Graded furrows of $80 \mathrm{~m}$ length and $0.75 \mathrm{~m}$ spacing are used for irrigating a field with an initial furrow stream of $100 \mathrm{~L} \mathrm{~min}^{-1}$. The initial furrow stream flow reaches the lower end of the field in 40 min. Thereafter, the furrow stream flow is reduced to $30 \mathrm{~L} \min ^{-1}$ and the cutback stream flow is continued for 1 hour. The average depth of irrigation over the field in $\mathrm{cm}$ will be_______________

Graded furrows of $80 \mathrm{~m}$ length and $0.75 \mathrm{~m}$ spacing are used for irrigating a field with an initial furrow stream of $100 \mathrm{~L} \mathrm{~min}^{-1}$. The initial furrow stream flow reaches the lower end of the field in 40 min. Thereafter, the furrow stream flow is reduced to $30 \mathrm{~L} \min ^{-1}$ and the cutback stream flow is continued for 1 hour. The average depth of irrigation over the field in $\mathrm{cm}$ will be_______________

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