Project: Granby 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). Lamp Rynearson was commissioned to provide survey and engineering services to address these inefficiencies.

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

Our survey team managed challenges of a rural, mountain environment, and tying into existing monuments, monitoring equipment, project specifications and unique hydrographic features. USBR compliant safety plans were created and natural habitats were kept in mind while creating designs. While our team was 3 hours from the site, distance never stalled data transfer or project communications.

Construction involved diversion of river flows of up to 120 cfs, installation 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.