抄録
This study was undertaken with the aim of observing the variation in seepage loss with the passage of time in irrigation canals of the Teesta Barrage Project (TBP) and thereby investigating what types of lining would be the most effective, durable, and suitable for the canals of the TBP. The experiments were carried out in lined and unlined canal sections at the testing site of the Bangladesh Water Development Board (BWDB) during the wet season of 1991 and the dry season of 1992. The linings used for ten canal sections were: brick lining on compacted soil, brick lining on cement mortar, tile lining on cement mortar, cast-in-situ concrete lining on compacted soil, and asphalt lining on cement mortar. One group of five lined canal sections of the above types plus two unlined sections represented secondary canals with a flow of 1.275m3/s, and the other such group represented tertiary canals with a flow of 0.567m3/s. For determination of seepage losses in these sections, the ponding method was applied.
The results revealed that of all the lining types, brick lining on compacted soil had the highest rate of seepage loss, followed by brick lining on cement mortar, tile lining, cast-in-situ concrete lining, and asphalt lining. During the ponding experiments, decreases in seepage rates varying from 64% to 966% were observed for different lining types. Looking at the seepage changes over the long time frames covering the wet season of 1989 to that of 1991 and the dry season of 1990 to that of 1992, increases in seepage rates were observed in most of the canal sections. In terms of the maximum and average seepage rates, brick lining on compacted soil showed the highest increase and cast-in-situ concrete lining showed the lowest, at least for the secondary canal sections. In fact, cast-in-situ concrete lining even showed decreases for some data categories. The results of the experiments as well as considerations of cost, durability, and other factors suggested that cast-in-situ concrete lining was the most recommendable for use in the TBP. At the conclusion of the present study, a recommendation was made that the seepage investigation should be continued for a few more years to obtain additional information on the life expectancy of the lining materials.
