November 23, 2011

Extreme flooding events like the 2011 Missouri River flood can leave farm fields scarred by erosion, layered with thick sand deposits, and littered with flood debris. Repairing these fields for future crop production can be expensive and time-consuming, and demands thoughtful planning.

Safety First

Erosion from flood waters and excavation or deep tillage during repair may endanger underground utilities. Before any repair work is begun, contact your state underground utility location and marking service to have underground lines located. In Iowa, call (800) 292-8989, in Nebraska (800) 331-5666, and in Missouri (800) 344-7483.

Evaluation

Inspecting and documenting the amount of damage will help you develop a plan of action. Marking severe erosion locations, sand deposits, and debris accumulations on an aerial photo or map makes it easier to plan where to move, stockpile, or borrow materials during repair efforts. Using a tile probe or other rod may help you determine the depth of sand deposits.

Debris Removal

Any potentially hazardous materials such as fuel tanks, pesticide containers, or unmarked containers should be documented and moved with care. Contact your state department of environmental quality or natural resources for specific instructions on handling hazardous wastes.

It may be permissible to burn trees, brush, plant residues, and wood on the field site. Ask your local environmental quality or natural resources department about any restrictions. Keep fire safety in mind if any burning is done. Ash disposal may require special measures in some states.

Thin layers (less than 4 inches) of plant residues free from other trash often can be successfully tilled back into the soil. Pushing debris back into the river is prohibited.

Sand

Sand deposits less than 8 inches deep may be incorporated into the soil. Depth of the sand and underlying soil properties will determine how deep and aggressive the tillage should be. Deeper sand deposits may need to be spread to a thinner layer before incorporation. Excessively deep sand may have to be moved to a stockpile or disposal area either within the field or along a field border. Use caution when filling eroded areas with sand. Wetland determinations may be required and finished soil properties may be unsuitable. Pushing sand back into the river is prohibited.

Erosion Repair

Areas subject to moving flood waters may have sustained severe erosion. Erosion no deeper than plow depth may be repairable with tillage. Deeper erosion may require earth-moving equipment for repair.

When filling deeper eroded areas, check first to see if wetland determinations are required. Contact your Natural Resources Conservation Service representative. Remember that fill sand may not provide adequate moisture-holding capacity as a topsoil layer. Flood irrigation or traveling sprinkler irrigation may dictate the degree to which land leveling and erosion repair is required.

In extreme cases, earth moving repair may be cost prohibitive. Selective abandonment or alternate land uses of some areas may be justified.

Compaction

Even in areas where severe erosion or sand deposition did not occur, prolonged inundation with flood waters can destroy soil structure and leave a layer of dense consolidated silt. While this is not technically soil compaction, the effect of this dense layer is similar. Tillage sufficient to break up this dense layer is recommended after the layer has dried.

Documentation

In cases where insurance or other financial assistance is potentially available, be sure to document all your repair actions and costs, keeping all receipts.

For more information on flooded field repair, refer to Flood Recovery for Cropland: Repairing Flood-Damaged Farm Fields at http://flood.unl.edu/crops or at http://www.extension.iastate.edu/topic/recovering-disasters

Shawn Shouse
Iowa State University Extension Ag Engineer