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hymosincludes the following measuring structures:
Broad-crested weirs:

• Rectangular profile weir
• Roundnose horizontal crest weir
• Romijn movable measuring/regulating weir
• Triangular broad-crested weir
• Faiyum weir
  Sharp-crested weirs:
• Rectangular thin plate weir
• Triangular thin plate weir
• Cipoletti weir
  Short-crested weirs:
• Triangular profile or Crump weir
• Triangular profile Plat-V weir
• WES-spillway
• Cylindrical crested weir
• General weir (tidal/non-tidal sluice)
  Flumes:
• Rectangular throated flume
• Trapezoidal throated flume
• Rectangular/triangular/trapezoidal flume
• Truncated triangular flume
• Parabolic flume
• Circular flume
• U-throated flume
• Parshal flumes (22 types: 1" - 50')
• H-flumes (14 types: HS: 0.4¹ - 1.0¹ , H: 0.5¹ - 4.5¹ and HL: 3.5¹ - 4.0¹ )
  In the following sections the structure discharge equation and the parameters are described.

In case your structure does not fit in the structures listed on the previous page reference is made to the hymosoption mentioned in section user defined structures which covers a more general type of structure equation.

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Rectangular profile weir (Herschy 1985, Bos 1978)

Parameters:

• h_r = reference level
• P = height of weir
• L = length of weir
• b = width of weir
• h₁ = upstream water level
• H₁ = upstream energy level
• H₂ = downstream energy level
  Q = C_g . C_d . b .Image Modified

C_d = 0.86 for h₁ /P £0.5 and h₁ /L £0.3
C_d = 0.888 - 0.093 + 0.133 - 0.021 !03 - Stage
discharge^image058.gif! - 0.151
+ 0.102 - 0.065 + 0.310
+ 0.028!03 - Stage discharge^image068.gif! - 0.102!03 - Stage discharge^image070.gif!
The modular limit is obtained from:
H₂ /H₁ = 0.66 for H₁ /L £0.33
H₂ /H₁ = 0.66 - 0.24 (H₁ /L - 0.33) for 0.33 < H₁ /L £1.5
H₂ /H₁ = 0.38 for H₁ /L ³1.5
In case the modular limit is exceeded a missing value is entered for the discharge.

Round nose horizontal crest weir (Herschy 1985, Bos 1978)

Parameters:

• h_r = reference level
• P = height of weir
• L = length of weir
• b = width of weir
• h₁ = upstream water level
• H₁ = upstream energy level
• H₂ = downstream energy level
  Q = C_g . C_d . b .Image Modified
  03 - Stage discharge^image052.gif!
  03 - Stage discharge^image073.gif!
  The modular limit is obtained from:
  H₂ /H₁ = 0.855 + 0.070 ln (H₁ /P) for H₁ /P < 2
  H₂ /H₁ = 0.869 + 0.049 ln (H₁ /P) for H₁ /P ³2
  In case the modular limit is exceeded a missing value is entered for the discharge.

Romijn movable measuring/regulating weir

Parameters:

• h_r = reference level
• L = length of weir
• b = width of weir
• h₁ = upstream water level
• H₁ = upstream energy level
• H₂ = downstream energy level
  Q = C_g . C_d . b .Image Modified
  Image Modified
  C_d = 0.9564 + 1.018!03 - Stage discharge^image077.gif! - 3.530!03 - Stage discharge^image079.gif!
  + 4.936!03 - Stage discharge^image081.gif! - 2.302!03 - Stage discharge^image083.gif!
  The validity range for calculating the C_d values is : 0.08 <Image Modified < 0.78
  The modular limit is obtained from:
  H₂ /H₁ = 0.30
  In case the modular limit is exceeded a missing value is entered for the discharge.
  

  Triangular broad-crested weir

  Image Modified
  Parameters:
• h_r = reference level
• P = height of vertex above the bottom
• L = length of weir
• b = width of weir
• h_tr = height of triangle
• H₁ = upstream energy level
• H₂ = downstream energy level
  Two cases are distinguished:
  a. H₁ £1.25 h_tr , then:
  Q = C_g C_d Image Modified
  Image Modified
  b. H₁ > 1.25 h_tr , then:

C_d = 0.764 + 1.895 - 6.204 {~} + 6.944 for!03 - Stage discharge^image097.gif! £0.25
C_d = 0.937 + 0.089 for > 0.25
The modular limit is obtained from:
for H₁ £1.25 h_tr : H₂ /H₁ = 0.80
for H₁ > 1.25 h_tr : equations for the round nose horizontal crest weir with
P replaced by P + 1/2 h_tr
In case the modular limit is exceeded a missing value is entered for the discharge.

Faiyum weir

Parameters:

• h_r = reference level
• L = length of weir
• b = width of weir
• h₁ = upstream water level
• H₁ = upstream energy level
• H₂ = downstream energy level
  Q = C_g . C_d . b . Image Modified
  03 - Stage discharge^image052.gif!
  C_d = 0.848 for h₁ /L < 0.43
  C_d = 0.765 + 0.194 Image Modified - 0.0003 Image Modified for h₁ /L ³0.43
  The modular limit is given by equations of the rectangular profile weir. In case the modular limit is exceeded a missing value is entered for the discharge.
  

  Sharp crested weirs

  If the crest length in the direction of flow of a weir is short enough not to influence the head-discharge relationship of this weir (H₁ /L greater than about 13) the weir is called sharp-crested or thin-plated. In practice, the crest in the direction of flow is generally equal to or less than 0.002 meter so that even at a minimum head of 0.03 meter the nappe can occur.
  Image Modified
  For the derivation of the head-discharge equations it is assumed that sharp-crested weirs behave like orifices with a free water surface, and the following assumptions are made:
  
• The height of the water level above the weir crest is h=h₁ and there is no contraction.
• Velocities over the weir crest are almost horizontal.
• The approach velocity head v₁ ² /2g is neglected.
  The general head-discharge equation of a sharp-crested weir reads:
  03 - Stage discharge^image103.gif!
  

  Rectangular thin plate weir (Herschy 1985)

Parameters:

• h_r = reference level
• P = height structure
• b = width of weir
• B = width of channel
• h_a = height of opening
• h₁ = upstream water level
  Q = C_g . C_d . b_e .Image Modified
  Image Modified
  C_d = a+ b Image Modified
  where:
  a = 0.587 + 0.01 b/B for b/B £0.7
  a = 0.610 - 0.056 Image Modified + 0.048 Image Modified for b/B > 0.7
  b = -0.002 for b/B £0.2
  b = 0.0016 - 0.0367 Image Modified + 0.1127 Image Modified for b/B > 0.2
  h_e = h₁ + 0.001
  b_e = b + 0.003
  The following limitations apply on the use of the above formulae:
  b ³0.15 m
  P ³0.10 m
  h_e ³0.03 m
  h₁ /P £2.0
  h₁ £h_a and h₂ £-0.05 m
  

  Triangular thin plate weir

  03 - Stage discharge^image118.jpg!
  Parameters:
• h_r = reference level
• b = width of triangle
• h_tr = height of triangle
• h₁ = upstream water level
• h₂ = downstream water level
  Q = C_g . C_d . Image Modified

C_d = 0.640 - 0.873 h₁ + 5.101 - 13.040 + 12.311 for q= 90⁰
C_d = 0.637 - 0.566 h₁ + 2.758 - 6.425!03 - Stage discharge^image126.gif! + 5.753 for q= ½ 90⁰
C_d = 0.612 - 1.288 h₁ + 6.804 - 16.686!03 - Stage discharge^image126.gif! + 15.345 for q= ¼ 90⁰
C_d = 0.614 - 0.074 q+ 0.046 q² - 0.009 q³ for 20⁰ £ q £100⁰
(qin radians)
The following limitations apply on the use of the above formulae:
h₁ £h_tr
h₁ £0.60 m and h₂ £-0.05 m

Cipoletti weir

Parameters:

• h_r = reference level
• b = width of sill of aperture
• h₁ = upstream water level
• H₁ = upstream energy level
• h₂ = downstream water level
  Q = C_g . C_d . b .Image Modified
  Image Modified
  C_d = 0.63
  The following limitations apply on the use of the above formulae:
  h₁ /b £0.5
  h₁ £0.60 m and h₂ £-0.05 m
  

  Short crested weirs

  The basic difference between a broad-crested weir and a short-crested weir is that nowhere above the short crest can the curvature of the streamlines be neglected; there is thus no hydrostatic pressure distribution
  

  Triangular profile or Crump weir (Herschy, 1985)

  
  Image Modified
  Parameters:
• h_r = reference level
• P = height of weir
• b = width of weir
• h₁ = upstream water level
• H₁ = upstream energy level
• h₂ = downstream water level
  Q = C_g . C_d . b .Image Modified
  Image Modified
  C_d = 0.633
  The modular limit h₂ /h₁ = 0.75. If this value is exceeded a missing value will be entered for the discharge. Further limiting conditions are:
  P ³0.06 m
  b ³0.30 m
  h₁ /P £3
  b/h₁ ³2
  

  Triangular profile flat-V weir (Herschy, 1985)

  Image Modified
  Parameters:
• h_r = reference level
• b = width of structure
• h_tr = height of triangle
• h₁ = upstream water level
• H₁ = upstream energy head
• h₂ = downstream water level
  For h₁ £h_tr :
  Q = C_g . C_d . m . Image Modified
  03 - Stage discharge^image142.gif!
  C_d = 0.615 for m £15
  C_d = 0.620 for 15 < m < 30
  C_d = 0.625 for m ³30
  m = b/2h_tr
  For h₁ > h_tr :
  Image Modified
  C_d = 0.620 for m £15
  C_d = 0.625 for 15 < m < 30
  C_d = 0.630 for m ³30
  The modular limit is:
  for h₁ £h_tr h₂ /h₁ = 0.70
  for h₁ > h_tr h₂ /h₁ = 0.75
  If the modular limit is exceeded a missing value will be entered for the discharge.
  

  wes*-spillway (Bos, 1978)*

  Image Modified
  Parameters:
• h_r = reference level
• P = height of spillway
• b = width of spillway
• x = slope parameter (x = 0: vertical)
• h₁ = upstream water level
• H₁ = upstream energy head
• H₂ = downstream energy level
  Q = C_g . C_e . b . Image Modified
  Image Modified
  C_e = C₀ . C₁ . C₂
  C₀ = 1.3
  C₁ = 0.693 + 0.516!03 - Stage discharge^image150.gif! - 0.438!03 - Stage discharge^image152.gif! + 0.089!03 - Stage discharge^image154.gif! ,P/h₁ £0.2
  C₁ = 0.692 + 0.521!03 - Stage discharge^image150.gif! - 0.311!03 - Stage discharge^image152.gif! + 0.063!03 - Stage discharge^image154.gif! ,P/h₁ = 0.33
  C₁ = 0.6907 + 0.544!03 - Stage discharge^image150.gif! - 0.313!03 - Stage discharge^image152.gif! + 0.056!03 - Stage discharge^image154.gif! ,P/h₁ = 0.67
  C₁ = 0.6906 + 0.544!03 - Stage discharge^image150.gif! - 0.309!03 - Stage discharge^image152.gif! + 0.063!03 - Stage discharge^image154.gif! ,P/h₁ = 1.00
  C₁ = 0.6896 + 0.553!03 - Stage discharge^image150.gif! - 0.307!03 - Stage discharge^image152.gif! + 0.061!03 - Stage discharge^image154.gif! ,P/h₁ ³1.33
  For values of P/h₁ in between 0.2 and 1.33 linear interpolation between the above formulae is applied.
  C₂ = 1.00 for x = 0
  C₂ = 1.012 - 0.0136!03 - Stage discharge^image157.gif! + 0.0038!03 - Stage discharge^image159.gif! for x = 1
  C₂ = 1.033 - 0.0379!03 - Stage discharge^image157.gif! + 0.0139!03 - Stage discharge^image159.gif! for x = 2
  C₂ = 1.050 - 0.0861!03 - Stage discharge^image157.gif! + 0.0333!03 - Stage discharge^image159.gif! for x = 3
  The modular limit H₂ /H₁ = 0.3. If this value is exceeded, the discharge is reduced by a factor f:
  f = 1.097 - 0.6796!03 - Stage discharge^image161.gif! + 1.438!03 - Stage discharge^image163.gif! - 1.159!03 - Stage discharge^image165.gif! for 0.3 <Image Modified £0.80
  f = 20.327 - 78.274 *Image Modified + 105.57!03 - Stage discharge^image163.gif! - 47.630!03 - Stage discharge^image165.gif! for!03 - Stage discharge^image167.gif! > 0.8
  

  Cylindrical crested weir (Bos, 1978)

  03 - Stage discharge^image169.jpg!
  Parameters:
• h_r = reference level
• P = height of weir
• b = width of weir
• x = slope parameter (x = 0: vertical)
• r = radius of weir sill
• H₁ = upstream energy level
• H₂ = downstream energy level
  Q = C_g . C_e . b .Image Modified
  03 - Stage discharge^image148.gif!
  C_e = C₀ . C₁ . C₂
  C₀ = 1.1846 + 0.1318 ln (H₁ /r) for!03 - Stage discharge^image171.gif! < 0.88
  C₀ = 1.1922 + 0.1915 ln (H₁ /r) for 0.88 £Image Modified < 4.8
  C₀ = 1.49 for!03 - Stage discharge^image171.gif! ³4.8
  C₁ = 0.9764 + 0.0914 ln (P/H₁ ) for!03 - Stage discharge^image173.gif! < 1.0
  C₁ = 0.9352 + 0.0494!03 - Stage discharge^image157.gif! + 0.00927!03 - Stage discharge^image159.gif! for 1 £Image Modified £2.4
  C₁ = 1.000 for!03 - Stage discharge^image173.gif! > 2.4
  C₂ is given by the equations for the Wess spillway.
  The modular limit H₂ /H₁ = 0.33. For higher values of H₂ /H₁ the discharge according to the first equation is reduced by a factor f:
  f = 1.224 - 1.671!03 - Stage discharge^image161.gif! + 3.605!03 - Stage discharge^image163.gif! - 2.829!03 - Stage discharge^image165.gif! for 0.33 <Image Modified < 0.85
  f = 5.361 - 20.649!03 - Stage discharge^image161.gif! + 32.105!03 - Stage discharge^image163.gif! - 16.789!03 - Stage discharge^image165.gif! for!03 - Stage discharge^image167.gif! ³0.85
  

  General weir

  Image Modified
  Parameters:
• h_r = reference level
• h₁ = upstream water level
• h₂ = downstream water level
• h_g = gate level or sill
• b = structure width
  For sub-critical flow:
  Q =Image Modified
  For critical flow:
  Q =Image Modified
  with:
  A₁ = B(h₂ - h_g )
  A₂ =Image Modified
  

  Flumes

  A critical depth-flume is essentially a geometrically specified constriction built in an open channel where sufficient fall is available for critical flow to occur in the throat of the flume. Flumes are 'in-line' structures, i.e. their centre line coincides with the centre line of the undivided channel in which the flow is to be measured.
  

  Rectangular throated flume (Herschy, 1985)

Parameters:

• h_r = reference level
• L = length of flume
• b = width of flume throat
• m_l = modular limit
• h₁ = upstream water level
• H₁ = upstream energy level
  Q = C_g . C_d . b .Image Modified
  03 - Stage discharge^image148.gif!
  C_d =Image Modified
  The modular limit is input, (generally in the order of 0.85 - 0.95). If the modular limit is exceeded a missing value is entered for the discharge.
  !h3. Trapezoidal throated flume (Herschy, 1985)
  03 - Stage discharge^image187.jpg!
  Parameters:
• L = length of flume
• b = width of throat bottom
• m = side slope
• m_l = modular limit
• h₁ = upstream water level
• H₁ = upstream energy level
  Q = C_g . C_d . C_s . b .Image Modified
  Image Modified
  C_d =Image Modified
  where:
  x = 0.972 - 0.878 m + 0.366 m² - 0.0543 m³ for m £2
  x = 0.438 - 0.127 m + 0.015 m² - 0.5976 m³ for m > 2
  C_s = 1.002 + 0.678 y + 0.0327 y² - 0.065 y³ for y £3
  C_s = 0.088 + 1.144 y - 0.0488 y² - 0.0016 y³ for y > 3
  with:
  y = m h₁ /b
  The modular limit is input, (generally in the order of 0.85 - 0.95). If the modular limit is exceeded a missing value is entered for the discharge.
  

  Rectangular/triangular/trapezoidal flume (Bos, 1978)

  03 - Stage discharge^image191.jpg!
  Parameters:
• h_r = reference level
• L = length of flume
• b = width of throat bottom
• m = side slope
• m_l = modular limit
• H₁ = upstream energy level
  Image Modified
  Image Modified
  C_d = 0.845 + 0.726!03 - Stage discharge^image077.gif! - 1.563!03 - Stage discharge^image079.gif! + 1.156!03 - Stage discharge^image081.gif! for!03 - Stage discharge^image097.gif! £0.5
  C_d = 0.957 - 0.017!03 - Stage discharge^image077.gif! + 0.046!03 - Stage discharge^image079.gif! + 0.017!03 - Stage discharge^image081.gif! for!03 - Stage discharge^image097.gif! > 0.5
  y_c =Image Modified for m = 0
  y_c =Image Modified for m > 0
  Following profiles can be covered:
  b > 0 and m = 0 rectangular flume
  b = 0 and m > 0 triangular flume
  b > 0 and m > 0 trapezoidal flume
  The modular limit is input, (generally in the order of 0.85 - 0.95). If the modular limit is exceeded a missing value is entered for the discharge.
  

  Truncated triangular flume (Bos, 1978)

  Image Modified
  Parameters:
• h_r = reference level
• L = length of flume
• b = width of flume
• h_tr = height of triangle
• m_l = modular limit
• H₁ = upstream energy level
  Image Modified for H₁ £Image Modified
  Image Modified
  C_d is given by the rectangular flume equations
  m = b/2h_tr
  Image Modified for H₁ >Image Modified
  Image Modified
  C_d is given by the rectangular flume equations
  The modular limit is input. If the modular limit is exceeded a missing value is entered for the discharge.
  

  Parabolic flume (Bos, 1978)

  03 - Stage discharge^image215.jpg!
  Parameters:
• h_r = reference level
• L = length of flume
• f = shape parameter
• m_l = modular limit
• H₁ = upstream energy level
  Q = C_g C_d Öf!03 - Stage discharge^image217.gif!
  03 - Stage discharge^image219.gif!
  C_d is given by the rectangular flume equations
  The modular limit is input. If the modular limit is exceeded a missing value is entered for the discharge.
  

  Circular flume (Bos, 1978)

  03 - Stage discharge^image221.jpg!
  Parameters:
  1. h_r = reference level
  2. L = length of flume
  3. d = diameter of flume
  4. m_l = modular limit
  5. H₁ = upstream energy level
  03 - Stage discharge^image223.gif!
  03 - Stage discharge^image195.gif!
  C_d is given by the rectangular flume equations
  y_c = H₁ {0.75183 - 0.04410!03 - Stage discharge^image226.gif! + 0.02578!03 - Stage discharge^image228.gif! - 0.04568!03 - Stage discharge^image230.gif! } for!03 - Stage discharge^image232.gif! £1
  y_c = H₁ {0.52496 + 0.53698!03 - Stage discharge^image226.gif! - 0.46709!03 - Stage discharge^image228.gif! - 0.09393!03 - Stage discharge^image230.gif! } for 1 <Image Modified £1.8
  y_c = H₁ {1.0505 - 0.34016!03 - Stage discharge^image226.gif! + 0.01743!03 - Stage discharge^image228.gif! - 0.005307!03 - Stage discharge^image230.gif! } for!03 - Stage discharge^image232.gif! > 1.8
  Image Modified
  a= 2. arccos (1 - 2 y_c /d)
  The modular limit is input. If the modular limit is exceeded a missing value is entered for the discharge.
  

  U-throated flume (Bos, 1978)

  Image Modified
  Parameters:
• h_r = reference level
• L = length of flume
• d=b = width of flume
• m_l = modular limit
• H₁ = upstream energy level
  For H₁ < 0.7 d the formulae of the circular flume apply.
  For H₁ ³0.7 d the discharge is computed by:
  03 - Stage discharge^image246.gif!
  03 - Stage discharge^image248.gif!
  C_d is given by the rectangular flume equations
  The modular limit is input. If the modular limit is exceeded a missing value is entered for the discharge.
  

  Parshall flumes

  Image Modified
  Parameters:
• h_r = reference level
• n_pf = throat width number (see below)
• h₁ = upstream water level
• h₂ = downstream water level
  The general discharge equation is of the form:
  Image Modified
  K and u follow from the underneath Table.
  Table Parameters of the discharge equation of Parshall flumes
  width n_pf K u m_l p a b c m_f
  1" 1 0.0604 1.55 0.50 1.64 -4.5837 11.118 -4.8464 1.0*10^-3
  2" 2 0.1207 1.55 0.50 1.48 -5.2025 12.141 -5.1189 1.0*10^-3
  3" 3 0.1771 1.55 0.50 1.65 -5.3387 12.834 -5.3693 1.0*10^-3
  6" 4 0.3812 1.58 0.60 1.57 -1.6117 5.3856 -1.3952 1.0*10^-3
  9" 5 0.5354 1.53 0.60 1.50 -4.2328 10.747 -4.0566 1.0*10^-3
  1' 6 0.6909 1.522 0.70 1.54 -5.0446 5.5661 -0.80775 1.0*10^-3
  1'6" 7 1.506 1.538 0.70 1.54 -5.0446 5.5661 -0.80775 1.4*10^-3
  2' 8 1.428 1.550 0.70 1.54 -5.0446 5.5661 -0.80775 1.8*10^-3
  3' 9 2.184 1.566 0.70 1.54 -5.0446 5.5661 -0.80775 2.4*10^-3
  4' 10 2.953 1.578 0.70 1.54 -5.0446 5.5661 -0.80775 3.1*10^-3
  5' 11 3.732 1.587 0.70 1.54 -5.0446 5.5661 -0.80775 3.7*10^-3
  6' 12 4.519 1.595 0.70 1.54 -5.0446 5.5661 -0.80775 4.3*10^-3
  7' 13 5.312 1.601 0.70 1.54 -5.0446 5.5661 -0.80775 4.9*10^-3
  8' 14 6.112 1.607 0.70 1.54 -5.0446 5.5661 -0.80775 5.4*10^-3
  10 ' 15 7.463 1.60 0.80 2.00 -26.086 49.689 -23.103 1.0
  12' 16 8.859 1.60 0.80 2.00 -26.086 49.689 -23.103 1.2
  15' 17 10.96 1.60 0.80 2.00 -26.086 49.689 -23.103 1.5
  20' 18 14.45 1.60 0.80 2.00 -26.086 49.689 -23.103 2.0
  25' 19 17.94 1.60 0.80 2.00 -26.086 49.689 -23.103 2.5
  30' 20 21.44 1.60 0.80 2.00 -26.086 49.689 -23.103 3.0
  40' 21 28.43 1.60 0.80 2.00 -26.086 49.689 -23.103 4.0
  50' 22 35.41 1.60 0.80 2.00 -26.086 49.689 -23.103 5.0
  The modular limit m_l varies from 0.5 to 0.8. In case this limit is exceeded the discharge is reduced with the quantity Q_e , where:
  Image Modified
  q =Image Modified with S = h₂ /h₁
  The parameters m_l , m_f , a, b and c are presented in the Table. The corrected discharge then follows from:
  Q_c = Q - Q_e
  

  H-flumes

  Image Modified
  Parameters:
• h_r = reference level
• n_H = flume depth number (see below)
• h₁ = upstream water level
• h₂ = downstream water level
  Image Modified
  The parameters a, b and c follow from the underneath table.
  Table Parameters of the discharge equation of H-flumes
  Type Depth n_H a b c m_l
  HS 0.4' 1 -0.4361 2.5151 0.1379 0.25
  HS 0.6' 2 -0.4430 2.4908 0.1657 0.25
  HS 0.8' 3 -0.4410 2.4571 0.1762 0.25
  HS 1.0' 4 -0.4382 2.4193 0.1790 0.25
  H 0.5' 5 0.0372 2.6629 0.1954 0.25
  H 0.75' 6 0.0351 2.6434 0.2243 0.25
  H 1.0' 7 0.0206 2.5902 0.2281 0.25
  H 1.5' 8 0.0238 2.5473 0.2540 0.25
  H 2.0' 9 0.0237 2.4918 0.2605 0.25
  H 2.5' 10 0.0268 2.4402 0.2600 0.25
  H 3.0' 11 0.0329 2.3977 0.2588 0.25
  H 4.5' 12 0.0588 2.3032 0.2547 0.25
  HL 3.5' 13 0.3081 2.3935 0.2911 0.30
  HL 4.0' 14 0.3160 2.3466 0.2794 0.30
  The modular limit is presented in the last column of the table. If this limit is exceeded, a missing value is entered for the discharge.
  

  Application

  Select the function <Measurement-Structure> from the Flow Measurements functions map. The required entries to run this function comprise:
  

  Series Codes

  Select a Discharge series by highlighting the series in the series list and pressing <Select> next to the discharge series textbox. HYMOSwill extract all relations for this series from the database and place them in the relations list box on the form.
  You can now add a new relation or use an existing relation. If you want to use an existing relation, choose the relation from the relation list box.
  

  Structure equation

  Select a structure equation by selecting the appropriate tab of the measurement structures spreadsheet and select the row with the type of structure. HYMOSwill now present all input fields for the selected equation type.
  

  Transformation period

  By double-clicking the date textboxes you can change the validity time period of the transformation equation.
  

  Add Relation

  If all coefficients of the relation is entered you can save the relation to the database by pressing the <Add Relation> button.
  After you made your selections press <Execute> and analyse the results as a graph, table and report. To show the graph on screen select <Graph> from the functions tab. To analyse the report press <Report> from the functions tab.
  You can also Save the generated series by pressing the <Save> button or exporting the series by selecting <Export>.
  

  Calculation of Discharges

  When the form is loaded a discharge series must be selected from the series list box. HYMOSwill look in the database if a relation for the selected discharge series exists. If so it will show all relations in the relations list box. Structures have relations which are valid for a defined period, for each period a relation can be made. A period is defined by a start and end date of a rating equation. When a discharge series is selected a new relation can be made for a structure or an existing relation can be selected from the relations list box. When a new relation is made the user must also select an upstream water level and a downstream water level. The downstream water level is necessary for checking if there is submerged flow or free flow. When the user does not want a check on submerged flow, a downstream water level in not required.
  For correction of the velocity head, a water level series must contain a cross-sectional profile. This profile is necessary to calculate energy levels from the measured water levels. Most measurement structure equations make discharge calculations based on energy levels. The cross-sectional profiles are measured profiles which can be entered in the Entry and Edit functions. These profiles are saved in the HYMOSdatabase with a link to the water level series.
  For calculating discharges over a structure, including check on submergence and velocity head correction, HYMOSthus requires two water level series with for each water level series a cross-sectional profile. If cross-sectional profiles are not available in the database, HYMOSwill give a warning when pressing EXECUTE and stop the discharge calculation.
  There is one structure, the 'General Weir' which requires also a gate level series for the calculation. This gate level series must be selected from the series list box.
  While calculating the discharges it is possible that HYMOSwill return missing values. Missing values are returned in the following situations:
  
• The upstream or downstream water levels are missing.
• If the date of the calculated discharge is outside the validity period of the relation.
• The upstream water level is above the structure height.
• The upstream water level is above the highest point of the upstream cross sectional profile.
• If the modular limit is exceeded.
• The downstream water level is above the highest point of the downstream cross sectional profile.
  A zero discharge is returned when:
  
• The upstream water level is below the Sill height of the structure.
• The upstream water level is below the lowest point of the upstream cross sectional profile.
• The downstream water level is below the lowest point of the downstream cross sectional profile.
  

  General computation procedure

  The general equation used for measurement structures is:
  Image Modified
  where:
  H = total head
  g = acceleration due to gravity
  b = width
  C_d = coefficient of discharge
  As mentioned earlier the total head H cannot be measured in practice. Therefore an iterative procedure is included to compute the discharge from the measured head h . This iterative procedure is as follows:
  1. The area of cross section flow A is computed from the cross-section profile data for the measured head h .
  2. The discharge is computed with the discharge equation, using the measured head h instead of the total head H .
  3. The total head H is computed from equations:
  Image Modified
  4. If the difference between the total head H and the measured head h is larger than 0.001 then the computed total head H is used and the computation is restarted in 1.
  Sometimes this iterative procedure is not used to compute the discharge. Instead a dimensionless velocity coefficient C_v is used in the equation to correct for the velocity of approach. This coefficient C_v can be obtained from a table from the cross-sectional area and C_d bh.