River linking in India: Downstream impacts on water discharge and suspended sediment transport to deltas

Abstract

Higgins, SA, et al. 2018 River linking in India: Downstream impacts on water discharge and suspended sediment transport to deltas. Elem Sci Anth, 6: 20. DOI: https://doi.org/10.1525/elementa.269 IntroductionTo expand agricultural production and address water scarcity, India is moving forward with a large-scale civil engineering project to connect 44 rivers via a vast network of canals (Joshi, 2013;Bagla, 2014). The National River Linking Project, or NRLP, aims to increase irrigated area by 350,000 km 2 and improve food security and clean water access. India receives between 50 and 90% of its annual precipitation during the summer monsoon, during which time water is abundant and floods are common. The NRLP will store and redistribute this water in an effort to reduce temporal and spatial inconsistencies in supply. The project is intended to address the substantial challenges of food production and clean water access that India will face in the coming century -challenges that are being confronted globally as countries face rising temperatures, and increasing populations with stressed water supplies ( Wallace, 2000;Battisti and Naylor, 2009;Hanjra and Qureshi, 2010). Interbasin water transfer systems are a common solution to water scarcity, and the NRLP is the largest of many new diversion schemes proposed or underway in China, Brazil, and Central Africa (Zhang, 2009; Lemoalle et al., 2012). However, large-scale river diversion projects such as the NRLP can result in farreaching consequences for downstream river discharge and delta maintenance. For example, due to damming, diversions, and increased water usage, the Colorado, Nile, Indus and Yellow (Huanghe) rivers discharge little to no sediment today, whereas they previously accounted for 10% of the global sediment flux to the ocean (Syvitski and Milliman, 2007).The NRLP in its current form was designed in the early 1980s, when the Indian government established the National Water Development Agency (NWDA) to manage implementation of the project. The project stalled between the 1980s and the 2010s, but it was renewed in RESEARCH ARTICLERiver linking in India: Downstream impacts on water discharge and suspended sediment transport to deltas To expand agricultural production and address water scarcity, India is moving forward with the National River Linking Project (NRLP), which will connect 44 rivers via 9,600 km of canals. Here, we compile the first complete database of proposed NRLP dams, reservoirs and canals, including operating schedules for Himalayan infrastructure. We evaluate potential NRLP-derived changes to mean annual water discharge for 29 rivers and mean monthly water and sediment discharge for six rivers flowing to five major deltas. Sediment rating curves are used to quantify the impacts of changing water discharge within the rivers, and basin-wide trapping efficiency is established for new reservoirs. Given full implementation of the NRLP, we forecast reductions in annual suspended sediment transport to deltas of 40-85% (Mahanadi), 71-99% (Godavari) ...

Spatial and temporal variations in source, diagenesis, and fate of organic matter in sediments of the Netravati River, India

“…During nonmonsoon/dry period (October to May), the estuarine region takes in seawater due to the reduction of freshwater discharge (Rajesh, Rajesh, & Reddy, ) and the tidal influence can be traced up to about 15 to 20 km inland due to the shallow and wide nature of the estuary mouth (Saravanan, Chowdhury, & Sivakumar, ). The average annual runoff and sediment load at the gauging site was 11.1 × 10 3 M m 3 and 1.2 × 10 6 ton, respectively (Dwarakish, Abdu Rahiman, & Natesan, ), and the mean annual river discharge was about 336 m 3 /s (Higgins, Overeem, Roggers, & Kalina, ). Sediment yield of the Netravati River has been projected to increase due to land use land cover (LULC) changes as a result of intensive agriculture and urbanization.…”

Seasonal Variability of Forces Controlling Sedimentation in the Sundarbans National Forest, Bangladesh

“…In both scenarios, dry season deposition is <0.2 cm ( Table 2). Of course, by reducing the freshwater discharge of these rivers by 24 and 6% respectively, we can also expect the effective duration of monsoon-like conditions to be reduced by a month or more (Higgins et al, 2018). Indeed, if we rework our initial estimate of deposition to reflect a substantially shorter monsoon season (i.e., from 3 to 2 months, or 180 platform-inundating events to 120), wetseason deposition drops to 1.2 cm.…”

“…For example, consider the possible impacts of a reduced sediment discharge associated with India's planned dams and diversions through the NRLP on sedimentation in the SNF: if fully implemented, one result would be a reduction in the annual suspended sediment load of the Ganges and Brahmaputra rivers by 39-75% and 9-25%, respectively, with the majority of this reduction occurring during the wet season (Higgins et al, 2018). Collectively, this amounts to a reduction in the total suspended sediment load by 14-18%.…”

“…While attributed to anthropogenic modification, this tidal amplification also impacts the SNF, andcoupled with eustatic sea-level change and compaction-has resulted in an effective sea level rise of 0.7 cm/year at the southern coast, increasing to 1.7 cm/year near the city of Khulna, which enhances flood risk across the entire tidal deltaplain (Figure 1; Steckler et al, 2010;Pethick and Orford, 2013). Furthermore, the National River Linking Project (NRLP) proposed by India is expected to reduce freshwater discharge of the Ganges River by 24%, with a corresponding reduction in sediment load by 39-75% if fully implemented (Higgins et al, 2018). Those authors further predict a reduction in delta-wide aggradation from 0.36 to 0.25 cm/year under this scenario.…”

“…Predicted change in seasonal deposition according to the projected changes in suspended sediment supply and fresh water due to the IRLP, as described byHiggins et al (2018).…”