GEOHYDROLOGY OF
THE FLINT HILLS

EAST-CENTRAL KANSAS

James S. Aber
Earth Science Department
Emporia State University
Emporia, Kansas 66801

Table of Contents
Introduction
Ground-water hydrology
Surface-water hydrology

Introduction

Water quantity and quality are subjects of broad concern. The Flint Hills region receives ample rainfall, about 32 inches (80 cm) average annual precipitation, containing carbon dioxide and traces of other substances. This water interacts with vegetation, soils and rock, which produce changes in water composition that affect water quality. The Flint Hills are, in general, a region of water surplus; water leaves the region via many surface streams and by subsurface migration. The Flint Hills are near the western edge of the Great Plains region of water surplus; western Kansas generally has a water deficit.

Ground-water hydrology

Ground water is readily available throughout the Flint Hills region. Most wells produce 10 to 100 gpm, although the eastern crest of the Flint Hills is not so productive. Well yields of 100 to 500 gpm are common in portions of central Marion and western Butler counties (KGS Map M-4a). Principal aquifers in the Flint Hills are the Nolands, Winfield, and Barneston Limestones--Figure 3. Sinkholes are common where these units crop out in uplands, and springs emerge from these units in valleys and stream channels Crystal Spring, near Florence, is one of the largest single springs in the Flint Hills. This spring supplies water for the city of Florence; the spring house has a pumping capacity of 370 gpm, and excess water flows into a nearby stream (O'Conner and Chaffee 1983). The spring emerges near the base of the Barneston Limestone on the northern side of the Cottonwood River valley.

Ground-water migration is generally from east to west. Recharge takes place where aquifers outcrop to the east, and water moves down the regional bedrock dip toward the west. The bedrock aquifers are separated by thick, relatively impermeable shale units. This leads to confined conditions, in which each aquifer may have a different hydraulic head. In the central part of Marion county, both the Winfield (upper) and Barneston (lower) aquifers supply water to wells. In these cases, it is not uncommon for water from the Winfield aquifer to drain down the well into the Barneston (O'Conner and Chaffee 1983). Artesian wells are common in several parts of Marion and western Butler counties.

Artesian well produces a natural flow of sulfur water from the Barneston aquifer near Chingawassa Springs, Marion County. Photo date 11/83, © J.S. Aber.

The vicinity of Chingawassa Springs, about four miles northeast of Marion, displays unusual ground-water conditions. The Barneston aquifer is confined and produces sulfur water. The Winfield aquifer, in contrast, is unconfined and has fresh water. Both types of water discharge in Chingawassa Springs. A nearby artesian well produces sulfur water from the Barneston, whereas springs close to the well discharge fresh water from the Winfield. Artesian and spring flows combine for about 2000 gpm total discharge in this vicinity (O'Conner and Chaffee 1983).

Ground water of the Flint Hills region generally has high total dissolved solids and high total hardness concentrations--Figures 21 and 22. The ionic composition of well water is dominated by Ca2+ and HCO3-, as expected for weathering of limestone by precipitation containing CO2. Magnesium, sodium, chloride, and sulfate are also added by weathering. The relatively high concentrations of calcium and magnesium exceed the recommended limit for hardness in drinking water in most cases. Ground water from Smith Cave is sampled regularly as part of the Groundwater Quality Monitoring Network (site I.D. 00017602) of the Kansas Department of Health and Environment.

Groundwater quality monitoring well at Smith Cave, Butler County. Photo date 10/92, © J.S. Aber.

Nitrate contamination of ground water is a serious problem throughout Kansas, believed to be the result of excessive fertilizer application rather than from natural weathering. The concentrations of nitrite plus nitrate vary from below the detection limit to above the drinking water standard within the Flint Hills. Dissolved iron and manganese exceed secondary drinking water standards at many sites. Although minerals containing these elements are abundant in the region, they become soluble only under reducing conditions. It is interesting to note that samples high in iron or manganese are usually low in nitrate; the same reducing conditions promote denitrification of nitrate to nitrogen gas or ammonia (Schroeder 1990).

Surface-Water Hydrology

The Flint Hills give rise to many perennial streams and rivers: Cottonwood, Walnut, Verdigris, Fall, Neosho, etc. Although many of these are spring fed, they tend to be flood prone. Flash floods may occur at any time of year, due to the combination of relatively impermeable soils and bedrock (shale) and potential for severe thunderstorms. Floods occur most often during the spring and early summer (April-July) with a second flood season in autumn (October-November).

Flood of the Cottonwood River at Emporia, Kansas in May, 1995. Floods of this magnitude (or higher) happened at least five times during the 1980s and 90s. Photo date 5/95, © J.S. Aber.

Army Corps of Engineers reservoirs at Council Grove, Marion, and El Dorado were constructed primarily for flood control--Figure 1. Operation of these reservoirs has greatly reduced the potential for downstream flooding. However, most other streams within the Flint Hills remain unregulated. As an example, the Cottonwood River in Chase and Lyon counties experienced severe flooding in Oct. 1985, July 1993, May 1995, April 1997, and Nov. 1998. The most recent flood took place in March 2004. During such floods, significant erosion, transportation, and deposition of sediment takes place within stream channels and on flood plains.

Records of chemical composition of surface water in the Flint Hills are less extensive than for ground water. One source is the Kansas Department of Health and Environment (KDHE) lake surveys, which include Council Grove Reservoir. In comparison with ground water of the same area, it has higher pH (7.9-8.7), lower concentrations of major ions, comparable phosphorus, and barely detectable nitrate.

Part of the difference in composition is due simply to the dilution of ground water seepage with surface runoff, but major changes are also produced by biological activity in the lake, especially by algae. Council Grove Reservoir, like most Kansas lakes, is highly productive in spite of limited light penetration. Photosynthesis tends to affect water chemistry in the following ways (Schroeder 1990).

The Neosho River, which drains from Council Grove Reservoir toward the southeast, tends to vary in composition depending on flow conditions (Schroeder 1990). At low flow, its composition closely resembles that described for Council Grove Reservoir. At high flow, the pH decreases to 7.1-7.4, ions decrease even further in concentration, but nitrate and phosphorus increase, as eroding soil and fertilizer residues enter the river.

The Neosho River is the primary source of drinking water for the city of Emporia, but requires extensive treatment, including: chlorination, softening, flocculation, activated carbon, filtration, ozonation, and fluoridation. In 2002, the water supply of Emporia was judged among the five best-tasting public water supplies in the nation!

Return to Flint Hills geology.
J.S. Aber © 2004.