Keywords

1 Introduction

Alluvial rivers flow on the sediments deposited by them and are sensitive to slight changes in geomorphic, tectonic, and anthropogenic processes occurring within the basin (Achyuthan, 2003; Joshi & Kotlia, 2014, 2018; Kale et al., 2014; Kothyari et al., 2016a; Dubey et al., 2017; Dar et al., 2019). In view of their sensitivity and quick response to various disturbing processes, alluvial rivers provide a vital opportunity to comprehend the tectonic deformation of an area (Seeber & Gornitz, 1983; Ouchi, 1985; Holbrook & Schumm, 1999; Jain & Sinha, 2005; Turowski et al., 2006; Amos & Burbank, 2007). The response of alluvial rivers to active tectonics can be inferred from varied channel dimensions, including channel sinuosity, channel avulsions, aggradation, and degradation (Willett & Brandon, 2002). According to Schumm et al. (2000) any deformation on a scale of few millimeters (2–3 mm annually) may induce morphological changes in a river basin. Besides, climate, lithology, folding, faulting, incision, etc., can result in the formation of various channel patterns and alluvial landforms (Schumm, 1986; Keller & Pinter, 1996; Whipple et al., 2013; Kothyari, 2014; Kothyari et al., 2016b, 2018; Taloor et al., 2017).

The Kashmir Valley located in the NW Himalaya is sandwiched between the Great Himalayan Range to the northeast and Pir Panjal Range to the southwest (Fig. 1). The geomorphic setting of the valley suggests that due to the tectonic uplift of the Pir Panjal Range, the ancient drainage got impounded and formed a vast lake (Dar et al., 2014; Paul et al., 2021). This lake, known as Karewa Lake, later on drained out through the Baramulla gorge giving rise to the River Jhelum and its tributaries. Flowing through the axial part of the tectonically active Kashmir Valley, the river is characterized by diverse morphology manifested in channel width variations, meandering bends, braid bars, channel avulsions, unpaired terraces, and perturbations in longitudinal profile. The river continuum extends from partly confined to laterally unconfined (alluvial) to confined variants. To ascertain the causes of this anomalous geomorphology, we divided the river into different reaches and used various techniques and river geomorphic indices to evaluate the river response to disturbing forces. The geomorphic indices used in this study have previously been tested in comprehending the role of active tectonics in triggering river geomorphic changes (Silva et al., 2003; El Hamdouni et al., 2008; Della-Seta et al., 2008; Dehbozorgi et al., 2010). It is good to mention here that the tectonic-geomorphic study of the Srinagar reach of the River Jhelum has previously been published (Dar et al., 2019), and the current chapter extends that work to the entire course of the river in the Kashmir Valley.

Fig. 1
A lithological map of the Kashmir Valley. River Jhelum flows along the center towards the North and then westward. Consolidated alluvium and reworked Karewas are along the river with members and formations to the west. Limestone, Panjal volcanics, agglomeratic slate and other formations are marked.

Lithological and Karewa distribution map of the Kashmir Valley modified after Dar et al., (2014) and Bhatt (1982) respectively. The course of the River Jhelum and the major lakes (Wular and Dal Lake) are also shown in the map

Full size image

2 Tectonic-geomorphic Setting of the Kashmir Valley

Geologically, the Kashmir Valley encompasses a complete stratigraphic record of lithologies of all ages ranging from Archean to recent (Gansser, 1964; Dar et al., 2015; Stojanovic et al., 2016). Recent alluvium and Quaternary sediments occupy almost all of the valley floor (Dar et al., 2017, 2021). The valley is bounded by a complex fault pattern, namely, the imbrication of northward rooted basal decollement branded as the Main Himalayan Thrust (Schelling & Arita, 1991). The Suring-Mustgarh anticline fold represents the southern-most deformation front extending between the River Jhelum in NE and Beas in SE (Ahmad et al., 2015). The other fault systems that are associated with the Kashmir Valley include the Himalayan Frontal Thrust, Main Boundary Thrust, Kotli Thrust, Riasi Thrust, Balapur Thrust, and Bagh-balakot Fault. It is believed that the Kashmir Valley evolved in the Late Miocene with the shifting of NE thrust complex to the SW front of Pir Panjal from the base of Great Himalayan side (Burbank, 1983; Burbank & Johnson, 1983). Owing to this shifting the existing structural system basement complexes of the Main Boundary Thrust/Main Central Thrust replaced the NE thrust complex (Ahmad et al., 2015). Nevertheless, there are some studies that propose that the evolution of the Kashmir Valley is a result of dextral strike slip fault accompanied by pull-apart character in NW Himalaya (Alam et al., 2015a, b). These fault systems along with other local faults have affected the geomorphology and the drainage of the entire NW Himalaya encompassing the Kashmir Valley.

3 Methodology

To study the alluvial river response to prevailing tectonics, the calculation of geomorphic indices occupies the central place (Jaan et al., 2015). In the present study we employed geomorphic indices to infer the impact of tectonic activity on the River Jhelum, in the Kashmir Himalaya. We employed an integrated approach using remote sensing and extensive field expeditions to study the influence of tectonic activity on the River Jhelum. Google Earth imagery and ALOS PALSAR DEM of 12.5 m resolution were used to calculate different geomorphic indices. Measurements of geomorphic indices and other related parameters were carried out in ArcGIS environment followed by the interpretation of river geomorphic features and geomorphic indices in terms of tectonic activity and/or lithological variation. The various geomorphic indices used include sinuosity index (SI), lateral entrenchment ratio (ER), stream length gradient index (SL), braided index (BI), and mountain front sinuosity (Smf) augmented with river width profile and river terrace analysis. The impact of channel sinuosity on channel erosion and channel shifting was validated from lateral entrenchment (ER) ratio which was measured as a ratio between the length of the two banks of a river along the corresponding reach (Goswami et al., 1999). The stream length gradient index of the River Jhelum was calculated using the formula SL = (ΔH/ΔL) L of Hack (1973), where ΔH/ΔL is the gradient of the reach or channel slope, ΔH is the elevation change along the reach, ΔL is the length of the reach, and L is the total channel length from the midpoint of the reach of computation. Braided index (Bi) is a measure of the degree to which bars and/or islands separate multiple flow paths and is measured as a ratio between twice the length bar and reach length (Goswami et al., 1999). Similarly, mountain front sinuosity (Smf) of the fronts (wherever necessary) was calculated as a ratio of straight-line length of the mountain front (Ls) to the length of mountain front along the mountain foot (Lmf) (Bull, 1977). The observations derived from the geomorphic indices were augmented by river terrace observations and width changes of the river. Besides, river reaches with anomalous river response were selected, and intensive field work was carried out for validation of the results. The motivation behind using geomorphic indices is that most of the Jhelum basin is covered by thick alluvium and Quaternary sediments (Dar & Zeeden, 2020) and the direct surface expressions of geological structures and their impact on river geomorphology are difficult to trace using conventional methods.

4 Results and Discussion

4.1 Sinuosity Index

For the calculation of sinuosity index (SI), the River Jhelum was divided into various reaches (Fig. 2a). Few of the tributaries, joining the river from Chhatargul and Tunj Mulla localities, (hereafter referred as Chhatargul and Tunj Mulla tributaries), were also studied for SI (Fig. 2a). The reaches located on the main River Jhelum are from Sheikh Gund to Nai Basti (Anantnag), from Anantnag to Wular Lake, and from Sopore town to Uri. The reaches of tributaries and main river were further subdivided into sub-reaches to determine the SI and other parameters discussed in the following sections.

Fig. 2a
A hydrological map of River Jhelum. Reach points R 1 to 3 and R 2 to 4 are marked along the Chhatargul and Tunj Mulla tributaries in the south followed by Sheik Gund to Nei Basti section with R 1 to 4, Anantnag or Nei Basti to Wular Lake with R 1 to 7, and Sopore to Uri westward from the lake.

Map showing the course of the River Jhelum. The tributaries (Chhatargul and Tunj Mulla) and reach scheme are also shown in the map

Full size image

The sinuosity index values (Fig. 2b) calculated for Chhatargul tributary (CT) are 1.08 (reach 1), 1.12 (reach 2), and 1.23 (reach 3). Similarly, for Tunj Mulla tributary (TT) the SI values are 1.14 (reach 1), 1.10 (reach 2), 1.17 (reach 3), and 1.18 (reach 4). The values lie between 1.06 and 1.30, suggesting low sinuosity. The SI values calculated for the main river from Sheikh Gund to Nai Basti (SN) along various reaches are 1.29 (reach 1), 1.37 (reach 2), 1.18 (reach 3), and 1.59 (reach 4). The values fall with the sinuous/meandering degree of sinuosity (Schumm, 1963). Similarly, the SI values from Nai Basti (Anantnag) to Wular Lake (NW) are 1.87, 1.33, 1.33, 1.64, 1.80, 1.37, and 1.28 for reaches 1, 2, 3, 4, 5, 6, and 7, respectively. These values again fall within the sinuous/meandering degree class of channel sinuosity. After its exit from the Wular Lake near the Sopore town, the river heads toward Baramulla town and finally leaves the Kashmir Valley, traversing through the Pir Panjal Range near Uri. The SI values of the River Jhelum from Sopore town to Uri (SU) are 1.43, 1.11, 1.87, 1.17, 1.18, 1.85, and 1.27 for reaches 1, 2, 3, 4, 5, 6, and 7, respectively, referring to a low river sinuosity. Thus, from the above results it is suggested that the River Jhelum sinuosity ranges from low sinuosity to sinuous/meandering degree.

Fig. 2b
A bar graph of sinuosity index versus reaches. R 3 for Sopore to Uri has the highest index of around 1.8 followed by R 1, R 5 and R 4 for Nai Basti to Wular Lake, R 4 and R 2 for Sheikh Gund to Nai Basti, and R 1 for Sopore to Uri. R 1 to 3 for Chhatargul tributaries have the lowest values.

Bar chart showing the sinuosity index of the River Jhelum along different reaches. CT Chhatargul tributaries, TT Tunj Mulla tributaries, SN Sheikh Gund to Nai Basti, NW Main River Jhelum (Nai Basti to Wular Lake), SU Sopore to Uri

Full size image

4.2 Lateral Entrenchment Ratio

Similar to sinuosity index, the lateral entrenchment ratio (ER) was calculated for the sub-reaches of the River Jhelum. It is good to mention here that ER values <1 indicate left bank erosion and >1 right bank erosion (Rosgen, 1994). For Chhatargul and Tunj Mulla reaches, the ER values are 0.99, 0.99, 1.02, 0.99, 1.02, 0.98, and 0.95 respectively. These values indicate that in reaches 1 and 2 of Chhatargul stretch, the value is close to 1 reflecting negligible river bank shifting. However, the right bank of the river has experienced slightly more incision relative to the left bank in the reach 3 as is reflected by the ER value of 1.02. The ER value for Tunj Mulla stretch reveals that the right bank has experienced slightly more incision and consequently has shifted toward right.

The ER calculated for the reaches from Sheikh Gund to Wular Lake (total 11 reaches; Sheikh Gund to Nai Basti = 4 reaches, and Nai Basti to Wular Lake = 7 reaches) are 1.0, 1.03, 1.02, 1.01, 1.06, 0.98, 0.97, 0.96, 1.02, 1.01, and 0.99 respectively. Analysis of the ER of these reaches suggests that the right bank has experienced more incision relative to the left bank. The meander growth and the slightly higher incision on the right side of the river could be attributed to the general tilt of the valley toward northeast owing to higher uplift of the Pir Panjal Range compared to the Greater Himalayan Range (Dar et al., 2014). This observation is substantiated by the presence of several meanders with wide concave bends on the right bank of the river.

However, the ER values in some reaches suggest that the left bank incision is comparatively higher than the right bank. Since a large number of fault/lineaments are observed in the valley floor (Ali & Ali, 2020), few of which trend along, and others cut across the river at several locations (Fig. 3a). The deformation associated with these faults/lineaments and the unconsolidated nature of the bank material lead to substantive erosion of the river banks. Besides the diversity in the river bank lithology with hard rocks forming one bank and alluvium the other bank (e.g., downstream from Baramulla town), the alluvial bank erosion outpaces the hard rock bank.

Fig. 3
2 satellite images of River Jhelum. a. A sharp bend of the river has 2 braided bars on either end connected by a dashed line. The left and right banks are marked with river flow direction to the west. b. The river flow is towards the west with outlines of T 2 and T 1 marked and an inset graph.

(a) Google Earth imagery showing entrenched meandering of Jhelum near Baramulla. The dashed line shows the possible fault, and the sharp bend and two braid bars are also associated with this fault. (b) Google Earth image showing the presence of terrace (T1, T2) on the left bank. AB represents the elevation profile showing the course of the River Jhelum (RJ) and the river terraces. Note the absence of terraces along the right bank

Full size image

ER values calculated from Sopore town to Uri are 0.97, 1.01, 1.0, 0.98, 0.97, 1.07, and 1.04 for the reaches 1, 2, 3, 4, 5, 6, and 7, respectively. The results suggest that reaches 1, 4, and 5 have experienced more incision in the left bank in comparison to the right bank, while reaches 2, 6, and 7 show that incision is more in the right banks of river. In case of reach 1 (from Wular to Sherwani Abad), the right bank of river is closer to a mountain with hard rock lithology, and in the left side it is bounded mainly by recent alluvium, so a chance of erosion and lateral migration toward left is more than right side. Also, mass wasting from the mountain has played an important role in confinement of the right bank and erosion of the left bank. Overall, the ER values are nearly close to 1 in all reaches of this stretch of the River Jhelum. This could be because of the presence of a fault that runs parallel to the river course, promoting down-cutting or confinement of the river valley due to the presence of hard rocks on both sides of the river. The preservation of older terraces along reaches 4 and 5 suggests more vertical erosion along the right bank and lateral erosion along the left. At reach 7, the ER values suggest slightly more erosion of the right bank. This is well substantiated by the presence of river terraces along the left bank (Fig. 3b). Overall, the river course shows a combined effect of lineaments/faults and lithology downstream from the Sopore town.

4.3 Stream Length Gradient Index

The SL values calculated for different reaches of the River Jhelum are shown in Figs. 5 and 6. The abnormality in SL of a river results from a variety of factors including river bed lithology, geological structures, slope, etc. (Dar et al., 2022). However, the drainage scaled upward is related to regional tectonic uplift (Chen et al., 2003; Dehbozorgi et al., 2010). The SL values for Chhatargul to Anantnag stretch of the River Jhelum range from 57 to 130 (Fig. 4). The relatively low values are due to the absence of hard rock lithology as the river here flows over alluvium with almost homogenous physical properties. The water elevation profile shows an almost constant decrease in slope. However, few perturbations are observed on the elevation profile which may be associated with the presence of lineaments/faults as indicated by the knickpoints with SL values of 88.6, 104.8, and 130. It is good to mention here that the SL values for the Srinagar reach of the River Jhelum are already published (Dar et al., 2019) and therefore were not incorporated in this study.

Fig. 4
2 line graphs plot gradient in meters versus distance in kilometers. Left. The line decreases with fluctuations indicated for S L 1 equals 57.5 to S L 6 equals 104.8. Right. The line fluctuates horizontally till around 30 kilometers with S L 1 and 2, and decreases with values for S L 3 to S L 6.

Stream length gradient index values of the River Jhelum from Sheikh Gund to Anantnag (left) and from Sopore to Uri (right). Note the increase in the SL values as the river here passes through the Baramulla gorge and finally exits the valley.

Full size image

Similarly, the SL values of the River Jhelum from Sopore to Uri range from 43.5 to 850 (Fig. 4). The values are comparatively higher than the upstream reaches of the River Jhelum from Chhatargul to Anantnag. Numerous convexities are observed on the elevation profile. Here, the river mostly flows over the hard rocks which may be responsible for the anomalous SL values. Besides, many lineaments are also observed, some of which cut across the river in this reach which might be responsible to the higher SL values in these locations (Ali & Ali, 2020). Therefore, both the hard rocks and the presence of lineaments/faults result in higher SL values for this stretch of the River Jhelum. Moreover, the change in valley confinement configuration downstream and anthropogenic activities like dam construction for hydropower generation also alter the SL values.

4.4 Braided Index (BI)

The BI values for reaches 1, 2, and 3 of Chhatargul tributary are 0.37, 0.25, and 0.19, respectively, with <5% degree of braiding for all reaches. However, the BI values for reaches 1, 2, 3, and 4 of Tunj Mulla tributary are 1.33, 0.79, 0.32, and 0.96, respectively, with degree of braiding ranging from 5% to 34% for reaches 1, 2, and 4 and <5% for reach 2. Downstream, the BI values for reaches 1, 2, 3, 4, and 5 of the main River Jhelum from Sheikh Gund to Anantnag are 0.42, 0.45, 0.71, 0.10, and 0.73, respectively, with degree of braiding <5% for reaches 1 and 2 and 5–34% for reaches 3, 4, and 5. The results suggest that braiding is less in the tributaries than in the main channel. The comparatively higher gradient of tributaries than the main river prevents braid bar formation, for example, in the Chhatargul tributary. However, owing to low gradient of the main River Jhelum, the deposition of the bedload takes place, thus resulting in the formation of braided channels, as observed in the Sheikh Gund to Anantnag reach of the river (Fig. 5). From Anantnag to Wular Lake the River Jhelum shows meandering character rather than the braided pattern as it is not fulfilling the prerequisite conditions (abundant sediment supply) for the formation of braid bars although occasionally some small braid bars are observed. These braid bars have been related to the presence of lineaments/faults by Dar et al. (2019). Further downstream from Sopore to Uri, the river is narrow and confined by hard rocks which decreases the chances of braid bar formation. Overall, the braiding decreases toward the downstream reaches of the River Jhelum due to the decrease in sediment load, occasional narrowing of the river course due to vertical incision along faults/lineaments, and the confinement of river by hard rocks.

Fig. 5
2 satellite images of River Jhelum. a. The river flow direction is from north to south around an oblong braided bar with the outline marked. b. The river flow direction is from south to north around a wider braided bar with the outline marked.

(a) Google Earth image showing braided bars in the course of the River Jhelum near Tail Wani (b) showing island bars at Thaji Wara

Full size image

4.5 River Width Profiling

Geomorphic studies carried out in the Kashmir Valley reveal numerous lineaments/faults running parallel, along, or cutting across the River Jhelum (Ganju & Khar, 1984; Alam et al., 2015b; Dar et al., 2019). The lineaments/faults running along the river course result in down-cutting instead of side-cutting, causing narrowing and deepening of the river channel. However, widening occurs where lineaments/faults cut across the river course (Dar et al., 2019). The narrow and long stretch of the river near Anantnag suggests the presence of fault that forced the river to incise deep and maintain a narrow course. The Google Earth image (Fig. 6) of the stretch shows that the river is confined from the right side by an elevated topography, a potential fault scarp that have constricted the lateral cutting. This part of the river also shows less sinuous behavior and follows a nearly straight course in this reach.

Fig. 6
A satellite image of River Jhelum. The river flow direction is from east to west, from Doni Pawa to Mominabad via Chitthi Singh Pora. A large fault scrap is indicated along the northern bank.

Google Earth image showing a fault scarp near Anantnag town and the course of the River Jhelum in its proximity

Full size image

Downstream, laterally unconfined settings have resulted in greater sideward erosion. The low slope of the valley floor also favors more lateral cutting and less vertical incision, resulting in river widening and meandering. Overall, the width profile from Sheikh Gund to Wular Lake shows narrowing for the initial 30 miles with widening in few narrow strips, but thereafter the river shows overall widening (Fig. 7a). This could be because of the high river gradient in initial course which favors vertical incision. Downstream, the river enters the valley floor, and the gradient decreases which increases lateral erosion and results in the overall widening of the river channel. The negligible gradient, less confined conditions, and erodible banks augment more side cutting, less vertical incision, and hence more channel width. In its Srinagar reach, the river exhibits high variability in width. Google Earth imagery and field survey reveal that in few places the narrowing is due to anthropogenic encroachments of the river banks, thus making the district more vulnerable to flooding (Romshoo et al., 2018).

Fig. 7
2 line graphs plot width in meters versus distance in miles. a. The fluctuating line has an increasing trend from (1, 60) to (79, 150). b. The fluctuating line has a decreasing trend from (1, 150) to (41, 100). Values are estimated.

(a) Channel width profile of the River Jhelum between Sheikh Gund and Wular Lake and (b) from Sopore to Uri

Full size image

The width of the River Jhelum from Sopore town to Uri shows an overall decrease in width (Fig. 7b). Near Sopore town, the river is wide and exhibits meandering because of low gradient and unconfined settings. The river width decreases downstream owing to the confined valley setting, hard rock lithology, and presence of geological structures. The river narrowing has resulted in increased stream power and vertical incision.

4.6 River Terraces

Analysis of the river geomorphology reveals the occasional preservation of river terraces along the course of the River Jhelum. However, along most of the river reaches, step features of river terraces were difficult to distinguish due to human settlement and anthropogenic activities on the river banks. The river terraces observed along the Sopore to Uri stretch of the River Jhelum are well preserved and occur along reaches 4, 5, 6, and 7. Field observations suggest that terraces are predominantly unpaired along this stretch (Fig. 8), as the right bank terraces are preserved while few of the left bank terraces are absent. However, along reaches 1 and 2, step features of river terrace are difficult to differentiate due to human settlements. Along reach 3 near the Baramulla gorge, the river has deeply incised, thus minimizing the chances of alluvial terrace formation. Downstream from Uri along reach 7, the River Jhelum changes its overall trend from SE to NW. Along this reach, the river terraces are also unpaired but well preserved along the left bank, showing uplift of the left and erosion along the right bank. Slow and continuous river incision with associated lateral erosion may have played a role in unpaired terraces formation as observed during field work. Therefore, the presences of unpaired terraces indicate that the river has responded to the structural deformations or/is still responding to tectonic activities.

Fig. 8
2 photographs of River Jhelum. a. The river has a road on one bank, and boundaries for terraces T 1 and T 2 marked on the opposite bank. T 2 is also marked along the bank near the road. b. The river flows around a braided bar at the center, with paired terraces indicated on both banks.

Field photograph showing unpaired terraces and braid bar near Baramulla town

Full size image

5 Summary and Conclusion

The tributaries and the main channel of the River Jhelum cut and flow over the alluvium in Kashmir Valley, NW Himalaya. The tributaries, coming from the surrounding mountain ranges, possess high gradient and usually follow low sinuous paths, bringing water and sediments to the trunk stream. The sediment load deposited in the main River Jhelum is transported and redeposited downstream, thus affecting the river course especially in the middle part of the basin where the slope is very low. Sediment deposition and lateral erosion along with low slope have resulted in meandering and increase in the river width. However, high variability in width is found with low carrying capacity in few middle reaches as compared to the lower and upper reaches. The right bank experiences more incision relative to the left bank with meandering growth on the right side due to higher rate of uplift of the Pir Panjal Range than the Greater Himalayan Range. Wherever, the river flows along the trend of the faults/lineaments, vertical incision, channel narrowing, straight channel course, and high water velocity have been observed. For example, an E-W trending fault reported from Baramulla has produced about 55 m high scarp in the area (Bilham & Bali, 2014). Traversing through this fault zone, the river exhibits incised activity into the bedrock and has carved a huge meandering loop and bifurcated the river into two parts, with one part flowing through the trace of the faults. Downstream from Baramulla town, the River Jhelum enters the confined valley setting with hard rock lithology. Before its exit from the valley through the Pir Panjal Range near Uri, confined valley setting, geological structures, and hard rock lithology result in low river sinuosity. The confined settings also control channel planform and width, thus increasing stream power and vertical incision. Further, the unpaired terraces observed show signs of tectonic uplift and slow and continuous river incision indicating valley floor deformations and river response to active tectonics.

Overall, the ongoing tectonic activity and the associated slow deformation of the valley floor have affected the fluvial systems of the Kashmir Valley. Besides, the rapid uplift of the Pir Panjal Range has also affected the climate of the valley shifting the climate toward temperate from subtropical type. Hence, it can be concluded that the comparatively higher degree of uplift of the valley towards the left side of the River Jhelum has produced a general tilt to erode and shift the river action toward the right bank. Our observations of the change in the intensity and the direction of river erosion and the consequent varying ER and SI ratios reflect that the geology, structure, and slope have played an important role in determining the course of the River Jhelum in the Kashmir Valley.