The NSS Bulletin - ISSN 1090-6924
Volume 38 Number 4: 79-87 - October 1976
A publication of the National Speleological Society

Hydrology and Geochemistry of the Upper Lost River Drainage Basin, Indiana
John Bassett

Abstract

The upper Lost Rivver drainage basin of south-central Indiana has long been regarded as one of the classic karst areas of the United States The upper basin is 163 sq mi in extent and is developed on Middle Mississippian limestones which dip to the west at about 30 ft/mile. The eastern part of the basin has a normal surface drainage net which terminates abruptly at the eastern margin of a broad sinkhole plain.

Several large sinking streams and two large karst springs are known in the basin. Stream tracing with fluorescent dye proved the existence of two major, independent karst drainage systems. One has a drainage area of at least 46 sq mi in the northwestern portion of the basin and discharges at the Orangeville Rise. The other has a drainage area of at least 110 sq mi, principally in the eastern part of the basin and discharges at the Rise of Lost River. The karst springs respond very rapidly to rainfall, and quantitative dye tracing has shown that flow velocities as great as 5.5 mi/day exist in subsurface drainage conduits.

Based on minimum monthly discharge per unit area calculations, base flow in the portion of the basin discharging at the Orangeville Rise is significantly higher than the base flow from the upper Lost River basin as a whole, indicating greater infiltration and storage in the karsted portion of the basin. The calculated water balance for the Orangeville Rise drainage basin substantiates the previous estimate of a 46 sq mi drainage area, based on dye-tracing experiments, and documents a roughly 10-fold increase in ET between summer and winter months.

Waters sampled from the Orangeville Rise have a dominatly CaCO3 composition at moderate to high flow rates, but, at low flow rates, contain appreciable Mg and SO4, are higher in CO2, and are closer to (or are at) saturation with respect to calcite. Concentrations of major dissolved chemical species are inversly porportional to discharge, as defined by regression equations of the form Y = 1 - b(log X), or Y = aXb. The molar rations, Ca/Mg and HCO3/SO4, relate directly to discharge, but the Ca/Mg molar ratio is inversely related to SO4 concentration. Saturation with respect to calcite in the spring waters is controlled both by discharge and by CO2 partial pressure. These have a seasonal trend, with high CO2 pressures in summer and late fall and low pressures in the spring and early winter.

Waters entering swallow holes along the eastern margin of the sinkhole plain are consistently saturated or supersaturated with respect to calcite and have equilibrium CO2 pressures about an order of magnitude lower than those at the Orangeville Rise. Supersaturation in sinking streams and downstream from springs is attributed to degassing of CO2.

Two principal forms of recharge occur in the basin: (1) direct and rapid rechange from open swallow holes and (2) diffuse infiltration from the sinkhole plain. At the Orangeville Rise, the observed changes inchemistry with decreasing flow rate may be attributed to either (1) a maxing mechanism, where a Ca-Mg-CO3-SO4 groundwater becomes dominant over CaCO3 water derived from sinking streams, or (2) a calcite saturation mechanism, where gradual saturation with respect to calcite and undersaturation with high-Mg-calcite, dolomite, and SO4 is the principal control.

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