Ecological Flows

Science Center Objects

Ecological flow is a central theme of AS Branch studies, as our research examines how water flows affect populations, communities, ecosystems, and hydroscapes. Our studies elucidate the interactions among hydrologic, geomorphologic, biogeochemical, biological, and anthropogenic processes. Branch scientists identify and quantify the spatial and temporal attributes of water flow for ecological needs. Flow alternations by humans are a primary contributor to the degradation of aquatic ecosystems and the loss of freshwater biodiversity, and we provide innovative scientific methods and tools on flow-related ecological issues to decisionmakers, policy-makers, and stakeholders.

Colorado River at Southerly International Boundary during the pulse flow.

Colorado River at Southerly International Boundary during the pulse flow, March 29th, 2014. Public domain.

Dams and Their Ecological Consequences - Principal Investigator - Quan Dong

Scientists in the Aquatic Systems Branch have been studying the impacts of dams on riverscapes for more than two decades. Our scientists have written many reports on the effects of dams on recruitment of bottomland pioneer trees, such as cottonwood, along the Upper Missouri River and the Bill Williams River, and the effects of dams on channel geometry and vegetation throughout the Great Plains. Understanding the effects of dams and the relations between flow, sediment, and vegetation have allowed AS Branch scientists to provide valuable information for managing flow releases from dams to enhance native tree recruitment, or to remove exotic plant species that are encroaching on the channel along several rivers. Recently, AS Branch scientists are monitoring changes to flood plain vegetation along the Elwha River in Olympic National Park in response to the removal of two large dams. This study will provide lessons and guidance to the design and planning of future aquatic restoration efforts. We also study the ecological consequences of the experimental pulse flow in the Colorado River.


a cross section of a tree used for dating

Reconstructing Flood History from Tree Rings - Principal Investigator - Quan Dong

Shifts in river flow regimes are a major threat to water supplies and riverine ecosystems. Understanding and predicting flow changes and their effects on vegetation are critical to effective river management. Aquatic Systems Branch scientists analyze rings of riparian trees relating tree growth and establishment to historical flow. We then use the tree rings to reconstruct the flow in past centuries. Flow reconstructions discover the frequency and magnitude of past droughts and floods—information that is essential for management of rivers and water supplies. We also use downscaled climate projections and watershed models to predict changes in fl ow and tree growth resulting from human-induced climate change. We have pioneered the use of cottonwood, a dominant riparian species, for tree ring analysis; this is a significant advance in arid regions where old trees of other species are otherwise scarce. Ongoing studies focus on rivers of the Upper Missouri Basin and the Tarim River in China.


Bill Williams River, Arizona, during an experimental flood in 2010. Photo by Pat Shafroth, USGS.

Bill Williams River, Arizona, during an experimental flood in 2010. Photo by Pat Shafroth, USGS. Public domain.

Large-scale streamflow experiments - Principal Investigator - Patrick Shafroth

Because the underlying cause of riparian system alteration is often attributed to the effects of dams on flow regime, managing flow releases, particularly high flows, from dams is an often-advocated approach to river and riparian restoration. Our work has focused on understanding effects of managed high flow releases (a.k.a., pulse flows, controlled floods) from dams along rivers in the lower Colorado River basin. On the Bill Williams River in western Arizona, we have had the opportunity to help design and monitor the effects of several high flow releases since the mid 1990’s. On the main stem of the Colorado River, we helped study the effects of the 2014 “pulse flow” to the Colorado River delta (Minute 319), and are working with a range of collaborators to provide input to possible future releases to the delta (Minute 32X). Finally, we are working with collaborators from USGS, USDA Forest Service, and Northern Arizona University to understand how different groups of riparian plants (“riparian response guilds”) respond to high flow experiments on the Colorado River in Grand Canyon.


The unregulated Santa Maria River in west-central Arizona.

The unregulated Santa Maria River in west-central Arizona. Photo by Patrick Shafroth, USGS. Public domain.

Streamflow-fluvial Geomorphology-riparian Vegetation Interactions - Principal Investigator - Patrick Shafroth

The foundation for applying science to river and riparian restoration contexts lies in a basic understanding of the factors that drive riparian vegetation dynamics. Much of our research is focused on clarifying relationships between streamflow, fluvial geomorphology, and riparian vegetation, including various feedbacks. In some cases this work involves studying river reaches or segments that are relatively unaltered by anthropogenic activities; in many cases it involves study of river segments that have been altered by human activities, most notably river damming. Our research often includes field studies, but also experiments (e.g., in greenhouses) to help control for specific factors hypothesized to influence riparian plants. This work is often done in collaboration with scientists whose primary emphasis lies in the physical sciences (e.g., fluvial geomorphology, hydrology).