8. WATER TRANSPORT STRUCTURES

8.0 Introduction

1. Several different kinds of structure may be used to transport water on a fish farm. The most common one is the open canal, which we will consider in detail first (Sections 8.1 to 8.6). Then we will look at other common structures, including:

• simple aqueducts to transport water above ground level (section 8.8)
• short pipelines to transport water above or under another structure such as a water canal or an access road (Section 8.9);
• simple siphons to transport water over an obstacle such as a pond dike (Section 8.9).

8.1 Types of open water canals

1. Different types of open water canals are used on fish farms to transport water, usually by gravity*, for four main purposes:

• feeder canals to supply water from the main water intake to the fish ponds. In a large farm with several diversion pond units, there is usually a main feeder canal branching into secondary and even tertiary feeder canals;
• drainage canals to evacuate water from the fish ponds, for example toward an existing valley;
• diversion canals to divert excess water away from barrage ponds;
• protection canals to divert water runoff away from the fish ponds.

2. In this chapter you will learn about feeder, drainage and diversion canals. You will learn more about protection canals later
(see Section 11.5).

8.2 Design of canals

1. All canals should be well designed to have the required water carrying capacity. The canals are designed using formulas that relate the carrying capacity of the canal to its shape, its effective gradient or head loss, and the roughness of the canal sides. The most commonly used formula incorporating all these factors is the Manning equation: