Laserfiche WebLink
<br />drop. Backwater problems can be alleviated by using Fujimoto entrance developed <br />by the USBR (Rhone, 1977) where the upper rows of baffles are moved one row <br />increment downstream. Trickle channels can be addressed by notching the crest <br />between baffles (Taggart, 1986, UDFCD, 1990). <br /> <br />Vertical Hard Basin Drqps <br />(VHB) <br />The vertical hard basin is <br />a general category which <br />can include a wide variety <br />of structure designs and <br />components. Maximum <br />drop height across the <br />structure is limited to 0.9 m (3 feet) for safety considerations. <br /> <br />If grouted rock basins are used for drops less than 0.6 m (2 feet), they must have 0.3 <br />m (1 ft.) minimum rock size with 0.2 m (.75 ft.) of grout, and 0.6 to 0.9 m (2 to 3 <br />foot) drops must have 0.45 m (1.5 ft.) minimum rock with 0.3 m (1 ft.) of grout. <br />Seepage must be controlled. <br /> <br />Grouted Slo.pin2" Boulder <br />]2rQps (GSB) <br />The GSB drop is designed <br />to operate as a hydraulic <br />jump dissipator, although <br />some energy loss is <br />incurred due to the <br />roughness of the grouted <br />rock slope. The quality of rock used, and proper grouting procedure are very <br />important to the structural integrity. It is important for structural and seepage <br />control that the grout depth extends from the subgrade up to a minimum of two- <br />thirds of the nominal rock size. Appearance and energy dissipation are improved <br />if the grout depth is held to a maximum of three-fourths of the rock size. Adequate <br />seepage provisions are critical to the design success. <br /> <br />~~ <br /> <br /> <br />-- <br /> <br /> <br />~~- <br />, Y"' ";........- ..:::- <br />:::--:::::::..... - <br />4' '11....']- <br /> <br />For drops less than 0.9 m (3 feet), minimum rock size is 0.45 m (1.5 ft.) with 0.3 m (1 ft.) of <br />grout. Larger drops must have minimumrock size of 0.6 m (2 ft.) with0.45 m(l.5 ft.) of grout. <br /> <br />This type of drop really belongs in a more general category of sloping mass gravity <br />drops. Other materials of construction include unreinforced concrete, rollercrete, <br />and soil cement. <br /> <br />Vertica1 Rjprap Drop (VRR) <br />The vertical riprap basin is <br />essentially a plunge pool <br />type of drop which <br />incorporates a crest wall <br />with a riprap lined <br />dissipation pool below. A ". <br />nearly rectangular crest . . <br />section is recommended to reduce the width of the plunge pool. Maximum drop <br />height is limited to 0.9 m (3 feet) due to safety considerations and the practicality of <br />obtaining large basin rock for higher drops. The ability of the riprap to rearrange <br /> <br /> <br />- <br /> <br />3 <br /> <br />Taggart, et al <br />