Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D5243-92 – Standard Test Method Technical Guide
📐 Scope and Applicability of D5243-92
The ASTM D5243 −92 (Reapproved 2019) standard, under the jurisdiction of Committee D19, establishes a test method for the computation of discharge (the volume rate of flow) of water in open channels or streams using culverts as metering devices. This method is designed for indirect measurements, making it particularly useful for evaluating flood events where direct velocity measurement is hazardous or impractical.
This test method produces the discharge for a flood event if high-water marks are used. A complete stage-discharge relation may also be obtained, either manually or by using a computer program, for a gauge located at the approach section to a culvert. The values stated in inch-pound units are to be regarded as standard, while SI conversions provided in parentheses are for informational purposes only.
Limitations and Responsibility: This test method does not generally apply to culverts with drop inlets, and applies only to a limited degree to culverts with tapered inlets. Furthermore, this standard does not purport to address all safety concerns; it is the responsibility of the user to establish appropriate safety, health, and environmental practices prior to use.
⚙️ Key Terminology and Computational Parameters
The computational framework of this method relies on specific hydraulic parameters. For general definitions of terms, users should refer to Terminology D1129. The following table summarizes the key terms and formulas specific to this standard.
| 🟦 Symbol | 📏 Parameter Name | 📐 Definition / Formula |
|---|---|---|
| α | Alpha (Velocity-Head Coefficient) | Adjusts the velocity head computed on the basis of the mean velocity to the true velocity head. It is assumed equal to 1.0 if the cross section is not subdivided. |
| K | Conveyance | A measure of the carrying capacity of a channel, having dimensions of cubic feet per second. Computed as: K = (1.486 / n) R2/3 A |
| n | Manning Roughness Coefficient | Dimensionless coefficient representing the roughness of the channel perimeter, used in the conveyance formula. |
| A | Cross-Sectional Area | The area of the flow cross section, in ft² (or m²). |
| R | Hydraulic Radius | The ratio of cross-sectional area to wetted perimeter (Area / Wetted Perimeter), in ft (or m). |
🔭 Cross Section Definitions and Field Layout
Proper identification and surveying of specific cross sections are required for the application of the energy balance. The standard defines three cross sections, numbered consecutively in downstream order, which are critical to the computation process.
| 🎯 Section Number | 🔭 Section Name | 📌 Location Description |
|---|---|---|
| 1 | Approach Section | Located one culvert width upstream from the culvert entrance. |
| 2 | Culvert Entrance Section | Located precisely at the culvert entrance. |
| 3 | Culvert Outlet Section | Located precisely at the culvert outlet. |
Subscripts are used with symbols that represent cross-sectional properties to indicate the section to which the measurement applies. By accurately surveying these sections and documenting high-water marks, the user can reconstruct the energy grade line for the flood event.
Gauging Tip: If a gauge can be installed at the approach section (Section 1), the user can develop a continuous stage-discharge relation. This transforms the culvert into a permanent metering station, allowing for ongoing monitoring without requiring repeated high-water mark surveys for every event.
❓ Frequently Asked Questions
🔍 Does this standard apply to all types of culverts?
No. This test method does not generally apply to culverts with drop inlets and applies only to a limited degree to culverts with tapered inlets.
💡 What is the purpose of the alpha (α) coefficient?
Alpha is the velocity-head coefficient that adjusts the velocity head computed on the basis of the mean velocity to the true velocity head. It is assumed equal to 1.0 if the cross section is not subdivided.
📌 What units are considered standard in D5243?
The values stated in inch-pound units are to be regarded as standard. Values given in parentheses are mathematical conversions to SI units provided for information only.
⚡ Where is the approach section (Section 1) located?
The approach section is located one full culvert width upstream from the culvert entrance.