Stefan BARTOSZEWSKI Institute of Earth Sciences Maria Curie-Skłodowska University Akademicka 19 20-033 Lublin, POLAND

Wyprawy Geograficzne na Spitsbergen UMCS, Lublin. 1995

CHARACTERISTIC FEATURES OF THE OUTFLOW FROM THE WYDRZYCA RIVER BASIN (BELLSUND, SPITSBERGEN)

INTRODUCTION

Characterization of the outflow in the river basins of Western Spitsbergen was the subject of numerous papers but the majority of these referred to glacial basins. Unglaciated (nival) basins were not so frequent an object of hydrological studies. The basin of Fugleberget stream, situated in the Hornsund region, is an exception. A particular role of these investigations is associated with the fact that hydrological and hydrochemical observations and measurements, carried out in this area, covered a complete cycle of water circulation in the basin (Pulina, Krawczyk, Pereyma 1984). In the period between 26 August 1979 - 24 August, 1980 the index of outflow from the basin was 822.2 mm and that of precipitation was 864.5 mm. The measurement disclosed a decisive effect of the spring season on the annual outflow from the basins of this type. During 39 days of hydrological spring, 594.3 mm water flowed out, which constitutes 72% of the total outflow. The expeditionary character of the studies carried out in other regions of Svalbard, mainly in the summer season, makes it difficult to get to know the variability of characteristic features of outflow from the unglaciated basins. The situation was different when the hydrological observations took place in the early spring. The studies carried out in the Bellsund region in 1987 during II Geographical Expedition of the Maria Curie-Sklodowska University were of this character.

THE AREA OF STUDIES

The object of investigations is a small basin of 1.29 km2 area, situated in Calypsostranda on the southern coast of Bellsund (Fig. 1). It is drained by a stream called Wydrzyca River which occupied a deep valley, with steep walls cutting the terrace 25 m deep down to its bottom. A hydrometrie profile, where a limnigraph B-2 is installed and periodical measurements of flow are made, have

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been localized there. The basin covers the slope of the massif Bohlinryggen and the eastern part of the terrace coastal plain - Calypsostranda going down in the NE direction to Recherche Fiord.

The bedding of this area is built of Hecla Hoek Formation rocks (Upper Proterozoic) developed as tillits, phyllites and quartzites. They constitute a bed of the coastal plain in the Calypsobyen region, which is built of gravels, sands, boulder clays and silts deposited on Tertiary sandstones with strata of coal. (Dallmann et al. 1990). The granulometric composition of Calypsostranda sediments provides favourable conditions for infiltration of water into the bedding.

HYDROMETEOROLOGICAL CONDITIONS

The outflow was observed from 14 June to 17 August 1987. At the time the field studies started, a compact snow-ice cover, being in an initial stage of ablation, was deposited on the tundra (Rodzik 1988). The thickness of cover was differentiated. Its maximum over 2 m was found in theravined part ofWydrzyca Valley and on the Bohlinryggen slope. A thick layer of band ice, deposited on the ground, was a characteristic feature of accumulation cover structure. Its water equivalent was estimated to be 30% of the total cover.

Mean day and night temperatures of the air were positive during the whole period of observations. The average was 3.8°C (Gluza 1988). Minimal tem-peratures were negative at the beginning. On 14 June -1.4°C was recorded. The total precipitation was 31.8 mm during the period of studies, and the highest day and night total reached only 5.6 mm.

The river outflow on the coastal plain, a sign of the beginning of the hydrological spring, started about 10 June. At the time of the outflow measurements, the Wydrzyca bed was slightly cut into the ice cover filling the valley bottom. It was unstable, increasing its depth and width gradually. Therefore it was necessary to make frequent measurements of outflow and to calculate a few consumption curves enabling changes of water states into flows.

A general characterics of outflow in 1987 from the unglaciated river basins situated on the forefield of Scott and Renard Glaciers was presented in earlier works (Bartoszewski, Rodzik 1988, Bartoszewski, Rodzik, Wojciechowski 1988). In the period of 14 June to 17 August 1987, a water layer H = 367 mm flowed out from the Wydrzyca River Basin which corresponds to the elementary outflow 66 l/s*km2 and the mean flow 851/s. The actual amount of water flowing through the hydrometrie profile, closing the basin under investigations, was over 10% higher which was due to the periodical inflow of water from the neighbouring bifurcation stream (Bartoszewski, Rodzik 1988).

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CHARACTERISTICS FEATURES OF THE OUTFLOW

The object of this analysis is the actual amount of outflowing water without differentiation into its own resources and inflow from outside the basin. The characteristics are based on the two-hour flow values (from even hours LMT) determined on the basis of two-hour states shown by limnigraphs and corresponding consumption curves (corrected compared with those in the earlier paper). Fig. 2 presents the course of two-hour flow values. The maximum flow reached 6401/s and minimum 41/s. The mean flow ofWydrzyca River during the study periods was 94 1/s. The set median was equal to 53 1/s and the mode value was 14 1/s.

Such great differentiation between mean, median and mode values indicates that the set of flows is not in character one of normal distribution. This is confirmed below by a classical, non-parametric test for significance. A set of data is presented as a histogram of frequency (Fig. 3). The Weibull distribution proved to be the best statistically fitted one. It is presented by the Weibull curve in the figure. The distribution fitting was checked by the Chi-square test, assuming the significant level to be 0.001. The calculated value x2 = 45.4113 corresponds to the significance level a=0.001529. As this number exceeds the assumed boundary value of 0.001, an assumption of compatibility of the variable "flow" distribution with the Weibull distribution can be accepted.

The diagram shows two types of flow variability: day and night fluctuations of a cyclic character, and long term variations caused by the changes of permafrost thawing rate, due to fluctuations of air temperature. The phenome-non of ablative, day and night rhythm of flow is of special interest. It has been known in the glacial basins for a long time, but rarely observed in the unglaciated basins (Parde 1957). Day and night fluctuation is periodical and observed only in the spring period, when almost the whole of the outflow comes from the thawing of the snow cover on the coastal plain. This phenomenon is not observed during the polar summer and autumn, when the rainfalls and water from permafrost degradation are a main component of outflow in the unglaciated basins of Svalbard. In 1987, the ablative rhythm of the Wydrzyca River outflow occurred from 14 June to 11 July. This period constitutes a hydrological spring. Another part of the measurement series, from 12 July to 17 August included a period of hydrological summer.

The analysis of the Wydrzyca River flows showed that the evolution of day and night hydrogram changes in time, as shown in Fig. 4, where a day and night rhythm of flow variability for ten-day periods (decades) beginning from 15 June 1987 is presented. During decade I (15-24 June 1987), the greatest flow, 387 1/s was observed at 8 p. m. and the smallest, 299 1/s at 8 a.m. The coefficient of amplitude flow, calculated as a quotient of the greatest and smallest values after multiplying by 100, was 59.2%. In the next decade, 25 June - 4 July 1987, the

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coefficient value dimnished to 52.5%. At the same time, the time of maximum appearance was transferred to 6 p. m. In decade III, 5-14 July 1987, a day and night variability of flow is not clearly visible, and maximum and minimum values were similar. The coefficient of variation was 77.2%. The time of maximum appearance was transferred to 4 p. m. The day and night hydrograms of the next three decades do not display a night and day rhythm. The hydrogram evolution of the river under consideration, took a reverse to that of the one for glacial basins. The changes of day and night fluctuations of the flows on the Matter Vispa River in four-day periods were the smallest in the spring season, and then increased gradually (Elliston 1973).

The decrease of day and night amplitude coefficient can be justified by a gradual reduction of resources of water, undergoing retention in the snow cover from 100% at the time ablation is begun, to a few percent in the final period of observation, when only single patches are preserved in the mountainous part of the basin and in the depressions. It should be pointed out, that the size of temporary outflow is not connected to the ablation intensity. The most intense ablation of snow cover, 10 cm/s day and night, was observed from 10 to 20 July (Rodzik 1988). In the period of 15-24 June it was on average only 3 cm/a day and night. The factor affecting the extent of outflow was not therefore the intensity of the process but its spatial range.

The transfer of time limits of maximum flow was connected with a shorter time of thaw water reach. In the first period, this phenomenon referred to the whole basin, but then only to the region of valley depression filled with snow for a long time.

Genetic differentiation of alimentation sources can also be seen during the statistical analysis of outflow variation. In the analyzed series two sequences of data were distinguished. The first one is connected with the period of hydrological spring, 14 June - 11 July 1987, and the second with the summer period, 12 July - 17 August, 1987.

The main characteristic of the spring period is ablative, day and night rhythm of outflow. This process can be described by means of the autocorrelation function, as there is a correlation between the two arbitrary values of the series which changes with the change of their interval. Fig. 5 shows the autocorrelation function of Wydrzyca River flows in the spring. It can be seen that the autocorrelation function of flows diminishes with the slowly fading sinusoidal oscillations. A time period equal to 12 two-hour intervals, i. e. one day and night, constitutes the fluctuation period. The studies carried out in the basin of Wydrzyca River showed that the size of summer outflow is connected with the size of water retention in the zone of active exchange. In the absence of heavy precipitation, the state of resources which underwent retention decreases gradually (Bartoszewski 1993, 1994), which causes the decrease of river outflow. The curve of flow run is in character a curve of drying, where the flow size is

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a function of time. A correlation coefficient must be taken into account while choosing a suitable statistical dependence. Fig. 6 presents the relation between the flow size and time in the summer 1987. The curve approximating dependence took the form of an exponential model:

Q _ e(4.233-5.41E-3*t)

where: Q is the flow after two-hour periods, "t", "e" is the basis of natural logarithm. There was a dependence statistically significant between time and flow size, the correlation coefficient was equal R=-0.895. The square of this value, R2 ==80.11 indicates that the regression equation explains 80.11% of flow value variability.

REFERENCES

Bartoszewski S., Rodzik J., 1988. Dynamika odpływu w zlewniach peryglacjalnych na przedpolu lodowców Renarda i Scotta (Zachodni Spitsbergen). Wyprawy Geograficzne UMCS na Spitsbergen UMCS. Lublin, 123-131.

Bartoszewski S., Rodzik J., Wojciechowski K., 1988. The outflow of water in permafrost environment - Spitsbergen. V International Conference on Permafrost, Trondheim, Norway, 543-545.

Bartoszewski S., 1993: Dynamics of underground waters in Calypsostranda region in 1990 (Western Spitsbergen). XX Polar Symposium, Lublin 1993, 285-292.

Bartoszewski S., 1994: Run-off and dynamics of Calypostranda underground waters (Western Spitsbergen). Wyprawy Geograficzne na Spitsbergen. UMCS Lublin, 37-46.

Dalimann W. К., Hjelle A., Ohta Y., Salvigsen O., Bjornerud M. В., Hauser Е. С., Mäher Н. D., Craddock С., 1990: Geological Map of Svalbard 1:100 000, Sheet В 1 IG Van Keulenfjorden. Norsk Polarinst., Oslo.

Elliston G. R., 1973. Water movement through the Gornegletscher. IASPH Publ., 95, 79-84. Gluza A. F., 1988. Warunki pogodowe w sezonie letnim 1987 r. w Calypsobyen (Zachodni

Spitsbergen). Wyprawy Geograficzne UMCS na Spitsbergen, UMCS Lublin, 21-29. Pulina M., Krawczyk W., Pereyma J., 1984. Water balance and chemical denudation in the

unglaciated Fugleberget basin (SW Spitsbergen). Pol. Polar Res. vol. 5, no. 3-4, 183-205. Rodzik J., 1988. Rozmieszczenie i struktura pokrywy śnieżnej na tundrze Calypsostrandy w sezonie

ablacyjnym 1987 r. Wyprawy Geograficzne UMCS na Spitsbergen UMCS, Lublin, 93-102. Parde M., 1957. Rzeki. PWN, Warszawa.

STRESZCZENIE

Analizę charakterystycznych cech odpływu z niezlodowaconej zlewni Wydrzycy (Fig. 1) oparto o wartości dwugodzinnych przepływów za okres 14.06-17.08.1987r. (Fig. 2). Duże różnice pomiędzy wartością średnią 94 l/s), medianą (53 l/s) i modalną (14 l/s) wskazują na skośny charakter rozkładu. Dalsza analiza pokazała, że krzywą rozkładu częstotliwości najlepiej dopasowną do histogramu jest krzywa Weibulla (Fig. 3). W okresie hydrologicznej wiosny od 14 czerwca do 11 lipca 1987 r. obserwowano dobowy, ablacyjny rytm odpływu. Dobowy hydrogram przepływu wykazuje ewolucję amplitudy przepływów skrajnych dobowych (Fig. 4).

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Pomiędzy dwoma dowolnymi wartościami szeregu istnieje korelacja zmieniając się wraz ze zmianą ich odstępu co opisuje funkcja autokorelacji (Fig. 5). Ma ona charakter malejący z wolno gasnącymi oscylacjami sinusoidalnymi.

Wielkość przepływów podczas hydrologicznego lata jest związana z wielkością retencji w strefie aktywnej wymiany. Krzywa przebiegu przepływów ma charakter krzywej wysychania (Fig. 6).

I •

1

t j

! i i

i >

Fig. 1. Situation of the investigations area: 1 - limnigraph, 2 - watershed, 3 - constant and periodical streams, 4 - place of bifurcation, 5 - pond, 6 - spring, 7 - margin, 8 - moraines

Fig. 2. The two-hour flow values of the Wydrzyca River

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» b * « W « • ' ' ' ' ' ' ' ' ' ' ' •

" П

i i i

Vi s .

i ъ п Т Г Т т т т ч ^ i

О 200 400 600 800

Ol/s

Fig. 3. Frequency histogram and the Weibull curve

Fig. 4. A day and night rhythm of flow variability for ten day-periods: 1 -15-24 June, 2-25 June-4 July, 3-5-14 July, 4-15-24 July, 5-25 July-3 August, 6-4-13 August

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0.5-

i.-.HNIIl .11.

-0.5-

-щр тщр -

11 i 111111111111111 i 11 i 1111 0 50

Fig. 5. The autocorrelation function of the Wydrzyca River two-hour flows

100 h

Q l/s

t Fig. 6. Relation between the Wydrzyca River two-hour flows (Q) and time (t)

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