Historic April Flooding; Many Reservoirs Almost Full

6pm Tuesday…

We’ve just seen a few light showers today, but rain picks up west slopes of Cascades and in the Cascades themselves.    That has allowed many rivers to drop west of the Cascades.  Of the Willamette River tributaries, only the Pudding and Coast Fork Willamette River remain under flood warnings.  The Willamette itself crested early today in Eugene and now that crest is working its way downstream.  Highest water at Albany and Salem will be tomorrow.  In the metro area, the much lighter rain totals the past 4 days up here mean no flooding on the Willamette River, but it’s still running high with lots of logs and debris in the water

Mark Flood Willamette River Stats3

In Eastern Oregon the flooding has been more serious, especially in the John Day River basin.  At Service Creek the 3rd highest crest on record is forecast for tomorrow.  Some pics from ODOT

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Warnings Flood Rivers 2

70% of Oregon’s population lives within the Willamette River Basin.  And it appears we have avoided a major flood event this time around.  That’s because 11 flood control reservoirs have been built since 1941.  It’s interesting to note that this same weather event pre-1941 would have produced a major flood in the Willamette River Basin.  The filling of those reservoirs has been amazing this week.  Take a look at current conditions

Flood Control Willamette Reservoirs 1

There is one reservoir that has filled beyond the “TOP OF FLOOD CONTROL” level; that’s Dorena.  It is spilling water “uncontrolled” today, which just means water is going over the spillway as it is designed to do during a flood.  That DOESN’T mean water is going “over the top of the dam”.  That would be bad and that’s definitely not the case.

Then there are 5 reservoirs (in yellow) where water is within 2 feet of that spillway level.  Luckily at most of those the incoming water volume has slowed quite a bit.

There are 5 reservoirs (in green) with room to store more water.  At a few of those (Detroit Lake) water has been filling the lake rapidly.  Check out Detroit Lake

Flood Control Willamette Reservoirs 2

A 50 foot rise in the past week!  Right now the lake is up to just 8′ under its “full” summer level of 1563.5′.  That lake is still 15′ or so away from an uncontrolled spillway release; plenty of storage available.

If another atmospheric river event with many inches of rain were to show up in the next few days?  We’d see widespread flooding in the Willamette Valley due to little water storage left.  Luckily that is NOT the case.  Sure, there will be more rain in the upcoming week, but not too heavy.  RPM model shows 2-4″ rain in Cascades the next 3 days, then lighter totals through the weekend.

RPM Precipitation Accumulation

Rivers are going to continue to run very high as an unusually wet April continues…

Chief Meteorologist Mark Nelsen

13 Responses to Historic April Flooding; Many Reservoirs Almost Full

  1. Roland Derksen says:

    Pretty cool temperature here this afternoon (45F at present). Feels like we’ve gone back several weeks instead of being in mid-April.

  2. Joshua Lake Oswego says:

    Yet another epic rain bust for PDX. With all this talk about rain, we will likely end April with very close to normal rainfall.

  3. Roland Derksen says:

    I’m not surprised to see this return to more typical spring weather. March was unusually dry. Comox (a station on Vancouver island) reported just 0.16 inches for March. that’s definetly not normal!

    • boydo3 says:

      You will get it next year!

      • boydo3 says:

        We’ve had 88″ of rain since Oct. 1st. Average for the water year is around 72″ in this area so we are well above average. Blame El Nino..

        • Roland Derksen says:

          I see it somewhat differently: We had more of our share of wet March months in the last several years. It was time we had a dry one. Next year- I’m predicting an average amount of precipitation for March! 🙂

  4. Joshua Lake Oswego says:

    Holy rain shadow for most of the metro area. Big busteroo so far.

  5. Tanis Leach says:

    The Wilamette at Corvallis has been forecast to be updgraded to moderate flood stage. Highest since 1996.

  6. Jason Hougak says:

    The John Day is the longest undammed river in Oregon at 284 miles.

    14” of fresh snow at Timberline. Major blizzard moving across the Midwest. 6” plus of snow on the summits on the Big Island of Hawaii. It may be spring but winters not over.

  7. Tanis Leach says:

    First, new phone.

    Corvallis update: many roads are flooded. Roads to OSU are being blocked now. The Mary’s is flooding too.

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