FLOODS AND DROUGHT - HYDROCLIMATIC RISKS IN SUHA RIVER BASIN
TÎRNOVAN ALINA1, ROMANESCU GH.1, COJOC MARIA GIANINA1
ABSTRACT. Floods and drought-hydroclimatic risks in Suha basin. Suha is a right tributary of Moldova River, and presents a typical discharge for the geographical unit of Obcinele Bucovinei. Data used in the paper have been taken from Siret Basin Water Administration, Bacău, and represent a time sequence of 40 years. The most significant floods occurred in 1975, 1981, 1984, 1991, 2005, 2006, 2007 and 2008. The most obvious droughts occurred in 1969, 1974, 1978, 1983, 1987 and 2001. It was observed that the evolution of hydrological risk phenomena is closely linked to climatic changes. Increasing population and the need to extend the building design must take into account the extreme values of river flow over time, water resources also being important. Because extreme events occur more often, considering preventive plans against floods is needed. For this reason are analyzed the temperatures, rainfalls and discharge rates.
Keywords: flood, drought, river catchment, hydroclimatic risk
1. INTRODUCTION
The growing concentration of population in Suha watershed drew out the attention on its protection against flooding and ensuring water demands. Currently, in this drainage basin are eight hydrometrical stations for daily monitoring river levels. Identification of hydroclimatic risk phenomena in the Suha basin was based on monthly and annual analysis of average discharge values, average temperatures and rainfalls over a period of 30-40 years, with data recorded at three of the eight gauging stations in the basin, considered representative: Stulpicani (on Suha River), Gemenea 2 (on Gemenea River) and Gemenea 5 (on Slătioara River). The present paper examines hydroclimatic risk phenomena manifested in Suha river basin.
2. GEOGRAPHICAL POSITION
Suha is a tributary of Moldova River (Fig. 1). Aspects regarding the flow rates on the river have been previously highlighted by Diaconu, 1988; Olariu, 1992; Romanescu, 2005, 2009, etc.
1 Alexandru Ioan Cuza University, Faculty of Geography, Iaşi, Romania e-mail: [email protected], [email protected], [email protected] 188
Fig. 1. Geographical position of the Suha river basin and gauging stations location
Suha basin is located in the flysch area of the Eastern Carpathians. Only Gemenea, a left tributary, springs from the crystalline Mesozoic area of Rarău Mountains. It has an area of 368 km2 and an average altitude of 876 m. The main collector is Suha, with tributaries on both right and left side. It is characterized by an almost circular shape, the value of C being equal to 1.42. The rivers’ slopes in the basin have values between 23 and 84%. The existence of small depressions at Negrileasa, Gemenea and Stulpicani gives the basin the character of an amphitheatre, which generates a rapid concentration of major floods. Another factor that influences river flow is the large sediment transportation and deposition, especially in the medium and lower sectors of the main watercourses: Suha, Gemenea, Slătioara, Negrileasa (Siret Basin Water Administration, Bacău, 2013; I.N.M.H., 1971). From a climatic point of view, Suha basin is located in the temperate- continental area, mountain-climate type. Rainfalls are relatively low because the basin is located in an area with a slight foehn manifestation.
189
3. DATABASE AND WORKING METHODS
The data analyzed were collected from Siret Basin Water Direction, Bacau. The methods used in the analysis and interpretation of data are specific to hydro- meteorological analysis, statistical analysis, comparison and data interpretation. For a clearer understanding have been used charts and tabular data. For the geographical localization of Suha basin was used the digital terrain model, scaled 1:5000. Mean monthly and annual values were compared with the multi-annual average.
4. RESULTS AND DISCUSSIONS
The liquid discharge in the Suha river basin between 1973- 2012 Multi-annual average discharge defines the hydrological potential of a watercourse (Romanescu and Nistor, 2011). From the analysis of data can be separated some periods of liquid discharge (Fig. 2, 3, 4, 5): - 1973-1983, with high flow rates; - 1984-1996, with the average annual values of very low flows, the only exception being the year 1991, which has an average annual flow rate much higher than the multi0annual mean value; - 1997-2008, with discharges that exceed the multi-annual average values; - 2001-2012, with discharge rates that are starting to fall gradually.
3.5 3.0 2.5 2.0
mm 1.5 1.0 0.5 0.0 2010 2011 2012 2007 2008 2009 2003 2004 2005 2006 2000 2001 2002 1997 1998 1999 1993 1994 1995 1996 1990 1991 1992 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 Year Hydrometrical station Stulpicani Hydrometrical station Gemenea 2 Hydrometrical station Slătioara 3 The multiannual average precipitation
Fig. 2. Average annual rainfall in Suha river basin (1979-2012)
3.500 3.000
2.500 2.000
Qmc/s 1.500 1.000
0.500 0.000 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2011 2012 Year The annual average flow The multiannual average flow Fig. 3. Average annual discharge at Stulpicani hydrometric station (1979-2012) 190
1.200 1.000 0.800 0.600 Qmc/s 0.400 0.200 0.000 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2011 2012 Year The annual average flow The multiannual average flowl Fig. 4. Average annual discharge at Gemenea 2 hydrometric station (1979-2012)
0.900 0.800 0.700 0.600 0.500
Qmc/s 0.400 0.300 0.200 0.100 0.000 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2011 2012 Year The annual average flow The multiannual average flow Fig. 5. Average annual discharge at Gemenea 5 hydrometric station (1979-2012)
Suha River basin is characterized by frequent oscillations of flows during the 30-40 years with records, under the direct influence of the rainfall quantities. The largest floods recorded at the hydrometrical stations in the basin were at Stulpicani (1975, 1981, 1984, 2005, 2006, 2007, 2008); Gemenea 2 (2006, 2008) and Gemenea 5 (1991, 2006, 2008). These discharges have reached flood insurances of 20, 10, 5 and 2. Temperatures influence the discharge rates by reducing the intake of precipitation in some periods of the year or by high evaporation. Analysis of the evolution of rainfall quantities is a starting point in understanding the behavior of hydrological phenomena. In recent years it can be seen that some of the hydrological events can be assimilated with climate changes. For Suha river basin area was constructed the multi-annual average monthly temperatures chart (Fig. 6), the monthly multi-annual average rainfall chart (Fig. 7), the annual average monthly rainfall graph in 1981 (Fig. 8) and the annual monthly average flow chart in 1981 (Fig. 9). These graphs give a clear picture of the relation between precipitation, temperature and discharge, justifying the reasons for high, average and respectively decreased annual flows.
191
18.0
12.0
6.0
0.0
Celsius degrees Celsius I II III IV V VI VII VIII IX X XI XII -6.0
-12.0 Month
Rarău meteorological station Câmpulung Moldovenesc meteorological station The annual average temperature
Fig. 6. Average multi-annual monthly temperature variation
160 140 120 100 80 mm 60 40 20 0 I II III IV V VI VII VIII IX X XI XII Month Rarău Stulpicani Gemenea 2 Gemenea 5 Frasin Fig. 7. Average monthly multi-annual precipitation
7.0 6.0 5.0 4.0
mm 3.0 2.0 1.0 0.0 I II III IV V VI VII VIII IX X XI XII Month The annual average precipitation Fig. 8. Average monthly precipitation at Stulpicani hydrometric station, 1981
9 8 7 6 5
Qmc/s 4 3 2 1 0 I II III IV V VI VII VIII IX X XI XII Month The monthly average flow Fig. 9. Monthly average discharge rates at Stulpicani hydrometric station, 1981
During January, February, March, November and December, when temperatures and rainfall quantities are very low, their contribution to the flow rates is very weak. Starting with April temperatures begin to rise and also do rainfall values (according to the monthly multi-annual trend). The flow dynamics copies the
192
same dynamics. The quantities and distribution of rainfall in time and space gives the area the characteristics of a moderately humid continental climate, with average values of 903.4 l/m2 in Rarău Mountains, 743.2 l/m2 in Stulpicani commune, 788.0 l/m2 at Gemenea 2 hydrometric station, 824.6 l/m2 at Gemenea 5 hydrometric station, and 782.2 l/m2 at Frasin. During the recent years the discontinuous and torrential character of rainfall was accentuated. Suha River basin has registered maximum values within 24 hours that are far above the monthly average. The complexity of the hydro-meteorological phenomena requires specific discharge analysis. Specific multi-annual average discharge (qmed) is obtained with the following formula: q = Qx1000/F, (l/s/km2), and expresses the flow with which each km2 from a basin area participates to flow formation, where: Q x 1000 is the transformation of m3/s in l/s, F = basin area in km2.
Table 1. Average discharge rates and specific monthly and annual discharge (multi- annual values) at the gauging stations in Suha basin
Hm River Station F km² (m) I II III IV V VI VII VIII IX X XI XII An. q l/sec/km²q Specific dischargSpecific Suha Stulpicani 131 0.518 0.542 1.19 2.93 2.68 3.03 2.83 2.65 1.56 0.853 0.666 0.567 1.67 12.7 Gemenea Gemenea 2 30.4 991 0.154 0.149 0.338 0.765 0.733 0.840 0.835 0.796 0.466 0.254 0.205 0.163 0.475 15.6
Slătioara Gemenea 5 33.5 944 0.132 0.146 0.357 0.794 0.788 0.865 0.776 0.698 0.412 0.221 0.174 0.139 0.459 13.7
Specific discharge rates show significant increases in the warm period of the year (table 1). Autumn and winter months participate with small percentages of the discharge volume (2.5-3.5%) (Table 2). In the warm period of the year, between April and October, the percentages are much lower. The percentages of April are higher due to the melting of snow layer, reaching values of 8.2-8.9%. The highest percentage contribution to the annual discharge volume is measured during May- July (14.5-13.5%).
Table 2. Monthly percentage distribution of discharge in Suha basin
River Station I II III IV V VI VII VIII IX X XI XII Year
Q 0.518 0.542 1.19 2.93 2.68 3.03 2.83 2.65 1.56 0.853 0.666 0.567 1.67 Suha Stulpicani % 2.6 2.5 6.0 14.4 13.6 14.9 14.4 13.4 7.7 4.3 3.3 2.9 100
Q 0.154 0.149 0.338 0.765 0.733 0.840 0.835 0.796 0.466 0.254 0.205 0.163 0.475 Gemenea Gemenea 2 % 2.8 2.4 6.0 13.2 13.1 14.5 14.9 14.2 8.0 4.5 3.5 2.9 100
Q 0.132 0.146 0.357 0.794 0.788 0.865 0.776 0.698 0.412 0.221 0.174 0.139 0.459 Slătioara Gemenea 5 % 2.4 2.5 6.6 14.2 14.5 15.4 14.4 12.8 7.4 4.1 3.1 2.6 100
193
In the periods with low rainfall quantities, the river receives an underground supply (Table 3). In this case the quantity of drained water on rivers is reduced. On some sections of the river, especially in the middle and lower sectors, where coarse alluvial deposits are consistent, rivers are drying up.
Table 3. Minimum instantaneous historical discharges at the hydro-electrical stations from Suha basin Historical F Hm No. River Station minimum Data (km²) (m) Q l/s 1 Valea lui Ion Slătioara 6.7 1039 0.006 08-25.09.1987 2 Valea Ursului Slătioara 6.1 1074 0.001 15.12.1983 3 Slătioara Slătioara 3 18.6 1007 0.008 13.01.1978 4 Slătioara Gemenea 5 33.5 944 0.000 23-25.01.1974 5 Gemenea Gemenea 1 14.5 1056 0.005 08.12.1969 6 Gemenea Gemenea 2 30.4 991 0.000 01.10.2001 /02.03.1969 7 Suha Stulpicani 131.0 966 0.035 17-24.01.2001
Between Slătioara 3 (F = 18.6 km²) and Gemenea 5 (F = 33.5 km²) hydrometric stations are lost substantial quantities of water. In the case of monthly average minimum annual discharge with a 95% insurance, the value at the Gemenea 5 hydrometric station is with 20.0 l/s less than that of Slătioara 3 station, although the surface of river basin is much larger. In the case of daily average annual minimum discharge with 95% insurance the difference is of 8.0 l/s. For some years, during periods with little discharge, these differences are much higher. For the dry year of 1986, in July and August, at Slătioara 3 station were recorded monthly average discharge rates of 30-35 l/s, while at Gemenea 5 station the rates were of 10-12 l/s. Riverbeds with gravel deposits contribute to phenomena of river dry up due to high infiltrations. It is not a proper “drying up”, meaning a lack of input of rainfall from the upper sector. In some sectors a very weak discharge occurs, disappearing again as going downstream. The minimum values provided are used for various water supply projects, regional ponds or for wastewater discharge. Monthly average minimum discharge with an 80% insurance is taken into account in planning of fishing lakes construction, but also in the discharge of wastewater, to ensure the dilution. In the light of European regulations, drinking water supply is not allowed from surface sources. In special situations such supplies can be permitted, in which case for a good insurance of the water resources the 80% insurance annual minimum daily average flow is taken into account (Table 4).
194
Table 4. Minimum flow values with different probabilities of hydrometric station in the Suha Q monthly minimum annual Q daily minimum annual F H No. River Station ( l/s) ( l/s) (km2) (m) 80% 90% 95% 97% 80% 90% 95% 97% 1 Valea lui Ion Slătioara 6.70 1039 12.8 10.2 8.2 7.2 10.8 8.8 7.2 6.2 2 Valea Ursului Slătioara 6.10 1074 8.5 5.8 4.0 3.0 6.0 3.4 1.4 0.6 3 Slătioara Slătioara 3 18.6 1007 33.0 29.0 27.0 25.0 20.0 14.0 10.0 8.0 4 Slătioara Gemenea 5 33.5 944 21.0 13.0 7.0 4.0 8.0 5.0 2.0 1.0 5 Gemenea Gemenea 1 14.5 1056 26.0 23.0 21.0 19.0 22.0 18.0 16.0 15.0 6 Gemenea Gemenea 2 30.4 991 38.0 29.0 24.0 20.0 26.0 19.0 15.0 13.0 7 Suha Stulpicani 131.0 966 75.0 130.0 105.0 90.0 80.0 52.0 38.0 30.0
4. CONCLUSIONS
In the last 15-20 years has increased the frequency and intensity of climate risks. In the Suha river basin have been recorded exceptional floods in 1975, 1981, 1984, 1991, 2005, 2006, 2007, 2008 and historical droughts in 1969, 1974, 1978, 1982, 1987, 2001. The Suha River basin enters the general characteristics of the northern sector of the Siret river basin, being influenced by local conditions.
REFERENCES
1. Diaconu, C. (1988), Râurile de la inundaţii la secetă. Editura Tehnică, Bucureşti. 2. I.N.M.H. (1971), Romanian Rivers. Editura I.N.M.H., Bucuresti. 3. Olariu, P. (1992), Impactul antropic asupra regimului scurgerii apei şi aluviunilor în bazinul hidrografic Siret. Lucrările Simpozionului PEA, IV, 121-130. 4. Romanescu, G. (2006), Inundaţiile ca factor de risc. Studiu de caz pentru viiturile Siretului din iunie 2005. Editura Terra Nostra, Iaşi. 5. Romanescu G. (2009), Siret river basin planning (Romania) and the role of wetlands in diminishing the floods. WIT Transaction on Ecology and the Environment, 125:439-453. 6. Romanescu G., Nistor I. (2011), The effect of the July 2005 catastrophic inundations in the Siret River’s Lower Watershed, Romania. Natural Hazards, 57(2):345-368. 7. * * * Administraţia Bazinală de Ape Siret, Bacău. (2013), Arhivă, Bacău.
195