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<br />25 <br /> <br />Conceptual Model of Inset <br />Floodplain Fonnation <br /> <br />The detailed data on the building of this deposit on the Green River <br /> <br />provides a good conceptual model for how inset floodplain deposits develop. <br /> <br />The formative steps identified by this research are (1) emplacement and <br /> <br />accretjon of a lateral bar as large amounts of sediment are being moved <br /> <br />through the system, (2) low flood magnitude in years following bar <br /> <br />emplacement, (3) rapid encroachment of riparian vegetation onto the bar <br /> <br />surface, (4) stabilization of the bar through extensive root system development, <br /> <br />and (5) continued vertical accretion of the bar surfa~e during episodic periods <br /> <br />of inundation. <br /> <br />These steps are clearly controlled by many factors,both natural and <br /> <br />anthropogenic, but a knowledge of the basic steps of inset floodplain formation <br /> <br />is critical if we are to understand how river systems respond to decreases in <br /> <br />effective discharge often caused by dams and diversions. The work of Pizzuto <br /> <br />(1994) clearly illustrates some of the steps outlined above, although they were <br /> <br />not specifically discussed. <br /> <br />The Cause of Channel Narrowing <br /> <br />Data from several sources presented in this chapter indicate that <br /> <br />changes in streamflow regime are the likely causal mechanism for the <br /> <br />narrowing of the Green River. Figure 10 shows a period of channel-width <br /> <br />stability from the 1940s to the mid-1950s, a time when saltcedar were well <br />