The city required we put in a french drain, but neither the city nor the engineer figured out where the drain was going to, well, drain. Luckily, our contractor had an idea the city signed off on.
These pipes are going into the bottom of the french drain and will run underground into our backyard to allow runoff to filter through the drain and then gradually seep out. This works out really well, because after we went on the Theodore Payne native plants house tour, we had thought about creating an underground cistern that would allow runoff to deep water our plants. These pipes will now form the basis of that irrigation system. Serendipity!