Floodplain, Reclaimed

impassableMy recent 99wetlands forays, and other travels, have been hampered by the flooding in much of Iowa. For example, two approaches to a wetland in Keokuk County were impassable, causing me inconvenience as I rerouted, followed by uncertain road conditions near the site (thankfully, it turned out all right in the end). However my frustration or disappointment means little compared to what others face: as I write this (October 14), flood warnings are posted for major rivers all over Iowa, affecting counties across the State; the Iowa Flood Center has 72 active alerts from sensors. Large cities such as the capital and largest city, Des Moines, but also Quad Cities (Iowa/Illinois), Cedar Rapids and Waterloo, Muscatine, Burlington, and Spencer are among the areas threatened by this flood event. Many families and business will be disrupted.

Then, there are the farms. The timing is unfortunate, as many fields across the State are still not harvested, and now the weather has turned cold (including widespread freeze warnings). Most farmers really should bring in the crop now. The fields are so wet in many cases that it’s too soft to run machinery for harvest. But in extreme cases, it’s not mud in the fields…it’s standing water. I imagine when the water recedes, it will leave behind damage to the soil and plant that present problems. A quick on-line search suggests that floods so late in the season are unusual, and farmers will need to proceed with caution as the grain or silage may be spoiled.

DSC_0251“But Paul,” you say. “This blog is about wetlands—what does any of that stuff have to do with wetlands?” Three things come to mind, actually.

First, much of the low-lying areas at danger of flooding, whether town or farm or other land-use, are located on an important wetland type: floodplains. In several past posts, I have taken you to floodplain wetlands. In Van Buren county, we made the hydrologic connection, seeing the surface connections between a floodplain wetland and the nearby river. In Wright County, we understood past flooding by observing snarled drift hung up in tree branches above the stream channel at Snarl Street wetlands. Not far from Des Moines in Polk County, we saw oxbows and other river-related wetlands at Chichaqua Bottoms.

DSC_0194But one of the very first wetlands I visited on this project, I revisited last week: Maskunky Marsh in Mahaska County. In my earlier visit, I explained that the marsh is in the floodplain of the South Skunk River, and is inundated through a horizontal pipe set at an appropriate elevation—a so-called “French Drain.” When the river is high, river water backs up through that pipe, and into the marsh…and therefore, areas downstream will experience less flooding.

On this quite recent visit, I saw that we were way, way past that type of flood stage. Indeed, the river was exceedingly high, and was completely reclaiming its floodplain. Roads, buildings, farm fields…all under water. The whole floodplain was a broad river channel. In such extreme flood events, the river will not be denied its floodplain.

 

This brings me to my second point: wetlands reduce flooding. Despite the extreme situation I just described, please remember: it can be worse. When I give talks about wetlands and flooding, I start by reminding listeners of their science lessons from childhood school days. Remember the famous hydrologic cycle (a.k.a. Water Cycle)? Yeah, that’s still a thing! Think of it this way: every drop of rain or snow falling within the borders of the State of Iowa must go somewhere. That water can basically go up, down, or sideways. Some portion of water falling from the sky, returns to the sky, through plants pumping it up (transpiration) or air lifting it up (evaporation). Only a very small amount travels down to deep groundwater (aquifers tend to recharge slowly). So, a lot of the water will flow sideways (laterally), across the land’s surface to ditches or streams or lakes or rivers; or, infiltrate only shallowly into the soil, and then emerge into a streambed or other surface water. And too much of that lateral flow means flooding.

Wetlands help reduce flooding, because water is held in soil and vegetation, and ponds up in the basin (standing water). Then, the accumulated water will slowly re-enter the air, or be more slowly released into streams and rivers.

The other big role of wetlands in flooding is indirect, through the process of climate change. This is a rather complex interaction, and I intend to discuss it in more detail in later posts. Suffice it to say, climate change can, among other things, make more extreme weather—and that will include flooding. Meanwhile, wetlands may—generally will—reduce a major driver of climate change, atmospheric carbon. For example, the carbon stored in peat—such as at Becky’s fen—is carbon NOT floating around the atmosphere, contributing to climate change. So, there’s a connection: wetlands reduce our risk from climate change. Add that to the flood reduction effects, and it’s clear that wetlands are here to help…and we need that help.

Everyone, please stay safe. Be careful with our current flood threats. And let’s work on measures to prepare for future risks. May I humbly suggest: wetlands will help us face our challenges…let’s protect, restore, and enjoy our wetlands…and help them, help us.DSC_0204

Author: Paul Weihe

Associate Professor of Biology at Central College, traditional author (Textbook of Limnology, Cole & Weihe, 5th ed.; Waveland Press), and now...blogger!

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