Contents preface (VII) introduction 1—37

5.14.5. Economics of Canal Lining
The economic viability of lining of a canal is decided on the basis of the ratio of additional benefits derived from the lining to additional cost incurred on account of lining. The ratio is worked out as follows (15):
Let C = cost of lining in Rs/sq. metre including the additional cost of dressing the banks for lining and accounting for the saving, if any, resulting from the smaller cross-sections and, hence, smaller area of land, quantity of earth work, and structures required for the lined sections. This saving will be available on new canals excavated to have lined cross-section right from the beginning, but not on lining of the existing unlined canals.
s and S = seepage losses in unlined and lined canals, respectively, in cubic metres per square metre of wetted surface per day of 24 hrs.
p and P = wetted perimeter in metres of unlined and lined sections, respectively, T = total perimeter of lining in metres,

d = number of running days of the canal per year, W = value of water saved in rupees per cubic metre, L = length of the canal in metres,
y = life of the canal in years,
M = annual saving in rupees in operation and maintenance due to lining, taking into account the maintenance expenses on lining itself,
and B = annual estimated value in rupees of other benefits for the length of canal under consideration. These will include prevention of waterlogging, reduced cost of drainage for adjoining lands, reduced risk of breach, and so on.

The annual value of water lost by seepage from the unlined section
= pLsdW rupees.
The annual saving in value of water otherwise lost by seepage
= (pLsdW – PL SdW) rupees
= {LdW (ps – PS)} rupees
Total annual benefits resulting from the lining of canal
Bt = {LdW (ps – PS) + B + M} rupees	(5.23)
Additional capital expenditure on construction of lined canal

= TLC rupees

CANAL IRRIGATION

213

If the prevalent rate of interest is x per cent per year, the annual instalment a (rupees) required to be deposited each year (at its beginning) for a number of y years to amount to TLC plus its interest at the end of y years is determined by the following equation:

F

TLC ^G 1 ⁺

H

∴

x I

J

100^K

y

R