John Weiss: Unusual rains recharge rivers

Heavy rains 10 days ago were unusual, sloppy, a bit of a shock — and might prove to be a gift to anglers.

Rochester received 1.72 inches, but further east, rains were much heavier. In northeast Iowa and southwest Wisconsin, the storm dumped up to 7 inches and sent some streams into low-flood levels.

Around here, the Mississippi River is up substantially, from about 8 feet at Lake City before the storm to 11 feet earlier this week. If there had been ice on the river backwaters or Lake Pepin, that rise would have really messed it up. But there's no ice, and it doesn't look like we'll get any soon, even when the river drops, so forget about ice fishing for a while at least.

Rivers like the Root rose a few feet at least and the little ice on them broke free and crinkled, popped and crunched as it floated down the river Saturday. Flows rose from 400 cubic feet per second at Pilot Mound to 1,900 within a few days after the rain.

This rain was much-needed. Much of the fall was relatively dry. The Zumbro River west of Rochester was the lowest I've seen it in many years. Frankly, I was worried.

Tough on fish

A winter or two ago, the river was solid ice everywhere, including at the Mantorville dam. What would happen if we had really low levels and that kind of ice? It could have killed a lot of fish that wouldn't have room or oxygen. Yes, I know that just happens in nature, it's part of the cycle of good years and bad years, and streams eventually would recover. But I would still worry about smallmouth bass and catfish.

Then came the rain, washing away worries.

To understand why, let's get a quick lesson in how rivers work from Greg Kruse, Department of Natural Resources supervisor of water monitoring surveys.

Think of the river and areas around it as a bank, he said.

Rivers will run, even in winter, even with zero surface runoff because they rely on deposits they made into their banks during the year. When water is high or during normal flows, some of the water seeps into those banks, he said. "You have the water in the soil profile and that water will slowly seep out," he said.

The South Fork Crow River near Delano, in 2010, for example, had a lot of rain in the fall and in winter, flows were double or triple normal, he said. When they walked out to check flows, ice was more than a foot thick in the middle but much thinner on the edges because that ground water, which is relatively warm from being underground, was seeping out, he said.

Another source is wetlands that slowly feed back into streams, although we're not blessed with a lot of wetlands around here.

Last week's rain should have helped a lot because the banks were probably not frozen, so that made some big deposits into the bank.

Recharging the aquifers

The other source of water into streams and rivers in winter are the aquifers around them, Kruse said. They are the true groundwater, the aquifers that go down many hundreds of feet, the ones we rely on for drinking water.

If the aquifer is high enough, it will feed directly into the streams. The Zumbro, though not in prime blufflands, still has a lot of small springs and seeps feeding into it.

It's in trout streams where aquifers really shine. The streams remain cool enough in summer because of the springs, which are around 48 degrees, and it's relatively warm in winter, so blue-ribbon streams continue perfect for trout.

Ron Benjamin, DNR fisheries supervisor in Lanesboro, said the rains were really good. He wasn't worried about a gully-washer, which could have damaged redds where trout laid their eggs.

With all trout streams opening up for catch-and-release fishing Jan. 1, "It looks like fishing will be pretty good," he said. Amid the heavy snow and cold a few winters ago, fishing was hard, often impossible. Just getting to open water was tricky, even dangerous.

Marginal streams, which can freeze over in hard winters, should still be in good shape and fish will still be there, he said. "It might be fine for them," Benjamin said. "But this could change in a week of two."

Mel Hayner, owner of the Driftless Fly Fishing shop in Preston, said some parts of the South Branch Root River were high but conditions on smaller streams, such as Canfield and Forestville in Forestville State Park, have been good.

Catching fish, however, has been another matter. "It's been tough for fishing," he said. He's been using flashy wooly bugger streams effectively, he said. "The key is stealth right now," he said.

When you're at a stream, the usual advice is to avoid walking in any riffles because the redds are there. "Even if you go into the water I haven't seen any research that demonstrates a significant impact," Benjamin said. "If you're worried, just stay in the finer substrates."