Earth Karst Streamflow in Bryant & Northfork

Streamflow in Bryant Creek and Northfork River

North Fork River and Bryant Creek, which drain adjacent basins in Douglas and Ozark Counties, about 50 miles southeast of Springfield in southern Missouri, have practically the same size drainage areas, and similar basin shape, climate, and surface geology. Since 1945, records from two continuous-record streamflow stations in the lower reaches of the streams have indicated that the groundwater runoff of North Fork River is twice that of Bryant Creek. 

Groundwater runoff is that part of the runoff that has passed into the ground, become groundwater, and then has discharged into a stream channel as springs or seepage water. 

In the fall of 1964, a hydrologic reconnaissance was made in the two basins to determine where the differences in groundwater runoff originate. 

Figure 1 shows the drainage network, locations of the measuring sites, and the results of discharge measurements made during the reconnaissance, in the Bryant watershed and the western part of North Fork watershed. 

The data revealed these facts: 

1) About two-thirds of the groundwater runoff is derived from the lower one-third of the watersheds, primarily because of the contribution of large springs. 

2) The discharge from the North Fork Springs/Double Spring system accounts for most of the difference in groundwater runoff between Bryant Creek and North Fork River. 

3) Major groundwater contributions are by springs on the main stems of the North Fork and the Bryant. 

4) Bryant Creek is an intermittent stream in the upper reaches, whereas North Fork River is perennial from headwaters to mouth. 

Since 1964 other data have been collected and observations have been made of physiography, geology, and variations in stream and spring flow at selected points in the basins. This article discusses the results of these observations and suggests some conclusions about the functioning of the hydrological system in the area. 

PHYSIOGRAPHY

The land surface in the divide areas is rolling, whereas near the streams it is moderately rugged. Valley floors rise from 600 feet above mean sea level to about 1200 feet at the northern end of the basin. Divides rise from 800 feet above mean sea level to 1600 feet at the northern end of the basin. The maximum relief is about 1000 feet. Although the land is generally maturely dissected, some variation in the sculpture of the terrain is present. Smoothness of the contours indicates rounding of the hills in the Bryant Creek watershed as contrasted with steeper slopes, flat divides and more intricate dissection of the lower end of the North Fork watershed, which suggests that collapse was an important agent in its development. 

Sinkholes are most common in the eastern part of the North Fork basin and in the adjoining divide area to the east. A small concentration of sinkholes occurs in the north end of Bryant Creek basin. Isolated sinkholes, which are both large and deep, occur in the reminder of the area. 

GEOLOGY AND HYDROLOGY

The North Fork and Bryant watersheds are developed on rocks of Ordovician age which have low dips (20 to 25 feet per mile) generally to the southwest (see Figure 2). Locally, where associated with collapse features, dips may be higher. Capping the higher hills are small outliers of residual chert from Mississippian strata. Limestone and shale of Osage and Kinderhook age are exposed in the vicinity of the Mansfield fault. 

The Ordovician strata consist, in ascending order, of the Gasconade Dolomite, Roubidoux Formation, and Jefferson City Dolomite. The Gasconade Dolomite, which is exposed in the valley floors and lower parts of the valley walls, contains most of the large springs. The Roubidoux Formation forms most of the valley walls and slopes to the uplands. The Jefferson City is chiefly found in the uplands. The stratigraphic section that includes all three formations is about 1000 feet thick and is largely dolomitic limestone. Sandstone occurs in both the Roubidoux Formation and the basal part of the Gasconade Dolomite, but only the upper part of the Gasconade is exposed in the basins. The formations are thinly to thickly bedded, and chert is relatively abundant throughout the section. 

Jointing of the rocks controls the development of solution of the dolomite and groundwater drainage to the North Fork River. In a sinkhole area around Willow Springs, in the eastern part of the North Fork watershed, many of the sinkholes are elongated in a north-eastward direction. Also, clusters of small round sinkholes are commonly aligned in a northeast direction. 

The following observations also suggest that a close relation exists between jointing, solution, and the flow of water from recharge to discharge areas. The influence of jointing and faulting in the northern part of Bryant Creek watershed is indicated by the trends and locations of the valleys as shown on aerial photographs. The northern part of the area has distinct northwest valley trends, whereas the southern part has many northeast trends. 

The Mansfield fault enters the Bryant creek watershed from the northwest (see Figure 2). Although in the field it has not been traced to Double Spring, projection of the fault intersects the North Fork in the vicinity of Double Spring. This suggests that possibly subsurface flow from the east is stopped at this fault line and that where the projected fault zone intersects northeast solution trends, a large outpouring of water occurs. 

The possibility should not be overlooked that some of the precipitation falling in the upper reaches of Fox and Brush Creeks (Figure 1) could ultimately be diverted to the North Fork basin by the Mansfield fault. Neither Fox Creek nor Brush Creek contributes much flow to the Bryant, much less than would be indicated by the size of their watersheds. 

(Note: The connection between the Mansfield fault line, Hodgson Spring on the Bryant, and North Fork and Double Springs on the North Fork has since been proven, using dye tracings and chemical analysis. See Denise Henderson Vaughn's article for the West Plains Daily Quill, Karst in the Watershed, Part 1.)