On behalf of the Mirror Pond Ad Hoc Committee, Steering Committee and Management Board
Q. What is the river bottom gradient between the Colorado Street bridge and the Pacific Power Dam?
Calculated from past and current survey data:
The bed elevation upstream of the Pacific Power dam is 3589.0 feet (average)
The bed elevation downstream of the Pacific Power dam is 3585.0 feet (average)
The top of the dam (impoundment) is 3595.0 feet
The bed elevation below the Galveston Street bridge is 3589.0 feet (average)
The bed elevation below the Colorado Street bridge is 3597.37 feet (average)
The distance between the Colorado Street bridge and the Pacific Power dam is approximately 7300 feet
The average gradient from the Colorado Street bridge to the upstream side of the Pacific Power dam is:
(3597.37-3589.0 = 8.37 feet)/7300 feet = 0.12% (average)
The average gradient from the Colorado Street bridge to the downstream side of the Pacific Power dam is:
(3597.37-3585.0 = 12.37 feet)/7300 feet = 0.17% (average)
Q. Won't creating wetlands at Mirror Pond create a mosquito problem?
Here are a few websites that indicate that healthy wetlands may actually reduce mosquito populations. The first is from the Missouri Department of Natural Resources. The second is from the University of Illinois Extension Service. The third and last is from the United States Environmental Protection Agency.
Q. How much water is flowing through Mirror Pond and how does it change seasonally?
The "Blue Whale Flow Diagram" illustrates variables in flow above and below the Pacific Power Dam throughout the year. The diagram is excerpted from the August, 2006 Deschutes Water Alliance (DWA) final report on "Instream Flow in the Deschutes Basin: Monitoring, Status and Restoration Needs".
Q. How much silt is there in Mirror Pond?
The 1981 Mirror Pond Rehabilitation Study identified (p.28) 352,806 cubic yards of silt and debris for possible removal. This may not have been all the silt present since it was not possible to measure areas where rocks, tree stumps, pageant foundations, and other debris obstructed efforts.
The full cost of removing the 352,806 cubic yards of silt in 1981 was estimated at $1,340,300.00 (p. 32), or $3.79/cubic yard. However, due to funding limitations only 60,000 cubic yards was actually removed in 1984 at a cost of $312,000 or $5.20/cubic yard. Silt was removed at an average depth of 5 feet to 6 feet starting at the Pacific Power Dam and moving south towards the Galveston Bridge. There were only three small areas where silt was not removed due large rocks and other debris that interfered with the dredging equipment; near Coyner Point; just north of the foot bridge on the west side of the river; and near the small islands at the south end of the pond.
The work was paid for by:
Q. What is the problem with Mirror Pond?
Casual observers understand that the Pond is filling in with sediment at an unnaturally rapid rate. (See Mirror Pond Sedimentation Staff Working Paper, June 2006) and Mirror Pond Technical Committee Summary Report for more details. If sedimentation continues unchecked, eventually broad mudflats will characterize portions of the Pond in late summer and fall, raising aesthetic issues for the community.
Q. What is causing the problem of rapid sedimentation?
(Questions and Answers shown below were gathered from City of Bend Mirror Pond Website and other research and are based upon public inquiries, technical reports, and other information gathered in past planning efforts)
Frequently Asked Questions
Increased sedimentation typically occurs behind dams, due to the fact that when water slows, the heavier particles of sediment fall out. The operation of the federally owned Deschutes Project, which stores and delivers irrigation water from the mountain reservoirs to 98,000 acres within the North Unit Irrigation District, Central Oregon Irrigation District and Crook County Improvement District No.1, also has adverse affects on the watershed, resulting in increased erosion of upstream banks. The Project's dominant feature is Wickiup Reservoir, which is managed by the Bureau of Reclamation to provide irrigation water with grain, hay, pasture, mint, potatoes, and seeds being the principal crops. It has been postulated that management of releases from Wickiup reservoir and use of the river upstream of Bend as an irrigation conduit substantially increases sediment loads above those that would occur naturally. Additional contributors to the sedimentation rate could include activities in the Little Deschutes tributary, as well as stormwater discharges within City limits.
* Garvin, William F., 1977; UDWC, 2004; UDWC, 2005; Winzler and Kelly et. al, 1981.
Q. What is going on with the river in Bend?
In general, when the Deschutes River enters the Bend city limits, several historical dams (Colorado Dam, Newport Dam (Pacific Power), Portland Bridge/Tumalo Dam, and North Dam ) result in a wider, shallower river channel that slows flows and decreases the available shade from the streambank canopy. This results in sediment deposition, higher water temperatures, and increased weed and algae growth that conspire against a healthy, sustainable river system.
The Mirror Pond Technical Committee has stressed that understanding the river hydraulics within Mirror Pond is important in achieving a well-conceived project that would increase the periods of time between the pond getting choked with sediment. The City is pursuing the necessary studies to provide that information.
Q. How soon would the Pond lose its character; how soon would we see broad mudflats?
According to the Mirror Pond Technical Committee, a committee of technical experts brought together to discuss these issues at Mirror Pond, the pond will not lose its character for another five to ten years from the spring 2006. This gives us time to plan, gain input, and implement a well-thought out project.
Q. Are there water quality problems in Mirror Pond?
The City is working together with the Upper Deschutes Watershed Council and the Department of Environmental Quality to determine the extent of water quality issues in the Deschutes River through Bend, including Mirror Pond. The City is conducting a 3-year monitoring effort in conjunction with the Upper Deschutes Watershed Council that will provide data on the presence or absence of suspected pollutants on the Deschutes River within the Bend Urban Boundary (Deschutes River Miles 172 and 159).
The Mirror Pond Sedimentation Working Paper provides additional information on water quality issues in Mirror Pond, including pollutants of concern.
In 2010 the City and UDWC completed a baseline ambient water quality report for the Deschutes River and Tumalo Creek.
Q. Has the City ever had to dredge the Pond before?
Yes. Sedimentation first became a major problem in Mirror Pond in the late 1970s and early 1980s. In 1984 the City dredged the Pond. At that time, the project engineer predicted that unless changes were made in the management of upstream flow, the Pond would again require dredging in about 20 years.
It is speculated that Pond sedimentation was not a major problem prior to then likely due to sawmill pond operations that included nearly continual dredging above the Mill Pond Dam at Colorado Avenue.
When the mills stopped floating logs on the mill pond, the last mill closing in 1994, the dredging stopped. That pond area has since been partially filled in and the river thre, adjacent to the Les Schwab Amphitheater, has developed a channel, creating higher stream speed, or velocity, in that reach.
Q. What is the City doing about the problem?
City staff began working with other community members, such as the Upper Deschutes Watershed Council, as early at 2004, to begin to examine the problem and provide education to the City Council. In early 2006, the City prepared a draft working paper defining the problem and outlining a proposed process for City Council consideration.
In Spring 2006, City staff received approval from Council to pull together a committee of technical experts to examine the technical issues surrounding the pond itself. The Mirror Pond Technical Committee has met five times since May 2006. Their work has culminated in a summary paper outlining their recommendations.
At its worksession on March 5, 2007, the Council reviewed this paper and recommendation, commending the work of the Technical Committee, and directing staff to continue working on this effort based on the recommendations of the Technical Committee. Staff was also directed to investigate the ownership associated with the bed and banks of the river in the area of the Pond. We will update this page as more information becomes available.
Q. What is the Mirror Pond Technical Committee?
On May 10, 2006 the City of Bend under the chairmanship of City Councilmember Jim Clinton, hosted the first of five meetings of the Mirror Pond Sedimentation Technical Committee. (See Appendix A of the Summary Report for a list of the Committee members). The purpose of the Technical Committee was to develop a better understanding of the options available for Mirror Pond, and to predict future impacts to help the decisionmakers make decisions based on sound science. The technical committee wanted to outline broad guidelines that were technically feasible and appropriate, within which specific alternatives could be examined and evaluated. The City Council provided a directive to the Committee at the joint June 7, 2006 meeting: "Do not do away with Mirror Pond."
Q. What alternatives are being examined?
The Mirror Pond Technical Committee reviewed several alternatives developed during the initial effort in 2004 to determine if they meet the goals defined by the Committee:
Develop a project that removes sediment and retains Pond while making the Pond more sustainable and healthful than at present to the extent practicable. The summary report describes the potential alternatives considered by the Committee, along with their preferred alternative.
Appendix B of the summary report summarizes this review.
Q. Who will pay for fixing Mirror Pond?
The answer to this question is unclear. The City applied for a federal grant in the spring of 2006 but did not receive any federal money. The City is again applying for federal appropriations in 2007, and is conducting a literature study of other communities with similar situations to determine how they paid for their projects. Any federal funds received would likely require local match funds.
The 1984 dredging project was paid for as follows:
Q. Does the City have the authority to Act?
The City is not a large landowner along the Pond. The largest landowner along the pond is the Bend Metro Park and Recreation District, a separate entity from the City. The main impoundments within Bend are (starting from upstream down): Colorado Dam, Newport Dam (Pacific Power), Portland Bridge/Tumalo Dam, and North Dam. None of these are owned or operated by the City. However, the Pond rests entirely within the City of Bend city limits, and is an important draw for the community, historically positively influencing both the community's sense of well-being along with bottom-line economics.
Q. What is the Timeline to address this problem?
The Mirror Pond Technical Committee conservatively estimates that we have approximately five to ten years from summer 2006 to act before the nature of the Pond as we know it changes to include broad mudflats. This gives us time to complete necessary studies, conduct advanced planning, gather public input, and proceed in approving and implementing a well-planned solution that addresses the main problematic symptom of sedimentation.
The City may also wish to pursue participating in discussions and activities aimed at solving the underlying causes of the rapid sedimentation upstream as well. This timeline will likely be much longer.
Q. How does this effort relate to Bend 2030 planning and implementation?
The components of the preferred project, as outlined by the Technical Committee on page 4 of the Summary report, would help meet several of the community vision elements for a quality environment, as described in the Bend 2030 Community Vision Statement (June 2006). See in particular, Our vision for a Quality Environment, number 3,4, 7, 8, 14; Our Vision for a Strong Community, number 14.
Q. Where can I get more information on this and related topics?