Project: Granby Parshall Flume Replacement

Grand County, Colorado

An existing 10-foot Parshall flume on the Colorado River did not collect the range of stream flow data desired by the client and required intensive repairs when the structure over-topped in high-flow events (>250 cfs).

Our engineers investigated three potential alternatives for the replacement of the existing structure. In partnership with the Bureau of Reclamation and USGS, the client selected a concrete weir structure as the preferred alternative because it met the following project objectives:

  • Ability to measure a full range of flows from 20 to 3,000 cfs
  • Allow for passage of rainbow and brown trout
  • Reduced operations and maintenance
  • No increase in backwater conditions at the hydroelectric plant
  • Be aesthetically pleasing and designed considering public access and safety

The project involved diversion of river flows of up to 120 cfs, construction of a river wide concrete weir, improvements to the channel geometry, and a USGS gauging station with stilling well, cableway, and cantilever measurement arm. During final inspection, trout were observed to be moving upstream and congregating in a pool on the upstream side of the weir.