|The Cheyenne Bottoms|
|Cheyenne Bottoms Morphology|
The elliptical depression shape of the Cheyenne Bottoms (see Figure 1) could be the result of several climatic oscillations that occurred in the Kansas region over several millions of years since the Precambrian period (see Fig. 2). The elliptical shape of the Cheyenne Bottoms can be attributed to more resent climatic oscillations that have affected the landscape that now dominates the region. Previous research published by Bayne (1977), included research by Latta (1950) and Cole and Ebanks (1974) that related the depression of the basin to erosion and deposition of subsurface geology using contour maps delineated from test holes and gamma ray logs from oil and gas wells drilled around the Cheyenne Bottoms. The contour maps published by Bayne (1977), were georeferenced and draped over topographic maps to create a subsurface map relative to the Cheyenne Bottoms basin. The maps show consistent evidence of depression and/or deposition of the subsurface geology layers that underlies the upper bedrock surface of the Cheyenne Bottoms basin. Above the bedrock surface, alluvial and dune sand deposits from stream and wind erosion dominate the topography of the area and forms the upper slopes on the southeast side of the basin. A Digital Elevation Model (DEM) and field collected aerial and ground photographs were used to study and evaluate the current processes affecting the landscape and the relationship between the existing topography and the processes that operated in the subsurface geology of the Cheyenne Bottoms based on the subsurface contours.
The Cheyenne Bottoms wetland area is located in Barton County, central Kansas, north of the Arkansas River between the cities of Hoisington to the northwest, Great Bend to the southwest, Ellinwood to the southeast, and Claflin to the northeast (see Fig. 1). The wetland area is relatively flat with an average elevation of 545 m above sea level. The elliptical shape is mainly shaped by a bedrock surface that gives rise to the uplands on the north, northwest, southwest, and south. The uplands to the east and southeast of the basin are formed by sand dunes and alluvial deposits. The wetland internal drainage is dependent on Deception Creek to the north, Blood Creek to the west, and from a canal located on the southwest that diverts water from Walnut Creek. The lower Cheyenne Bottoms basin has been modified by a network of pools and canals with floodgates that control the flow of water between wetlands during wet and dry periods. The basin has only one drainage outlet is located on the southeast that becomes Cheyenne Creek.
Figure 1. Cheyenne Bottoms Map created from Landsat ETM bands 1,2,3, the natural-color composite was processed and enhanced with shading IDRISI Taiga. Enhanced relief shows bedrock rims along the southwest and northeast of Cheyenne Bottoms and small valleys cut across the scene with vertical (north-south) formation. The Cheyenne basin and Arkansas River floodplain are relatively flat covered with alluvium deposits and sand hills. The vegetation along the floodplains is mainly croplands and grasslands. The lowest elevations of the Cheyenne Bottoms are covered with wetlands and pools. The slopes east of Cheyenne Bottoms between Cheyenne Creek and Claflin are formed by dune sand.
Figure 2. Kansas Geologic Timetable obtained from Kansas Geological Survey (KGS). Based on subsurface contours (see Fig. 4-9) it is possible that the Cheyenne Bottoms began to form as early as the Precambrian period over a low area that underlies the area and elliptical shape during the Cretaceous period. The timetable shows several ancient seas and dry periods existed in the Kansas region. The layers of sandstone, limestone, salt and shale left by the seas were subject to several wet and dry periods, which could have eroded causing depressions and/or synclinal bends as shown on Fig. 4-10.
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The layer of alluvium in the lower Cheyenne Bottoms basin and the uplands that delineate the depression suggest erosion from climatic oscillations that affected the region. Outside the basin, creeks to the north and northwest carved v-shaped watersheds that flow southeast allowing loads of sediment to reach the lower Cheyenne Bottoms. The bedrock surface that shapes the uplands mainly formed from Dakota formation has been eroded during wet years shaping deep channels that now dominate the uplands and delineate the elliptical shape of the basin. From the Kansas timetable (see Fig. 2) it is assumed that climatic oscillations included the existence of several seas that left layers of salt, limestone, and gypsum prior to the Cretaceous period. The layers of sediments left by the seas were then exposed to extensive dry and wet periods, which could have caused erosion or deposition of the subsurface that underlies the elliptical depression.
The several layers that make up the subsurface geology of the basin were mapped with contours delineated from samples obtained from test holes and gamma ray logs obtained from drilling into the subsurface of the Cheyenne basin. The subsurface contour maps published by Bayne (1977) were georeferenced with ArcGIS 9.3.1, using control points on the township and range intersections shown on the contour maps and referencing the same township and range intersections of a USGS 1:250,000 topographic map of the Great Bend (see Fig. 3). The georeferenced subsurface contour maps were then draped over the USGS topographic map to spatially correlate the contour information with the Cheyenne Bottoms surface. All contour maps show elevations flowing in a southeast direction with an anticline bend on the southwest and above the Precambrian depressions forming around the Cheyenne Bottoms with a synclinal bend on the southeast (see Fig. 4-10).
Figure 3. Subset of USGS 1x2 degrees Digital Raster Graphic (DRG), 1:250,000 topographic map of the Great Bend. The map shows the relatively flat basin of the Cheyenne Bottoms with the linear levees forming the main pools and canals with floodgates that control the water flow into and between the pools. The irregular shapes of the contours are formed by the sand hill topography of the region. The map shows several oil fields in and around the basin. All streams north of the Arkansas River flow in a southeast direction.
Figure 4. Georeferenced bedrock surface contours draped over the USGS topographic map. The pattern of the generalized bedrock surface contours correlate with the elevations on the contours shown on the topographic map on the southwest, northwest, and north of the Cheyenne Bottoms, which suggests some bedrock exposure. The bedrock surface at the pools of the Cheyenne Bottoms is shown to be approximately 30 meters below ground level and it decreases towards the southeast. The differences in elevation between the bedrock and the ground surface elevation at the pools are assumed to be alluvial deposits from Blood Creek and Deception Creek and dune sand on the east and southeast slopes of the basin. The contours show the elevations of the bedrock surface flowing into the Arkansas River floodplain with a channel cutting from what is now Cheyenne Creek flowing into the Arkansas River at Ellinwood.
Figure 5. Georeferenced top of the Stone Corral formation contours draped over the topographic map. The Stone Corral formation possibly formed during the late Permian period (see Fig 2). The contours show a depression on the northwest side of the basin. The noted elevations give a difference of 185 meters below the bedrock surface in the center of the Cheyenne Bottoms and increasing elevations towards the southeast. The contours show an synclinal bend running in a southeast direction, which lines up with Walnut Creek. The surface of the Stone Corral formation increase towards southeast.
Figure 6. Top of Hutchinson Salt Member of the Wellington Formation (Bayne, 1977) georeferenced contours. Contours are draped over USGS topographic map. The contours show a depression 320 meters below the bedrock surface in the northwest Cheyenne Bottoms. The surface of the Hutchinson salt increase towards the southeast.
Figure 7. Base of Hutchinson Salt georeferenced contours. The contours draped over the USGS topographic map show the base of Hutchinson Salt increases towards the east. The contours show the base of the Hutchinson Salt to be approximately 400 meters below the bedrock surface around the Cheyenne Bottoms.
Figure 8. Base of Winfield Limestone georeferenced contours. The contours show a depression around the Cheyenne Bottoms. The base of the limestone is shown to be approximately 450 meters below the bedrock surface.
Figure 9. Top of Heebner Shale Member of the Oread Limestone (Bayne 1977) georeferenced contours. The contours draped over the USGS topographic map show a depression around the Cheyenne Bottoms and other depressions mainly on the southwest and northwest. The limestone layer is shown to be about 850 meters below the bedrock surface at the Cheyenne Bottoms.
Figure 10. Precambrian surface georeferenced contours. Bayne (1977) noted that only 3 wells reach the Precambrian surface around the Cheyenne Bottoms. The generalized contours show the Precambrian surface to be over 1000 meters below the bedrock surface. The generalized contours show the possible existence of synclinal bend around the Cheyenne Bottoms and a high area to the east. However, no relationship is formed between the depressions shown on the upper subsurface layers and the Precambrian surface other than the high areas to the east, which could have become a physical barrier allowing for deposits to accumulate forming a detention basin.
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Cheyenne Bottoms Morphology
The topography of the Cheyenne Bottoms is dominated by the relatively flat playa basin delineated by the upland bedrock and vegetated sand dunes. The wetland areas that operate within basin serve as a sanctuary for migratory birds and other wetland species. The landscape of the basin often changes with climatic fluctuations. Wetlands occasionally suffer from extended droughts that cause wetlands to dry up and vegetation becomes scarce exposing alluvium deposits. During extended droughts the sandy soils that dominate the region are subject to the prevailing winds blowing from the southwest eroding soils and reshaping the sand dunes and sand hills. During wet years, floods washes down the wind eroded material into the lower elevations and the pools and marshes in the lower elevations of the playa basin become flooded. During extended wet periods floodwaters that fill the basin create waves that erode material from the upper slopes creating sharp ridges on bedrock surfaces and dune forms in softer sand slopes.
Before all the existing levees and pools were built in the lower basin, the entire playa basin was covered with alluvium deposits that washed down from Deception Creek, Blood Creek, and from internal streams that formed in a vertical north-south direction across the bedrock surface. The climatic oscillations that modified the playa basin also contributed to the sand hill formation around the Cheyenne Bottoms. The elevated areas to the north, northwest, southwest, and south that shape the depression of the Cheyenne Bottoms are composed of bedrock and are covered with sandstone and sand hills. During extensive drought periods sand and alluvium deposits were blown in from other states (see Fig. 2) and from floodplains such as the Arkansas River floodplain near the Great Bend. During the wet periods the some of the sand hills that formed during droughts grow vegetation and hardened forming physical barriers such as the slopes on the east and southeast of the playa basin.
The existing playa basin has been modified to provide a drainage system that feeds the marshes and serves as water storage. The water within the basin is dependent on the creeks that drain water from the upper elevations on the northwest, the north, and from Walnut Creek through a channel that cuts across the bedrock uplands on the southwest diverting water into the lower pools. The vegetation that grows in and around the playa includes croplands, grasslands and patches of deciduous trees that grow near ditches, around wet areas and along the streams. Wetlands are dominant in the lower elevations, cover mainly with cattail and bulrush. The most noticeable changes in the lower elevations are no longer related to climatic oscillations. In the lower basin the landscape as been modified by a network of levees, pools, and channels that control the flow of the floodwaters that enters and exits the Cheyenne Bottoms (see Fig. 1 and Fig. 11-17). The new pools and wetland areas shaped by levees observed in the lower playa now serve two very diverse purposes; nature statuaries and hunting grounds.
The use of a DEM to analyze the Cheyenne Bottoms delineates patterns not visible in topographic maps or aerial images. The enhanced DEM map (see Fig. 11) shows the surface elevations of the Cheyenne Bottoms region decrease towards the southeast and a pattern of small valleys that run in a vertical north-south direction emerges across the region. A sudden change in elevations marked by the elliptical shape of the Cheyenne Bottoms delineates the depression and linear shapes delineate the pools in the southeast basin. The watersheds from Deception Creek and Blood Creek are delineated by the sharp ridges formed on the eroded upland bedrock. The elliptical shape of the basin cuts sharp ridges and appears as ancient lakebed with a single drainage outlet in the southeast. The elongated sand hills that are shown as irregular contours on topographic maps (see Fig. 3) are show as network of dunes shaped in the direction of the prevailing winds of the area (see Fig. 11-17).
Figure 11. DEM made from USGS 1 arc-second (30 m) resolution National Elevation Dataset (NED). DEM map was enhanced with shading processed with IDRISI Taiga. Notes on map: A (elevated areas made of bedrock); B (floodplains filled with alluvium deposits); C (sand dunes and elevated areas made from sand deposits); D (prevailing wind direction of the region). e, f, g (locations of ground and/or aerial photographs, see Fig. 12-17).
Figure 12. Oblique kite aerial photography taken from camp Aldrich (see Fig. 11, location e). The west view shows the undulated landscape is shaped by the sand hills covered with grasslands and patches of deciduous trees and linear areas of deciduous trees along the streams, the Cheyenne Bottoms are in the far left background. (photograph taken on Oct. 9, 2009 during field trip)
Figure 13. West view from hwy 4 (see Fig. 11, location g). Ground photograph shows the elevations decrease towards the left, the road forms a levee and areas to the right of the road are relatively flat croplands with some residential buildings. (photograph taken Oct. 9, 2009 during field trip)
Figure 14. Oblique kite aerial photograph of the sand hills at camp Aldrich (see Fig. 11, location e). The aerial photograph shows of the sand hills that dominate the landscape covered with vegetation. The sand hills standout from the flat grounds in the lower left and cropland on the upper right. (photograph taken on Oct. 9, 2009 during field trip)
Figure 15. Wide angle Oblique blimp aerial photography taken from the Nature Conservancy marsh area (see Fig. 11, location f) north view. The marsh area shows partially flooded marshes and wetland vegetation. The levee on the left side was built to contain the water within the wetland areas. The white patches are formed from salt deposits left from higher water levels. (photograph taken on Oct. 9, 2009 during field trip)
Figure 16. Zoomed view of the upper bedrock surface across the wetlands of the Nature Conservancy area (see Fig. 11, location f). The ground photograph was taken from the levee shown on Fig. 15. The picture shows a sudden change in elevation caused by the depression that delineates the Cheyenne Bottoms alluvial surface from the upper sandstone and bedrock surface. (photograph taken on Oct. 9, 2009 during field trip)
Figure 17. Ground photograph of the floodgates taken from the levees near the south at the Cheyenne Bottoms main pools. The floodgates control the flow of water between the pools and incoming water from the canal that diverts water from Walnut Creek. (photograph taken on Oct. 10, 2009 during field trip)
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The subsurface contour maps (see Fig. 5-9) suggest a depression that extends several meters below the bedrock surface and began to form prior to the Cretaceous period. The depression can be related to the erosion and deposition of the subsurface sea deposits that accumulated up until the late Cretaceous period from sea oscillations (see Fig 2). Following the sea oscillations came several wet and dry periods that weathered limestone creating depressions and carving stream channels. Between the late Cretaceous period and early Holocene, layers of limestone, sandstone, and other sea deposits were exposed to erosion from high water tables, floods, and wind for several million years. The erosion of sea deposits was followed by dry periods that shaped the dry landscape.
Between the Cretaceous and Holocene periods, water accumulated in the porous rocks from wet periods and water table was high. During the dry periods, sand blown from the southwest and from the Arkansas River floodplain to the south accumulated across the landscape and on the lower basin forming dunes. In the lower elevations southeast of the existing playa, streams that drained water from the upper northwest would become trap forming a lakebed. The high water tables helped stabilize the sand and alluvial deposits in the Cheyenne Bottoms, while the prevailing winds blowing from the southwest shaped the upper sand hill landscape of the region.
Subsequent climatic oscillations that followed the late Cretaceous period could be related to the existing shape of the playa basin. During extensive dry periods sand dunes formed creating physical barriers and shaping the existing landscape. Sand dunes later cover with vegetation resistant to drought conditions hardening the physical barriers. The vegetated sand dunes served as natural levees during floods. The east and southeast slopes of the Cheyenne Bottoms are made of sand dunes that could have acted as natural levees, which allowed water to accumulate from the streams coming from the uplands to the north and northwest. During subsequent floods that followed the dry periods, a lake could have formed and a combination of percolation and wave movement could have contributed to the size and shape of the playa basin.
As suggested by the DEM (see Fig. 11) and geologic events of that affected the region, the existing elliptical shape of the playa basin can be attributed to the oscillations of water levels that filled the Cheyenne Bottoms during major floods and the stable high water table. The floods that filled the basin carved the upper bedrock, forming sharp circular ridges, and created a shoreline on the playa basin.
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