The computation of channel flow is similar to that of shallow flow. TR-55 again points to the use of Manning’s equation as the basis of the computation. Again, the actual T5-55 manual is silent on the assumption that should be used for hydraulic radius when using Manning’s equation. StormShed3G™ follows the same procedure to develop a set of k coefficients that are suitable for channel flows. In this case, two conditions have been developed. They are intermittent channel flow (R=0.2) and continuous channel flow (R=0.4). The following table lists the values of k available in StormShed3G™.
|
"k" Values Used in Travel Time/TC Channel Flow computations |
|
Kc values for Intermittent Channel Flow (R=0.2) |
|
Forested swale with heavy ground litter (n=0.100) |
5 |
|
Forested drainage course/ravine with defined channel bed (0.050) |
10 |
|
Rock lined waterway (n=0.035) |
15 |
|
Grassed waterway (n=0.030) |
17 |
|
Earth lined waterway (n=0.025) |
20 |
|
CMP pipe (n=0.024) |
21 |
|
Concrete pipe (n=0.012) |
42 |
|
Other waterways and pipes |
0.508/n |
|
Kc values for Continuous Channel Flow (R=0.4) |
|
Meandering stream with some pools (n=0.040) |
20 |
|
Rock lined stream (n=0.035) |
23 |
|
Grass lined stream (n=0.030) |
27 |
|
Other streams, man-made channels and pipes |
0.807/n |