Module 4:

Materials

4.4 How much is needed?

4.4.7 Water

During early summer an average of 12.5mm of water is applied per m² each week of a football pitch that has an overall size of 7000m2.

[Note: 1 cubic metre of water contains 1,000 litres of water. If this is applied at a rate of 1mm per m², then the cubic metre would cover 1,000m².]

What is the total quantity of water that is used each week during this time?

1. Do you need some initial help with the calculations?

The note that was given with the question said that 1 cubic metre of water contains 1,000 litres of water. If this is applied at a rate of 1mm per m², then the cubic metre would cover 1,000m².

If this rate of 1mm per m² was applied over the entire pitch of 7,000m² then this would apply 7 cubic metres of ater, or 7,000 litres.

Hopefully this helps you do the remainder of the calculation.

2. Do you need some more help with the calculations?

If you haven't already done so you need to multiply the total 7 cubic metres (which is 7,000 litres), which is for 1mm per m² by the required amount per week of 12.5 mm to arricve at the correct answer.

Can you now work out the final quantity that is used each week?

3. Do you need some other help with the final calculation?

If the required amount was say 10mm per week, then it would be multiplying the 7,000 litre by 10, which would be 70,000. So we know the answer is going to be in that region because the actual required amount is only a little bit more (i.e. an extra 2.5mm).

So, we have 7,000 litres x 12.5 mm (per week).

The answer is therefore 87,500 litres per week.

There can be another way to arrive at a correct answer, but hopefully the above approach has been clear

1 The quantity of water required is going to be significantly influenced by the geographic location of the pitch, the construction and soil type, availability of irrigation equipment and supplies, and especially the prevailing weather conditions and in particular the amount of rainfall which is in excess or deficit of what the plant requires.

2 As a general guide, and if estimated during hotter, dry UK weather when no rainfall occurs a pitch might theoretically need the equivalent of 25mm of water (per m²) per week, assuming optimum water uptake. In practice, due to the way a grass plant adapts to varying soil moisture and temperature conditions, the actual amount of water that is needed will be less than this.

3 The grass plant will gradually reduce its leaf growth and extend its root growth to explore for more water resources, and reduce its overall water consumption, without much of a detrimental effect on the grass plant - at least not in the short term of a week or so.

4 However, as a water deficit continues then the grass plant will start to struggle and will eventually become dormant due to a lack of water, with no growth taking place. Keeping a suitable amount of soil moisture is the key as during warmer weather you don’t want to be putting excessive quantities of water on as most of this will just be used to create leaf growth, which is then mown of, so a sense of proportion needs to be taken here. Clearly a certain amount is also needed to ensure that a suitable quality of surface is maintained during the off season.

5 If we calculate the likely, but arguably unrealistic, maximum quantity of water needed per week, then for a full-sized pitch of 7,000m², this can equate to 25mm x 7,000m = 175m³ of water, or 175,000 litres of water.

6 A more realistic estimation might be no more than half this rate (i.e. 12.5mm), so about 87,500 litres of water. If this is evenly applied over 7-days, then this would mean having watering facilities that can supply and apply a minimum of 12,500 litres per day (or 2,753 gallons using the old imperial measures). Having this type of facility is usually essential for pitches that have what is called secondary drainage installed (for example sand-slits, or sand banding), or a specially constructed sand profile pitch. For many pitches the ability to apply this quantity of water will not be available.

Module progress: 82%

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