Instream Flow Assessment: From Holistic Approaches to Habitat Modelling

Abstract

The conflict between the ever-increasing demand for river water (hydroelectric development, irrigation, drinking water, etc.) and the environmental need for sustaining flows during drought and low flow periods is a recurring problem in water resource management. Competition between water abstraction (offstream use) and instream flow needs (minimum flow for the protection of fish habitat) will undoubtedly increase in the future, as it is estimated that worldwide more than 50% of total accessible runoff is presently being used. Instream flow methods are the primary and essential tools used during environmental impact assessments to evaluate the level of aquatic habitat protection for rivers under reduced flow conditions. Since the 1970s, methodologies, applicable to various scopes of water utilization and of a range of sophistication, have been developed. These can be classified into three categories: historical streamflow, river hydraulics and habitat preference methods. New methods are widely used in North America, but important questions related to validation and range of applicability remain. Existing and new instream flow methods also need to take into consideration changing environmental conditions such as climate change, in establishing a level of protection. The research reported here focuses on the current knowledge, strengths and weaknesses of a variety of instream flow methods as well as their associated level of aquatic habitat protection. Recommendations are provided for future instream flow research depending on the range of complexity of applied methods being contemplated.