Picket Fence Design Solid Settling Basin
Warren D. Johnson
Eastern Iowa contains a large number of smaller scale livestock operations. The area also has varied topography with steep hills, shallow to bedrock soils, significant forest resources, and a large number of drainage ways and smaller streams including Iowa's only cold water streams. Problems of feedlot runoff control for smaller scale livestock operations present a special challenge. The economy of scale prevents a large investment in manure storage facilities. In addition, the producers do not have equipment necessary to handle liquid wastes.
With increasing emphasis on livestock waste control and awareness of environmental issues, more and more producers are interested in implementing some type of runoff control facility. Cost for complete containment systems are generally prohibitive for smaller scale feedlot operations and an alternative was needed to reduce runoff that was affordable to these producers. Many of the livestock operations in east central Iowa are cattle feeding operations. In these operations minimum requirements for runoff control are solid settling facilities with filter strips for handling the liquids that pass through the settling basin. The traditional solid settling basin involves a concrete wall with a stop log style structure that liquids pass through one segment of the wall. Eastern Iowa also contains a significant hardwood forest resource with a good supply of lower quality hardwood species such as burr oak, white oak, red oak, black locust, or red cedar that could be incorporated into some type of structure.
With available lumber on site, a project was initiated to demonstrate the use of hardwood species in an animal waste control facility. Gary Ballina, Engineering Technician with the NRCS in Manchester, Iowa, developed a "picket fence" solid settling basin as a demonstration in 1995. In 1996 the Limestone Bluffs RC&D expanded this idea to four additional demonstration sites and developed information and marketing materials to promote their use around the region.
The picket fence solid settling basin is a wooden wall built perpendicular to the slope of a feed lot. The practice is best suited for cattle feeding operations as hog wastes are more difficult to separate liquids from solids. The picket fence solid settling basin involves a wood wall made with posts set 4 feet apart along the length of the wall. Attached to the posts are 4 inch x 4 inch horizontal support members 1 1/2 feet apart on the post with the bottom support members 6 inches above the floor. Vertical 2 inch x 6 inch or 2 inch x 8 inch wood pickets are attached to the horizontal members leaving a 1/2 inch gap between the pickets to allow liquids to pass through the fence and enter into a grass filter area below.
The height of the pickets will vary with the size of the lot, but generally would be 2 1/2 inches to 3 1/2 inches high. A flat concrete slab is used on the uphill side of the fence at least 16 inches wide to facilitate clean out of the solids. The picket fence is not a storage facility so regular clean out is needed especially after runoff events.
The main benefit of the picket fence design is the simplicity of construction. In most cases the fence can be built by the farmers themselves since the concrete is flat work and construction involves setting posts and nailing horizontal members and vertical pickets.
Through the demonstration sites it was found that a heavy duty nail gun that would handle 100 pounds of pressure in the compressor greatly reduces the labor for nailing the pickets in place.
The material in the posts is the key to the longevity of the fence. In the demonstration sites black locust was the dominant species used in posts due to its resistance to decay. red cedar was also used and osage orange could work if available. Other species such as oak may need to be treated to prevent rotting. The pickets in the demonstrations were lower quality white oak or burr oak and were available on the farm. Logs were selected and were cut into pickets using a portable saw mill that was brought to the site.
The out of pocket cost to the landowner in construction of the picket fence was less than the cost involved in a concrete settling basin. The material costs averaged $50.89 per foot of fence for four demonstration sites built in 1996. The main cost savings on construction would be in labor since the landowners can provide most of that themselves.
Picket fences have proven to be effective in settling solid waste from cattle feeding operations. Very little visual evidence exists of solids passing through the facilities. The filter strips below the fence have proven effective to complete the system. To date, the posts on the demonstration sites have shown little signs of deterioration.
In summary, picket fence solid settling basins appear to be a cost effective feedlot runoff control alternative for smaller scale livestock producers. The design is relatively simple and the practice can be built by farmers themselves. In addition, the practice can provide uses or markets for lower quality hardwood species such as black locust, burr oak, and red cedar for producers in eastern Iowa.