Historical Changes in European Rivers

by

Francesco Comiti, Vittoria Scorpio

• LAST REVIEWED: 15 January 2019
• LAST MODIFIED: 15 January 2019
• DOI: 10.1093/obo/9780199363445-0110

Introduction

River morphology is dynamic in nature, in that it is dictated by unsteady driving variables (water, sediment, and wood fluxes). Focusing on centennial to decadal changes, these driving variables are subject both to naturally and anthropically induced variations and may occur both at the basin and the channel scales. Indeed, the traditional “river equilibrium concept” in fluvial geomorphology is challenged by the more recent concept of “evolutionary trajectory,” which emphasizes how channel characteristics (width, bed elevation, morphological pattern, habitats) undergo variations over time in response to changing driving variables. In Europe, geomorphologists have long identified how rivers responded to major climatic variations (e.g., Pleistocene glaciations). In contrast, climate-induced morphological changes that occurred in historical times (e.g., associated with the Little Ice Age [LIA], 15th–19th centuries), have received far less attention, surely also because they were less dramatic compared to the former ones. Direct human pressures both on basins and channels have instead greatly affected the vast majority of river systems of Europe. Localized morphological alterations and floodplain deforestation, aimed to protect villages and towns from flooding and to increase pastures, can be traced back to ancient times. In order to augment agricultural productivity for a growing population, extensive channel rectifications coupled with floodplain drainage and basin-scale deforestation took place from the late Middle Ages onward, peaking in the 19th century. Several European rivers in these centuries widened and aggraded, as well as during the concurrent “flood-rich” LIA period. However, the trajectory soon reversed, since from the middle of the 20th century onward, natural afforestation, erosion control works, and hydropower dam construction led to a general reduced sediment supply to the downstream river reaches, causing channel narrowing and bed degradation. Nonetheless, in-channel gravel mining—very pronounced from the 1960s to the 1980s—was the most important cause of stream degradation in several rivers. Most of the European rivers are still sediment and wood starved, are subject to flow regulation, and feature impaired longitudinal and lateral connectivity. Since the end of the 20th century, restoration actions have started to be implemented, though, also to comply with the goals of the European Union (EU) Water Framework Directive. Finally, ongoing global warming, increasing in severity since the late 20th century, could determine channel variations in those (few) rivers that are still free to adjust, and the most-relevant changes are expected at the higher elevations and latitudes, where glacial and periglacial processes still exert strong controls on river dynamics.

General Overviews

Before presenting a selection of study cases from the main geographic domains of Europe for which studies of river evolution are available (Alpine Rivers, Mediterranean Rivers, British Islands, and Central-Eastern Europe), this sections aims at highlighting the publications providing regional-scale analysis or representing already summarizing overviews on the topic. Petts, et al. 1989 is—to the best of our knowledge—one of the first works addressing the historical changes in several large rivers in western Europe, mostly originating in the Alps, and it has been a reference publication for many years. Rumsby and Macklin 1996 analyzes the relevant effects of climatic variations associated with the Neoglacial period (Little Ice Age), mostly drawing from earlier case studies carried out in the United Kingdom and central Europe. The first decade of the 21st century was quite rich in terms of multiple, comparative investigations. Liébault and Piégay 2002 addresses the overall river trends observed in the French Southern Alps during the 20th century. Soon after, Rinaldi 2003 and Surian and Rinaldi 2003 summarizes the knowledge available at that time on the evolution of Tuscanian and Italian rivers, respectively, while Hooke 2006 presents an overview of river changes covering the whole Mediterranean region. The relevant channel variations that occurred during the 20th century in the several rivers of the Polish Carpathians are analyzed in Wyżga 2007, and the specific, large impact of gravel mining on channel variations is addressed in Rinaldi, et al. 2005, on the basis of Italian and Polish examples. An updated, comprehensive analysis of channel changes over the last two centuries in alluvial rivers of northern and central Italy is contained in Surian, et al. 2009, whereas a focus on Alpine rivers is presented in Comiti 2012, in which examples from different basin scales are utilized. Finally, the authors of Belletti, et al. 2015 performed a regional-scale analysis on river braiding in the French Alps, highlighting the role of flood history on such morphological patterns.

• Belletti, B., S. Dufour, and H. Piégay. 2015. What is the relative effect of space and time to explain the braided river width and island patterns at a regional scale? River Research and Applications 31.1: 1–15.

  DOI: 10.1002/rra.2714

  The paper analyzes the evolution of fifty-three braided reaches of the French Alps from the 1950s to the first decade of the 21st century, focusing on variations in channel width and island pattern. The introduction presents a detailed analysis of river-braiding characteristics and evolution worldwide. The results show that braided-river morphology strongly depends on flood history, and especially on the time since the last large event.

• Hooke, J. M. 2006. Human impacts on fluvial systems in the Mediterranean region. Geomorphology 79.3–4: 311–335.

  DOI: 10.1016/j.geomorph.2006.06.036

  This paper investigates the role of human impacts on fluvial systems in the Mediterranean region (Spain, France, Italy), starting from the Bronze Age. It highlights how during the 20th century the most-dramatic changes were determined by channelization, bank stabilization, dam construction, and gravel mining.

• Comiti, F. 2012. How natural are Alpine mountain rivers? Evidence from the Italian Alps. Earth Surface Processes and Landforms 37.7: 693–707.

  DOI: 10.1002/esp.2267

  This paper presents a summary of historical channel adjustments in rivers of the Italian Alps in order to document the impacts deriving from human pressure at different basin scales, from steep, confined streams to large, unconfined rivers. The work stresses how human pressure on Italian—but not only—Alpine basins has been relevant for several centuries, and that nowadays, “reference conditions” cannot be found even in mountain channels.

• Liébault, F., and H. Piégay. 2002. Causes of 20th century channel narrowing in mountain and piedmont rivers of southeastern France. In Special issue: Geomorphic responses to land use changes. Edited by G. Brierley and M. Stankoviansky. Earth Surface Processes and Landforms 27.4: 425–444.

  DOI: 10.1002/esp.328

  The introduction contains a detailed discussion of how climate and land-use changes may determine channel narrowing, and a conceptual model is also proposed. The role of 20th-century afforestation over the Southern French Alps in reducing bedload supply appears to be the dominant factor responsible for channel narrowing. This regional-scale study observed also how the narrowing along the analyzed rivers has been longitudinally synchronous.

• Petts, G. E., H. Möller, and A. L. Roux, eds. 1989. Historical change of large alluvial rivers: Western Europe. Chichester, UK: John Wiley & Sons.

  DOI: 10.1002/iroh.19900750412

  This book is composed of thirteen chapters written by several authors. Some chapters cover general and methodological issues related to historical, paleoecological, and geomorphological analysis of large rivers, whereas others represent either specific study cases (the lower Rhine, the Rhône, and the Po Rivers) or more-general overviews drawing from observations carried out in France, Britain, and Switzerland.

• Rinaldi, M. 2003. Recent channel adjustments in alluvial rivers of Tuscany, central Italy. Earth Surface Processes and Landforms 28.6: 587–608.

  DOI: 10.1002/esp.464

  The paper analyzes the observed channel adjustments in alluvial rivers of Tuscany (central Italy). Human impact and especially sediment mining appear to be the dominant factors causing narrowing in the 20th century (up to 75 percent compared to the 1950s) and incision (from to 6.6 to 29.5 feet). Conceptual models relative to planforms and vertical changes, and their relationships with geomorphic surfaces (bars and floodplain evolution), are proposed.

• Rinaldi, M., B. Wyżga, and N. Surian. 2005. Sediment mining in alluvial channels: Physical effects and management perspectives. In Special issue: Sediment management in river systems: A need to assess changing processes in the long term and at a large scale. Edited by H. Piégay and D. M. Hicks. River Research and Applications 21.7: 805–828.

  DOI: 10.1002/rra.884

  The paper discusses the role of sediment mining on river channels. The Tagliamento, the Brenta, and the Arno Rivers in Italy and the Ropa and the Wisłoka Rivers in Poland are analyzed. The introduction provides a general review of the observed impacts of sediment mining on alluvial rivers worldwide. The effects of mining are found to be related to the rivers’ sediment yield and as a consequence to the initial channel pattern.

• Rumsby, B. T., and M. G. Macklin. 1996. River response to the last neoglacial (the “Little Ice Age”) in northern, western and central Europe. In Global continental changes: The context of palaeohydrology. Edited by J. Branson, A. G. Brown, and K. J. Gregory, 217–233. London: Geological Society.

  Channel responses to the Little Ice Age (LIA) are analyzed from several European rivers, mostly from the United Kingdom. LIA effects on temperature, precipitation, and flood frequency are described, and the river response is defined in term of changes in pattern and bed level. The transitional phases (cooling between 1250 and 1550 CE and warming between 1750 and 1900) are found to be those featuring the stronger fluvial activities.

• Surian, N., and M. Rinaldi. 2003. Morphological response to river engineering and management in alluvial channels in Italy. Geomorphology 50.4: 307–326.

  DOI: 10.1016/S0169-555X(02)00219-2

  This paper reviews the available knowledge on channel changes that occurred over the previous one hundred years in unconfined Italian rivers, which were dominated by bed incision, channel narrowing, and changes in planform morphology, highlighting a reduction in bedload supply. A conceptual channel evolution model for Italian rivers is then proposed on the basis of the predisturbance channel morphology.

• Surian, N., M. Rinaldi, L. Pellegrini, et al. 2009. Channel adjustments in northern and central Italy over the last 200 years. Geological Society of America Special Paper 451:83–95.

  DOI: 10.1130/2009.2451(05)

  The paper provides a review of channel adjustment that occurred over the previous two hundred years in twelve rivers located in northern and central Italy (draining both the Alps and the Apennines). All rivers show similar evolutionary trajectories, which can be subdivided into four periods. Channel narrowing and bed incision were at their strongest pace in the third period, from the 1950s to the 1990s.

• Wyżga, B. 2007. A review on channel incision in the Polish Carpathian rivers during the 20th century. Developments in Earth Surface Processes 11:525–553.

  DOI: 10.1016/S0928-2025(07)11142-1

  The paper describes at the regional scale the vertical river changes that occurred in rivers of the Polish Carpathians during the 20th century. Incision ranged between 4.3 and 12.5 feet, downcutting progressed in the upstream direction, and it became very rapid after the 1950s. The increase in transport capacity caused by channelization works and the decrease in sediment supply were identified as the main causes, as well as gravel mining in some of the rivers.