In response to increasing groundwater demand and declining groundwater levels in the Harney Basin of southeastern Oregon, the U.S. Geological Survey and Oregon Water Resources Department conducted a groundwater-availability study during 2016–22. Read to learn about the key findings
Groundwater in the Harney Basin
When groundwater in the Harney Basin is pumped, the aquifer can produce substantial amounts of water in some areas but little amounts in others. More- and less-productive areas are determined by underlying rocks and sediments, and the amount of groundwater recharge and discharge. Like a stream, groundwater flows from higher to lower elevations, from recharge areas - water entering the system- toward discharge areas - water exiting the system.
In Harney Basin, the main groundwater-recharge processes are infiltration of rain/snowmelt in higher-elevation uplands such as the Steens Mountain and infiltration of surface water in lower-elevation lowlands such as the area between Burns and Malheur Lake. A lesser amount of upland groundwater exits by direct evapotranspiration (ET) from wetland vegetation. No evidence of any substantial movement of groundwater into Harney Basin from surrounding basins was found.
Upland groundwater recharge and discharge
Groundwater recharge is largest in the uplands—however, the rocks that underlie most upland areas limit groundwater flow. Most upland rocks have low permeability. Because of low permeability, groundwater-flow paths in upland areas generally are short and shallow. More than 80 percent of water that recharges the upland groundwater system discharges to nearby streams and springs rather than flowing deep underground. This upland groundwater discharge is crucial to maintaining flow in streams, springs, wetlands, and meadows during the dry summer months. A portion of the groundwater exiting to upland streams eventually flows as surface water to the lowlands where it sustains wetlands (such as the Malheur National Wildlife Refuge), is diverted for irrigation, or seeps into the ground recharging the lowland groundwater system.
Lowland groundwater recharge and discharge
The lowland groundwater system in Harney Basin is mostly recharged by infiltration of surface water through lowland stream channels and flooded areas (irrigated and natural). Most lowland recharge from surface water occurs during the spring snowmelt, although seepage in lesser amounts occurs year-round from perennial stream channels and flooded wetlands. Surface-water infiltration provides about two-thirds of the recharge to the lowland groundwater system. Deep groundwater inflow from the uplands provides the other one-third. The amount of precipitation falling in the lowlands is not a significant source of groundwater recharge.
Natural discharge of groundwater in the lowlands occurs primarily through ET by (1) deep-rooted dryland plants such as greasewood and salt grass, (2) wetland vegetation, and (3) springs and seeps. A substantially smaller amount of groundwater exits as groundwater flow into the Malheur River Basin to the east.
Groundwater discharges through pumping in upland and lowland parts of Harney Basin. In the uplands, the volume of groundwater removed through pumping (pumpage), represents an exceedingly small portion of the total groundwater discharge. In the lowlands, however, pumpage, primarily for irrigated agriculture, is the largest source of groundwater discharge. In the lowlands, pumpage is about 1.2 times greater than natural discharge.
Groundwater Budget
A groundwater budget accounts for water that enters and exits a groundwater system. Prior to groundwater development in the Harney Basin, the groundwater budget was in balance, meaning the amount of groundwater exiting to streams, springs, and native plants was roughly equal to the water entering the system through precipitation and surface-water infiltration. When the system is in balance, water levels in wells generally fluctuate around a long-term average value and fluctuations reflect natural cycles of wetter and drier conditions.
The Harney Basin upland groundwater budget is minimally affected by groundwater development and generally represents the budget of the natural system. The lowland groundwater budget represents a combination of natural conditions and human activity.
Imbalance in the lowland groundwater budget
The Harney Basin groundwater budget in the lowlands is substantially out of balance. Total groundwater exiting the lowlands (283,000 acre-feet per year) exceeds recharge to the lowlands (173,000 acre-feet per year) by 110,000 acre-feet per year. The imbalance is largely a result of pumping for irrigated agriculture, which accounts for 95 percent of all groundwater use in Harney Basin. Groundwater pumped for irrigation tripled during 1991–2018, increasing from 51,000 acre-feet per year to about 150,000 acre-feet per year. The imbalance in the groundwater budget is why groundwater levels have declined in many areas of the Harney Basin lowlands.
Groundwater-level declines in Harney Basin
Groundwater levels in the Harney Basin fluctuate seasonally and over multi-year periods. Fluctuations reflect natural variations in groundwater recharge and discharge due to seasonal or multi-year cycles of wetter and drier conditions and warmer and cooler temperatures. In some areas of Harney Basin, particularly in the lowlands, groundwater-level fluctuations are largely the result of groundwater pumping.
Groundwater levels typically reach their highest in the late winter or early spring because of (1) the weight of ponded snowmelt on the surface and re-wetting of soils in the lowlands, (2) recharge from winter precipitation and runoff, and (3) recovery from irrigation pumping as groundwater moves in from adjacent areas of the groundwater system. Groundwater levels decline during summer as groundwater is removed from the system through ET and by pumping.
When groundwater pumpage consistently exceeds groundwater recharge, year-to-year groundwater-level declines develop as water is removed from storage in the groundwater system. In the Harney Basin, the nature of groundwater-level declines depends on:
(1) the number of wells and intensity of pumping, (2) the proximity to recharge areas and their respective recharge volumes, and (3) the permeability of rocks and sediments in and around pumping locations.
Ancient Groundwater
Most of the groundwater beneath the Harney Basin lowlands was recharged thousands of years ago (pre-modern). Analyses of stable isotopes of water, tritium, and carbon-14 in water samples from wells, springs, and streams indicate that most of the lowland groundwater was recharged about 30,000–5,000 years ago. Most lowland groundwater in Harney Basin was recharged when the climate was cooler and wetter than it is today. Groundwater recharged after 1953 (modern) generally is limited to a thin, shallow zone beneath lowland recharge areas. These recharge areas include stream channels, floodplains, flood-irrigated fields, and flooded wetlands. Little modern recharge circulates through the lowland groundwater system and most lowland wells are extracting ancient, pre-modern water. Lowland areas with the largest groundwater-level declines receive little or no modern recharge, which contributes to the continued growth and extent of their declines.
In response to increasing groundwater demand and declining groundwater levels in the Harney Basin of southeastern Oregon, the U.S. Geological Survey and Oregon Water Resources Department conducted a groundwater-availability study during 2016–22. Read to learn about the key findings
Groundwater in the Harney Basin
When groundwater in the Harney Basin is pumped, the aquifer can produce substantial amounts of water in some areas but little amounts in others. More- and less-productive areas are determined by underlying rocks and sediments, and the amount of groundwater recharge and discharge. Like a stream, groundwater flows from higher to lower elevations, from recharge areas - water entering the system- toward discharge areas - water exiting the system.
In Harney Basin, the main groundwater-recharge processes are infiltration of rain/snowmelt in higher-elevation uplands such as the Steens Mountain and infiltration of surface water in lower-elevation lowlands such as the area between Burns and Malheur Lake. A lesser amount of upland groundwater exits by direct evapotranspiration (ET) from wetland vegetation. No evidence of any substantial movement of groundwater into Harney Basin from surrounding basins was found.
Upland groundwater recharge and discharge
Groundwater recharge is largest in the uplands—however, the rocks that underlie most upland areas limit groundwater flow. Most upland rocks have low permeability. Because of low permeability, groundwater-flow paths in upland areas generally are short and shallow. More than 80 percent of water that recharges the upland groundwater system discharges to nearby streams and springs rather than flowing deep underground. This upland groundwater discharge is crucial to maintaining flow in streams, springs, wetlands, and meadows during the dry summer months. A portion of the groundwater exiting to upland streams eventually flows as surface water to the lowlands where it sustains wetlands (such as the Malheur National Wildlife Refuge), is diverted for irrigation, or seeps into the ground recharging the lowland groundwater system.
Lowland groundwater recharge and discharge
The lowland groundwater system in Harney Basin is mostly recharged by infiltration of surface water through lowland stream channels and flooded areas (irrigated and natural). Most lowland recharge from surface water occurs during the spring snowmelt, although seepage in lesser amounts occurs year-round from perennial stream channels and flooded wetlands. Surface-water infiltration provides about two-thirds of the recharge to the lowland groundwater system. Deep groundwater inflow from the uplands provides the other one-third. The amount of precipitation falling in the lowlands is not a significant source of groundwater recharge.
Natural discharge of groundwater in the lowlands occurs primarily through ET by (1) deep-rooted dryland plants such as greasewood and salt grass, (2) wetland vegetation, and (3) springs and seeps. A substantially smaller amount of groundwater exits as groundwater flow into the Malheur River Basin to the east.
Groundwater discharges through pumping in upland and lowland parts of Harney Basin. In the uplands, the volume of groundwater removed through pumping (pumpage), represents an exceedingly small portion of the total groundwater discharge. In the lowlands, however, pumpage, primarily for irrigated agriculture, is the largest source of groundwater discharge. In the lowlands, pumpage is about 1.2 times greater than natural discharge.
Groundwater Budget
A groundwater budget accounts for water that enters and exits a groundwater system. Prior to groundwater development in the Harney Basin, the groundwater budget was in balance, meaning the amount of groundwater exiting to streams, springs, and native plants was roughly equal to the water entering the system through precipitation and surface-water infiltration. When the system is in balance, water levels in wells generally fluctuate around a long-term average value and fluctuations reflect natural cycles of wetter and drier conditions.
The Harney Basin upland groundwater budget is minimally affected by groundwater development and generally represents the budget of the natural system. The lowland groundwater budget represents a combination of natural conditions and human activity.
Imbalance in the lowland groundwater budget
The Harney Basin groundwater budget in the lowlands is substantially out of balance. Total groundwater exiting the lowlands (283,000 acre-feet per year) exceeds recharge to the lowlands (173,000 acre-feet per year) by 110,000 acre-feet per year. The imbalance is largely a result of pumping for irrigated agriculture, which accounts for 95 percent of all groundwater use in Harney Basin. Groundwater pumped for irrigation tripled during 1991–2018, increasing from 51,000 acre-feet per year to about 150,000 acre-feet per year. The imbalance in the groundwater budget is why groundwater levels have declined in many areas of the Harney Basin lowlands.
Groundwater-level declines in Harney Basin
Groundwater levels in the Harney Basin fluctuate seasonally and over multi-year periods. Fluctuations reflect natural variations in groundwater recharge and discharge due to seasonal or multi-year cycles of wetter and drier conditions and warmer and cooler temperatures. In some areas of Harney Basin, particularly in the lowlands, groundwater-level fluctuations are largely the result of groundwater pumping.
Groundwater levels typically reach their highest in the late winter or early spring because of (1) the weight of ponded snowmelt on the surface and re-wetting of soils in the lowlands, (2) recharge from winter precipitation and runoff, and (3) recovery from irrigation pumping as groundwater moves in from adjacent areas of the groundwater system. Groundwater levels decline during summer as groundwater is removed from the system through ET and by pumping.
When groundwater pumpage consistently exceeds groundwater recharge, year-to-year groundwater-level declines develop as water is removed from storage in the groundwater system. In the Harney Basin, the nature of groundwater-level declines depends on:
(1) the number of wells and intensity of pumping, (2) the proximity to recharge areas and their respective recharge volumes, and (3) the permeability of rocks and sediments in and around pumping locations.
Ancient Groundwater
Most of the groundwater beneath the Harney Basin lowlands was recharged thousands of years ago (pre-modern). Analyses of stable isotopes of water, tritium, and carbon-14 in water samples from wells, springs, and streams indicate that most of the lowland groundwater was recharged about 30,000–5,000 years ago. Most lowland groundwater in Harney Basin was recharged when the climate was cooler and wetter than it is today. Groundwater recharged after 1953 (modern) generally is limited to a thin, shallow zone beneath lowland recharge areas. These recharge areas include stream channels, floodplains, flood-irrigated fields, and flooded wetlands. Little modern recharge circulates through the lowland groundwater system and most lowland wells are extracting ancient, pre-modern water. Lowland areas with the largest groundwater-level declines receive little or no modern recharge, which contributes to the continued growth and extent of their declines.