Operation schedule
The operation schedule is for a pond complex having the annual production target of 1 million fingerlings, which corresponds to that of the Hub complex. The pond pattern of the Mangla complex has been worked out before the first visit of the Aquaculture Consultant and project draft was under evaluation.
The annual water demand is computed on the basis of the following assumptions:
Brood fish ponds are filled once a year.
Two nursery and two rearing ponds are prepared for stocking each week. Altogether 56 pond fillings are taken into account in case of the rearing ponds. Thus the average number of pond fillings is:
in case of nursery ponds, and
in case of rearing ponds it is:
The seventeenth rearing pond is excluded from the operation schedule, but its water demand is included in the calculations.
Pond filling
| Pond | No. | Water depth m | Average area ha | Total volume m3 | Number of filling | Total demand m3 |
| Brood fish pond | 7 | 1.7 | 0.17 | 20 600 | 1 | 20 600 |
| Nursery pond | 10 | 1.0 | 0.10 | 10 100 | 5.6 | 56 600 |
| Rearing pond | 17 | 1.5 | 0.35 | 88 600 | 3.5 | 310 100 |
| Total | 34 | 387 300 |
Replacement of evaporation losses
The ponds operate all year round and evaporation losses are computed in due course.
| Brood fish ponds | January – December | Evaporation = 2 239 mm |
| Nursery ponds | February – August | Evaporation = 1 649 m |
| Rearing ponds | March – October | Evaporation = 1 893 mm |
| Brood fish ponds | 2 239 mm × 1.20 ha = | 26 900 m3 | (rounded) |
| Nursery ponds | 1 649 mm × 1.01 ha = | 16 700 m3 | (rounded) |
| Rearing ponds | 1 893 mm × 5.93 ha = | 112 300 m3 | (rounded) |
| Total evaporation loss | 155 900 m3 | ||
Replacement of seepage losses
Some soil investigations have been carried out on site, but they did not contain infiltration test. Therefore the seepage is only estimated with 20 mm/day seepage rate, to be on the safe side.
| Brood fish pond | 20 mm/day × 365 days × 1.20 ha = | 87 600 m3 | (rounded) |
| Nursery pond | 20 mm/day × 28 weeks × 1.01 ha = | 39 600 m3 | (rounded) |
| Rearing pond | 20 mm/day × 34 weeks × 5.93 ha = | 282 300 m3 | (rounded) |
| Total seepage loss | 409 500 m3 |
Inflow due to rainfall
The ponds are filled from the Bong irrigation canal and therefore the amount of rain may only be calculated on the pond surfaces.
| Brood fish pond | 757 mm × 1.20 ha = | 9 100 m3 | (rounded) |
| Nursery pond | 613 mm × 1.01 ha = | 6 200 m3 | (rounded) |
| Rearing pond | 634 mm × 5.93 ha = | 37 600 m3 | (rounded) |
| Total inflow from rainfall | 53 900 m3 | ||
Summary
The annual water demand is the sum of the above amount with the appropriate sign.
| Pond filling | + 387 300 m3 |
| Evaporation loss | + 155 900 m3 |
| Seepage loss | + 409 500 m3 |
| Rainfall | - 53 900 m3 |
| Annual water demand | 898 800 m3 |
| (rounded to) | 900 000 m3 |
