The Neva Marsh, a wetland developed through the Natural Resources Conservation Service, Wetlands Reserve Program (Howard,2009), functions as a riverine wetland: in that, the main hydrologic source is ground water accompanied by occasional flooding of the Cottonwood River. Riverine wetlands are located near a slope within a stream corridor where groundwater flow is transected and collects into a depression (Brinson, 1993). The water’s presence in the depression creates anerobic conditions that develops a hydric soil . The condition of hydric soils inhibits the growth of some indigenous plants while promoting the growth of hydropytic plants (NRCS, 2008). The western 4ha. of the current marsh has continuously existed as wetland (yellow triangle Figure 1). However, the eastern 17ha. were drained and tilled for crops. The farmed section was restored to wetland. Construction on the restoration began October 28, 2005. A retaining wall was built from east to west and enclosed at the ends with earthen dikes to raise the water level approximately 0.3m. Borrows were placed on the discharge side of the retaining wall to slow the migration of the water. The intention is to allow favorable habitat and cover for wildlife while slowing the effects of sediment migration (NRCS 2007)
The Neva Marsh an Emporia State University Natural Area, comprised of 21ha., in Chase County (Figure 2), 2.4 Km west of Cottonwood Falls, Kansas is situated on the margin of the Cottonwood River (red triangle Figure 1). The river meanders from west to east along a path just north of the marsh area. Directly east, a bend in the Cottonwood River extends to within 250 meters from the marsh. Along the southern border of the marsh, Permian limestone and shale strata rise 150 meters above the flood plain. Twelve springs issue from limestone formations and serve as the main water source for the marsh (note the white arrow Figure 1). At the hilltop and to the south, a small spring feeds a pond used for livestock. Downhill and to the west from the pond is a second spring fed pond that drains north to the Cottonwood River. Prather Creek and Chase County State Fishing Lake, located on the hilltop south of the stock ponds, are fed by a large spring. Drainage from the State Fishing Lake follows Prather Creek, 950 meters east of the Neva Marsh, to discharge into the Cottonwood River.
Figure 1. Satellite view of Neva Marsh and surrounding area.
Ground water normally travels with topography and on occasion the gradient is dominated by rock formation dip (Fan 2007). At the Neva site, the underlying rock formations are sedimentary limestone and shale of early Permian age beginning with the Grenola Formation and layering up to the Wreford Limestone Formation. (stratigraphy)
Limestone and fine grained shale limits ground water flow to fissures and fractures in the formations (Cooke, 2006). Mechanical/bedding plane interfaces provide openings for water to accumulate (Figure 3). Weathering generates a crack allowing more water to enter into the crevasse. Chemical dissolution occurs if the water is acidic and contacts the carbonate constituents of the limestone which further enlarges the space. Water motion can manipulate grains to grind at the rocks surface which wears the fissures deeper into the rock (Eaton, et al. 2007). Fissures eventually branch out.
Peritidal carbonate rocks will promote multiple smaller fractures due to varied conditions such as fossils, wavy textures, and breccias. Basinal carbonates offer fewer horizons and bedding planes that facilitate fracturing (Graham Wall, 2006). The difference in the sedimentary conditions also thwarts the vertical direction of water flow, in that; the deeper the rock, vertical fractures occur less often. Water then seeks to continue down gradient in the superior layer and continues to flow in multiple layers. Overtime the mechanisms will continue to increase the conductivity of the aquifer. Eventually, water escapes to the surface through a fracture or other conduit that is down gradient from the aquifer. Artesian pressure may force water upwards into an opening.
According to driller’s logs, two wells drilled in the Cottonwood Alluvium near the elevated limestone formations show potentiometric pressure exists in the aquifer. Depth to water 4.5m and later 2.4m were monitored.
The Cottonwood River segment from Diamond Creek to Cottonwood Falls has a draiange area of 3279km2 and recieves on average 211m3/s of flow (USGS 2001). Figure 4 is a cross section of the Cottonwood River alluvial plain showing the bedrock basin, and sedimentary layers. The unconsolidated alluvial sediments are approximately 12 meters thick. The upper 1.5 meters of topsoil are under lain by 5 meters of silty clay. The next 5.5 meters consists of sand, gravel, and broken limestone. Water is found at 6.0m with a static water level of 2.4m.The Cottowood Falls low water dam raises the river level two to three miles up stream which increases the water table (O'Conner,1951).
The source of water for the Neva Marsh is from 12 springs in the upland formations to the south. The water travels via a drainage ditch along the road and into a culvert that is near center of the marsh’s southern edge. Water then moves west, fills the retention area, and discharges over wood blocks placed opposite the culvert. Beyond the culvert a slight depression slows the water’s path before it drains north via a small stream to the Cottonwood River (NRCS 2007). The soil in the Neva Marsh is classified as Osage hydric. A soil comprised of 60 percent fine clay and silt as a result of long periods of standing water. The soil’s low permeability, hydraulic conductivity of 0.01 - 0.42 µm/s, most likely prohibits vertical infiltration of recharge to the alluvial aquifer(Watts,2009). The Cottonwood River reached flood stage every 1-2 Years over the last 17 year period. The river crested between 3.0 - 5.0m. A flood stage of 2.7m will bring river water into the marsh (NWS, 2010).
The cities of Cottonwood Falls and Strong City draw municipal water from the alluvial aquifer to supply 1400 people with 109 gallons per day per capita(KSDA 2007). Cottonwood Falls pumps 3 wells in the alluvium north east from the marsh. Well locations are shown in Figures 1 and 3. The wells supply 90, 90, and 160 gpm.
The upland area is primarily used for pasture and remains grassland. Therefore, spring water is diverted to ponds for stock.
Soy beans and corn are grown on the alluvial plain. Kansas Department Agriculture reports 52ha. as irrigated with an annual use of 17 hectare meters (KSDA 2007a).
The Kansas Watershed Association and the Environmental Protection Agency has deemed the Lower Cottonwood watershed area as impaired, with low priority. Fecal coli measures high in the Upper Cottonwood River Watershed and Diamond Creek due to a large number of feedlots. Upstream influence causes impairment of the beginning segment of the Lower Cottonwood River Watershed; however, organic constituents become diluted at this point (EPA WaterLINK, 2009). The Neva Marsh area experiences some levels of chlordane and imazapic which are constituents of insecticides and herbicides respectfully. The chemicals are water soluable, and will break down in sunlight. However, they can bind to soils. The NRCS reports the contaminant level as less than a the maximum contaminant limit(NRCS 2007).
This web site created by Darrel J. Drake, May 2, 2009, as a requirement for GO571 Hydrogeology, Emporia State University.
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O’Conner , H. G., 1951, Ground-water resources of Chase County Rock Formations of Chase County, Part 3 of Geology, Mineral resources, and Ground-water resources of Chase County,http://www.kgs.ku.edu/General/Geology/Chase/pt3_avail.html
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