Map showing the major tritium-monitoring sites in the NGWOS study area of the Upper Colorado River Basin where Water Isotope Network samples of precipitation and streamflow are collected, as well as sites where snowpack samples are collected for comparison to total precipitation.
Colorado River Headwaters, Water Isotope Network
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By Colorado Water Science Center
March 5, 2025
Water availability is controlled by processes that can be hard to measure, like the process of groundwater discharging from a streambed that becomes streamflow. Naturally occurring, radioactive and stable (non-radioactive) isotopes can help trace those processes, particularly the isotopes of hydrogen and oxygen that are part of the water molecule. Tritium, the radioactive isotope of hydrogen, has a half-life of 12.3 years and can serve as a clock tracing how long it takes snowmelt to become stream flow. Stable isotopes of hydrogen and oxygen can trace losses of water by evaporation because the heavier isotopes evaporate more slowly. The Water Isotope Network in the Colorado River headwaters region collects data on the isotopic composition of precipitation and streamflow. Those data are then analyzed to help understand and predict water availability. The project is part of the U.S. Geological Survey Next Generation Water Observing Systems (NGWOS).
Media
View upstream from U.S. Geological Survey streamgage 09112200 East River below Cement Creek near Crested Butte, Colorado, during base flow conditions in October 2023.
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View upstream from U.S. Geological Survey streamgage 09112200 East River below Cement Creek near Crested Butte, Colorado, during snowmelt conditions in May 2022.
Sources/Usage: Public Domain. View Media Details
Thanks to hydrologic research, we now understand that much of the water in rivers was once groundwater and travelled underground for years to become streamflow. The combination of storage and release from such underground settings keeps rivers flowing in winter when the soil is frozen and during droughts when precipitation is scarce. The times when streamflow is dominated by groundwater discharge are called baseflow conditions. In contrast, runoff conditions occur during snowmelt and rain events and such events mix new water with additional groundwater pushed out by infiltration of snowmelt and rain. Groundwater storage and flow happen in heterogeneous settings like hillslopes, meadows, fractures in bedrock, and deposits of sand in river valleys. Understanding the influence of underground flow paths, and the groundwater storage associated with them, is important to predicting streamflow and the broader availability of water for humans and natural ecosystems. However, measuring such flows of water and groundwater storage can be challenging because they occur underground and can happen slowly.
Media
Sources/Usage: Public Domain. View Media Details
The NGWOS Water Isotope Network in the Colorado River headwaters region monitors concentrations of tritium in precipitation and streamflow by collecting and analyzing periodic samples. A major goal is to trace groundwater contributions to streamflow. Through the natural radioactive decay of tritium atoms in the water molecule, the mean transit time, or age, of water in a river is calculated. That information then can be leveraged, along with standard streamgage measurements of streamflow, to estimate how much groundwater exists upstream from the sampled streamflow location. Continued monitoring can reveal how much groundwater storage changes from year to year in response to droughts or years of above-average precipitation. That information, in turn, can help provide understanding and support modeling of water availability as precipitation patterns in the region change and demands for water resources increase. The network also monitors stable isotopes in precipitation and streamflow across a larger number of sites. The stable isotope data can help assess the contributions of snowmelt from different elevations to streamflow and the fingerprint of natural and agriculture-related evaporation on rivers.
Media
Sources/Usage: Public Domain. View Media Details
Water Isotope Network map
Map showing the major tritium-monitoring sites in the NGWOS study area of the Upper Colorado River Basin where Water Isotope Network samples of precipitation and streamflow are collected, as well as sites where snowpack samples are collected for comparison to total precipitation.
How groundwater contributes to streamflow
A conceptual diagram of how groundwater storage and flow paths contribute to streamflow. Three key processes are illustrated: the process of infiltration (groundwater recharge), groundwater discharge along faster and slower flow paths to a stream, and variations in groundwater storage in response to wetter years and drought.
A conceptual diagram of how groundwater storage and flow paths contribute to streamflow. Three key processes are illustrated: the process of infiltration (groundwater recharge), groundwater discharge along faster and slower flow paths to a stream, and variations in groundwater storage in response to wetter years and drought.
High elevation precipitation collector
The Water Isotope Network precipitation collector at U.S. Geological Survey site 385303107060301 Lake Irwin Meteorological Station near Ruby Anthracite Creek, Colorado in October 2023.
The Water Isotope Network precipitation collector at U.S. Geological Survey site 385303107060301 Lake Irwin Meteorological Station near Ruby Anthracite Creek, Colorado in October 2023.
Tomichi Creek at Gunnison, Colorado
View upstream from U.S. Geological Survey site 09119000 Tomichi Creek at Gunnison, Colorado, showing topography and standing water in a flood irrigated pasture.
View upstream from U.S. Geological Survey site 09119000 Tomichi Creek at Gunnison, Colorado, showing topography and standing water in a flood irrigated pasture.
Lower elevation precipitation collector
The Water Isotope Network precipitation collector at U.S. Geological Survey site 395811105480401 Devils Thumb Meteorological Station near Fraser, Colorado, in September 2020.
The Water Isotope Network precipitation collector at U.S. Geological Survey site 395811105480401 Devils Thumb Meteorological Station near Fraser, Colorado, in September 2020.
Water availability is controlled by processes that can be hard to measure, like the process of groundwater discharging from a streambed that becomes streamflow. Naturally occurring, radioactive and stable (non-radioactive) isotopes can help trace those processes, particularly the isotopes of hydrogen and oxygen that are part of the water molecule. Tritium, the radioactive isotope of hydrogen, has a half-life of 12.3 years and can serve as a clock tracing how long it takes snowmelt to become stream flow. Stable isotopes of hydrogen and oxygen can trace losses of water by evaporation because the heavier isotopes evaporate more slowly. The Water Isotope Network in the Colorado River headwaters region collects data on the isotopic composition of precipitation and streamflow. Those data are then analyzed to help understand and predict water availability. The project is part of the U.S. Geological Survey Next Generation Water Observing Systems (NGWOS).
Media
View upstream from U.S. Geological Survey streamgage 09112200 East River below Cement Creek near Crested Butte, Colorado, during base flow conditions in October 2023.
Sources/Usage: Public Domain. View Media Details
Media
View upstream from U.S. Geological Survey streamgage 09112200 East River below Cement Creek near Crested Butte, Colorado, during snowmelt conditions in May 2022.
Sources/Usage: Public Domain. View Media Details
Thanks to hydrologic research, we now understand that much of the water in rivers was once groundwater and travelled underground for years to become streamflow. The combination of storage and release from such underground settings keeps rivers flowing in winter when the soil is frozen and during droughts when precipitation is scarce. The times when streamflow is dominated by groundwater discharge are called baseflow conditions. In contrast, runoff conditions occur during snowmelt and rain events and such events mix new water with additional groundwater pushed out by infiltration of snowmelt and rain. Groundwater storage and flow happen in heterogeneous settings like hillslopes, meadows, fractures in bedrock, and deposits of sand in river valleys. Understanding the influence of underground flow paths, and the groundwater storage associated with them, is important to predicting streamflow and the broader availability of water for humans and natural ecosystems. However, measuring such flows of water and groundwater storage can be challenging because they occur underground and can happen slowly.
Media
Sources/Usage: Public Domain. View Media Details
The NGWOS Water Isotope Network in the Colorado River headwaters region monitors concentrations of tritium in precipitation and streamflow by collecting and analyzing periodic samples. A major goal is to trace groundwater contributions to streamflow. Through the natural radioactive decay of tritium atoms in the water molecule, the mean transit time, or age, of water in a river is calculated. That information then can be leveraged, along with standard streamgage measurements of streamflow, to estimate how much groundwater exists upstream from the sampled streamflow location. Continued monitoring can reveal how much groundwater storage changes from year to year in response to droughts or years of above-average precipitation. That information, in turn, can help provide understanding and support modeling of water availability as precipitation patterns in the region change and demands for water resources increase. The network also monitors stable isotopes in precipitation and streamflow across a larger number of sites. The stable isotope data can help assess the contributions of snowmelt from different elevations to streamflow and the fingerprint of natural and agriculture-related evaporation on rivers.
Media
Sources/Usage: Public Domain. View Media Details
Water Isotope Network map
Map showing the major tritium-monitoring sites in the NGWOS study area of the Upper Colorado River Basin where Water Isotope Network samples of precipitation and streamflow are collected, as well as sites where snowpack samples are collected for comparison to total precipitation.
Map showing the major tritium-monitoring sites in the NGWOS study area of the Upper Colorado River Basin where Water Isotope Network samples of precipitation and streamflow are collected, as well as sites where snowpack samples are collected for comparison to total precipitation.
How groundwater contributes to streamflow
A conceptual diagram of how groundwater storage and flow paths contribute to streamflow. Three key processes are illustrated: the process of infiltration (groundwater recharge), groundwater discharge along faster and slower flow paths to a stream, and variations in groundwater storage in response to wetter years and drought.
A conceptual diagram of how groundwater storage and flow paths contribute to streamflow. Three key processes are illustrated: the process of infiltration (groundwater recharge), groundwater discharge along faster and slower flow paths to a stream, and variations in groundwater storage in response to wetter years and drought.
High elevation precipitation collector
The Water Isotope Network precipitation collector at U.S. Geological Survey site 385303107060301 Lake Irwin Meteorological Station near Ruby Anthracite Creek, Colorado in October 2023.
The Water Isotope Network precipitation collector at U.S. Geological Survey site 385303107060301 Lake Irwin Meteorological Station near Ruby Anthracite Creek, Colorado in October 2023.
Tomichi Creek at Gunnison, Colorado
View upstream from U.S. Geological Survey site 09119000 Tomichi Creek at Gunnison, Colorado, showing topography and standing water in a flood irrigated pasture.
View upstream from U.S. Geological Survey site 09119000 Tomichi Creek at Gunnison, Colorado, showing topography and standing water in a flood irrigated pasture.
Lower elevation precipitation collector
The Water Isotope Network precipitation collector at U.S. Geological Survey site 395811105480401 Devils Thumb Meteorological Station near Fraser, Colorado, in September 2020.
The Water Isotope Network precipitation collector at U.S. Geological Survey site 395811105480401 Devils Thumb Meteorological Station near Fraser, Colorado, in September 2020.