Calculate the weir loading rate for clarifiers and sedimentation tanks.
Enter value in Gallons per Day (GPD)
Linear / Rectangular Weir
Circular Weir (Clarifier)
Enter in Feet (ft)
Calculated Results
Total Weir Length: 0 ft
0
Gallons per Day per Foot (GPD/ft)
Understanding Weir Overflow Rate
The Weir Overflow Rate (WOR), also known as the weir loading rate, is a critical hydraulic design parameter used in wastewater treatment and civil engineering. It measures the volume of liquid flowing over a weir per unit length of the weir per day. This metric is essential for the proper design and operation of sedimentation tanks and clarifiers.
The Formula
The calculation relies on the relationship between the influent flow rate and the physical length of the overflow weir:
WOR = Q / L
WOR: Weir Overflow Rate (GPD/ft)
Q: Flow Rate (Gallons per Day)
L: Total Length of the Weir (Feet)
For Circular Clarifiers, the weir length is often the circumference of the tank (assuming the weir is located at the perimeter): L = π × Diameter
Why is WOR Important?
The weir overflow rate directly impacts the efficiency of the sedimentation process.
High WOR: If the rate is too high, the velocity of the water flowing over the weir increases. This creates strong currents near the outlet, which can pull settling solids (floc) up from the bottom and carry them out of the tank, degrading effluent quality.
Low WOR: While generally better for settling, an excessively low WOR might indicate an unnecessarily large (and expensive) structure for the required flow.
Typical Design Values
Standard design guidelines (such as Ten State Standards) often suggest the following maximum weir loading rates:
Primary Settling Tanks: 10,000 to 15,000 GPD/ft
Secondary Clarifiers (Activated Sludge): 10,000 to 20,000 GPD/ft (varies based on peak vs. average flow)
Small Plants (< 1 MGD): Often designed conservatively at lower rates.
function toggleDimensionLabel() {
var shape = document.getElementById('worShape').value;
var label = document.getElementById('worDimLabel');
if (shape === 'circular') {
label.innerText = "Tank Diameter (D)";
} else {
label.innerText = "Weir Length (L)";
}
}
function calculateWeirOverflow() {
// Get Input Values
var flowRate = parseFloat(document.getElementById('worFlowRate').value);
var dimension = parseFloat(document.getElementById('worDimension').value);
var shape = document.getElementById('worShape').value;
var resultBox = document.getElementById('worResult');
var resValueDisplay = document.getElementById('resValue');
var resLengthDisplay = document.getElementById('resLength');
var resEvaluation = document.getElementById('resEvaluation');
// Validation
if (isNaN(flowRate) || isNaN(dimension) || dimension <= 0) {
alert("Please enter valid positive numbers for Flow Rate and Dimensions.");
return;
}
// Calculate Length based on Shape
var effectiveLength = 0;
if (shape === 'circular') {
// Circumference = pi * d
effectiveLength = Math.PI * dimension;
} else {
// Linear length is just the input
effectiveLength = dimension;
}
// Calculate WOR
// Formula: Flow Rate / Length
var wor = flowRate / effectiveLength;
// Display Results
resultBox.style.display = 'block';
resLengthDisplay.innerText = effectiveLength.toLocaleString('en-US', {maximumFractionDigits: 2});
resValueDisplay.innerText = wor.toLocaleString('en-US', {maximumFractionDigits: 0});
// Basic Evaluation Logic (General Wastewater Guidelines)
var msg = "";
var color = "";
if (wor = 10000 && wor <= 20000) {
msg = "Rate is Moderate (Typical Range)";
color = "#d39e00"; // dark yellow
} else {
msg = "Rate is High (Potential Solids Carryover)";
color = "#c82333"; // red
}
resEvaluation.innerHTML = "" + msg + "";
}