Guidance on Environmental Flows - Integrating E-flow Science with Fluvial Geomorphology to Maintain Ecosystem Services

Fluvial systems provide a wide range of necessary services for human society to thrive on. These are the so-called ecosystem services: food, drinking water, natural flood mitigation, energy and so forth. Such services are linked to an appropriate level of functionality of fluvial processes, which can be accounted for in terms of ecological objectives. These ecological objectives in watercourses can be reached only if appropriate flow and sediment regimes and related quality of channel morphology are guaranteed. The establishment and maintenance of such flow regimes, namely environmental flows (e-flows), is therefore an essential element in preserving riverine ecosystems and the services they provide, and should be included as a constraint in water resource assessment and in national legislative frameworks. It is well established that e-flows refer to the typical seasonal and interannual variability of the natural flow regime, and not only to the minimum amount of water (low flows) to be maintained in a river. In addition to this pure hydrological assessment of natural flow variability, there is also the necessity to link e-flow definition to the related hydromorphological processes and local ecological objectives of a river. This guidance therefore presents a methodology (based on knowledge and literature on river system processes) to consider hydrological and morphological aspects in defining e-flows for environmental river management. The report has been produced within the context of an agreement between the WMO Commission for Hydrology and the Italian National Institute for Environmental Protection and Research (ISPRA), to cooperate in the implementation of activities related to managing river flows and maintaining services offered to human society and ecosystems. The research can be contextualized inside the implementation of the WMO Hydrology and Water Resources programme.