the cover above (or on the road) is a little far (close or near or any distance) to prevent mosquitoes from getting inside but still allowing water to pass through. The tubes on the road and all others would be covered (or not covered at all) by metal just like the metal covers in manholes but with holes to allow water to pass all the way through the tubes. I believe flooding is partly caused by the roads. Water is meant to be shared by the water and by land (sand and all others). Canals channels water in the end to the sea which for me is not so right, canals, water ways, drainage systems, emburnal, water channels should both channel and absorb water all at the same time. If this won't affect road safety for vehicles; and weaken the roads, canals, and all the others above then it would be fine but I believe it won't because the length of the tube would prevent the soil foundations of the roads and all the above from weakening, besides there are buildings who stood even if their surroundings are not cemented. I have a feeling that these tubes could even strengthen the roads and all others above because it could serve as multiple pillar just like pillars or posts in buildings. These tubes should be installed on roads, canals waterways and all of the above as few or as many as it is safe, structural wise. I hope this article is helpful to you.... or to everyone......