Please enter valid positive numbers for Flow Rate and Weir Length.
Calculation Results
US Customary–GPD / ft
Metric System–m³ / day / m
function calculateWOR() {
var flowInput = document.getElementById('wor_flow');
var lengthInput = document.getElementById('wor_length');
var flowUnit = document.getElementById('wor_flow_unit').value;
var lengthUnit = document.getElementById('wor_length_unit').value;
var errorMsg = document.getElementById('wor_error_msg');
var resultBox = document.getElementById('wor_result_box');
var flowVal = parseFloat(flowInput.value);
var lengthVal = parseFloat(lengthInput.value);
// Validation
if (isNaN(flowVal) || isNaN(lengthVal) || flowVal <= 0 || lengthVal <= 0) {
errorMsg.style.display = 'block';
resultBox.style.display = 'none';
return;
}
errorMsg.style.display = 'none';
// 1. Normalize Flow to Gallons Per Day (GPD)
var flowGPD = 0;
if (flowUnit === 'gpd') {
flowGPD = flowVal;
} else if (flowUnit === 'mgd') {
flowGPD = flowVal * 1000000;
} else if (flowUnit === 'm3d') {
// 1 m3 = 264.172 gallons
flowGPD = flowVal * 264.172;
} else if (flowUnit === 'ls') {
// 1 L/s = 86400 L/day. 1 L = 0.264172 gallons.
// 1 L/s = 22824.5 GPD
flowGPD = flowVal * 22824.5;
}
// 2. Normalize Length to Feet
var lengthFt = 0;
if (lengthUnit === 'ft') {
lengthFt = lengthVal;
} else if (lengthUnit === 'm') {
// 1 meter = 3.28084 feet
lengthFt = lengthVal * 3.28084;
}
// 3. Calculate WOR in US Units (GPD / ft)
var worUS = flowGPD / lengthFt;
// 4. Calculate WOR in Metric Units (m3 / day / m)
// Convert Flow GPD back to m3/day: GPD / 264.172
var flowM3d = flowGPD / 264.172;
// Convert Length ft back to meters: ft / 3.28084
var lengthM = lengthFt / 3.28084;
var worMetric = flowM3d / lengthM;
// 5. Update UI
document.getElementById('res_gpd_ft').innerText = worUS.toLocaleString(undefined, {maximumFractionDigits: 1});
document.getElementById('res_m3_m').innerText = worMetric.toLocaleString(undefined, {maximumFractionDigits: 1});
resultBox.style.display = 'block';
}
Understanding Weir Overflow Rate (WOR)
The Weir Overflow Rate (WOR), often referred to as "Weir Loading Rate," is a critical hydraulic parameter in the design and operation of sedimentation tanks and clarifiers within water and wastewater treatment plants. It measures the volume of water passing over a weir per unit of weir length over a specific timeframe.
Properly managing the overflow rate ensures that the velocity of the water leaving the tank does not create excessive turbulence, which could resuspend solids that have already settled.
The Formula
The calculation is straightforward but requires consistent units. The basic formula is:
WOR = Q / L
Where:
WOR = Weir Overflow Rate
Q = Flow Rate (e.g., Gallons per Day or m³/day)
L = Total Length of the Weir (e.g., Feet or Meters)
Why is WOR Important?
In a clarifier, the goal is to allow solids to settle to the bottom via gravity while clear water (effluent) exits over the weirs at the surface. The physics of this process rely on low velocity.
High WOR: If the rate is too high, the water velocity near the weir increases. This "suction" can pull settled light particles (floc) up from the sludge blanket and over the weir, reducing effluent quality.
Low WOR: While generally better for settling, an extremely low WOR might indicate that the tank is underutilized or over-designed for the current flow.
Typical Design Standards
While state regulations and specific machinery designs vary, general guidelines for conventional settling tanks often suggest:
Average Flow: 10,000 to 15,000 GPD/ft (124 to 186 m³/d/m)
Peak Flow: 20,000 to 30,000 GPD/ft (248 to 372 m³/d/m)
Always consult your local environmental regulatory agency (such as the EPA or state-specific DEQ) for the exact permitting requirements in your region.
Example Calculation
Suppose a treatment plant has a flow rate of 1 Million Gallons per Day (1 MGD) and a circular clarifier with a total weir length of 80 feet.
Convert MGD to GPD: 1,000,000 GPD.
Identify Weir Length: 80 ft.
Calculate: 1,000,000 / 80 = 12,500 GPD/ft.
This result falls within the typical range for average flow conditions.