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Open channel spillways are dam spillways that utilize the principles of open-channel flow to convey impounded water in order to prevent dam failure. They can function as principal spillways, emergency spillways, or both. They can be located on the dam itself or on a natural grade in the vicinity of the dam. == Spillway Types == Chute spillways carry supercritical flow through the steep slope of an open channel. There are four main components of a chute spillway:〔Beauchamp, K.H. Engineering Field Manual (Chapter 6 (Structures)). United States Department of Agriculture – Soil Conservation Service. http://directives.sc.egov.usda.gov/OpenNonWebContent.aspx?content=17545.wba〕 * Inlet * Vertical curve section (ogee curve) * Steep-sloped channel * Outlet ''Design'' In order to avoid a hydraulic jump, the slope of the spillway must be steep enough for the flow to remain supercritical. ''Advantages/Uses'' * Helps with flood control * Prevents erosion at the ends of terraces, outlets, and waterways * Reduces runoff over drainage ditch banks * Simple construction ''Disadvantages'' * Can only be constructed at sites with natural drainage and moderate temperature variation * Shorter life expectancy than other spillways Stepped Spillways Stepped spillways are used to dissipate energy along the chute of the channel. The steps of the spillway greatly reduce the kinetic energy of the flow and therefore reduce flow velocity. Roller-compacted concrete (RCC) stepped spillways have become increasingly popular because of their use in rehabilitating aged flood control dams.〔Hunt, S.L. Kadavy, K.C. (2010). Energy Dissipation on Flat-Sloped Stepped Spillways: Part 2. Downstream of the Inception Point. American Society of Agricultural and Biological Engineers. ISSN 2151–0032. Vol. 53(1): 111–118. http://naldc.nal.usda.gov/naldc/download.xhtml?id=41026&content=PDF〕 ''Design'' Design guidelines for these spillways are limited. However, research is currently being conducted to assist engineers with the design of stepped spillways. The two main components of design are the inception point (where flow bulking first occurs—increased flow depth) and the energy dissipation that occurs.〔 ''Advantages/Uses''〔Frizell, K.H. Hydraulics of Stepped Spillways for RCC Dams and Dam Rehabilitations. PAP-596. United States Department of the Interior – Bureau of Reclamation. http://www.usbr.gov/pmts/hydraulics_lab/pubs/PAP/PAP-0596.pdf〕 * Used for discharge of excess water (flood control) * Used for increasing dissolved oxygen (DO) levels downstream of a dam * Used at wastewater treatment plants for air-water transfer of gases and for volatile organic compound (VOC) removal * Cost benefit (reduces length or eliminates need for stilling basin) ''Disadvantages''〔 * There are not many design guidelines in place * Stepped spillways have only been successful for small unit discharges where step height can influence the flow Side Channel Spillways Side channel spillways are typically used to discharge floods perpendicular to the general direction of flow by placing the control weir parallel to the upper portion of the discharge channel.〔Hager, W.H. Phister, M. (2011) Historical Development of Side-Channel Spillway in Hydraulic Engineering. Brisbane,Australia. http://infoscience.epfl.ch/record/170044/files/2011-805_Hager_Pfister_Historical_development_%20of_%20side_channel_spillway_hydraulic_engineering_1.pdf〕 ''Advantages/Uses'' * Low flow velocities upstream * Minimizes erosion ''Disadvantages'' * Can cause a sudden increase in reservoir level if the channel is submerged 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Open channel spillway」の詳細全文を読む スポンサード リンク
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