DIGITALNA ARHIVA ŠUMARSKOG LISTA
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| ŠUMARSKI LIST 5-6/2021 str. 53 <-- 53 --> PDF |
2015). In the FW, the monthly maximum and minimum water yields were 154.6 mm (January 2015) and 4.9 mm (August 2015), whereas in the AW these values were 107.8 mm (February 2015) and 6.0 mm (August. 2014) (Fig. 5). Although the total amount of precipitation measured in the research area in 2015 was lower compared to 2014, an increase was observed in water yields of the watersheds. In 2014, with a total rainfall of 1156.9 mm, a water yield of 323 mm occurred in the FW and 224.6 mm in the AW. In 2015, despite a total rainfall of 1060.4 mm, a water yield of 544.6 mm occurred in the FW and 430.3 mm in the AW. This was due to the melting of the accumulated snow as a result of heavy snowfall in late December 2014 and in January, February and March of 2015. Thus, the snowmelt contributed to the water flow in the streams, which led to higher water yield values in these months compared to the amount of rainfall (Fig. 5). The two-year average runoff coefficients of the FW and AW were calculated as 0.39 and 0.30, respectively. The two-year total water yield of FW and AW was 2.89 and 4.55 million m3, respectively. Although the area of the AW is twice as large, the 2-year total water yield was approximately 1.5 times bigger that of the FW. According to the t-test, there is no significant difference between watersheds for two years in terms of monthly water yield, flow coefficient and unit surface flow (P>0.05). However, with the exception of July and August 2015, the unit surface water yield of the FW was higher than that of the AW. In a similar study conducted in Canada, water yields ranging from an agricultural dominated watershed to a forest dominated watershed were found to be 0.588, 0.849 and 0.901 million m3/km2/year, respectively (Chow et al., 2011). This may have resulted from increased evapotranspiration due to intensive cultivation and management of the agricultural areas, or to increased infiltration through from diversion terraces and grassed waterways. One study investigated the effect of land use and precipitation regime on surface flow and soil loss on karst hill slopes over a four-year period and found the annual surface runoff coefficient of the forested slope to be lower than agricultural slope in the first two years and higher in the last two years (Peng and Wang, 2012). As a result of this, it has been suggested that surface flow and soil loss in agricultural areas are very low for many rainfall events due to improved infiltration capacity of the soil by tillage, and that high runoff and soil loss occur in these areas only with heavy rainfall events. However, in the present study, it is thought that the land use had little effect on the lower water yield of the AW because partial and surface tillage is carried out for fertilization purposes in the hazelnut areas. Although the difference between the water yields of the watersheds was great during the rainy period, it was less during the dry period. The response of the watersheds to precipitation varied seasonally. For example, when a 41-hour precipitation event occurred in November 2014 under moist soil conditions, the peak flow level of the FW was higher than that of the AW, and it reacted to the precipitation in a short time (Fig. 6). In July 2015, under dry conditions, the AW reacted to a 2-hour precipitation event in a shorter period, but the peak flow level was lower than that of the FW (Fig. 7). These findings are similar to the results of a study conducted in 11 subwatersheds of a river basin in Thailand (Sriwongsitanon and Taesombat, 2011). The researchers |