Interval and outlet discharge, 11 hour canal

Given: $ET_c = 5$ mm/day, AM = 220 mm/m, $D_r = 1.2$ m, only 50% of AM is readily available, $\eta_a = 65\%$, CCA = 450 ha, canal runs 6 AM to 5 PM = 11 h/day.

Step 1: Net depth per irrigation

$$d_{net} = 0.50\times 220\times 1.2 = 132\ \text{mm}$$

Step 2: Irrigation interval

$$I = \frac{132}{5} = 26.4\ \text{days}\approx 26\ \text{days}$$

Step 3: Gross depth and volume for the whole CCA

$$\begin{aligned} d_{gross} &= \frac{132}{0.65} = 203.08\ \text{mm}\\ V &= 0.203077\times 450\times 10^4 \approx 913,846\ \text{m}^3 \end{aligned}$$

Step 4: Outlet (canal) discharge. All the CCA must be irrigated within one interval of 26 days, with the canal flowing 11 h each day:

$$T = 26\times 11\times 3600 = 1,029,600\ \text{s},\qquad Q = \frac{V}{T} = \frac{913,846}{1,029,600} = 0.888\ \text{m}^3/\text{s}$$

Answer: interval = 26 days; required (outlet) discharge $\approx$ 0.89 cumec (888 l/s).