Sidewalk-porch drainage principles

Please forgive me for my bad English.

I am wondering if somebody could help me with one particular issue that has been puzzling me for some time.
I started reading the NDS Principles of Exterior Drainage publication. On page 55 of that publication they solved the impervious surface drainage of the sidewalk in front of the house and the cement porch behind the house, by simply angling them towards the lawn:

Why is this so? Is this the correct approach in solving the impervious surface drainage of the sidewalk and the porch? Or should both of them have a catch basin in the middle of them?
What confuses me is this principle of simply angling them (the sidewalk and the porch) towards the lawn. Is this a good approach or not?

I would be very grateful for any kind of reply.

I apologize if this question is at the moment not directly related with SWMM. I tried contacting the NDS but never got any kind of reply.
Thank you in advance.


You need to be a member of SWMM 5 or SWMM or EPASWMM and SWMM5 in ICM_SWMM to add comments!


Email me when people reply –


  • Hi, I am still thinking about this sloping issue.  You have broken no rules (really the only rule is not to spam about non engineering subjects).  I will attend to this matter later.

    • Thank you Robert.
      That's a relief.

      In the mean time I have been throwing some guesses if what they intended was to use the channel drains for both the front sidewalk and back porch:


      Due to lack of knowledge, I am unable to solve the whole plan's stormwater layout, so I do not know how upper channel drains will fit into it, so it might be that I am completely wrong on this guess.
      How would you solve the drainage of the upper impervious sidewalk and the porch surfaces, disregarding the angling of the surfaces given by the NDS photo?

      Thank you in advance, and sorry for interrupting your thoughts.

This reply was deleted.