Cold Water Refugia

Stream reach with good overhanging vegetation and undercut banks.

As stream temperatures continue to rise in many of Cook Inlet’s salmon streams in the years ahead, cold water refugia – areas within a stream which are persistently colder than adjacent areas – will be critical to the survival and persistence of salmonids and other fish species. Researchers on other rivers in the Western United States have identified deep pools, overhanging vegetation and undercut banks as potentially important for providing refuge from the warmest temperatures. Stream reaches with groundwater interactions (i.e. springs and seeps) may also result in measurably cooler water. Mapping these cold water habitats is valuable to plan future fisheries research, direct monitoring efforts and protect and restore critical fish habitat as thermal change continues.

 

Inletkeeper Strategies

Overhanging vegetation along the south bank provides shade and cooler temperatures instream.

Starting in 2006, Cook Inletkeeper, in collaboration with the Homer Soil and Water Conservation District and the Alaska Department of Fish and Game, began identifying critical habitat conditions for cool water refugia on the Anchor River. Inletkeeper’s monitoring staff used temperature probes and waded the stream channel to determine spatial variability of stream temperatures. On each transect, and at 9 equally-spaced stations between transects, temperatures were taken at the left bank, center of channel, and right bank. Differences across the transects and stations could indicate a temperature difference related to a specific habitat, such as deep pools, overhanging vegetation, undercut banks or large wood. Other relevant habitat conditions, which included shade, flow rate, channel width, channel depth, solar angle, and aspect, were recorded. Based on this in-stream survey, overhanging vegetation, which provided shade during the mid to late afternoon, was the most significant habitat type for cool water refugia. Stream-side vegetation along stream reaches which flow to the northwest have the greatest potential to provide shade along the SW (or NE facing) bank. Once these critical habitat conditions were determined, the next step was to identify reaches along the lower Anchor River that provide these habitat conditions and to encourage their protection in an effort to improve watershed resiliency to climate change.

Map of high priority parcels on the lower Anchor River.

Now working together with the Kachemak Heritage Land Trust, we have identified 51 private parcels along the lower Anchor River that could potentially provide cool water habitat in the years to come.  This important layer of information has been added to maps the Land Trust uses in the process of identifying conservation priorities for future land trust partnerships.  By providing science-based information for prioritizing conservation of important salmon habitat, Cook Inletkeeper is playing an important role in protecting the Anchor River.

 

Current Work

With support from the U.S. Fish and Wildlife Service to continue this important work, Cook Inletkeeper contracted with Watershed Sciences, Inc. to map cold water habitat using airborne thermal infrared (TIR) imagery along 34 miles of the south fork of the Anchor River.  This exciting technology is an effective method for mapping small-scale temperature patterns in streams.  The TIR imagery provides a snapshot of stream temperatures at the time of the survey. And although temperature values change year-to-year, the cool water refugia remains persistent over time.

Thermal infrared imagery (left) with corresponding aerial image (right) showing cold water inputs (purple) to the mainstem of the Anchor River (orange).

Watershed Sciences personnel hired a local Bell Jet Ranger helicopter and flew the river on June 30th, 2010. The helicopter flew at an altitude of 2,000 feet and the TIR sensors collected images every second which resulted in a 2-foot image resolution. And even in the cool summer of 2010, the location and thermal influence of 18 tributaries, 23 seeps and springs, 11 sloughs, and 9 small side channels and drains is apparent in the imagery.  To learn more about thermal infrared imagery and the results from this work, please check out the completed report here.

The spring on the left contributes colder water as it enters into the main channel of the Anchor River.

With TIR images and GPS in hand, Inletkeeper is out in the field “ground truthing” the data this summer. We are searching out these cold water inputs so we know what they look like along the river. We have discovered springs and seeps that are in fact contributing cold water to the main stem, sometimes as much as 5^oC (9^oF) colder. These areas often are rust colored as the iron-rich groundwater reaches the surface and is oxidized. And in a few cases we have found tributaries adding warmer temperatures. This ground truthing is an important step to validate the TIR images. With on-the-ground confidence that the images accurately reflect thermal conditions, we can look to take this work into new watersheds.