Holiday irrigation for a kura māra kai
Te Kura o Te Awa has a 30 m² māra kai on sandy soil. Water comes from a 200 L tank fed by the whare roof; there is no mains supply. Tamariki water by hand twice a week. The garden has 20 kūmara plants and 8 tomato plants. The school holiday is 3 weeks in January, and no one will be on site. The board has $250. Three options were priced: a drip line with battery timer, $180; six unglazed clay olla pots buried beside the rows, $120; and a 100 mm layer of bark mulch, $60. The caretaker notes that the timer's battery went flat in term 3 and nobody noticed for four days. The principal wants a system that survives the holiday and that tamariki can still explain and maintain.
1. Recommend a combination of options and justify it within the $250 budget.
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The timer alone is not reliable: the caretaker's evidence shows a flat battery went unnoticed for four days. The budget allows a combination: ollas ($120) plus mulch ($60) = $180, leaving $70. Add a simple battery timer only if it can be checked weekly; otherwise skip it.
Ollas deliver water slowly to the root zone and are hard to break unless struck; mulch reduces evaporation from sandy soil. For 20 kūmara and 8 tomatoes, place one olla per 4–5 plants (about 6 ollas) and mulch the full 30 m² to 100 mm. This combination is passive, so it does not depend on a battery or a tap. The trade-off is that ollas need filling before the holiday; a 200 L tank can fill them once and still leave reserve. Spend the remaining $70 on a second fill by the caretaker in week 2, or on shade cloth.
2. Identify the most likely failure mode over the three weeks and explain how you would reduce it.
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The most likely failure is not the ollas cracking; it is the tank running dry or the ollas being filled once and then drying out because no one checks them. The evidence is the timer battery failure-the school has a pattern of assuming a system is working.
Reduce it by: (1) filling the tank and all ollas on the last day of term and recording the date; (2) asking the caretaker to do one mid-holiday check in week 2, even if only to look at the tank level and lift one olla lid; (3) leaving a simple checklist and a spare 20 L container; (4) mulching heavily so the soil holds moisture. A second failure mode is a blocked olla lid or a cracked pot from a lawnmower; keep a spare olla and mark the garden edge. The judgement is to design for the human system, not just the hardware.
3. Explain how you would measure success after the holiday.
Read the worked answer
Measure success with evidence, not opinion. On the first day back, record: (1) number of surviving plants out of 28; (2) soil moisture at 100 mm depth at three points (dig a small hole and feel or weigh a sample); (3) tank level; (4) whether each olla still holds water; (5) any cracked pots. Compare with a control row watered by hand before the holiday if one exists.
Success would be at least 25 of 28 plants alive, no cracked ollas, and moist soil under mulch. Also ask tamariki to explain how the system works-if they cannot, the system is not maintainable. Record the results and the cost, then decide whether to keep, modify, or replace the setup for the next holiday.