DIGITALNA ARHIVA ŠUMARSKOG LISTA
prilagođeno pretraživanje po punom tekstu



ŠUMARSKI LIST 5-6/2021 str. 51     <-- 51 -->        PDF

The AW area is larger than that of the FW. For the FW and AW, the elevation is between 210‒780 m and 140‒600 m a.s.l., respectively. The mean watershed slope, main channel slope, drainage density and stream frequency values of the FW are higher than those of the AW. According to the Kirpich (1940), the FW has a short concentration time. The watershed characteristics, determined by digitizing 1/25000 scale topographic and stand maps in ArcGIS software, are shown in detail in Table 1.
Precipitation, streamflow and total suspended sediment (TSS) measurements – Mjerenje količine oborina, otjecanja vode i produkcije suspendiranog erozijskog nanosa (TSS)
Precipitation was measured with three monitoring rain gauges (Tipping Bucket Rain Gauge, RG-200, Akim Hydrometry Co.) placed in sheltered areas at the upper and lower part of the watersheds (He et al., 2012; Nadal-Romero et al., 2016). Using the precipitation data, the average monthly precipitation of the study area was estimated according to the Thiessen polygon method (Liu et al., 2016; Duan and Cai, 2018).
Water level and discharge measurements were performed in both watershed outlets where the streamflow gauging stations were installed before the settlement sites. The water level was measured by automatic water level recorders (OEL-104, Akim Hydrometry Co.) (Serengil et al., 2007; Gökbulak et al., 2008; Durán Zuazo et al., 2012). These devices recorded the water level at 30-min intervals for two years (Fig. 3). Thus, 48 items of level data were obtained per day. The sediment accumulated at these gauging stations was cleaned at regular intervals to ensure that the water level recorders were measuring accurately.
Discharges were determined using velocity-area method. Streamflow velocity (m s-1) was measured with a small current meter (MCM-02, Akim Hydrometry Co.) at four different points of the cross section every fifteen days or after a precipitation events and then average velocity was found. Thus, discharges (m3 s-1) for various water levels in the watersheds were calculated (Coulter et al., 2004; Zengin et al., 2017; Ebabu et al., 2018). Water samples taken at the same time as the discharge measurements were later evaporated in a drying oven. This evaporation method was used to find the TSS concentration per 100 mL of water (Gökbulak et al., 2008; Erdoğan et al., 2018).
Calculation of streamflow and TSS yields – Kalkulacija otjecanja vode i produkcije TSS
In order to determine the water yields of the watersheds, regression equations were produced showing the relationship between the measured discharges and water levels. These equations were used to estimate the unmeasured discharge values corresponding to the 30-min water level data recorded over the two years. The monthly average discharge values were found and than the monthly and annual water yields were determined for the watersheds (Özhan, 2004; Zengin et al., 2017). The runoff coefficients of the watersheds were determined for 2014 and 2015 based on the total precipitation and water yield data. The TSS yield of the watersheds was calculated by multiplying the monthly average suspended sediment concentration and the monthly water yield.
Statistical analyses – Statistička analiza
We conducted an independent t-test using SPSS to determine the differences between watersheds for two years in terms of monthly water yield and monthly TSS yield.