Borrow Pits EarthCache

Borrow Pits

Sandpit Lakes in the Platte River Valley

This EarthCache is located in the Fort Kearney State Recreational Area.

A Nebraska Park permit is required for all vehicles.

Tools needed to log this EarthCache include the chart found below,

A trowel, spoon or other small digging tool and a tape measure or ruler,

And a camera.

The Geology

Platte River Valley Sedimentation

Down through the valleys of Colorado and Wyoming, across the plains of Nebraska, transported by the shallow waters of the Platte River, bedloads (particles swept along the riverbed, not particles in suspension) of sands and gravels are deposited, swept away again and re-deposited, creating an ever changing braided river with multiple channels that wind and shift, bypassing sandbars or eroding them away.  By this action, the river itself tends to roughly sort the particle sizes, leaving pockets of similar sized sediments. Times of flood or high velocity flow would move the largest particles along, while times of lower volume flow could only transport smaller particles. As the river meandered and wove its braids of sediments throughout the ages, these deposits were spread out through the Platte River Valley flood plain quite some distance from where the river currently runs.

The Hydrology

The Oglala Aquifer and Water Tables

An aquifer is an underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand, silt, or clay) from which groundwater can be usefully extracted using water wells. A Water Table is the surface of the saturated porous material. The beach provides a model to help visualize an aquifer. If a hole is dug into the sand, very wet or saturated sand will be located at a shallow depth. This hole is a crude well, the wet sand represents an aquifer, and the level to which the water rises in this hole represents the water table.

The Oglala Aquifer is a vast yet shallow underground water table aquifer located beneath the Great Plains. One of the world's largest aquifers, it covers an area of approximately 174,000 mi² (450,000 km²) in portions of the eight states of South Dakota, Nebraska, Wyoming, Colorado, Kansas, Oklahoma, New Mexico, and Texas. It is said to contain primarily fossil water from the time of the last glaciation.

The Resources Put to Use

The I-80 Sandpit Lakes

Most lakes along I-80 are borrow pits, especially from North Platte to Grand Island where the interstate runs parallel to the Platte River. When I-80 was built, the easiest and cheapest route was the flat, wide-open Platte River Valley. Building the highway along the river was a challenge because of high groundwater levels and because there were no hills to provide fill material. Wherever road builders needed fill for an overpass or roadbed, they took it from the valley floor. Groundwater soon seeped into the borrow pits. Knowing this would happen, engineers and fisheries biologists collaborated to ensure that the pits were dug with fish and anglers in mind. The result was the creation of more than 50 clear, deep and productive fishing waters now known as the “I-80 lakes.”
Forty of them are open to the public.

Logging Requirements

In an email to the cache owner:

Grab a small handful of sand from the lake shore and describe the size and shape of the particles. Are there widely different sized grains or mostly similar sized grains?

And

Using the Huljstrom chart below estimate the river velocity it would have taken to originally transport these particles.

OR

Using a small trowel dig a shallow well into the beach several feet away from the lakeshore. Measure the depth you have dug to and the depth of the water that flowed into your well. How does this level compare to the water level of the lake? Be sure to fill in your well when your observations are complete.

Optional

 Post a photo of yourself, your gps or an avatar at the sign post on the beach

Optional, Just For Fun

Create a small sand sculpture or drawing at the swimming beach and upload a photo.
Plan ahead and be creative!!

Family friendly images only.

This EarthCache has been developed by a Platinum EarthCache Master and member of Nebraskache.

Wikipedia contributors, "Water table," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Water_table&oldid=303101920 (accessed July 20, 2009).
Wikipedia contributors, "Aquifer," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Aquifer&oldid=305778841 (accessed August 3, 2009).
Wikipedia contributors, "Ogallala Aquifer," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Ogallala_Aquifer&oldid=307531695 (accessed August 12, 2009).
A Guide to Public Fishing Lakes in the I-80 Corridor
By Rick Eades, Urban Fisheries Specialist NEBRASKAland ? May 2006