Description: River Habitat Survey Habitat Modification Score (HMS) and Habitat Modification Class (HMC) is an indication of artificial modification to river channel morphology. To calculate the HMS for a site, points are allocated for the presence and extent of artificial features such as culverts and weirs and also modifications caused by the re-profiling and reinforcement of banks (Habitat Modification Score Rules 2003). Greater and more severe modifications result in a higher score. The cumulative points total provides the Habitat Modification Score (HMS). A Habitat Modification Class (HMC) protocol has been developed which allocates the condition of the channel in a site to one of five modification classes, based on the total score (1 = near-natural; 5 = severely modified). In contrast to HQA, higher HMS scores reflect more artificial intervention and modification of the river channel within a site.
RHS made an important contribution to development of the CEN guidance standard for assessing the hydromorphological features of rivers and is a recommended method for the agreed protocol for field survey and recording of morphological features. RHS was also used to help develop and test the associated CEN guidance standard on determining the degree of modification on river hydromorphology. In the UK, RHS has been used for several Water Framework Directive (WFD) purposes, helping to identify water bodies in ‘reference condition’, those classified as ‘heavily modified’ and also assessing morphological pressures affecting river catchments.
The STAR (STAndardisation of River Classifications) project was a research initiative funded by the European Commission and was completed in 2005. The main aim was to provide standard biological assessment methods compatible with WFD requirements. It also set out to develop a standard for determining the class boundaries of ‘ecological status’ and another one for inter-calibrating existing methods. In Austria, The Czech Republic, Denmark, Germany and Italy ‘core’ RHS sites were chosen to reflect a gradient in habitat and morphology degradation. Results from the STAR project were published in a special issue of Hydrobiologia in 2006.