Overton Bottoms North Scour Holes EarthCache

This cache has been archived.

Geocaching HQ Admin: It has now been over 30 days since Geocaching HQ submitted the disabled log below and, unfortunately, the cache owner has not posted an Owner maintenance log and re-enabled this geocache. As a result, we are now archiving this cache page.

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Hidden : 6/17/2010
Difficulty:
1 out of 5
Terrain:
3 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

What is a scour?

A scour, or “blow hole,” is the hole left behind when sediment is washed away from the bottom of a river. Scours can occur at anytime but are more prevalent during flood events. This is because flood waters have a much faster current and higher energy than calm water enabling water to easily lift and carry sediment down river.

NOTE: Do not rely on Google Maps to lead you to these caches. For accurate directions, please see (visit link)

During flood events, a river can carry large amounts of sediment suspended in the flow. Surface runoff containing material such as clay, silt and fine sand are washed into the river and additional sediment comes from the river’s own bed and banks. These materials from the bottom of the river are most crucial for providing fish habitat.

Scour holes become pools ideal for aquatic turtles and fish such as flathead catfish, largemouth bass, crappie and gar. River floods naturally restock these pools and provide enriching nutrients.

There are five scour holes on the Overton Bottoms Unit of Big Muddy National Fish & Wildlife Refuge. Some may be inaccessible depending on river levels and vegetation conditions. Please beware of this when visiting the Refuge and do not try to access land that is underwater for your own safety. These bodies of water were created during the raging floods of 1993 and 1995 when the river scoured out depressions in the floodplain, some over 50 feet deep.

These scours were formed as the flood waters became so high that they breached the levees and fell almost vertically from the top of the levee, pouring down the opposite side of the levee like a waterfall. The strength of this waterfall increases with the volume of water passing over the levee, and the height of the fall.

If the bed materials are small enough to be eroded by the falling water, a scour hole develops immediately below the levee. The smaller materials are scoured out first, followed by larger particles until only those remain which are too large to be moved by the water.

Material moved from a natural scour hole is carried downstream where, as the velocity decreases, it forms a gravel/sand bar. Such bars are excellent spawning beds for fish.

By locating the position of this Earthcache, you will find a bridge that crosses a flow of water connecting two of the scours on the unit. One is the Diana Scour; please provide the name for the other scour which is named after the trees that surround the area. These trees can be recognized during the growing season by their glossy green leaves or by their bright yellow color in the fall. When pioneers first arrived on the Great Plains where vegetation was scarce, they searched for these trees to offer them wood and shade. This tree also meant there was water nearby because they tend to grow in wet areas.

E-mail your answer to tim_haller@fws.gov.

Sources:
Great Plains Nature Center. Cottonwoord. 28 June 2010.

U.S. Department of Transportation Federal Highway Administration. Flow in Natural Streams. 28 June 2010.

Warren, Linda P. Stream Stability and Scour Assessment at Bridges in Massachusetts.

Additional Hints (Decrypt)

(Uvag: Cvpx hc n znc bs gur nern ng bhe xvbfx sbe uryc.)

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)


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