A Butte County farmer Wednesday filed a $15 million claim with the state over the crisis at Oroville Dam, saying water rushing down the Feather River wiped out part of a walnut orchard. The claim was filed by JEM Farms and Chandon Ranch, which run a 2,000-acre walnut farm downstream of the dam. Farmers along the Feather complained earlier this year that dramatic fluctuations in water flows from the dam in the aftermath of the February crisis caused damage to properties as riverbanks caved in.