Butler County, KS
The Flint Hills are composed of highly resistant chert-capped hills which stand in contrast to the surrounding stream-cut channels or valleys which wind their way through less resistant limestone. The wind farm is located over 500 m (~1650 ft) above sea level, making this site one of the highest points in the eastern half of Kansas. Much of the area is covered with native prairie grasses including big and little bluestem, switch and Indian varieties. The cherty soil made the land difficult for early European settlers to plow and farm so ranching was, and still is, the most suitable and dominant form of land use for this area.
In terms of climate, this area receives approximately 76 - 88 centimeters (cm) (~30-35 inches) of rain per year (HPRCC 2011). The climate is considered moderate with an average annual temperature of 13.33 degrees Celsius (56 degrees Fahrenheit) and an average wind speed of 8.5 - 9 meters per second (m/s) (19 to 20 miles per hour) at wind turbine hub height (100 m) (Climate and Energy 2011). This hub height wind speed is ideal for wind power generation.
The Elk River Wind Project is a 150 megawatt (MW) capacity site with 100 wind turbines (Iberdrola Renewables 2011). The total site is over 2800 hectares (7,000 acres) and spans the properties of five local land owners. It is important to note that the land is also used for cattle grazing and that the turbines do not significantly interfere with the pre-existing agricultural land use.
General Electric Energy supplies the 100, 1.5 MW turbines and the height of each turbine is 120 m (389 feet (ft)). The turbine weights by component are: tower ~ 122,000 kilograms (kg) (270,000 lbs), rotor ~ 33,000 kg (73,000 lbs), and nacelle ~ 52,000 kg (115,000 lbs). With such a large weight and tall height, it is critical for each turbine to have a solid foundation. Each turbine has a concrete octagonal footing 14 m (48 ft) in diameter (Iberdrola Renewables 2011), spaced 150 to 300 m (~500 to 1000 ft) apart from the adjacent turbine's foundation, and containing approximately 190 cubic meters (250 cubic yards) of concrete per turbine (or 2,700 truckloads). Weaving across the wind farm site are over 30 km (~20 mi) of gravel surfaced roads, which provide access to each turbine.
|Image to the left by Molly Reardon: View of a gate into Ferrell Ranch. This image is facing toward the Southeast. Approximately fifty percent of the entire Elk River Wind Farm lies within the boundaries of Ferrell Ranch. Image to the right by Molly Reardon: This is a view of the substation site on the South end of the Wind farm site. This station feeds into the power lines on the right side of the photo.|
Electricity is generated within each turbine and then runs underground to the project's above ground substation. From here, the electricity runs through approximately 7 km (4 mi) of transmission line which connects into a main power grid. The Empire District Electric Company purchases this power from Iberdrola Renewables and together, these companies have entered into a 20 year agreement which will supply 42,000 homes with electricity annually.
Image by Kyle Jackson: This is a North facing image taken from the same location as the Ferrell Ranch Sign photos above. The three turbines in this location lie at a slightly lower formation (Wreford Formation) than the turbines directly to the south.
The Flint Hills physiographic region stretches from the southeast corner of Washington County, Kansas to north-central Oklahoma. The eastern margin of the region is characterized by a steep escarpment which leads to the Osage Cuestas region, whereas the western edge of the Flint Hills can be generally described as having a gentle, downward slope tapering into the Wellington-McPherson and Arkansas River Lowlands. The entire region ranges in elevation from approximately 280 m (~920 ft) to above 500 m (~1,640 ft) and is underlain by lower Permian limestone and shale which exist in alternating patterns called cyclothems. The cyclothems are a classic example of "layer-cake stratigraphy" (Aber 2006).
The Elk River Wind Farm is located in the southern portion of the Flint Hills and is situated on the drainage divide between two basins, the Verdigris-Fall to the east and the Arkansas-Walnut to the west. Central Butler County is also known for well-developed Karst features including, sinkholes, cave systems, disappearing streams and numerous springs (Aber 2009).
The alternating layers, or cyclothems, of lower Permian limestone and shale beneath the Flint Hills and Elk River Wind farm were deposited approximately 250-290 million years ago from multiple transgressions and regressions of an ancient shallow inland sea (Aber 1991). Tropical climates of the time allowed layers of limestone to form through a process known as lithification which occurred as remains of calcium-rich marine organisms fell to the bottom of the sea. Shale, was formed as mud and clay were deposited on the floor and also underwent the lithification process (NPSFH 2011). Cyclothems, in turn, were formed as this process repeated itself over millions of years. The general cyclothem model for the Flint Hills, specifically Butler county, includes the following six units from the top down: Limestone (tan to gray); Shale (gray or green); Cherty Limestone (tan or light gray); Shale (gray, tan or green); Limestone (gray or tan); and Shale (maroon above green and black) (Moore 1964).
The chert or flint which defines the region is found predominately within the Florence and Three Mile limestone members within the Barneston and Wreford Limestone formations (both of the Chase group), respectively (NPSFH 2011). Chert is found as both a layer (laminated) and as a roughly-spherical concentration (nodule). Chert concentrations are thought to be the remains of silica-rich marine organisms which sank to the ocean floor and migrated together before becoming embedded in the limestone, while layers may have formed as silica on the ocean floor recrystallized and chemically replaced the surrounding limestone (NPSFH 2011). The end of the inland sea brought about the landscape which for the next 250 million years would be shaped into the Flint Hills of today.
The overall development of the Flint Hills has been destructive in nature and was driven predominantly by differential water erosion and to a lesser extent eolian forces. The stair-step landscape of terraces and valleys which define the Flint Hills were formed as rivers, streams and weather down-cut through, or chemically eroded, less resistant limestone and left in place erosion-resistant chert (Aber 2009). Chert rubble and layers, thereby, cap the terraces of the region and provide long-lasting, erosion-resistant structure to the hills. The repetition of eroded limestone valleys and chert-capped terraces are the characteristics which distinguish the Flint Hills from other physiographic regions throughout Kansas.
In addition to the differential water and eolian erosion which has shaped (and continues to shape) the contemporary Flint Hills, pre-Cambrian basement tectonics and the Nemaha Uplift (western Butler county), Humboldt Fault zone (eastern Butler county) and various joints have added to the development of many of the surfical features, anticline, synclines, dips and general southeast drainage of the Elk River Wind Farm site (Aber 1991). Further erosion occurring on the site is considered to take place at geologic time scales with the possible exception of catastrophic events such as floods which can erode and transport massive amounts of soil in brief, single events. Likewise, the wind farm's location on the stable mid-continent craton makes changes from tectonics rare despite the deep, pre-Cambrian joints, faults, synclines and anticlines of the region.
In general, the Elk River Wind Farm site should not see significant geological changes within the foreseeable future. The wind farm is situated on a flat drainage divided within the southern Flint Hills physiographic region, atop one of the highest and windiest points in eastern Kansas. The chert-capped hills provide turbine towers with fairly stable and erosion-resistant ground for anchoring purposes, while adjacent valleys allow for unimpeded flow of sustainable wind delivery to the turbine blades. The rich ranching heritage of the Flint Hills was largely unaffected by the development of the Elk River Wind Farm which fulfills the annual power needs of nearly 42,000 homes with renewable and reliable energy.