Historically, the groundwater budget was in balance. The average annual recharge is 220,000-250,000 acre feet and the average annual natural discharge is 210,000-240,000 acre feet.

The groundwater budget was in balance until people started using water. The amount of groundwater used by people is the amount that we are out of balance. On average, people are removing about 130,000 acre feet from the basin each year. 

Groundwater users are using (removing) “stored” groundwater, which is water that had been stored in the pore space around sub-surface rocks and sediments for hundreds or thousands of years. This is why we see declining water levels. 

The depth and extent of cones of depression are influenced by the rate and volume of groundwater pumping as well as the surrounding geology. 

The major cones of depression are in the following areas: Weaver Springs, Sunset Valley-Dog Mountain, North of Crane to Windy Point, North of Highway 20 between Rattlesnake and Cow Creeks, and the Central Harney Valley. 

Some of these areas where groundwater levels are declining the fastest (such as Weaver Springs) are where groundwater pumping wells are surrounded by lower permeability rocks and/or sediments that slow water flow to the wells and slows how quickly surrounding water can replenish the pumping area or zone where water is being removed. 

In the Silver Creek and Virginia Valley areas, the declines are spread out over a larger area due to the more permeable geology, which allows the pumping influence to capture and more easily draw groundwater from a larger area.

Groundwater is flowing through various geologic materials at different rates depending on the type of rock and sediment and how permeable it is. 

The geology, the types of rocks and sediments in the basin, varies from place to place, and so the permeability of the groundwater system varies from place to place. That variability affects where groundwater moves, how fast it flows, the rate at which it can be pumped by wells, and the response of the groundwater system to pumping. 

In general, the rocks at high elevation are older, less permeable rocks, meaning that these rocks don’t let much water in and generally don’t yield large quantities of water to wells. Generally speaking, the water that falls at higher elevations does not infiltrate deeply into the rock to recharge the regional groundwater system. Instead, upland groundwater recharge tends to remain shallow and discharges to nearby springs and streams close to where it infiltrates. 

Recharge to the groundwater system happens where the rock is more permeable and also where water is available. Generally speaking, the majority of recharge to the regional groundwater system happens in a few areas in the basin, such as where the Silvies River spreads out onto the basin floor and the northern edge of Steens Mountain. 

Groundwater moves from higher elevation areas in the basin to one of two lower elevation areas. Virginia Valley and Harney Lake were the historic low points in the basin where water eventually flowed to. 

Groundwater that historically flowed towards Harney Lake now flows towards the Sunset Valley/Weaver Springs area because the groundwater use (pumping) has lowered the water table in the Sunset Valley/Weaver Springs area, making it the new “low point” in the basin. 

Groundwater flow paths in the basin can coincide with or differ from the river drainages, depending on location. The groundwater system does not necessarily resemble or mimic the surface water system. 

Groundwater generally moves very slowly, it can take a long time (years, decades, centuries, or more) for water to move in the groundwater system since it has to move through available, interconnected open spaces within rocks and sediments. 

Generally speaking, older groundwater is found deeper in the groundwater system and further away from recharge areas. This water can be thousands or tens of thousands of years old in some places. 

Most of the groundwater in the basin is old, except where it is shallow and near recharge areas.

Shallow, young groundwater was detected where the Silvies River flows into Harney Valley and where at the bottom of Steens Mountain relatively young groundwater is leaving through Virginia Valley.