Environ Geol (2005) 48: 579–589 DOI 10.1007/s00254-005-1314-2
Harish Gupta G. J. Chakrapani
Received: 5 November 2004 Accepted: 11 April 2005 Published online: 24 June 2005 Springer-Verlag 2005
H. Gupta Æ G. J. Chakrapani (&) Department of Earth Sciences, Indian Institute of Technology, Roorkee, 247 667, India E-mail:
[email protected] Tel.: +91-1332-285080 Fax: +91-1332-273560
ORIGINAL ARTICLE
Temporal and spatial variations in water flow and sediment load in Narmada River Basin, India: natural and man-made factors
Abstract The Narmada River flows through the Deccan volcanics and transports water and sediments to the adjacent Arabian Sea. In a firstever attempt, spatial and temporal (annual, seasonal, monthly and daily) variations in water discharge and sediment loads of Narmada River and its tributaries and the probable causes for these variations are discussed. The study has been carried out with data from twenty-two years of daily water discharge at nineteen locations and sediment concentrations data at fourteen locations in the entire Narmada River Basin. Water flow in the river is a major factor influencing sediment loads in the river. The monsoon season, which accounts for 85 to 95% of total annual rainfall in the basin, is the main source of water flow in the river. Almost 85 to 98% of annual sediment loads in the river are
Introduction Rivers are dynamic geologic agents on Earth and are the main pathways for transport of continental materials to the oceans. The continental weathered products in the form of suspended and dissolved loads are important inputs to the world’s oceans, thus influencing biogeochemical cycling of elements. To understand geochemical mass balance between land and oceans, estimation of mass transfer from continents to oceans is very essential. However, despite numerous attempts, exact estimation and magnitude of global sediment flux to the oceans is fraught with uncertainties, firstly due to lack of data
transported during the monsoon season (June to November). The average annual sediment flux to the Arabian Sea at Garudeshwar (farthest downstream location) is 34.29·106 t year)1 with a water discharge of 23.57 km3 year)1. These numbers are the latest and revised estimates for Narmada River. Water flow in the river is influenced by rainfall, catchment area and groundwater inputs, whereas rainfall intensity, geology/soil characteristics of the catchment area and presence of reservoirs/dams play a major role in sediment discharge. The largest dam in the basin, namely Sardar Sarovar Dam, traps almost 60–80% of sediments carried by the river before it reaches the Arabian Sea. Keywords Water flow Æ Sediment load Æ Narmada River Æ India
from several medium and mountainous rivers and secondly, the estimates are frequently revised due to changes influenced by humans, in river flow and its dynamics. The peninsular rivers in India are not as massive as the Himalayan rivers, such as the Ganga or Brahmaputra. However, they constitute an important water domain, because the drainage areas along these rivers are highly urbanized and, hence, support dense populations. Very little published information is available on the water discharge as well as concentrations and loads of suspended sediments of rivers flowing into the Arabian Sea from the Indian sub-continent. Narmada River is the
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largest river draining the Deccan Traps. The Deccan Traps in India represent one of the largest basaltic provinces on the Earth’s surface with present-day volume of 106 km3 and cover an area of 5·105 km2. Courtillot and others (1986) estimate that the total initial volume of lava may have reached 3·106 km3, out of which about two thirds of the initial basalts have disappeared by erosion during the last 65 My. As basalt (a silicate rock) weathering consumes atmospheric CO2, river erosion is likely to have an important effect on long-term climatic evolution. Dessert and others (2001), on the basis of chemical composition of the dissolved loads in the rivers draining Deccan Trap basalts, calculated the annual atmospheric CO2 consumption rate to be 0.58–2.54·106 moles of carbon per km2. Similar studies on the island of Reunion by Louvat and Allegre (1997) show higher chemical erosion rates (63–170 t km)2 year)1) and specific atmospheric CO2 consumption rates (1.3–4.4·106 mol C km)2 year)1) during basalt erosion. These results indicate that denudation rates of basaltic rocks are quite significant in atmospheric CO2 consumption. Many of the world’s major rivers are now impounded along their course for multifarious purposes. These activities have altered the natural flows of rivers to such an extent that there is hardly any flow to the oceans during dry seasons. More than 45,000 large dams with an approximate height of 15 m or higher have been built around the world to meet the water and energy supplies Fig. 1 Location map of Narmada river basin along with location numbers of gauging stations
and for flood management practices (World Commission on Dams 2000). The environmental implications of such man-made structures could be deleterious to the global water cycle. Sediments trapped by reservoirs in India are estimated to be 480·106 t (Narayana and Babu 1983), which is almost half of the direct sediment flux from India to the oceans. Information and dissemination of data on distribution patterns of sediment load during various seasons is a prerequisite for better management of water systems. The present study is aimed at quantifying and observing the variations in water and sediment discharge in the Narmada River Basin (hereafter referred to, as NRB), and to identify the natural and man-made factors responsible.
Narmada River Basin The Narmada River is the seventh largest river in terms of drainage area, preceded only by the Ganga, Brahmaputra, Godavari, Krishna, Indus and Mahanadi. The Narmada River Basin (NRB) lies in the central part of India, between 7232¢E to 8145¢E longitude and 2120¢N to 2345¢N latitude with a drainage area of 98,796 km2 and a mean elevation of 760 m. The total length of the river is 1312 km. The catchment area of the river extends in the administrative states of Madhya Pradesh (86.18%), Gujarat (11.6%), Maharashtra (1.5%) and Chattisgarh (0.72%). In contrast to the other peninsular rivers in India (Godavari, Krishna, Cauvery and Mahanadi), which flow into the Bay of Bengal, Narmada along with Tapi Rivers drain westward into the Arabian Sea.
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Narmada River has its origin from Amarkantak, on the eastern fringe of the Maikala plateau of Satpura range, in Anuppur district of Madhya Pradesh and empties into the Arabian Sea at Bharuch (Fig. 1). It arises as groundwater seepage from a small pond (Narmada Kund) at an elevation of 1,057 m. The basin is bounded on the north by Vindhyans, on the east by the Maikala range, on the south by the Satpuras and on the west by the Arabian sea. Most of the basin is at an elevation of less than 500 m above mean sea level. The river has 41 tributaries of which 22 are on the left bank and 19 on the right bank, although only Burhner, Banjar, Hiran Tawa, Chota Tawa, Orsang and Kundi are the major tributaries with catchment area of more than 3,500 km2. Approximately 35% of the basin area is under forest cover and 60% under arable land and 5% are grassland, wasteland, etc. The approximate basin population is about 16 million; the urban share of the total population is only 20%, which indicate the sustenance of rural population in the basin (CPCB, 1994). The Tropic of Cancer crosses the Narmada basin in the upper plains and a major part of the basin lies just below this line. The climate of the basin is humid tropical, although at places extremes of heat and cold are often encountered. Average rainfall of the basin is 118 cm, whereas the annual rainfall for the entire basin varies from 80 cm to 160 cm. A major portion of the precipitation in the basin takes place during southwest monsoon (July to September), which accounts for about 85–95% of the total precipitation. Temperature varies from 40C to 42C in summers to 8C to 13C in winter. The evaporation rates in the basin vary from 6 mm to 28 mm in summer (April to June) and 1 mm to 9 mm in winter (October to March). A number of dams have been constructed on the Narmada River and its tributaries. More than 4000 water related projects of various scales and purposes are in operation in the basin. Bargi dam, Barna, Indra Sagar, Kolar, Omakareshwar, Maheshwar, Bhagwant Sagar, Tawa and Sardar Sarovar dam are some of the major projects in the basin. Among the 29 large dams planned for Narmada, the Sardar Sarovar dam is the largest with a proposed height of 110.64 m and with a reservoir capacity of 3,700· 106 m3. The major lithology in the basin are the Deccan basalts followed by sedimentary rocks of Vindhyan and Gondwana Super Groups. The Bijawar Group of metasediments and gneissic complex of Archean-Proterozoic age are the minor constituents contributing to the basin geology. Quaternary alluvium is confined essentially to the Narmada valley. The Narmada River occupies the Son-Narmada-Tapi lineament zone, a mega-tectonic feature. The zone consists of several longitudinal faultbounded blocks that have an episodic history of vertical and lateral movements (Shankar 1991). The soils are predominantly black soils rich in smectite clays, which have high water-holding capacities. The
black soils in the upper basin are often interspersed with red sandy or lateritic soils. The profile of soil is rather shallow and covers the hilltops and plateau regions. The red soils result from intense chemical weathering of basalts whereby all the minerals in the rocks are leached out except the oxides of silica, iron and aluminum. Due to intense leaching, these soils show good drainage conditions. The Vindhyan and Satpura plateau region of the middle basin range from shallow black soils to medium black soils. Black soils are the major soil types in the lower stretches of the basin. On the other hand, mixed red and black soils occur in the northern plateau. The mouth of Narmada is characterized by Pliocene rocks and recent alluvium (CWC 1996–99). Data collection Central Water Commission (CWC), an organization of the Ministry of Water Resources, Government of India, has a number of gauge-discharge stations along Narmada River and its major tributaries for hydrological studies. Daily water discharge and sediment load data for 12 years (CWC 1987 to 1999) and annual water discharge and sediment load data for 22 years (CWC 1978–1999) of NRB were obtained from Narmada Basin Organization in Bhopal. In addition, monthly water discharge data for the year 1999–2002 and rainfall data of 33 years were also obtained. The location of the gauging stations and the corresponding site numbers are also shown in Fig. 1. The data thus obtained are interpreted for the variations shown in NRB. The water discharge at the gauging stations are measured once every day by area-velocity method. The total stream width is divided into 15 to 20 segments. The width of the river is measured by steel tape or nylon rope stretched across the river. The depth is measured by using sounding rod, which is normally 3 to 6 m long. When the river flow is very deep and swift, lead lines/echo-sounders are used. Necessary airline correction and wet-line corrections are made to the sounding observation. The velocity is measured by using a cup type current meter by lowering at the requisite depth (0.6 times of the depth of water in the river channel) vertically at every segment by suspension arrangement. At high velocities, boats fitted with power engines or motor launches are used. Drift is measured and corrections for the same are made. Where observations by boat or launch are not possible, measurement of velocity is conducted from bridge or cableway. The suspended sediment concentrations are obtained by filtering known volumes of water samples through 0.45 lm filter papers and weighing the difference in dry filter paper before filtration and after filtration. The suspended sediments are separated into three size grades, coarse (>0.2 mm diameter), medium (0.2–0.075 mm) and fine (90% sediments are carried in finer sizes (30C have extreme sediment yields (3,648 t km)2 year)1).
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Fig. 8 Relationship of sub-basin area with water discharge (km3 year)1) and sediment discharge (106 t year)1)
taries and entrapment of sediments in the reservoirs. Comparative studies of average sediment loads at various locations on Narmada River for more than two decades show overall reduction in sediment loads in the river. Reservoirs are the sites of major sediment accumulation, resulting in a large reduction in sediments reaching the oceans. Vorosmarty and others (2003) estimated that 30% of global sediment flux is trapped behind large reservoirs. Several large basins such as the Colorado and Nile, show near complete trapping of sediments due to large reservoir construction and flow diversion. The previous estimations of the sediment flux by Narmada River are 61·106 t year)1 (Narayana and Ram Babu 1983) and 70·106 t year)1 (Subramanian 1993), whereas the present estimation is 28.93·106 t year)1, establishing the fact that sediment transfer from rivers to the oceans has been reduced over the years.
Conclusions The water flow in the Narmada River Basin shows temporal and spatial variations. Monsoonal rainfall is a major factor in contributing water flow to the river. A few days during monsoon are responsible for huge amounts of water flow in the river. At some locations the contribution from groundwater to mainstream is also Fig. 9 Narmada river profile from its source to mouth along with very significant during non-monsoon periods. The flux water discharge (km3 year)1) and sediment load (106 t year)1) of water to the Arabian Sea by Narmada River is 34.29 km3 year)1 at Garudeshwar (farthest downstream deterioration of coastal marine ecosystem. For example, gauging station on the river). The sediment load varies the Aswan Dam was completed in 1964, and since then from 5.82 to 28.93·106 year)1 for Narmada River at the sardine fish catch was reduced by 95% and the delta different locations. Some of the tributaries show high concentrations of total suspended sediments due to high shrank rapidly (Saito et al. 1994). Sardar Sarovar Dam, largest dam in NRB, traps large erosion rates, caused by type of soil and incapacity to proportions of sediments being carried by the river store sediments in the sub-basins. The suspended (Fig. 10). The dam is between Rajghat and Garudeshwar sediment concentrations vary from 5.4 mg l)1 to and is 8 km upstream of Garudeshwar. Sediment load 275.3 mg l)1, whereas the tributaries show comparaestimations during the three years (1996–1999) indicate tively high concentrations of suspended sediments large trapping of sediments during the monsoon season, (596.0 mg l)1 and 437.7 mg l)1 for Burhner and Chhoto the extent of 60–80%. From its source to mouth, ta-tawa river, respectively). Similar to the effects of Narmada River shows significant changes in water and monsoonal rains on water flow, sediment loads also sediment loads, influenced by contributions from tribu- show significant temporal variations. A few days in Fig. 10 Trapping of sediments in Sardar Sarovar Dam (sediment load in ·106 t)
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Fig. 11 variations in water discharge (km3 year)1) and sediment load (·106 t year)1) at various locations of Narmada river from source to its mouth
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monsoon are responsible for huge sediment discharges in the basin. Sediment flux at Garudeshwar is 329.24 t km)2 year)1. However, there has been significant decrease in sediment flux over the years, due to construction of dams/reservoirs across the river.
Acknowledgements The authors would like to thank the personnel of Narmada Basin Organization, Central Water Commission, Bhopal, Tapi River Division, Central Water Commission, Surat and Narmada Control Authority, Madhya Pradesh for providing necessary data. Editorial handling by Ann McCarley and comments by the reviewers are deeply appreciated.
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