2011 and 2014). The affected agricultural land is excavated at differential rate. One tree remained at the middle of that land. From the tree root up to the bottom of the excavated agricultural land, the depth was about 2.5 m, whereas at the periphery the depth reduced to 0.6 m (fig. 11E). Based on this data it is estimated that in the first 2 years period (2009-2011) the brick fields have excavated 27,664.5 m³ and in the next 3 years time period (2011-2014) they have excavated 45900 m³ of soil from the agricultural land.

Fig. 11 – Location of brick fields and agricultural land and evidences of degradation of agricultural land within the Haora River Basin.
Fig. 11 – Localisation des champs de brique et des terres agricoles et indices de la dégradation des terres agricoles dans le bassin de la rivière Haora.

Fig. 11 – Location of brick fields and agricultural land and evidences of degradation of agricultural land within the Haora River Basin.   Fig. 11 – Localisation des champs de brique et des terres agricoles et indices de la dégradation des terres agricoles dans le bassin de la rivière Haora.

A. Distribution of agricultural land and brick field within Haora River basin; B. Condition of the agricultural land at the opposite bank of the Lakshmi Narayan Brick Industry (LNBI) in 2009; C. Google image of that agricultural land (opposite of LNBI) in 2011; D. Google image showing further degradation of the land in 2014; E. Photograph of the left out tree in that agricultural land (opposite of LNBI) indicating maximum limit of vertical excavation; 1. Location of LNBI; 2. Agricultural lands; 3. Brick fields; 4. Direction of river water flow.
A. Répartition des terres agricoles et des champs de brique dans le bassin de la rivière Haora ; B. État des terres agricoles sur la rive opposée à la briqueterie de Lakshmi Narayan (LNBI) en 2009 ; C. Image Google de ce secteur agricole (à l'opposé de LNBI) en 2011 ; D. Image Google montrant l'évolution de la dégradation du secteur en 2014 ; E. Photographie de l'arbre laissé à l'abandon sur cette terre agricole (à l'opposé de LNBI) indiquant la hauteur maximale de l'excavation verticale ; 1. Emplacement de LNBI ; 2. Terres agricoles ; 3. Champs de brique ; 4. Direction de l'écoulement de la rivière.

4.4. Impact of road construction directly on river bed

20In most cases the Brick fields located along the left bank of the river do not have proper road connectivity with the NH44 as it is situated at the right bank of the river and most of the brick fields are at the left bank. So those brick fields have to transport their materials across the river. Even those brick field which are lying along the right bank are using the river beds to collect their raw materials from the agricultural land located along the left bank of the river.

21Between Champaknagar to Jirania (11.83 km) there are only two bridges. To access those bridges all the trucks, caring raw materials as well as the finished products of the brick fields, have to travel a long distance, which increases the cost of production. That is why most of the brick fields have constructed some temporary roads across the river and even sometimes they use the river bed itself as their means of transportation by dumping bricks particles. This dumping of brick within river bed were making the bed hard and affecting the rugosity of the Haora River.

4.5. Impact of sand mining

22Brick fields and some other constructional industries are collecting sand from the Haora River as the texture of the sand is very fine and it is of high demand for their production purpose. This mining of sand from the river bed as well as from the river bank causes different types of hydrological changes within the river system (Kondolf, 1993, 1998; Saviour, 2012). Quarrying of sediment from the river bed is commonly treated as a good practice that reduces the sedimentation problem of a river. But in the present case it creates further problem to the river because the sediments are quarried randomly from the river bed between Champaknagar and Khayerpur areas that makes the river bed irregular and fragile and generates further sedimentation to the lower reaches of the river. Sometimes they use pump machine for lifting sand from the river bed.

23In order to find out the impact of sand collection from the river bed and banks, cross section of 3 sequential years (2010-2012) have been taken from two different places (major sand collection spots) along the river (Cross-section 13 and 17 in Figure 2B). The 1st cross section has taken near Mohonpur Bazar. In the year 2010 the width of the river was about 27.75 m and maximum depth was 0.51 m but the width has come down to 24.6 m and the maximum depth had increased to 0.65 m in 2011 (fig. 12A). The condition has further been deteriorated in 2012, when the river has become narrower (21.05 m) and the maximum depth (1.4 m) has increased considerably (fig. 12A). Continuous scouring of river bed due to sand collection is not only affecting the bed, but also the right bank the river experiences erosion. From these 3 years trend it is found that the main course of the river is shifting towards right. Same scenario is found in the 2nd cross section taken at 100 m upstream from the Khayerpur Bridge, where width of the river bed is reducing and depth is increasing. In this place the right bank is experiencing erosion and severe bank failure takes place during monsoon season (fig. 12B).

Fig. 12 – Sequential changes within the river bed due to unscientific quarrying of sand.
Fig. 12 – Changements séquentiels dans le lit de la rivière dus à l'extraction non contrôlée de sable.

Fig. 12 – Sequential changes within the river bed due to unscientific quarrying of sand.   Fig. 12 – Changements séquentiels dans le lit de la rivière dus à l'extraction non contrôlée de sable.

A. Cross section taken near Mohonpur Bazar; B. Cross section at 100m upstream from the Khayerpur Bridge; 1. Cross section of the year 2010; 2. Cross section of 2011; 3. Cross section of 2012; 4. Wetted part.
A. Coupe transversale prise près du Bazar de Mohonpur ; B. Coupe transversale à 100 m en amont du pont de Khayerpur ; 1. Coupe transversale en 2010 ; 2. Coupe transversale en 2011 ; 3. Coupe transversale en 2012 ; 4. Section mouillée.

4.6. Impact of bridge piers on the Haora River

24Constructions of bridge piers have some morphological impacts (Lane, 1955) on rivers. Pier scouring occurs when water discharge is suddenly increased and it washes away big amounts of soil materials adjacent to bridge piers (Ashmore and Parker, 1983; Heidarnejad et al., 2010). Most of the soil particles removed surrounds the bridge piers by turbidity currents (Pasiok and Stilger-Szydło, 2010), and they are deposited as bars at the immediate downstream of the bridge.

25Further this sediment free water is started eroding the downstream banks of the river (Biswas, 2010; Mani and Patwary, 2000; Naik et al., 1999; Seiyaboh et al., 2013). There are several bridges located along the Haora River (fig. 13A). Along the Haora River it is evidenced that when there was no bridge near Khayerpur in 2001, no bar was noticed along that section of the river (fig. 13B). But from 2010 Google image both bridge and bar have been noticed in the downstream and the size of that bar became extensive within next two years (fig. 13C). In 2014 the width of the Haora River became narrow (20.4-9 m). Active bank erosion can be evidenced from 20 m downstream of the bridge (fig. 13D). From field survey it is found that the effects of bridge piers vary with their size and composition. Along the Haora River it is found that big and extended bars (22 m × 3.2 m) have been formed near the concreted heavy- weight bridge piers (fig. 13E), whereas near the light weight bridge piers (fig. 13F) the length of the bar is less. Moreover, no bar in the Haora River has been noticed near the hanging bridge located very close to International border (fig. 13G).

Fig. 13 – Evidence and variability of bar formations as an impact of different types of bridge constructions within the Haora River.
Fig. 13 – Évidence et variabilité des formations de barres consécutives à la construction de différents types de ponts dans la rivière Haora.

Fig. 13 – Evidence and variability of bar formations as an impact of different types of bridge constructions within the Haora River.   Fig. 13 – Évidence et variabilité des formations de barres consécutives à la construction de différents types de ponts dans la rivière Haora.

A. Location of bridges along the Haora River; B. Google image showing the condition of the Haora River before the construction of the bridge near Khayerpur in 2001; C. Google image depicting the channel narrowing and the formation of bar after the construction of bridge pier in 2011; D. Google image showing further advancement of the bar along the bridge pier in 2013; E. Formation of large elongated bar near heavy weight bridge with concrete piers; F. Formation of small bar near light weight bridge with wooden piers; G. Trace of no bar below the hanging bridge; 1. Direction of flow; 2. Bridge.
A. Emplacement des ponts le long de la rivière Haora ; B. Image Google montrant l'état de la rivière Haora avant la construction du pont près de Khayerpur en 2001 ; C. Image Google montrant le rétrécissement du chenal et la formation d'une barre après la construction du pont en 2011 ; D. Image Google montrant la progression du banc le long de l'arche du pont en 2013 ; E. Formation d'une grande barre allongée près d'un pont massif réalisé avec des piliers en béton ; F. Formation d'une petite barre près d'un pont léger réalisé avec des piliers en bois ; G. Absence de barre sous le pont suspendu ; 1. Direction de l'écoulement ; 2. Pont.

26After analyzing the human activities along the Haora River, the average limit of the impact of 5 different activities i.e. sand collection, causeways/ roads, brick fields, bridge piers and tilla cutting (fig. 14E-I), buffer zones have been estimated. Firstly, the numbers of each category of activity along the Haora River are measured. Among them in some selected sections surveys have been conducted for consecutive five years (2010-2014) and the extension of changes in the river have been observed. Based on this method the final limit of anthropogenic activities both in upstream and downstream reaches of the Haora River have been estimated (tab. 2).

Tab. 2 – Estimation of the limit of impacts of the individual activities along the Haora River.
Tab. 2 – Estimation de la limite des impacts des activités par catégorie le long de la rivière Haora.

Tab. 2 – Estimation of the limit of impacts of the individual activities along the Haora River.   Tab. 2 – Estimation de la limite des impacts des activités par catégorie le long de la rivière Haora.

27From the anthropogenic activity map (fig. 14A) a total length of 44.75 km of bank is considered under very less affected areas, but only 48 patches under this category have been found along the river. It is because an extensive area particularly in the upper catchment (up to Purba Debendranagar along the river) remains almost unaffected from anthropogenic activities (fig. 14C). In Champaknagar area the river banks are considered as moderate to highly affected. There are 64 patches, covering a length of 28.25 km along the river, are considered as moderately affected (fig. 14B). Both in Champaknagar and Jirania Blocks (fig. 14D), maximum area is falling in high to very high affected zones. The major anthropogenic activities noticed in these two blocks are sand collection, brick fields, bridges and tilla cutting (fig. 14G-I).

Fig. 14 – Anthropogenic impact map of the Haora River bank along with the graph showing total lengths in individual parameters.
Fig. 14 – Carte de l'impact anthropique le long des berges de la rivière Haora incluant un graphique montrant les longueurs totales impactées selon les paramètres pris en compte.

Fig. 14 – Anthropogenic impact map of the Haora River bank along with the graph showing total lengths in individual parameters.   Fig. 14 – Carte de l'impact anthropique le long des berges de la rivière Haora incluant un graphique montrant les longueurs totales impactées selon les paramètres pris en compte.

A. Anthropogenic impact map prepared from multi-buffer zonation of six individual anthropogenic activities evidenced along the Haora River; B. Pie graph showing the coverage of different impact zones; C. Expanded picture of the selected stretch showing very high, high and moderate impact zones of the Haora River; D. Expanded picture of the second selected stretch showing low and very low impact zones of the Haora River; E. Picture of sand quarrying from the river; F. Road or causeway across the river; G. Brick fields along the river; H. Bridges across the river; I. Picture tilla cutting along the Haora River. 1. River; 2. Zone of very low anthropogenic impacts; 3. Zone of low anthropogenic impacts; 4. Zone of moderate anthropogenic impacts; 5. Zone of high anthropogenic impacts; 6. Zone of very high anthropogenic impacts.
A. Carte de l'impact anthropique réalisée à partir de la sectorisation multi-buffer de six activités anthropiques observées le long de la rivière Haora ; B. Diagramme-secteur montrant la répartition selon le degré d'importance des zones impactées ; C. Zoom sur un tronçon à zones d'impact très élevé à modéré ; D. Zoom sur un tronçon à zones d'impact faible à très faible ; E. Photo d'extraction de sable en rivière ; F. Route ou chaussée traversant la rivière ; G. Champ de brique le long de la rivière ; H. Pont ; I. Tilla incisé le long de la rivière Haora. 1. Rivière ; 2. zone à très faibles impacts anthropiques ; 3. Zone à faibles impacts anthropiques ; 4. Zone à impacts anthropiques modérés ; 5. Zone à forts impacts anthropiques ; 6. Zone à très forts impacts anthropiques.

28Due to the unscientific construction across the river, the natural behavior of the river has been changed. For readjusting the condition, the river changes its behavior and possess a great pressure on those constructional structures ending with collapsing most of it. For instance along the Haora River a causeway, in the northern most part of the bypass road between Bisalgarh to Champaknagar (fig. 15A), was constructed across the river (dike constructed). During the field survey in 2010, it was found that the river is getting obstructed at the upstream part of the causeway, spilling over it and had created an artificial break of slope at the downstream part (fig. 15B). But in 2012 it was found the causeway has been damaged and the water is passing through it (fig. 15C). Same scenario has been found near Battala area (major market place of Agartala city), where a causeway was constructed in 2010 to carry heavy vehicles (fig. 15H), in the next monsoon it was damaged (fig. 15I). Similarly an artificial scouring was noticed along a bridge pier near Rajnagar area (fig. 15E) and that wooden bridge was also collapsed (Arthur et al., 1998; Heidarpour et al., 2007; Dahal et al., 2012) during heavy downpour (fig. 15F-G).

Fig. 15 – Evidences of construction activates and damages along the Haora River.
Fig. 15 – Évidence des dommages causés par l'activité humaine le long de la rivière Haora.

Fig. 15 – Evidences of construction activates and damages along the Haora River.   Fig. 15 – Évidence des dommages causés par l'activité humaine le long de la rivière Haora.

A. Inset of location of causeway between Bisalgarh to Champaknagar in Google Image; B. Condition of the causeway in 2010; C. Damage of the causeway in 2012; D. Picture of a wooden lightweight bridge located across the Haora River near Rajnagar; E. Inset showing evidence of artificial scouring found along that wooden bridge pier; F. Inset showing ultimate collapsing of that bridge during monsoon; G. Evidence of repairing of that bridge after damage; H. Conditions the of causeway near Battala before monsoon; I. Picture of washed out causeway after monsoon.
A. Emplacement du gué construit entre Bisalgarh et Champaknagar (Google Image) ; B. État du gué en 2010 ; C. Progrès de la détérioration du gué en 2012 ; D. Photo d'un pont léger en bois situé sur la rivière Haora près de Rajnagar ; E. Excavation artificielle localisée au pied de ce pont de bois ; F. Effondrement de ce pont pendant la mousson ; G. Le même pont en réparation ; H. État du "pont-jetée" près de Battala avant la mousson ; I. Image du "pont-jetée" emporté après la mousson.

5. Conclusion

29It is clear from the aforesaid study that none of this individual activity plays any major role in changing the physical behavior of the river, but their combined activity lead threat to the river. The intensity of damage of the river is also clearly visible from the consequences noted during the survey period. Huge sedimentation (both natural and artificial) change in river bed rugosity, reduction of channel width, formation of mid channel and point bars and frequent migration of channel are indicating the vulnerable condition of the Haora River. No major flood event took place during the study period (2010-2014). Thus, it is quite sure that any major type of change in the physical behavior of the river in terms of bank erosion, bank failure, damage of land resources and other environmental destruction may take place during any major flood event (Gharbi et al., 2016; Kale, 2003; Mili et al., 2013; Peppler, 2006).

30To cope with such hazards some easy and quick measures can be proposed to save the river as well to save the lives and properties of the residents within the river basin. Conservative dredging of the Haora River sediment and its use in commercial sectors, plot wise collection of soil from tilla lands, use of waste brick materials (e.g. brick fragments) for filling of land, road construction and some alternative ceramic sectors, introduction of dumping ground near the Agartala City for recycling of solid wastes not only can check the risk, but also they are economically beneficial.

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Annexe

Version française abrégée

Depuis le début du XXe siècle, la rivière Haora, ligne de vie de la ville d'Agartala (District de Tripura, Inde), a été intensément utilisée par les citadins pour satisfaire leurs propres besoins. Les habitants, directement ou indirectement, polluent non seulement l'eau de la rivière, mais aussi impactent sa morphologie et sa dynamique. La rivière Haora est l'une des principales rivières du district du Tripura occidental situé entre les latitudes 23˚37' et 23˚53'N et les longitudes 91˚15' et 91˚37'E (fig. 1). Le bassin hydrographique d’une superficie de 405,8 km² (en Inde et au Bangladesh) est situé dans la partie sud du district du Tripura occidental, limitrophe des districts de Khowai et de Shipahijola à l'est et au sud, et du Bangladesh au nord. C'est une rivière de piémont dans son cours moyen qui s'écoule à partir de Chandrasadhubari à travers un paysage de plaines vallonnées sur une distance de 21,8 km avant d'atteindre Jirania (32 m). À partir de Jirania, la rivière Haora traverse une plaine, à une altitude inférieure à 30 m, jusqu'au point de confluence avec la rivière Titas au Bangladesh (10 m). Cette rivière a une longueur totale de 61,2 km dont 52 km en Inde. Le débit annuel moyen de la rivière Haora, enregistré par la Central Water Commission (CWC), est d'environ 180 m³/s (fig. 16).

Sur cette longueur de 52 km, trois longues sections ont été identifiées, où le cours de la rivière ainsi que les écoulements ont été modifiés en raison d'activités anthropiques. Partant de la frontière internationale, ces tronçons couvrent respectivement 5,35 km, 4,74 km et 5,47 km de longueur. Pour la détection des changements de tracé de la rivière Haora, la période 1932-2005 a été considérée, en fonction de la disponibilité des cartes et des images.

L'étude diachronique des tracés de la rivière Haora (fig. 2) ne montre aucun changement majeur entre 1932 et 1956. Le cours de la rivière est resté inchangé même après le séisme de 1950. Entre 1956 et 2005 ont été repérés quatre sections où des changements majeurs se sont produits. Elles sont identifiées a, b, c et d sur la Figure 2. Sur le tronçon a, environ 9,89 km du tracé de la rivière Haora ainsi que le cours de l'un de ses affluents (la Katakhal) ont radicalement changé (fig. 2). Un tel changement est dû à l'activité néo-tectonique, à savoir l'élévation de la zone d'interfluve entre la rivière Haora et la rivière Katakhal (fig. 3), résultant d'un plissement près de leur confluence (Bandyopadhyay et al., 2013a). Sur les autres tronçons (b, c et d), ce sont des changements anthropiques qui sont à l'origine de l'évolution de la rivière, comme la dérivation des chenaux le long du tronçon b, le stockage de déchets issus des marchés le long de la berge (tronçon c) et le stockage de déchets résiduels provenant de l'activité des fours à briques (tronçon d).

Sous le régime du Maharaja Birendra Kishore Manikko (1909-1923), un canal, le cours actuel de la rivière Haora, a été creusé (fig. 4) afin de préserver la ville d'Agartala des inondations. Mais la pente du canal et son lit étaient plus faible et plus bas que ceux de la rivière Haora. De ce fait, la rivière Haora a été capturée par le canal et l'embouchure du cours d'origine, près de la capture, se colmate. Sur le tronçon C, les marchés déversent leurs déchets le long de la rive droite de la rivière (fig. 5). Ces dépôts contiennent du plastique et d'autres composants artificiels ; ceux-ci se mélangent très rapidement avec les sédiments en suspension et forcent le dépôt. Cela entraîne un rétrécissement du chenal (fig. 7) et une migration de la rivière. Des dépôts similaires sous la forme de barres sont observés, agrégeant les sédiments aux apports fournis par les décharges de brique le long des rives (fig. 8).

La plupart des "champs de brique" situés dans le Jirania Block (fig. 6) prélèvent les boues issues de la dégradation des terres des tilla environnantes (d'après Eswaran et al. (1993), et Eswaran (1999), les tillas définissent un relief de dénudation, collines et buttes, incisées par un réseau de cours d'eau intermittents aux vallées étroites, les lunga) (fig. 9-10). Les sédiments fins alimentent la rivière Haora et favorisent une importante sédimentation (Davinroy et al., 2003 ; Arohunsoro et al., 2014). Outre les terres de tilla, les "champs de brique" prélèvent également les sols issus des terres agricoles (Rahman et Khan, 2001 ; Khan et al., 2007), car ils sont considérés comme la meilleure matière première pour la production de briques. Cette collecte sur le long terme participe à la dégradation des terres agricoles (fig. 11). L'exploitation du sable dans le lit de la rivière est encore une activité qui affecte non seulement son lit, mais également la rive droite de l'Haora. Si on suit l'évolution des transects sur 3 ans (2010-2012), on constate que le cours principal de la rivière s'est déplacé vers la rive droite (fig. 12). On a également observé la formation de grandes barres allongées (22 m × 3,2 m) près des piliers de ponts en béton (fig. 13), tandis qu'à proximité des piles de pont construits en matériaux plus légers, la longueur de la barre est moindre.

La carte recensant le degré d'activité anthropique affectant les berges montre que les zones les moins impactées (48 parcelles) représentent un linéaire d'une longueur totale de 44,75 km (fig. 14). Soixante-quatre parcelles, couvrant une longueur de 28,25 km, sont considérées comme modérément affectées. Dans les blocks de Champaknagar et de Jirania (4,64 km), le linéaire de la rivière concentre les zones les plus affectées. Les principales activités anthropiques observées dans ces deux blocs sont l'extraction du sable, les briqueteries, la construction de ponts et l'extraction de la terre des tilla, matière première des briqueteries. En raison de ces activités anthropiques, la dynamique fluviale est modifiée et contribue à altérer les ouvrages construits dans le lit mineur, jusqu'à provoquer leur ruine. Par exemple, dans la partie la plus au nord de la route de contournement entre Bisalgarh et Champaknagar, une chaussée a été construite en travers de la rivière (fig. 15). Sa présence a constitué un obstacle à l'écoulement de la rivière, provoquant son débordement par-dessus l'ouvrage jusqu'à son effondrement. Le même type de pont-jetée en terre battue construit dans la région de Battala a été emporté lors de fortes averses. L'extraction du sable autour des piles d'un pont en structure légère près de Rajnagar a entrainé son effondrement au cours de la mousson de 2012 (fig. 15).

D'après l'étude susmentionnée, aucune de ces activités prises isolément ne joue un rôle majeur dans le changement de la dynamique fluviale, c'est leur action combinée qui engendre une dégradation de la rivière. L'intensité des transformations de la rivière a été également clairement perçue lors de notre période d'étude. Une forte sédimentation (naturelle ou d'origine anthropique) entraîne une modification de la rugosité du lit de la rivière, une réduction de la largeur du chenal, la formation de bancs médians et de bancs de convexité, ainsi que la migration fréquente du chenal, indicateurs d'un contexte de vulnérabilité pour la rivière Haora.

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Table des illustrations

Titre Tab. 1 – List of some published works on human’s impacts on different rivers of the world. Tab. 1 – Liste de quelques références bibliographiques traitant des impacts de l'homme sur différentes rivières du monde.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12019/img-1.png
Fichier image/png, 100k
Titre Fig. 1 – Location map of the Haora River Basin. Fig. 1 – Carte de localisation du bassin versant de la rivière Haora.
Légende A. Map of India indicting NE India; B. State wise division of NE India highlighting Tripura and Tripura map locating the Haora River Basin; C. Entire drainage basin map of the Haora River; 1. Perennial rivers; 2. Non perennial rivers; 3. National Highway; 4. International border between India-Bangladesh. A. Carte de l'Inde ; B. Carte des États du Nord-Est de l'Inde localisant le district de Tripura et le bassin versant de la rivière Haora ; C. Réseau hydrographique du bassin de la rivière Haora ; 1. Cours d'eau pérenne ; 2. Cours d'eau non pérenne ; 3. Autoroute ; 4. Frontière internationale entre l'Inde et le Bangladesh.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12019/img-2.png
Fichier image/png, 1,7M
Titre Fig. 2 – Superimposed courses of the Haora River with the location of cross-sections across the river. Fig. 2 – Cartographie diachronique des tracés de la rivière Haora avec l'emplacement des transects recoupant la rivière.
Légende A. Super-imposed map of the Haora River courses for the period 1932-2005. a. 1st stretch of course change in Bangladesh; b. 2nd stretch of course change between the College-Tilla to the Bangladesh Border; c. 3rd stretch of course change along the major market disposal sites; d. 4th stretch of course change between the Jirania and Ranir Bazar Blocks; 1. River course for the year 1932; 2. River course for the year 1956; 3. River course for the year 2005; 4. India-Bangladesh Border. B. Locations of cross-sections along the Haora River. 4. India-Bangladesh Border; 5. Cross sections. A. Carte des cours de la rivière Haora sur la période 1932-2005. a. 1er secteur au Bangladesh ; b. 2ème secteur entre College-Tilla et la frontière du Bangladesh ; c. 3ème secteur le long des principaux sites de dépôt d'ordures des marchés ; d. 4ème secteur entre les blocks de Jirania et Ranir Bazar ; 1. Tracé de la rivière en 1932 ; 2. Tracé de la rivière en 1956 ; 3. Tracé de la rivière en 2005 ; 4. Frontière Inde-Bangladesh. B. Localisation des transects réalisés le long de la rivière Haora. 4. Frontière Inde-Bangladesh ; 5. Transects.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12019/img-3.png
Fichier image/png, 435k
Titre Fig. 3 – Diagrammatic representation of tectonic changes that lead to the changes in courses and the confluence of the Haora River and the Katakhal River (after Bandyopadhyay et al., 2013A). Fig. 3 – Représentation schématique des changements tectoniques qui entraînent des changements dans le tracé des cours et de la confluence de la rivière Haora et de la rivière Katakhal (d'après Bandyopadhyay et al., 2013A).
Légende A. Condition of the Katakhal River and the Haora River confluence zone during 1932; B. Condition of the Katakhal River and the Haora River confluence zone after detachment; 1. Traces of the oscillations of the Titas River meander; 2. The directions of shifting of both the rivers. A. État de la zone de confluence de la rivière Katakhal et de la rivière Haora en 1932 ; B. État de la zone de confluence de la rivière Katakhal et de la rivière Haora après leur séparation ; 1. Localisation des tracés du méandre de la rivière Titas ; 2. Directions de migration des deux rivières.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12019/img-4.png
Fichier image/png, 216k
Titre Fig. 4 – Changing course of the Haora River between the College-Tilla to the Bangladesh Border. Fig. 4 – Changement de tracé de la rivière Haora entre le Collège-Tilla et la frontière du Bangladesh.
Légende A. Latitudinal and longitudinal extension of the area; B. Google Image depicting the river course change between College-Tilla to Bangladesh Border; C. Inset depicting the trace of earlier abandoned channel as elongated water bodies; 1. River course for the year 1932; 2. River course for the year 2005; 3. India-Bangladesh Border. A. Extension latitudinale et longitudinale de la zone ; B. Image Google illustrant le changement de tracé de la rivière entre le Collège-Tilla à la frontière du Bangladesh ; C. Encart représentant le tracé d'un ancien chenal abandonné occupé par des plans d'eau allongés ; 1. Tracé de la rivière en 1932 ; 2. Tracé de la rivière en 2005 ; 3. Frontière entre l'Inde et le Bangladesh.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12019/img-5.png
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Titre Fig. 5 – Changing course of the Haora River along the major market disposal sites. Fig. 5 – Changement de tracé de la rivière Haora le long des principaux sites de dépôt d'ordures des marchés.
Légende A. Picture of the market site taken in the year 2010; B. Picture of the market site of 2011; C. Market site picture of 2012; D. 3 years consecutive cross sections of the Haora River along the market site; 1. Cross section of 2010; 2. Cross section of 2011; 3. Cross section of 2012. A. Photo du site du marché prise en 2010 ; B. Image du site du marché en 2011 ; C. Photo du site du marché en 2012 ; D. Trois ans consécutifs de coupes transversales de la rivière Haora le long du site du marché ; 1. Coupe transversale de 2010 ; 2. Coupe transversale de 2011 ; 3. Coupe transversale de 2012.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12019/img-6.png
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Titre Fig. 6 – Changing course of the Haora River between the Jirania and Ranir Bazar Blocks. Fig. 6 – Changement de tracé de la rivière Haora entre les blocks de Jirania et de Ranir Bazar.
Légende 1. Haora River course of 1932; 2. Haora River course of 2005; 3. Brick fields. 1. Cours de la rivière Haora en 1932 ; 2. Cours de la rivière Haora en 2005 ; 3. Champ de briques.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12019/img-7.png
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Titre Fig. 7 – Evidence of river course changes and sequential cross sections (2010-12) of the Haora River near Debendranagar. Fig. 7 – Indices des changements de tracé de la rivière Haora et transects séquentiels (2010-12) près de Debendranagar.
Légende A. Photograph showing the condition of the Haora River near Debendranagar in the year 2010; B. River course of 2011; C. River course of 2012; D. River course for the year 2014; E. Superimposed cross sections of 3 consecutive years (2010-12); 1. Direction of flow; 2. Location of the cross section; 3. Cross section of the year 2010; 4. Course section of 2011; 5. Cross section of 2012; 6. Wetted part, line joining two extreme points of the wetted part of a particular year is considered the water level during the time of survey of that particular year. A. Photo montrant l'état de la rivière Haora près de Debendranagar en 2010 ; B. Cours de la rivière en 2011 ; C. Cours de la rivière en 2012 ; D. Cours de la rivière en 2014 ; E. Transects superposés de trois années consécutives (2010-2012) ; 1. Direction de l'écoulement ; 2. Emplacement de la section transversale ; 3. Transect de 2010 ; 4. Transect de 2011 ; 5. Transect de 2012 ; 6. Section mouillée, la ligne joignant deux points extrêmes de la section en eau d'une année donnée est considérée comme le niveau de l'eau au moment de l'étude.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12019/img-8.png
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Titre Fig. 8 – Location of the brick fields, the places and photographs of sediment samples collected along the course of Haora River. Fig. 8 – Emplacement des champs de briques, des sites et des photographies des échantillons de sédiments recueillis le long de la rivière Haora.
Légende A. Location of the brick fields; B. Photo of R.B.I Brick field located just along the right bank of the Haora River; C. Photo of sediment sample collected from upstream part of the river; D. Condition of sediment sample collected near R.B.I. brick field; E. Sediment sample collected from Debendranagar; 1. Brick fields; 2. Traces of tiny brick particles within the sediment sample. A. Emplacement des champs de brique. B. Photo du champ de brique R.B.I situé le long de la rive droite de la rivière Haora ; C. Photo d'un échantillon de sédiments prélevé dans la partie amont de la rivière ; D. État de l'échantillon de sédiment recueilli près du champ de brique R.B.I. ; E. Échantillon de sédiment prélevé à Debendranagar ; 1. Champs de briques ; 2. Traces de minuscules particules de brique dans l'échantillon de sédiment.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12019/img-9.png
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Titre Fig. 9 – Location of brick fields and cut off lands in 3D model. Fig. 9 – Emplacement des champs de briques et des terres incisées dans le modèle 3D.
Légende A. Location of the brick fields; B. Superimposition of brick fields and tilla cut off in 3D DEM; 1. Brick fields; 2. Tilla cut off. A. Emplacement des champs de brique ; B. Superposition de champs de brique et de tilla incisés dans le modèle 3D ; 1. Champ de briques ; 2. Tilla incisé.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12019/img-10.png
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Titre Fig. 10 – Evidences of areal reduction and step by step sequential degradation of tilla lands (Near National Brick Industry - N.B.I). Fig. 10 – Évidences de la réduction de surface et de la dégradation séquentielle progressive des terres à tilla (Near National Brick Industry - N.B.I).
Légende A. Google image of 2009 showing the N.B.I. Brick field and surrounding tilla land; B. Google image of 2011 of N.B.I Brick field; C. Google image of the year 2014; D. Photograph showing condition of the N.B.I. surrounding tilla land in 2010; E. Photo of vertical reduction of the tilla in 2012; 1. Area coverage of the tilla in 2009; 2. Tilla land areal coverage in 2011; 3. Areal coverage in 2014. A. Image Google de 2009 montrant le champ de brique N.B.I. et les tilla environnantes ; B. Image Google de 2011 du champ de brique N.B.I ; C. Image Google de l'année 2014 ; D. Photographie montrant l'état de la N.B.I. dans le secteur des tilla en 2010 ; E. Photographie du décapage vertical du tilla en 2012 ; 1. Couverture de la zone des tilla en 2009 ; 2. Couverture du secteur des tilla en 2011 ; 3. Couverture géographique en 2014.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12019/img-11.png
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Titre Fig. 11 – Location of brick fields and agricultural land and evidences of degradation of agricultural land within the Haora River Basin. Fig. 11 – Localisation des champs de brique et des terres agricoles et indices de la dégradation des terres agricoles dans le bassin de la rivière Haora.
Légende A. Distribution of agricultural land and brick field within Haora River basin; B. Condition of the agricultural land at the opposite bank of the Lakshmi Narayan Brick Industry (LNBI) in 2009; C. Google image of that agricultural land (opposite of LNBI) in 2011; D. Google image showing further degradation of the land in 2014; E. Photograph of the left out tree in that agricultural land (opposite of LNBI) indicating maximum limit of vertical excavation; 1. Location of LNBI; 2. Agricultural lands; 3. Brick fields; 4. Direction of river water flow. A. Répartition des terres agricoles et des champs de brique dans le bassin de la rivière Haora ; B. État des terres agricoles sur la rive opposée à la briqueterie de Lakshmi Narayan (LNBI) en 2009 ; C. Image Google de ce secteur agricole (à l'opposé de LNBI) en 2011 ; D. Image Google montrant l'évolution de la dégradation du secteur en 2014 ; E. Photographie de l'arbre laissé à l'abandon sur cette terre agricole (à l'opposé de LNBI) indiquant la hauteur maximale de l'excavation verticale ; 1. Emplacement de LNBI ; 2. Terres agricoles ; 3. Champs de brique ; 4. Direction de l'écoulement de la rivière.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12019/img-12.png
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Titre Fig. 12 – Sequential changes within the river bed due to unscientific quarrying of sand. Fig. 12 – Changements séquentiels dans le lit de la rivière dus à l'extraction non contrôlée de sable.
Légende A. Cross section taken near Mohonpur Bazar; B. Cross section at 100m upstream from the Khayerpur Bridge; 1. Cross section of the year 2010; 2. Cross section of 2011; 3. Cross section of 2012; 4. Wetted part. A. Coupe transversale prise près du Bazar de Mohonpur ; B. Coupe transversale à 100 m en amont du pont de Khayerpur ; 1. Coupe transversale en 2010 ; 2. Coupe transversale en 2011 ; 3. Coupe transversale en 2012 ; 4. Section mouillée.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12019/img-13.png
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Titre Fig. 13 – Evidence and variability of bar formations as an impact of different types of bridge constructions within the Haora River. Fig. 13 – Évidence et variabilité des formations de barres consécutives à la construction de différents types de ponts dans la rivière Haora.
Légende A. Location of bridges along the Haora River; B. Google image showing the condition of the Haora River before the construction of the bridge near Khayerpur in 2001; C. Google image depicting the channel narrowing and the formation of bar after the construction of bridge pier in 2011; D. Google image showing further advancement of the bar along the bridge pier in 2013; E. Formation of large elongated bar near heavy weight bridge with concrete piers; F. Formation of small bar near light weight bridge with wooden piers; G. Trace of no bar below the hanging bridge; 1. Direction of flow; 2. Bridge. A. Emplacement des ponts le long de la rivière Haora ; B. Image Google montrant l'état de la rivière Haora avant la construction du pont près de Khayerpur en 2001 ; C. Image Google montrant le rétrécissement du chenal et la formation d'une barre après la construction du pont en 2011 ; D. Image Google montrant la progression du banc le long de l'arche du pont en 2013 ; E. Formation d'une grande barre allongée près d'un pont massif réalisé avec des piliers en béton ; F. Formation d'une petite barre près d'un pont léger réalisé avec des piliers en bois ; G. Absence de barre sous le pont suspendu ; 1. Direction de l'écoulement ; 2. Pont.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12019/img-14.png
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Titre Tab. 2 – Estimation of the limit of impacts of the individual activities along the Haora River. Tab. 2 – Estimation de la limite des impacts des activités par catégorie le long de la rivière Haora.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12019/img-15.png
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Titre Fig. 14 – Anthropogenic impact map of the Haora River bank along with the graph showing total lengths in individual parameters. Fig. 14 – Carte de l'impact anthropique le long des berges de la rivière Haora incluant un graphique montrant les longueurs totales impactées selon les paramètres pris en compte.
Légende A. Anthropogenic impact map prepared from multi-buffer zonation of six individual anthropogenic activities evidenced along the Haora River; B. Pie graph showing the coverage of different impact zones; C. Expanded picture of the selected stretch showing very high, high and moderate impact zones of the Haora River; D. Expanded picture of the second selected stretch showing low and very low impact zones of the Haora River; E. Picture of sand quarrying from the river; F. Road or causeway across the river; G. Brick fields along the river; H. Bridges across the river; I. Picture tilla cutting along the Haora River. 1. River; 2. Zone of very low anthropogenic impacts; 3. Zone of low anthropogenic impacts; 4. Zone of moderate anthropogenic impacts; 5. Zone of high anthropogenic impacts; 6. Zone of very high anthropogenic impacts. A. Carte de l'impact anthropique réalisée à partir de la sectorisation multi-buffer de six activités anthropiques observées le long de la rivière Haora ; B. Diagramme-secteur montrant la répartition selon le degré d'importance des zones impactées ; C. Zoom sur un tronçon à zones d'impact très élevé à modéré ; D. Zoom sur un tronçon à zones d'impact faible à très faible ; E. Photo d'extraction de sable en rivière ; F. Route ou chaussée traversant la rivière ; G. Champ de brique le long de la rivière ; H. Pont ; I. Tilla incisé le long de la rivière Haora. 1. Rivière ; 2. zone à très faibles impacts anthropiques ; 3. Zone à faibles impacts anthropiques ; 4. Zone à impacts anthropiques modérés ; 5. Zone à forts impacts anthropiques ; 6. Zone à très forts impacts anthropiques.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12019/img-16.png
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Titre Fig. 15 – Evidences of construction activates and damages along the Haora River. Fig. 15 – Évidence des dommages causés par l'activité humaine le long de la rivière Haora.
Légende A. Inset of location of causeway between Bisalgarh to Champaknagar in Google Image; B. Condition of the causeway in 2010; C. Damage of the causeway in 2012; D. Picture of a wooden lightweight bridge located across the Haora River near Rajnagar; E. Inset showing evidence of artificial scouring found along that wooden bridge pier; F. Inset showing ultimate collapsing of that bridge during monsoon; G. Evidence of repairing of that bridge after damage; H. Conditions the of causeway near Battala before monsoon; I. Picture of washed out causeway after monsoon. A. Emplacement du gué construit entre Bisalgarh et Champaknagar (Google Image) ; B. État du gué en 2010 ; C. Progrès de la détérioration du gué en 2012 ; D. Photo d'un pont léger en bois situé sur la rivière Haora près de Rajnagar ; E. Excavation artificielle localisée au pied de ce pont de bois ; F. Effondrement de ce pont pendant la mousson ; G. Le même pont en réparation ; H. État du "pont-jetée" près de Battala avant la mousson ; I. Image du "pont-jetée" emporté après la mousson.
URL http://journals.openedition.org/geomorphologie/docannexe/image/12019/img-17.png
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Shreya Bandyopadhyay et Sunil Kumar De, « Anthropogenic impacts on the morphology of the Haora River, Tripura, India », Géomorphologie : relief, processus, environnement, vol. 24 – n° 2 | 2018, 151-166.

Référence électronique

Shreya Bandyopadhyay et Sunil Kumar De, « Anthropogenic impacts on the morphology of the Haora River, Tripura, India », Géomorphologie : relief, processus, environnement [En ligne], vol. 24 – n° 2 | 2018, mis en ligne le 21 juin 2018, consulté le 14 novembre 2018. URL : http://journals.openedition.org/geomorphologie/12019 ; DOI : 10.4000/geomorphologie.12019

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Auteurs

Shreya Bandyopadhyay

Department of Geography, Maharaja Nandakumar Mahavidyalaya, Purba Medinipur – West Bengal – 721632, India (shreyageo@gmail.com).

Sunil Kumar De

Department of Geography, North-Eastern Hill University – Shillong - 793022, India (desunil@yahoo.com). Tel: +91,364 2723205; Fax: +91,364 2550076.

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