Environmental setting and natural factors and human influences affecting water quality in the White River Basin, Indiana
The White River Basin drains 11,349 square miles of central and southern Indiana and is one of 59 Study Units selected for water-quality assessment as part of the U.S. Geological Survey's National WaterQuality Assessment Program. Defining the environmental setting of the basin and identifying the natural factors and human influences that affect water quality are important parts of the assessment. Interrelated natural factors help determine the quality of surface and ground water in a river basin. The White River Basin has a humid continental climate, characterized by well-defined winter and summer seasons. Geologic features in the basin include glaciated and nonglaciated areas; a region of karst geomorphology that is characterized by caves and sinkholes; and a thick, sedimentary bedrock sequence underlying the entire basin. Unconsolidated glacial deposits of clay, silt, sand and gravel cover more than 60 percent of the basin. Soils developed in unconsolidated glacial deposits are typically fertile, naturally or artificially well drained, and farmed. Soils in the unglaciated south-central part of the basin are thin, have low fertility, and are best suited for forest or pasture. Agriculture is the principal land use in the White River Basin. Approximately 70 percent of the basin is used for agriculture, and about 50 percent of the basin is cropland. Corn and soybeans are the major crops. Other significant land uses are forest (22 percent) and urban and residential (7 percent). The population of the basin was 2.1 million in 1990. Water use in the White River Basin totaled 1,284 million gallons per day in 1995, of which 84.5 percent was surface water and 15.5 percent was ground water. Despite the predominant use of surface water, ground water was the primary source of drinking water for approximately 56 percent of the population. The general water chemistry in the White River Basin is determined by natural factors such as soils and geologic materials that water contacts as it moves through the hydrologic system. In the southern part of the basin, bedrock upland areas are dominated by non-carbonate bedrock, thin soils, and high runoff-rainfall ratios. These areas have small chemical concentrations in streamwater. Conversely, in the northern part of the basin where glacial deposits are thick and in the southwestern part of the basin where loess deposits are thick, water has longer periods of time to react with soils and aquifers and to acquire substantial quantities of dissolved constituents. As a result, streams in the till plain and glacial lowland have higher concentrations of most constituents than streams in the unglaciated parts of the basin. Water quality is significantly modified by human influences. Water quality is affected locally by point sources of contamination that include combined-sewer overflows, power-generation-plant cooling stations, and wastewater-treatment-plant effluents that are generally associated with densely populated areas. Water quality is additionally affected by non-point sources of contamination related to agriculture, urban runoff, and mining. Six hydrogeomorphic regions of the White River Basin are delineated on the basis of distinct and relatively homogeneous natural characteristics. These six regions are used in the White River Basin study as a framework for examining the effects of natural factors on water quality in the basin. Bedrock is exposed or near the surface in three hydrogeomorphic regions the bedrock uplands, bedrock lowland and plain, and karst plain; streams and shallow aquifers in these regions are susceptible to contamination, especially in the karst plain, and show rapid response to rainfall. The other three hydrogeomorphic regions the fluvial deposits, till plain, and glacial lowland are in the glaciated part of the basin. Where thick fine-grained unconsolidated sediments are present, primarily in the till plain, ground-water supplies are protected from contamination, and extreme high and low streamflows are moderated.