Aquaculture Engineering

Site selection for Brackish water fish farms - Topography and Tidal amplitude

Unit 8 - Brackish and marine water fish farms

Site selection for Brackish water fish farms

Topography and Tidal amplitude

Topography is one of the most important criteria in the process of site selection. When selecting a site for aquaculture, preference should be given to locations where the gravitational flow may be used to fill the ponds, as gravity flow is economical. It is also advantageous to drain the ponds by gravity flow. To take the advantage of gravity flow, the pond bottom should be at a higher elevation than the water table when the pond is drained (for pond drainage).Topography refers to the changes in the surface elevation of natural ground i.e. whether the ground is flat, sloping, undulating, or hilly. The best area for fish ponds/shrimp ponds is where the ground is levelled (flat) or where there is a slight slope. The optimum slope is between 0.5 to 1.0%. The ground slope shouldn’t be more than 2%, as it needs construction of high and costly embankments. Rectangular or square shaped flat areas located near the active creek and other natural water resources like rivers/canals/reservoirs/streams, etc; with an average natural ground elevation of 1 to 3 meter above the mean sea level, having minimum vegetation on it and slight sloping in one or two directions are ideal for coastal aquaculture development.

Sites with excessive undulating topography should be avoided as a lot of cut and fill would be needed during the construction, which will increase the cost of construction. Sites with average elevation lower than the mean low water should be avoided as ponds cannot be drained properly. Areas covered with large number of big trees and thick vegetation should be avoided as cleaning of the site will be difficult and will increase the cost. Proper elevation of the site in relation to tidal datum is another question, which needs to be considered especially in brackish water projects. At the places where tidal fluctuations (daily fluctuations) are too high (say 4 m and above) would be problematic because very big and costly dikes would be required to prevent flooding during the high tide. Areas where tidal fluctuations are too small (say 1 m or less) would pose serious problems because filling and draining of the pond cannot be fully executed. In general, the sites where tidal fluctuations are moderate (say between 2 m and 3 m) are most suitable for proper management. Ideal tidal amplitude for extensive and semi-intensive culture is 1.5 meter.