TAMARISK AND FLUVIAL GEOMORPHIC FORM IN DINOSAUR NATIONAL MONUMENT, COLORADO AND UTAH

The availability of fine-grained alluvial sediment is the primary large-scale control on the distribution of tamarisk, an invasive riparian shrub, along both the regulated upper Green River through Lodore Canyon, and the unregulated Yampa River through Yampa Canyon. Managed reservoir releases have been suggested as a complementary control method in some regulated rivers. Effective control strategies must be founded on a sound understanding of the hydrogeomorphic controls on tamarisk's distribution. Local boundary shear stress influences tamarisk's distribution at the site scale, and areas where shear stress remains low at high discharge often develop dense stands of tamarisk. The style, magnitude, and frequency with which floods rework alluvial deposits determine their suitability for tamarisk's establishment. Although tamarisk germinates between the stage of base flow and the flood of record on both rivers, this is a narrow elevation range on the regulated upper Green River. On the upper Green River, more than 70% of all tamarisk are on deposits which formed since flow regulation began in 1962 and have only been inundated 5 times since then. Managed flooding has been suggested as a passive control method for invasive tamarisk (tamarix ramosissima). Where reservoir releases are considered as a complementary control method with mechanical removal, an effective control program requires a scientifically based strategy for targeting removal efforts. One strategy to predict where managed floods will be an effective complement to mechanical removal is a comparison of tamarisk's distribution along a wild river and a regulated river. However, accurate prediction with this approach requires that comparisons be made between analogous hydrogeomorphic environments on the two rivers. We describe a methodology to compare locations of analogous hydrologic, hydraulic, and geomorphic conditions, and to apply these comparisons to develop spatially discrete recommendations for tamarisk's removal. We compare the wild Yampa River through Yampa Canyon and the regulated upper Green River through Lodore Canyon in Dinosaur National Monument as a case-study of this methodology, and describe where tamarisk removal in Lodore Canyon would complement higher-magnitude floods proposed on the upper Green River.