Hydrology

The U.S. Geological Survey’s Southwest Biological Science Center, and more specifically, its River Ecosystem Science branch which includes the Grand Canyon Monitoring and Research Center (GCMRC), is a preeminent science group that has more than 20 years of experience of providing high-quality, detailed science to resource managers and stakeholders primarily concerned with the effects of dam...

Glen Canyon Dam has altered flow and fine sediment (sand, silt, and clay) dynamics of the Colorado River in Grand Canyon. Before the dam, the Colorado River experienced highly variable flows and carried a large amount of sediment through Grand Canyon, which maintained sandbars (highly valued camping areas in Grand Canyon) and provided sand that protected archeological and cultural sites from...

The Upper Mississippi River (UMR) provides critical habitat for hundreds of aquatic species and provides Minnesota with a transportation link to the rest of the world. Reliable measurements of sediment are important for making decisions as part of maintaining the channel. In 2014, sediment deposition in the navigation channel caused channel closures of the UMR delaying commercial navigation for 3...

The goal of Grand Canyon Monitoring and Research Center’s (part of the Southwest Biological Science Center) riparian vegetation monitoring program is to assess changes and trends in plant species composition and cover and relate those changes to Glen Canyon Dam operations, river hydrology, climate, and geomorphology. Monitoring is done by annual field-data collection on plant cover and diversity...

Riparian areas are conspicuous belts of dense, green vegetation along streams and rivers, and can be considered “ribbons of life”. Despite covering less than 2 percent of the land area in the southwestern U.S., riparian areas tend to have high species diversity and population density, making them valuable to managers, scientists, and the public. These unique ecosystems act as a link between dry...

Aquatic invertebrates are critical food for fish and other species that inhabit large rivers. In the Colorado River Basin, invertebrates that get transported down the river (“in the drift”) are particularly important to rainbow trout and other species of interest to recreational users. This research seeks to compare rivers downstream of large dams throughout the Colorado River Basin in order to...

Algae, phytoplankton, and rooted macrophytes represent the base of many aquatic food webs and are known as primary producers. Through photosynthesis, these organisms convert sunlight energy into chemical energy (i.e., carbon) that in turn fuels the growth of animals such as macroinvertebrates and fish. This project uses high frequency measurements of dissolved oxygen, which is a by-product of...

We study the links among different geomorphic processes that affect river valley landscapes in the Colorado River downstream from Glen Canyon Dam, Arizona. Dam-released flows affect the deposition and retention of sandbars that serve as sources for other sand resources, such as windblown sand dunes, throughout the Colorado River ecosystem. The degree to which the landscapes are differentially...

Drylands cover 40% of the global terrestrial surface and provide important ecosystem services. However, climate forecasts in most dryland regions, especially the southwest U.S., call for increasing aridity. Specifically, changing climate will alter soil water availability, which exerts dominant control over ecosystem structure and function in water-limited, dryland ecosystems. This research seeks...

Floodplain red gum forests are sites of high biodiversity in arid regions of south Australia. They depend on periodic floods from rivers, but dams and diversions have reduced flood frequencies, leading to deterioration of the trees. We determined the water requirements of red gum trees so environmental flows can be used to restore and maintain the forests. We used measurements of transpiration of...

The Upper San Pedro River is one of the few remaining undammed rivers that maintain a vibrant riparian ecosystem in the southwest. However, its riparian forest is threatened by diminishing groundwater and surface water inputs, due to either changes in watershed characteristics such as changes in riparian and upland vegetation, or human activities such as regional groundwater pumping. We used...

The Rio Grande/Rio Bravo (hereafter referred to as the Rio Grande) in the Big Bend region of Texas, USA, and Chihuahua, and Coahuila, MX has substantially narrowed since the early 1900s. This narrowing has been caused by the construction and operation of dams and irrigation diversions in upstream reaches of the Rio Grande in the U.S. and the Rio Conchos in Mexico that has reduced mean and peak...