Water Regime and Flow Trends of Sitnica River
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RESEARCH ARTICLE European Journal of Environment and Earth Sciences www.ej-geo.org Water Regime and Flow Trends of Sitnica River Arban Berisha ABSTRACT River Sitnica is one of the large rivers of Kosovo, which makes problems through its river basin, such as frequent floods and pollution. Especially if Published Online: July 08, 2021 we add impact of climate change, then problems get worse. Among all, there ISSN: 2684-446X is a lack of continuous hydrometrical observation. Those existing data are not complete, and not so confident. So, before any estimation of water DOI :10.24018/ejgeo.2021.2.4.149 regime, flow trends and identification of climate change, there is first to analyze flow data, to complete them with the known statistical methods. In Arban Berisha this case, this problem has been solved by method of correlation with “H. Prishtina” University, Civil neighbourhood well-observed data. Just after data validation, there has Engineering Faculty, Prishtina, been analyzed and shown its water regime, estimated flow trend, and is Kosovo. given correlation of temperatures, precipitations and flows for main (e-mail: arban.berisha@ uni-pr.edu) gauging station. Correlation of these basic parameters has been extended for 21 years, where can be seen strong increasement of precipitation, certain increasement of temperatures and flows, as well as strong extremization of these parameters. At the end is given impact of convection rainfall, due to intensiv urbanization. These results should alarm competent authorities, on preventive action, to soft consequences, in next two decades. Keywords: correlation, extremization, parameters, prediction, trend. days results 96 %, and 98 % without seven outliers. Down in I. INTRODUCTION the figure 3, is given yearly hydrograph, of the year 1965, on Sitnica River has the same destiny as other rivers of format of logarithmic flows. Kosovo, which are not hydrometrically observed continuously on long-term, having not complete and confident data, without which, could not be estimated main parameters of regime and hydrological trends, especially considering obviously climate changes. Rive Sitnica yields along Sar mountain ridge between Ferizaj (Urosevac) and Shtime (Stimlje) towns, then flowing to north, collecting on left and right side, streams of Gadime, Gracanica, Drenica, Pristina and Lap, up-to discharge on Ibri (Ibar) river at Mitrovica town. The best existing flow data of Sitnica river, Fig. 1. Kosovo regional position. on gauging station Nedakovac, nearby Mitrovica, are average daily flows, of years 1963-1985, accept years 1972 and 1979 [9], and years 1991-1998 [8]. After these years, there is not any flow continual and confident data. Therefore, without data completion, cannot be estimated any hydrometrical parameter, important for hydrotechnical problems solution. II. MATERIAL AND METHODOLOGY For data completion, was assumed the methodology of Correlation on regional similarity. There was chosen river Topljica at gauging station Doljevac, which is near to Sitnica river and is well observed. Those daily average flow data, can be downloaded on internet from Hydrometeorological Station of Republic of Serbia. After correlation of flow data of both Fig. 2. Sitnica river basin. rivers for existing years, the best result has been achieved for year 1965. The correlation coefficient for that year for 365 DOI: http://dx.doi.org/10.24018/ejgeo.2021.2.4.149 Vol 2 | Issue 4 | July 2021 11 RESEARCH ARTICLE European Journal of Environment and Earth Sciences www.ej-geo.org 푄표푏푠−푄푐표푟 dQMIN = 8 % 푑푄푖 = ∗ 100 (%) 500 푄표푏푠 dQAVE = 9 % 50 dQMAX = -9 % After completion of daily average flows, for time period from 1963 until 2016, in the next figure are given long-term 5 monthly average flows. There are long-term average monthly flows hydrographs, for total period time of 1963-2016, and Topljica-Doljevac 1965 13.2 for two sequent time periods of 1963-1990 and 1990-2016. Sitnica-Nedakovc 14.7 98% Winter months (traditionally with snow) are showing flow 0,5 decreasing due to snow pack thickening. Last two decades in 1 35 86 18 52 69 137 188 120 154 171 205 222 239 256 273 290 307 324 341 358 103 Aprille month, the flow is increasing due to precipitation Fig. 3. Daily average flows Hydrographs of river Sitnica at Nedakovac and increasing. During spring and summer season, the flow river Topljica at Doljevac, with the correlation coefficient 98%. doesn’t change (zero snowpack, les precipitation, typical continental flow regime). Further in autumn months, the flow Being that this is the biggest correlation coefficient, this is decreasing, last two decades, flows are decreasing due to year correlation parameters a and b were selected for precipitation decrease. This is rainy-snow regime of hilly- generation of data of missing years. After data generation of field catchment area, with one maximal flow during winter- missing years, there, has been tested correlation between spring snow melting, and one minimum during summer, observed data and generated data for year of 1997. The best usually in August. coefficient of determination (Pearson) results 89%. In the next figure, are given Hydrographs of daily average flows of 30 /s) observed and correlated (simulated) data for year 1997. 3 Qave 25 Qo 1963-2016 Q (m Q Qo 1990-2016 500 20 Qo 1963-1990 /s) 3 15 50 10 Log Qo (m Qo Log 5 0 5 1 2 3 4 5 6 7 8 9 10 11 12 t (month) Sitnica-Nedakovc Observed 1997 12,7 Fig. 5. Long-term hydrographs of monthly average flows, of Sitnica- 0,5 Sitnica-Nedakovc Correlated 11,7 89% Nedakovac. 1 20 39 58 77 96 267 134 153 172 191 210 229 248 286 305 324 343 362 115 In the Fig. 6, are given Long-term Hydrographs of annually t (days) Fig. 4. Daily average flows hydrographs of year 1997 observed and average flows, of Sitnica river, and its trend for all correlated of Sitnica river at Nedakovac. characteristic: 1963-1990 and 1990-2016. Hydrograph of early time period is periodic with developed variances and Testing has been done, by Nash-Sutcliffe coefficient, and it flow, while last time period hydrograph is not periodic, is as follows: showing increase of variances (oscillation) and increase of 2 flow trend (due to precipitation increase). The total time 2 ∑(푄푂퐵푆−푄퐶푂푅푅) 푅푁푆 = 1 − 2 for i =1-365 period hydrograph is showing trend decrease of annually ∑(푄푂퐵푆−푄퐴푉퐸,푂퐵푆) average flows. where is: 2,5 2 /s) 푅푁푆 – fitting quality indicator of observed and correlated 3 1963-2022 hydrographs according to Nash – Sutcliffe; 2,0 Qave 1963-1990 QOBS – observed flows; Qmax (m Qmax 1990-2022 QCORR – correlated flows; 1,5 QAVE – average flow of observed flows. In this case, the fitting quality indicator is 78%, which is 1,0 very well quality, comparing with no data at all. There are also other fitting indicators, which will determine fitting 0,5 quality in higher scale, as fitting of averages, fitting of forms, fitting of dry and wet seasons [1]. 0,0 R² = 1,3% Relative residuals for minimal, average and maximal flows 2018 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 are: t (years) Fig. 6. Long-term hydrograph and its trends of annually average flows during three time periods of Sitnica river at Nedakovac gauging station. DOI: http://dx.doi.org/10.24018/ejgeo.2021.2.4.149 Vol 2 | Issue 4 | July 2021 12 RESEARCH ARTICLE European Journal of Environment and Earth Sciences www.ej-geo.org In contrary, are presented long-term hydrographs of 2,2 63 2,2 average annual flows, of river Ibar at station Ribaric. This is 2,0 76 2,0 KP KT KQ Poly. (KP) a hydrograph of mountain river, which was not impacted by 1,8 1,8 Poly. (KT) 06 Poly. (KQ) 73 human activity and urbanism. 80 84 10 15 1,6 81 18 1,6 (mm) P Precipitation 70 96 05 1,4 65 74 1,4 20 10 15 16 7778 9799 R² = 0,05 55 16 1,2 79 R² = 0,1709 14 1,2 63 66 18 69 8687 98 17 95 04 76 14 1,0 71 82 1,0 05 8385 91 03 16 79 09 72 75 8889 70 73 64 92 0002 13 93 08 (celz..)(m3/s) Qo,n and Temper. T Flows 58 02 0,8 07 12 0,8 62 94 01 14 74 81 84 67 90 11 64 01 04 08 12 57 66 78 0,6 68 0,6 67 72 77 96 99 06 12 60 65 69 13 48 54 80 86 R² = 0,57 49 5253 59 75 97 0,4 0,4 56 68 71 91 07 63 84 69 72 75 78 81 87 90 93 96 99 02 05 08 11 14 17 10 4647 61 82 00 03 66 Axis Title Axis 83 8889 95 98 11 50 8587 92 8 51 Time t (years) 9394 6 90 Fig. 9. Long-term Hydrographs of residuals of temperatures T(OC), precipitations P(mm) and average flows Q(m3/s) during time period 1963- 4 2018. 2 76 46 49 52 55 58 61 64 67 70 73 79 82 85 88 91 94 97 00 03 06 09 12 15 2,2 63 2,2 Axis Title Bistrica - Pec Ibar-Ribaric 2,0 76 KP KT 2,0 KQ Poly. (KP) Fig. 7. Long-term hydrograph of average annual flows of river Ibar at 1,8 Poly. (KT) Poly. (KQ) 1,8 Ribaric and Bistrica at Pec. 06 73 84 10 15 1,6 80 R² = 0,05 1,6 81 18R² = 0,12 3,5 63 70 1,4 96 05 1,4 3,0 65 74 76 16 2,5 7778 9799 1,2 79 09 14 1,2 2,0 06 66 87 98 69 86 04 17 73 84 10 15 95 8081 1,0 71 82 1,0 1,5 (mm) P Precipitation 70 8385 91 03 96 05 72 75 8889 19 1,0 65 74 0,8 64 92 0002 08 13 0,8 16 93 07 12 777879 97 99 14 T (celz..) Temper.