From: Tom Hovey
To: LSIA
Sent: Thursday, October 23, 2003 4:10 PM
Subject: Re: Questions for Tom Hovey
Lake Sarah Distribution List:
Here's the questions I rec'd and my answers:
1). Given that we have no outflow below the Ordinary High Water mark, what purpose would a control device serve?
Answer - A control device may serve prove important for two issues. First, if the current runout, which appears to consist of sediment and rocks, is unstable, a structure may be useful to provide the stability that is desired.
Second, it may occur that a channel cleaning project alone will take care of the high water too efficiently and result in unacceptable drainage. A structure may be useful in reconstructing or maintaining the proper hydraulics (the conditions that affect the volume and rate of water leaving the lake) to avoid the negative possibilities of channel work. I should mention that if the project can be done successfully without an additional structure, that is generally our preference, as structures have problems of their own, including vandalism, maintenance, perceptions, and extra permitting.
2). What would a control device cost?
That's another down side of structures; they need to be designed and constructed, at a cost. This cost will depend a great deal on the location and type of structure. The one that was added at Coon Lake a few years ago is not a good comparison, because there was an existing structure that was just modified at a cost of around $2000.00. I think that a new structure could easily run in the 10s to 100s of thousands of dollars. But then it might be a possibility to beef up the old railroad grade if necessary, possibly a much cheaper alternative. It would be very hard to nail down even a ballpark figure at this time.
3). Would consideration of the inclusion of a control device in our current outflow project delay the project and if so, for how long?
Addition of a control structure would likely delay the current permit process, possibly several months.
4). Is further input by either LSIA or various individuals regarding the outlet project helpful at this point, or does it just serve to delay the project?
I don't think additional input at this point will delay the project. Unless it's something new, it probably won't help the process either.
5) You could update the members on the status of the permits, new OHW level for the lake, potential impact on the Lake with the project, with and without a permanent control structure.
Most of this has been posted on the Lake Sarah web site. By the way, that web site is an excellent resource, and we're lucky to have it. I suspect more lake associations would be successful in their ventures if they had as nice a tool as this one.
I'm hesitant to comment on the potential impact on the lake until the modelling is done. If the modelling indicates that a control structure will help the situation we'll recommend one. If it looks like one is necessary to prevent negative effects of the project that's permitted, we'll require one.
6) Explain the hydraulic study conducted so that people would better understand how the lake works in the watershed, and how the modifications to the outlet not only affect how much water gets out of the lake, but it may effect the normal water level seasonal fluctuations during a normal year, if there really is such a thing as normal and unusual events like we have had of the last few years.
You are correct that modifications to the outlet, including the channel, affects the lake levels and how it reacts to climatic events. This is exactly why we are being cautious. Also, as you suggest, "normal" water levels are relative to the weather preceeding them.
Regarding the modelling, this is how it's supposed to work: Our engineer takes all the available data from the surveys, the flow information that Three Rivers Parks provided, water level records, precipitation records and calibrates a computer model that will be able to mimic water levels when given some known inputs, such as outlet configuration and precipitation. When that's working satisfactorily, he can change variables, such as the outlet channel geometry or the resistance of the outlet to flow (vegetation growth typically) to find out how the lake responds with the altered conditions. When we are satisfied that a specific change can be made that will do what were looking for, (in this case, lowering the intensity and duration of the periods of high water without significantly affecting the ordinary high water level) a permit can be issued.
7) From an informal survey it appears residents feel the lake level is now low and would like to find a way to keep about there. If it would be beneficial, we would be willing to take a survey of all the lake shore property owner to see what they think of the current lake level. Would this information help with anything?
Surveys may be interesting, and if it was a very controversial project, they might take on more importance. I'm not sure that's the case here. Our intent is to solve the problem with the minimal impact solution, as the permit rules require us to.
8) Isn't the review period over for this permit application?
Yes, the comment period for the agencies is well past. Since this is such a complicated project, and one with a high possibility of problems if done wrong, we are taking the extra time to get the data and do the modelling. The alternative at the end of sixty days from the application date is to conclude that there wasn't sufficient information to show that the resources would be protected and deny the permit. Another alternative would have been to try to figure out exactly what type of information and modelling was necessary and not accept the application as complete untill it was provided. This would have greatly increased the time and cost in submitting an application. I had no intention of going those routes and I assumed that we would be met with a reasonable amount of patience, which I have experienced. Thank you.
I expect the actual modelling to take place in the next couple weeks. A permit should be expected shortly after.
9) If your supposition is correct that the channel has not been plugged due to a sediment buildup over the years, why would the lake level be consistently trending higher over the past ten years? Are you now of the opinion that we don't need to dredge the outflow ditch?
Sorry for the unclear message. The profile of the ditch has not changed much with sediment over the years. The cross sections of the channel may have become more restrictive, or cattails may have increased the resistance of flow through the wetland. I do believe that some maintenance is needed. I haven't seen modelling yet, but I think it's safe to say that the amount of excavation proposed is more than necessary, possibly quite a bit more than necessary.
I hope these answers help. We are trying to be as forthcoming as possible with information as it becomes available. As always, please feel free to contact me if you need further clarification or answers.
Tom Hovey
Area Hydrologist
DNR Waters
Phone 651.772.7923
Fax 651.772.7977
Visit our website @ www.dnr.state.mn.us/waters