Irrigation Engineering
In a syphon aqueduct

Drainage passes over the canal and F.S.L. of the canal is above the bottom of the drainage trough
Canal passes over the drainage and H.F.L. of the drainage is above the bottom of the canal trough
Canal passes over the drainage and H.F.L. of the drainage is below the bottom of the canal trough
Drainage passes over the canal and F.S.L. of the canal is below the bottom of the drainage trough

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