Erosion by rivers
PHOTOS BY GARRY BRANDENBURG — The outside curves of rivers are always where the highest flow rates of the current can be found. At high flow rates, or at times of actually flooding on adjacent floodplain lands, the current is very strong and relentless. Such was the case on Feb. 28, between 6 and 7 a.m., when the Iowa River crested during its most recent high flow times due to heavy rain. The crest was measured at 17.52 feet, or an actual river depth increase over “normal low flow” of about seven feet. River bend soil erosion has been a fact of life for decades. With each bit of soil loss, the bend cuts deeper. On the opposite side of one river bend north of Sand Lake, near the northeast pool, the pressure of high river water finally broke through, creating a rushing cascade of soil and flood water into the northeast pool. It took a while for the river level and the pool levels to equalize. In today’s images, the view from the air depicts the missing sliver of land that fishermen used to use. Not anymore. About 75 feet of land is missing. A steep and dangerous vertical cut bank remains where the river now accesses the old sand pit. Winter frost retains its temporary grip on the topsoil, and flood waters have undercut and eroded soils below the frost that were saturated by high water.
Erosion by rivers is a persistent active force of streams and rivers all across the globe. It is an unstoppable natural act of physics and geological processes as surface waters find exits to lower elevations.
There are other erosional events such as earthquakes that over long term time frames can and do erode mountain ranges into hills, and hills erode toward low lying floodplains. Heavy rain events can cause erosion.
Numerous past geologic episodes of glaciers building, advancing, and retreating also caused erosion. Wind can and does sculpt landscapes by removing material, holding some of the smallest particles in suspension.
By far, however, the most active present day erosion forces are those times when high water and/or flood events are powerful enough to move large quantities of materials.
Sand Lake witnessed such an episode in late February of this year. All last year, the river was running very low and slow due to lack of rain.
And at Sand Lake, its water levels reflect approximately the same levels in their isolated pools. Those pools are the holes remaining after sand and gravel excavation operations of many decades in the past. Sands and gravel removed by mining left deep holes of about 30 to 35 feet deep, deep enough that groundwater always seeped into those holes and stabilized at a level called water table.
Water levels in Sand Lake mirror water levels in the river. Normally, there is no direct river connection. Water levels adjust slowly via percolation through underground layers of soil strata. Many times in the past, and even during public access to Sand Lake beginning in 1999, high flows in the river eventually sees higher water levels in the pools of this popular fishing and boating site. Likewise, if the river is running very low for a long period of time, Sand Lake’s water levels leak out and stabilize. Water levels between the river and Sand Lake are like a yo-yo, going up and down but in very slow motion.
Mother Nature made her move on Feb. 28, at or near the peak flow rate of high water in the river at that time. The hydraulic pressure of high river water against a thin soil line separating the northeast Sand Lake pool was too great.
The land slipped away quickly as a mad rush of river water cut away any remaining soil for about 75 feet. That loss of soil allowed river water to roll into the northeast pool. Erosion by the river won, like it always does.
Marshall County Conservation staff was well aware of this inevitable outcome. They just did not know when it would happen.
Over the course of past decades, discussions with Iowa Fisheries staff and others considered what to do, if anything, about the river getting closer and closer as erosion altered the river’s course. The conclusion was a realization that nature was going to win this battle, regardless of what people might have thought could be done. I agree with that assessment.
Now there is a river connection to this pool, and fish will undoubtedly exploit new territories of aquatic environments. The Iowa River’s channel remains where it has always been as it curves back and forth within the floodplain. Time will help tell the story in another chapter of how erosion by rivers is a persistent active geologic force or nature.
——-
Recent warm weather, recent rain, and the fact that mid-March’s time frame will result in many returning birds to our area of the state, are all welcome admonitions that spring is soon going to happen. On March 20, the official first day of spring season will be upon us.
Equal daytime and nighttime hours will greet us. So will more and more robins, red-winged blackbirds, waterfowl of all species, and the beginning of many songbirds. Look for them diligently at backyard feeders or at other outdoor habitats.
One new arrival that this author found delightful to his ears were the deep twillering calls of Sandhill Cranes. I heard them for the first time on March 15. This big tall bird of the wetlands is back into the old oxbows and ponds located between northwest Marshalltown and the Mann Wetlands complex south of Albion.
It is good to hear the cranes called again.
——-
Another calling I want to remind you of is called Iowa’s Wildlife Diversity Program. You and many others are encouraged to support this program in an easy way — via a donation made at Iowa income tax preparation time.
Monies donated to the informal name “Chickadee Checkoff” help support the goals of guidance to landowners and land managers for nongame wildlife species. Conservation efforts take money. This is a fact of life, and lots of folks also want to go above and beyond in efforts to assist.
Funds donated to the Wildlife Diversity program are used for research and surveys, to obtain data and information. Part of the funds may be used for critical land acquisitions.
Diversity money also supports education efforts to foster appreciation and public events. The program assists landowners with management of habitats, and exciting re-introductions of species like Osprey, Peregrine Falcons, Trumpeter Swans, River Otter and Greater Prairie-chicken were and continue to be recognized.
More recent programs involve monitoring frogs and toads, bald eagles, monarch butterflies, wood turtles, barn owls and more. A basic inventory and monitoring of nongame species on a statewide standardized survey format is underway. Habitats that are critical and unique are
identified and woven into a long term plan for wildlife diversity.
The Chickadee Checkoff began in 1982 when it was first added to the Iowa income tax forms. The potential is enormous. If every Iowa taxpayer donated just one dollar, the Wildlife Diversity Program would have $1.5 million to utilize.
The reality is, however, that not everyone uses this painless method to add funds to this aspect of wildlife resource research and management. I just ask you to carefully consider the need and make your own decision on how much to donate this year to the Wildlife Diversity Program. Thank you.
——-
Trees for Iowa, Trees for People is the title of a free program this coming Tuesday, March 21, from 11:30 a.m. until 12:30 p.m. Call 752-5490 to register.
Learn the history of trees in Iowa and locally, which species to plant or avoid, and the scientific benefits obtained from trees. The program location is the Grimes Farm and Conservation Center.
——-
“Never let yesterday use up too much of today.”
— Anonymous
Garry Brandenburg is the retired director of the Marshall County Conservation Board. He is a graduate of Iowa State University with a BS degree in Fish & Wildlife Biology.
Contact him at:
P.O. Box 96
Albion, IA 50005
-
- PHOTOS BY GARRY BRANDENBURG — The outside curves of rivers are always where the highest flow rates of the current can be found. At high flow rates, or at times of actually flooding on adjacent floodplain lands, the current is very strong and relentless. Such was the case on Feb. 28, between 6 and 7 a.m., when the Iowa River crested during its most recent high flow times due to heavy rain. The crest was measured at 17.52 feet, or an actual river depth increase over “normal low flow” of about seven feet. River bend soil erosion has been a fact of life for decades. With each bit of soil loss, the bend cuts deeper. On the opposite side of one river bend north of Sand Lake, near the northeast pool, the pressure of high river water finally broke through, creating a rushing cascade of soil and flood water into the northeast pool. It took a while for the river level and the pool levels to equalize. In today’s images, the view from the air depicts the missing sliver of land that fishermen used to use. Not anymore. About 75 feet of land is missing. A steep and dangerous vertical cut bank remains where the river now accesses the old sand pit. Winter frost retains its temporary grip on the topsoil, and flood waters have undercut and eroded soils below the frost that were saturated by high water.
Columnists
No, demonstrations today not like the 1960s
The current demonstrations on college campuses against Israel remind some of the unrest on college campuses during ...
Looking for a better paying job? Good news
History informs farm policies of today
Weeks before the spring warmth began thawing the soil, farmers across Iowa felt the itch to get in the fields. As a ...
The impact of the 2024 legislative session on Iowa’s Area Education Agencies: What was cut and how will it impact services?
As Iowa’s Area Education Agencies (AEAs) approach their 50th anniversary of services to Iowans, they do so in the ...
Terminating AI funding to our adversaries
Artificial intelligence (AI) was engineered to make our lives easier but poses the possibility of being twisted ...
