Rainfall Simulator Project

OVERVIEW OF THE RAINFALL SIMULATOR PRESENTATION

EMBARRAS RIVER MANAGEMENT ASSOCIATION

The Rainfall Simulator Unit (RSU) is designed to show what happens to topsoil on cropland fields or construction sites during rainstorms. It demonstrates the benefits of crop residue management in protecting the topsoil during rainstorms. The simulator shows the results of a 2-3 inch rainstorm in approximately 15-20 minutes. A rainstorm of this intensity has the potential of causing excessive runoff with severe soil loss.

The River Simulator Manual can be viewed or downloaded as a Micorosft Word document (143 MB file!) or Adobe PDF file (119 MB file). Please note the large size of these files since they contain many images.

Up to five soil trays can be placed below the oscillating raindrop nozzle, which is special-sized to create a droplet very close to what occurs with a natural rainstorm. Dry, loose soil is poured and leveled in the 10”x 20”x 2.5” trays, with varying levels of crop residue then placed on the soil surface. The five soil trays can be set at up to an 11 percent slope, which would be considered a steep slope in cropland conditions. The percent slope is how much elevation rise there is in 100 feet. In this example, it would be comparable to a crop field with 11 foot of rise in elevation in 100 feet of distance.

The crop residue in the soil trays can be wheat straw, soybean stubble, or corn stalks. The residue is placed on the soil surface and not incorporated into the soil. Incorporation would not add additional protective benefit. The residue will provide the same protective benefit for wind and water erosion just lying on the soil surface.

The soil trays exhibit various levels of crop residue. The simulator shows the protective benefit of crop residue is in direct proportion to the level of residue covering the soil surface, the more crop residue, the less soil loss. A photograph of a raindrop, magnified approximately 50 times, is included with the traveling demonstration. The raindrop photograph shows the explosive energy released as a raindrop hits a bare soil surface. A straight down raindrop travels at approximately 15 to 20 miles per hour, depending on the size of the raindrop, and separates the soil particles upon impact with bare ground. The loosened soil particles are then pulled downhill by the force of gravity, resulting in soil erosion. When a raindrop hits a piece of crop residue, the explosive energy is absorbed by the residue, which leaves the soil particles in place. The rainwater then runs off the residue, percolates into the soil profile and is stored for future crop needs.

Many people believe that soil crusting occurs after a rainstorm has ended and the sun comes out baking the ground. But in reality, soil crusting occurs in the first few minutes of a rainstorm. Raindrops hitting bare ground will separate soil particles and form a sealed barrier, or crust, which greatly slows the percolation of water into the soil profile. This can be demonstrated with the rainfall simulator. The 0% residue or bare soil tray will crust over in the first few minutes of the rainfall, simulating what happens to the soil in real field conditions. Soil crusting does not allow the water to infiltrate into the soil but rather forces the water to run off the field, carrying soil particles loosened by the raindrops’ miniature explosions. This can be proved at the end of the demonstration by turning over the soil trays that have 0% cover and 100% cover. The soil in the 0% cover tray will only be wet approximately half way down, while the remaining soil in the bottom of the 2.5” tray is dry. In contrast, the soil in the 100% cover tray will be completely saturated with water to the bottom of the tray. The jars placed at the bottom of each tray also confirm this. While the receiving jar for the 0% cover tray contains a large amount of sediment-laden water, the receiving jar for the 100% cover tray contains much less water, and this water is virtually free of any sediment.

Fields with terraces, waterways, and crop residue provide the best protection against water erosion. The residue protects the soil from the force of the raindrops. The terraces walk the rain water slowly off the field to a grassed waterway. These grass strips at the bottom of cropland fields or next to streams are very effective in intercepting or trapping soil sediment, organics, pesticides and other potential pollutants before they reach a body of water. The protective water quality benefits of grass buffer strips can also be demonstrated with the simulator. A soil tray with sod can be included in the demonstration to show the value of filter strips. After a rainfall cycle has been completed, it is quite noticeable that the collection jar under the sod tray contains much less water, and that the water is very clean and clear. Utilizing the rainfall simulator for conservation education events can bring about better crop residue management on the land that will make a difference for better soil and water quality.

Presentation Outline
A very beneficial aspect of the Rainfall Simulator is that it can be utilized to demonstrate a variety of environmental scenarios. Presentations can be tailored to deliver focused agendas and share specific conservation and environmental information. Following is the basic presentation agenda that ERMA has been utilizing. While the degree and depth of information delivered during a presentation varies depending on the circumstances of the event, the allotted time, and the targeted audience, this basic format is still followed and the key points addressed.

Explanation of a Rainfall Simulator: What it is, how it works, and how it is utilized.
Overview of the demonstration and lesson.
Define and discuss watersheds.
Discuss the vital importance of protecting our drinking water and valuable top soil. Define and discuss wells, aquifers, and the ground water table.
Operate rainfall simulator long enough that water run-off from the trays to the jars begins. Discuss what is happening with each tray and jar as the rain falls.
Refer to photo of raindrop impacting bare soil. Discuss the fact that a raindrop falls out of the sky at 15 to 20 mph, and the effect this has on the soil. Define soil erosion, nutrient runoff, and stream sedimentation. (Point out all of the soil that has splashed onto the sign and framework around the bare soil tray, while the signs and framework around the 100% Crop Residue and Grass trays are clean.) Discuss how conservation practices reduce water and nutrient run-off, soil erosion, and stream sedimentation, thereby protecting the quality and quantity of our drinking water and preserving the top soil.
Explain what each of the five trays represents.

Tray 1: Bare, Unprotected Soil. Represents conventional tillage or a bare construction site. Exhibits tremendous water run-off and soil erosion. Define and discuss conventional tillage or clean till farming.
Tray 2: 30% Crop Residue. Represents minimum till farming. Exhibits a reduction in water run-off and soil erosion over the bare soil tray. Define and discuss conservation tillage and minimum tillage.
Tray 3: 100% Crop Residue. Represents no-till farming. Protects water quality and quantity. Demonstrates a dramatic reduction in water run-off and soil erosion. Define and discuss no-till farming.
Tray 4: Grass. Represents a grass waterway, field border or filter strip. Protects water quality and quantity. Demonstrates a tremendous reduction in water run-off and soil erosion. Define and discuss filter strips and buffers.
Tray 5: Urban. Represents impermeable surfaces such as concrete and asphalt streets, parking lots and walks found in an urban setting. Exhibits 100% water run-off. Demonstrates the problems of flooding and pollution. Define and discuss urban pollution, its causes and sources. Discuss solutions such as urban detention ponds, water treatment, proper waste disposal, proper application of lawn fertilizers, etc.

Discuss benefits conservation tillage has for wildlife habitat. Show picture of pheasant in bare field vs. no-till field of corn stalks. Define “Daily Calorie Intake”.
Elaborate on our environmental responsibility and how we live in a global community.
Question how nutrient run-off from Illinois could affect a fisherman’s livelihood in the Gulf of Mexico. Discuss the geography of the local land and rivers and where the drainage flows. Define and discuss eutrophication and hypoxia, and the consequences for the Gulf of Mexico.
Lesson summary and affirmation of our environmental responsibility.

Photographs from presentations

2003

2004

RSU Handout

Last updated 2 March 2005