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# Hydraulic calculation storm sewer network using the Rational method

## Hydraulic calculation storm sewer network using the Rational method

(OP)
Hello!

1. I would like to ask a question about the slopes that are used in the hydraulic calculation of rainwater networks. As far as I understand, the estimated bias of the rainwater drainage network can be accepted by anyone, provided that it provides Vfull>Vmin and Qfull>Qdes For example, 0.001; 0.0015; 0.002; 0.0025; 0.003; 0.0035; 0.004; 0.0045; 0.005 and so on. Or even 0.0011; 0.0012; 0.0013; 0.0014; 0.0015; 0.0016; 0.0017; 0.0018; 0.0019 or 0,0035; 0,0036; 0,0037; 0,0038; 0,0039; 0,0041 i.e. a finer ranking than in the example above. That is, modern equipment during the construction of the network can provide such a small ranking (0,0014; 0,0015; 0,0016) and can create any slope of the pipe?

2. And as far as I understand, is the maximum maximum rainfall rate in the rainwater drainage network 12 feet per second?
Replies continue below

### RE: Hydraulic calculation storm sewer network using the Rational method

Its been years since i have done drainage design but to me providing drainage levels to more than 0.001m is rediculous. I think the same to gradients to more accuracy than 0.01%. Yes there are levels etc that can read more accurately but can you get the guy or gal down at the bottom of a trench in the lashing rain to do it. Probably not.

I thought 4m/s (13ft/s) was the limit to avoid internal erosion of concrete pipes. Again its been years since i have looked at a drainage design.

### RE: Hydraulic calculation storm sewer network using the Rational method

(OP)
Thank you for your answer. I'm interested in slopes for sewer networks. I know about the minimum slopes and the fact that they are regulated by the minimum speeds that prevent the formation of sediment in the pipeline. But I'm not interested in the minimum biases, I'm interested in the biases that you can create during the design and what they can be, or rather, I'm interested in the ranking. Which of the proposed options is correct?
1) 0.001; 0.0015; 0.002; 0.0025; 0.003; 0.0035; 0.004; 0.0045; 0.005 ranking through 0.0005 (that is, it is possible to set the slope multiple of 0.0005 during the calculation)??????
2) 0,0011; 0.0012; 0.0013; 0.0014; 0.0015; 0.0016; 0.0017; 0.0018; 0.0019 ranking through 0.0001 (when calculating, it is possible to accept any slope)??????
!!!!!I'm interested in what slope values can be taken when designing sewage networks!!!!

### RE: Hydraulic calculation storm sewer network using the Rational method

This can be computed externally using pipe hydraulics and Manning's Equation. One must make some assumptions; i.e. non-pressure flow and either partial or full flow. I have set up a spread sheet.

### RE: Hydraulic calculation storm sewer network using the Rational method

I do not know what you mean by ranking?

All i know is that i see too many digits after a decimal point....

### RE: Hydraulic calculation storm sewer network using the Rational method

For the most sewer network design, the recommended minimum pipe slope is 0.5% or 0.005. Anything flatter than that will just not drain effectively and sediments likely to accumulate.
Also, construction issues arises due to specialized tool - Laser level - required to install the pipe. The contractor will have a difficult effort staying within specified tolerance (+/-), especially when the length of the pipe is more than 50-ft.

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