Let me begin with a story. In the 1930s, the US Bureau of Reclamation had a very ambitious plan to divert water resources from the western slope of the Colorado Rockies to the dryer eastern slope. This was to be achieved by a series of dams and reservoirs, including hydropower stations.

The US Senate agreed to finance this expensive and elaborate infrastructure on the condition that the project preserved the Colorado River and ensured an adequate water supply for irrigation, sanitation and aquatic species preservation.

This led to what may well have been the first true, ecologically based, environmental flow assessment. From 1947 to 1949, the federal Fish and Wildlife Service undertook a series of studies around the downstream reaches of the Colorado River.

There, they began to associate different levels of downstream flows with the quality of the habitats necessary for the different life stages of the trout, an important species for the communities depending on the river as a major fishery.

Eventually, the service provided the Bureau of Reclamation with a daily flow release schedule. Unfortunately, these recommendations were never adopted. The bureau chose only to release small amounts of water that were already allocated through water rights to downstream users. So, sadly, the quality of the river degraded, and the Colorado’s blue ribbon fishery was lost.

Hydropower projects can have a significant impact on downstream river flows, either by changing flow dynamics to follow energy demand or by reducing flows to a bypassed stretch. Many experts have called for increased or dynamic flow regimes to support a river’s ability to deliver vital ecosystem services.

These changes can have financial and service implications for hydropower generation, which has meant that operators have often been reluctant to adopt them. Nonetheless, a number of innovative projects, often based on better communication between the hydropower industry and conservation sector, now attempt to find workable and sustainable compromises.

A lot has changed since the Colorado project. For one thing, there has been an exponential growth in reservoir storage in the last 65 years, from around 500 to roughly 6,000 cubic kilometres.

And we’ve also changed ourselves during those years. We’ve become aware of the extent of the damage we have caused to natural ecosystems. We’ve begun to think very differently about our place in the world, and our role in managing natural resources.

More recently, we have examined the impact that our actions have had on populations of wild organisms – how we have compromised biodiversity.

There are many examples of new partnerships between the hydropower industry and the conservation sector."

Today, about half of the length of the large rivers in the world have been regulated and artificially modified. Many kilometres of smaller rivers have also been affected by human interventions. As we know, these changes have a significant impact on connectivity and healthy flows in these systems.

So as we go into this next phase of hydropower development, with our commitment to do things more sustainably, we need to do things differently.

Innovation in freshwater policy and management

There’s already a lot to work with. For example, we have begun to classify the conditions of our freshwater systems and to set goals to ensure that they are managed sustainably.

Consider the EU Water Framework Directive. This framework classifies the ecological status of water bodies into five categories: high, good, moderate, poor, and bad.

We can use these categories to evaluate the state of a freshwater system. If the system achieves a rating of “good” or “high”, then we work to maintain this status. If the system falls into one of the three lower categories, then we work to restore them.

We’re also learning that it is very important to plan a project well from the beginning. In a recent publication, The Power of Rivers, the Nature Conservancy argues that good planning means we can avoid constructing dams in those areas where hydropower development would impede downstream flows too dramatically.

Instead, we can focus our efforts in those areas that allow for sustainable development, with minimal impact on the watercourse.

Perhaps the most important change is that we’re beginning to work together differently. There are many examples of new and innovative partnerships between the hydropower industry, the conservation sector and regulators.

With these productive collaborations, we can now see a real possibility of bringing sustainable principles to the heart of hydropower development.

You can find out more about the EU Water Framework Directive here.

You can download The Nature Conservancy’s report, The Power of Rivers, here.

This is the first part in a series of three articles exploring the topic of downstream flows from different perspectives. You can also read Rebecca Tharme's article on a basin-wide approach here, and Helen Locher's article on the perspective of the hydropower industry here.