After visiting the project states, the Hatchery Engineering Consultant suggests that the following be considered to speed up the slow progress, improve the quality of workmanship, reduce the cost of construction, as well as ensure the partial operation of the hatcheries as early as possible:
To prevent any flood problems during the construction period, the drainage and central canals, including ancillary structures, will have to be completed before the monsoon season.
As, in the majority of cases, there is not enough water for construction purposes, dikes have usually been compacted without watering or with less water used than required. The proposed tubewells, located near the outlet point of the central canals, should, therefore, be drilled during the tendering period in order that a source of water is available before commencing construction works.
Construction of the ponds should be started from the outlet point of the central canal. In this way the ponds between the division boxes can be operational by the next spawning season, taking into account that all their structures have to be completed also.
All plants and grasses as well as the topsoil up to required depths must be removed from the foundation of the dikes and pond sides. No topsoil and grass should be used for diking. These should be deposited outside the ponds and used for growing a grass cover.
For diking, each layer of earth should be maximum 20 to 25 cm, well watered if needed, and thoroughly compacted by sheepsfoot or power rollers.
It seems that there is difficulty in levelling the pond bottoms, as with the exception of the Demar Hatchery, unevenness could be observed on the pond floor of all other hatcheries. To ensure good levelling, the work should be carried out in two steps: first a rough excavation has to be done using as bench marks, a number of pegs pre-set by the Assistant Engineer, showing the required depths of the excavation from the top of each peg. Having excavated the pond bottoms, levelling now follows. This must be controlled by the Assistant Engineer.
To save time, the pipes for gates and division boxes should be constructed and laid first, before the dikes are built. If the pipes are covered with 60 to 70 cm thick earth layer, manually compacted, a tractor with a sheepsfoot roller can cross them.
To save construction costs, pitching in the central canal should be omitted and only adequate bed protection provided to all structures. The subsidiary gates and division boxes should be built according to the plans supplied by the Consultant to the CPU in March 1982. However, all these structures may only have a single tower which should be located at the pond and upstream side of the central canal.
To ensure quality of the construction of the gates, their walls and grooves should be vertical and parallel to each other. The concrete in the walls must be continuously casted, with no joints being allowed. If the contractor is not able to provide vertical grooves with a smooth surface, 'U' form or equal angle steel (50-50-4 MM) may be used.
To achieve a proper surface for the concrete works and speed up their construction, steel shuttering with bigger tables may be used for the gates and hatching cisterns of the indoor hatchery.
Of the buildings, the indoor hatchery, including the overhead tank and store buildings, will have to be completed first.
To save on construction time of the hatchery building and ensure its early operation, AC roofing with steel trusses may be used.
As two additional circular tanks will be built into the hatchery building, increasing considerably the water requirement, the volume of the overhead tank should be 70–75 m3 and 30–40 m3 for 25 ha and 10 ha hatcheries respectively as proposed by the IDA Review Mission in the Aide Memoire dated 30 April to 18 May 1983. The head between the plinth level of the indoor hatchery and the bottom level of the overhead tank should be 6.5 m.
Considering that the local contractors are not at all keen on construction of the overhead tanks, prefabricated steel overhead tanks may be used.
To ensure good quality water for the hatcheries, water samples should be taken from the existing and the first deep tubewells for analysis. This concerns the hatcheries built in Bihar and West Bengal where the iron content in the ground water is sometimes much higher than that allowed. Annex 1 shows the threshold of toxicity and maximum permissible concentration of toxic substances for fish and in water supply of the indoor hatchery respectively.
