Reservoir Management and Research
There are a number of management and research projects in and near Chester Morse Lake.
The primary purpose of this component of the HCP is to evaluate the potential for using water stored below the natural gravity outlet of Chester Morse Lake (termed “dead storage”) and to assess potential environmental impacts of this significant operational change in reservoir management.
- Water Storage Challenges in the Cedar River
- Engineering, Water Quality, and Economic Studies
- Bull Trout Spawning Impedance Assessment Study
- Bull Trout Spawning Passage Assistance Plan
- Bull Trout, Pygmy Whitefish and Rainbow Trout Studies
- Delta Plant Community Monitoring
- Common Loon Nesting Habitat Monitoring
Water Storage Challenges in the Cedar River
The Overflow Dike looking toward Masonry Pool
The reservoir complex in the Cedar River Municipal Watershed consists of two bodies of water connected by a narrow outlet channel. Water from the larger body, Chester Morse Lake, flows through the outlet channel, passes through (or over) the Overflow Dike (a small control structure) and into the Masonry Pool, which is the smaller body of water immediately upstream of the Masonry Dam.
When water levels are highest, the two parts of the system form a continuous reservoir, controlled by the Masonry Dam. But when water levels decline (typically through summer and fall), the two bodies of water can be operationally separated (i.e., Masonry Pool lower than Chester Morse Lake), using the Overflow Dike as a secondary control structure between the two.
Under drought conditions the level of Chester Morse Lake may decline to levels at which gravity flow at the outlet from the lake is not sufficient to meet demand for municipal water supply or provide instream flows adequate to protect fish in the lower reaches of the river. In order to provide enough water in the Cedar River to meet water supply and instream flow needs under these conditions, water must be pumped from deeper portions of the main lake into the Masonry Pool. This block of water is currently accessible by use of a temporary, barge-based pumping system and only deployed during emergency drought conditions.
In order to have more flexibility and reliability in using water stored in Chester Morse Lake, the City is evaluating the development of a permanent, land-based pumping system that would more readily allow use of “dead storage” water below the lake’s natural outlet.
Engineering, Water Quality, and Economic Studies
SPU is conducting studies to assess the feasibility and practical aspects of building and implementing a permanent pumping system for moving water from Chester Morse Lake to the Masonry Pool when the water level in the lake falls below the natural outlet, sometimes called “permanent dead storage.” These include engineering and water rights evaluations, cost estimates, yield analyses, and water quality assessments.
Bull Trout Spawning Impedance Assessment Study
Cedar River delta at Chester Morse Lake during very low water levels.
Bull trout, pygmy whitefish, and rainbow trout all migrate into tributaries of Chester Morse Lake to spawn during fall, winter, and spring months, respectively. If water levels are excessively low during any of these spawning periods, fish could be adversely affected by impeded upstream passage or warm water temperatures at low stream flow levels.
The broad delta fans of the Cedar and Rex rivers have a steep face, or foreset, at their downstream edge where the streams flow into the lake. If the water level of the lake drops below the top of the foreset, the streams flowing down the steep slope of the now exposed foreset may become impassable to fish swimming upstream to spawn. Such a situation could potentially develop under drought conditions when lake levels can become extremely low.
A geomorphological field investigation was performed in order to better understand and assess whether the configuration of the delta fans, particularly the steep delta foresets, might present a partial or complete physical barrier for spawning fish moving into lake tributaries. This study assessed the current geomorphological characteristics of the delta fan, including topography, slope of foreset, and type and depth of substrate materials. Based on this information, the potential for a passage barrier occurring under various fill and drawdown regimes and stream flow conditions was evaluated. The study found that, initially, downcutting could be a primary cause of barrier formation (i.e., steepen the foreset); however, stream flows could subsequently reconfigure the channel, thereby reducing the foreset gradient and restoring passage.
Results from the study (Chester Morse Spawning Impedance Study pdf ) indicate that the formation of such a barrier in any given year is a possibility, but there is only a small likelihood of this barrier persisting on either the Cedar or Rex delta in successive years. The interaction of extremely low lake levels and low volume or velocity streamflow within the spawning timeframe has the potential to create a barrier on either river system until streamflow increases sufficiently to breach or reduce the slope of such a physical passage barrier, presumably via continued downcutting action.
For more information, contact:
Dwayne Paige
(206) 233-1517
dwayne.paige@seattle.gov
Bull Trout Passage Assistance Plan
In addition to the geomorphology study described for the Bull Trout Spawning Impedance Assessment, other information is being collected to determine whether or not a bull trout passage assistance plan will be developed to address fish passage when dead storage is being utilized. Several HCP studies are assessing fish behavior and movements in the lake and tributaries, and additional geotechnical information is being collected as part of the planning and design phase of the proposed, land-based pumping system currently under development.
The results of these studies will be used to assess possible impacts on adfluvial fish populations from use of dead storage. If the combined results of these studies indicate that either the present or potentially altered morphology of the delta foresets at low lake levels poses a significant barrier to bull trout during spawning migrations, the City will develop a bull trout passage assistance plan. The assistance plan can be implemented when the reservoir level is extraordinarily low, whether or not the dead storage project is in operation.
For more information, contact:
Dwayne Paige
(206) 233-1517
dwayne.paige@seattle.gov
Bull Trout, Pygmy Whitefish and Rainbow Trout Studies
A pygmy whitefish spawning swarm in Cedar River above Chester Morse Lake.
Concurrent studies of bull trout, rainbow trout, and pygmy whitefish behavior and movements are being conducted in the reservoir and in selected streams. These three species occur together in the reservoir complex and tributary streams. Bull trout are federally listed as threatened. Pygmy whitefish are a major prey species for bull trout, and little is known about their ecology. Rainbow trout (especially younger age /size classes) provide an alternative food source for bull trout. These studies are providing information on species distribution and life history, seasonal movement patterns, spawning behavior, response to water temperatures in the reservoir system, effects of inundation on egg and alevin survival (bull trout), and growth and productivity for each of these species.
Such studies provide information for interpretation of fish behavior in the reservoir system under current conditions and will also form the basis for predicting potential impacts of future changes in operating regimes, such as the use of dead storage with the implementation of a permanent pumping system. The information being provided by these investigations, as well as future research and monitoring efforts, will serve as an invaluable resource to better inform SPU biologists and water managers on the dynamic inter-relationships between adfluvial fish species and reservoir management.
For the unique spawning movements and behavior of bull trout, view the poster (pdf), presented at the American Fisheries Society Conference in September 2011.
For more information, contact:
Dwayne Paige
(206) 233-1517
dwayne.paige@seattle.gov
Delta Plant Community Monitoring
Transition of the Cedar River delta plant community from sedge and shrub-dominated to deciduous forest.
If the Cedar permanent dead storage project is implemented, seasonal fill and drawdown regimes and other periodic water level fluctuations in the reservoir will change relative to current operational guidelines. Higher lake levels as a result of greater water storage in the reservoir are another possible change. Such operational changes in reservoir levels management could significantly affect plant communities on the deltas of the Cedar and Rex rivers and smaller tributaries and in perimeter areas of the Masonry Pool. The deltas support an extensive and diverse wetland plant community system that is important habitat for a variety of flora and fauna.
As part of the Cedar permanent dead storage project evaluation, the City is monitoring changes in species composition and distribution of delta plant communities, evaluating effects of past reservoir management on the delta plant community characteristics, and modeling the potential effects of new reservoir operating regimes.
Based on the results of these modeling exercises, more informed decisions can be made as to the need for additional future monitoring of these delta plant communities, given that reservoir operating regimes may change substantially if use of dead storage becomes more frequent.
For more information, contact:
David Chapin
(206) 615-0839
david.chapin@seattle.gov
Common Loon Nesting Habitat Monitoring
A loon nesting platform about to be deployed.
The City is documenting changes over recent decades in the distribution and availability of suitable nesting habitat for common loons in the reservoir complex. This information will be used to evaluate the potential impacts to nesting habitat conditions that may result from future changes in reservoir operating regimes (e.g., use of dead storage, increased fill levels). The study will determine if impacts to vegetation, such as recession and reestablishment of willow vegetation, might have potential negative impacts to loon nesting habitat and behavior. Common loon nesting surveys are conducted annually, and if prevailing reservoir levels and seasonal timing are conducive to favorable nesting conditions, SPU staff deploy artificial nesting platforms.
For more information, contact:
Dwayne Paige
(206) 233-1517
dwayne.paige@seattle.gov