160-6 Woody Vegetation Colonisation Impacts Dryland Channel Dynamics in Floodplain Wetlands of the Río Senguerr, Chubut Province, Argentina

Session: Advances in Fluvial Processes and Sediment Transport, Part I

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Abstract:

The Río Senguerr is one of the most important water resources in the extra-Andean region of Chubut Province, Argentina.  Snowmelt and seasonal rainfall in the upper catchment ensure perennial flow to the lower catchment, supporting extensive irrigation agriculture in an arid to semiarid setting. The river remains undammed, but agricultural water use in the upper and lower reaches has resulted in flow modifications (e.g. surface and ground water abstraction, channel engineering). At present, the middle reaches are characterised by 2-3km wide floodplain wetlands marked by numerous active, partially active and abandoned channels and remain free from significant anthropogenic alterations. Nevertheless, in common with other rivers in the region, progressive colonisation by riparian woody vegetation (including non-native willows/poplars) poses threats to natural channel-floodplain dynamics, with implications for downstream water supply.

Here, we integrate high-resolution timeseries earth observation imagery and coarse-resolution ERA5-Land reanalysis data to provide a preliminary assessment of the woody vegetation, channel, and floodplain interactions in an ~60 km long section of the middle reaches. The main channel has exhibited minimal lateral migration over the past decade, despite occupying a valley floor historically conducive to meandering and avulsion. In some locations, there has been an increase in shrub/tree density including encroachment into active channel zones. Overall, 85% of the valley floor is showing increase in greenness between 1986 and 2024. Under the prevailing low-to-moderate unit stream powers (<15W/m²), woody vegetation establishment appears to stabilize banks and bars, which in turn reduces channel lateral mobility, and promotes further vegetation growth. This dynamic may herald a transition from laterally active to more stable, single or anabranching channels, as is evident along other Chubut Province rivers with denser riparian vegetation.  Changes along the Río Senguerr have implications for flow and sediment transport, channel-floodplain connectivity, and riparian ecology but have yet to be investigated in detail.  One particular concern is the potential for woody vegetation to act as significant ‘evapotranspirative pumps’ that may reduce downstream water availability, especially under future scenarios of changing snowmelt/rainfall and atmospheric warming. The Río Senguerr provides a rare opportunity to monitor the early stages of woody vegetation colonisation in a hitherto minimally disturbed setting, with implications for wider understanding of dryland river geomorphological, hydrological and ecological resilience under changing boundary conditions.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7807

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