I've had a couple of questions about flooding and have added the Snow Melt Runoff Report from the Provo City website for those that are interested and will try to remember to post again when the next one is out. You can access this and more information at provo.org.
SNOW MELT RUNOFF REPORT
May 2, 2011
Summary
High snow pack levels in the mountains east of Provo, combined with high soil moisture conditions and cool, wet weather throughout April; have created great potential for significant spring runoff this year. Current snow pack levels are at, or above 30-year highs for this time of year. Expectations are that
The elevation of Utah Lake is
0.7' above compromise. It will likely rise a another foot, or more this spring; possibly reaching, or exceeding the nearly 2' above compromise experienced in 1997 and ‘98. However, the elevation of the Lake is 2½ feet lower than at this time in 1983. The capacity of the Jordan River has been increased since the 80's, and more water has been released early from the reservoirs, in anticipation of high runoff, than occurred in 1983. These factors will keep Utah Lake from getting anywhere close to the elevations seen in the 1980's. Current Elevation
Estimated 2011 Peak 4491.0' 2.0' above compromise
2010 Peak (2/6) 4489.2' 0.2' above compromise
Elevation 5/2/10 4488.9' 0.1' below compromise
Elevation 5/2/83 4492.3' 3.3' above compromise
1984 Peak 4495.0' 6.0' above compromise
Flows in the lower Provo River are approx.
925 cfs. The River spiked up to 1200 cfs on April18th, with the rain storm that day. Peak flows this spring are still weather dependent, but Provo River flows will likely be near the 2000 cfs range late this month, or in early June, similar to the 1900 cfs in 2005. Over 100,000 acre feet of storage capacity currently exists in Jordanelle Reservoir. This flood control capacity, combined with the early release of water out of the reservoirs, will keep peak flows on the Provo River well below the 2400 cfs seen in 1983. Current Flow: Approx.
Estimated 2011 Peak: 1600 - 2100 cfs
2011 Peak 5/1 @ 47"
2010 Peak: 600 cfs (5/18) Current
925 cfs (cubic feet/second) Snow Pack at Trial Lake47" 2005 Peak: 1900 cfs (5/31)
2010 (5/2) 20"
1983 Peak: 2400 cfs (6/3) Peak 5/15 @ 21"
Note: Flows are measured below Geneva Road
Peak 5/13 @ 35"
Expected Remaining Runoff: 202,000 acre-feet (171% of normal)
Current Storage Capacity: 116,000 acre-feet 1983 (5/2) 31"
Peak 5/20 @ 35"
2005 (5/2) 33" Frontal Canyons
Snow pack levels in the frontal canyons east of Provo are essentially the same as they were on
April 1
the frontal canyons will be well above average, but still within system capacity; or whether they
will be much higher. The main difference between 1983 and 2005 was that even though the May 2
st. Weather over the next few weeks will still be critical in determining if runoff flows out ofnd snow pack in ‘83 was lower than in ‘05; it only dropped 2" between the 2nd and 25th of May 1983, while in 2005, it dropped almost 2/3 (24") by May 25th. The 2005 flows were well below system capacity, which had been significantly increased (enhanced detention basins and improved outfall piping) since the high runoff of the 1980's. Current Flows Snow Pack at Timp. Divide and Cascade Mtn.
Rock Canyon
2010 Peak - 6/8 @ 25 cfs Current
- Not yet started 2011 Peak 4/16 @ 48" 4/11 @ 24"45" 21" 2005 Peak - 5/23 @ 64 cfs
2010 Peak 4/15 @ 23" 4/14 @ 18"
Slate Canyon-
2010 Peak - 6/7 @ 4 cfs
2005 Peak - 5/23 @ 29 cfs 2005 Peak 4/11 @ 41" 4/1 @ 27"
(5/2) 37" 22"
Not yet started (5/2) 13" 10" Little Rock Canyon- Dissipating above Sherwood Dr
2010 - No runoff 1983 (5/2) 32"
2005 Peak - 5/16 @ 4 cfs Peak 5/3 @ 32"
Note: Flows measured at canyon mouths
Outlook
The “nightmare” scenario would be another 2 or 3 weeks of cool, wet weather; followed by
suddenly hot weather, combined with heavy rain storms. This would result in a high percentage
of the snow pack running off over a very short duration of time. The “dream” scenario would be
at least a couple weeks of dry, warm (70's and low 80's) weather, before it gets hot. This would
allow the low and medium elevation snow pack to melt and runoff before the high elevation snow pack does; stretching out the duration of runoff, and reducing the magnitude of peak flows. The “likely” scenario is somewhere in between.
The good news is that the forecast over the next week is for dry, warm (70's, Thur - Sun) weather. This may start the melting of low elevation snow pack, but will have no significant impact on runoff in the Provo River, or the frontal canyon channels through Provo this week.
The next update will be issued Monday (5/9).
Little Rock Canyon, which has had flows trickling out of the canyon mouth for the last two weeks, will likely increase in flow; but not to significant levels. If flows in Rock and Slate Canyons reach the canyon mouths this week, they will be at very low levels. Flows in the Provo River are projected to remain in the 900 -1000 cfs range this week. The elevation of Utah Lake will likely continue to rise slowly, another inch or two over the next week. Provo City Public Works Department
Greg Beckstrom, Deputy Public Works Director
801-852-6720 Utah Lake
PROVO CITY
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