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Missouri Valley in Harrison County, Iowa — The American Midwest (Upper Plains)
 

Terracing in the Loess Hills

 
 
Terracing in the Loess Hills Marker image. Click for full size.
By Cosmos Mariner, August 10, 2017
1. Terracing in the Loess Hills Marker
Inscription.  The Loess Hills of Western Iowa are made of wind-blown soils that are highly susceptible to erosion if not protected by a patchwork of conservation practices. All throughout the Loess Hills region, farmers use multiple practices, placed in specific areas of their farm, to provide the most protection against erosion.

Terraces Help Prevent Erosion
Water gains speed and power as it runs downhill, similar to a sled on a snow-covered hill. Terraces are constructed on hillsides to reduce the length of the slope to slow rain water, capturing it and reducing its erosive power. They catch water much like eave spouts on a house. Slope is the rise in land over a certain distance. For example, if the land rises 10 feet in height over 100 feet, it has a 10% slope.

A terrace is made of compacted soil, usually spaced 120 feet apart. Almost all terraces in Western Iowa are constructed on the contour around a hill. This is a practice unique to the Loess Hills, because the deep loess soil allows the captured water to quickly soak away from the surface, preventing crop loss from standing water. Terraces across the rest of Iowa are typically
Marker detail: Terraces Help Prevent Erosion image. Click for full size.
2. Marker detail: Terraces Help Prevent Erosion
designed with an intake and underground outlet, so that captured water can move downslope through drains.

Types of Terraces
Not all terraces are alike. There are four types of terraces in Iowa: broad base, narrow base, grassed back slope and basin.

Broad base: Usually has crop on both sides and is built on a fairly flat slope which is 6% or less.

Narrow base: Also known as A-frames because they have steep sides that look like an "A." This terrace, which is the most popular style with farmers, has grass seeded on both sides and is never farmed.

Grassed Back Slope: Farmed on the upper side and seeded to grass on the lower side, thus getting its name, grassed back slope.

Basin: Constructed on non-cropland such as pastures where livestock graze. Basins are all seeded to grass.

Grassed Waterway: Sometimes water flow will concentrate in a field to form a rill or gully, where erosion cuts down into the field. To help prevent this type of erosion, farmers plant grassed waterways which act like a waterslide to safely carry concentrated flowing water from a field.

In western Iowa, grassed waterways are shaped like a cup and planted to grass. They are normally 30 to 40 feet wide and up to 2 feet deep. A grassed waterway will typically collect water from an area equal to 23 football fields (about
Marker detail: Grassed Waterway image. Click for full size.
3. Marker detail: Grassed Waterway
30 acres or less). Areas with flatter terrain can have grassed waterways that collect water from hundreds of acres.

Other Loess Hills Conservation Practices

Water and Sediment Control Basin: A large terrace or small dam usually constructed on a property line between neighbors with a fence built on top of it. Unlike terraces, this practice can capture runoff from a drainage area up to 50 football fields in size. Some basins hold all the water until it soaks down into the soil; others safely drain the water within a 24-hour period through a pipe.

Dam: A dam is usually constructed across a stream or natural watercourse to create a water source for irrigation, municipal water supply, recreation or livestock. In western Iowa, dams also provide floodwater and gully control.

Contour buffer strips: This is a strip or a series of strips of grass on the side of a hill; the steeper the hill slope, the greater the number of strips required. These strips slow the flow of rainwater and catch sediment (eroded soil). Sediment may carry fertilizers, herbicides (for weed control) and pesticides (for bug control), so keeping sediment in fields helps protect water quality.

Harmony Watershed
When the Harrison County Soil Conservation District was organized in 1942, farmers used plows to construct 15 miles of terraces, some of
Marker detail: Water and Sediment Control Basin image. Click for full size.
4. Marker detail: Water and Sediment Control Basin
the first built in Iowa. Just 15 years later, conservationists used heavy equipment like road scrapers, graders and bulldozers to build 263 miles of terraces within the District.

On December 7, 1953, the Harrison County Soil Conservation District Commissioners, along with other agricultural agencies and area farmers, organized the Harmony Creek Watershed Association. Four years later the Harmony Creek watershed was approved as Iowa's first federal watershed project (Public Law 566).

Since 1957, conservation construction has increased. Conservationists have built hundreds of dams and many thousands of miles of terraces, which are now adapted to handle today's 16- to 24-row farm equipment. Other advances include abandoning the plow and adopting no-till, which leaves the soil undisturbed thus reducing erosion. In 1942, farmers were losing 60 to 70 tons of soil per acre per year through erosion; this is now down to 4 to 5 tons of soil loss per acre per year.

Text and Photos: Dennis Perkins, Natural Resources Conservation Service
Laura Greiner, Natural Resources Conservation Service

 
Erected by Golden Hills Resource Conservation & Development, Loess Hills National Scenic Byway Council, Loess Hills Alliance, and Western Iowa Tourism Region.
 
Topics. This historical marker is listed in these topic lists: Agriculture
Marker detail: Harmony Watershed image. Click for full size.
5. Marker detail: Harmony Watershed
Environment.
 
Location. 41° 35.008′ N, 95° 50.813′ W. Marker is in Missouri Valley, Iowa, in Harrison County. Marker can be reached from Lincoln Highway (U.S. 30) just west of Monroe Avenue, on the right when traveling west. Marker is located along the walkway at the Harrison County Historical Village & Iowa Welcome Center, overlooking the Lincoln Highway. Touch for map. Marker is at or near this postal address: 2931 Monroe Avenue, Missouri Valley IA 51555, United States of America. Touch for directions.
 
Other nearby markers. At least 8 other markers are within 11 miles of this marker, measured as the crow flies. Agriculture in the Loess Hills (here, next to this marker); Loess Hills of Western Iowa (a few steps from this marker); 3389 Miles from New York to San Francisco... Join the Ride! (a few steps from this marker); Missouri Valley Veterans' Memorial (approx. 3.6 miles away); Lewis and Clark Campsite Area (approx. 9 miles away in Nebraska); Steamboat Bertrand (approx. 10.4 miles away in Nebraska); The Lewis and Clark Expedition (approx. 11 miles away in Nebraska); Up the Missouri (approx. 11 miles away in Nebraska). Touch for a list and map of all markers in Missouri Valley.
 
Terracing in the Loess Hills Marker image. Click for full size.
By Cosmos Mariner, August 10, 2017
6. Terracing in the Loess Hills Marker
(Lincoln Highway in background)
 
 
Credits. This page was last revised on December 13, 2020. It was originally submitted on December 12, 2020, by Cosmos Mariner of Cape Canaveral, Florida. This page has been viewed 38 times since then and 5 times this year. Photos:   1. submitted on December 12, 2020, by Cosmos Mariner of Cape Canaveral, Florida.   2, 3, 4, 5, 6. submitted on December 13, 2020, by Cosmos Mariner of Cape Canaveral, Florida.
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Feb. 25, 2021