Geog 1030 Discussion Assignment-Water Resources #4
Graded--Due at the beginning of discussion the week beginning Feb 22, 2004
The following questions require that you go to the appropriate web sites. You might also look in chapter 9 of your textbook. Look at pages 272-73 in particular. Last year students had some problems in reading the maps so I have added some supplementary web sites and explanation to assist you
Background. I suggest you go over each of the following links one at a time to make sure you understand what each link is illustrating or showing you. Then after you have gone over the links go to the bottom of the page and answer the qeustions.
1. Annual Precipitation over High Plains (Ogallala) Aquifer http://ne20dnelnc.cr.usgs.gov/highplains/normprec.html. This map shows precipitation in general terms over the entire Great Plains. Note the general drop in annual precipitation from east to west
2. Great Plains Precipitation http://www.greatplains.org/resource/atlas/atlas/prec.htm This map is in somewhat more detail and shows precipitation over the area covered by the Ogallala Aquifer by means of isohyets. Isohyets are just like isotherms and isobars except they illustrate the distribution of precipitation
3. Map of major watersheds in Nebraska- illustrates the areas that contribute to discharge of a specific stream.http://maps.unomaha.edu/Peake/1030/watershed.gif
4. Discharge of Nebraska Rivers--thickness of green lines indicates relative discharge. Note that much of the discharge of the Platte occurs in eastern Nebraskahttp://maps.unomaha.edu/Peake/1030/discharge.gif
5 Generalized land use map of Nebraska . Sorry for the lack of detail. http://maps.unomaha.edu/Peake/1030/lcvr.gif
6 This map illustrates some of the major land resource regions in Nebraskahttp://maps.unomaha.edu/Peake/1030/major.gif
7 Shows the thickness of the major aquifer in all areas of Nebraska. The thickness represents the zone where all available openings are filled with water. The amount of water stored depends on the pore spaces in the underground rock but in general one foot of bedrock may hold one to two inches of water or morehttp://maps.unomaha.edu/Peake/1030/pathick.gif
8. This chart illustrates the average depth to the water table in various parts of Nebraska. In general the closer the water table is to the surface the easier (and cheaper) it is to draw water up from below. Given the large amounts needed for agriculture and the low price for many agricultural commodities it is vital to keep the energy costs as low as possiblehttp://maps.unomaha.edu/Peake/1030/dtlevel.gif
9.Shows areas of Nebraska where the water table has either declined (withdrawl of water exceeds replenishment) or risen (replenish of groundwater has exceeded withdrawl)http://www.cnppid.com/Assets/gwmap.jpg
10. This map illustrates the number of center pivot irrigation systems and their location. Each center pivot generally covers 140 acres of land with about 15 inches of water during the growing season. Most of this water comes from groundwater sourceshttp://maps.unomaha.edu/Peake/1030/pivots.gif
11 Shows the precipitation received over the United States in the past week. Based on Doppler Radar estimateshttp://www.intellicast.com/LocalWeather/World/UnitedStates/WeeklyPrecipitation/
12. This is the real time water discharge data for Frenchman Creek near Palisade, Nebraska which is in the far southwestern corner of the state. Note the top chart shows the continuous discharge in cubic feet per second over the past seven days. Compare this to the median (i.e. normal) discharge at this station over the period of record (the triangular shaped symbols near the top of the chart. In winter the discharge data is often inaccurate because of ice but if you look at the gage height you can get an idea of the trend of stream flow. This year (2004) it is defiintely less than the median flow.http://water.usgs.gov/ne/nwis/uv?06834000
13 This map is a generalized indication of what areas of the United States are suffering from a drought. If you look at Nebraska you can see the abnormally dry conditions in southwest Nebraska. Note the severe drought in the upper reaches of the Platte River Basin (Northern Rockies)http://www.drought.unl.edu/dm/monitor.html
Some additional images that might be of help
Great Plains Drainage and Precip
ANSWER THE FOLLOWING QUESTIONS ON THE BACK OR ON A SEPARATE SHEET OF PAPER
1. In general, what part of Nebraska (based on rainfall) could use irrigation water.? Keep in mind that in general areas with less than 24 inches of rainfall would benefit considerably from supplementary water (Links 1 and 2)
2. Where along the Platte is the most water available. Hint- look for a storage location (Link 3 and 4)
3. Which makes a greater contribution to Nebraska water supplies, the North or the South Platte? Think about where the South Platte rises and what area it flows through. Does this help explain why so little water is available to Nebraska? (Link 4)
4. Compare the distribution of center pivots to declines in the Ogallala Aquifer . What areas in Nebraska are most in decline? (link 9) Why is this so? (link 10)
5.Look at the discharge graph for Frenchman Creek. Over the past week is the flow above or below the normal discharge? Given the fact that it often takes several days for precipitation to flow into streams do you think precipitation over the past week is going to increase the discharge? (link 11 and 12). This area has been hit badly over the past 3 years by drought in Nebraska
6. Related to Question 6 how does the discharge you see on the chart relate to the Drought monitor website? (link 13)
7.Here is link to the discharge for Homer Creek in northeast Nebraska (Thurston County). Look at the Drought Monitor page where it is on the edge of the "yellow"area. Is there much difference between Homer Creek and Frenchman Creek? Same problem in winter as Frenchman Creek but if you look at the gage height you can get an idea of recent trends. The discharge at Homer is almost certainly closer to the median flow.http://waterdata.usgs.gov/ne/nwis/uv?06601000
8. What areas of Nebraska have the greatest groundwater resources? (link 7) How does this relate to link 10?
9. As a general rule groundwater that is closest to the surface is the easiest and cheapest to draw up and use to irrigate crops. Look at the charts and identify in general those areas in Nebraska which both have groundwater close to the surface and very thick aquifers. (links 7 and 8)How does this relate to the distribution of center pivots? (link 10)
Lake McConaughy is a major holding area for Nebraska irrigation water along the Platte with most of the water coming from mountain snowpacks in Wyoming and Northern Colorado
10a--Are the headwaters of the Platte suffering drought--see Drought Monitor site? The headwaters are in north central Colorado and southeastern Wyoming
The following can be answered by examining http://www.cnppid.com/Lake_levels.htm and clicking on the Lake mcCanaughy symbol for different time periods.
10b. Look at the long term record of lake levels since 1940. What similarities do you see to the long term Missouri River Basin drought pattern you looked at last week. What drought periods relate to low water levels?
10c. Look at the pattern over the past year. How does the trend relate to net inflows and outflows of water?
Now look at http://www.cnppid.com/Elevation_Flows2.htm
10 d.What is the water level of Lake Mac today as compared to one year ago. What are the implications of water availability for irrigation this summer. These data appear on the first chart
10 e The irrigation season normally begins about July 1 which is about 120 days away. It would take approximately1.8 million acre feet (an acre foot is one acre covered to a depth of one foot) to bring the lake to full capacity. This comes out to a discharge of approximately 7500 cubic feet per second at Lewellen which is at the head of the reservoir on the North Platte (just scroll down the web page) . What is the current flow at Lewellen.? Use last week's flow if current is unavailable. Is the current flow going to be enough to fill the lake? By how much is it short?
