Lesson plan Grade 7 Engineering & Design
Meridian Bluffs Recharge Basin: Designing for Drought Resilience
Students design a managed aquifer recharge basin for a fictional town, choosing a site and shape that refill a falling aquifer within real constraints.
Objectives
- Students will design a managed aquifer recharge basin by choosing a site and shape that match soil and land limits.
- Students will justify their design against criteria and constraints for refilling a drought-stressed aquifer.
Vocabulary
- Aquifer
- An aquifer is an underground layer of rock, sand, or gravel that holds water in the tiny spaces between its grains. Wells reach down into aquifers to bring water up to the surface.
- Recharge
- Recharge is water soaking down through the ground to refill an aquifer, the way rain refills an underground sponge. Aquifers stay healthy only if recharge keeps up with pumping.
- Infiltration
- Infiltration is when rain or melted snow soaks down into the soil instead of flowing away across the top of it. Water that infiltrates can feed plant roots or keep sinking to become groundwater.
- Drought
- A long stretch of drier-than-normal weather that leaves too little water for people, farms, and nature. Droughts build slowly and can last for years.
Also: constraint
Teacher overview
Meridian Bluffs is a fictional town that pumps its drinking water from an aquifer, a layer of water-filled sand and gravel underground. During a long drought the town has been pumping faster than rain can refill the aquifer, so the water level underground keeps dropping. In this lesson students design a managed aquifer recharge basin: a shallow pond that catches stormwater in the wet season and lets it soak down to refill the aquifer. The lesson turns on a design idea students often miss: a recharge basin only works where the soil actually lets water soak through, so a site with a clay bottom, which blocks water, would fail no matter how large the basin is.
Procedure
Before class: No map is printed with this lesson. Draw a simple site map showing the river, downtown, and the neighborhood, with the three candidate sites labeled by soil type, and copy it for each group.
Hook (5 min): Ask students to imagine a sponge that people keep squeezing water out of but rarely wet again. Connect it to the aquifer under Meridian Bluffs, which is being pumped faster than the rain refills it. Ask: "How could the town put water back into the ground on purpose?"
Background (10 min): Explain that less than 1 percent of Earth's water is fresh and easy to reach, and that groundwater can sit underground for a very long time before it is used. Introduce managed aquifer recharge: capturing extra water in the wet season and spreading it in a shallow basin so it soaks down. Show that sandy or gravelly ground lets water infiltrate quickly, while clay blocks it.
Model the design move (10 min): Project the site map with three candidate sites: a sandy field near the river, a clay-bottomed low spot downtown, and a gravel bench above the neighborhood. Think aloud about the clay site: it has room, but water will not soak through, so it fails the most important criterion. Rule it out on the board and explain why.
Group design work (15 min): In groups of three or four, students complete the Student Handout. They pick a site, sketch a basin shape, and write the design's criteria and constraints. Circulate and ask each group why their chosen site's soil will let water infiltrate.
Share (5 min): One or two groups present their chosen site and one constraint they had to design around. The class checks whether each plan picked a site where water can actually soak in.
Closure and exit ticket (5 min): Show a fourth surprise site with a clay bottom but plenty of space, and ask for a thumbs up if it would make a good recharge basin and thumbs down if it would not. The class understands the key constraint if at least 80 percent give a thumbs down and can say the clay blocks infiltration.
Student Handout
Your team is designing a managed aquifer recharge basin for the fictional town of Meridian Bluffs. The basin must catch stormwater in the wet season and let it soak down to refill the aquifer. Your site map shows three candidate sites: a sandy field near the river, a clay-bottomed low spot downtown, and a gravel bench above the neighborhood.
Choose one of the three sites for your recharge basin. Write one or two sentences explaining why the soil at your site will let water soak in.
On the map, sketch the shape of your basin. Explain why you chose that shape and size for the space you have.
Write two criteria your basin must meet (what a successful design must do) and two constraints it must work within (limits you cannot change).
Name one problem that could happen if the basin holds water too long or overflows, and describe one design choice that would prevent it.
Explain why filling the basin during the wet season helps the town during the next drought, using the idea that the aquifer stores water underground for a long time.
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Answer Key
Answer: Accept the sandy field or the gravel bench, with a reason tied to soil that lets water infiltrate quickly. The clay-bottomed downtown site should be rejected because clay blocks water from soaking through.
Answer: Accept any reasonable basin shape that fits the chosen site, with a justification. Strong answers note that a wider, shallower basin spreads water over more ground so it soaks in faster.
Answer: Accept two workable criteria (for example, "refill a set amount of the aquifer each wet season" and "keep water from flooding nearby homes") and two real constraints (for example, "limited land," "soil must let water soak in," or "a fixed budget").
Answer: Accept answers naming a real risk, such as flooding neighbors, breeding mosquitoes, or water evaporating before it soaks in, paired with a prevention choice such as an overflow outlet, a maximum depth, or a faster-draining site.
Answer: Accept any answer explaining that water added underground in the wet season stays stored in the aquifer for a long time, so it is still there to pump during the next dry stretch when little rain falls.
Differentiation
Support
Give these students the clay site already crossed out with a short note ("clay blocks water"), so they choose between the two workable sites. Provide a simple soil key showing which materials let water soak in and which do not.
Extension
Have students compare the sandy field and the gravel bench in more detail, listing one advantage and one drawback of each (such as distance from the river or nearness to homes), and defend a final choice using their criteria.
ELL supports
Provide a labeled cross-section picture showing rain soaking down through sand into an aquifer, with "recharge," "infiltration," and "aquifer" marked. Allow students to answer items 1 and 3 with short phrases and to use the diagram to explain their thinking.