3D render of a 0.5-foot H flume with approach section, inlet bulkhead, inlet stub, and outlet drop box (shaded in blue) with pipe stub.  H flumes require a free-spilling discharge off the end of the flume.  Normally this precludes them from being used to measure flow in gravity pipes.  However, Openchannelflow outlet drop boxes allow HS / H flume to not only have free spiling discharge, but also to connect to piping on the downstream side of the flume.