THE POSSIBILITY OF ESTIMATION OF LONG-TERM AVERAGE ANNUAL EROSION BASED ON MEASUREMENTS OF EROSION FROM A FEW RAINFALL EVENTS

A lot of soil loss and sediment data have been measured at the end of erosion plots during recent decades under natural as well as simulated rainfall. As an important task, the rate of soil loss could be estimated using this kind of data.  To achieve reliable average erosion, several years of record are nessasary, which requires a lot of cost and time.  In this article, the role of extreme events on plot soil loss and basin sediment load was explained by giving a few exmples from Iran and the world. Based on the reviewed refrences, two different approaches were found in order to reach reliable average erosion rate in the absence of adequate data. In the first approach, which is based on the greatest erosion/ sediment events, it had been realized that the summation of a few events are responsible for about 50 percent of soil loss and sediment yield produced. The second approach is based on the probabilitiies and could be categorized into two strategies including a) application of sampling designs in field sampling and b) measuring only the yield of events with predifined high return periods.