Laserfiche WebLink
W-Weir <br /> General Description. The design of the W-Weir(W as looking in the downstream direction)was <br /> initially developed to resemble bedrock control channels on larger rivers. Various rock weirs <br /> installed across larger rivers for fish habitat, grade control and bank protection often create an <br /> unnatural and uniform"line of rocks"that detracts from visual values. The W-Weir is similar to <br /> a Cross-Vane in that both sides are vanes directed from the bankfull bank upstream toward the <br /> bed with similar departure angles. From the bed at 1/4 and 3/4 channel width,the crest of the weir <br /> rises in the downstream direction to the center of the bankfull channel creating two thalwegs <br /> (Figure 5). The objectives of the structure are to provide grade control on larger rivers, enhance <br /> fish habitat,provide recreational boating, stabilize stream banks, facilitate irrigation diversions, <br /> reduce bridge center pier and foundation scour, and increase sediment transport at bridge <br /> locations. Double W-Weirs are constructed on very wide rivers and/or where two center pier <br /> bridge designs(three cells)require protection. <br /> Habitat for trout is enhanced by maximizing usable holding, feeding and spawning areas. Fish <br /> hold in the multiple feeding lanes created by the two thalweg locations and pools. Various age <br /> classes of trout also hold in the deep glide created upstream of the structure and against both <br /> banks due to the increased depth and reduced velocity of flows in the near-bank region. <br /> Spawning habitat is created in the tail-out of the pools due to upwelling currents and a sorting of <br /> gravel bed material sizes preferred by trout. <br /> J-Hook Vane <br /> General Description. The J-Hook Vane is an upstream directed, gently sloping structure <br /> composed of natural materials. The structure can include a combination of boulders, logs and <br /> root wads(Figures 6-7)and is located on the outside of stream bends where strong downwelling <br /> and upwelling currents, high boundary stress, and high velocity gradients generate high stress in <br /> the near-bank region. The structure is designed to reduce bank erosion by reducing near-bank <br /> slope,velocity, velocity gradient, stream power and shear stress. Redirection of the secondary <br /> cells from the near-bank region does not cause erosion due to back-eddy re-circulation. The <br /> vane portion of the structure occupies 1/3 of the bankfull width of the channel, while the"hook" <br /> occupies the center 1/3. <br /> Maximum velocity, shear stress, stream power and velocity gradients are decreased in the near- <br /> bank region and increased in the center of the channel. Sediment tr.nsport 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. <br /> The scour pool in the center 1/3 of the channel provides energy dissipation and holding cover for <br /> fish. The flow separation zones, or"seams"of fast and slow water that mark the zones of <br /> downwelling and upwelling currents, are habitat features utilized by trout. The"hook"portion <br /> of the vane produces a longer, wider and deeper pool than that created by vane-only structures. <br /> The downstream pool dissipates energy and provides fish habitat. The 1/4- 1/3 rock diameter <br /> gaps between the rocks associated with the hook creates a vortex or corkscrew flow that <br />