Effect of plot scale on runoff under natural rainfall (Case study; Saravan region, Rasht)

One of the challenges to progress in hydrology and soil science researches is that the theories applied just to certain time-space scales. This study was carried out to examine the effect of plot size on runoff generation and quantify scale effects. For this purpose, 6 experimental plots with the length of 3 to 60 m and the width of 1 to 6 m were established on a hillside in Saravan region of Rasht, located in Guilan province. Outflow runoff was collected from October 2015 to May 2015 and then the data were analyzed. Also, rain height was measured for each plot by installing rain gauges. Results showed that the amount of runoff per unit area decreases with plots length in non-linear form. Compare the mean values between the plots confirmed that there are no significant differences among plots with length longer than 10 m in terms of runoff yield. However, there were significant differences among plots shorter than 10 m and longer plots (P >0/05). The results verified the optimal length of 10 m for scaling proposes. A two-parameter model was used for scaling hillslope runoff ratio. Model parameters were determined using model calibration. The evaluation of the model showed its appropriate efficiency for plots shorter than 30 m long.