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Dairy Focus
www.guardianonline.co.nz
ON FARM STORAGE FEATURE
Guide helps on-farm water For many dairy farmers in the South Island, especially those outside the West Coast, parts of Otago and Southland, if you’re talking about storage the first thing that springs to mind is water. In short, how do you store enough of it to get you through the dry periods? Colin Williscroft looks at what Irrigation New Zealand has to say on the subject. To help farmers who are thinking about their options when it comes to water storage Irrigation New Zealand has published a guide on the subject, especially designed for those thinking about going down the irrigation path. It examines the process of constructing a freshwater storage facility for irrigation – also known as building a dam. The guide takes you through each part of the dam-building process – from concept through to construction and sign-off. It includes information on council requirements and engaging professionals (like designers and engineers). So what will a dam mean to you and your farming system? A correctly designed and constructed pond will provide: • Surety of supply (reliability).
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Design and of Irrigatio Construction n Storage P onds
DESIGN AND
• • •
Flexibility – you choose when you irrigate. Effective utilisation of water. Reduced risk of non-
CONSTRUC TION
OF IRRIGATION
STORAGE
PONDS
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compliance. Through the feasibility, design and construction phases of the pond you need to ensure:
You have enough water to recharge the dam every year – or the recharge period for which it is designed. • Consideration has been given to the lining material – clay or artificial. • The dam is the appropriate size for your irrigation area and crops. • The pond meets all regional and district council Resource Management and Building Act requirements. The guide also introduces the fundamental questions that need to be answered before, and while engaging third party professionals, to deliver the most suitable on-farm storage option for your needs. It provides a detailed outline of the decision-
making process required to ensure you build storage that is best suited to your needs along with basic design and construction information. There are two key factors used to define dams in New Zealand, the guide says. Firstly, the height of the dam wall from toe to crest, and secondly, the volume of water stored. The volume of water stored is not the same as the water able to be used, the guide says. To determine the active storage, two water levels need to be known – the highest level that water can be safely stored, at and the lowest level from which water can be abstracted. The difference between the two is called the draw down. The draw down height, multiplied by the area of the reservoir gives the usable volume of water – the
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