Monitoring lake level to prevent flood

[LTD]

glad I'm at the top of the mountain not the bottom

[Fancy]

The ground is saturated now and we do monitor this site:
https://wateroffice.ec.gc.ca/search/rea ... nage_area=
We also pay attention to the runoff from the creeks and looks like we're going to be doing some sandbagging again this year.

[Glacier]

The April 1st snow index for the Okanagan is 152% of normal, which is tied with April 1999 for the highest snow pack dating back to 1980.

Also, forest fires burned the largest area in BC’s history during the summer of 2017. These fires affected many watersheds, including large areas in the Cariboo Chilcotin, Thompson Okanagan, West Coast, and Kootenay Boundary regions. Disturbances such as fire affect the hydrologic response of streams, rivers and lakes relevant to potential flooding. Specifically, flows from snowmelt dominated watersheds impacted by fires tend to be greater and peak earlier as compared to undisturbed areas, even under normal weather conditions. Many of the regions affected by burns last summer have above normal snow packs this year. Areas that will be more susceptible to earlier and higher flows due to potential fire impacts and a high snowpack include: Bonaparte River (Cache), Baezaeko River, Nazko River, Chilcotin River, Deadman River, and West Road River; including minor tributaries/creeks.

[andrea-lake]

Has anyone seen an official forecast of how high the lake level is expected to rise this year?

CORD Emergency Bulletin of April 20th states “Properties along Okanagan Lake are currently not at risk of flooding. The Okanagan Lake level is being closely monitored and managed by the province and is not anticipated to be a concern in 2018”.
https://www.cordemergency.ca/updates/20 ... 04-20-1556
We appreciate their statement, but they don't provide any data about their assumptions, nor do they give a specific forecast of the lake level as they did last year.

Last year, they had to revise their forecast lake level upwards a couple of times and we understand this is not an exact science. All the more reason for the public to be told what the range of uncertainty is. We should know what assumptions are being used as input to their forecasting models, i.e., the expected temperatures impacting snow pack melt, expected precipitation, ground water, etc. The public should be able to assess for themselves how reliable these inputs are likely to be and prepare according to their individual risk preferences.

CORD Emergency Bulletin of April 18th states:
“At this time freshet (spring runoff) is anticipated to be three to five weeks away.
• Snowpack levels, temperatures and rainfall are all variable factors that can combine to elevate the risk of flooding from creeks.
• While the snowpack is around 150 per cent right now, it is not known whether this will lead to flooding; how fast the snow melts based on temperature and rainfall are the influencing factors and unknown at this time”.
This appears to be a justification for not providing a specific forecast but we know they have models (paid for by taxpayers) that are currently predicting the lake levels.

We know the authorities base their real-time water release decisions on updated versions of the Okanagan Fish/Water Management tool that received a Premier’s Innovation and Excellence Award in 2008. However, the information produced by this award-winning tool doesn’t appear to be made public.

Ideally, we would like to see a base forecast with an error margin that accounts for unusual events such as a faster snow melt, heavier rainfall, etc. Below is a sample that demonstrates what that ideal would look like. (Keep in mind that the levels in the sample below don’t include any extra margin for wave action, which were explained in the CORD Emergency Bulletins last year).

The above sample shows a “best guess” from a layperson. If anyone has a better sense of what the levels might be, especially based on professional experience, it would be good to see your estimate of:

Base Forecast
Upper Error Margin
Lower Error Margin

[andrea-lake]

We finally got an official forecast in the May 8th webinar. Below is the data Shaun Reimer published as part of his presentation (see YouTube link below for the full presentation. Mr. Reimer’s section starts at minute 19.00)
Okanagan Water Supply Update by Okanagan Basin Water Board Webinar on May 8th
https://www.youtube.com/watch?v=h_-LlLjOE6Y
Previous webinar on April 16th Webinar
https://www.youtube.com/watch?v=14RCgaQmJ2Q

The chart below is a little too technical for most of us and doesn’t give a clear picture as to what he is forecasting for lake levels. To determine how the 691 kdam/m3 translates into lake level you must divide it by 3.46 = 199.71 cm rise. This rise is offset by the outflow at Penticton Dam by about 1 meter between April 16th and June 30th or 1.33 cm/day (assuming average outflow per Reimer’s comments of 40 m3/sec at the dam). Since the lake normally peaks between June 10 and June 15 (say June 13 for simplicity) the outflow by that time may only be 75 cm for a net increase of 1.25 meters (i.e. up 2 meters and down .75 meter) excluding the effect of rain. Add in normal rain and one gets maybe 1.4-meter total rise, and if the rain is very heavy, say 1.6-meter total rise. (This is a best guess, as Reimer wasn’t explicit on the effect of rain on lake level). This math is all implied from Reimer’s webinars in April and again in May. (see the above YouTube links).

The numbers in the preceding paragraph don’t quite match Reimer’s comments where he clearly states that the lake will rise above full pool by as much as 10 to 25 cm. His exact quote in the May 8th webinar at minute 21:57: “And previously we had thought that our management would be able to keep us within or below full pool on Okanagan Lake but right now the projections show we will go a little bit above and that would be more in the line of 10 to 25 cm above full pool. And like I said in many of these phone calls it is so conditional on the precipitation and how quickly the water comes into the lake.”

The graph below is my attempt to translate his words into a forecast that’s easier to visualize. It shows his base forecast and what I think are his upper and lower error margins. I am not sure if his uncertainty about precipitation is fully accounted for in the error margins shown below so my apologies if it’s not correct. If anyone knows, perhaps you could clarify this point. I think he is saying that if we get unusually heavy rains, the lake could rise higher than the top error margin on the graph below.

[tsayta]

Does the last few plots on the Okanagan lake gauge show a flattening out?

[andrea-lake]

Yes,Tsayta's observation appears correct. See graph below. The lake rise seems to be slowing slightly. Based on this I stick with my forecast made on March 18th (see my original post in an earlier page on this topic).

[andrea-lake]

Below is the link to Shaun Reimer’s updated forecast as of May 17 th. His most relevant quote from the video is: “I am not necessarily saying were going to reach that 343-meter elevation, but I think it is very prudent that people who were flooded and local government plan for the lake potentially hitting the 343 meter level".

https://www.castanet.net/news/Kelowna/2 ... he-weather

Based on his wording I interpret this to mean that 343 meters is his upper error margin, so let’s assume that his base forecast is 20 cm below that. The chart below is a visual interpretation of his forecast.

[andrea-lake]

CORD just published their latest forecast at 3:00 pm today (see link below). They buried the forecast at the bottom of a long line of tips to boaters, without a headline to bring it to anyone's attention. Below is the relevant quote:

"Okanagan Lake currently sits at 342.42 metres and normal high-water level is 342.48. This is expected to rise to 2017 levels".

https://www.cordemergency.ca/updates/en ... 05-17-1504

They appear to be forecasting 27 cm above Mr. Reimer's forecast of today's date. His was 343 meters at the top end. CORD's forecast states that it will hit the 2017 level, which peaked at 343.27 meters.

We respectfully request CORD to clarify whether their forecast is a planning level (as Mr. Reimer's was), or if they indeed expect the lake to actually rise to the 2017 flood level. Is CORD's base forecast 343.27 plus or minus 20 cm or is it the maximum?

[DGMOK]

I understand the flooding in Osoyoos.
So they decide to reduce the outflow from Okanagan Lake from 60 to 37
And now flood Okanagan Lake to 343.00 or above. 50 cm above full pool!!
And somehow 25cm below last years devastating flood level is good news!!!

[Glacier]

Well we haven't had rain in 10 days and the snowpack is below where it was last year at this time, so we won't hit last year's peak unless we get a lot of rain over the next couple of weeks.

[andrea-lake]

How did we end up with these unnecessary costs this year?

I think we can all accept that the costs related to flood mitigation along the creeks and rivers were necessary. However, what you may not appreciate is that the costs incurred for flood mitigation along the lake front were not necessary. (Those costs are detailed at the end of this post).

How could we have avoided those costs? Simple. Just follow the Lake Operating Procedures which clearly stated the lake should be drawn down by up to 30 cm below the level the officials drew it down this year (see highlighted rules below). If this had been done, the lake would now be at most 10 cm above Full Pool when it peaks instead of 32 cm above as they are projecting. Under this scenario they would NOT have had to incur any flood preparation costs or cause everyone to worry over reliving the 2017 flood disaster.

In addition, if they had followed the Rules on drawing down the lake they would have had sufficient contingency to cover for the following uncertainties: 1) faster snow melt from high temperature; 2) above average rainfall; and, 3) room to reduce the outflows at the Penticton dam to alleviate the flooding in Oliver and Osoyoos.

Many people on this forum claimed that the lake was drawn down sufficiently to avoid any flood concerns. However, this was an unusual year and the Rules required the lake to be drawn down another 30 cm (roughly 1 foot) lower to provide for the extra snow melt. Most have never experienced this low level because Lake Management has rarely drawn it down this low and understandably many people made comments that it was drawn down too far. Responsible communication of the Rules by officials could have cleared up these concerns.

This year we will likely avoid the flood disaster we had last year, notwithstanding the high snowpack, only because of below average rainfall in May. If the rainfall were normal or close to what we had last year, the flood would have been close to, the same as, or possibly worse than last year. Lake managers gambled and just barely avoided disaster this year but we all could have lost big-time like last year when they gambled by not following the rules. This is a topic of a future post under Flood Review forum.

Some lake flood preparation costs that could have been avoided this year:
• Manpower and material for sand bag walls, bladder dams, gabion barriers, weighted barrels on docks, log booms, etc.
• Lost tourism from negative publicity predicting likely flood
• Costs of manning the Emergency Operations Center re lake flooding
• Cost of preparations by private property lake front owners
• Emotional stress suffered by people told they must relive the 2017 flood

Extract of Lake Operating Procedures from Canada-British Columbia Okanagan Basin Agreement as summarized by B. J. Symonds, P.Eng., in his 2000 report “Background and History of Water Management of Okanagan Lake and River”
http://www.obwb.ca/obwrid/docs/023_2000 ... n_Lake.pdf

[Glacier]

There hasn't been any flooding on Okanagan Lake that I know of. The lake has peaked at the 1 in 5 level, which is not flood stage. The lakes that did get serious flooding were downstream, namely Osoyoos Lake. If the selfish Kelownites got there way, there would be even more flooding on Osoyoos Lake. Thankfully, the operators knew what they were doing, and didn't flood Osoyoos more than they had to.

[seewood]

There hasn't been any flooding on Okanagan Lake that I know of. The lake has peaked at the 1 in 5 level, which is not flood stage. The lakes that did get serious flooding were downstream, namely Osoyoos Lake. If the selfish Kelownites got there way, there would be even more flooding on Osoyoos Lake. Thankfully, the operators knew what they were doing, and didn't flood Osoyoos more than they had to.

Much of the flooding in Osoyoos was from the Okanagan river getting backed up because the larger Similkameen had an extraordinary volume in it from melt water. Acted as a bit of a dam at the confluence of the two rivers.
^^^ Regardless, Your right in the ministry did a great job I believe in adjusting the flows to minimize downstream conflicts.

[Poindexter]

Well we haven't had rain in 10 days and the snowpack is below where it was last year at this time, so we won't hit last year's peak unless we get a lot of rain over the next couple of weeks.

Went ATVing Saturday and because the snowpack has melted more than usual, we were able to get to elevations not accessible in previous years. Hopefully that means, barring heavier than normal rain, that the worst is behind us.