Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D5716 – Standard Test Method Technical Guide
📐 Test Method Overview and Scope
This test method, designated as D5716/D5716M-20, covers the construction and operation of a circular orifice weir for measuring the discharge from a well. It is part of a series of standards prepared for the in situ determination of hydraulic properties of aquifer systems by single- or multiple-well tests. The discharge rate determined is commonly used for aquifer test methods and to evaluate well and pump performance. Limitations include its focus on temporary or test conditions, and the method is based on work performed by the Civil Engineering Department of Purdue University during the late 1940s. All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.
⚙️ Equipment and Installation Requirements
The circular orifice weir consists of a sharp-edged orifice plate installed in a pipe or channel. The orifice diameter should be selected based on expected discharge rates. Proper installation requires the weir to be level and the orifice centered. The head over the orifice is measured using a stilling well or similar device. Selection of this measurement method should follow Guide D5737M. Agencies conducting testing should comply with Practice D3740 for minimum requirements.
💡 Tip: For accurate head measurement, ensure the stilling well is designed to dampen fluctuations and that a hook gauge or pressure transducer is used for precise readings. Verify the weir is level before each test.
📊 Discharge Measurement and Calculation
The discharge rate (Q) is calculated using the formula Q = C × A × √(2gh), where C is the discharge coefficient, A is the orifice area, g is the acceleration due to gravity, and h is the head over the orifice center. The discharge coefficient varies with the ratio of head to orifice diameter (h/d). Selected types based on the referenced Purdue University work and industry practice are provided in Table 1.
| 🟦 Head to Diameter Ratio (h/d) | 📐 Discharge Coefficient (C) |
|---|---|
| 0.5 | 0.607 |
| 1.0 | 0.611 |
| 1.5 | 0.616 |
| 2.0 | 0.620 |
Orifice diameter is selected based on expected discharge. Table 2 provides recommended diameters for typical temporary test conditions as derived from common hydraulic engineering practice.
| 📏 Expected Discharge Range (gpm) | 🎯 Recommended Orifice Diameter (inches) |
|---|---|
| 10 – 50 | 2 |
| 50 – 200 | 4 |
| 200 – 500 | 6 |
| 500 – 1000 | 8 |
⚠️ Warning: The orifice plate must be sharp-edged and free from burrs or debris. Deterioration of the edge can significantly alter the discharge coefficient and render measurements invalid. All values calculated must adhere to the significant digits guidance of Practice D6026.
❓ Frequently Asked Questions
🔍 What is the primary purpose of this test method?
This test method is used for measuring the rate of well discharge under temporary or test conditions using a circular orifice weir, primarily for aquifer tests and evaluation of well and pump performance.
💡 What are the limitations of this test method?
The method is limited to temporary or test conditions and assumes specific hydraulic characteristics based on the original Purdue University research. It is not intended for permanent installation without additional validation.
⚡ How is the discharge rate calculated?
The discharge rate is calculated using Q = C × A × √(2gh). The discharge coefficient C is determined from the head to orifice diameter ratio, and the area A is derived from the measured orifice diameter.
📌 What referenced standards are essential for this test method?
Essential referenced standards include D653 (Terminology), D3740 (Minimum Requirements for Agencies), D5737M (Guide for Measuring Well Discharge), D6026 (Significant Digits in Geotechnical Data), and USGS GWPD 10.