Here are some detail shots.  Steel rod, threaded at the ends and using nuts and washers, is used to keep the plank sides of the beds the correct distance apart.  It is buried in the cinders, underneath the soon-to-be-installed plastic liners.  The “U” drains, all of 4” PVC, connect the water from each bed to the next.  The beds were designed with a plumbing access space, so that any future leaks or modifications will be easy to address.  Cement slabs were poured today to receive the circulation pumps.