Triple diagram models for changeability evaluation of precipitation and flow discharge for suspended sediment load in different time scales

Suspended sediment load (SSL) records in streams can be highly variable in time and space, making it difficult to quantify sediment fluxes and to discriminate particular patterns. The deep study on effective factors and their variability in different time scales is, therefore, a vital task. In the present study, the variability of precipitation and streamflow has been analyzed in Gorgan-roud River Basin, Iran in different time scales. Towards this attempt, daily precipitation, streamflow and SSL records spanning during 4 years (i.e. 1982–1985) from the Ghazaghli station situated in the main stem of the Gorgan-roud, were analyzed using Triple Diagram Model. The results indicated that the temporal streamflow and flood frequency variations largely affected the SSL. The results also showed that the pattern of SSL was more apparent by increasing the time span of the recorded data. According to the results, the sediment load in the study station has been affected by different streamflow magnitudes at monthly, seasonal and yearly time scales. According to the results, some 25 % of SSL has been carried out by streamflow probability of 40 % (i.e., 2.5 years of return period), while the transportation of SSL occurred in all ranges of precipitation amount. The amount of SSL moved by less frequent flows and not influenced by precipitation magnitudes, which indicates that the variations of SSL were mainly the result of temporal variations in evaporation rate, soil and vegetation cover conditions, affected precipitation–discharge–SSL relationships.