Restoration Considerations

Lake Zumbro Restoration considerations

Approximately half of the volume of Lake Zumbro has already been lost to sedimentation since it was formed, and those processes continue. The bathymetric study that was done in 2005 compared lake depths from the original land survey in 1916 with depth maps completed in 1957, 1978, and 2005. A follow up study was completed in 2007 for one of the areas where the most rapid filling is now occuring. That study shows that Lake Zumbro is continuing to fill at a rate of approximately 35,000 cubic yards per year. While this is a lot of sediment, it is only 10% of the rate of filling that occurred between 1919 and 1957. If no action is taken, Lake Zumbro will be filled just as Lake Shady has been filled. Many of you may remember fishing Lake Shady.

1916 Depths1957 Depths

1978 Depths2005 Depths

The above 4 charts represent different years of depth information for Lake Zumbro, but using the same color coding for depths. The years represented inclued 1916 original contours before the dam was completed. The next chart represents 1957 after a period of poor farming practices. 1978 shows further degradation, but not at the same rate as earlier. The final chart was collected in 2005. Note that the shallowest areas in the orange and red colors, continue to move North along the main channels.

The Lake Zumbro Improvement Association (LZIA) volunteer that developed the 2005 depth map used that map to identify which areas of the lake are being lost to siltation and a rough idea of how much sediment would need to be removed to restore depths needed for navigation. That was necessary to get some sense of the scale of a potential dredging project. The design and engineering work has not even begun and from the very beginning of the planning for this project, the fishery has been a major consideration.

Lake Zumbro is listed by the Minnesota Pollution Contriol Agency as an “Impaired Water”. In response to that listing, the MPCA has a two-year study that is underway on the Lake as well as in the upstream watershed. The preliminary results of that study were presented at the spring meeting of the LZIA. Like the DNR fisheries studies, the MPCA studies will provide information that is necessary for the long term management of the fishery on the lake. The Lake Association provides volunteers for both the fisheries and pollution studies.

The Zumbro Watershed Partnership is a non-profit organization working to improve land management and water quality in the Zumbro watershed. The Lake Association has been a supporter of the ZWP since its inception. Improving sediment management in the watershed is the single best way to extend the life of Lake Zumbro. It is also the best way to improve the quality of all of the streams in the watershed and their associated fisheries.

Another resource for consideration when looking at sedimentation issues is Rochester Public Utilities (RPU) usage of the lake for hydropower production. Lake Zumbro was formed by the hydroelectric dam that supplies the utility with 3 MW of renewable power. RPU needs the renewable energy from the dam to meet the state mandates adopted in 2007 that require the utility to get 25% of its power from renewable sources by 2025. If sedimentation continues to fill the lake, hydropower capacities will be reduced.

Funding has included the financial and volunteer contributions that the Lake Association members have already made and are committing to make. A non-profit, tax exempt 501(c)(3) organization, Lake Zumbro Forever, has been established to allow Lake residents and others the ability to make tax free contributions to retore the lake. Lake residents contributed $15,000 to complete an assessment of lake sediment quality which included an analysis of 13 metals, 32 pesticides, 8 species of PCBs and 20 other chemicals. Only arsenic and copper were found at levels that affect the management of the sediment and those were found at the same levels that occur naturally in the till-derived soils that drain to the lake.

The Lake Association is setting up a special taxing district to pay a portion of the lake restoration costs. That district, which will include all of the residences and businesses on the lake is expected to be put in place within the next year.

As has been suggested, they could be asked to pay all of the costs of the restoration. That would make more sense if it were a private lake and the sediment was entirely from soil losses on their properties. Sediment is after all a pollutant and generally where it’s feasible, the cost of pollution remediation is borne by the party responsible for the pollution and/or the current land owner. In the case of Lake Zumbro, most of the sediment was contributed by soil loss on upstream agricultural lands and construction sites. The Lake is public water so the owner is the State of Minnesota.

Nearly every property in the watershed contributed some sediment to the Lake and State law does provide for a means of assessing the clean up costs back to those properties. Counties can establish a Watershed District with the authority to levy taxes. Such districts have recently been established in the Cedar River and Shell Rock River watersheds in Mower and Freeborn Counties. There is no such district in the Zumbro watershed. The Zumbro Watershed Partnership is the only watershed organization in the Zumbro and it is a non-profit entity that lacks taxing authority.

Because Lake Zumbro is public water, and a regionally significant recreational area, there are a lot people that might benefit from a restoration project. Those people might also be expected to pay a portion of the restoration costs. However, since many of them live outside of the watershed, that adds some complexity to assigning the costs based on the benefits received.

The lakeshore owners and RPU are the only entities that are easy to assign benefits to. Consequently, they have already committed to paying a portion of the cleanup costs. The inability to fairly assign all of the costs of cleanup based on who contributed to the pollution problem and who benefits from its cleanup is the compelling reason that state and federal funding is being requested.

Discussions on other web forums suggests that the Lake Assocaition has left fishermen out of the discussion about dredging and restoration. That isn’t the case. as many fishermen rely on the Lake Association’s 2005 map of Lake Zumbro. That map is posted on this website and for sale at some of the local bait shops. Those maps were each supplied to the fishing community by someone from the Lake Association. Additionally, the Lake Association includes many fishermen and the Association has in the past discussed the project with many fishermen including representatives from the bass fishing clubs that hold tournaments on Lake Zumbro and other community groups. However, much more needs to be done.

Fishermen with a knowledge of the critical spawning and other fisheries management areas on Lake Zumbro can identify those areas as well as the factors that make them critical areas. That would be the first step in integrating that information into any restoration design. Those of you that have fished the lake for many years may also remember similar areas on the south end of the lake that have been lost to sedimentation. That too would be critical information in the restoration design — possibly the most critical information. Once that information is pulled together, I would suggest that representatives of the fishing community sit down with the DNR Fisheries staff and the Lake Association representatives to see how to use that information in any dredging and restoration design. LZIA would volunteer to arrange for that meeting.

A board member of the Lake Zumbro Forever (LZF) organization is a volunteer for DNR Fisheries and has helped with fish studies on Lake Zumbro. Additionally, the Lake Association always invites the DNR Fisheries staff to make presentations at their Spring and Fall meetings.

While efforts to develop support for this project have been in the works for several years, until funding was designated in the spring of 2008, there wasn’t much that could be planned. Serious planning will get underway later in the summer so now is the time to get involved.

A serious concern that some fishermen have raised is that dredging will destroy spawning habitat. That is a legitimate concern. The lake is being filled with sediment at a rate of about 34,000 cubic yards a year so it is just a matter of time before that becomes the single biggest impact on the fishery. With enough information about the fishery and the sedimentation patterns, we ought to be able to project about when that will occur. If it is many years from now, then taking no-action may make the most sense for the fishery.

Representatives from the Lake Association did meet last year with the DNR Fisheries staff in Lake City. The state funding that was awarded is being administered by the DNR so it is expected that several of the DNR divisions will participate in the planning process.

Some have suggested that the Waterski Club may have outgrown the lake. Others have noted that their experience on the lake is that it doesn’t feel like a public lake and questioned whether the lake was big enough to accommodate fishing and be a recreational hot spot. All of these concerns are going to be heightened as the lake contracts in size. If you don’t like it now, you’re going to like it a whole lot less as it shrinks even further. People tell me that there was a time when all of the waterskiing was done in the area south of Cedar Beach and that it was rare for skiers to go north of Fisherman’s Inn. Today, it is rare for a skier to go south of Fisherman’s Inn.

Still others have complained that anglers aren’t allowed to access the Fisherman’s Inn landing during the ski shows. At the current rates of sedimentation that will soon be a moot point since that area will be too shallow to host the ski show. The upstream area has been largely filled and now the sediment is being deposited between Fisherman’s Inn and the County Line. It won’t be all that long before the only accessible launch on the lake will be the DNR’s at Ponderosa. The ski show used to be held at Sandy Point. Today there are only a few boats that even get put in at the County’s public launch at Sandy Point.

When the Lake Association began looking at restoring Lake Zumbro in 2001, there was a near consensus that most of the sediment in the lake came in during the 1978 flood, as a result of the County constricting the flows with the realignment of the new County 12 bridge, or during the construction of the Rochester Flood Control Project. The 2005 detailed bathymetric study found that was not the case at all. Those events contributed to the sediment accumulation during that period but the rate of sedimentation from 1957 to 2005 was pretty consistent overall. The bathymetric study showed that it was the period 1919 to 1957 when most of the sediment entered the lake. Few people noticed that sediment accumulation until it began to interfere with navigation. The same thing is happening on the reach between Fisherman’s Inn and the County Line. Based on the 1957 and 2005 maps, it appears that there has been up to 20 ft of sediment accumulated in that reach. That hasn’t alarmed anyone because until recently, there was still plenty of water depth through that entire reach.

In response to the concerns about needing more public access and places on the lake, note that the Lake Association submitted a state grant application in 2006 to fund a large public park on the lake so that there would be a place for non-boaters to access and enjoy the lake as well as provide a place for recreational boaters to take a break. The publicly owned lands on the lake are in areas where sedimentation currently limits access and use of the property. While that funding wasn’t received, restoring access to publicly owned lands on the lake will be a high priority in the restoration design.

There are concerns about whether a project should be done before the sediment sources are brought under control. The sources of sediment will never be brought completely under control so the question is what would be enough control to make the project viable. As noted earlier, the bathymetric study shows that the sedimentation levels are already reduced to only 10% of what they were between 1919 and 1957. In fact studies in other areas of the Midwest suggest that the primary source of sediment coming into the lake today may be from the streams themselves. Those studies suggest that about 20% of the sediment is coming from soil erosion off of farmland and from construction sites and about 80% from stream downcutting and stream bank erosion. That change is due almost entirely to the effectiveness of soil conservation practices that have been adopted by farmers. Our Soil and Water Conservation Districts and the Zumbro Watershed Partnership are working to further reduce the sediment losses and certainly more can be done.

No action that results in a lake that resembles Lake Shady would be the most detrimental outcome possible and one that we would all like to avoid.

After Lake Zumbro is dredged, what is to prevent it from filling back in?

The restoration committee has shared this concern from the beginning, and while we realize that sedimentation cannot be completely eliminated, we feel that it can be managed.  Our approach is based on the following:

1) Sediment accumulation data: A study was done to assess lake depths and sediment accumulation rates. The lake was formed by the construction of a dam in 1919. This study used 1916 land survey data, 1957 and 1978 lake depth maps, and 2005 bathymetric data to calculate the amount of sediment.  The data shows that most of the sedimentation occurred during the first 50 years and that it has been significantly lower for the past 30 years.  Following this initial study, bathymetric data was again generated in 2007 for portions of the lake. The engineering team will use this data along with additional measurements to monitor and predict sedimentation rates.

2) Reducing sedimentation rates: The Zumbro Watershed Partnership was created in 2004. One of the primary goals of this tax exempt nonprofit organization is to reduce sediment in the Zumbro River by 30% over the next 5 years.  ZWP has worked with member agencies including the Soil and Water Conservation Districts, the Minnesota Pollution Control Agency, the Minnesota Department of Natural Resources, and others, to produce a Watershed Management Plan that will help achieve this goal.


3) Urban storm water management: The city of Rochester has been very active in addressing storm water pollution prevention.  Things being done to reduce sedimentation in the river system include:

–         Creating and maintaining storm water ponds.

–         Ongoing street sweeping using 4 brush sweepers and one vacuum sweeper

–         Each new sanding truck is purchased with a calibration computer to more accurately control the application of sand and salt.

–         Meeting the requirements of the (MPCA) Municipal Separate Storm Sewer System (MS4) Permits.

–         Capital Improvement Projects to stabilize eroded ravines and stream banks.

–         Within Rochester there are numerous private entities also managing discharges to prevent pollution.  Regarding sediment, construction sites over one acre operate under MPCA’s Construction Storm Water Permit.

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4) Funding future maintenance: Lake Zumbro Forever Inc, a tax exempt non profit, was formed in 2006 with the mission of preserving the lake for future generations. This organization is responsible for raising funds via donations, grants, community fundraisers and so on, to be used for the ongoing maintenance of the lake following restoration.