STREAM HYDROLOGY

I've had several folks ask me lately why a specific amount of rainfall can mean the creek is blown sometimes and not even bump the flows at others. It all boils down to simple stream hydrology. Once you have a very basic understanding of stream hydrology, you'll better be able to predict the effect of rainfall or snowmelt on your favorite Great Lakes tributary.

Streams are created when excess water from rain, snowmelt, or near-surface groundwater accumulates on the ground surface and begins to run downhill. Excess water from rain or snowmelt occurs when the water accumulates at a faster rate than the soil and organic matter can absorb the water, plants can use it, or the water can be evaporated into the air.

Let's repeat that, "...water accumulates at a faster rate than the soil and organic matter can absorb the water, plants can use it, or the water can be evaporated into the air." This is what you have to consider for each season when trying to figure out what impact the rain is going to have on a creek you want to fish.

So, lately folks are wondering, "Why does half an inch of rain do nothing for the creek in September or early October, yet create several days of sustained flows in December?"

It's easy really. The ground is bone dry right now. The trees still have leaves and all of the ground flora is still using significant water as well. And, the air temperatures are still warm and causing a greater amount of evaporation.

Once the temperatures drop, the leaves fall off of the trees, and the grasses and weeds go dormant, the soil will saturate more quickly (or the ground surface will just plain be frozen). This will result in higher sustained flows and smaller amounts of rainfall will have a greater impact on flows.

It's that simple. Not everyone has an educational background in the earth sciences, so there is no reason for this to be intuitive to everyone. Now you know and now you can better predict how NOAAs rainfall projections may impact your favorite streams. Keep track of it and within a couple of years you'll always know what is likely to be going on where you like to fish!

Who's ready for a steelhead trip? Call me! LET'S GO FISHIN'!