Mirror Pond Options

Natural Succession: A Management alternative for Mirror Pond if the current Dredge proposal is not implemented.

In an earlier communication I presented my arguments against public funding of the proposed dredging of Mirror Pond. In this communication I will present one perspective on the future of the pond if dredging is not implemented. It can be termed management for natural succession. Part II of this communication will illustrate a possible integrated strategy with fish passage for the pond based on natural succession.

I) Natural Succession.  What is this? In a river that has been dredged, predictable changes follow. Initially there is rapid accumulation of sediment in areas of slowing current where the sediment carrying capacity of the flowing river drops (areas that were dredged). Over years this accumulation slows to the point of minimal further sediment accumulation while channels of more rapid current become defined which carry sediment downstream. These changes occur more and more slowly until the river finds a natural balance. As this occurs aquatic and riparian vegetation finds a footing, insects and other aquatic organisms proliferate, water quality improves and fish and wildlife prosper. These beneficial developments can be accelerated by judicious plantings. This option requires minimal funding and does not require private land owner’s permission; it is simply letting nature take its course as it has for 35 years since the last dredging in 1984.

Some history. The management option of allowing Mirror Pond to find stability through the natural process of succession has received minimal attention in the many studies, discussions, ad hoc committees, Bend Parks and Rec and City Council proceedings dating back to the early 1980s. Clearly there has been an embedded bias for dredging based management strategies.

Arguably however the successional option for managing Mirror Pond is very viable. Let us consider that further.

A current perspective. Consider first the Old Mill log pond above Colorado established by a dam built in 1915. What has happened over the subsequent 103 years? Google Earth photos of 7/27/2018 are revealing. What we see are small wetlands just above the dam (Old Mill log pond 1), and small areas of riparian vegetation above that (Old Mill log pond 2). Siltation has created stable shallow areas upstream. There is a clean river with riparian vegetation. Google Earth photos show large numbers of inner tubers floating here in bliss (Old Mill log pond 3). Is this not a window into a future Mirror Pond? If we allow Mirror Pond to evolve as the Old Mill log pond has (the successional process), what could we expect?

We are 35 years into successional evolution since the last dredging in 1984. Google Earth photos provide further insight. Since 2003 we have what appear to be stable shallow areas of the river and defined primary flow channels (see dated photos). Nor can it be argued that we are at imminent risk of losing the “iconic” pond views as evidenced by photos from January 12, 2019; no mud banks are seen even at the low winter pool levels. It would be reassuring to have quantitative measures as to future sedimentation. In fact, a report to the Mirror Pond management Committee on 4/30/2013 suggests we are nearly at a stable state for sedimentation in the pond. But experts on this caution against predictions given complexities of sedimentation in any given place and time. Empirical observation as I have presented seems to be the final arbiter.

Succession to date suggests we will have a pond view of blue water and historic iconic views without dredging, although it might not match historic views pixel for pixel. If some areas of pond bottom emerge above normal water levels, they can be vegetated with attractive wetland plantings. As nature unfolds, we can tweak pond characteristics if needed with modest interventions. While the “designer dredge” concept captured public support in the public proceedings of 2013-2015, technical issues prevented further implementation of that as conceived. However, the natural succession management strategy allows for adaptive management as we experience empirically the evolution of the pond. Features of the creative thinking behind the “designer dredge” concept could well be implemented. That is an attractive option.

The new pond views could well be preferred by many to the historic view.



The Old Mill log pond, 2018

Google Earth photos show Mirror Pond has stable shallow areas and primary river channels over the past 16 years.

In conclusion, the management strategy of natural succession offers an attractive potential future management strategy for the pond. Why when or how did it get dropped from current considerations?

In point of fact, the currently proposed dredging is the B1 option considered in the Visioning Project; it was dropped for lack of support. And before that a panel of community leaders rejected the current proposal in 2013; a “replay of the 1984 dredge and walk away” intervention was rejected, but in fact that is what the current dredging proposal is. By what process did it now become the intervention of choice?

Recent Funding Committee and Council discussions have repeatedly brought up the idea that too many years have passed without resolution of the issue; that we need to act now to put this behind us. It is understandable that many are frustrated by discussions and studies spanning years. But it seems clear that actions were deferred on prior occasions because proposed actions did not find sufficient support, i.e. were flawed and inadequate. Rather than act out of frustration, inadequacies of prior evaluations and proposed solutions should be fully understood.

The public expects and should demand that appropriate evaluation continue until a solution is proposed that passes muster by stakeholders; the residents of Bend.  There is no justification for rushing into dredging at this time. There is plenty of time to get this right.

II) An Integrated Solution Alternative based on Natural Succession.

In the discussion of natural succession reference was made to prior public processes focused on the future of Mirror Pond. It seems clear that the public desires a more holistic, if you will, strategy for managing the pond.

Returning to the Mirror Pond Visioning Project, one component of the preferred alternative is in fact being implemented by Bend Parks and Rec. That is the trail and bank enhancement project, estimated to cost more than $6M when completed. It is considered a major component of the “Enhance Recreation” goal.

Next let’s consider fish passage, also one of the 5 community goals. The value of this hardly needs exposition; it is so widely accepted that there are laws mandating when dams must include fish passage provisions. That the Pacific Power dam has been exempted is a controversy beyond the scope of this essay. However, we can emphasize one point which is derived from the 1995 FERC Environmental Assessment referred to elsewhere.

In the 1995 FERC EA, fishery issues were addressed in detail. One aspect of that evaluation was economic. ODFW estimated that restoring passage at the dam would create a viable recreational fishery with economic value of ~ $700,000 annually (inflation adjusted to 2018 dollars). It was noted then that factors limiting the value of this option were the lack of passage at the North Union irrigation diversion just downstream from the PacifiCorp dam and the low summer flows of 35 cfs below the NUI dam. Those problems have been resolved. Passage has now been secured at the NUI dam and summer flows below the dam restored to 125-150 cfs. The recreational fishery downstream on the Middle Deschutes has rebounded nicely. Finally, as previously noted, fish passage will impact ~40 miles of river permanently. It seems clear that restoring fish passage at the dam is not only of idealistic ecologic value but also has a substantial return on investment for the community. By way of contrast it is noted that dredging will damage fish habitat and reduce water quality, while natural succession will create improved habitat for fish.

If the public is to invest in the Deschutes River in Bend, investments in dredging versus fish passage at the dam should be compared in both ecologic and economic terms. Based on the widely cited City of Bend 2015 survey, 77% would favor investments that promote a healthy river. Fish passage is a major component of that effort. While dredging impacts ~1 mile of river for 10-20 years only, fish passage impacts ~40 miles of river permanently.

With these points in mind we can now score this integrated solution for Mirror Pond against the community goals scorecard. The contrast with the Dredge scorecard ( see prior essay) is dramatic.

Based on the community goals of the Visioning project, the integrated strategy based on natural succession offers many advantages over the recent “dredge and walk away” proposal.

M. Tripp M.D. January 31, 2013