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<br />-10- <br /> <br /> <br />. " <br /> <br />to external loading on the top face are compressive upon the rock and grout material. Both of <br />these materials are very strong in compression. <br /> <br /> <br />~. , <br />~ .~ -. <br />, _ ,'" '.' ,., Qt,'fk;w: <br /> <br />. . . . <br /> <br />Figure 3. A section view of the aPex of the U-structure. <br /> <br />Figure 3 shoWs a section view of the apex of the arch. ,This Figure shows that the arch is <br />sunk into the riverbed such that the crest of the structure, which is the highest point on the <br />upstream side, is even or below the existing grade of.~e riverbed. Setting the structure . or <br />below grade has two effects. First it ensmes that the un,constricted river level is no higher than <br />the existing river level and secondly it e~ that there are no dynamic fluid forces on the <br />structure due to current,flow. Sinking the arch in the riverbed alSQ supports the structure, <br />laterally and prevents torsion on the structure. <br /> <br />A base rock, also shown in Figure 3, is shown at the downstream end of the struCture. <br />The'base rock is SUnk mto ffie-'eobble ana IS keyeairitO the rock,th8t forms the st:ructure in order ' <br />to reinforce the structure and to protect th~' structUre from erosion caused by ~dy c~ts. <br /> <br />These structures are designed such that the river is usable at a variety of water level.s. <br />Figure 4 shows a profile view of the U-stlucture looking upstream. This view highlights the <br />versatile design of these structures. The low flow channel can be designed to provide deep <br />passage and a usable hydraulic feature during typical low tlows. During the mid-range flows the <br />