Spatial and temporal variability of sediment and dissolved loads from two alpine watersheds of the Lesser Himalayas Omvir Singh a, ⁎, Milap C. Sharma b , A. Sarangi c , Pratap Singh d a Division of Environmental Sciences, IARI, Pusa Campus, New Delhi 110012, India b Centre for the Study of Regional Development, Jawaharlal Nehru University, New Delhi 110067, India c Water Technology Centre, IARI, Pusa Campus, New Delhi 110012, India d HydroTasmania Consulting,12th Floor, Eros Corporate Tower, Nehru place, New Delhi 110019, India abstract article info Article history: Received 17 January 2008 Received in revised form 7 August 2008 Accepted 21 August 2008 Keywords: Sediment transport Denudation rate Weathering Himalayan Watersheds Estimation of sediment load from Himalayan basins is of considerable importance for the planning, designing, installation and operation of hydro-power projects, including management of reservoirs. In the present study, an assessment of physical and chemical load, sediment yield and erosion rate has been undertaken at eight different locations in the Sainj and Tirthan watersheds. The analysis revealed that the maximum load was transferred during the monsoon season. Moreover, the estimated average chemical erosion rate of the Sainj (83 t km - 2 yr - 1 ) and Tirthan (80 t km - 2 yr - 1 ) watersheds were higher than that of the Indian average (69 t km - 2 yr - 1 ) representing all the rivers. Both watersheds were eroding physically and chemically at a faster rate than that of the world global average erosion rate (185 t km - 2 yr - 1 ). The flattish nature of the channels in some segments of these watersheds showed a lower transport of sediments, where as the constricted segments having steep bed slopes increased the velocity of flow and the sediment transport rate. These findings have important implications for water resource management in the context of sediments mobilization, erosion, channel management, ecological functions and operation of the hydro- power projects in the Lesser Himalayan region. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Pollution from non-point sources is being recognized as a major source of surface water quality deterioration. Sediment transportation from land surfaces to oceans through rivers is one of the most important processes that affect riverbank stabilization, soil formation, upliftment rates, biogeochemical cycling of elements, crust evolution and many other earth related processes (Chakrapani, 2005). The transport dynamics of sediments in fluvial systems have been studied by engineers, hydrologists, soil scientists, geologists and process geomorphologists in different parts of the world (Holeman, 1968; Subramanian, 1979, 1993; Milliman and Meade, 1983; Jha et al., 1988; Chakrapani and Subramanian, 1990, 1993; Lu and Siew, 2006; Soler et al., 2007; Vanacker et al., 2007). Presently, the rivers alone contribute to about 95% of sediments entering the oceans in a global scale (Syvitski, 2003). It is estimated that 65% of water and 80% of the sediments are being transported to oceans each year from Southern Asian, Oceania and north-eastern South American rivers (Syvitski et al., 2003). It is also reported that the Himalayan Rivers are the major contributors, which transport about 50% of the global sediment flux (Stoddart, 1969). Therefore, research interests pertaining to fluvial sediment trans- port in the Himalayan river systems have attracted much attention in recent times (Kumar, 1987; Rawat and Rai 1997; Singh et al., 2003, 2005; Sharma and Rai, 2004; Haritashya et al., 2006; Singh, 2007; Bhattacharya et al., 2008). The estimation of the sediment load and the transport rate governs the geomorphological, hydrological, sedimen- tological and ecological processes of river basins. Further, its estimation from basins is of much significance for planning, designing, installation and operation of hydro-power projects, including man- agement of reservoirs. However, there exist hardly any studies related to the transportation and quantification of sediment fluxes from the Lesser Himalayan watersheds, which are currently being developed for various hydro-power projects. Hence, in view of this research gap related to the study of sediment fluxes in the Lesser Himalayan watersheds, the present work was undertaken with an objective to collect and analyze the primary hydrologic and water quality data. The acquired data pertaining to quantity and quality of the sediment (physical) and dissolved (chemical) loads transported by two alpine watersheds were analyzed to understand the watershed hydrology and sedimentation processes. Such type of investigations assumes importance in preparation of the water and sediment load budget at Catena 76 (2008) 27–35 ⁎ Corresponding author. Tel.: +9111 25841490; fax: +9111 25848037. E-mail addresses: ovshome@yahoo.com, ovshome@gmail.com (O. Singh), asarangi@iari.res.in (A. Sarangi). 0341-8162/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2008.08.003 Contents lists available at ScienceDirect Catena journal homepage: www.elsevier.com/locate/catena