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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 I 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 />