So I have a townhouse in New York City and I've been getting sewage backup from storm water. I added a sewage backflow prevention valve at the front of the house at the sewer, but the shared storm water sewage system in my house still overflows in the basement because of the roof and yard water that goes into my backyard storm drain.
If I wanted to mitigate the flooding by stormwater from the roof, can I just simply run the storm downspout away from my storm drain and 20 feet away from the house foundation over the concrete pavers and into my small garden patch in the back yard? I'm not sure what effect dumping the water into the yard would be on the house and foundation - even if it's 20 feet away. Is there enough drainage at that distance away to not affect my foundation? Most all of the backyards in the neighborhood are all concrete including mine except for small patches of soil, and the backyards face inwards into each other each block, with the rowhouses pointing outwards.