Sand Land

Class Setting
The students are divided into groups of 4-5. The instructor has prepared one sandbox for every group. It is better if the sandboxes are prepared but kept aside, so that the students do not get distracted. The instructor has one sandbox to illustrate how it works. It takes 1 1/2 hours to complete the two activities described in this module. A modification, described below, allows the instructor to complete the lesson in 1 hour.

 

Script of class interaction

Recap the previous discussion of watersheds. (Hand-Land)

Introduce the water cycle drawing.
click to enlarge


Introduce the concept of a model.

Explain how this model relates to a watershed and the water cycle.

Where does rain water come from?

Where does rainwater go?

Are you related to the water cycle? If so how?

Are trees and lawns related to the water cycle? If so how?

 
Display materials
Overhead projection
Watershed as a macrocosm
Watershed as a microcosm
Water cycle
Maps

 

Where does rain water go to?

How does rainwater effect the soil?

What happens to water and other liquids, once underground?

How do humans change the affects of rain on soil?

Activities

Activity 1: Understanding the model
Overview

  • Fill the 1/8"-hole, drip container with water to about 4.5 inches high, covering the hole with your finger.

  • Carefully place the container on the ruler, which spans the back of the Sand-Land pan's rim.

  • Remove your finger to let water drip for 1.5 minutes.
    Water will flow over and through the soil (forming stream-like erosion patterns) and eventually through the hole of the pan into the collection bucket.
    After 1.5 minutes, cover the hole with your finger, mark the height of the water, and remove the drip container.

Notes: The higher the level of the water in the drip container, the faster the water will flow. It is a good idea to make a separate measurement of how quickly water flows out. It helps to fill the drip container to the brim and mark in advance the level of water at 1 and 1.5 minutes. By repeating the experiment with the 3/16"-hole drip container, different erosion patterns can be observed as water flows faster.

  • Introduce the Sand-Land Model concept and materials to the students.
  • Have each team of students set the pan at an angle using the blocks to simulate a slope condition.
  • Explain to students how to they will model "rain" by letting water drip from a container onto the soil slope in the sandbox.
  • Explain that the 1/8" hole simulates a smaller rainstorm than the 3/16" hole.
  • Ask each group to balance the drip container on the pan's rim and the ruler being careful to center it on the marks made previously on the ruler.

Activity 2: Developing a hypothesis from previous experience
Ask students to make a drawing of what is going to happen when rain starts falling on our Sand-Land Model

Where is the water going to go?

What is the water going to do to the sand?

Think about the relationships that may exist in our model: soil versus water, static vs. dynamic, straight vs. curved, additive vs. subtract, constructive vs. destructive, made by humans vs. made by nature.

 

Activity 3: Investigation, running and observing the model
  • Explain how each group will simulate rain and assign specific roles to team members (a "cloud", a timer and two or three observers).
  • The "cloud" rains for 1.5 minutes (places the drip container on the supports and removes finger from the hole), until the "timer" tells the cloud to cover the hole. Meanwhile, the observers are paying attention to what is happening with the soil and the flowing water.
  • The "timer" keeps time until no more water drips from the container (when the drops slow down significantly, say until two consecutive drops are separated by 2 minutes).
 
 
Activity 4: Evaluating our hypothesis and investigation
  • Ask students to mark the boundaries of the existing stream channel with 5-6 toothpicks.
  • Ask students to draw what actually happened on the tracing paper on top of previous sketch in the activity card.
    click to enlarge

  • Ask students to write a brief description (3-4 sentences) of their observations in their notebooks.
  • Ask students to place the "sandbox" in the water cycle, by marking the components of that we are modeling on the water cycle schematic.
  • Have teams share their observations during class discussion, prompted by questions such as:

How did the water move?

Did it move any different than what your sketch?

What happen to the soil?

How is our Sand-Land model different than the real world?

Are the differences found in the soil?

Are the differences found in the way the water moves? (tug question: water cycle)

 

Science Prerequisites
Students have already discussed the watershed concept in class. Students are familiar with the idea of "modeling" aspects of real phenomena with simple physical experiments.

Science Themes
It takes time for phenomena to evolve in nature. Human activities can go on for quite some time before we notice their impact on the environment (e.g., air pollution, groundwater contamination, global warming).