Hydrologic System Related to Geology and Soils, Four Mile Creek Area, Tama County, Iowa

摘要

Topography in the Four Mile Creek area, Iowa consists of stepped levels that rise along interfluves from the main valley to divides. The drainage net is incised along tributary and side streams. Maximum relief in the area is 135 feet. Wisconsin loess covers 54% of the area and buries paleosols and glacial till. The loess varies in thickness from 4 to 35 feet. Alluvium is confined to the main, tributary, and side valleys. The main valley alluvium occupies 22% of the area. In relatively drier years, runoff is only 4 to 6% of rainfall, and in wetter years, runoff may be 11 to 17% of rainfall. The hydrologic regimen within small first-order watersheds in loess is related to stratigraphic zoning in the loess reservoir and to topography inherited from paleogeomorphic surfaces. These surfaces have associated clayey paleosols that are more impermeable than the loess. Parts of the buried surfaces are cut in till, also more impermeable than the loess. Subsurface water transmits downward and laterally through the permeable loess reservoir above the buried surfaces to alluvium along the first-order drainage. The subsurface water subsequently flows to alluvium of higher order valleys in the drainage net and ultimately to the main alluvial body along Four Mile Creek. (Author)