ASSESSING THE EFFECTS OF ALTERNATIVE SETBACK LEVEE SCENARIOS EMPLOYING A RIVER MEANDER MIGRATION MODEL

River channel migration and cutoff events within large river riparian corridors create a heterogeneous landscape with high biological diversity. Riparian areas are impacted by water management activities, which include channel stabilization (riprap and levees), but these impacts can be mitigated by levees set back from the main channel. We used a meander migration model together with an empirically-based cutoff algorithm to examine the relationship between setback distance and habitat formation through a measure of the land reworked. We simulated 100 years of channel migration and cutoff events under different setback levee scenarios on a 28 km reach of the Sacramento River, California, USA. Eleven scenarios were simulated, one with existing riprap and 10 assuming no riprap and setback levees from 100 to 1000 m from the channel. Results suggest three basic patterns of rate of land reworked – complete restriction of cutoffs, partial restriction of cutoffs, and no restriction of cutoffs – based on different migration and cutoff dynamics. Our study section showed complete cutoff restriction at distances less than about one channel width (300 m) and showed no cutoff restriction at distances greater than about three channel widths (700 m). Results suggest that management decisions concerned with land reworked could usefully identify the site-specific cutoff thresholds to optimize habitat benefits versus cost of acquired land.