Runoff

Guest Blogger: Mike Cline, Bozeman, Montana

Although it takes many forms in different parts of the country, in our western states, particularly the rocky mountain states, runoff is a time of great anxiety and anticipation. Like the earth revolving around the sun, runoff is predictable. It is going to happen every year. The anxiety associated with runoff has much to do with taking advantage of usually excellent pre-runoff fishing in our larger rivers. Pre-runoff is that agonizingly unpredictable time between too cold and nasty and just warm enough to turn things on. As our rivers begin to come out of their winter doldrums, they are low, they are cold and the weather can be nasty, wet and windy. Yet in early March through April things do change. As the days lengthen, the temperatures slowly rise. A few warm days and any remaining lowland snow melts away muddying up the river for a few days, but adding little to the overall flows. As the river clears and warms, the fishing is good if you can find yourself on the river with decently calm weather. By the time late April comes around, the rivers have crept up from their lethargic winter flows to more normal levels. Hatches of midges, caddis and mayflies become more regular. At home, the grass is greening, the perennials sprouting and the fruit trees are budding. Spring is here and runoff can’t be far away.

With both anxiety and anticipation, the big question is when. When will runoff start? How many good days to we have before the rivers going into their annual spring flood? Even more important what are we going to do during runoff? How long will it last? And of course, what changes will it bring? Although I will use the Yellowstone and Madison Rivers as examples, these questions can apply to any drainage subject to spring flooding. For the SW Montana angler, runoff is a big deal. The Yellowstone drains over 70,000 square miles of Montana and Wyoming. That’s a larger area than all but 18 US states. The Madison, one of three major Missouri River headwaters, is not near as large, but does drain most the western Yellowstone Plateau and slopes of the Madison, Gravelly and Tobacco Root ranges—peaks that range over 9000ft. It is a huge amount of water stored in snow pack that will eventually flow downhill.

There is one event every year that coincides with runoff and that’s the Mother’s Day caddis hatch. If the rivers warm to approximately 54 degrees before runoff blows out the river, massive caddis hatches will occur on warm, sunny afternoons and evenings. This year, the Yellowstone was holding around 2500-2900 CFS the last week of April. The river had approximately two-three feet of visibility and several warm sunny days brought out the caddis in huge numbers. The shuttle services on the Yellowstone got a workout as anglers from around the valley headed to the Yellowstone. Interrupted by one day of inclement weather, the fishing on May 2nd was a fine example of the possibilities of pre-runoff fishing. It drizzled all day, but the water was warm and clear enough to produce a massive Western March Brown hatch along with Blue Wings and midges. It is hatches like these that demonstrate the tremendous fish density in rivers like the Yellowstone.

I had fished the river on April 30th in a section about 10 miles upstream. On the 30th, the river was running at 2800CFS and relatively clear. By the 2nd of May, the flow has creeped up to 2900CFS and was still clear. But the warming trend that was bringing out the caddis was also affecting the snow pack deep in the mountains. I got on the river one more day on May 4th. When the day started, river clarity was still good with flows slightly up. By mid-afternoon, things had changed. The water became a bit murky and flows were definitely going up. Rocks along gravel bars that were exposed in the morning were now covered with water. The increase in flows was noticeable in small side channels. As I floated back to the take out it was evident that the river was rising fast. My best guess was that run off had started in earnest. When I got home and checked, the flow was at 3400CFS and we had two or three days of warm weather in the forecast.

As you can see from the USGS graph, it didn’t take long for the snow pack to break loose. In a matter of four days, the flows went from 3000 to over 10000CFS and to 18000CFS within another week. The river went from clear to chocolate milk, safe to dangerous, warm to cold and more importantly a new river was forming. In the four to eight weeks that might pass before run off subsides, the river will change. New gravel bars will form, old gravel bars may wash away. The shoreline will change as banks erode, trees collapse into the river and snags force raging waters into new paths. The Yellowstone’s river bottom is rocky with everything from softball size rock to massive boulders. Every year during runoff, those rocks move a bit more downstream. How the river will change is a bit of an unknown, but it will change. On April 30th as I waded up along a moderately steep gravel and sand bank, I found myself stepping on or touching rocks as large basketballs and suitcases. They were loose and easily tumbled into the river. When runoff came, 100s if not 1000s of these rocks along this sandy bank would make their way to the stream bed and begin their journey downstream. The river would reclaim a bit more of this bank during this year’s runoff.

Anxiety will continue for the next month or so as anglers search out early clearing creeks, spring creeks not effected by runoff, and the various reservoirs and lakes that remain clear during this spring time flood which inevitably occurs every year. Temporary respite will come on May 27th when the Yellowstone National Park season opens. Although impacted by runoff, the Madison, Firehole and Gibbon in the park generally fish well in early June. But inevitably, runoff will subside. All our creeks and rivers will return to their normal, fishable self. Every angler must anticipate a great summer of fishing in SW Montana every Spring during runoff. It’s in the state constitution.

One thought on “Runoff

  1. Michael Vorhis

    Good article on the natural runoff cycles Mike; as you’ve said before it’s a complicated thing. Trying to understand its nuances puts us a little closer to being in sync with what the fish and insects and other stream creatures are naturally tuned to. We have to put off certain activities until water conditions allow, and they do too. Again, good article.

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