Editorial Preface to the volume Large Rivers The study and knowledge of the geomorphology of large rivers in- creased significantly during the last years and the factors that triggered these advances are multiple. On one hand, modern technologies became more accessible and their disseminated usage allowed the collection of data from large rivers as never seen before. The generalized use of high tech data collection with geophysics equipment such as acoustic Dopp- ler current profilers-ADCPs, multibeam echosounders, plus the avail- ability of geospatial and computational tools for morphodynamics, hydrological and hydrosedimentological modeling, have accelerated the scientific production on the geomorphology of large rivers at a glob- al scale. Despite the advances, there is yet a lot of work ahead. Good parts of the large rivers are in the tropics and many are still unexplored. The tropics also hold crucial fluvial basins that concentrate good part of the gross domestic product of large countries like the Parana River in Argentina and Brazil, the Ganges-Brahmaputra in India, the Indus River in Pakistan, and the Mekong River in several countries of South East Asia. The environmental importance of tropical rivers is also out- standing. They hold the highest biodiversity of fluvial fauna and alluvial vegetation and many of them, particularly those in Southeast Asia, are among the most hazardous systems for floods in the entire world. Trop- ical rivers draining mountain chains such as the Himalaya, the Andes and insular Southeast Asia are also among the most heavily sediment loaded rivers and play a key role in both the storage of sediment at con- tinental scale and the transference of sediments from the continent to the Ocean at planetary scale (Andermann et al., 2012; Latrubesse and Restrepo, 2014; Milliman and Syvitski, 1992; Milliman and Farsnworth, 2011; Sinha and Friend, 1994). But these systems are at high risk, not only by the degradation of their basins by land use change-deforestation and pollution but also be- cause of the construction of dams is rampantly growing in the tropics of Africa, Asia and Latin America (Latrubesse et al., 2017; Siciliano and Urban, 2017). If the construction of dams continues unstoppable, then the massive environmental impacts on these fantastic natural systems will be irreversible and it would happen very quickly before “civilized” humans get a basic understanding of their original natural functioning. During the last years, we particularly have concentrated our effort to create opportunities and venues for intellectual discussion on large riv- ers and tropical rivers in a diversity of symposiums, working groups, and meetings. One of the main engines has been the Tropical Rivers Working Group of the International Association of Geomorphologists, chaired in collaboration by E. M. Latrubesse (USA), R. Sinha (India) and J.C. Stevaux (Brazil). The working group has worked in cooperation with the International Geosciences Program 582-Tropical Rivers, also chaired by the same researchers. Diverse meetings, seminars training courses, and other activities were organized in recent years by our group in a variety of countries such as Brazil, India, Peru, Argentina, Colombia and Congo, and our working group also offered special ses- sions at the 8 th International Conference of Geomorphology- Interna- tional Association of Geomorphologists-IAG in Paris, 2013, American Geophysical Union-AGU, Brazilian Union of Geomorphology-UGB, and the 9 th International Conference of Geomorphology in New Delhi, 2017. The 9 th River Coastal and Estuarine Morphodynamics Interna- tional Symposium organized by Jorge D. Abad Cueva and local collab- orators from the Service of Hydrography and Navigation of the Peruvian Navy and the Center for Research and Education of the Am- azon Rainforest- CREAR in 2015 offered the perfect setting to discuss morphodynamics of large rivers. This event gathered more than 250 scientists from all around the world in the heart of the Peruvian Am- azon, Iquitos city, Peru. Therefore, this special issue is the natural consequence of the joint effort between the organizers of the RCEM and the IAG working Group Tropical Rivers, demonstrating our com- mitment to contribute to the knowledge of large rivers and tropical rivers. The special issue is a collection of seven articles that cover from the- oretical aspect on fluvial science to new developments in the under- standing of channel patterns and islands in large anabranching rives, human impacts, or tools for river management. The first article by Gerald C. Nanson and He Qing Huang introduce us to philosophical aspects of fluvial science and attempt to explain the self-adjustment of alluvial channels from the perspective of the least ac- tion principle (LAP) as based on the concept of maximum flow efficien- cy (MFE). Into this theoretical and methodological context, the second article by P. Carling and collaborators Are equilibrium multichannel networks predictable? The case of the regulated Indus River, Pakistan, discuss the current anabranching planform of the Indus. Since Latrubesse (2008, 2015) demonstrated that the largest alluvial rivers of the planet are dominantly anabranching systems, articles like this one by Carling and collaborators, and the one by Leli, Stevaux and Assine in this issue bring new insights into the functioning and generation of anabranching channel patterns in large alluvial rivers. Consequently, the role of blind channels and islands in the evolution of the anabranching pattern of the upper Parana River in Brazil is assessed in the fourth paper by Leli, I, Stevaux, J.C., and M.L. Assine. The fifth paper, Integrating channel form and processes in the Gangetic plains rivers: Implications for geomorphic diversity by N.G. Roy and R. Sinha evaluate the geomorphic diversity at planform, cross-sectional, and longitudinal scale of the rivers of the western Ganga plain (WGP) and suggest that at short time decadal scale the influence of human im- pacts is significant on river diversity but rivers have remained in dy- namic equilibrium with respect to the variation of southwest monsoon precipitation over longer timescales of ~100years. Geomorphology 302 (2018) 1–2 https://doi.org/10.1016/j.geomorph.2017.12.015 0169-555X/© 2017 Published by Elsevier B.V. Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph