Environmental flow management using transparency and translucency rules

摘要: River flow regimes and their variability are considered by many authors to be the most important factor structuring their physical and ecological environment. In regulated rivers, environmental or instream flows are the main management technique used to ameliorate the ecological effects of flow alteration. We highlight two concepts that are not commonly used in a managed flow regime but help return natural flow variability to a managed river, namely, transparent and translucent flow rules. Transparency flows target lower flows up to a defined threshold so that all inflows are released from a dam or are protected from ion. Translucency flows form a percentage of inflows greater than the transparency threshold that are released to maintain a proportion of flow pulses in the river system. The main ecological concept underlying transparency and translucency flows is that riverine biota are adapted to the historical flow regime. Although the loss of small to moderate flood events may arise from implementation of translucency and/or transparency flow regimes, we advocate that these rule types would, nonetheless, be beneficial in many managed flow regimes and present two case studies where they have been defined and implemented.