For those of you who like word puzzles and problems, consider the following: We have a bathtub with a capacity of 150 gallons (yes, it’s a big tub; the old cast iron type with the “claw and ball” feet), and the tap to this tub can supply 40 gallons per minute when fully opened. As an aside, the tap only gets fully opened once every year or two. Now consider the tub’s drain, which is capable of allow-ing 30 gallons per minute to pass on to places down-stream. How long would it take, if we open the tap fully, before we start to run water onto the bathroom floor?
Now, what happens to this time interval (to a wet bathroom floor) if we increase the capacity of the tap (at fully open) to 80 gallons per minute, increase the frequency at which we fully open the tap to at least once yearly, and leave the drain alone? And just to provide additional interest or com-plexity, let’s say we add two tiers of bricks to the bottom of the tub.
You don’t need a smart phone with a calculator app to know that your bathroom floor is going to get wet more quickly and more frequently with this new set of conditions. Sadly, this latter set of conditions is what we have in Wildcat Creek.
The watershed (the tub) does not change size, as watersheds are defined by topography, the ridges around the perimeter being the drainage divides be-tween watersheds. The dis-charge (the amount of water in the stream flow (the tap capacity) increases as we create more impermeable surfaces — parking lots, roofs, streets, etc. — in the watershed and thus reduce the area that allows water to soak into the ground (infiltration). The drain (outlet) of the water-shed is at the Kansas River, which also varies in flow and, if it is running at higher levels, can back Wildcat Creek up.
What of the bricks? Rivers never build themselves big enough to handle flood flows. For this they build a floodplain, a flat surface next to the channel that gets wet every year or so. Thus, this surface is a part of the river channel at high flow, providing temporary storage of the water and sediment conveyed at flood conditions (and also reducing the water velocities and depths associated with these high flows). The bricks in my crude analogy represent the filling of this geomorphic floodplain, which is all too common in urban areas. Such floodplain filling is certainly evident between Seth Child Road and Fort Riley Boulevard.
I think those of you who have stayed with me until now can see where we are headed as we continue to fill the floodplain to allow development and increase the amount of impermeable surface, thus increasing rapid runoff and decreasing infiltration. Throw in some climate change that may well make for more powerful storms in the coming years and things just get more interesting and urgent.
I don’t live in the Wildcat Creek watershed; I don’t even live in Riley County, but I have observed, measured and studied the Wildcat Creek for the last dozen years or so. I’ve been a professor of various ranks at KSU for 30 years now and have many friends and associates who do live in the Wildcat Creek watershed. Flooding in the watershed will not get better on its own; there are measures that can help, but these will take money and informed manage-ment decisions. It seems to me that formation of a watershed district is one way to facilitate and sustain both.