Hydrogeomorphic effects of beaver dams on floodplain morphology: avulsion processes and sediment fluxes in upland valley floors (Spessart, Germany) [ Les effets hydro-géomorphologiques des barrages de castors sur la morphologie de la plaine alluviale : processus d'avulsions et flux sédimentaires des vallées intra-montagnardes (Spessart, Allemagne).]

Abstract

In a two years study, several methods were used to visualise and analyse beaver-induced hydrogeomorphic changes of channel pattern, sediment fluxes and erosion processes on the upland valley floor of the 3rd order river Jossa (Spessart/Germany). There, the re-introduced population of Castor fiber albicus shows intensive dam-building activity Using GIS and aenal photography, different stages of river and floodplain morphology (1998-2001) were mapped In addition, length of water courses, areal extent of ponds and wetlands, sediment depths, volumes and sedimentation rates, as well as erosion rates and amounts of eroded matenal were calculated. The results revealed that beaver dams create large wetlands and greatly increase the area of open water surface and quiet reaches by damming-up ponds. Moreover, they enhance the total water flow length by diverting water onto the floodplain, resulting in a multi-channeled (anastomosing) drainage network Where pond drainage was concentrated on a few relative stable channels, headcut erosion led to the development of one single dominant channel. Five stages of this development to a channel relocation were observed, resembling stages of a gradual avulsion. This implies that beaver dams should be recognised as possible - or even as important - avulsion triggers Intensified deposition of predominantly sands and organic silts occurred within the beaver ponds. Moreover, extended avulsion deposits caused by permanent overbank flow revealed the multi-channeled drainage network to be an important depositional environment of beaver sites. The highest amounts of sediments were deposited within the channel-bed and adjacent anthropogenic ditches, smaller amounts were accumulated on the inundated floodplain. The results may provide a rationale for attributing beaver activities a high significance as a forcing factor of Quaternary floodplain development along low order rivers in Central Europe.

Rediscovering, Reevaluating, and Restoring Lost River-Wetland Corridors

“…Obstructions within the active channel(s) and floodplain associated with the presence of vegetation, large wood, and beaver dams increase subsurface hydrologic connectivity and hyporheic exchange flows (e.g., Sawyer and Cardenas, 2012;Wang et al, 2018;Doughty et al, 2020). Similarly, these obstructions can further influence surface hydrologic connectivity by promoting lateral channel migration (e.g., Eaton and Hassan, 2013), formation of a multi-threaded channel planform (John and Klein, 2004;Collins et al, 2012;Polvi and Wohl, 2013), and enhanced overbank flows (Brummer et al, 2006;Westbrook et al, 2006). Local variability in hydrologic connectivity, in turn, influences the elevation of the floodplain water table, which directly affects the types, densities, and vitality of vegetation.…”

Spatial and Temporal Variability of Channel Retention in a Lowland Temperate Forest Stream Settled by European Beaver (Castor fiber)

“…In anticipating the role of beaver dams and ponds for the enhancement of channel retention capacity of small, temperate forest streams, one should assure the continuous presence of beavers within the site. Otherwise, the ongoing process of sedimentation, debris and plant encroachment in abandoned beaver ponds will entail a decreasing role of the small reservoirs in shaping channel retention of streams historically settled by beaver [3,5,11,13,14,16,18]. However, from a long term perspective, the total capacity of beaver ponds, along with the increased water levels in riparian forest habitats transformed and abandoned by beaver, provided a prerequisite of exceptional potential as a natural water retention capacity in a catchment scale [26].…”

“…in shaping landscapes, ecological feedbacks and hydrological conditions of riparian forests challenges the management of these ecosystems [1][2][3][4][5][6][7][8][9][10][11]. Among the ecosystem alterations induced by construction activity of beaver, increased water storage capacity and related changes in flow regime and sedimentation-erosion balance remain of the highest importance for both catchment-scale water management and local-scale maintenance of forest environment [12][13][14][15][16][17][18][19][20]. The increasing abundance of European beaver (Castor fiber) populations in Central and Eastern Europe, reported in the late 20th and in the beginning of the 21st century, entailed colonization of new habitats by these rodents, which along with the intensification of agriculture and forestry, remained a cause of conflict at the interface of land use and environmental conservation [21,22].…”

Modelling long-term alluvial peatland dynamics in temperate river floodplains

“…The formation of an anastomosing pattern can be explained by the low floodplain gradients in both the Dijle and Grote Nete river basins and the erosion resistance of peat layers. In such a river system, the formation of new channels is triggered by avulsions, which can be caused by obstructions such as log jams or beaver dams (Diefenderfer and Montgomery, 2009;Gradziński et al, 2003;Makaske, 2001;Polvi and Wohl, 2012;Stefan and Klein, 2004).…”