8 August 1997


By Jessica Buss

COVERING cattle yards may be cheaper than storing water when rainfall is above 1000mm (40in), according to Genus Managements buildings specialist Paul Henman.

However, the individual system and yard area must be taken into account to justify the best option for investment, he stresses. And storage may not be needed on farms that can spread dirty water through the winter without risking run-off into water courses.

"But producers wishing to store dirty water to protect nutrients, or who are unable to spread it in winter, should look at roofing as an alternative to collecting extra water," he says.

"Start by working out the yard area and the winter rainfall on it," suggests Mr Henman. For example, a 500sq m (600sq yd) open yard in a 1000mm (40in) rainfall area may have 600mm (24in) of rain in winter; a 2.75m (9ft) deep store would, therefore, need to hold 446cu m (16,500cu ft) of rainwater.

Building an earth lagoon to store this amount of dirty water would cost about £6700, but a steel tank or concrete pit could cost £13,400. This gives annual storage costs of £1090 and £1565 respectively at 10% annual interest over 20 years.

Spreading based on typical contractors costs would add a further £660 to the annual cost. This equates to an annual storage and disposal cost of £1750 and £2225 for the two storage options.

Covering the 500sq m yard could cost as little as £11,000 if a simple lean-to is constructed using farm labour. However, a multi-span building, with walls and put up using builders, could increase the cost to £32,500. Therefore, the annual cost, including interest over 20 years, could be from £1793 for the lean-to to £5298.

When winter rainfall is 600mm (24in) the cost of storage would be similar to roofing, but with higher rainfall or higher storage costs roofing works out cheaper, according to Mr Henman.

"In practice, when dirty water is stored in a lagoon it may not be expensive to extend it, but there is also the cost of spreading to take into account."

There are additional benefits from roofing yards, claims Mr Henman. Feed spoilage in high rainfall areas can be costly and cows eat more of a drier feed. Roofs also add to cow and stockman comfort, but it is difficult to quantify these benefits, he adds.

Collecting rainwater could also reduce costs for producers charged by meter for water.

Mr Henman claims rainwater can be suitable for washing yards and parlours, and for cow drinking water although it is best to run it through a filtration system first.

On newer dairy units it can be easy to collect rainwater and pump it to a header tank, and it would be worth costing out a collection system.

But beware of the contamination risks, such as from bird muck on building roofs, says Mr Henman. &#42

Producers wishing to store dirty water and not spread in winter should consider roofing as an alternative to collecting the extra water, says Paul Henman.

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