Annual Water Budget for a Marron Farm

For one pond with a surface area of 1000 square metres (50 x 20 metres or 40 x 25 metres) and an average depth of 1 metre (1.5 - 2.0 metres maximum depth at the outlet), the volume of water is 1000 cubic metres. The water losses during the year, for this size of pond, are due to:

Evaporation (depending upon locality) = 1 metre of pond depth = 1000 cubic metres, and

Seepage = 1000 cubic metres for a well constructed pond in good clay ( the loss can be much higher if ponds are poorly constructed).

Evaporative and seepage losses occur mostly over the production or growing season from spring to autumn, so for each 1000 square metre pond, the farm needs to have 2000 cubic metres of water stored or available over the summer, if ponds are not to go dry.

Note : the ponds should be equipped with aerators so that no additional water is required to control water quality by flushing the ponds ( without aerators the amount of water needed for water exchange would be prohibitive, if feeding at the proper rates is followed).

Since drain harvesting and refilling for restocking occurs during winter, the additional volume of 1000 cubic metres may not be difficult to supply but this volume, needed to refill the pond, should be added to the annual water budget. Some consideration can be given to reusing most of the drain-down water, if supply is poor or costly and/or there are effluent treatment conditions for the locality.

The farm will need a water supply of 3000 cubic metres of water for each pond of area 1000 square metres.

Note: 1 hectare of pond area = 10,000 square metres

The total water supply requirement or annual water budget for a farm would be:

15,000 cubic metres of water for 0.5 hectares of pond area (minimum area for restricted licence).

75,000 cubic metres of water for 2.5 hectares of pond are (minimum area for an unrestricted licence).

A more detailed water budget can be calculated for each month of the year.