Stream channel incision is severe in the loess-dominated region of western Iowa and eastern Nebraska, with recent incision related to sediment capture by reservoirs on the Missouri River. This study confirms that the temporal pattern of incision follows the rate law proposed by Graf (1977) with half-lives ranging from two to nine years and stream channels throughout the affected watersheds approaching a new dynamic equilibrium in one to three decades. The resulting spatial pattern of incision on tributaries is demonstrated to follow a simple rule of base-level lowering at the outlet multiplied by a flow-length ratio (R2 = 0.71). This rule is used to estimate depth of channel incision along all tributary streams of the Nebraska reach of the Missouri River and confirms that Missouri River degradation, along with other local disturbances such as channelization, is an important cause of tributary stream incision in the study area. Using the flow-length ratio rule, a spatial model of stream channel incision is developed that accounts for influences of channelization, grade controls, the erodability of geologic materials, and time.