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omite

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rCh

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nes

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Sout

hern

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rift P

lain

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ly G

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gy:

The

high

est p

oint

on

the

ride

to

day

will

be

just

bef

ore

the

tow

n of

Sta

te C

ente

r, w

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ride

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o up

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r the

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aine

that

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ks

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es

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ys th

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ut d

own

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siss

ippi

an-a

ge (3

30-

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mill

ion

year

s ol

d) d

olo-

mite

s an

d lim

esto

nes.

RAGBRAIDay 42018Wednesday, July 25

As you bike across the state of Iowa you will primarily be riding on paved roads, but what are they paved with? Some are paved with concrete and some with asphalt. What is the difference? Well, both are composed mostly of aggregate, fragments of crushed limestone or dolomite and sand. It is the material that glues these fragments together that is the primary difference. Concrete (the white or light gray road surface) uses Portland cement to glue the aggregate together. Portland cement is made by firing a finely crushed mixture of limestone, sand, clay, and other materials to 2,600° F in a kiln to produce a clinker that is mixed with gypsum and crushed to a fine powder to make the cement. The cement is mixed with water and the aggregate and applied to the road base to create a concrete roadway. Asphalt is a viscous petroleum product that is heated, mixed with aggregate and applied to the road base to create an asphalt roadway. 94% of asphalt and 80% of concrete is made up from aggregate.

The Science of Roads

* Cover photo: Aerial photo showing the unique topog-raphy of the Des Moines Lobe.

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Nevada

Melbourne

Baxter

1148 ft.

751 ft.

Elevation

StateCenter

Colo

Ames

NewtonSqu aw Creek

SouthSkunk

River

South Skunk River

Fourm

ile Cre ek

Indian Creek

Parks and preserves

Cities and towns

USGS streamflow station

Ames lies in the heart of the Des Moines Lobe, the last glacial advance into Iowa. The gentle topography, small lineated

ridges, and closed drainages (prai-rie potholes) are signatures of this

landscape. Around 5.8 miles east of Colo and 1 mile west of State Center on Highway 930, riders will encounter the Bemis Mo-raine. This feature represents the

terminal margin of the Des Moines Lobe.

Moraines are curved, concentric bands of ridges and hummocky terrain that

outline the maximum extent of active ice advances and the position of prolonged, stationary margins of stagnant ice masses. The deposits marooned around these ice margins became well-defined features of the land surface once the ice melted away. It is important to realize that Iowa’s end moraines are not uniform or consistent in their appearance or composition be-cause so many different environments of deposition existed along a single ice border. Consequently, these features do not conform to the classic “recessional” moraines caused by active and repeated glacial advance and retreat, which was more common in states to the north and east of Iowa. Instead, we see rapid glacial advances into northcentral Iowa, followed by regional stagnation of the ice-a picture more consistent with surge-type glacial activity.

Roadside Hydrology The Bemis MoraineAs you bike across the Iowa landscape, do you ever notice the roadside ditches? Did you know that roadside ditches line more than 6.3 million km of public roads in the U.S.? Ditches located throughout urban and rural landscapes are integral components of watershed-scale hydrol-ogy. They cross topographic boundaries and concentrate water flow from road-

ways and the catchment areas that drain into them, thereby efficiently delivering runoff, sediment and pollutants to down-stream surface water systems. Researchers at the Iowa Geological Survey recently completed a study of roadside ditches in an eastern Iowa watershed to see if roadside ditches can process nutrients delivered to them from agricultural areas. Study results showed that nitrate concen-trations in roadside ditch groundwater decreased an average of 60% as water flowed downslope in the ditch. In fact, the nutrient processing capacity of some roadside ditches were equivalent to some Iowa nitrate-treatment wetlands! Keep this in mind as you travel through the Iowa country-side and envision how we could better utilize roadside ditches to capture and remediate nutrients as part of watershed management plans.