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Border-Dyke Irrigation Overview

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Border-Dyke Irrigation Overview

You are advising a Canterbury farm that uses border-dyke irrigation. Read the farm brief, then answer the questions. Show your working for calculations. Water use and environmental effects should both be considered.

Farm brief

Kauri Farm has a broad, gently sloping paddock divided into long strips by low earth banks called borders or dykes. Water is released from a headrace onto the high end of a strip. It flows downhill across the soil, soaking into the root zone. The system can be relatively simple to operate, but uneven ground or poor timing can leave some areas too wet and others too dry. Water may also be lost through runoff, seepage or evaporation. The farm is considering whether to keep the system or invest in a spray system. Any decision needs to account for water availability, soil, crop needs, energy use, cost and maintenance.

Understand the system

1.Which description best explains border-dyke irrigation?

Water is channelled over the soil surface between low earth borders.
Water is sprayed into the air from rotating sprinklers.
Water is delivered directly to each plant through buried pipes.
Water is collected from rain using a roof and storage tank.

2.According to the farm brief, what are the low earth banks along the sides of each strip called, and what do they do?

3.Why is a broad, gently sloping paddock generally more suitable for border-dyke irrigation than steep, uneven land?

4.Select two possible limitations of border-dyke irrigation.

Water can be lost through runoff or seepage.
Poor timing can cause waterlogging or uneven watering.
It always uses less water than every spray system.
It needs no land preparation or maintenance.

Evaluate and calculate

5.A 1-hectare paddock receives 10 mm of water in one irrigation. Calculate the volume applied in cubic metres. Use 1 hectare = 10,000 m² and 10 mm = 0.01 m. Show your working.

6.Give one reason a farmer might choose to keep a border-dyke system, and one reason the farmer might consider changing to spray irrigation.

7.A farmer notices water ponding at the lower end of a strip while the upper end is already drying. Suggest one practical adjustment to investigate and explain how it could help.

8.Explain one way irrigation water leaving a paddock could affect the surrounding environment.

9.The farm must choose between keeping border-dyke irrigation and investing in a spray system. Name two pieces of information the farmer should gather before deciding.

10.Write a short recommendation to the farm. State whether it should keep, improve or replace its border-dyke system, and support your recommendation with two relevant factors from the brief.