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Irrigation dams & irrigation reliability

Clarke Goldie & Partners view irrigation reliability as the degree to which the crop or pasture has adequate soil moisture to prevent stunting or wilting – the more days that soil moisture drops below the level required to sustain crop or pasture growth the lower the reliability of the irrigation system.

Clarke Goldie & Partners create sophisticated water balance models that can be used to estimate irrigation reliability. The need (or not) for an irrigation dam can be determined using such a model.

The primary function of an irrigation dam is almost always to improve the reliability of the irrigation system in terms of crop or pasture performance as described above. In order to achieve this objective, the following aspects are important:

Irrigation reliability and dam size

The reliability of an irrigation system should be modeled in a way that accounts for the variably of the water source, the resource consent conditions, the irrigation system capacity, the soil water holding capacity, the local climate variability, and the crop type. A variable dam capacity can be added to such a model and the response of the daily soil moisture balance can be assessed. By minimizing the number of days on which the crop or pasture would have been stressed, the size of the dam can be optimized. Failing to consider all of the variables mentioned above when sizing a dam can result in a dam that is too small (and fails to provide the potential level of reliability), or too big (a poor investment in an expensive asset that is not well matched to constraints associated with the other features of the irrigation system).

Dam integrity

While losses (evaporation and infiltration) from any dam are inevitable, these should be kept to an absolute minimum. Given that seasonal volumes are (or will soon) be measured at the point of abstraction from the resource, any losses from the dam will be for the farmer’s account. A leaky dam can therefore let you down when you need it most. Also, leaky dams are difficult and expensive to fix.

Other aspects

An irrigation dam should be a robust structure that needs little or no maintenance and can safely deal with unusual stresses and emergencies such as earthquakes, strong winds and over-filling. Ongoing energy, compliance and maintenance costs should be kept to a minimum.

How we work

Clarke Goldie & Partners have the knowledge and experience required to undertake the sophisticated modeling work required to estimate irrigation reliability and to size a dam. We also investigate a dam site thoroughly and design a dam that makes the best use of the naturally occurring materials at the site. We will tell you if we think the materials or the site are not suitable for dam construction. We will design a dam that is robust, safe and tolerant of unexpected or infrequent stresses. We will openly discuss any risks with you and will provide professional advice regarding both the engineering aspects of your dam as well as the resource management issues that you may face. We work systematically and logically. We make a point of looking at the “big picture”. When the time comes for construction we work closely with an experienced contractor with a track record of well sealed dams and a reputation for quality workmanship.