Geomorphic monitoring and response to two dam removals: rivers Urumea and Leitzaran (Basque Country, Spain)

Abstract

Dam removal has been demonstrated to be one of the most frequent and effective fluvial restoration actions but at most dam removals, especially of small dams, there has been little geomorphological monitoring. The results of the geomorphological monitoring implemented in two dams in the rivers Urumea and Leitzaran (northern Spain) are presented. The one from the River Urumea, originally 3.5 m high and impounding 500 m of river course, was removed instantaneously whereas that in the River Leitzaran, 12.5 m high, and impounding 1500 m of river course, is in its second phase of a four‐stage removal process. Changes in channel morphology, sediment size and mobility and river bed morphologies were assessed. The monitoring included several different techniques: topographical measurements of the channel, terrestrial laser scanner measurements of river bed and bars, sediment grain size and transport; all of them repeated in four (May, August, November 2011 and May 2012) and five (July and September 2013, April and August 2014 and June 2015) fieldwork campaigns in the River Urumea and River Leitzaran, respectively. Geomorphic responses of both dam removals are presented, and compared. Morphological channel adjustments occurred mainly shortly after dam removals, but with differences among the one removed instantaneously, that was immediate, whereas that conducted by stages took longer. Degradational processes were observed upstream of both dams (up to 1.2 m and 4 m in the River Urumea and River Leitzaran, respectively), but also aggradational processes (pool filling), upstream of Inturia Dam (2.85 m at least). Less evident aggradational processes were observed downstream of the dams (up to 0.37 m and 0.50 m in the River Urumea and River Leitzaran, respectively). Flood events, especially a 100 year flood registered during the monitoring period of Mendaraz Dam removal, reactivated geomorphological processes as incision and bank erosion, whereas longitudinal profile recovery, grain‐size sorting and upstream erosion took longer. Copyright © 2016 John Wiley & Sons, Ltd.

Humans and the Earth's surface

“…In addition, since the 1980s, industrial-touristic infrastructures have developed on the emerging land surface and are associated with growing geomorphic hazards in the coastal zone. Ibisate et al (2016) analyzed the geomorphic responses of dam removals. Sofia et al (2016) present a methodology based on the slope local length of auto-correlation (SLLAC, Sofia et al 2014a) method, to portray and to delineate the morphological alterations produced by road networks.…”

“…Comiti (2012) summarizes research into the historical channel adjustments of rivers in the Italian Alps, presented in order to document the impacts of human pressure at different basin scales and for different river morphologies. Ibisate et al (2016) analyzed the geomorphic responses of dam removals. Two dams in the north of Spain were considered.…”

River response to large‐dam removal in a Mediterranean hydroclimatic setting: Carmel River, California, USA

“…This was the third‐tallest dam removed intentionally thus far globally (Major et al ., ), and provided a case study that is unusual in three respects. First, as the largest dam removal in a Mediterranean hydroclimatic setting (Ibisate et al ., ), the potential for transporting sediment and restructuring channel morphology differed from previous large‐dam‐removal situations. As is typical for Mediterranean‐type rivers, the Carmel River flow varies over more than three orders of magnitude seasonally; all of its sediment‐transport capacity occurs during a winter rainy season, with no secondary contribution from spring snowmelt high flows.…”

Increased sediment load during a large-scale dam removal changes nearshore subtidal communities

“…Dam removals are becoming more common, particularly in North America [ 34 , 35 ] but also in other parts of the world (e.g., Europe and Asia) [ 36 – 39 ]. Sediment released during and following dam removal, especially in cases with significant storage of reservoir sediment, is a primary driver of physical and ecological change in fluvial systems [ 40 – 42 ].…”