A multi-scale analysis and classification of the hydrogeomorphological characteristics of Irish headwater streams

We present a spatially hierarchical, hydrogeomorphological stream classification, based on data collected in Ireland and reflecting our hypothesis that local (site scale) stream physical habitat characteristics are related to the physical properties of the extended reach within which a site is located, and, in turn, to the physical character of the catchment. Using a top-down approach, data on catchment, reach and site-scale stream physical properties were collected for 42 Irish headwater streams. The summary catchment properties (rock type, topography, soil type and hydrology) were extracted from secondary sources. Reach-scale physical controls on stream hydrogeomorphology (planform, gradient, degree of confinement, bed material) were assembled mainly from secondary sources. Site-scale information on the stream physical habitat mosaic was collected by field survey. Data analysis identified six new ‘River Types’ for steep mountain streams that extend a pre-existing classification system developed for English streams and rivers. Five of the new types with sufficient replication were associated with ‘indicator’ habitats and characteristic habitat assemblages. The classification method is simple to apply and so it is suitable for operational use. We believe that it is applicable beyond Ireland and England to other areas of northern and western Europe with similar climate−landscape conditions.