At what specific flow depth does the discharge over a broad-crested weir reach its peak value_______________?
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Answer: D. 2 H/3
Explanation
Critical flow theory establishes that maximum discharge over a broad-crested weir occurs at specific depths. Mathematical optimization of specific energy equations shows this peak flow happens at two-thirds of total head. At this critical depth, the Froude number of the flow over the weir crest equals exactly unity. A broad-crested weir is a flat-topped hydraulic structure used for measuring open-channel flow rates. Specific energy is the total mechanical energy of fluid measured relative to the channel bottom. Critical flow represents the condition where specific energy is at a minimum for a given discharge.
Civil engineers utilize broad-crested weirs as reliable flow measurement devices in irrigation canals. Knowing the critical depth allows designers to predict upstream water surface profiles accurately. This principle prevents flooding by ensuring spillways pass maximum discharge efficiently. A flow depth of H/3 does not satisfy the specific energy optimization criteria for maximum discharge. A flow depth of H/2 represents critical depth parameters for rectangular channels rather than broad weirs. A flow depth of 2 H/5 underestimates the theoretical peak discharge threshold for these structures.
- Subject
- Engineering
- Category
- Civil Engineering
- Topic
- —
- Difficulty
- medium
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