M1Q10 PART#2

During storm conditions, a culvert runs with submerged inlet and free outlet (the submerged ratio is 1.6). The width of the barrel is B = 4.3 m, which coincides with the width of the river channel. The normal depth downstream the culvert is 2.8 m. PART#1: Calculate the flow rate. (Answer in m3/2).

Question

M1Q10 PART#2

During storm conditions, a culvert runs with submerged inlet and free outlet (the submerged ratio is 1.6). The width of the barrel is B = 4.3 m, which coincides with the width of the river channel. The normal depth downstream the culvert is 2.8 m. PART#1: Calculate the flow rate. (Answer in m3/2).

BlackTom AI · Accepted Answer

Restating the task and data to ensure clarity: you are asked to calculate the flow rate through a culvert under storm conditions where the inlet is submerged and the outlet is free. The submerged ratio is given as 1.6. The culvert has a width B = 4.3 m, which matches the river channel width. The normal depth downstream is y2 = 2.8 m. This is a numerical fill-in question (no multiple-choice options). The provided answer is 22.6 (presumably m^3/s).

First, identify what information is actually available and what might be missing for a unique calculation:
- Submerged ratio of 1.6 is given. In culvert analysis, a submerged inlet ratio often relates to the ratio between upstream head and downstream head or a coefficient that indicates how submerged the inlet is. However, the exact interpretation can vary by the standard or formula being used (some curricula define it as h1/h2, others define a different non-dimensional ratio). 
- Width B = 4.3 m is known, so the cross-sectional flow area is likely A = B * something (e.g., upstream depth h1 or a head difference). 
- Downstream normal depth y2 = 2.8 m is given, which is essential for energy/pressure calculations and for evaluating whether the outlet is truly free.
- No explicit culvert type (rectangular box, oval, circular) or roughness coefficient, and no explicit head loss terms are provided. In many standard problems, a rectangular, sharp-edged culvert with known upstream depth h1 and downstream depth h2 uses a specific discharge equation that includes coefficients for entrance losses, outlet losses, and friction losses.

Because the problem statement does not specify all required elements to compute Q definitively, several key steps would be needed to proceed unambiguously:
- Determine upstream depth (h1) or the upstream water surface condition, using the submerged inlet ratio (the exact definition of 1.6 in this context must be clarified). If the ratio is h1/h2, then h1 could be 1.6 * y2, but this interpretation must match the course’s convention. If the ratio is defined differently, the calculation path changes.
- Choose the appropriate flow relation for a submerged inlet, free outlet culvert. Common approaches include a weir-like or orifice-like formulation or a specialized culvert equation that combines the conduit area, velocity head, and head losses (entrance, contraction, friction, and exit losses). The chosen model will determine how Q depends on B, h1, h2, and g.
- Apply the energy equation and loss coefficients to relate upstream head, downstream head, and velocity head inside the culvert. Then compute Q from the resulting velocity and cross-sectional area.
- Verify units: if the answer is given as 22.6, ensure that the units align to m^3/s (not m^3/2; the latter is not a standard unit for discharge). If the expected unit is m^3/s, the computed Q should reflect that.

In the absence of explicit formulas, here is a structured way to approach the calculation, illustrating what would typically be done in a standard course (without asserting a specific numerical value):
- Step A: Clarify the submerged inlet ratio meaning and determine h1 (upstream depth) from y2 = 2.8 m and the ratio definition. If h1 = 1.6 * y2, then h1 = 4.48 m; if a different relation is intended, substitute accordingly. 
- Step B: Compute the provisional cross-sectional area for flow. For a rectangular culvert, A = B * y1 where y1 is the upstream depth inside the culvert. If the culvert carries flow with a full-depth assumption, y1 might be taken as h1, but many problems use the actual head and geometry to determine velocity. 
- Step C: Use the standard culvert discharge relation appropriate for the problem context (e.g., Q = C * A * sqrt(2 g ΔH) or a more detailed head-loss equation that includes entrance, friction, and contraction losses). Here ΔH would involve upstream and downstream water surface elevations, and g = 9.81 m/s^2. 
- Step D: Compute Q with the chosen model, ensuring that all terms (A, ΔH, loss coefficients, B, and g) are consistently incorporated.

Why the lack of a single definitive path can lead to ambiguity in this case:
- Different curricula define the submerged ratio and the exact discharge formula in slightly different ways, and the problem statement does not specify which standard to apply. 
- The problem does not provide upstream depth (h1) directly, nor does it specify the culvert shape and roughness coefficients, which are typically essential inputs. 
- Without a clearly stated equation or a definition of h1 from the submerged ratio, multiple discharge values could be obtained depending on the assumed model.

Given these considerations, the stated numerical answer of 22.6 (presumably m^3/s) could be correct under a particular interpretation and set of assumptions, but a complete, unambiguous solution requires explicit definitions for:
- The meaning of the submerged ratio in this context, and the exact relationship it imposes on upstream depth h1 or head loss terms,
- The culvert geometry beyond width (e.g., height, shape), and
- The specific discharge equation or coefficients to be used for this problem.

If you can provide the exact interpretation of the submerged ratio as used in your course (e.g., whether it defines h1/h2 or another non-dimensional parameter) and the culvert model to apply (rectangular box culvert with specific loss coefficients, or a simpler head-difference approach), I can carry out the numerical calculation step-by-step to verify or compute the discharge value and show the intermediate quantities.

CVEN90051_2025_SM2 Mock Exam 2025

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