CHANGES IN HYDROLOGIC RESPONSE DUE TO STREAM NETWORK EXTENSION VIA LAND DRAINAGE ACTIVITIES1 (original) (raw)

2003, JAWRA Journal of the American Water Resources Association

The objective of this work is to determine the effects of extension of a stream network through land drainage activities during the late 1800s on the hydrologic response of a watershed. The Mackinaw River Basin in Central Illinois was chosen as the focus and the pre-land and post-land drainage activity hydrologic responses were obtained through convolution of the hillslope and channel responses and compared. The hillslope response was computed using the kinematic wave model and the channel response was determined using the geomorphologic instantaneous unit hydrograph method. Our hypothesis was that the hydrologic response of the basin would exhibit the characteristic effects of settlement (i.e., increases in peak discharges and decreases in times to peak). This, indeed, is what occurred; however, the increase in peak discharges diminishes as scale increases, leaving only the decrease in times to peak. At larger scales, the dispersive effects of the longer hillslope lengths in the pre-settlement scenario seem to balance the dispersive effects of the longer path lengths in the postsettlement scenario, thus the pre-settlement and post-settlement peak discharges are approximately equivalent. At small scales, the dispersion caused by the hillslope is larger in the pre-settlement case; thus, the post-settlement peak discharges are greater than the pre-settlement. (KEY TERMS: surface water hydrology; watershed management;

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