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ŠUMARSKI LIST 5-6/2021 str. 54     <-- 54 -->        PDF

found that a high forest cover reduced the runoff coefficient for smaller flood events, while for larger flood events, a high forest cover increased the runoff coefficient compared to agricultural areas due to increased antecedent soil moisture content and subsequent reduction of the moisture retention capacity. In this study, the streamflow of the FW was found to be high for many precipitation events. Similarly, Wang et al. (2014) examined the effect of land use change on runoff generation in two basins by using hydrological model and stated that forest areas have positive effect on runoff generation.
One of the important reasons for the low unit surface water yield of the AW may be the large area covered by limestone bedrock. As a matter of fact, it has been stated that the fissures and fractures in limestone on karst slopes play an important role in surface flow due to their large storage capacity and high infiltration rate (Peng and Wang, 2012). In a study conducted in karst watersheds in China, it was determined that carbonate rock reduced the runoff coefficient (Zhang et al., 2014).
However, in this study, the main reason for the high unit surface water yield of the FW in both wet and dry seasons, compared to that of the AW, was that the values were high for the watershed slope, main channel slope, drainage density and stream frequency, whereas they were low for the watershed area, stream length and flow concentration time. This result is consistent with the findings of studies conducted in other countries. For example, Chen et al. (2010) found that of two forested watersheds, the one on a steep slope generated a more runoff and has a larger quick flow rate than the watershed on a slight slope. Similarly, Liu et al. (2016) reported that the effect of reforestation on the hydrological response was limited and slower in the steeper watershed than the other. This means that in general, steep sloped watersheds have higher streamflow than slight sloped watersheds (Nippgen et al., 2011; Zhang et al., 2014; Wang et al., 2018). Zhang and Wei (2014) found that the varying hydrological responses of two neighboring watersheds where forest harvesting was at a similar level were related to the topography, geology and highly heterogeneous climate characteristics of these watersheds. Zhang et al. (2010) studied watersheds of different sizes and found that measures to reduce surface runoff such as reforestation and terracing in agricultural areas were similarly effective in large watersheds at different rainfall levels, whereas they were less effective in small watersheds at high precipitation levels.
Total suspended sediment (TSS) yields of watersheds – Produkcija suspendiranog erozijskog nanosa (TSS) u slivovima
The relationship between the average monthly discharge and the TSS yields of the watersheds was strong and significant (R2 = 0.65 and P<0.05 for FW; R2 = 0.77 and P<0.05 for AW) (Fig. 8). Gökbulak et al. (2008) and Bywater-Reyes et al. (2018) have also found similar results in their studies. Accordingly, it can be seen that the TSS yield increased with increasing discharge in both watersheds. However, different factors were effective on the amount of TSS in the FW. Therefore, in order to more reliable relationship, more data collection is required at the peak flows in watersheds.