Nebraska’s water resources

Lecture outline for Environmental Geology


Nebraska surface water overview

USGS map of Nebraska drainage. The dots are where USGS river gauging stations exist that keep real time track of river flow amounts. Note the W to E drainage, all feeding the Missouri River. Image source: USGS site.

This is a computer generated, shaded relief image of Nebraska. The grey values are assigned on the basis of elevation at that point, and an illumination factor. It is as you are looking at an image showing just the surface geometry/form, where other than position and shape all other surface factors are removed (e.g. the difference between water, soil, vegetation). This is a striking image full of information. Can you pick out the portions with different 'character'? For example can you pick out the Sand Hills? Other portions? The different larger - N-S bands of grey values reflect the slow rise from east to west.


Nebraska Rivers

Niobrara River:

Loup, Dismal, and Snake rivers:

This view shows the Loup River just down stream of the town of Scotia. For those of you who know this area the Scotia chalk mine is below us. Here the Loup is no longer flowing through the Sand Hills but through a loess landscape. Note the sand bars in the river. These are constantly shifting and moving. Also note the wide flood plain here. A good bit of the water in the river here originates as groundwater in the Sand Hills.

Platte River

Republican River

Republican River downstream of Harlan Reservoir dam. Note the abundant riparian vegetation that comes right up to the banks. It has been a while since the channel was scoured by higher flow conditions.

Missouri River

View of Boyer Chute splitting off to right from Missouri River flowing downstream to left. This and the images below were taken one year after the 2011 flood.

Image of Boyer Chute channel. Note the point bar sand deposit on the far bank and the cutbank the image was taken from on the near side of the channel. During the 2012 flood significant channel wideing occurred.

Example of some of the damage the 2011 Missouri River flood did along the Chute. As erosion and bank cutting occurred the support for this walkway overlook was undermined and it sank into the river. Also note the flood sand on the far side.

The elongate pile of larger rocks was the original bank of the river where rip rap was emplaced to armor and protect against bank erosion. This is where the some of the flood waters left the main channel and flowed over the flood plain, depositing sand, including that in the foreground.

Large and deep plunge pool near the entrance of Boyer Chute and caused by a large eddy near the channel mouth as the river waters flooded this area.

One of the houses damaged by the flood. The sand in the foreground and background was deposited during the flood, and was being moved to recover from the flood.


Reservoirs and irrigation canals

Merritt Reservoir:

UNO students on a Nebraska geology field trip inspecting Merritt Reservoir in 2007. Because of the drought in this area the reservoir pool is down. The

Lake McConaughy

USGS map of Lake McConaughy - source: http://ne.water.usgs.gov/projects/lakemcconaughy.html

Ground water fed stream feeding Lake McConaughy. As the lake rises water seeps into the basin sediments recharging groundwater. As it falls the opposite happens. Image source USGS report on Lake McConaughy - http://ne.water.usgs.gov/projects/lakemcconaughy.html.

Harlan Reservoir

Irrigation canal system

This the Ainsworth irrigation canal that comes out of Merritt Reservoir. Note the dune forms just on the other side. Also note that the canal is 'lined' - it has a cement bank and bottom. Obviously this made building this canal more expensive, but it is necessary. Why?

Importance of connection between surface and ground water.


Nebraska Groundwater

High Plains (Ogallala) aquifer - Nebraska's most significant aquifer.

The following quote gives you some idea of its importance. "Approximately 20 percent of the irrigated land in the United States is in the High Plains and about 30 percent of the ground water used for irrigation in the U.S. is pumped from the High Plains aquifer. Irrigation withdrawals in 1990 were greater than 14 billion gallons per day. In 1990, 2.2 million people were supplied by ground water from the High Plains aquifer with total public-supply withdrawals of 332 million gallons per day. " Originally from USGS site http://webserver.cr.usgs.gov/nawqa/hpgw/HPGW_home.html (link now dead).

Geologically - a large wedge of silts, sands and gravels transported by rivers that originated in the Rocky Mountains to the West; i.e. it is the apron of debris that built out from the Rocky Mountains to the west. Three major units (Ogallala, Arikaree and White River Groups) are typically recognized. It is the youngest one, the Ogallala Group, that is a key geologic unit that often lends its name to the aquifer, and it is rich in gravels and sands making it excellent aquifer material.

Map from USGS showing the extent and changes in water level in the High Plains Aquifer. Image from James Miller, 1999. USGS Ground Water Atlas for the United States. United States Geological Survey, Introduction and National Summary. http://capp.water.usgs.gov/gwa/index.html

The High Plains aquifer withdrawals are related to irrigation withdrawals and center-pivot irrigation systems. Tbe above graphs show how irrigated acres and groundwater withdrawal have fluctuated over time. This includes both surface and groundwater sources. Source: USGS site - http://ne.water.usgs.gov/ogw/hpwlms/physsett.html

Aerial view of center pivot at Elkhart, Kansas - source: http://co.water.usgs.gov/nawqa/hpgw/GALLERY.html

View of water seeping out of the Valentine Formation sands within the Ogallala Group along the Niobrara River (near Fort Falls E of Valenine). The arrrows show the bottom of the Valentine Formation sitting on top of a clay rich aquiclude/aquitard unit, where wetting by the groundwater is bringing out the red coloration in the underlying strata. This is basically leakage out of the High Plains aquifer.

Role of the Sand Hills in the surface-ground water system.

Traits of the Sand Hills:

Schematic diagram showing the relationship between the Sand Hills aquifer, subirrigated meadows (and lakes) in the interdune areas, and the underlying High Plains Aquifer. The sand acts as a sponge that soaks up the rain and feeds the surface or near surface water, and the underlying aquifer.

Image from NASA's Visible Earth showing a concentration of lakes in the Crescent Lake area in the western Sand Hills of Nebraska. Note that these lakes are not fed by stream drainage - they are a surface manifestation of a shallow ground water table. Some speculate that this is because the dunes migrated into a previously existing drainage, and 'dammed' it up. Many of these lakes have very distinctive water chemistry, a consideration when thinking from a resource perspective.

This is what some of the dune forms look like on the ground. This picture was taken near Halsey, within the Nebraska National Forest. The dunes are presently 'inactive', stabilized by the grass cover. Research by Dave Loup, Jim Swinehart and others at University of Nebraska at Lincoln demonstrate that several times in the past significant portions of the Sand Hills have lost their grass cover, and become active.

Windmill used to pump shallow ground water up out of the ground for the cattle to use. This picture is from the middle of the Sand Hills.

In the foreground is an interdune area, with grass covered and stabilized dunes in the background. Note how the grass is much greener in the interdune area than up on the dunes. The groundwater table is very shallow here and the roots of some of the plants can tap directly into it. These areas are known as subirrigated meadows. The irrigation in this case is natural, not man-made.


Eastern Nebraska aquifers

Schematic cross section diagram showing the variety of geologic units. Which ones do you think would make potential aquifers. Naturally in order to make educated guesses you need to know something about the various geologic units.

Geologic units in eastern Nebraska and depicted above:

Nitrates in Nebraska's groundwater - link to map. Please take a look and think about the pattern and why the hotspots exist where they do.

Useful links:

Remember to ask questions.