Developing a Modular Farmers Screen Project
Many small diversions are located in remote areas with poor site access. Field fabrication and pouring concrete can become extremely difficult and costly at many remote sites. The Farmers Screen Modular System was developed to provide for a relatively quick and cost effective installation. The Modular System consists of pre-fabricated steel sections and components that simply bolt together on site. The screen system rests on a bed of compacted gravel and is backfilled with native material. No concrete, welding, or electricity is required on site.
- Gather initial information about the project. This includes high and low water diversion rates, stream flow information, existing site conditions, and project proponent goals. This can be gathered by FCA, an engineering firm, or any other project developer.
- Perform site visit and conduct survey. The site visit includes verifying any previously gathered information, interviewing operators, land owners, and field biologists as well as conducting a survey of the site. Again, this step can be performed by FCA, an engineer, or any other project developer. A full topographic survey of the site is preferred; however a simpler survey can suffice.
- Analyze project information with particular emphasis on available stream flow in relation to desired screened flow. Using the survey data, analyze the hydraulic grade line in both the stream and the diversion. Head loss through the entrance flume and screen structure must be accounted for to ensure adequate head exists to allow for the screen installation and the associated by-pass/fish return structure.
- Develop final project design and implementation plan. Include input from all project partners and ensure project goals and objectives will be met. Again, ensure all project information is accurate and expectations are realistic.
- Apply for and obtain all relevant permits and approvals.
- For a modular screen installation, plan on 1 to 3 days total construction time.
- De-water the diversion. Ensure that the head-gate is sealed in order to provide as dry a construction site as possible. If a head-gate installation is part of the project, then sand bagging and dewatering of the installation point is necessary. Make sure the necessary fisheries biologists have been consulted and have given consent to this procedure.
- Using a laser level or other method for accurate determination of elevation, excavate screen installation location. Typically, excavation must be deep enough to allow for a minimum of 6” of compacted gravel under the Farmers Screen Modular structure. Local soil conditions and types will dictate required site preparation. If high water table could be an issue, then ensure adequate drainage to eliminate the possibility of the screen structure floating (reduce the upward hydraulic pressure by giving an outlet to water that could accumulate under the screen).
- Place Farmers Screen Modular sections. Each section weighs between 800 and 1000 pounds, so a machine capable of lifting and placing these components is required. Ensure that the screen structure is at the proper elevation and that it is level in all directions. Bolt together screen sections using supplied hardware. Lay a bead of 100% silicone caulk (provided) along attachment seams prior to attachment.
- Place the intake flume. Ensure that the intake flume is at the proper elevation and that it is level in all directions. Attach the intake flume with the supplied hardware. Lay a bead of 100% silicone caulk along the attachment seams prior to attachment.
- Place the fish return flume or plenum. Ensure that the return flume or plenum is at the proper elevation and is level in all directions. Attach the return flume with the supplied hardware. Lay a bead of 100% silicone caulk along the attachment seams prior to attachment.
- Place fish return pipe or construct fish return channel. The design of the fish return will typically be determined by the local fisheries biologist from the relevant state or federal agency. Typically, the return will be in a pipe and will be set at a slope that provides in pipe velocities that meet National Marine Fisheries Service standards (1.3% slope is a good starting place).
- If the Farmers Screen Modular system includes a sediment management system, then installation of the pipes and valve outside of the screen structure must occur prior to backfilling around the screen. Install the control valve on the exterior of the screen structure. Install the pipe for returning the sediment to the stream and connect it to the previously installed valve. Ensure that some type of an access box is installed to allow access to the valve.
- Back fill around all components. Typically native material is adequate, however, in high water table applications, drain rock might be a good alternative.
- If the conveyance between the headgate and the entrance flume is open channel, then providing some large rock armoring around the flume entrance is necessary. Using rock to shape an entrance to the flume that is roughly the same width as the flume will provide better entrance hydraulics and will reduce the chance of erosion around the entrance flume.
- Open the head gate and test the screen through the expected range of flows. A flow measuring device such as a velocimeter is necessary to accurately determine actual flow. Ensure that the screen is operating properly and that the by-pass system is operating as expected.
- Perform any planting or restoration activities necessary for the completion of the project.
- Conduct any post-project site inspections/visits for project partners, permitting entities, or funders.
- Distribute Farmers Screen operation manuals to project partners that will be operating, inspecting, or helping to maintain the project.
- Provide monitoring forms to project partners who will be visiting the site periodically. Collecting monitoring data will help to identify any operational or design issues that need to be addressed to ensure a successful project.
- Monitor the project at least through the first complete season of operation, and preferably for the first three seasons. It is important to ensure that the project operates as expected through the entire range of flows and conditions.
- If an issue arises with screen performance or operation, contact FCA for input and review prior to making any changes to the screen system.