Screening for Sediment Management and Organic Debris

Head gate to Eliot Creek, a glacially fed stream with significant sediment loads.

These Farmers Screen projects handle significant loads of sediment and debris, including organic debris such as large maple leaves.

  • Coe Creek, high sediment on glacially fed stream.
  • Crabtree Creek, large deciduous trees, heavy organic debris loads

Sediment and organic debris are two of the most difficult issues in fish screening.  When organic debris like leaves, sticks, and grasses adhere to a screen surface the effective screen area is decreased, causing higher approach velocities, which in turn causes more debris to impinge on the surface.  Fine sediment can accumulate within a screening system, causing excessive wear on seals and mechanical cleaning systems and decreasing the effective screen area by blocking flow through the screen surface.

FCA was fortunate to develop screening projects in basins with very high levels of organic material, as well as large sediment loads.  The Farmers Screen™ moves debris over the screen and back to the river without using a mechanical cleaning mechanism. An effective sediment management system was developed to address a constant flow of glacial and other sediment into Farmers Screen installations.

Sediment Management System valve and pipes

The huge amount of sediment carried in glacially-fed systems or other systems with high sediment loads can cause big headaches for fish screens. Not all diversions have this problem, but many do and for those, FCA’s simple sediment management system takes care of the problem.

Larger pebbles and stones are carried across the Farmer Screen’s screen material by the fast-moving bypass water. Fine sediment, however, can get through the screen material and build up under the screen, potentially disrupting proper operation. That’s where the sediment management system comes in. The system is made up of a series of PVC pipes, varying in length from 6-8 feet. Each section has its own valve and a series of slots. The fine sediment is sucked into these slots and the outflow of each pipe returns the sediment to the river.

This system keeps the weir wall clear. Keeping the weir wall clear is important for proper operation of the Farmers Screen.