On April 6, 1998, at 1134 hours mountain standard time, a Bellanca BL17-30A, N125SU, was substantially damaged when it veered to the left off of runway 21L at Love Field, Prescott, Arizona, and encountered a drainage ditch that ran parallel to the runway surface. There were minor injuries to the solo private pilot and no property damage. The flight departed from Lordsburg, New Mexico, on a visual, personal flight and no flight plan was filed. Visual meteorological conditions prevailed at the time of the accident. The pilot stated in his accident report that he felt that the actual surface wind conditions at the landing runway were not the same as those reported by the ATIS, and that the accident would not have occurred had the drainage ditch been covered. However, the airport is a tower controlled field and the current runway wind conditions are broadcast to any pilot requesting landing. Also, an investigation of the airport terrain indicated that the drainage ditch is approximately 6 feet deep and 24 feet wide with a side slope of 14 degrees, and is located 600 feet from the centerline of the runway that it parallels. He reported no mechanical malfunctions with the aircraft.