Source, Occurrence, and Movement of Ground WaterThe discussion of the occurrence of ground water in Douglas County is based partly on a detailed treatment by Meinzer (1923, 1923a). A general discussion of the principles of ground-water occurrence with special reference to Kansas has been given by Moore and others (1940).
Ground water is the part of the water below the surface of the land that is in the zone of saturation and supplies wells and springs. It is derived mainly from precipitation, falling as rain or snow, some of which reaches the zone of saturation by percolation downward through the soil and subsoil.
The rocks in the outer crust of the earth are not solid but contain many openings, or voids, that hold air, water, or other fluids. Generally, the rock formations below a certain level are saturated with water. The upper surface of the zone of saturation is not a level surface nor a static surface, but one that has many irregularities, which on a modified scale are generally similar to the irregularities of the surface topography. Under natural conditions, the small part of the precipitation that reaches the zone of saturation moves slowly toward the streams and discharges into them or is lost by transpiration and evaporation in the valley areas.
Water in the zone of saturation, available to wells, may be unconfined or confined. Unconfined or free ground water is water that does not have a confining or impermeable body restricting its upper surface. The upper surface of unconfined ground water is called the water table. Shallow wells constructed in the near-surface weathered limestone, sandstone, and shale, the alluvial deposits in stream valleys, and the colluvial slope deposits generally tap unconfined ground water. Ground water is said to be confined if it occurs in permeable zones between relatively impermeable beds that confine the water under pressure. Most of the wells constructed in the unweathered Pennsylvanian bedrock tap confined ground water.
Ground-water Recharge and DischargeThe addition of water to the underground reservoir is called recharge and may be effected in several ways. The most important source of recharge is local precipitation; for shallow upland wells local precipitation is the only source of recharge. Lesser amounts are contributed elsewhere by influent seepage from streams and ponds and by subsurface inflow from adjacent areas. Locally, however, influent seepage from streams may contribute an important amount of recharge to adjacent alluvial deposits and to the bedrock where streams cut across permeable zones in bedrock.
Recharge is seasonal in the Midwest, including Douglas County. Generally the water levels of wells have been lowered by natural drainage into streams during the winter, when the soil is frozen and precipitation is slight. During the spring months precipitation is fairly abundant, temperature is moderately cool, and transpiration and evaporation demands are low, resulting in considerable recharge. Recharge may occur in other seasons, also, whenever precipitation is sufficient to overcome soil-moisture deficiency built up during a preceding dry period.
Ground water moves downward through the permeable rocks in accordance with the character and structure of the rocks, to points of lower elevation. It may discharge directly into a stream as a spring or seep or may discharge by evaporation or transpiration where the water table is near the surface. A part of the ground water is discharged from wells, but, with the exception of the municipal, industrial, and irrigation pumpage in the Kansas River valley in the vicinity of Lawrence, the amount discharged by wells in Douglas County is small compared with that discharged by other means.
Under natural conditions, over a long period of time, approximate equilibrium exists between the amount of water that it added annually to ground-water storage and the amount that is discharged annually.
Kansas Geological Survey, Geohydrology of Douglas County
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Web version Aug. 1999. Original publication date Dec. 1960.