The Sisters are located in a privileged position above the groundwater table in the region.Modified from Lite and Gannett, 2002

Note: When it comes to discussing water, or lack thereof, in central Oregon, there is a wide range of opinions, depending on who is speaking. Not all of these opinions are based on facts. Over the next several weeks, The Nugget will present articles addressing many factors relating to the water supply in the Deschutes River Basin, particularly within Sisters Country. This week we’ll look at some of the basics of water (hydrology) to provide a basic understanding for future articles.

Sisters City residents receive their household water from the municipal water network, which has four wells from which they access water. The Department of Public Works is responsible for this system. Residents outside the city limits depend on their individual or communal wells for water. All wells access groundwater.

Ground water vs surface water

Groundwater is water that collects or flows beneath the earth’s surface, to fill pore spaces in soil, sediment, and rock. It arises from rain and melting snow and ice and is the source of water for aquifers, springs and wells.

The groundwater table is an underground boundary between the soil surface and the area in which groundwater completely saturates the spaces between sediments and fissures in rocks. The saturated zone is bounded from below by impenetrable rocks or sediments. The aquifer from which Sisters City derives its water is a basalt aquifer.

Surface water is the water available above the earth’s surface in the form of rivers, streams, oceans, lakes and wetlands. Surface water is mainly collected from precipitation. However, in the Deschutes River Basin, studies have identified a hydraulic connection (actuated by water pressure) between groundwater and surface water. Groundwater appropriations (wells) have the potential to significantly overlap with surface waters and can significantly reduce stream flows. Likewise, low current flows can reduce the amount of groundwater available to pump from the well.

What is an underground water reservoir?

Aquifers are often identified by the way they were formed. Aquifers are water deposits (usually by water transfer), and glacial aquifers build up by the gradual movement of glaciers. Large aquifer systems may consist of several geological formations, including alluvial and glacial deposits.

Coarse sand and gravel, transported and deposited by fast-moving water, turn into permeable aquifer deposits when buried. It can extend laterally from a few feet to several miles and can be paper-thin up to hundreds of feet.

The Dechot Basin aquifer has been described as a large bowl, with the deep end near the Cascade (and Sisters) Mountains becoming shallow as far as the northeast and Madras. Much of the eastern side of the Cascade Range drains into this bowl, which is lined with large expanses of permeable volcanic rock. When significant annual precipitation collects at higher elevations on this permeable rock, the result is a large regional aquifer system and stream system largely dominated by groundwater, with either springs resulting when the groundwater is high or low at the lower groundwater level. The headwaters of the Metolius and Voul rivers, as well as the springs downstream that feed the Metolius, are examples of those groundwater being released.

When it comes to water, the Sisters location is perfect. Groundwater ridges rise near the Cascade Mountains in the west and Newbury volcano in the south and fall to the northeast and north toward the confluence of the Deshot and Crooked Rivers. The city only needs to dig more than 300 feet to reach the abundant groundwater.

Surface water became the source of irrigation by early farmers and ranchers in Sisters Country and beyond. A large network of open canals carries water throughout the area. Gradually, over the years, a number of these canals were replaced by irrigation wells and ponds. In recent years, irrigation districts have extended the remaining channels to prevent seepage into the ground.

For nearly 100 years, due to those leaky channels, the entire area had an artificially high water level. With pipes, the water table returns to its original normal level, leaving some shallow wells dry, intermittently or permanently.

Increasing demand for water

Demands for water in the region come from all angles – a rapid increase in the region’s population, agriculture, environmental projects, hydropower, business, and entertainment. Additional appropriations for surface water have been closed. In a collaborative effort, a new water bank project by the Deschutes River Conservancy will provide payments to irrigation district customers in central Oregon in exchange for leasing their water to the North Unit for a year. There are many collaborations working towards possible solutions to a variety of water-related issues, but in the case of water, every possible solution can also have unintended consequences.

The effect of climatic cycles

In addition, the current climate cycle has the area undergoing drought, so the amount of melting ice in the mountains is currently reduced, leaving less ground and surface water to meet the increasing demands. Glaciers are an integral part of the ecosystems and economies of central Oregon, and they are disappearing, likely due to regional climate change. There is now a new, unnamed lake on the sides of the North Sister where the Thayer Glacier used to flow.

Some recent modeling performed in the Upper Deschutes Basin, in collaboration with the Oregon Water Resources Department (OWRD), is exploring the impact of well location and geological structure on current capture by pumping wells. The OWRD report states:

Wells were simulated at three locations within a 12-mile area near known groundwater drainage areas and traversed through a regional rift zone. The simulations indicate that the magnitude and timing of flow capture from pumping is largely controlled by the geographic location of the wells. , but malfunctions can have a significant impact on increasing pumping pressures.”

Sisters Rift Zone

In addition to the regional flow pattern from higher groundwater elevations near the mountains, groundwater levels in the central part of the Upper Deschutes Basin range from several feet to several hundred feet below the surface, indicating that the current reaches the central part of the basin. The basin is separated from the regional groundwater flow system by an unsaturated zone, possibly along the Sisters Fault Zone that extends northwest from the upper Deschutes Basin to south-central below the Sun River. Some scholars believe that the fault may be responsible for the disruption of the equal flow of groundwater to the east from the higher western elevations.

Long-term groundwater level records in the central part of the Upper Deschutes Basin have shown that some areas are experiencing a continuous drop in the groundwater level, particularly in an area extending from the vicinity of Bend, northward toward Lake Billy Chinook, and northeast toward Redmond and Powell. bot. The Deschutes Basin Groundwater Dilution Program allows limited and additional groundwater development using the mitigation to offset the effects on the state’s scenic waterways and selected broadcasting rights.

Sister wells area is drying up

In Sisters Country, last summer, there were reports of wells drying up, and the need to either lower the pump or drill a completely new well. Some of the reports came from properties in Harrington Loop, Gold Coach Road, and around the Cloverdale area, as well as Terrebonne and Redmond. It is important to remember that most wells, depending on conditions, have a life of 30 to 50 years and most well pumps typically last anywhere from eight to 15 years.

In later articles, we will explore a long-time sisters’ experience with wells, what to do if your well runs dry, as well as water as it relates to growth, development and the political umbrella for more regulated uses, higher costs, etc.