Wednesday, November 9, 2011

SWMM 5 Loss Term Values for various velocities and K values

Subject:   SWMM 5 Loss Term Values for various velocities and K values

SWMM 5 has three loss terms available for each link:  Entrance, Exit and Other losses.  The Entrance loss uses the upstream link velocity, the  Other loss uses the center link velocity and the Exit loss uses the downstream link velocity.  The general form of the loss term in the St. Venant equation is K*V^2/2g Table 1 shows the loss in feet of head for various combinations of velocity and K value.  If you want to  simulate a little loss of head at each node then a small value of K should be used otherwise the cumulative loss in the whole networks will be many feet of head.

  Loss Term units equals K * V^2/2g = ft/sec * ft/sec * sec^2/ft = ft

Table 1:  Loss in feet of head for various combinations of velocity and K values.

Velocity (ft/sec)
K
K
K
K
K
K
0.050
0.100
0.250
0.500
0.750
1.000
1
0.001
0.002
0.004
0.008
0.012
0.016
2
0.003
0.006
0.016
0.031
0.047
0.062
3
0.007
0.014
0.035
0.070
0.105
0.140
4
0.012
0.025
0.062
0.124
0.186
0.248
5
0.019
0.039
0.097
0.194
0.291
0.388
6
0.028
0.056
0.140
0.280
0.419
0.559
7
0.038
0.076
0.190
0.380
0.571
0.761
8
0.050
0.099
0.248
0.497
0.745
0.994
8
0.050
0.099
0.248
0.497
0.745
0.994
9
0.063
0.126
0.314
0.629
0.943
1.258
10
0.078
0.155
0.388
0.776
1.165
1.553

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