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<br />HYDRAULIC STRUCTURES <br /> <br />DRAINAGE CRITERIA MANUAL (V. 2) <br /> <br /> <br />Photograph HS-7 <br /> <br />An overall view of the drop structure from the previous page is illustrated here to emphasize the <br />opportunities available for creating an attractive urban hydraulic setting for the riparian corridor. <br /> <br />2. Grouted boulders must cover the crest and cutoff and extend downstream through the energy- <br />dissipating basin. <br /> <br />3. The vertical cutoff should be located at the upstream face of the crest at a minimum depth of <br />0.8Hd or 4 feet, whichever is higher. Evaluate specific site soils for use in seepage analysis and <br />foundation suitability. <br /> <br />4. The trickle or low-flow channel should extend through the drop crest section. Downstream, the <br />trickle or low-flow channel protection should extend past the main channel protection, or large <br />boulders and curves in the trickle or low-flow channel can be used in the basin area to help <br />dissipate the energy. <br /> <br />5. Grout thickness, Dg, and rock thickness, D" should be determined based upon a minimum safety <br />surplus net downward force of 30 pounds. The rocks must be carefully plaoed to create a <br />stepped appearance, which helps to increase roughness. Minimum criteria for the simplified <br />design process are referred to in step 3, below. <br /> <br />HS-22 <br /> <br />06/2001 <br />Urban Drainage & Flood Control District <br /> <br />e <br /> <br />e <br /> <br />e <br />