Development of An Operating Mechanism For A Flap On A Bl-84 Sampler

In response to the FISP’s FY 2019 call for proposals to, in part, provide improvements to physical sediment load measurements, Tetra Tech partnered with Colorado State University’s Hydraulics Laboratory to design, fabricate, and test an attachment to the FISP-approved BL-84 pressure-difference bedload sampler. The purpose of this partnership was to mitigate scooping effects on bedload transport measurements. From various alternatives identified and screened, the team selected a top-mounted flap as the attachment best suited to prevent scooping. The team fabricated a prototype, completed hydraulic efficiency testing in a flume, and started informal field testing to confirm the prototype could successfully prevent scooping. The team recommended as a next step development of a mechanism to operate the flap. This presentation will summarize the development of this operating mechanism.

The FISP Technical Committee sponsored a project for a 2021-2022 civil engineering senior design class at Colorado State University to develop the needed operating mechanism, with Tetra Tech serving as the technical liaison between the seniors and the FISP Technical Committee. The students identified seven alternatives and evaluated and ranked the alternatives using design criteria. The top alternative was a truss attachment to the flap and a secondary reel for operating the flap from a USGS E-reel and crane.

The truss attachment to the flap was fabricated, and testing revealed that excessive force was needed to open the flap. Therefore, a pulley system was designed and fabricated to reduce the required force, and further testing confirmed the effectiveness of the pulley system mounted to the flap and the BL-84.

The secondary reel was fabricated and tested, revealing potential to accurately control the flap using the pulley system. A dial was added to this reel to indicate to operators at the crane the position of the flap when the sampler is on the bed. However, the team realized synchronization of the secondary reel with the E-reel needs further development to allow operation of the flap without disturbing the sampler.

The FISP Technical Committee agreed the partnership with the senior design class enabled low cost and impressive progress in the development of an operating mechanism for a flap on a BL-84 bedload sampler to mitigate scooping.