Lab 2

BRAE 340 Irrigation Water Management 1 Flow Measurement BRAE 340 Irrigation Water Management Lab – Flow Measurement Name: ______________________________ Date: _______________________________ BRAE 340 Lab: Day: ____________ Time: ___________ Names of Others in Your Discussion Group: _________________________________ _________________________________ _________________________________ _________________________________ _________________________________ _________________________________

BRAE 340 Irrigation Water Management 2 Flow Measurement Flow Measurement Introduction The goal of this lab is to give you some experience with different types of water measurement devices. Water measurement is important because it is difficult to manage a resource if you have no idea what the flow rate is or how much (volume) of the resource has been used. Irrigation districts in many cases must be able to measure water in order to deliver and bill for the correct amount. Farmers must understand flow rate and volumes to effectively manage their irrigation systems and schedule irrigations. As you work with the different devices, think about how each measurement might be more or less accurate than the others, and under what conditions this might be so. Read the instructions and questions below before completing the lab. Lab Preparation Watch the tutorials and lab videos on Canvas prior to completing the labs. You will use data that you must collect from the Part 2 video to answer the questions and determine the flow rate for each device. Field Work While the canal is still dry, take all the measurements necessary to describe the size of that device. The instructor will start the flow through the canal and adjust the valve at the meter gate as necessary. Once the flow rate has stabilized, take the measurements necessary to estimate the flow through each device. Data Collection Use the Data Collection and Analysis forms below to record the values for your measurements that you will get from the videos. Data Analysis Use the flow rate tables (on Canvas) to determine the flow rate through each device. Draw a bar graph illustrating the results of your calculations on the grid area provided (after the Data Collection and Analysis forms). Learning to plot your graph in Excel would be a very useful skill to have – try it! Discussion Questions Think about the questions at the back of the lab. Write your own answers to the questions in the space provided. Grading • Participation (5%) • Data Collection & Analysis (55%) • Discussion Questions (40%) Useful Conversion Factors • 1 acre-foot = 43,560 cubic feet • mm ÷ 25.4 = inches • GPM ÷ 448.8 = cfs • inches ÷ 12 = feet • Gallon ÷ 7.48 = cubic feet I 9 p m = 4 4 8 . 8 4 s

BRAE 340 Irrigation Water Management 4 Flow Measurement Triangular Weir / V-notch Weir (5 pts) The equation is: Flow Rate (CFS) = 0.00154 x H 2.5 / 1000 H = head measured in millimeters (use the stilling well) Head (H): ___________________ mm Flow Rate = ____________________CFS Submerged Orifice (5 pts) Orifice = 3" x 18" The equation is: Flow Rate (CFS) = 0.28 x Area (ft 2 ) x H 0.5 H = head measured in millimeters (use a ruler) Upstream Measurement: ________ mm Downstream Measurement: _______ mm Head Difference (H) = Downstream Measurement – Upstream Measurement Head Difference (H): ___________ mm Flow Rate = ____________________CFS Trapezoidal Weir (18-in) (5 pts) The equation is: Flow Rate (CFS) = 0.00095 x H 1.5 H = head measured in millimeters (use the stilling well) Head (H): ____________________ mm Flow Rate = ____________________CFS Head Head (H) Head (H) c r i t i c a l f l o w d e v i c e 1 8 8 2 4 6 2 9 0 c r i t i c a l f l o w d e v i c e 8 9 0 . 7 5 4 4 D . 7 0 0 . 8 0

BRAE 340 Irrigation Water Management 5 Flow Measurement ITRC Weir Stick in Trapezoidal Weir (5 pts) Staff Reading (D): _______ Width (ft): ________ Flow Rate = D x Width (ft)_________CFS Rectangular Weir (12-in) (5 pts) Determine the flow rate using the provided table. The equation is: Flow Rate (CFS) = 0.00063 x (1 - H/1524) x H 1.5 H = head measured in millimeters (use the stilling well) Head (H): __________________ mm Flow Rate = __________________CFS Parshall Flume (5 pts) The equation is: Flow Rate (CFS) = 2.06 x H 1.58 H = head measured in feet (use the staff gauge) Head (H): ___________________ ft Flow Rate = __________________CFS Head Head (H) Height (D) 1 . 5 f t 0 . 5 1 1 8 0 . 5 4 0 . 7 5 0 . 7 4 0 . 7 8

BRAE 340 Irrigation Water Management 7 Flow Measurement Discussion Questions (5 pts each) Discuss the questions posed among your group, taking notes as necessary to remember the key points of the discussion. Write your own answers to the questions in the space provided. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 Mag Meter (Reading) Mag Meter (Calculated) Metergate V-notch Submerged Orifice Trapezoidal Weir ITRC Weir Stick Rectangular Weir Parshall Flume Replogle Flume Flow Rate (CFS) Measurement Device Flow Rates Measured in CFS p u r p l e l i n e = c a l c u l a t e d f l o w r a t e 0 . 7 8 5

BRAE 340 Irrigation Water Management 8 Flow Measurement 1. Based on the data you gathered, which device has the most deviation in flow rate from the magnetic meter? Does that make the other devices more accurate? Why or why not? 2. How would “dead stem” affect the reading from a meter gate? Explain how you account for it. 3. What condition is needed, for a pipeline meter (like the mag meter), to read the flow rate correctly? Explain . 4. Why would someone choose to use the trapezoidal weir over a triangular weir for flow measurement? Explain . H u m a n e r r o r i n r e a d i n g A c c u r a c y o f m e a s u r e m e n t T h e m o s t d e v i a t i o n w a s i n t h e s u b m e r g e d o r f a c e . I d o n ' t b e l i e v e t h i s m a k e s t h e o t h e r d e v i c e s m o r e a c c u r a t e o r l e s s b a s e d o n o n e s e t o f d a t a c o l l e c t e d . I f o u n d i t s l i g h t l y d i f f i c u l t t o t a k e a n a c c u r a t e r e a d i n g o f t h e u p s t r e a m a n d d o w n s t r e a m m e a s u r e m e n t s s o h u m a n e r r o r i s l i k e l y f o r t h e g r e a t e r d e v i a t i o n . T o d e t e r m i n e w h i c h s y s t e m i s m o s t a c c u r a t e I w o u l d b e m o r e c o n f i d e n t a f t e r r u n n i n g m u l t i p l e t r i a l s t o s e e i f I c o u l d m i t i g a t e s o m e h u m a n e r r o r . I a l s o b e l i e v e e a c h s y s t e m i s o n l y s o a c c u r a t e j u s t b y h o w i t i s m a d e o r u s e d . d e a d s t e m i s w h a t o c c u r s w h e n i n i t i a l l y o p e n i n g a m e t e r g a t e . T h e v a l v e i s t u r n i n g y e t t h e g a t e i s n o t y e t o p e n i n g w h i c h w o u l d s w a y t h e m e a s u r e m e n t s . T o a c c o u n t f o r t h i s , y o u d o n o t t a k e a n i n i t i a l s t e m r e a d i n g u n t i l t h e w h e e l b e c o m e s d i f f i c u l t t o m o v e . T h i s w i l l g i v e a m o r e a c c u r a t e m e a s u r e m e n t . T h e p i p e l i n e n e e d s t o b e f u l l . T h e m e t e r w i l l r e a d r e g a r d l e s s o f a m o u n t o f w a t e r d u e t o e l e c t r i c i t y b e i n g c o n d u c t e d o r a p r o p e l l e r r o t a t i n g e t c . . . s o , t o e n s u r e a p r o p e r r e a d i n g , t h e p i p e n e e d s t o b e f u l l t o a c c u r a t e l y d e t e r m i n e t h e v e l o c i t y o f w a t e r a n d i n t u r n a n a c c u r a t e f l o w r a t e . S o m e o n e m e a s u r i n g a l a r g e f l o w r a t e w o u l d w a n t t o u s e a t r a p e z o i d a l w e i r o v e r a t r i a n g u l a r w e i r . w h e n t h e d i s c h a r g e d w a t e r e x c e e d s t h e s i z e o f t h e v , t h e e x c e s s w a t e r m o v e s o v e r t h e w e i r a n d c o u l d n o t b e a c c u r a t e l y m e a s u r e d . A t r a p e z o i d a l w e i r a l l e v i a t e s t h i s p r o b l e m b y h a v i n g a g r e a t e r s t r e t c h o f w e i r f o r w a t e r t o f l o w o v e r i n t u r n a l l o w i n g a m o r e a c c u r a t e m e a s u r e m e n t