E l e c t r o n i c   r e p r i n t


HYDRAULIC GEOMETRY
OF A SUPRAGLACIAL STREAM,

RAGNARBREEN, SPITSBERGEN

Andrzej Kostrzewski and Zbigniew Zwolinski

RESEARCH METHODS

The studies were made in the early afternoon hours on 24 July 1985. This was supposed to ensure the most frequent discharges, i.e. ones resembling the means. Ten cross-sections of the stream reach, spaced from 50 to 100 m apart, were selected within segments where the channel ran straight to carry out morpho- and hydrometric measurements. Channel depth was measured every 2-5 cm with 1 mm accuracy. Flow velocity was measured using the float method, which is sufficient assuming a reduction coefficient (0.825, after Kostrzewski et al. 1989) in its calculation (Dozier 1976, Park 1981). Local gradients at each station were measured using a clinometer.

The measurements helped calculate the following geometric and hydraulic parameters of the supraglacial stream channel cross-sections :

  • discharge Q,
  • width W,
  • mean depth D,
  • mean velocity V,
  • cross-section area A,
  • wetted perimeter P,
  • width/depth ratio F,
  • hydraulic radius R,
  • Froude number Fr,
  • Reynolds number Re,
  • stream power Ω,
  • shear velocity V*,
  • shear stress τ,
  • Manning resistance coefficient n, and
  • Darcy-Weisbach friction factor ff.
  • For each parameter exponential functions were determined of the water discharge down the long profile of the stream using regression equations calculated with the help of the least-squares method. These functions served to reveal dependences in the downstream hydraulic geometry of a supraglacial stream channel. Hydraulic geometry expresses the fit between water discharge as an independent variable and dependent variables (Leopold, Maddock 1953), i.e. the above parameters.

    Weather conditions were studied at a meteorological station at Skottehytta lying at a distance of 4.4 km from the glacier front on a raised marine terrace (8 m a.s.l.) on the eastern shore of the Petuniabukta. The question of the location of a meteorological station with regard to the glacier is raised by Pulina et al. (1984), who draw attention to the similar magnitudes and patterns of major climatic elements recorded at stations situated in Hornsund and the Werenskioldbreen foreland. They emphasise, however, that there were slight differences between stations on the glacier foreland and on its surface. At Skottehytta, measurements were taken four times a day starting with 28 June 1985 (Kostrzewski et al. 1989). They included:

  • air temperature,
  • wind direction and velocity,
  • total and diffuse radiation, and
  • precipitation.
  • The temperature was measured using an August psychrometer; wind direction was defined with the help of an eight-point wind-rose, and its speed with a Robinson anemometer at an altitude of 2 m; radiation was recorded using a Janiszewski pyranometer, also at an altitude of 2 m; and precipitation was collected in a Hellmann rain-gauge.