How to calculate water flow for culverts

Written by cinda roth
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How to calculate water flow for culverts
Culvert flow may vary throughout the culvert due to rocks and other obstructions. (cygnes et frémissements image by rachid amrous-spleen from Fotolia.com)

Determining the water flow for a culvert enables a landowner to determine the approximate amount of water pushed through a culvert at any time. Operators of hydraulic energy generators or pumps running off the culvert utilise this information to estimate their peak, average, and minimal energy generation. Calculating the water flow for culverts also facilitates wetland and wild-land restoration efforts by enabling conservationists to determine if culvert modifications are necessary.

Skill level:
Easy

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Things you need

  • Stopwatch
  • Small floating object
  • Rope
  • Tape measure

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Instructions

  1. 1

    Measure a length along the culvert, drop a floating object at one event of the culvert, and utilise the stop watch to time how long it takes to reach the other end of the span you have measured.

  2. 2

    Divide the length chosen along the culvert by the time for the floating object to travel from one end of the culvert to the other end to determine the velocity of the culvert.

  3. 3

    Tie a rope from one size of the culvert to the other and mark off each foot.

  4. 4

    Utilise a tape measure to measure the depth of the culvert at each one foot interval and average all measures to estimate the average depth of the culvert.

  5. 5

    Measure the width of the culvert.

  6. 6

    Multiple the velocity by the average depth of the culvert by the width of the culvert to determine the water flow for the culvert.

Tips and warnings

  • Repeat the assessment of the velocity several times and average the results for increased accuracy.
  • Utilise intervals of less than one foot for depth measurements to increase accuracy.
  • Divide the culvert into smaller areas and calculate the velocity and volume for each area independently for more accurate flow calculations.

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