A predictive typology for characterising hydromorphology

Whilst traditionally poorly quantified, the link between physical habitat and ecological response in rivers is widely recognised, and is currently rising up legislative and policy agendas. In Europe, this is reflected in the Water Framework Directive which dictates that ‘hydromorphological’ condition of water bodies should be capable of supporting ‘Good Ecological Status’. Methods are developed that integrate river system hydrology, geomorphology and ecology (and the complex interplay between these three variables). Whilst hydrological and biological methods for characterisation are relatively well established, geomorphological methods are not. Effective characterisation of geomorphology (physical habitat) with full spatial coverage, at a range of scales, can be used to explore spatial interactions between habitat and biological data and potentially further our understanding of ecological response. Managers need to know what aspects of physical habitat and at which critical locations intervention will lead to greatest improvements in ecological condition. This requires information on hydromorphological character and condition. Existing applied approaches for capturing geomorphological data are highly dependent on intensive fieldwork, which is unlikely to be resourced at sufficiently extensive scales to meet management needs. This paper outlines a typology approach for characterising the physical template of rivers. It draws on a range of hydromorphological data to develop a framework for a channel typology; with data collation from secondary sources followed by targeted fieldwork to (i) assess to what extent individual channel types are characteristic of field conditions and (ii) to collect information on reach-scale variability within each type. Results suggest that characterisation of channel types based on stream power, floodplain width and stream order does result in a distinct set of channel types. Field survey subsequently found that these types had a characteristic suite of patch-scale habitat features (flow types). The approach was applied to a catchment where geomorphological processes exert a dominant control over physical habitat.