Geospatial Analysis and Geographic Information System Techniques
Applied to the Ogallala Aquifer under Southwest Kansas
M. Driessen, J. Howard
ES 351 : Introduction to Geospatial Analysis
The Ogallala aquifer is only a part of the High Plains aquifer, yet it is the single most important water source of the southwest corner of Kansas. The High Plains aquifer underlies an area of about 45,660 km2 (174,000 mi2) that extends through parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming. The High Plains aquifer system approximates the boundary of the Great Plains physiographic region. The Ogallala aquifer is one of four major formations of the High Plains aquifer system. The water level in the Ogallala aquifer ranges from 15 to 120 meters (50 to 400 feet). Because of its lack of contact with the surface, the water contained in the Ogallala aquifer is very clean, and is used for agricultural, livestock, industrial, and domestic consumption.
In 2003, many different studies were done on the portion of the Ogallala aquifer underlying southwest Kansas. One report was investigating the impact of community water systems on the Ogallala aquifer. In this report, the conclusion was that very little was done to monitor the water coming from the Ogallala, due to its relative availability, and the actual impact on the aquifer water level was extremely insignificant when compared to the biggest influence in water level: farming. Much of the former prairie of western Kansas is now irrigated cropland, major crops being corn, wheat and sorghum. Corn is among one of the biggest cash crops of Kansas, and also the one of the many crops raised that requires substantial amounts of water. This has lead to a disturbing trend in the availability.
In these two satellite images (Landsat 5 MSS; EROS Data Center), one can see the aggressive growth in farming in just the area surrounding Garden City, Kansas, located in Finney county. One of three substantially-populated cities in the southwest quarter of Kansas, the population relies heavily on the water availability.
16 Aug, 1988
Red areas symbolize healthy vegetation, based on the infrared reflectivity of the active vegatation. Light-colored fields in the images were recently harvested wheat fields. Black represents water, and white shows the bare patches of ground, either altered by local population, or unused fields. Red circles are center-pivot irrigation systems. An increase of 1.5 to 2.4 million acres was reported for Kansas farmland from 1969 to 1987, with Finney county leading with 184,000 estimated acres. The following map (HERO-HPO) was constructed based from surveys done in the southwest corner of Kansas. It shows most notably the change in 20 years of massive amounts of rangeland that have been turned to croplands.
Land Cover Change of SW Kansas
Satellite images are good for showing the increase of croplands, but how to show the impact on the aquifer? By going out and sampling wells and recording the depths over time, a database was formed and utilized to draw a map using GIS technology. The maps generated used basic GIS data, such as the political features (county boundaries), lines to represent the local drainage pattern and river systems, and the polygons that formed the boundaries of the aquifer in question. The following maps (KGS) show the quantized results of well sampling in this region. Note the legend and what it shows throughout the aquifer over time, especially in Finney county, near Garden City.
Current Saturated Thickness (1999)
Change in Saturated Thickness (1999)
Recharge from 1991 - 2000
Thickness is only partially determined through the underlying strata. Kansas is underlain by limestone bedrock, and shale, both very porous. The strata is uneven though, and in some areas you might drill a few feet, some areas you might drill much more. In areas that use is heavy, the water is depleted around the well, and forms a cone of depression. As the use continues over time, the well would have to be either redrilled, or capped for a small time to allow for recharge. Capped wells can give a good idea of the intensity of the use when abandon wells for this area are mapped out.
Combining the data of increased farmland over time, and decrease in well water levels over time, an accurate map of the deterioration of the Ogallala availability can be accurately portrayed, and then emphisized through the use of satellite images.
Driessen, M., Montoya, S., Paull, D. 2003: Vulnerability of Community Water Systems to Climatic Change in Southwest Kansas. Kansas: Human-Environment Regional Observatory Collaborative.
Human-Environment Regional Observatory (HERO). 2000. Human-Environment Regional Observatory - High Plains Ogallala (HERO-HPO) Homepage. [http://www.ksu.edu/geography/research/hero.htm]. Accessed November 2004.
Kansas Geological Survey (KGS). 2000. An Atlas of the Kansas High Plains Aquifer. [http://www.kgs.ukans.edu/HighPlains/atlas/index.html]. Accessed November 2004.
Kansas Geological Survey (KGS). 2002. Ogallala-High Plains Aquifer Support Study Reports. [http://www.kgs.ku.edu/HighPlains/OHP/]. Accessed November 2004.
All images are the property of the noted sources.