Laserfiche WebLink
<br />\.~~~ <br /> <br />11 <br /> <br />purposes, these inputs likely have a short residence time in critical reaches, similar to those sand <br />inputs derived from the Paria River (see section on Mass Balance, above), This is important <br />information that further supports development of a fine-sediment budget for the ecosystem, as <br />well as technical discussions about how best to conserve fine sediment inputs through dam <br />operations, Perhaps more importantly to the ecosystem, lesser tributaries below Lees Ferry <br />continue to input fine-to-coarse size gravel into the main channel. The implications for these <br />ongoing, accumulated gravel inputs is still being studied, but several possibilities exist for how <br />these deposits may influence the aquatic and terrestrial elements of the Colorado River <br />ecosystem: I) aggradation of the channel's rapids leading to increased navigational challenges, <br />but also expanded eddies where sand can accumulate, 2) aggradation of low-velocity pools and <br />higher velocity runs, with potential changes to aquatic food base dynamics, 3) increased spatial <br />abundance of fine gravels that effectively expand spawning and rearing habitats throughout the <br />main channel in Glen, Marble and Grand Canyons, 4) burial and/or erosion of existing sand bars <br />during debris flows and stream-flow floods, <br />A long-term monitoring program for coarse-sediment inputs and impacts throughout the <br />ecosystem was initiated in FY 2001, although coarse-sediment inputs from lesser tributaries have <br />been studied since 1984, The current annual monitoring effort for coarse sediment inputs is also <br />intended to document the occurrence of periodic debris flows within 800 lesser tributaries, where <br />and when they occur. The project is also focused on documenting how such coarse-sediment <br />inputs alter the geomorphic framework of the river by directly impacting both sediment and non- <br />sediment resources of the ecosystem at hundreds oflocations through time under dam operations, <br />This project represents one of the lead participants in the Advanced Conceptual Modeling project <br />that was conducted from FY 2001 through 2003 (see below), <br />Summer storms of August and September 2002 and 2003, resulted in numerous localized <br />changes in the river ecosystem's geomorphology owing to several new debris flows and <br />widespread tributary stream flow flooding, Extensive deposits of new gravel were deposited in <br />the river throughout Marble and eastern Grand Canyon, The debris flows that occurrcd in <br />September 2002, buried or eroded some existing campsite areas, and in one case created a <br />significant new rapid near river mile 74. <br /> <br />GCMRC FY2005-2006 Draft Annual Work Plan (November 10,2003) <br />