Graphic organizer Grade 12 Engineering & Design
Fettleworth Orchard Irrigation: A Weighted Decision Matrix
A grade 12 organizer where students set criteria, assign weights, and score solid-set sprinklers against subsurface drip for a fictional orchard facing a pumping limit.
Objectives
- Students will state a measurable criterion and a target for each factor in an irrigation decision.
- Students will assign weights that reflect a stated constraint rather than personal preference.
- Students will total weighted scores for two systems and identify the criterion that most changes the outcome.
Vocabulary
Key words: weighted decision matrix, criterion, constraint, application uniformity, subsurface drip, frost protection
Teacher overview
This organizer is a two-part decision frame: a criteria table that forces every factor to have a measurement and a target, followed by a weighted matrix that turns those criteria into a comparable score for two systems. The setting is the fictional Fettleworth Orchard, 140 acres of apples on the fictional Bramthwaite Brook, where the groundwater district has capped the orchard's seasonal withdrawal and the owner is deciding whether to keep solid-set overhead sprinklers or convert to subsurface drip. The misconception this organizer exists to expose is that drip irrigation is simply the better technology. Drip applies water far more precisely, yet it cannot protect blossoms from a spring frost and it cannot flush salts down through the root zone, so a matrix that weights only water use will recommend a system the orchard cannot actually run alone.
Organizer
Complete both tables for the fictional orchard. Weights and ratings each run from 1 to 5, and a weighted score is the weight times the rating.
| Criterion | Why it matters to this orchard | How it is measured | Constraint or target |
|---|---|---|---|
| Water applied per season | |||
| Capital cost of conversion | |||
| Pumping energy per season | |||
| Application uniformity | |||
| Maintenance and clogging risk | |||
| Frost protection capability | |||
| Labor hours per week |
| Criterion | Weight | Sprinkler rating | Drip rating | Weighted sprinkler | Weighted drip |
|---|---|---|---|---|---|
| Water applied per season | |||||
| Capital cost of conversion | |||||
| Pumping energy per season | |||||
| Application uniformity | |||||
| Maintenance and clogging risk | |||||
| Frost protection capability | |||||
| Labor hours per week | |||||
| Total |
Recommendation: state which system the totals favor, then name the one criterion that would flip the result if its weight changed.
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Completed Exemplar
The entries below use the fictional Fettleworth Orchard's constraints.
| Criterion | Why it matters to this orchard | How it is measured | Constraint or target |
|---|---|---|---|
| Water applied per season | The groundwater district caps what the orchard may withdraw each season | Acre-feet pumped, read from the well meter | Stay at or under the district cap every season |
| Capital cost of conversion | The owner is financing the change over a fixed loan term | Installed cost per acre | Keep total installed cost within the approved loan |
| Pumping energy per season | Drip runs at lower pressure, which lowers the power bill | Kilowatt-hours per acre-foot delivered | Reduce energy per acre-foot compared with the current system |
| Application uniformity | Uneven water leaves parts of the block over-watered and parts stressed | Distribution uniformity from a catch-can or emitter flow test | Reach the uniformity the district requires for a conservation credit |
| Maintenance and clogging risk | Emitters plug on iron and fine sediment from this well | Emitter flow loss between flushes | No more than one plugged emitter per 100 checked |
| Frost protection capability | Spring frost can take an entire bloom in one night | Degrees of protection the system can provide overhead | Keep a method of frost protection available every spring |
| Labor hours per week | The orchard runs with a small crew during harvest | Crew hours spent running and repairing lines | Reduce weekly crew hours spent on irrigation |
| Criterion | Weight | Sprinkler rating | Drip rating | Weighted sprinkler | Weighted drip |
|---|---|---|---|---|---|
| Water applied per season | 5 | 2 | 5 | 10 | 25 |
| Capital cost of conversion | 4 | 5 | 2 | 20 | 8 |
| Pumping energy per season | 3 | 2 | 4 | 6 | 12 |
| Application uniformity | 4 | 3 | 5 | 12 | 20 |
| Maintenance and clogging risk | 3 | 4 | 2 | 12 | 6 |
| Frost protection capability | 2 | 5 | 1 | 10 | 2 |
| Labor hours per week | 3 | 2 | 4 | 6 | 12 |
| Total | 76 | 85 |
Recommendation: the totals favor subsurface drip, 85 to 76, because the heaviest weight sits on the seasonal withdrawal the district has capped. Frost protection is the criterion that would flip the decision. It carries a weight of only 2 here, yet drip cannot supply it at all, so raising that weight to 5 moves the totals to 91 for sprinklers against 88 for drip and reverses the recommendation. The honest answer for this orchard is a combined system, with drip for the season and a retained sprinkler set for frost nights.
Differentiation
Support
Pre-fill the weight column for all seven rows at the fictional orchard so students begin by rating the two systems rather than by negotiating priorities. Provide the first row completed across both tables as a worked model, and let students verify the arithmetic of the weighted score before moving on.
Extension
Ask students to add two criteria the orchard's neighbors would raise, such as effects on the fictional Bramthwaite Brook's late-summer flow or the cost of removing plastic drip tubing at end of life, assign weights they can defend, and report how the totals move.
ELL supports
Provide a side-by-side sketch of a solid-set overhead sprinkler system and a subsurface drip line with the water path drawn on each, so "uniformity" and "clogging" attach to something visible. Offer sentence frames for the recommendation: "The totals favor ___ because the largest weight is on ___," and "The result would change if ___ were weighted higher."
Extensions
Suppose the fictional groundwater district offers the orchard a rebate that covers a third of the conversion cost, but only if the orchard removes the sprinkler set entirely. Ask students to rescore the capital cost and frost protection rows under that condition and to write two sentences on whether a rebate that forbids a backup system is a good deal for this orchard.