JFRCalifornia
Keeper of San Juan Secrets
Just an update and perspective on the slow lake level rise and what we can expect ahead (don't read on unless you want a number headache). As of June 3, the lake was at 3585.94, which is a pretty good recovery so far from its low point of about 3568 on April 10—just about 18 feet. But some might wonder: why it isn’t rising even faster, and should we panic? The simple answer of course is the unusually cold May, and no, don't panic. How unusual has this May been in terms of temperature? Well, if you accept that the timing of high inflows correlate to when the weather turns from cool to hot, this has got to be one of the coolest springs there’s been in some time.
I looked at all the heaviest inflow years of since the lake began to fill, and wanted to see on which date the inflow really began to jump up, and how long it sustained that high rate of flow. To do that, I used the (somewhat arbitrary) figure of 50,000 cfs as the benchmark, which we've normally hit by June, but not this year (as of June 3, it's only about 34,000 cfs). These were the questions:
1. For 8 out of those 11 years, inflow exceeding 50,000 cfs started in late May, mostly between May 23-31. In 1973 and 1984, it came early (May 14 both years). Only in 1995 and 2017 did the big flows start in June—June 5 and June 7 respectively. And even in those years, the June 3 flows were already over 40K cfs…whereas in 2019 they are still in the 30-35K range. So this tells me that 2019 is about as delayed a start as we’ve ever seen in a big flow year...
2. The sustainability of the high flow varied tremendously, which is a function of how much water was tied into the snowpack, and how fast it melted. The typical duration of 50K+ cfs inflows was about a month. The shortest duration was 10 days, in 2017 (from June 7 to June 17). The next shortest was 2014, at 14 days. This explains why we didn’t get much of a real bump up after a promising start for either of those years. On the flipside, the four monster years in terms of sustained high flow duration were 1983, 1984, 1995 and 2011. Each lasted for about 50 days +/-, and in the case of 1984, two full months! (See item 4 for a discussion of the outliers of 1983-84). I imagine we are looking at something similar this year in terms of timing pattern. And a clue to what is most likely to happen this year comes from 1995, which didn’t really hit its high flow stride until June 5. That year it sustained a 50K+ flow until July 24.
3. The peak flows of those 11 years were also highly variable. On the low end, you had 2014 and 2017, which registered a peak inflow of only 60K (on 6-13-17) and 64K (on 6-5-14). Those were years that fizzled out early. Most big year peak inflows ranged in the 70-90K cfs range, generally in early to mid-June. In the case of 1973, 1984, and 2005, the peak inflow actually happened in late May! So 2019 is considerably different than those in that regard. The closest corollaries to 2019 among those years (in terms of timing) might be 1983 and 1995. In 1995, the peak inflow didn’t happen until June 21 (95K cfs), and of course that huge 1983 the peak didn’t happen until July 1 (122K cfs!!), a near dam buster. In 2011, the peak inflow was a bit earlier—June 16, but it was big at 95K cfs.
4. 1983 and 1984 were both off the charts in terms of flow, but very different in terms of timing. Both years saw sustained peak inflows of 100K+ cfs, and both hit a peak of over 120K cfs. In 1983, that 100K+ flow lasted 9 days, and in 1984 it lasted 2 weeks!! Wow… In both years, you had sustained inflow of 85K+ cfs lasting roughly a month—5 weeks in the case of 1983! The big difference was that in 1984, the peak happened in the last week of May and first week of June. In 1983, it snuck up on everybody—and the peak flow was delayed until the last week of June and the first week of July. I don’t think 2019 stacks up anywhere near like either year in terms of intensity, but in terms of timing, it looks a lot like 1983.
5. If I had to guess, 2019 is looking most closely like 1995. That year, the high inflow didn’t hit its stride until the second week of June, peaking on June 21 at 95K cfs, and sustained at least 50K inflows through July 24. 2019 could also be something like 2011. That year saw a slightly earlier date for ramping up the inflow (5-31), but also peaked at about 95K (June 16), sustaining 50K+ flows until July 22. In 1995, the lake added a net 6.8 MAF, and rose 49 feet (impressive considering it started at 3645!). In 2011, the lake added a net 5.9 MAF, and rose 51 feet, from 3610 to 3661.
6. Bottom line—2019 may have a delayed start, but it’s still looking like big things are coming. It’s not 1983-84, but it’s also nothing like the disappointing promise of 2014 and 2017… This year is likely to have the longest delayed high volume inflow ever recorded among the big years on the lake, which could lead to a very late peak inflow in early July, and sustained 50K+ cfs inflows possibly into the first week of August… And if it ends up anything like 1995 or 2011, we’d end up with a net volume increase of about 6 MAF, which translates to a lake level of somewhere around 3630-3635…. Of course, it might end up a bit lower than that if releases are higher than in those years, or if more of the runoff ends up in the ground to replenish past years of drought… Let’s see what happens!
I looked at all the heaviest inflow years of since the lake began to fill, and wanted to see on which date the inflow really began to jump up, and how long it sustained that high rate of flow. To do that, I used the (somewhat arbitrary) figure of 50,000 cfs as the benchmark, which we've normally hit by June, but not this year (as of June 3, it's only about 34,000 cfs). These were the questions:
- At what date did inflow sustainably hit 50,000 cfs?
- How long did that last until the inflow subsided to below 50,000 cfs?
- When was the peak inflow, and what was that peak?
1. For 8 out of those 11 years, inflow exceeding 50,000 cfs started in late May, mostly between May 23-31. In 1973 and 1984, it came early (May 14 both years). Only in 1995 and 2017 did the big flows start in June—June 5 and June 7 respectively. And even in those years, the June 3 flows were already over 40K cfs…whereas in 2019 they are still in the 30-35K range. So this tells me that 2019 is about as delayed a start as we’ve ever seen in a big flow year...
2. The sustainability of the high flow varied tremendously, which is a function of how much water was tied into the snowpack, and how fast it melted. The typical duration of 50K+ cfs inflows was about a month. The shortest duration was 10 days, in 2017 (from June 7 to June 17). The next shortest was 2014, at 14 days. This explains why we didn’t get much of a real bump up after a promising start for either of those years. On the flipside, the four monster years in terms of sustained high flow duration were 1983, 1984, 1995 and 2011. Each lasted for about 50 days +/-, and in the case of 1984, two full months! (See item 4 for a discussion of the outliers of 1983-84). I imagine we are looking at something similar this year in terms of timing pattern. And a clue to what is most likely to happen this year comes from 1995, which didn’t really hit its high flow stride until June 5. That year it sustained a 50K+ flow until July 24.
3. The peak flows of those 11 years were also highly variable. On the low end, you had 2014 and 2017, which registered a peak inflow of only 60K (on 6-13-17) and 64K (on 6-5-14). Those were years that fizzled out early. Most big year peak inflows ranged in the 70-90K cfs range, generally in early to mid-June. In the case of 1973, 1984, and 2005, the peak inflow actually happened in late May! So 2019 is considerably different than those in that regard. The closest corollaries to 2019 among those years (in terms of timing) might be 1983 and 1995. In 1995, the peak inflow didn’t happen until June 21 (95K cfs), and of course that huge 1983 the peak didn’t happen until July 1 (122K cfs!!), a near dam buster. In 2011, the peak inflow was a bit earlier—June 16, but it was big at 95K cfs.
4. 1983 and 1984 were both off the charts in terms of flow, but very different in terms of timing. Both years saw sustained peak inflows of 100K+ cfs, and both hit a peak of over 120K cfs. In 1983, that 100K+ flow lasted 9 days, and in 1984 it lasted 2 weeks!! Wow… In both years, you had sustained inflow of 85K+ cfs lasting roughly a month—5 weeks in the case of 1983! The big difference was that in 1984, the peak happened in the last week of May and first week of June. In 1983, it snuck up on everybody—and the peak flow was delayed until the last week of June and the first week of July. I don’t think 2019 stacks up anywhere near like either year in terms of intensity, but in terms of timing, it looks a lot like 1983.
5. If I had to guess, 2019 is looking most closely like 1995. That year, the high inflow didn’t hit its stride until the second week of June, peaking on June 21 at 95K cfs, and sustained at least 50K inflows through July 24. 2019 could also be something like 2011. That year saw a slightly earlier date for ramping up the inflow (5-31), but also peaked at about 95K (June 16), sustaining 50K+ flows until July 22. In 1995, the lake added a net 6.8 MAF, and rose 49 feet (impressive considering it started at 3645!). In 2011, the lake added a net 5.9 MAF, and rose 51 feet, from 3610 to 3661.
6. Bottom line—2019 may have a delayed start, but it’s still looking like big things are coming. It’s not 1983-84, but it’s also nothing like the disappointing promise of 2014 and 2017… This year is likely to have the longest delayed high volume inflow ever recorded among the big years on the lake, which could lead to a very late peak inflow in early July, and sustained 50K+ cfs inflows possibly into the first week of August… And if it ends up anything like 1995 or 2011, we’d end up with a net volume increase of about 6 MAF, which translates to a lake level of somewhere around 3630-3635…. Of course, it might end up a bit lower than that if releases are higher than in those years, or if more of the runoff ends up in the ground to replenish past years of drought… Let’s see what happens!
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