Double O Springs on the Malheur National Wildlife Refuge

Springs occur throughout the Malheur NWR ranging from the southern end of the Blitzen Valley to the Double-O. Springs on the Refuge provide stable permanent high-quality sources of water for ponds and marsh areas and in some cases, such as on the Double-O, meadow irrigation. Spring pools provide an abundance of submergent vegetation and aquatic invertebrates supporting a diverse assemblage of fish and other aquatic species and wildlife such as waterfowl, wading marsh-birds, and shorebirds. Spring habitats are important to native avian and amphibian species for breeding, feeding, and over-winter refugia. 

Springs on the Refuge are supported by the groundwater aquifers. The groundwater system underlying the Malheur Lakes basin occurs at two distinct levels. There is the shallow unconfined aquifer that occurs in the upper alluvial fill, commonly within 20 feet of the ground surface. The shallow aquifer is fed by infiltration of precipitation and streamflow on the valley floor. The shallow water table fluctuates seasonally from 3 to 4 feet below the surface during spring months and 8 to 10 feet in fall months. 

The second and deeper aquifer is confined and occurs in the lower part of the Quaternary fill and the underlying Tertiary rocks. Groundwater in this aquifer occurs in porous layers such as gravel, sand, or porous rock, and is confined by impermeable clay in the upper part of the Quaternary fill. The confined aquifer is fed by infiltration of precipitation, streamflow in the uplands, and infiltration of streamflow where the waterways enter the alluvial basin floor. This is generally within 50 feet or less of the surface. Pressure in the deeper confined aquifer causes water to leak upward to the shallow aquifer. 

A number of springs on the Refuge are located in lowland areas around the margins of Malheur, Mud, and Harney Lakes in addition to several large springs on the Double-O. The current combined discharge from the Double-O springs is approximately 40 CFS and is used to maintain water levels in marsh ponds year-round and for irrigation of meadows during spring and summer. Spring discharge not utilized for marsh ponds and meadow irrigation empties into Harney Lake through the Silver Creek channel. The ability of Refuge springs to provide high-quality aquatic habitat has been compromised by climate change, invasive species, and loss of deeper groundwater. 

Written by Jeff Mackay, Refuge Manager/Project Leader, Malheur NWR

Image courtesy of https://malheurfriends.org/refuge-history/