Weather Summary and Dredge

Weather Summary and Dredge
Water Quality - 10/7/2019


Cirrocumulus clouds on the morning of October 2. This high altitude (above 20,000 ft.) cloud is short lived and made up of ice crystals. They are present during cold, clear weather.


As the weather cools into fall it closes out a summer with very good water quality and no major algae bloom. In fact, algae in the lake was dominated by diatoms (Fragilaria crotonesis as represented by the image from University of Victoria) instead of cyanobacteria. This was aided by summer weather closer to normal for this region and noticeably cooler temperatures. There were only a few days above 90 degrees and mornings were dominated by marine layer fog. This was not the case the past few years where the lack of fog allowed daytime high temperatures to regularly climb above 90 degrees. That much sunlight provides plenty of energy to grow algae and warm the lake, resulting in conditions decaying by late summer. The figure below shows how hot it was last year vs. this year. The solid black line represents last year’s high temperature with the top of the grey shading representing high temperature this year.


Air and water temperature and rainfall for June 1 to September 30, 2019. The grey shading represents the daily air temperature range with the bottom edge of the shading the daily low and the top edge the daily high. Above that is a solid black line, which represents the daily high temperature from last year. As you can see, for most of the summer the black line is above the grey shading, meaning the high temperature last year was warmer than the high temperature this year. Red circles show the lake temperature near the surface. Blue circles show the lake temperature near the bottom. Columns near the bottom of the graph show daily rainfall amounts. Rainfall amount in inches is on the left Y axis and temperature in F is on the right Y axis.

Warm weather came early this spring with near 100 degree high temperature in early June. Fortunately this was not a bellwether for the rest of the summer and was followed by only 10 days with a daytime high temperature above 90 degrees compared to 34 days last year. Cooler air temperature means cooler water temperature so the lake did not get as warm as it has in the past. This was hardly noticeable for lake users because it was only a couple degrees F, but it makes a difference in what algae species are dominant in the lake. Cyanobacteria prefer warm weather and we did not have much this year. Another benefit this year was relatively low phosphorus in the lake. We had to open the headgate briefly in mid June, but closed it June 27th until July 18. This is important because phosphorus in the river is four to five times the concentration we want in the lake. Every week we delay bringing in river water means we less phosphorus for feeding algae and cyanobacteria.

Lake Meetings
This is a busy time of year for lake association meetings starting with the Oregon Lakes Association conference October 25-26 in Bend. Their agenda lists speakers from University’s and State agencies discussing Waldo and Crater lakes, the current state of cyanobacteria bloom science and policy, and several other talks about lakes in the region.

This is followed by the Washington Lakes Protection Association conference the end of the month on Lake Chelan. WALPA has not posted an agenda yet but they always put on a good event.

Finally the annual North American Lakes Management Association meeting is in Burlington Vermont November 11-15 this year. I am on the board of directors as a regional representative so will be going out early for business meetings, followed by the symposium Tuesday to Thursday. NALMS is a great organization and resource for lake associations and professional lake managers. The professionals in attendance provide great insight into the current state of water quality management.

Dredge Planning
We are looking at the feasibility of dredging during the next drawdown. The lake will be lowered a year from now and it may be possible to remove sediment from exposed parts of the lake. The last time we dredged was during the LOIS drawdown winter 2010/2011 were we removed around 30,000 yards of material. We would not remove that much this time but would concentrate on areas that have filled in since the last dredge. It may not be practical to dredge during the next drawdown so have not committed to the project.

We are also exploring ongoing maintenance dredging that does not require a drawdown. As we learned from the last dredge there are areas where sediment does not fully de-water during a drawdown, even when the lake was lowered in September. Springs and storm drains constantly keep water in West Bay and both canals, which means we were trucking out as much water as sediment in these areas. In addition, there is the cost of building temporary access ramps and truck loading areas before the first load of sediment is removed.

There are some areas that are not accessible by machinery. We dredged Springbrook and Lost Dog deltas during the LOIS drawdown because the lake was lowered 24 feet. That is not going to happen any time soon so having the ability to dredge these placed again would be beneficial. Also, the upper canal needs dredged and there is no way to get traditional dredge equipment into that location.

Using a wet dredge method is not without its own concerns. Sediment would be pumped into large felt bags where water would be allowed to drain from the captured material. Transporting and disposing these bags would have to be done in a way that allows efficient removal without lengthy dewatering delays. These are minor issues that should be easy to overcome and worth it to have the flexibility to dredge without requiring a drawdown.

Weather Station
The LOC weather station at the Lake Grove swim park is operating correctly now and data can be seen on our home page. It is mostly self-explanatory, but I want to point out “Water Temperature” is taken from a sensor approximately 30 inches below the surface and “Wind Gust” represents the highest gust in a 24 hour period, reset at midnight. The map shows where the weather station is located, at the end of the Lake Grove swim park dock. There is a camera on the same mast as the weather station that looks east so you can look at weather data and a live image of the lake both from the home page.