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June 4,2009 <br /> TASK 3 -Install J-Hooks <br /> Description of Task Install rock material for two J-Hook instream structures under NRCS <br /> supervision.. <br /> Method/Procedure—The tasks for the placement of J-hooks will follow standard accepted <br /> procedures and will conform to NRCS specifications.The J-Hook Vane is an upstream directed, <br /> gently sloping structure composed of natural materials,in this case rock. Each structure is <br /> located on the outside of the stream bend where strong downwelling and upwelling currents, <br /> high boundary stress,and high velocity gradients generate high stress in the near-bank region. <br /> The structure is designed to reduce bank erosion by reducing near-bank slope,velocity,velocity <br /> gradient,stream power and shear stress.Redirection of the secondary cells from the near-bank <br /> region does not cause erosion due to back-eddy re-circulation. The vane portion of the structure <br /> occupies 1/3 of the bankfull width of the channel,while the"hook"occupies the center 1/3. <br /> Maximum velocity,shear stress, stream power and velocity gradients are decreased in the <br /> nearbank region and increased in the center of the channel. Sediment transport competence and <br /> capacity can be maintained as a result of the increased shear stress and stream power in the <br /> center 1/3 of the channel.Backwater is created only in the near-bank region, and the small <br /> departure angle gently redirects the velocity vectors from the near-bank region,reducing active <br /> bank erosion. Contractor will place and bury foundation rocks the same size as the top rocks, <br /> wedged in below the riverbed level to avoid their being washed out and proceed with rock <br /> placement, including foundation and keyway, in compliance with NRCS engineering <br /> specifications and accepted Rosgen J-Hook river stabilization technology.Create fish holes on <br /> bottom side of J-hooks. <br /> Equipment—Excavator with opposable thumb-42 excavator hours. <br /> Deliverable- This work was completed under supervision of NRCS according to Phase I in <br /> Project proposal. Two J-hooks were installed plus a spur to protect the existing rip rap bank, <br /> resulting in enhanced fish habitat, reduced erosion,and stabilized flows,optimizing the natural <br /> hydrology of the river and protecting the El Codo Ditch irrigation system and surrounding <br /> communities from flood. In preparation for Phase II,this task returned this severely eroded <br /> reach of the San Antonio River to a natural state of hydraulic stability by stabilizing the banks <br /> and the bed of the stream and optimizing the river's ability to transport and utilize its sediment <br /> effectively. <br /> Gravel transport down the main channel has been improved to reduce the gravel bed load in front <br /> of the Core and the Diversion Gates during high flows.Flows into the Ditch diversion will be <br /> increased and stabilized,especially during low flow regimes on the main channel. Water quality <br /> will be improved by reducing sediment loading, stabilizing the stream-bank and reconfiguring <br /> the stream channel to enhance sediment transport. <br /> TASK 4--Backfill and Final grade <br /> Description of Task --Complete Phase 1 with backfill and final grade. <br /> Equipment-Excavator— <br /> Method/Procedure—Create proper slopes by regrading eroded banks; fill in around keyways; <br /> plant willows and install root wads in bank. Direct gravel transport down the main channel and <br /> away from the diversion structures.Revegetate riparian areas. <br /> El Codo Ditch Company 4 Updated Statement of Work <br />