Cover Image
close this bookHandbook for Agrohydrology (NRI)
close this folderChapter 2: Measurement of runoff
View the document(introduction...)
View the document2.1 Estimates of runoff
View the document2.2 Collecting runoff data
View the document2.3 Water level recording instruments
View the documentEquipment costs
View the documentAppendix A: Measurement of runoff

Appendix A: Measurement of runoff

Appendix A1: Rating tables for H flumes, HS flumes and HL flumes

Rating Tables given in the USDA Agriculture Handbook 224 are in feet and inches. If metric measurements are required, conversions can be made using the following conversion factors. 1 inch 2.54 centimetres 1 foot 0.3048 metres 1 cubic foot 0.02832 cubic metres 28.32 litres

Because of the size of increments used in the rating tables (0.1 and 0.01 ft.), interpolation may be necessary when conversions to SI units are undertaken. Linear interpolation is permissible and does not lead to serious inaccuracies. Below are presented two conversions of rating tables to SI units, for a 30 cm deep H flume and for a 90 cm deep H flume. Together, these two sizes of flume and their rating table conversions will cover the range of discharge measurements encountered by most agrohydrological projects.

Rating Table 30 cm H Flume (litres second-1)

Rating Table 90 cm H Flume (litres second-1)

90 H Flume Rating Table continued

Rating Tables for Various Depths of H Flume (feet3 second-2)

Flume 0.5 foot deep

Flume 0.75 foot deep

Flume 1.0 foot deep

Flume 1.5 feet deep

Flume 2.5 feet deep

Flume 2.5 feet deep - Continued

Flume 4.5 feet deep

Rating Tables for Various Depths of HS Flumes (feet3 second-1)

Rating Tables for HL Flume 4 Feet Deep (feet3 second-1)

Appendix A2: Construction details of multislot dividers



Appendix A3: Construction details rotary slot dividers



Alternate Design for N-1 Coschocton-Type Runoff Sampler


Appendix A4: Rating table for broad crested (triangular weirs)

For conversions into SI units:

1 foot = 0.3048 metre,
1 square foot = 0.09290 square metre

Rating Tables for Various Cross-sectional Areas of Channel 10 Feet (3m) Upstream of Centre of Crest (feet3 second-1)

2:1 Triangular weirs

3:1 Triangular weirs

3:1 Triangular weirs continued

5:1 Triangular weirs

Appendix A5: Capacities and dimensions of parshall flumes

For conversion to SI units

1 inch = 25.4 mm
1 foot = 0.3048 metre
1 cubic foot per second = 1 second-foot = 0.02832 cubic metres per second = 28.32 litres per second