Tonka reaches highest level in 3 years, 70s ahead

Our spring deluge is making it tough to keep your feet dry on some Lake Minnetonka docks this year.

Heavy spring snow melt and recent rainfall pushed Lake Minnetonka to the highest level in almost three years this week. Tuesday's lake level was recorded at 930.25 feet above sea level according to data from the Minnehaha Creek Watershed District. That's the highest water level since May 23, 2011, when the lake reached 930.26 feet. The lake level is up about 20 inches from last fall.

The high water levels have some docks, and even boats under water in Deephaven. City boat ramps are adjustable to a point, but high water can make it difficult for some boat owners to moor boats and keep them dry.

I asked Deephaven Mayor Paul Skrede if the city is seeing any issues with the high lake levels.

Paul,

We have, and will have for some time I suppose, some water issues as a result of the Lake levels. Primarily, some drainage systems currently do not drain because the lake is higher than the the outflow pipes.

Yards seem to have not caused a lot of wetness in basements, but their runoff has gathered in the street in several areas.

I am dry, are you?

Paul

Thanks Paul.

Yes I am dry. It pays to live on top of a watershed where my back yard drains into Lake Minnetonka and my front yard drains into Purgatory Creek!

Seasonal Weather Whiplash: From fall drought to spring flood

The high water is quite a turnaround from conditions last fall when the Lake Minnetonka watershed was in drought. 

 Spring Deluge

The past 90 days have featured heavy rain and snowfall totals in eastern Minnesota. Many lakes and rivers have rebounded dramatically from low levels last fall. Eastern Minnesota has soaked up 8 to 10 inches or more of precipitation in the past 90 days. Recent storm tracks have kept western Minnesota's precipitation totals lower.

Here's a look at the 90-day precipitation analysis from NOAA's Advanced Hydorlogic Prediction Service.

High water sparks wake restrictions

The high water levels on Lake Minnetonka triggered a High Water Declaration from the Lake Minnetonka Conservation District. Wake restrictions are in effect.

Managing lake levels

High water in Minnetonka and limited discharge capacity on Minnehaha Creek can pose some challenges for the Minnehaha Creek Watershed District who manages lake levels and flow into Minnehaha Creek. High water and fast flow in the creek can impact many west Twin Cities metro communities between Minnetonka and Minneapolis.

It can be a balancing act. Too much water Lake Minnetonka poses problems for lakefront communities. Too much water in the creek can flood creek side residents downstream.

I asked the water district's Telly Maymayek about how the MCWD anticipates changing lake levels, and makes decisions about controlling flow into Minnehaha Creek. Here are some selected portions of her response.

Hi Paul,

Here are the answers to your questions – please let me know if there’s anything else you need. Thanks!

 The District does not typically issue lake level forecasts, however it can have its engineer model/project what the lake level will be for a certain timeframe if normal precipitation levels are encountered. For example, given today’s lake level of 930.21 we could ask Wenck Associates to model what the lake level would be in 2 weeks if we keep discharging at 300 cfs (cubic feet per second) and the watershed receives normal precipitation over those two weeks. However, this type of modeling is limited in that it is not able to account for the amount of water flowing into the lake from the upper watershed creeks.

Technically whenever the lake is above 930.00 the operating plan allows for “unrestricted discharge”, which means the District can open the dam gates all the way and not restrict the water. However, we have chosen to keep 300 cfs as the highest discharge as this has been observed to be the “maximum creek capacity” without flooding downstream communities.

Secondly, if the District were to open the dam gates to allow “unrestricted discharge” the maximum flow through the dam and into the wetland at the headwaters would still likely be around 300 cfs. This is due to the fact that the culvert under the road at McGinty Road, which acts at the first pinch point on the creek, is only capable of allowing so much water through and that seems to be around 300 cfs. In fact last summer during the large rain events in June/July, Lake Minnetonka and the headwaters wetland reached the same level and therefore reached somewhat of an equilibrium and the flow then was limited to the capacity of water flowing through the McGinty Road culvert. This is known as a “backwater effect.”

Our current sources of weather forecast information are the National Weather Service and the National River Forecast Center.  The District has been in discussions with Hennepin County Emergency Management about using their Mesonet weather forecasting tool, which would be very useful for dam operations when it’s operational. Any other suggestions you have regarding meteorological assistance for our dam operations would be most welcome.  

Thanks Telly. I can appreciate the tough job of managing water levels for Lake Minnetonka and Minnehaha Creek. My guess is MCWD gets plenty of "feedback" from folks in the watershed on which lake and creek level is best. To be fair, this has been a tough transition from fall to spring given the rapid change from drought last fall -- to near flood conditions this spring.

It might benefit MCWD to use more focused (paid) operational meteorological support. The heavy late season snow and multi-inch spring rains were well forecast, and a more focused effort could have allowed district to release more water from Lake Minnetonka before the "Hrydo Vortex" hit in late April and spiked lake levels to a 3-year high. Not being overly critical of MCWD here, but professional meteorological support saves many business and government operations save significant revenue and increases operational effectiveness. It can help the operational decision making process more than most organizations realize.

The good news? A drier forecast, milder temperatures and increased evaporation over the next few days should allow lake levels to drop steadily on Lake Minnetonka for the next several days. NOAA's 5-day rainfall outlook suggests under a quarter of an inch for the Twin Cities area.

Improving Forecast

We endure two more frosty mornings in much of the Upper Midwest. Once again freeze warnings  and frost advisories are out for a big chunk of our region.

Blue remains the dominant fashion color on the weather maps this week.

Milder temperatures gradually build in by this weekend. In fact, the weekend looks fairly fantastic at this point. Two mostly sunny dry days on a weekend? Alert the media.

The European Model is the most optimistic about our chances for 70 degrees on Sunday.  A low spinning through early next week may bring a return to some showers with temps int he 60s, but Old Man Euro is cranking out 70s again by late next week as we approach Memorial Day Weekend.

Our first of the big three summer holiday weekends is just over a week away? How did that happen?

Stay tuned.