River morphology is a scientific field that concerns with changes in river forms in plan and cross-sections that result because of erosion and sedimentation processes. The principal elements are the dynamics of sediment transport and river flow. Studies on the river morphology provide important information required for the management of water resources, constructions along the river banks and in mitigating hazards such as floods, etc (Sarkar, 2016).
Approaches to Studies on River Morphology in India
India is a land with a long history of geological and tectonic activity that has shaped the physical appearance of its surface features. The land is thus one of both long timescales and diversity in terms of topographical or spatial scales modified by different climatic processes. This makes studying river morphology in India interesting as there is a wide variation of fluvial characteristics in our river systems. For example, there is a great variety of channel and basin characteristics, sediment flow and deposit characteristics, river discharge patterns, and so on.
The unpredictable character of seasonal rain in the Monsoons in India can encourage diverse behaviour in river flow that can alter channel or basin characteristics and result in floods, changes in drainage patterns and sediment deposition. With river basins being the major source of irrigation in a flood prone country such as ours, where land is mostly used for agriculture, the studies on river behaviour attain considerable significance. Early studies on river morphology in India were mostly carried out by hydraulic engineers who attempted to understand river characteristics in terms of their flow pattern.
Although contemporary studies still look to understand river morphology in terms of the unpredictability of river systems, in recent years the shift in emphasis has been moving towards process-based research in river morphology. This reflects a change from studies on basin morphometry and on drainage networks to studies that undertook to understand the processes at work in terms of the special characteristics of the monsoon-influenced river systems in India (Kale, 2002). Studies of river morphology in contemporary times utilize a great number of technological tools as well such as instruments utilized in field-studies and the use of satellite technology through remote sensing.
Studies on river morphology first look to identify the order of streams and the river reaches, or the stretches, through the length of the rivers. In this the demarcation of cross-section lines in the river basins is important to identify areas of flows. The second step involves data collection, which can occur through field surveys or through data collected with the help of remote sensing. Both methods can involve the use of considerably sophisticated technology. Remote sensing in particular can provide large amounts of information in terms of temporal and spatial scales. The data from both the methods can be used in the validation and calibration of mathematical and/or hydraulic models.
On the basis of this data, qualitative or quantitative studies can be undertaken to understand the behaviour of rivers. The qualitative aspects in studies on river morphology include analysis of structure, the stage of landform development in terms of drainage pattern, and process-based studies in terms of stage of landform development and its relations to river discharges. The quantitative aspects in the characteristics of river morphology studies include width in terms of river banks, flow characteristics, the characteristics of the river bed, transport of sediments, river platforms, river bars and shoals, energy slopes of flowing rivers, river channel migration, and so on.
Uses of Studies on River Morphology
An understanding of river morphology and the behaviour of rivers provides a scientific approach in considerations of the design and planning of water management projects and also provide solutions to various problems that might arise in terms of hazards such as floods. Many times the problems in river morphology can be intertwined such that one can influence the other.
Sarkar (2016) of the National Institute of Hydrology, Roorkee identifies problems in river morphology which can be natural or man-made. The natural problems in river morphology can for example include the effects of rainfall on river flows, changes in river course that can sometimes be frequent, one river avulsing (forming a new channel) into another, river capturing, diversion of river current towards the banks because of heavy shoal formation, changes in the meandering pattern of rivers, instability due to sudden increases in silt load such as through landslides joining upstream flows, river bed aggradation (increase in land elevation) due to deposits of sediments resulting in overflowing of banks and even floods in some instances, erosion of banks by hill streams, the effects of seismic activity on river bed slopes, rivers behaving in an erratic manner in deltaic areas, shoal formation creating navigational issues, and so on.
Man-made problems in river morphology can include for example downstream degradation of morphological features of a river due to the construction of a barrage or dam, effects on upstream river width due to the construction of a barrage or dam, effects on river flow regimes due to flood embankments, the effects of activities over extracting sand and boulders from river beds and from areas close to rivers, the effects of inter-basin transfers on river morphology, effects due to activities undertaken by farmers throughout the river reach, effects due to channelling or dredging of river beds, the effects of constructing bathing ghats, the effects of heavy urbanization by the river banks, and so on (Sarkar, 2016). There can thus arise many natural and man-made problems in rivers and many a time these problems form part of the needs in managing water resources from the rivers.
Using Technology to Study River Morphology
The contemporary age of employment of sophisticated technology to validate and calibrate mathematical and/or hydraulic models to aid studies of river morphology help in better achieving the need to systematically identify the actual and possible environmental effects of changes in river landscapes and flow regimes. The analysis also needs to evaluate these effects in terms of probability and/or magnitude. The use of technology helps in assessing river dynamics as can be seen in the study of the Brahmaputra river. Sarkar, Garg & Sharma (2011) analyze the Remote Sensing-Geographical Information System (RS-GIS) based assessment of river dynamics of the river Brahmaputra in the state of Assam in India. The integrated RS-GIS-based assessment covered the course of the river from Dibrugarh until Dhubri near the border with Bangladesh covering a stretch of about 620 km.
The information gained from analyzing satellite data using IRS 1A LISS-I and IRS-P6 LISS-III satellite images pertained not only to data on channel configuration for the river but also brought about significant other findings in terms of river morphology in the Brahmaputra. The RS-GIS-based assessment for example, was able to bring out changes in river morphology in the Brahmaputra including changes in the main channel, and also reaches in the river banks that were stable or not stable. The assessment was able to provide updated information in terms of both precise temporal and large spatial scales that substitute for cumbersome processes in the field in taking measurements. The use of technology thus in contemporary times is becoming more and more widespread, although field studies are required for particular site-specific inquiries. The idea is to bring out more precise information on large spatial scales that can streamline developmental processes and provide better responses in tracking rivers and in mitigating disasters such as floods.