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Feasibility of Canal Lining in the Large Scale Irrigation Systems : a Case Study

Abul Fazal M. Saleh
Associate Professor
Institute of Flood Control and Drainage Research, Bangladesh University of Engineering and Technology, Dhaka

Abstract/ Executive Summary:

The feasibility of lining the secondary and tertiary canals of Teesta Barrage project was analysed through collection of field data on seepage loss through unlined and five lined canal sections using ponding method. For the silty fine sand of the project area, the average seepage loss varied from 0.50 m/day to 1.00 m/day. The average seepage rates of the different linings ranged from 0.005 m/day to about 0.20 m/day. Considering the seepage rates, the linings were broadly classified into two groups. The high loss linings (with seepage rates of 0.05 m/day) and above, were brick linings on compacted soil, brick lining on cement mortar and tile lining on cement mortar. The low loss linings (seepage rates of about 0.01 m/day and below), consisting of asphalt lining on cement mortar and cast in situ concrete lining had a seepage rate much below the acceptable rate of seepage of 0.03 m/day for linings. From the economic analysis it was observed that, lining the canal system of Teesta Barrage Project is feasible with three of the five types of linings studied: brick lining on compacted soil, asphalt lining on cement mortar and cast in situ concrete lining. Among the three types of feasible linings, the values of the economic indicators used (BCR, IRR and NPV) were the highest for cast in situ concrete lining, hence, it was considered as the most cost effective lining for Teesta Barrage Project.

Keywords: Irrigation, Calan lining, Teesta barrage

Location:

Start Date:

End Date:

Program Area: Resource Development and Management

Commodity: Water management

Objectives:

To determine the economic feasibility of canal lining in the large scale irrigation system .

Methodology:

BWDB (Bangladesh Water Development Board) proposed to line only the secondary and tertiary canals of Teesta Barrage Project with capacities below 1.417 cumec (50 cusec). Thus, seepage loss data collection was carried out in two different types of canal sections: one representing secondary canals with a flow of 1.275 cumec (45 cusec) and another representing tertiary canals with a flow of 0.567 cumec (20 cusec). In consultation with BWDB, six different types of linings were tested for suitability. They were: a) Brick lining over compacted soil, b) Brick lining over cement mortar, c) Asphalt lining over cement mortar, d) Cast in situ concrete lining, e) Tile lining over cement mortar, and f) Buried Polyethylene lining. These linings were selected because they were durable, could withstand animal traffic and were accepted by the farmers. Many low cost linings such as additives to the soil, soil-cement, asphalt impregnated mats etc. have not been considered due to lack of acceptance by farmers (MPO, 1985). The data collection programme was carried out for one year and in two phases. In the first phase, data were collected during the period July-October, when the canal system of Teesta Project is expected to be in full operation. In the second phase, data were collected during the period January-April. Although the canal system of Teesta Project is not expected to be in full operation during the winter season, the data collection was continued in order to observe the change in the seepage rates during the two seasons. After making the necessary corrections in the daily water level data for evaporation and rainfall (where applicable), the water level data were plotted against the corresponding elapsed times. Sample Plots of water level and the corresponding elapsed time for one of the lined and unlined tertiary canals are consider. Similar plots were also obtained for secondary canals. The following formula as suggested by Kraatz (1977) for computing the seepage rate was used in this study: S = (W/P) * (Δd/Δt), where, S = Average seepage rate in m³/m²/day; W = average width of water surface of the ponded section; P = average wetted perimeter; and Δd/Δt = change in water level d, with time t. In order to get the seepage rate at the designed depth, the Δd/Δt value or the recession rate as required in the above equation was computed from the slope of the tangent drawn at hte designed depth. From the seepage analysis presented in the preceding section, it is evident that a significant volume of the supplied water of Teesta Barrage Project that would otherwise be lost to groundwater could be conserved through lining the canal system. It had already been mentioned that, in Teesta Project, only about 43% of the available land can be irrigated with the supply from Teesta river. Three standard measures of economic feasibility: benefit cost ratio (BCR), net present value (NPV) and internal rate of return (IRR) were used in the economic analysis. The cost involved In canal lining was the construction cost. The actual construction costs for the different types of lined and unlined canal sections used in this study were supplied by Design Circle VII, Bangladesh Water Development Board. The costs per 18.3 m section of the different lined and unlined canals and calculated incremental costs of linings (per square metre). By considering the costs, benefits and durability of linings, as presented in the preceding section, each of the three economic measures of feasibility (BCR, NPV and IRR) were calculated. The BCR, IRR and NPV of the different linings for secondary and tertiary canals were given.

Source of Information: Bangladesh Journal of Water Resource Research, Vol. 12. December 1991

Article Link (Online Journal):

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

It was observed that lining of the secondary and tertiary canal system of Teesta Barrage Project was feasible with three of the five types of linings studied; namely, brick lining on compacted soil, asphalt lining on cement mortar and cast in situ concrete lining. Benefits of lining were reflected by, increased water availability for irrigation, reduced land acquisition cost and right of way cost. Because of lack of data on reduced maintenance costs due to lining, such benefits could not be incorporated in the economic analyses. Among the three types of feasible linings, the values of the economic indicators used (BCR, NPV and IRR) were the highest for cast in situ concrete lining and was recommended for application in Teesta Barrage Project.

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