Annals of Geographical Studies Volume 1, Issue 1, 2018, PP 34-50 Rainfall and Flood Studies of the Ganga River Basin in India S.S. Nandargi1 and A. Shelar2 1Scientist E, Indian Institute of Tropical Meteorology, Pashan, Pune -411008, India 2M.Sc. Student, SP Pune University, Pune, India *Corresponding Author: S.S. Nandargi, Scientist E, Indian Institute of Tropical Meteorology, Pashan, Pune -411008, India, E-mail: [email protected] ABSTRACT The Ganga basin is one of the largest river basins in the northwest to north region of India. Since, the region is located in the foot hills of the Himalayas is the area of highest rainfall in the downstream areas of north India causing severe to unprecedented floods during the monsoon season. Examination of rainfall and flood data for the period 1986 to 2016 showed that among all the Himalayan rivers joining the Ganga from the north, the major contributions come from the Kosi, Ghagra and Gandak and their tributaries joining the Ganga along its course through Gangetic plains. The most frequent flood experiencing states are Bihar, Uttar Pradesh and West Bengal. Frequency of floods was less in the years 1992, 2009, 2012, 2014, 2015 and it was highest in 1987, 1998, 1999, 2001, 2003 and 2013 years. Since all these Himalayan rivers are perennial in nature due to their source being in Himalayan glaciers and ice caps, this water resource can be utilized for power generation wherever the necessary drop in water level is available. The progress and prosperity of this country is very much linked with the harnessing of the waters of these main important Himalayan rivers, e.g. the Kosi, Ghagra and Gandak. The study will be useful to design engineers, flood forecasting authorities, power generation, etc. Keywords: Himalayan rivers, Ganga river basin, Rainfall, Floods INTRODUCTION India is one of the top five countries of the world (Brazil, Canada, Congo, India and Floods have been occurring from time Russia), having enough water resources. Nature immemorial. It may be said that ever since has been kind to give this country a four to five monsoon activity started in this part of the months long monsoon period and moreover the world, floods have been occurring regularly orographic features of India are responsible for every year. Over the global scenario, floods are causing heavy rainfall which ultimately results common events in South Asia. In fact, it has in flooding of rivers and valleys during the been said that after Bangladesh, India is the monsoon months. Indian rivers constitute major worst flood affected country in the world share in the total water resources of the country. (Agarwal and Narayan, 1991) and about one Seven major rivers (Indus, Ganga, Brahmaputra, fifth of global death occurs due to floods. Narmada & Tapi, Mahanadi, Godavari and Therefore, it is essential to have the knowledge Krishna) along with their numerous tributaries about the magnitude and frequency of floods make up the river system of India. experienced by rivers for flood forecasting, proper design of water resources projects viz. The water discharge from India accounts for dams, culverts, highways, etc. The frequency about 4.5% of global river discharge. A monthly with which such damage may occur must be discharge pattern of Indian rivers is the considered in determining the size or strength of reflection of rainfall received maximum the structure, its location, or the feasibility of generally during July-August months. Some of building it at all. Besides, flood frequency the rivers draining eastern India also receive the analysis indicates the catchment characteristics, northeast monsoon rains; their discharge pattern water availability and possible extreme therefore shows the effect of these rains as well. hydrological conditions at various locations of Relating to the climate, the frequent natural any river system. This is very much essential disaster experienced in India are droughts, flash from country‟s economy point of view and to floods, landslides, avalanches, cyclones, overcome human loss and property. hurricanes and Tsunami. It is said that floods are Annals of Geographical Studies V1 ● I1 ● 2018 34 Rainfall and Flood Studies of the Ganga river basin in India the deadliest of natural disasters as all other Flood Analyzer (AGFA) quantifies and disasters like landslides, avalanches and even visualizes the reality of global flood risk. WRI hurricanes fall short when a heavy gush of water ranked 164 countries and found that the 15 comes in a short time. It has a record of causing countries account for nearly 80% of the total the maximum amount of damage in terms of life population affected every year. Among these, and property. World Resources Institute (WRI) India ranks on the top (see Fig.1). developed a tool known as Aqueduct Global Figure 1. Annual Expected Population affected by river floods (in millions) (Source: http://www.wri.org/) Being hazardous to human life and wealth, study for the Kosi river. Flood management has countries economy; floods are studied by many been studied by Mavalankar and Srivastava more authors worldwide. In India, flood (2008) for the Surat city and by Gupta et al frequency analysis of different river basins has (2012) for Leh (Ladakh).The above mentioned been carried out using different statistical studies are mostly restricted to small sub-basins distributions by many authors viz. Khan (2013) of the large rivers. Dhar and Nandargi –Narmada river at Gurdeshwar site, Sathe et al (1989,1992,1993,1994,1995,1998,2000,2001a& (2012) – Upper Krishna river basin, Mukherjee b,2002,2003,2004a&b), Nandargi and Dhar (2013) - Subarnrekha river, Das and Kureshi (1996,1997,1998,2003a&b,2004,2008),Nandarg (2014) – JiyaDhol river of Brahmaputra valley, i et al (2007, 2010) have carried out a number of Sah and Prasad (2015)- Kosi river, Guru and Jha flood studies of Indian rivers based on available (2015) - Tel basin of the Mahanadi river system, rainfall and flood data to study different aspects Kamal et al (2016). Flood disaster management of floods in different regions of India. studies are done by Nirupama (2015) and Tayal In the past thirty years, the country has et al (2015) - Uttarakhand region. Bapalu and experienced ten worst floods namely over Bihar Sinha (2006) carried out flood hazard mapping (1987,2004,2008), Uttarakhand (2013), Jammu 35 Annals of Geographical Studies V1 ● I1 ● 2018 Rainfall and Flood Studies of the Ganga River Basin in India & Kashmir (2014), Ladakh (2010), Assam Brahmaputra, Ganga and Indus. The Ganga (1998, 2012), Maharashtra (2005) and Chennai drains the Indo-Gangetic plains of northern (2015). It is, therefore, clear that north India India between the Himalayas in the north and experience floods, more particularly, the regions the Vindhya-Satpura mountain ranges in the falling in the sway of Ganga basin (see Fig.2) south covering eleven states in north India (see are more prone to severe or worst floods. Fig.2, Table 1). According to Rao (1975) the According to a Central Water Commission total catchment area of the Himalayan or (CWC) Report, nearly 37 million hectares northern tributaries of the Ganga is (nearly 1/8th of India‟s geographical area) of approximately 420000 sq.km while that of the fertile land are prone to floods at one time or southern tributaries, is 580000 sq.km extending another during the monsoon (Valdiya, 2004). over India, Nepal and Bangladesh. However, the Among the major Himalayan rivers, Ganga river northern tributaries of the Ganga, which system is the largest river system in the north originate in the Himalayas, contribute much India experiencing floods during every monsoon more than the southern tributaries. Due to heavy season. In view of this, the present study deals precipitation over the Himalayas, especially with the flood frequency analysis of the Ganga during monsoon months, the normal annual river and its major tributaries in the Indian runoff from the northern tributaries is about 25 region. times more than what it receives from the southern tributaries. The average annual flow of MORPHOLOGICAL AND HYDROLOGICAL the Ganga at Farakka before entering into the CHARACTERISTICS OF THE GANGA BASIN Bangla Desh is 459,040 MCM (Rao, 1975). The river Ganga is one of the three great rivers of the Indian sub-continent, viz. the Figure 2.Location map of Ganga basin showing states covered by the basin and its major tributaries The river originates from the Gangotri Glacier at elevation of about 4100 m asl as named Gomukh in the Garhwal Himalayas at an Bhagirathi. On the Bhagirathi river Tehri dam Annals of Geographical Studies V1 ● I1 ● 2018 36 Rainfall and Flood Studies of the Ganga river basin in India has been built in Uttarakhand for hydropower the Yamuna has not been considered as a generation mostly for regulating the additional northern tributary of the Ganga. As most of its water discharge during the lean period. The tributaries flow into the Yamuna, to a large Bhagirathi flows through the Himalayas and extent their flow originates from the western and joins with the Mandakini and the Alaknanda at central Indian region causing considerable flow Dev Prayag, the point of confluence forming the between Allahabad (Uttar Pradesh) and Malda upper reaches of Ganga. The combined stream in West Bengal. The Farakka, end site on the is then known as the Ganga (Fig.2). Ganga Ganga river in West Bengal regulates the flow enters the plain area at Haridwar, where a large of the river and diverts some water into a feeder quantity of water is diverted from this site into canal linking Hoogly to keep it relatively silt- the Upper Ganga Canal, to provide water for free. Downstream of the Farakka site, Ganga irrigation. During the monsoon months, water gets river splits into two, Bhagirathi (Hoogly) on the diverted at two barrages one at Bijnor into the mid- right and Padma on the left.