Minimum Environmental Flow Regimes

Abstract

Abstract Environmental flows, sometimes referred to as ecological or instream flow requirements, or compensation flows are defined as the amount and quality of water necessary to preserve ecological functions and values in watercourses. One set of challenges in water resources planning today is to define environment flow requirements (quantity, timing, and quality on a seasonal basis), integrate them in water allocation policies and achieve consensus on this, and translate and incorporate those requirements into the operating rules for flow regulating structures, such as dams, reservoirs, and diversion schemes. In this article, basic concepts of environmental flow are introduced. A minimum environmental flow will have significant benefits toward maintaining a macroinvertebrate population by providing suitable habitat refugee between discharge peaks. A minimum environmental flow, however, would not be expected to fully mitigate the effects of increased hydropeaking. Establishing a minimum environmental flow is partly aimed at mitigating the effects of variable flows. Policies on environmental flows are perhaps the most important direct connection between water resource and wetland resource management. A number of new planning approaches are emerging to quantify and apply environmental flow standards, which have been grouped in three main categories: hydrologic or historical flow record methods, hydraulic and habitat modeling, and holistic methods. The first category consists of approaches where historical flow records are used to develop environmental flow, or instream flow recommendations, based on subjective assessments of ecosystem needs. Hydraulic and habitat rating methods use relationships between habitat condition and discharge to develop instream flow recommendations. The final and more complex method is the holistic approach to the assessment of instream flows and water quality aspects, in which all components or attributes of the ecosystem and their interrelationships are addressed.