Week 7 Tutorial: The supply curve, and submitting Assignment 1

Week 7 tutorial — compute monthly roof yield from the enHealth formula, lay it against week 2's demand, and do the last pass on the measurement programme

22 April 2027

Time

90 minutes in the room, plus about 30 to tidy the output

Graded

Checkpoint 6 of 10, 2 % — a good-faith attempt at the output below

Due

5 pm, 23 April 2027

What this tutorial is for#

You know what the garden wants and what the household wants. Today you work out what the site actually produces, month by month — and you do the final pass on Assignment 1, which is due at 5 pm on Friday.

Story stage. The hinge. Assignment 1 is due at the end of this week. Monday’s lecture previewed what a measurement year at your home produced; the full specialist handover follows the deadline. Nothing you were shown on Monday changes what your register should say, and nothing you compute today is an observation of this house.

Open these first#

• Your workbook, sheet 2 (week 2’s demand curve) and sheet 3 (the register).
• Week 7’s lecture for the enHealth Appendix B formula and its worked example.
• Your home’s roof zones on its dossier — you need the guttered and connected areas, not the roof plan area.

If you missed week 6#

Bring whatever register you have. If you have none, the Assignment 1 brief lists the columns and the measurement primer supplies the instrument classes; two hours will get you a defensible draft. For the supply half use PRACTICE — Wattle Street: 219.8 m² of roof, 24.8 m² currently connected, a 5 kL tank. Invented round numbers.

The words this week uses#

• Runoff coefficient — the fraction of rain landing on a roof that reaches the tank. Not 1.0; the course uses 0.8 unless you argue otherwise.
• Initial loss — rain absorbed by the roof and gutter before anything runs. The enHealth method deducts about 2 mm per event.
• First flush — the first volume off the roof, diverted because it carries the dirt. Sized by a stated rule, in litres per square metre of roof.
• Supply curve — twelve monthly volumes in kL reaching storage. The mirror of week 2’s demand curve.

Do this#

1. Validate before you compute (15 minutes). Put 750 mm and 200 m² into your sheet and confirm it returns 116,160 L. Only then point it at your own site. A formula that reproduces the published worked example is a formula you can defend; one that does not is a formula you are about to build a tank on.

2. Then the twelve rows (30 minutes). Applying the formula to an annual total instead of month by month is the error that survives longest, because the answer looks plausible. It overstates a dry site badly: Alice Springs has months where rainfall is below the 2 mm initial loss and the correct contribution is zero, not negative.

Deduct the first flush, and name the rule you sized it by.

3. Then the overlay (20 minutes). Supply curve against demand curve, same axis, both in kilolitres. Most students see the gap for the first time here, and it is usually wider than they expected and in a different month.

4. Then the last pass on Assignment 1 (25 minutes). Run week 6’s two cross-checks again on the register: every row points at a decision, every decision has at least one row. Then check the total against $1,500 and write the headroom down. Ask the tutor about anything in the brief you are unsure of — this is the last session before it is due.

The output#

A twelve-row monthly supply curve for your site, in kilolitres, with the first flush deducted and every source named, laid beside week 2’s demand curve. Plus a measurement register ready to submit.

Check your own before you submit#

1. Does your sheet return 116,160 L for the published worked example?
2. Is runoff computed per month, never from the annual total?
3. Is any monthly contribution negative? It should be floored at zero.
4. Is the first-flush deduction there, with its sizing rule named?
5. Are supply and demand on the same axis in the same units?
6. Did you use the connected or guttered roof area rather than the roof plan area?
7. Is Assignment 1 finished, costed and ready for Friday?

Where it goes next#

Submit Assignment 1 by 5 pm Friday. From week 8 your inputs are the specialist findings rather than scoping estimates, and the gap between these two curves is week 9’s problem.

Back to week 7 overview