Keywords

1 Introduction

Rivers are the lifeline of the human race across the world. Many of the villages, towns, hamlets and cities in the world are located along the river banks. However, the intervention of humans with the natural process of the fluvial streams has contaminated the water, damaged the ecology, altered the transit capacity, raised the suspended load, and triggered the fluvial hazards (Singh and Kumar 2017; Jain et al. 2021; Pu et al. 2021; Shankar et al. 2021; Chaudhuri et al. 2022). For instance, due to rapid growth of population and raising demand for land, humans began to live within the valleys and flood plains of rivers. Consequently, these inhabitants are constantly threated during high- and low-discharge intervals (Singh and Singh 2011; Shivashankar et al. 2022). The most prevalent fluvial risks encountered in river systems are generally classified as follows: floods, lateral erosion, strainers, and undercuts. Floods are the most common, widespread, and devastating natural disaster, causing significant social, economic, and environmental damage in both developing and wealthy countries (Mohapatra and Singh 2003; Singh et al. 2022; Wallwork et al. 2022). Developing nations, particularly South Asian countries, are predominantly exposed to flood hazards occurs due to heavy rainfalls, dynamic terrain forms, and high population density (Saleem Ashraf et al. 2017). In recent years, flooding has claimed more lives in these regions than any other natural calamity. From 1976 to 2005, the total number of people impacted by floods in South Asia was close to one billion, and in Bangladesh more than half of the country’s population is affected due to flood in 1988 (Wahiduzzaman 2021). The economic losses due to floods across the globe stood at a humongous $58.7 billion. In India, floods accounting for over 68% of total economic losses due to natural hazards. Some of the widely recognized major floods occurred in Huang Ho, China, 1931 and Bangladesh, 1987 and 1988 in the USA, 1998 in Mozambique, are all widely recognized. Floods in India affected around 100 million people in the states of Assam, Madhya Pradesh, Haryana, Jammu and Kashmir, Gujarat, Punjab, Himachal Pradesh, Chandigarh, and Rajasthan in 1993 (Shrestha and Takara 2008). Along with Bangladesh, India is one of the countries that has been severely impacted by river hazards on several occasions.

Aside from floods and stream bank erosion during periods of high flow, lateral migration has been found to act as an independent hazard during low-discharge periods (Singh and Awasthi 2011). Lateral migration of the river bank occurs due to the movement of a stream channel, fluctuations in fluid flow, and sediment discharges (Dekaraja and Mahanta 2021; Pandey and Md Azamathulla 2021). The combination of distinct sediments, inadequate compaction, scouring action, and the development of fractures causes the river bed configurations to change, forcing the river channel to migrate laterally. Many studies reported that increased urbanization and changes in land use land cover patterns increase the frequency and intensity of such disasters in the future (Ali et al. 2019). Lateral erosion and shifting of channel dimensions are geomorphological processes that have been investigated by a number of researchers in recent years (Bordoloi et al. 2020; Das et al. 2007; Pati et al. 2008; Phillips 1991; Sarma 2013). The important river hazards that affect the lives of human being and their resources are floods, lateral erosion, strainers, and undercuts. In this paper, a detailed introduction to river hazards, their impacts on human being and mitigation techniques have been explained considering some of the case studies.

2 Natural Hazards

2.1 Floods

Floods are the outcome of imbalances in natural forces and processes and are inevitable in the scheme of nature and that occur with a predictable frequency year after year, causing widespread morbidity and mortality over the continent (Subrahmanyam 1988). Floods have a significant influence on the global population because of their location and geography, as well as human demographics and built-environment features (Tripathi 2015). The majority of India’s population lives in the riverine and coastal plains. Because of their topography, certain places are frequently prone to flooding. As a result, a great number of individuals and their livelihoods have been severely impacted. The main causes of river floods are shown in Fig. 1.1. When flow exceeds the capacity of the river, flooding occurs in neighbouring places, which can be disastrous. It is caused by two factors: (a) Waterlogging and spreading as a result of severe rainfall and (b) Hydraulic structure failure as a result of rising water levels in the river channel. We briefly describe the distinct geomorphic configurations of three significant recent flood-affected locations in India: Uttarakhand flood in Upper Ganga Valley in June 2013 (Rana et al. 2013), Kashmir flood in Jhelum River occurred in September 2014, and Chennai flood happened on December 2015.

Fig. 1.1
A flow chart illustrates 4 root causes of river floods. They are atmospheric, seismic, technologic and land use hazards, with their respective examples below.

Causes of river floods

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2.1.1 Uttarakhand Flood (2013)

In June 2013, the banks of the Chorabari Lake in Kedarnath fell owing to a cloudburst that caused a large flash flood in Uttarakhand, inflicting widespread devastation and becoming the country’s greatest natural catastrophe (Martha et al. 2015). The Kedarnath valley is built on the glacial outwash plain. The disaster struck Kedarnath on the morning of the 17th, with the immediate cause being torrential rain (375% more than average) and abrupt overflow from the Chorabari glacier lake on the upstream of the Kedarnath valley, followed by a landslide on another slope a few hours before. Ten feet of flood water carrying a massive load of muck, trash, and rocks suddenly inundated Kedarnath and the surrounding valley, destroying everything but the main shrine. The flood waters proceeded downstream via the Mandakini, Alkananda, and Bhagirathi rivers, wreaking havoc on a huge region of 40,000 km2 across Chamoli, Rudraprayag, Pithoragarh, and Uttarkashi districts. Nearly 6054 people died as a result of the flood, and 4550 communities have been damaged (Rana et al. 2013). Because of the extreme flooding, bridges, towers, poles, and roads were destroyed. A total of 2052 homes were demolished, 147 bridges were damaged, and 1307 roads were devastated.

2.1.2 Kashmir Flood (2014)

The Jammu and Kashmir area saw severe floods over the bulk of its districts during the first week of September 2014, triggered by multi-day heavy rainfall storms. Flooding in Kashmir caused by heavy rain, mismanagement, unplanned development, and a lack of readiness (Alam et al. 2018). This flood caused localized devastation of property and public infrastructure, as well as a significant impact on life, communities, and communication. According to statistics released by India’s Home Ministry, several thousand villages were impacted across the state, with 390 villages entirely inundated. The early estimate of property loss ranged from INR 50,000 million to INR 60,000 million. Approximately 277 individuals were killed.

2.1.3 Chennai Flood (2015)

Heavy rains in Tamil Nadu and Andhra Pradesh in early December 2015 caused significant flooding. A deep tropical depression passed over the Bay of Bengal and impacted India’s south-eastern coast, pouring torrential rain. From December 1 to 2, Chennai got nearly 33 cm of rain in a 24-h period, causing significant flooding and damage. The catastrophic calamity was exacerbated by a sudden and uncontrolled discharge of water from the Chembaramkkam reservoir (Gupta and Nair 2011). In Tamil Nadu, the districts of Chennai, Cuddalore, Kanchipuram, and Tiruvallur were the most damaged. Unfortunately, as a result of this tragic disaster, over 500 people have died in Tamil Nadu. Flooding has impaired the educational system, food availability, transportation, and access to electricity in Chennai (Vishnu and Sridharan 2016). There were 500 confirmed deaths in the flooding catastrophe, and almost 1.8 million people were affected. The primary cause of this predicament is Chennai’s unscientific urbanization and growth. Many studies have issued warnings against converting marshy area to concrete infrastructure, which exacerbated the situation.

2.1.4 Kerala Flood (2018)

Due to abnormally heavy rainfall during the monsoon season, major floods struck the South Indian state of Kerala on August 16, 2018. The extreme rainfall in the monsoon season resulted in flooding, which is significantly higher than the capacity of reservoirs. The total rainfall is received by Kerala during the period 1 June 2018 to 19 August 2018 is 42% higher than the average monsoon rainfall for the same period. The return period of extreme rainfall is about 145 years and the occurrence of the extreme rainfall is due to the monsoon depressions over the Bay of Bengal as per India Meteorological Department (IMD). Approximately a million people were evacuated, primarily from Chengannur, Pandanad, Edanad, Aranmula, Kozhencherry, Ayiroor, Ranni, Pandalam, Kuttanad, Malappuram, Aluva, Chalakudy, Thrissur, Thiruvalla, Eraviperoor, Vallamkulam, North Paravur, Chellanam, and 483 casualties were reported. According to the Kerala government, the floods and related occurrences directly affected one-sixth of the state’s entire population.

In a warming climate, extreme weather events such as convective storm rainfalls are projected to cause an increase in the number of floods that endanger minor catchments. Despite this, the government always appears to treat these issues as a matter of crisis management rather than taking early actions to reduce the factors that lead to the crises (Singh and Kumar 2017). Moreover, there is a dearth of substantial national planning for surface water management, such as water storage, the construction of check dams, desiltation, and assuring seepage of water into the ground rather than runoff. Several entities at the state and national levels have attempted to lessen flood susceptibility by employing a variety of techniques (Abbas et al. 2016). Significant afforestation is also required in the higher portions of river systems to act as a buffer against excessive rainfall and to prevent silt and boulders from becoming dislodged and rushing down to clog water channels, resulting in siltation. Desiltation efforts should engage not only the government, but the entire community who benefits from this.

2.2 Flood Management and Control

The flood hazard management system in the country has been developed over the years. It helps states to develop, implement, and maintain all water resource management plans in accordance with their requirement (Ranjan 2017). After an exceptional and disastrous flood occurrence in Bihar in 1954, the importance of flood prevention and the necessity for an action plan to safeguard floodplains were recognized (Khan and Sharma 2020). Since then, major flood-prevention efforts have focused on controlling riverine floods, with significant expenditures in building structural measures such as river embankments and detention reservoirs, as well as improving river basin drainage. These solutions have not proven to in the long run, as the number of flood-prone areas in the country has expanded over the previous five decades. For the floods with a return period higher than the design return period of the structure, in the long run we have to adapt for non-structural measures such as enhancing catchment storage, flood plain zoning, flood forecasting and early warning system, awareness-raising, etc., serves as an alternative to structural measures for effective flood management (Jain et al. 2018; Kundzewicz and Menzel 2005; WMO 2011). Although flood management comes under water resources management, the responsibilities of construction and maintenance of flood control systems are linked with state government and state agencies. The federal government establishes numerous committees, task groups, and policies to assist states in developing an effective flood control system (Bhattacharjee and Behera 2017). According to the directives of several committees, various agencies of the central government operate as a catalyst to provide financial and technical aid to the states through qualified initiatives.

2.2.1 National Level Organizations

It is the role of the central government to oversee the country’s catastrophe management procedure. The central ministries coordinate with other agencies to execute disaster preventive and mitigation measures. Flood control is a multi-disciplinary process that necessitates collaboration and coordination among several entities. The primary co-ordinator/supervising department is the Ministry of Jal Shakti, Department of Water Resources, River Development, and Ganga Rejuvenation (MoWR; http://mowr.gov.in/). However, the Central Government has formed a multitude of distinct agencies and expert committees to more thoroughly monitor the flood concerns. The following sections describe the various organizations and their roles in flood management.

2.2.2 Central Water Commission (CWC)

Central Water Commission (CWC) (http://cwc.gov.in/), the country’s nodal body for water resource management, has decades of experience in water resource development planning, management, and design. It was established to promote flood management methods and to assist in policy-related matters as a technical advisory body to the MoWR and the states. It is in charge of developing infrastructure, maintaining information, and developing a flood forecasting system, as well as disseminating it to various end-users. It also conducts and coordinates research on water-related issues and provides guidance on different development initiatives involving river basins, such as flood control techniques. To give special attention to two of India’s largest river basins, the Ganga and Brahmaputra, the MoWR established the Ganga Flood Control Commission (GFCC), and the Brahmaputra Board as statutory entities to handle flood control initiatives in their respective basins.

2.2.3 National Disaster Management Authority (NDMA)

The National Disaster Management Authority (NDMA) (https://ndma.gov.in/en/) is in charge of initiating a comprehensive and accelerated response to floods or other disasters. It is responsible for conception of national policies and action plans for disaster management. It offers guidelines to implement the plans and conduct essential disaster preparedness and capacity building setups by collaborating with the states and other agencies. These recommendations aim to improve post-flood response, relief, and rehabilitation methods while also enhancing existing flood preparedness and mitigation measures.

2.2.4 Other Organizations

Although the India Meteorological Department (IMD; https://mausam.imd.gov.in/), the National Remote Sensing Centre (NRSC; https://www.nrsc.gov.in/), and the National Institute of Disaster Management (NIDM; https://nidm.gov.in/) are not subsidiary bodies for flood management, their assistance is critical. For instance, IMD’s frequent weather predictions give critical information for flood forecasting. At the same time, the NRSC’s remote sensing capabilities are important for a variety of observational research and flood mapping projects. NIDM’s flood management research is primarily concerned with policy formulation and capacity building through the development of training modules.

3 River Bank Erosion

River bank erosion is a major natural hazard and a major source of concern. It originates from the sediment composition, which is mostly made of different proportions of sediment materials such as clay, silt, and sand. According to granulometric studies, geomorphological and facies, the lower and middle regions of the Sand and silt assist compensate for stream banks and ridges that are prone to erosion, scouring, and mass movement, resulting in lateral erosion. The abandoned river route has a sandy bottom, which leads to lateral erosion. The spatio-temporal migration of river channel is critical to many geomorphological and river management challenges (Shah 1995). Every year, it brings unspecified misery to hundreds of individuals who live along river banks. Only erosion has displaced millions of people and has become a significant societal disaster. People who live along riverbanks suffer from erosion, forcing them to shift their livelihood and society. The majority of riverbank erosion victims end up living in slums in towns and metropolitan cities (Hasnat et al. 2018). From the literature survey, the contributing factors to riverbank erosion are: excessive flood, extreme precipitation in the upstream, increased flow of water with strong wind, and insufficient land cover along the line (Das et al. 2017).

River bank erosion has several effects, including social, economic, health, education shown in Fig. 1.2. The first and most evident social consequence is homelessness caused by soil erosion, which drives people to migrate. They face economic catastrophe as a result of forced migration, including loss of work and property, and they experience poverty (Iqbal 2010). For these displaced people, identity crises is inescapable because their membership in any specific neighbourhood, state, or nation is routinely denied.

Fig. 1.2
A flow chart illustrates 3 root impacts of river bank erosion. They are social, economic and other impacts, followed by their respective examples.

Impacts of River bank erosion

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3.1 River Bank Erosion in India

The river bank erosion across four regions of India is explained in the following sections.

3.1.1 North West Region

There are five main rivers in this region, namely Sutlej, Ravi, Chenab, Beas, and Jhelum, all of which are the tributaries of the Indus river that originates from the Himalayas (Sarma and Acharjee 2012). Flood and erosion hazards are quite modest in this region when compared to the Ganges and Brahmaputra regions. The biggest concern is insufficient surface drainage, that causes flooding and water logging across large regions.

3.1.2 Central India and Deccan Region

The major rivers in this region includes Krishna, Godavari, Cauvery, Tapi, Narmada, and Mahanadi. These rivers’ courses are typically well-defined and steady. Except in the delta area, they have sufficient capacity inside the natural banks for carrying the flood runoff. The lower portions of the East Coast’s major rivers have been embanked, essentially alleviating flood and erosion concerns. Orissa is another state where river banks are eroding. The state’s largest river, the Mahanadi, and its two branches, the Kathajodi and the Kuakhai, are continually expanding and altering their path. These rivers devour a few settlements every year. Many people have already been affected by erosion or are at risk of being swept away by these three rivers. These individuals have no other option except to relocate, and the government refuses to acknowledge the erosion problem.

3.1.3 Brahmaputra Region

This region includes seven states: Arunachal Pradesh, Assam, Mizoram, Meghalaya, Tripura, Northern West Bengal, Nagaland, and Manipur as well as the rivers Barak and Brahmaputra and their tributaries. Islam and Guchhait (2017) demonstrated the effects of river bank erosion in Brahmaputra floodplain zones. For this study, an interview, field observation, secondary data sources, focus group discussion, and a semi-structured questionnaire were used. There are ten unions in Gauripur upazila, with Bhangnamari union mainly destroyed by riverbank erosion between 1988 and 2015 (Bhuiyan et al. 2017). Recent riverbank erosion has mostly impacted Bhangnamari, Kashiar Char, Bhatipara, and Gazariapara villages in Gauripur upazilla Bhangnamari union.

According to Guchhait et al. (2016), there was considerable evidence of frequent and rapid erosion rate along the Jamuna and Brahmaputra rivers between 1973 and 1992, the average width of the Brahmaputra River in 1830 was 6.2 km, and by 1992, it had expanded to 10.6 km. The canal extended at a pace of 27 metres per year on average between 1830 and 1914. The eroded area (ha) of the Brahmaputra River’s left and right banks from 1995 to 2020 is depicted in Fig. 1.3. The results suggest that more than 1000 ha of land are eroded every 5 years on the left bank, while more than 800 ha are degraded on the right bank. According to the findings, the communities located along the river’s left bank are prone to lateral erosion.

Fig. 1.3
A double bar graph of erosion rate, in hectares, from 1995 to 2020, for left and right banks. Left bank has the highest value between 1995 to 2000.

Eroded areas of banks of Brahmaputra River during past decades

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3.1.4 Ganga (Ganges) Region

The Ganges and its various tributaries drain Uttaranchal, Delhi, Uttar Pradesh, Madhya Pradesh, Bihar, South and Rajasthan, Himachal Pradesh, and Haryana. Despite the fact that the Ganges is a lengthy river with a streamflow up to 70,000 m3/s, only a few locations are susceptible to erosion (Thakur et al. 2012). Flooding and erosion are major issues in the lower Ganges area, notably in West Bengal. Chatterjee and Mistri (2013) investigated the socioeconomic impacts of river bank erosion in various communities in the Shantipur block of West Bengal’s Nadia district. Methiadanga was formerly a community in Shantipur block that had been gradually submerged by the river. As the river inundates the settlement, the people who lived there were migrated. The population of this community is being altered by the river bank erosion for every 20 years from the date of the census.

4 Mitigation

Recent hazards data show an ominous trend of rising hazard losses. The primary causes of this phenomenon are land use and climate change. This factor increases vulnerability to natural catastrophes. It is suggested that internal variables such as catastrophe-related science and policy are partly to blame for the inability to stop or reverse the growing trend in disaster damage (Birkland et al. 2003).

Nature causes floods and river bank erosion, but the anthropogenic interference are making them lethal. While there is no known way to avoid flooding and lateral erosion, much may be done to minimize the effects of river hazards (Mehta 2007). Increasing urbanization creates new difficulties in decreasing catastrophe risk. However, calamities are usually ignored until they happen, at which stage the damage is done and relief is the only solution. There should be a perceptible shift in policy, with a greater emphasis on loss reduction through mitigation, preparedness, and recovery.

Flooding and river bank erosion could be reduced by assessing structural and non-structural measures shown in Fig. 1.4. The construction of embankments, lateral dams to regulate the flow of the river, vegetation, and the dumping of sand and cement bags and boulders are all examples of structural control. Plants are utilized to stabilize and reduce the erosion of stream banks by reducing stream flow velocity and trapping sediments, vegetation lowers stream bank erosion. Controlling deforestation, denudation, and soil erosion, as well as adequate planning, are the primary ways to tackle stream bank erosion and the growing flood threats.

Fig. 1.4
A flow chart of river hazard mitigation with the respective examples. Structural has in the river vicinity and catchment area. Non-structural has scientific and social.

Mitigation of River Hazards

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The non-structural factors such as emergency security, flood and lateral erosion zone delimitation, land use planning, forecasting, palaeocurrent and facies research, and warning systems are examples of non-structural variables. Policy should be implemented to prevent people from settling near the river’s danger zone.

5 Conclusions

The research work presented in this paper explains the various types of river hazards such as floods, lateral erosion, and their impacts on human resources along with their mitigation techniques. The river channel, water, sediment, and nutrient flows have all changed as a result of human ecologically disruptive activities. When the river’s capacity is exceeded, flooding occurs in nearby areas, which can be devastating. Despite decades of catastrophic flooding and numerous flood-prevention initiatives, the exposure to disasters has not decreased to projected levels. For effective flood management and mitigation, both structural and non-structural measures are being adapted to reduce flood risk and disaster relief preparedness. However, due to the feasibility issues related to structural measures, a paradigm shift to non-structural measures such as flood forecasting and warning systems has been witnessed in recent times. Moreover, non-structural flood protection measures are reversible and economically feasible. The scientific advancements in remote sensing and instrumentation aids in generating more observables such as soil moisture, evapotranspiration, and other earth surface and atmospheric variables. These variables are useful in data assimilation of Numerical Weather Prediction models, land surface models, and hydrological models for improving the forecast quality. Many of the existing flood forecasting systems across the world are using deterministic forecasts for shorter lead times (ranging from few hours to 3 days). A probabilistic approach (ensemble flood forecasting) for medium range lead times (up to 15 days) is suggested for improved flood preparedness. An active federal role is anticipated for taking effective actions to mitigate floods and carry out disaster relief duties in coordination with local authorities. However, the implementation highly depends on regional governments. The coordination between regional water resource councils is important as watersheds do not respect any political boundaries. Adequate training of communities is necessary for maintenance and operation purposes.

The growing frequency of disasters is seen as a sign of unsustainable development, according to the researchers. The majority of river-borne tragedies are caused by humans. As the human population has grown, people have begun to live in the river’s danger zone. As a result, lateral erosion is a dangerous concern. To protect civilization from natural hazards, the trend of erosional pattern, river channel shifting, river discharge, and facies association should be studied. The mitigation of river-borne disasters requires a thorough understanding of river dynamics. Improved floodplain and river valley management, flood and lateral erosion mitigation strategies, greater disaster readiness, and the implementation of a forecasting and warning system can all assist to lessen damage effects. Hydrographic data and a digital elevation model of flood plain can be utilized for hydraulic and sedimentation prediction of Indian river reach; future flood and riverbank erosion risk maps may be developed and are extremely valuable for future mitigation and hazard preparation programmes to be conducted by government authority.