Anthropogenic impacts upon the hydrology of rivers and lochs
The project was commissioned to produce a set of methods for assessing the extent and severity of anthropogenic changes to the hydrology of running and standing freshwaters in Scotland and Northern Ireland. It arises in the context of the European Water Framework Directive, in which information is required describing changes in the hydromorphology of water bodies.
It was required that the methods should be appropriate to the ecological impacts caused by hydrological change. A literature review was carried out, covering relevant studies of the impacts of hydrological change on specific species, and also more general reports of relevant water management strategies and the hydro-ecological studies underpinning them. The Indicators of Hydrological Alteration (IHA) methodology developed by Dr Brian Richter and colleagues at the (US) Nature Conservancy was identified as offering a system by which a broad spectrum of ecologically-relevant indicators of hydrological change could be quantified and used to derive a composite measure of alteration.
Separate methods were produced for running waters and standing waters, drawing on some common elements of conceptual background. Common hydrological changes to running waters include those resulting from abstractions (e.g. for water supply or agriculture), effluent discharges, and regulation, e.g. due to hydro-power generation. The main changes to standing waters are those resulting from impoundment of natural lochs and artificial reservoirs, and also those due to changes in the regime of running waters upstream.
The methods developed for running waters require comparison of hydrologic indicators based on series of daily mean flow values for both unimpacted and impacted conditions, i.e. without and with the source(s) of hydrological alteration pertaining to the site of interest. In some cases, observed (measured) data may be available but, in many situations, there will be a need to produce synthetic data to describe one or both situations. Simple methods are presented for these tasks, involving the use of Micro Low Flows for the production of a flow duration curve at the ungauged site, information transfer methods and methods for representing common anthropogenic effects. Once the daily mean flow series are available, their characteristics can be compared - a WindowsTM software tool is being developed for practical application.
The methods developed for standing waters are more straightforward and less data-demanding. Again, daily data are required, but only for the impacted condition. Mean annual range, the frequency of water level reversals, the magnitude of weekly level oscillations and seasonality characteristics are used as the basis of the description.
For both running and standing waters, results are reported on a 5-class scale of alteration. Application to standing waters is for whole water bodies while, for running waters, reaches defined by major tributaries should be used.
The method is deliberately general in its design, pending much future monitoring and research on the ecological effects of hydrological change. In Scotland and Northern Ireland, where there is much variety in geology, channel slope, water chemistry and other physical factors, there is a corresponding diversity in ecosystem structure and species abundance, and ecological response to hydrological change is assumed to be complex. Refinements of these methods may be appropriate once progress is made in this sphere.
Copies of this report are available from the Foundation, price £15.00, less 20% to FWR members.