An ecologically sustainable water management program must always be built upon a foundation of knowledge about the river flows needed to sustain ecosystem health. When the water needs of a river ecosystem are clearly defined by scientists, water managers will be able to find ways of meeting human needs for water while maintaining adequate river flows for the ecosystem.
A river ecosystem’s water needs are defined in an “environmental flow prescription.” This flow prescription describes the necessary seasonal and inter-annual variation needed in low flows, high flow pulses and floods to support native species and critically important ecological functions. Environmental flow prescriptions may be as specific as quantifying the magnitude, frequency, duration, timing and rate of change of each environmental flow component, as illustrated by Richter et al (2006) or expressed in more general terms such as allowable percent-of-flow alteration (Flannery et al, 2002). Across different methods of developing a flow prescription, the emphasis is on maintaining the portions of the hydrograph necessary to support a healthy river ecosystem.
Scientists at The Nature Conservancy have developed new processes and frameworks for developing ecosystem flow prescriptions that emphasize collaboration among scientists and water managers, working together to integrate human and ecosystem needs for water. The following reports document environmental flow prescriptions resulting from the Conservancy’s collaborative, adaptive approach (Richter et al, 2006):
