Salaojien ruostetukkeutumien torjumisesta vesilukkoja käyttämällä

Authors

• Niilo Seppälä Pellonraivaus Oy, Helsinki

DOI: https://doi.org/10.23986/afsci.71456

Abstract

The paper presents the results of tests carried out during 1955—1957 at the Salvela estate, located in the Piikkiö commune, southwestern Finland, as well as observations made on the drainings of rust containing soils in other parts of the country. The two draining systems used in the tests, are shown in Fig. 1. The soil in the area was heavy clay which was liable to crack. The tests primarily tried to ascertain whether the installing of drain traps would increase the iron content of the drain water discharging from the draining system. From each outlet 5 simultaneous water samples were taken. On June 7, 1955, the draining system 28 was closed by means of trap in the outlet. From each draining system 5 simultaneous water samples were again taken. On October 11, 1956, the draining system 26 was likewise closed by means of traps above the outlet and below the catch basin to prevent free air circulation. At the same time the trap of the draining system 28 was made water tight. Subsequently 11 simultaneous samples of water were still taken from each outlet. The iron content of the water samples is indicated in Table (p. 237) and Fig. 4. The fixing and the tightness of the drain traps appear considerably to contribute to the increase the iron content of the water samples. In accordance with Fig. 4 the samples are, however, distributed in different ways in the different seasons of the year, prior to and after the fixing of the traps. A greater number of water samples would have been useful. The effect of the test on the rust sediment of the covered drains was observed as follows; in draining system 26 and prior to fixing the traps the lower portions of laterals 4, 5 and 8 were opened the density of sediment being measured in each tile. Since the traps had been effective in this draining system during one year, the lower sections of drains 6 and b were opened and examined. The sediment profiles are shown in Fig. 2. with the exception of drain 8, which appeared clear from rust sediment. Regarding the density of the sediment the test cannot be proved as having been effective in one year. On the other hand, at least in ditch b, there were distinct corrosive traces present in the form of 0.5—1.5 cm deep channels at the edges of the sediment (Fig. 3 b). Corrosion from the sediment is also indicated by the fact that after the traps were fixed in the water discharged from the outlets flaky (d = 1—2 mm) clay or fine sand silt were found, and it also settled in the silt basins made on the upper side of the traps. In general the drain water silt on clayey soils is quite finely divided and does not in any noteworthy degree settle in the silt basins. Observations in respect to other drainings on rust containing soils show that in such drainings, if they are blocked with rust, the air in the drainage pipes has generally been able to circulate freely through the outlet. Merely the fact that during the greater part of the year the outlet is under the surface of water has essentially retarded its becoming blocked, A covered drain, the rust content of which touches such an unusually high level as 640 mg Fe/l, is still after a period of two years after draining quite clear of rust sediment, because its outlet is under the surface of the water. As a conclusion it is maintained that the creation of rust stoppages in drainage pipes will at least in a noticeable degree be retarded and very possibly entirely obviated by means of drain traps even to the extent of bringing about a cleaning of the system of pipes from the rust sediment earlier deposited therein. The procedure is inexpensive and can frequently be put into effect without additional expenses. It can likewise be easily employed in existing draining systems. The drain trap should be approximately 2—3 metres long as well as watertight. In the event of the open ditch waters or other surface waters being conducted in a covered drain on soil containing rust, this should preferably be constructed apart from other draining systems and have an outlet of its own.