For smaller size H Flumes the approach section is integrally molded with the flume.  On the 4.5-foot H and 3.0/4.0-foot HL Flumes, the approach section is molded separately from the flume and then factory attached (bolted and sealed) to the inlet of the flume.  

In either case, if it more convenient for you, the approach section can be fabricated as a separate piece (or pieces!) that are then loosely bolted together at the factory for shipment.  This allows the flume / approach section to be broken down into its component parts, making the unit easier to handle and move into position.  

Once the flume / approach section pieces are in postion, they can then be bolted back together and the connection joints sealed (RTV silicone is recommended).