Stream Flows

Seasonal stream flows in the Little Deschutes are substantially different from what would naturally occur.  The chart below shows the estimated median natural stream flow by month as a green dashed line.  Actual stream flows (median discharge in cubic feet per second) are shown in light blue.  Actual flows are lower than natural in October through June and higher than natural in the summer months of July through September. 

(Figure 4 and Table 18 are from the August 2006 final report of the Deschutes Water Alliance on Instream Flow in the Deschutes Basin, prepared by the Deschutes River Conservancy under a grant from the Bureau of Reclamation.  The report is available at http://www.deschutesriver.org/Water_Summit/Summit_InstreamFlow/default.aspx )

The photo on the left shows the river at high water in May 2008 (with  flooding on the wetlands beyond the river).  The photo on the right shows the river at low water in November.

Actual stream flows differ from natural flows because water is stored in Crescent Lake in the fall, winter, and spring.  Crescent Creek, which empties from Crescent Lake, is the largest tributary of the Little Deschutes.  Even after Crescent Lake Dam was first built in 1922, there may have been less water stored behind it in the 1920's and 30's than now and stream flows may have been closer to natural.  Grace Vandevert reports, "We had to tie a boat to the back porch when the water got very high a couple of times.  Almost the whole meadow below the house (just to the northwest in that first bend of the river) would be flooded. Dad had to still milk the cows that were across the footbridge in the corral - - and he couldn't wade in the water.  I doubt the footbridge was even very safe with all that water.  It didn't last too long - -maybe two or three days and then receded."

The Deschutes River Conservancy has established target monthly flows that it believes will be most beneficial for the Little Deschutes and for the Deschutes River into which it drains.  The target flows (shown in dark blue in the chart above) are all equal to or less than the estimated natural flows.  The targets assume that some water will be stored and then released later on but the flow will be more even over the year.  Actual flows are significantly different from the targets (i.e. higher in April through September and lower in October through March).

Stream Flow Impact on Fish Habitat

The Deschutes Subbasin Plan reports that a loss of riparian habitat and a reduction in the complexity of the instream habitat are factors that limit fish production in the Little Deschutes subbasin.  The plan suggests that flow alterations have contributed to these problems.  It appears to the authors of the Vandevert Stewardship Plan that the lack of naturally high spring floods to dig the channel deeper has made the river wider and shallower – and therefore more susceptible to heating up from the rays of the sun.  The lack of spring floods has also left sediment between river bottom rocks, making the river less suitable for spawning.  See “Trout Habitat”, the next page after this in the Riparian Section of the Stewardship Plan.  The Deschutes Subbasin Plan is available at http://www.nwcouncil.org/fw/subbasinplanning/

Flow Impact on Temperature

As evaluated by the Deschutes Water Alliance, the most important problem is not that the seasonal flows are too great or too little, but that the storage of water in Crescent Lake during the fall and winter allows the water to warm up before it is released into the river in the spring and summer.  The water is stored and released to supply the Tumalo Irrigation District which owns the rights to the water.

Opinions on the ideal water temperature for trout range from 57 degrees to 62 degrees Fahrenheit, although trout can adapt to a wide range of temperatures if the temperature does not change too rapidly.  Over 70 degrees trout are stressed and at 80 degrees they are likely to die if they cannot find cooler water deep in the river.  At the LAPO gauge upstream near La Pine, the water temperature reached 80 degrees only once in the last five years, on July 24, 2006.  This would suggest that, while the water temperature is not ideal for trout, it is not an insurmountable barrier to their surviving in the river.  Maximum water temperatures by year were as follows:

Little Deschutes Maximum Water Temperature by Year – LAPO Gauge

For historical measurements of stream flow and water temperature at the LAPO gauge, see www.usbr.gov/pn-bin/arcread.pl?station=LAPO

Dissolved Oxygen

Oxygen dissolved in the water is essential for the survival of fish, all other water animals, and zooplankton.  Oxygen also improves the odor, clarity, and taste of water.  The Little Deschutes is listed by the EPA from its mouth up to well above the ranch for low levels of dissolved oxygen year round.  Water storage in Crescent Lake from late September until April or May is a major factor in increasing the water temperature (for which the river is federally listed for 50 to 73 miles above the ranch).  Higher water temperatures are a factor in causing low dissolved oxygen levels. 

Restoring Stream Flows

Partnering with federal, state, and regional agencies – and with many non-governmental organizations - the Deschutes River Conservancy (DRC) is leading efforts to restore stream flows and improve water quality in the Deschutes Basin.  Principal programs are water conservation (e.g. reducing leaks in irrigation canals), water purchase, water leasing, and habitat enhancement.  Through the Deschutes Water Alliance Bank, the DRC enables farmers to keep the right to maintain their water rights while leaving the water in the river or leasing it to other water users.  This means that less water needs to be stored for irrigation, average and maximum water temperatures decrease, and stream flows can more closely approximate ideal and natural patterns.  The DRC programs are working well but have barely begun to impact the overall river system.

In 2008 the Tumalo Irrigation District, which owns the rights to much of the water flowing out of Crescent Lake, agreed with the state to forego 8 cfs (cubic feet per second) of this water during the irrigation season (April 1 through October 31). This means the Oregon Water Resources Department (OWRD), which actually controls the release of water from Crescent Lake Dam, will have about 145 million cubic feet of water each year to release when it sees fit during the irrigation season. Oregon Fish and Wildlife, which advises (OWRD), expects to request most of the water in July through October with possibly a little in April. The objectives of Fish and Wildlife are to provide adequate water for fish during low water periods and to even out flows as much as possible in order to stabilize streambanks and provide as stable an environment as possible for fish. The "new" water will increase average stream flows in July through October by roughly fifteen percent.

Continue to Trout Habitat
Return to Stewardship Plan Table of Contents