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Water Losses: SSP Assumptions and Realistic Values
Source of Water Loss SSP Assumptions Observed and Literature Values
Lined Canal Seepage 2 cfs/msft 1 3 cfs/msft (WB2)
2.22-5.93 cfs/msft 3
Unlined Canal Seepage 5 cfs/msft 8 cfs/msft 4
5% / 100m canal (WB)
Field Application Loss 20% NIR 5 20-40% NIR (SSNNL 1989:368)
Operational Losses 5% Total Water Demand 20% NIR (WB)
1. Cubic feet/second/million square feet surface area.
2. World Bank report on Irrigation Development in India.
3. Observations on Mahi and Dantiwada Canal Systems (SSNNL 1989:357).
4. Observations on Bhakra system (SSNNL 1989:357).
5. Net Irrigation Requirement at the field.

The SSP authorities have given no concrete reasons for their assumptions. For example, seepage losses in fined canals have been assumed at 2/3 of the value considered appropriate by the World Bank in its report "Irrigation Development in India" (WB 1987). Average losses observed on lined canals in the Mahi and Dantiwada systems (in Gujarat, in similar agro-climatic regions) are double the value assumed for the SSP. Similarly, seepage loss rates in unlined canals are assumed to be 60% of observed loss rates in existing systems. It is completely unclear why this figure is used. A recent Narmada Control Authority publication says that the distribution system will be bricklined (NCA 1991b), resulting in higher seepage than the totally concrete-lined distribution system assumed while carrying out efficiency calculations. Field application and operational losses have also been assumed to be much lower than reasonable, without providing any concrete explanation.

The irrigation efficiency for the SSP was calculated using more realistic and observed estimates (As shown in the second column of Table 5). The results are shown in Table 6, along with the SSP calculations for comparison. The irrigation efficiency of the SSP is likely to be only 46% (ignoring evaporative losses) and not 60% as claimed. The water available for irrigation

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