Development of a method to assess ecological impact due to hydrological regime alteration of Scottish rivers

The Water Framework Directive (WFD) of the European Union is the principal driver behind the development of protocols for the assessment of anthropogenic impacts on the hydrology of Scotland's rivers, lakes and transitional waters. A new approach for rivers, known as the Dundee Hydrological Regime Assessment Method (DHRAM) has been developed. The underlying rationale is to assess the risk of significant impact on biota arising from changes in hydrological regime, as distinct from chemical or hydromorphological influences. This approach is based on the Indicators of Hydrologic Alteration (IHA) methodology of Richter et al. (1996), in which the degree of alteration of a range of hydrological variables that are significant to biota are estimated. The DHRAM method classifies the degree of alteration to hydrological regime using a five-point scale, which correlates with the risk of ecological damage. These categories are compatible with those of the WFD. The acquisition of appropriate biological data for calibration and validation of DHRAM has, however, proved problematic. This paper proposes the future development of a calibration scheme which compares the biota of neighbouring water bodies (pairs whose physical attributes are as similar as possible in all relevant respects, except in the degree of disturbance to their hydrological regimes).