Spatial and temporal sensitivity of hydrogeomorphic response and recovery to deforestation, agriculture, and floods

Clear-cut logging followed by agricultural activity caused hydrologic and g eomorphic changes in North Fish Creek, a Wisconsin tributary to Lake Superi or. Hydrogeomorphic responses to changes in land use were sensitive to the location of reaches along the main stem and to the relative timing of large floods. Hydrologic and sediment-load modeling indicates that flood peaks w ere three times larger and sediment loads were five times larger during max imum agricultural activity in the 1920s and 1930s than prior to about 1890, when forest cover was dominant. Following logging, overbank sedimentation rates in the lower main stem increased four to six times above pre-settleme nt rates. Accelerated streambank and channel erosion in the upper main stem have been and continue to be primary sources of sediment to downstream rea ches. Extreme floods in 1941 and 1946, followed by frequent moderate floods through 1954, caused extensive geomorphic changes along the entire main st em. Sedimentation Fates in the lower main stem may have decreased in the la st several decades as agricultural activity declined. However, geomorphic r ecovery is slow, as incised channels in the upper main stem function as eff icient conveyors of watershed surface runoff and thereby continue to promot e flooding and sedimentation problems downstream.