Parameterizing V-notch Weir Equations for Flow Monitoring in a Drainage Control Structure

Podsumowanie

This protocol describes methods for obtaining weir flow equation coefficients for a V-notch weir within a drainage control structure using (1) a laboratory calibration procedure and (2) an online tool, the "Weir Flow Equation Coefficients Calculator", developed by the authors. These methods apply to flows contained within the V-notch and overtopping flows.

Streszczenie

Accurate estimation of drainage discharge (flow rate or water volume per unit time) is essential for calculating nutrient loads delivered to surface water and assessing the performance of edge-of-field conservation practices. Determining drainage flow rates requires monitoring the head in a drainage control structure and applying an appropriate equation for the weir installed in the structure. Previous studies that developed calibrated equations for weirs in control structures have produced different equations (i.e., different weir flow equation coefficients) for the same type of weir and control structure size. This study describes procedures for setting up experimental water flow rate and head measurements within a drainage control structure and developing a weir equation for flows contained within a V-notch weir. Additionally, the procedure for obtaining a weir equation for overtopping flows -- when the water level exceeds the top of the V-notch weir -- is outlined. This process involves using the weir equation developed in the laboratory for a V-notch weir and an online tool, the "Weir Flow Equation Coefficients Calculator", developed by the authors. The online tool can also generate weir flow equation coefficients for both V-notch-contained and overtopping flows across various sizes of Agri Drain water control structures, even when users lack site-specific flow rate vs. head relationship.

Wprowadzenie

In evaluating the performance of edge-of-field conservation practices that reduce nutrient loss from subsurface drainage water (saturated buffers, bioreactors, and drainage water management), it is important to accurately determine drainage discharge and nutrient concentrations. Standard methods are readily available for accurately determining nutrient concentrations (e.g., nitrate), such as laboratory methods from water samples¹ or sensors for continuous monitoring of nutrients^2,3. Determination of drainage flow rates in edge-of-field conservation practices, on the other hand, is not a

Protokół

The details of the consumables and equipment used in this study are listed in the Table of Materials.

1. Obtaining weir flow equation coefficients for flows contained within the V-notch by laboratory calibration in a drainage control structure

1. Setting up the drainage control structure for a calibration experiment
   1. Connect the inlet section of the control structure to the pump assembly (consisting of a pump, a flow meter, and the necessary pipes, fittings, and valves) and the outlet section to the drainage pipe (see Figure 1). Ensure to seal additional out

Wyniki

The calibration of a stainless-steel 45° V-notch weir was performed in 15 cm (6 in), 20 cm (8 in), and 30 cm (12 in) Agri Drain control structures for flows contained within the V-notch¹¹. The measured values of flow rates and heads and the weir equations obtained by fitting a power function (equation 1) to the measured data for flows contained within the V-notch, as described in the protocol, are presented in Figure 9A-C...

Dyskusje

The protocol (step 1) describes a method for developing a calibration equation for a 45° V-notch weir in an Agri Drain drainage control structure. However, the method can be adapted for developing calibration equations for different types of weirs, such as a rectangular weir, a trapezoidal weir, or a V-notch weir with various angles in any drainage control structure. During the calibration procedure, it is particularly important that accurate heads are obtained, especially at greater flow rates when the water level ...

Materiały

Name	Company	Catalog Number	Comments
Flow meter	Banjo Corp	MFM300	Electromagnetic flowmeter, accuracy within ± 2-3% for flow rates between 0.88 and 42.3 L.s-1 (14 to 670 gpm), and operating temperature range of -12 to 54 °C
Pipe and fittings	N/A	N/A	The pipe length and fittings should be as necessary but fulfill the miniumum straigth pipe requirements for upstream and downstream of flow meter according to manufacturer's recommendation.
Pump	US Motors	15706017-100	Model 15411 60 HP 3 Phase VFD driven
Stoplogs	Agri Drain	700320 (5 in. stoplog), 700321 (7 in. stoplog), 700333 (7 in. bottom stoplog with bottom gasket)	Three types of PVC stoplogs of heights 5 inch, 7 inch, and 7 inch bottom stoplog with bottom gasket
Tape Measure	Stanley PowerLock	33-158	5m/16' tape measure
V-notch weir	Agri Drain	701132	Stainless steel 45° (3 mm thickness, V-notch depth of 17.145 cm) notched weir with PVC carrier (13 mm thickness)
Water Level Drainage Control Structure	Agri Drain	3CINLINE06X08PVC	A 3-chambered inline water level control structure with nominal size of 20.32 cm (8 inch) and V-notch weir present in the first gate (Stoplogs included in purchase)