A long, cold winter has finally ended in Minnesota! With a deep cold conclusion and late winter snowfall in April, we have finally seen the earliest blooms of chokecherry and the greening of pastures by mid-May. A late ground-thaw and frequent thunderstorms have kept surface runoff at high levels, making stream conditions for fishing high, cloudy, and downright muddy for the past month. With each passing storm, we have seen a rapid spike in flow and turbidity in our larger streams. Spring creeks, near their headwaters, have offered the only clear water in the region, but water temperatures have remained low, and insect hatches have been few and sparse.
All this is about to change as we approach the traditional Trout Days celebration at Preston, MN, in the Root River valley. The hydrograph at Carimona, just upstream of Preston, shows the influence of precipitation (green lines on the hydrograph) on South Branch Root River streamflows (blue lines). Each of the nearly weekly rainstorms in April and May, immediately boosted the flow rates, which subsided to more normal stream flows over the following week. hydrograph_May 2018
The month of April ended with a typical stream flow of about 100 cfs (cubic feet per second). But May came with a succession of thunderstorms that flooded the watershed, leaving mid-month flows at nearly 4 times the typical summer flow rates. This heavier flow contains not only topsoil draining from uncovered farmland, but silt and sediments from the stream banks re-suspended by the heavy currents. Transparency of the rivers has plummeted from clear (greater than 1 meter) to cloudy (30-40 cm), or worse (muddy: 0-15 cm).
Back to the promises–the weather forecast for the third week in May shows little likelihood of heavy thunderstorms or rain in the week before the Trout Days celebration. The Carimona hydrograph indicates that streamflows can drop to near-normal levels in as little as 3 days in the absence of additional storms. All this should take us to hungry trout by the end of the week, just in time for Preston’s annual “big fish contest”. As with all promises, We Shall See!