%0 Research Notes
%T Additional drainage with subsurface drains in a milled peat harvesting site
%A Menonen, Juha
%A Päivänen, Juhani
%D 1979
%J Suo - Mires and peat
%V 30
%N 2
%U http://suo.fi/article/9489
%X The layout of a drainage system for a milled peat harvesting site is seen in Fig. 1. The ditch spacing used is 20 m and the ditches are about 1.5 m deep. However, sometimes it is necessary to use subsurface drains to increase the drainage effect of open ditches. In the rick areas at the end of the strips, where the harvested peat is stored, subsurface drains are the only method to drain the peatlayers.
Eight different kinds of subsurface drains were tested in summer 1978 at Kaikonsuo (63°40'N, 26°40'E) peat harvesting field managed by The State Fuel Centre (VAPO). Two experimental fields were laid down: one in the strip area (Fig. 2) and the other in the rick area (Fig. 3).
Five of the subsurface drain types used in the experiment were so called material drains: a board pipe drain with an inner cross-section of 64x102 mm (Fig. 8), and two sizes of plastic pipe drains (PVC) with an inner diameter of 40 and 65 mm. Two types of both drainsizes were used, one of which was bare (Fig. 9) the other covered with a filter material (Fibertix; Fig. 10). Three types of "nonmaterial" subsurface drains were tested in the experiment: a mole drain made with the Pajulahti Oy mole drain trencher (Fig. 4 and 5), a mole drain made with the VAPO mole drain plow (Fig. 6), and a narrow water furrow made with the Suokone Oy disc trencher.
The ground water level in each drainage treatment was measured once a week. In the strip area, in each treatment, there were measuring wells in two rows; five in a row. In the rick area there were five wells in each treatment.
In the strip area (Fig. 11) the distance to the ground water level in the control strips was about 50 cm. The mole drains or the narrow water furrows did not have any effect on the ground water level. The board pipe drains had the greatest lowering effect on the ground water level. In the strips with the plastic pipe drains the distance to the ground water level was about 80 cm. In the rick area the results obtained with the board pipe drain, with the mole drains and those of the control were similar to the results of the strip area. In the treatments drained with the plastic pipe drains the distance to the ground water level varied from 55 to 95 cm. The filter material did not increase the drainage effect of the pipe drains as expected, the case was rather the reverse.
It would be necessary to continue the experiment to find out the duration of the drainage effect reached with the different kinds of subsurface drains and, after that, to make economical calculations on the profitability of the types of subsurface drainage studied.