What Is the Broad-Crested Weir Tailwater Submergence & Discharge Calculator?
Broad-crested weirs function as critical flow measurement structures in irrigation canals and flood control channels, provided free outfall conditions prevail.
When tailwater elevation rises above the crest elevation (h2 > 0), the downstream water level begins to drown out the critical depth jump, reducing the discharging capacity.
This calculator computes free discharge Q_free, tailwater submergence ratio h2/h1, Villemonte reduction factor C_s, and actual submerged discharge Q_sub.
How Does the Broad-Crested Weir Tailwater Submergence & Discharge Calculator Work?
The calculation evaluates user-provided measurements using recognized domain equations, converts between measurement units, and adjusts for real-world efficiency factors.
Broad-Crested Weir Tailwater Submergence & Discharge Calculator Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
Villemonte empirical submergence correction formula for drowned broad-crested open-channel weirs.
How to Use the Broad-Crested Weir Tailwater Submergence & Discharge Calculator
- Enter your primary measurements in the input fields above.
- Select your preferred units (e.g. metric or imperial) if applicable.
- Review or adjust operational assumptions such as field efficiency.
- Click Calculate to instantly generate the full results breakdown and visual chart.
- Use the Reset button at any time to clear the form and test a new scenario.
Step-by-Step Example Calculation
4m Wide Canal Weir Submerged by Tailwater (h1 = 0.8m, h2 = 0.55m)
Input Values:
Understanding Your Result
Your calculated result represents the realistic operational capacity or baseline output under the specified conditions. Comparing theoretical and effective outputs reveals the direct impact of turns, overlap, and practical downtime.
Factors That Affect the Result
Field terrain, operator experience, equipment maintenance, overlap margin, and weather conditions can significantly influence real-world output.
When Should You Use This Calculator?
Use this calculator whenever you need quick, verified estimates for job planning, budgeting, equipment sizing, or project timelines.
Assumptions & Limitations
- Free-Flow Discharge: Q_free = C_d · b · √(2·g) · h₁^(1.5).
- Submergence Ratio: S = h₂ / h₁.
- Villemonte Reduction Factor: C_s = [1 - (h₂ / h₁)^1.5]^0.385.
- Actual Submerged Flow: Q_sub = C_s · Q_free.
Frequently Asked Questions
Calculation Accuracy & Reference Note
This calculator implements verified, deterministic mathematical equations based on published standards. Results should be treated as professional engineering estimates; always verify critical operations with local equipment manuals and site inspections.