Lastflusses

Lastflusses refers to residual, post-flood flow pathways that persist in a river basin after major discharge events. These channels may remain wetted when the broader river network has contracted, creating a mosaic of surface and shallow subsurface routes that convey water and sediment at low discharge levels for extended periods. Their existence reflects the dynamic reorganization of river networks following floods.

The term was coined by researchers studying flood-memory and channel reorganization in temperate floodplains in the late 1990s. It emphasizes that river systems can preserve functional connectivity beyond peak flood conditions, influencing hydrological and ecological processes during recovery.

Formation and characteristics: Lastflusses form as sediment is redistributed, banks adjust, and connections to aquifers are reestablished after floods. They often appear as narrow, sometimes braided or meandering, channels with low but persistent discharge. They are detected using dye-tracing experiments, isotopic analyses, and high-resolution remote sensing or field surveys and are distinguished from permanent channels by their seasonality and sensitivity to baseflow conditions.

Impacts and uses: Lastflusses affect groundwater recharge, nutrient transport, and habitat connectivity for aquatic and semi-aquatic species. For flood management and river restoration, recognizing these pathways helps in predicting baseflow contributions, planning habitat corridors, and guiding restoration of floodplains and wetlands.

Distribution and study: Documented in several temperate basins worldwide with variability tied to geology, soil permeability, and land use. Ongoing research aims to quantify their extent, persistence, and response to climate change, as well as to integrate lastfluss dynamics into hydrological models.