It's still there

The Stillwater lift bridge hasn't floated off its foundation, but it is closed to traffic even though it isn't overtopped.  The St. Croix was cresting at Stillwater Tuesday when I took this shot and the river is falling slowly.  The bridge should reopen to traffic on Monday.

Slow flood

A long slow melt produced a much more modest flood than expected, but it's lasting a bit longer, too.  The water was already dropping Tuesday when I visited Interstate Park (Minnesota) on the St. Croix River.

No melt, no flood

It's hard to cook up a good flood when the snow's not melting. 

Temperatures 20 degrees below normal have produced precious little melting, causing flood crest forecasts to trend down, at least for now.  The major rivers are high and fast, but not rising much.  The result is likely to be a much longer duration flood, but the crests won't be near as high.

Third day of spring

Schools are closed, roads are horrible.  Don't worry, it'll melt--but it's not supposed to get over 32 until next Tuesday.

Here comes the water...

Flooding is beginning in earnest now, and conditions are worsening. 

It's Tuesday morning and it's raining hard in the Twin Cities, and dumping snow further north.  The Mississippi is rising fast in St. Paul:  it was at 8.5 feet this morning and is expected to hit 13.4 feet--a five-foot rise--by Thursday morning.  And that's not taking into account any rain/snow after 7 a.m. today.  It takes serious water to make a river as big as the Mississippi rise five feet in two days, and current precipitation means this forecast is low and will be revised upward very soon.

Streets near the river are closing and the Upper Landing housing project--which should never have been allowed in the first place--is getting ready to evacuate.  Long-range flood forecasts are already out of date and will need to be revised, but even the current projection suggests a 40 percent chance of exceeding the record flood crest of 26.4 feet on April 16, 1965.

It's worth noting that the record flood levels are all from mid-April.  The northern part of the Mississippi and St. Croix watersheds still contain lots of old snow, and new snow is piling up quickly.

On the St. Croix, the much-discussed Stillwater bridge will likely close on Saturday, if not sooner.  The river there stood at 679.15 this morning (Tuesday), and will rise to 686--the level needed to close the bridge--by late Saturday (and that's assuming we don't get all the precipitation we're now getting).

The flood of record on the St. Croix at Stillwater is 694.1, reached on April 18, 1965.  The chance of exceeding that currently stands at 20 percent.

Now that our snowpack is melting in earnest, flood forecasting will become a rapidly changing game.  But with a significant precipitation event ongoing and another coming over the weekend, the odds of this being a major flood event are rising faster than the river.

No, the dams don't hold flood water back

Every time we have flooding on the Mississippi I hear people complain that the Corps of Engineers is holding water back behind the dams to reduce flooding downriver, making local problems upriver worse.

Not true.

The lock and dam system on the Mississippi is designed to maintain minimum water levels during a drought.  The dams have no effect on flooding and were never intended to be used for flood control.  As the river rises, the gates are lifted out of the water and the river rolls on through.  During floods, you could run a motorboat right through the dam's gates (if you were crazy enough) because there's really no drop in river level anymore.

For whatever reason, this complaint circulates most frequently on the St. Croix River, where water levels are affected up to a bit north of Stillwater by Lock/Dam 3 at Red Wing.  Lock/Dam 3 maintains the river level at 675.0 feet above sea level--thanks to the dam, the river won't drop below that.  The dam effectively guarantees the river at Stillwater will be about five feet above the natural low water that would otherwise occur during a drought if the dam weren't there.  But most of the time the river is much higher than "flat pool" (675.0) and that's caused by flow from upstream--and sometimes backwater effect from a higher-flowing Mississippi--not by anything that's happening at the dam.

Slow melt helps

We're experiencing only gradual melting, which should help with flooding on major rivers in the area. We're seeing our first 50-degree temperatures today, and tonight may be the first night without below-freezing temperatures in many months. That will hasten runoff and push rivers up, but cooler weather is returning in a few days.

River ice may be an issue. The St. Croix is rising and there is water over the ice at Hudson, suggesting river ice is still pretty solid and holding fast to the shoreline. If the rivers rise very fast, the ice will break up while still fairly solid, increasing the risk of ice jams.

As recently as Friday, Mississippi River ice on Lake Pepin was largely in excess of 19 inches of blue ice (blue ice is the hard stuff).  This won't break up easily anytime soon.