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

Abstract

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) and 60–97% (Krishna) due to profound reservoir trapping and peak streamflow reductions. The Ganga before its confluence with the Brahmaputra is projected to experience a 39–75% reduction in annual suspended load. The Brahmaputra before its confluence with the Ganga is projected to experience a 9–25% reduction in suspended load, despite losing only 6% of its annual water flow. We calculate a projected corresponding aggradation decrease for the Ganga-Brahmaputra delta from 3.6 to 2.5 mm y–1, which is a large enough change to drive relative sea-level rise at the delta front. At the remaining four deltas, the NRLP will exacerbate current sediment starvation. We reconstruct the annual water transfer volume proposed for the NRLP to be 245 km3 y–1, higher than previous estimates due to the inclusion of along-canal usage. If completed, the NRLP will transform watershed boundaries, with more than half of the land in India contributing a portion of its runoff to a new mouth. These impacts may have profound environmental and public health implications, particularly in the context of future climate change.