Helping Desert Communities Find Hidden Water

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Desert communities throughout the Southwest are putting water availability at the top of their municipal agendas.

Helping Desert Communities Find Hidden Water

In the 1800s, cowboys, ranchers, and miners quarreled over water in the American Southwest, over where to find it and who could use it. Today, people in the region are faced with even greater concerns. Rapid population growth combined with the impact of longer droughts may present a greater demand for water resources in the future.

However, one area stands out from the rest: the upper Santa Cruz Basin in Arizona has shown a remarkable capacity to store water. The Santa Cruz River area was the site of the first European settlements in the region because of its water availability and lush environment.

What causes the higher water availability in this area?

Population Growth in Nogales, Arizona

Rapid population growth, as shown by new homes in the Nogales, Arizona area, has increased the demand for groundwater in the upper Santa Cruz Basin. Photograph credit: William Page, USGS

Looking Deeper Underground

During the rainy season in southern Arizona, water seeps into the ground and is stored in big, underground bathtubs called aquifers. Groundwater in aquifers can be brought to the surface by natural springs or wells. The aquifers that provide much of the groundwater to the city of Nogales and the surrounding communities are collectively called “the microbasins.” The microbasins are narrow, and scientists originally thought they were shallow—100–150 feet below the surface—because solid bedrock is close to the surface and water cannot pass through it easily.

Could water be leaking beneath the shallow aquifers, making more water available?

Keith Nelson, a hydrologist at the Arizona Department of Water Resources (ADWR) in Phoenix, worked to find the answer. He used a water simulation program and entered data that included the possibility of aquifers deeper than 150 feet beneath the surface. The model produced results closer to the actual conditions.

“Although that was reassuring,” said Nelson, “I was reluctant to consider the findings more than preliminary until I could get field data on whether the rocks in the area would actually let water through to lower levels.”

Cutting Edge 3D Modeling and Integrated Research

Nelson then collaborated with geologist William Page of the U.S. Geological Survey (USGS). After Nelson had explained his dilemma, Page shared results of his studies in the area. Page has worked in the region for many years and collects data about geologic formations and faults to determine how they affect surface water and groundwater flow.

A three-dimensional (3D) geologic model developed by the USGS was one of several techniques used to understand how water flows in the Santa Cruz Basin. The model helped define the geometry and thickness of the basin aquifer system and enabled the viewing of subsurface data interactively in 3D space. This gives scientists the ability to slice through and rotate the modeled geology into various orientations, thereby better understanding the internal complexities of the basin. These types of interactive models are cutting-edge in the scientific community.

Data from Page’s collective geologic studies revealed many areas of fractured sediments throughout the Santa Cruz Basin and numerous deep aquifers, some reaching 2,500 feet below the surface. Where sediments are fractured, channels form, allowing water to flow at deeper levels. The sediments let water through easily and are also porous and store even more water.

3D of the Upper Santa Cruz Basin

USGS video of the 3D model looking at the upper Santa Cruz Basin in Arizona. The top layers (yellow and gold) are the shallow and deep aquifers. The bottom layer (green and red colors) is solid bedrock underneath. The red lines are faults, which play a significant role in controlling groundwater flow through the basin aquifers.

Progress Is Enthusiastically Received

Studies based on data from both the USGS and the ADWR provide insight into how the regional hydrologic system works. Their efforts are enthusiastically received by residents, the City of Nogales, and other regional water users and managers.

“[Page’s] work confirmed our unexpected results that there are deep aquifers beneath the shallow ones in the microbasins,” Nelson commented. “The ADWR will use the results of the new USGS studies to create more effective water management strategies.”

Santa Cruz Basin

Geologists collecting data on a fracture (in foreground) in the Santa Cruz Basin. Photograph credit: William Page, USGS

For More Information

For more information, contact Jennifer LaVista, USGS Public Affairs Specialist, at jlavista@usgs.gov.

Read more stories about USGS science in action.

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20 Years Researching Harmful Algal Blooms Supports Sustainable Water Supply in Wichita

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Two decades of harmful algal bloom, nutrient and sediment research by the U.S. Geological Survey is helping to support Wichita’s long-term vision of a sustainable water supply into the future. Early warning indicators of harmful algal blooms have been developed for Cheney Reservoir, Kansas, according to a new USGS publication done in cooperation with the City of Wichita, Kansas.

Image: Harmful Algal Blooms

Harmful algal blooms are an accumulation of tiny organisms known as algae and can release harmful toxins into the environment. 

Cheney Reservoir, located in south-central Kansas, is one of the primary drinking-water supplies for the city of Wichita and an important recreational resource. Because of population growth, urban development and water-supply needs, the city of Wichita will continue to rely on Cheney Reservoir as a drinking-water supply for the foreseeable future. Since 1990, harmful algal blooms have been present occasionally in Cheney Reservoir, resulting in increased treatment costs and decreased recreational use. Findings from long-term research may help resource managers make informed decisions regarding algal bloom occurrences in Wichita and across the globe.  

Since 1996, the USGS, in cooperation with the City of Wichita, has conducted studies in the Cheney Reservoir Watershed to understand environmental effects on water-quality conditions. In 2001, the USGS started to continuously measure water-quality conditions to develop a real-time notification system of factors that may affect drinking-water treatment. Scientists created tools that serve as early warning indicators of event occurrence in near real-time. These products, which include predictive models, allow for a more proactive approach to managing harmful algal blooms. A new USGS fact sheet is also available that summarizes two decades of work.

“Knowledge gained from USGS studies in the Cheney Reservoir Watershed has assisted in the development, implementation, maintenance, and assessment of watershed-management goals and plans,” said Don Henry, assistant director of the City of Wichita’s Public Works and Utilities. “This data has allowed us to ensure a safe and reliable water supply and put us ahead of the curve in terms of sediment management.”

Freshwater harmful algal blooms may contain toxins which have been implicated in human and animal illness and death in at least 43 states in the U.S., including Kansas. Many of these states have established monitoring programs to minimize potential exposure through recreational activities. Several countries, including the United States have set national standards or guidelines for these toxins in drinking water.

“Long-term data have been critical in improving our understanding of how to prevent and mitigate harmful algal bloom outbreaks,” said Jennifer Graham, USGS scientist and lead author of the new USGS study. “This information is not only important to the City of Wichita, but can help water managers around the globe make informed decisions on resources.”

Water-quality concerns can arise with the presence of harmful algal blooms, including the potential to produce toxins and taste-and-odor compounds. Toxins and taste-and-odor compounds may cause substantial economic and public health concerns and are of particular interest in lakes, reservoirs, and rivers that are used for drinking-water supply and recreation.

For More Information

Additional USGS resources on harmful algal blooms are available in this recent USGS featured story.

Pipe installation to monitor harmful algal blooms at Cheney Reservoir

John Rosendale installs a pipe to monitor harmful algal blooms at Cheney Reservoir in Kansas. (Credit: Ariele Kramer, USGS. Public domain.)

Sensors are cleaned with an automatic wiper brush on the continuous water-quality monitors. 

Sensors are cleaned with an automatic wiper brush on the continuous water-quality monitors. (Credit: Trudy Bennett, USGS. Public domain.)

Cheney algal bloom

Algae bloom near Cheney Reservoir Dam, Kansas. (Credit: Trudy Bennett, USGS. Public domain.)

Cheney Res water samples

Discrete samples collected from a near-shore accumulation of cyanobacteria (left) and an open-water area (right) in Cheney Reservoir, Kansas. (Credit: Trudy Bennett, USGS. Public domain.)

Cheney Reservoir, KS

Water sample collection on ice-covered Cheney Reservoir, Kansas. (Public domain.)