Graphic organizer Grade 6 Engineering & Design
Refining a Silt Fence at the Rookhill Ridge Build Site
A grade 6 iteration log for a fictional construction site, tracking four silt fence trials against a clarity target and a standing target, with a completed exemplar.
Objectives
- Students will record what changed, what the data showed, and what to change next for four trials.
- Students will judge each trial against two written targets rather than against opinion.
- Students will propose a fifth trial that follows from the pattern in the log.
Vocabulary
Key words: silt fence, sediment, iteration, clarity, target
Teacher overview
This organizer is an iteration log, a table that holds one trial per row and pushes students to write the next change before they run it. The setting is a fictional school addition at Rookhill Ridge, where bare soil drains toward Jessamy Brook, and students record four trials of a model silt fence built in a sloped tray. The misconception this addresses is one that survives from elementary school: students think a silt fence is a filter that strains dirt out of water, so they expect finer fabric to always work better. A silt fence works mainly by ponding water so that heavy particles settle before the water seeps through, which is why burying the bottom edge and shortening the post spacing help more than changing the cloth.
Organizer
Rookhill Ridge is a fictional build site. A model of the slope sits in a tray, and 500 mL of muddy water is poured at the top of each trial. Two targets must both be met.
- Target 1, clarity: after the water passes the fence, a printed dot under a jar of the collected water must still be visible.
- Target 2, standing: the fence must still be upright, with no water running around either end.
Iteration log
| Trial | What we changed | What the data showed | Both targets met? | What we will change next, and why |
|---|---|---|---|---|
| 1 | Posts 30 cm apart, fabric laid flat on the soil | |||
| 2 | ||||
| 3 | ||||
| 4 |
Closing box
| Question | Your answer |
|---|---|
| Which single change helped the clarity reading the most? | |
| Which change helped the fence stay standing? | |
| Describe trial 5 and say what you expect it to show. |
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Completed Exemplar
| Trial | What we changed | What the data showed | Both targets met? | What we will change next, and why |
|---|---|---|---|---|
| 1 | Posts 30 cm apart, fabric laid flat on the soil | Water ran under the fabric in about 4 seconds. The collected water hid the dot. | No, neither target | Bury the bottom edge, because the water is going under the fence instead of ponding behind it. |
| 2 | Bottom edge buried 3 cm in the soil | Water ponded for about 20 seconds. The dot was faintly visible. The fabric bowed and one post leaned. | Clarity yes, standing no | Move the posts closer together, because the bowed fabric shows the fence cannot hold the pond it just made. |
| 3 | Posts moved to 15 cm apart, bottom edge still buried | Pond held. The dot was clearly visible. Water ran around the left end of the fence. | Clarity yes, standing no | Turn the ends uphill, because water is escaping around the side rather than through the fabric. |
| 4 | Both ends turned uphill in a short hook | Pond held for the full pour. The dot was clearly visible. No flow around either end. | Yes, both targets | Keep this design and test it with a larger pour, because a real storm delivers more water than 500 mL. |
| Question | Exemplar answer |
|---|---|
| Which single change helped the clarity reading the most? | Burying the bottom edge in trial 2. The dot went from hidden to faintly visible as soon as the water had to pond instead of slipping underneath. |
| Which change helped the fence stay standing? | Moving the posts from 30 cm to 15 cm apart in trial 3, which cut the bowing that had leaned a post in trial 2. |
| Describe trial 5 and say what you expect it to show. | Repeat the trial 4 design with a 1,000 mL pour. I expect the pond to rise higher and the fence to hold, because the failures we fixed were leaking underneath, bowing between the posts, and leaking around the ends, not the strength of the fabric. |
Differentiation
Support
Fill in the "what we changed" column for all four trials in advance so these students record only the data and the next step. Provide the sentence frame "The water ____, so next we will ____ because ____."
Extension
Have students add a cost column in which each post is worth one token and each meter of buried fabric is worth two tokens, then argue in writing whether the trial 4 design is worth the extra tokens it spends compared with trial 3.
ELL supports
Provide a labeled side-view drawing of a silt fence showing the post, the fabric, the buried edge, and the pond of water behind it. Post the words "pond," "seep," "bow," and "hook" with a small picture beside each. Allow the log to be completed with short phrases.
Extensions
Have students look for a silt fence near any construction work in their own community, sketch what they see from the sidewalk, and mark on the sketch whether the ends are turned uphill and whether the bottom edge appears to be buried.