Posted: May 13th, 2015

Laboratory Investigation of a Crump Weir

This assessment brief contains a lot of information. It is important that you read through the assessment brief carefully before you start this sub task.

 

Learning File

 

Sub Task 2 Laboratory Investigation of a Crump Weir

 

Preparation for this assessment

• Make sure you have accessed the assessment subtask 2 folder in the assessment section of the module site
• Prior to the laboratory class you are advised to familiarise yourself with the location of the laboratory (Harmer 2003c).
• Read the Hydrometry in the UK document in the folder for week 10 in the learning materials section of the module site
• Carry out some background research/reading into flow measurement and Stage/Discharge relationships
• Read Chapter 6 (Flow in Channels) of Fundamentals of Fluvial Geomorphology by Ro Charlton
  • This is available as an online resource. Look at the Resource list online available in Support Resources for access

 

Gauging Stations and Stage/Discharge Relationships

The water level (or stage) of a river or watercourse is measured from gauges installed at gauging stations. The gauging station often has an artificial control which consists of a fixed structure which is installed on the river bed. These artificial controls may be notches, weirs or flumes. In some cases there may be ultrasonic devices installed at the gauging station to measure the stage and flow of the river. Telemetry may be used at some gauging stations to transfer the water level data. In the UK daily and monthly river flow data is collected by the Environment Agency from over 1500 gauging stations. “The Centre for Ecology and Hydrology holds the National Rivers Flow Archive (NRFA). It collates and archives data from the gauging station networks throughout the UK. The data obtained from the gauging stations are used for high (flood prediction) and low (water quality and aquatic life) water management” (CEH, 2014).

        

Figure 1.0 Brant Broughton Gauging Station (Croft, 2014)

Figure 1.1 EA River Level Recorder on the River Wear, North Burns (Environment Agency, 2014)

Crump Weir

A Crump weir is to be tested in a hydraulic flume in the laboratory. Readings in the laboratory are to be taken using a pointer gauge, a weigh tank and a stop watch. The Crump weir is a solid long base weir which can operate under a wide range of flow conditions. These weirs are commonly used in the UK for discharge measurement in rivers. It relies on critical conditions occurring on the apex of the weir for the discharge formula to work. It has a triangular shaped section. The upstream slope is 1 in 2 and the downstream is 1 in 5. The sloping upstream face helps to reduce the dead water region which occurs with other types of long-based weirs.

Figure 1.3 General Arrangement of the triangular profile weir (BSI, 2014)

Figure 1.4 Model of a Crump Weir (TecQuipment, 2014)

Method

1. Measure dimensions width, b, and height, P for the weir.
2. Lower the pointer gauge down to the channel bed just upstream of the weir and record the reading in the box provided.
3. Lower the pointer gauge down until it just touches the apex of the weir and record the reading in the box provided.
4. Open the inlet valve and allow water to flow over the weir.
5. Close the valve to the weigh tank and allow the flow to steady.
6. When the pointer on the gauge reaches 120 kg on the red scale start the clock and record the reading.
7. Stop the clock at 220 kg record the reading and also the corresponding time.
8. Open the valve to the weigh tank.
9. Lower the pointer gauge down until it just touches the water surface and record the reading on the table provided.
10. Increase the discharge over the weir and repeat steps 5 – 10.

 

 

 

 

 

 

 

 

Results/Calculations

 

Calculate:

• Volume (m³)

• Discharge, Q (m³/s)
• Upstream Depth, d (m)
• Measured stage, h (m)

 

 

Graphs

 

Using the results measured in the laboratory

• Plot a graph of Measured stage against Discharge (flowrate, Q) for your experimental data (include a line of best fit on your graph).

 

 

Conclusions

 

• Comment on your graph of measured stage against discharge from your laboratory work.

 

 

 

Sub Task 2 Laboratory Report (20%)

 

You are expected to produce a clear and concise laboratory report. The report must be word processed and all calculated data tables and the stage/discharge graph produced using a spreadsheet. You should use either Times New Roman size 12 or Arial size 11. Details of the content of the report are provided below. The order in which you structure your report and what additional information you decide to include is at your discretion. You need to submit your report to the Assignment Handling Point (Owen 431) by the date specified in your assessment diary. The indicative length for this report is 350 words (do not include your data, graph or reference list in this count).

 

• Brief introduction

 

• The introduction needs to include:
  • the aims of the laboratory work,
  • the experimental procedure written in your own words and
  • a sketch/annotated diagram or annotated photograph(s) of the apparatus.

 

NB: Use of Beth’s photographs of the laboratory apparatus will not be permitted for this assessment

 

• Well presented experimental data table

 

• Well presented and accurately calculated data table produced using excel

 

• A sample calculation showing all of the calculations for one set of data from your data table (this can be either neatly hand written or typed)

 

• Well presented graph of stage against discharge for your results produced using excel (with a line of best fit)

 

• Conclusions on your laboratory investigation which include comments on your graph of stage against discharge

 

• Referencing – You should include a full list of references using Harvard referencing.

 

References

 

BSI (2008) Hydrometry – Open channel flow measurement using triangular profile weirs BS ISO 4360:2008 [online] last accessed on 17^th March 2014 at URL: BS ISO 4360 2008 Hydrometry – open channel flow using triangular weirs.pdf

 

CEH (2014) National River Flow Archive (NRFA) [online] last accessed on 17^th March 2014 at URL: http://www.ceh.ac.uk/data/nrfa/

 

Croft Richard (2014) Brant Broughton Gauging Station on the River Brant from Welbourn Road Bridge [online] last accessed on 17^th March 2014 at URL: http://www.geograph.org.uk/photo/166904

 

Environment Agency (2014) Environment Agency River Levels North West – river recorder, river Wear, Noth Burns [online] last accessed on 17^th March 2014 at URL: com/environment-agency-river-levels.htm”>http://vyturelis.com/environment-agency-river-levels.htm

 

TecQuipment (2014) Crump Weir [online] last accessed on 17^th March 2014 at URL: http://www.tecquipment.com/prod/H12D.aspx

 

Equations for Calculations

 

 

	Pointer gauge reading at water surface
			Pointer gauge reading at weir apex

 

 

Pointer gauge reading at channel bed

 

Volume (m³)

 

 

 

Take the Density of Water (_w) = 1000 kg/m³

 

 

 

 

 

Discharge, Q (m³/s)

 

 

 

Upstream Depth, d (m)

 

d = pointer gauge reading at water surface (m) – pointer gauge reading at channel bed (m)

 

Height of weir, P (m)

 

P = pointer gauge reading at weir apex (m) – pointer gauge reading at channel bed (m)

 

Measured stage, h (m)

 

h = d – P

 

h = depth upstream above the weir crest

 

d = depth upstream of weir (m)

 

P = height of weir (m)

 

Or

 

h = pointer gauge reading at water surface (m) – pointer gauge reading at weir apex (m)

Crump Weir: Table of Measured Readings

 

 

 

Pointer Gauge Reading of Weir Apex

mm

 

Pointer Gauge Reading of Channel Bed

mm

 

 

 

Reading No.	Pointer Gauge Readings	Weigh Tank Readings			Time (Secs)
	(mm)	Initial Reading (kg)	Final Reading (kg)	Diff. (kg)
1
2
3
4
5
6
7
8

 

 

 

Crump Weir: Table of Calculated Results (this should be produced on Excel)

 

Height of weir, P

m

 

 

Reading No.	Volume (m³)	Discharge Q (m³/s)	Upstream Depth d (m)	Measured Head Over weir h (m)
1
2
3
4
5
6
7
8

 

 

 

 

 

Assessment Criteria

 

Name:

 

Excellent Equivalent to   70 +	Very good Equivalent to 60 – 69%	Good Equivalent to 50 – 59%	Adequate Equivalent to 40 – 49%	Fail Below 40%
Brief introduction to the laboratory work (15%) The introduction needs to include the aims of the laboratory work, the experimental procedure written in your own words and a sketch/annotated diagram of the apparatus /15%
10.5%+ Excellent introduction with clear aims, experimental procedure written in your own words and professionally presented sketch/annotated diagram or annotated photograph(s) of the apparatus	9% – 10.5% Very good introduction with clear aims, experimental procedure written in your own words and clearly presented sketch/annotated diagram or annotated photograph(s) of the apparatus	7.5% – 9% Good introduction with reasonable aims, experimental procedure needs to be written more in your own words and reasonably well presented sketch/annotated diagram or annotated photograph(s) of the apparatus	6% – 7.55% Adequate introduction with poor aims, experimental procedure not written in your own words and poorly presented sketch/annotated diagram or annotated photograph(s) of the apparatus	Less than   6% Unsatisfactory introduction lacking aims, poor or missing experimental procedure or procedure copied from assessment brief and poorly presented or missing sketch/annotated diagram or annotated photograph(s) of the apparatus
Experimental data table (20%) Calculated data table produced using excel /20%
14%+ Excellent Professionally formatted and presented experimental and calculated data tables including correctly calculated values	12% – 14% Very good Clearly formatted and presented experimental and calculated data tables including correctly calculated values	10% – 12% Good Reasonably well formatted and presented experimental and calculated data tables which have some incorrectly calculated values	8% – 10% Adequate Poorly formatted and presented experimental and calculated data tables which include several incorrectly calculated values	Less than   8% Unsatisfactory experimental and calculated data tables which have not been formatted or are poorly presented, are incomplete, incorrect or missing
Sample Calculation (20%) /20%
14%+ Excellent Sample calculation which is correctly calculated and all of the required calculations have been produced	12% – 14% Very good Sample calculation which contains small errors or some units are missing but all of the required calculations have been produced	10% – 12% Good Sample calculation which contains some errors and/or not all of the required calculations have been produced and/or several units are missing	8% – 10% Adequate Sample calculation which contains errors or may be incomplete	Less than   8% Unsatisfactory Sample calculation which is incorrectly calculated, incomplete or missing

 

 

Graph of stage against discharge for your results produced using excel (10%) /10%
7%+ Excellent Professionally presented, clearly labelled stage/discharge graph including correct line of best fit	6% – 7% Very good Clearly presented and labelled stage/discharge graph including correct line of best fit	5% – 6% Good Reasonably presented and labelled stage/discharge graph, line of best fit incorrect	4% – 5% Adequate Poorly presented and labelled stage/discharge graph, line of best fit incorrect	Less than   4% Unsatisfactory Stage/discharge graph, is incomplete or missing or the wrong type of graph has been selected, line of best fit is incorrect or missing
Conclusions on your laboratory investigation which include comments on your graph of depth against discharge (15%) /15%
10.5%+ Excellent conclusions on laboratory investigation	9% – 10.5% Very good conclusions on laboratory investigation	7.5% – 9% Good conclusions on laboratory investigation	6% – 7.5% Adequate conclusions on laboratory investigation	Less than 6% Unsatisfactory conclusions on laboratory investigation or conclusions are missing
Overall Presentation (including structure, spelling and grammar)  (10%)                                                     / 10%
7%+ Excellent professional standard of presentation – no spelling or grammatical errors; very well-structured.	6% – 7% Very good standard of presentation – minor spelling or grammatical errors; well-structured	5% – 6% Good standard of presentation – several spelling or grammatical errors; reasonably well-structured.	4% – 5% Adequate presentation – spelling and grammatical errors present; less well-structured.	Less than 4% Unsatisfactory very poor presentation – work littered with spelling and grammatical errors. Poorly structured
Referencing (10%) / 10%
7%+ Excellent All sources are properly referenced using the Harvard system.	6% – 7% Very good The majority of sources are properly referenced using the Harvard system.	5% – 6% Good There are a number of inconsistencies with the use of the Harvard system.	4% – 5% Adequate Reference list is present, but not using the Harvard system	Less than 4% Unsatisfactory Referencing incomplete or missing

 

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