Oregon Water Resources Department (OWRD) and U.S. Geological Survey (USGS) are working together to estimate groundwater recharge across the state.
Groundwater, water stored underground in pore spaces and fractures, is an essential resource across Oregon. Groundwater flows underground, moving from areas of recharge to areas of discharge. Groundwater recharge occurs when water sinks underground to replenish groundwater reservoirs. Groundwater can remain underground briefly or for thousands of years, depending on the route, rock types, and geologic structures encountered. Eventually, groundwater resurfaces, discharging from springs, flowing into rivers, seeping into lakes, or is pumped for human use.
A groundwater budget accounts for water that enters and exits a groundwater system. Quantifying the elements of a water budget provides resource managers with important information as they work to maintain a balance between water availability and demand. For example, if groundwater extraction is greater than recharge, groundwater levels can drop. Lower groundwater levels can cause wells to go dry. Lower groundwater levels can also cause springs and streams to diminish because less groundwater is discharging to support their flow.
Oregon’s Groundwater Challenges
In some parts of the state, the amount of groundwater pumped from aquifers is far outpacing recharge - and groundwater depletion is occurring at a rapid and unsustainable rate.
In Oregon, about 1,220 wells went dry or declined below their pumping capacity between June 2021 and December 2023. Reporting dry wells is not required in Oregon, however, so this number is likely much higher.
Streams and rivers that depend on groundwater for a portion of their flow have been reduced, impacting water-quality and water availability for people and habitats. This is evident by USGS groundwater studies in the Klamath, Deschutes, and Harney basins.
Groundwater availability may decrease with climate change. Generally, as temperatures rise, evaporation from water bodies and transpiration from plants increases. This means more water is moved from the land and vegetation into the atmosphere. As evapotranspiration rates rise, soil becomes drier, reducing the amount of water available for groundwater recharge.
Groundwater-level drawdown in the Harney Basin:
Below are some of the many dry wells that property owners received help with thanks to OWRD's Well Abandonment, Repair and Replacement Fund.
The USGS and OWRD: What we're doing
Effectively managing Oregon’s groundwater-resource challenges requires improved estimates of groundwater budgets across the state - but before researchers can estimate groundwater budgets, they need up-to-date estimates of recharge and discharge, and the many complex components of these variables.
To estimate a basin’s groundwater discharge, researchers gather and analyze data on streamflow, spring flow, and groundwater pumping rates. Groundwater uptake by plants may also need to be estimated in areas where varieties of plants that directly access groundwater are widespread.
Quantifying recharge is trickier because it commonly happens underground and cannot be directly measured. Unlike rain falling directly into a bucket, groundwater recharge occurs slowly as water seeps into soil and percolates downward. Groundwater recharge rates vary depending on soil type, vegetation cover, and the local climate, among other variables. Estimating recharge tends to require a variety of data-intensive techniques, ranging from long-term measurement of groundwater levels to complex modeling.
To help estimate recharge across Oregon, researchers are using a customized version of the USGS National Hydrologic Model (NHM).
The NHM uses daily precipitation, air temperature, and the hydrogeologic properties of the landscape to estimate surface runoff, streamflow, and groundwater discharge to streams, among other components of the hydrologic cycle.
One of the ways the NHM is being customized to Oregon is by using base-flow estimates for Oregon’s rivers and streams to calibrate the model to accurately simulate recharge.
Groundwater and surface water interaction
Base flow is the portion of streamflow that does not come directly from runoff of rain and snowmelt. When groundwater levels are higher than the overlying streams and rivers, groundwater discharges to the stream, becoming base flow. Groundwater is a significant source of flow for many of Oregon’s rivers and is especially important for sustaining them during hot, dry months.
Base flow typically has more dissolved minerals and salts than precipitation runoff because it interacted chemically with the rocks and soil it passed through. Water with dissolved salts and minerals can conduct small amounts of electricity that can be measured with specific conductance sensors.
Much like recharge, distinguishing base flow from surface runoff in a stream is difficult. By measuring specific conductance in the stream water, we can get an idea of how much groundwater is contributing to the streamflow. Generally, higher specific conductance values indicate a higher proportion of groundwater in the streamflow, while lower values indicate more surface runoff.
Researchers in Oregon are monitoring specific conductance along with streamflow volumes over time to estimate what portion of streamflow is base flow. When they measure higher specific conductance during dry periods, this indicates that most of the streamflow is supplied by groundwater discharge. During heavy rain events or when the stream contains a lot of snowmelt, specific conductance might drop as surface runoff dilutes the water.
Once base flow estimates and other model components are gathered, scientists will use the Oregon version of the NHM to develop groundwater recharge estimates that can inform the development of water budgets across the state.
This is an active and evolving project that is being tailored to meet the needs of Oregon’s water resource managers. The story continues, stay tuned for updates!
Oregon Water Resources Department (OWRD) and U.S. Geological Survey (USGS) are working together to estimate groundwater recharge across the state.
Groundwater, water stored underground in pore spaces and fractures, is an essential resource across Oregon. Groundwater flows underground, moving from areas of recharge to areas of discharge. Groundwater recharge occurs when water sinks underground to replenish groundwater reservoirs. Groundwater can remain underground briefly or for thousands of years, depending on the route, rock types, and geologic structures encountered. Eventually, groundwater resurfaces, discharging from springs, flowing into rivers, seeping into lakes, or is pumped for human use.
A groundwater budget accounts for water that enters and exits a groundwater system. Quantifying the elements of a water budget provides resource managers with important information as they work to maintain a balance between water availability and demand. For example, if groundwater extraction is greater than recharge, groundwater levels can drop. Lower groundwater levels can cause wells to go dry. Lower groundwater levels can also cause springs and streams to diminish because less groundwater is discharging to support their flow.
Oregon’s Groundwater Challenges
In some parts of the state, the amount of groundwater pumped from aquifers is far outpacing recharge - and groundwater depletion is occurring at a rapid and unsustainable rate.
In Oregon, about 1,220 wells went dry or declined below their pumping capacity between June 2021 and December 2023. Reporting dry wells is not required in Oregon, however, so this number is likely much higher.
Streams and rivers that depend on groundwater for a portion of their flow have been reduced, impacting water-quality and water availability for people and habitats. This is evident by USGS groundwater studies in the Klamath, Deschutes, and Harney basins.
Groundwater availability may decrease with climate change. Generally, as temperatures rise, evaporation from water bodies and transpiration from plants increases. This means more water is moved from the land and vegetation into the atmosphere. As evapotranspiration rates rise, soil becomes drier, reducing the amount of water available for groundwater recharge.
Groundwater-level drawdown in the Harney Basin:
Below are some of the many dry wells that property owners received help with thanks to OWRD's Well Abandonment, Repair and Replacement Fund.
The USGS and OWRD: What we're doing
Effectively managing Oregon’s groundwater-resource challenges requires improved estimates of groundwater budgets across the state - but before researchers can estimate groundwater budgets, they need up-to-date estimates of recharge and discharge, and the many complex components of these variables.
To estimate a basin’s groundwater discharge, researchers gather and analyze data on streamflow, spring flow, and groundwater pumping rates. Groundwater uptake by plants may also need to be estimated in areas where varieties of plants that directly access groundwater are widespread.
Quantifying recharge is trickier because it commonly happens underground and cannot be directly measured. Unlike rain falling directly into a bucket, groundwater recharge occurs slowly as water seeps into soil and percolates downward. Groundwater recharge rates vary depending on soil type, vegetation cover, and the local climate, among other variables. Estimating recharge tends to require a variety of data-intensive techniques, ranging from long-term measurement of groundwater levels to complex modeling.
To help estimate recharge across Oregon, researchers are using a customized version of the USGS National Hydrologic Model (NHM).
The NHM uses daily precipitation, air temperature, and the hydrogeologic properties of the landscape to estimate surface runoff, streamflow, and groundwater discharge to streams, among other components of the hydrologic cycle.
One of the ways the NHM is being customized to Oregon is by using base-flow estimates for Oregon’s rivers and streams to calibrate the model to accurately simulate recharge.
Groundwater and surface water interaction
Base flow is the portion of streamflow that does not come directly from runoff of rain and snowmelt. When groundwater levels are higher than the overlying streams and rivers, groundwater discharges to the stream, becoming base flow. Groundwater is a significant source of flow for many of Oregon’s rivers and is especially important for sustaining them during hot, dry months.
Base flow typically has more dissolved minerals and salts than precipitation runoff because it interacted chemically with the rocks and soil it passed through. Water with dissolved salts and minerals can conduct small amounts of electricity that can be measured with specific conductance sensors.
Much like recharge, distinguishing base flow from surface runoff in a stream is difficult. By measuring specific conductance in the stream water, we can get an idea of how much groundwater is contributing to the streamflow. Generally, higher specific conductance values indicate a higher proportion of groundwater in the streamflow, while lower values indicate more surface runoff.
Researchers in Oregon are monitoring specific conductance along with streamflow volumes over time to estimate what portion of streamflow is base flow. When they measure higher specific conductance during dry periods, this indicates that most of the streamflow is supplied by groundwater discharge. During heavy rain events or when the stream contains a lot of snowmelt, specific conductance might drop as surface runoff dilutes the water.
Once base flow estimates and other model components are gathered, scientists will use the Oregon version of the NHM to develop groundwater recharge estimates that can inform the development of water budgets across the state.
This is an active and evolving project that is being tailored to meet the needs of Oregon’s water resource managers. The story continues, stay tuned for updates!