A new survey shows that Iowa's soil and water conservation structures have suffered $40 million worth of damage as a result of heavy rain and flooding this year.

The survey by the Iowa Department of Agriculture and Land Stewardship shows that an estimated 2.3 million acres — about 10 percent of Iowa's cropland — has suffered severe erosion damage, which is defined as the loss of 20 tons or more of soil per acre.

The Natural Resources Conservation Service defines tolerable soil erosion levels at 3 to 5 tons an acre annually.

Iowa Agriculture Secretary Bill Northey says the widespread erosion is troublesome, particularly at a time when corn and soybeans are in high demand for feed and fuel.

He says when you lose soil you undermine agriculture.

State officials say emergency repairs to Iowa's roads are costing about $30 million and climbing.

State officials say the funding has been needed after record flooding last month. Flooding forced the closure of 464 miles of Iowa's state highway system, including 303 bridges and culverts. Officials say county roads also suffered.

The estimates came as the Iowa Department of Transportation began submitting damage reports on Tuesday to the Federal Highway Administration to seek federal disaster money.

Department of Transportation Director Nancy Richardson says it's too early to describe the full extent of damage to Iowa's roads.