Infiltration measures how easily water moves vertically through the soil which can then indicate how flood-prone an area is. The purpose of the Infiltration Protocol is to determine the rate at which water soaks into the ground. This rate will change with time as the soil pore space fills with water. The three flow regimes students might encounter are unsaturated flow, saturated flow and ponding. Unsaturated flow is when the initial flow rate is high as the dry soil pores fill with water. Saturated flow is when the flow rate is steady and ponding is when the flow rate approaches zero and the ground becomes totally saturated. Students should practice this protocol before they take the official measurements so that they can become comfortable using the timer and making the measurements. Students can then push two cans into the soil and add water to both to a depth of at least 5 cm. The time it takes that water to drop a fixed 2 – 4 cm distance is recorded and the measurement is repeated.
How to Construct a Dual Ring Infiltrometer
Students can use a permanent marker to mark the top reference line on the inside of a coffee can. Students must then mark another line 20 – 40 mm below the top mark. These lines should be roughly 9 cm from the bottom of the can. Students can then record the width of the reference band and the diameter of the two bands.
Timing
Students can use a stopwatch or a watch with a second hand to time the water flow into the soil. When using a stopwatch, start it as water is first poured into the inner ring.
How to Measure Infiltration
Students must first clip vegetation and remove all loose organic cover over around the area. Students can then twist the smaller can into the soil to a depth of about 2 – 5 cm. A hammer may be used, but students must be careful not to break the can. Students must then measure the height above the ground level of the bottom and top of the band marked on the inside of the smaller can. Students must then pour water into both rings, maintaining a level in the outer ring that is equal to the level in the inner ring. Students will then pour water in the inner ring to just above the upper reference mark. Record the time it takes for the water level in the inner can to reach the lower reference mark. Repeat these steps until two consecutive intervals are within 10 second of one another. The infiltration rate is calculated by dividing the distance between the upper and lower reference rings by the interval time.
![Protocols [Image: Blue-Eyed Grass]](images/protocols_h.jpg)
