Aquaculture Engineering

Unit 10 - Race way culture

Race way system

Site selection and Layout plan of raceway culture

Site selection for earthen raceways must be done with care. Raceway culture is water intensive. Therefore, the most important consideration is the water supply. Most raceway culture is in mountain regions where gravity flow conditions can be taken advantage of to supply the needed water to the raceway system. In the trout culture industries in the Northeast and Northwest united sates. Freshwater springs are the main water source due to their relatively low and constant water temperature. The water quality and temperature required depends upon the species cultured and the size of the operation.

In actuality incoming water usually requires some degree of pretreatment before it can be used. Pretreatment may consist of nothing more than sedimentation or it may consist of a combination of a number of processes including aeration, heating, cooling, degassing or filtration. Depending on the effluent water quality, discharge water may also require post treatment before it can be released into the environment.

Multiple raceway facilities are arranged either in series or in parallel. Series raceway system can be used in regions where there is sufficient land slope so that the outlet for one raceway serves as the inlet for the next in the series. A 1-2% slope is considered adequate for good water flow (Pillay 1990). Waste build up can be a serious problem in the series systems since the wastes from the upstream unit enter the next unit downstream etc., Wastes tend to increase as the water traverses through the system.

For this reason there is a practical limit to the length of raceways and the number of unit in serious (These limitations will be demonstrated in example problems).
The waste problem is some what alleviated by arranging the raceway units in parallel. There are no culture units down stream receiving wastes from upstream units. Therefore, waste build up and aeration problems are minimized. However, the quantity of water required increases in direct proportion to the number of raceways. Thus if pumping is required, operating costs are higher in the parallel arrangement.

Many large raceway farms use a combination of the serious and parallel configuration. The figure illustrates a re-circulation technique using a large pond for waste deposition and water recycling.