Hydrology and Erosion of Loessial Watersheds

Five agricultural watersheds in the Missouri Valley deep loess soils region in western Iowa were instrumented to determine their hydrology, gully erosion, and surface erosion. Two watersheds (75 and 83 acres) were singly cropped in contoured corn, another (150 acres) in level-terraced corn, and a fourth (107 acres) in pastured grass. A fifth watershed (389 acres) was level-terraced with varied cropping. Average annual stream flow (1964-1969) from the level-terraced corn watershed was almost identical with the 7.5 in from the contoured corn watersheds; but 86% was base flow, compared with only 32% from the contoured areas. Total stream flow from the grass watershed was 60% of that from the corn watersheds. Peak rates from the grassed and level-terraced watersheds have been less than 10% of those from the contoured watersheds which ranged up to 5.84 in. per hr. Measured suspended sediment, derived from both gully and surface erosion, was 38 tons per acre per yr. and 30 tons per yr. from the two contoured-corn watersheds; but the grassed and level-terraced corn watersheds had only 0.8 tons per acre per yr. and 0.9 tons per acre per yr., respectively.