Worked example
Two equal slopes receive 40 L of rainfall. A covered slope produces 31 L of collected runoff. A loose soil slope produces 18 L, and sensors below the surface get wetter. The moisture reading supports infiltration in the soil. The runoff difference alone cannot show the exact infiltration amount without knowing other paths.
Contrast and common error
Pervious soil can still produce substantial runoff if it is already wet or rainfall exceeds the rate at which water can enter. Match rainfall, slope and surface area before attributing a difference to cover. Check for pooling and evaporation when using a water balance.
Transfer check
A plot receives 30 L. It releases 17 L as runoff and 3 L evaporates, with no pooling. Estimate infiltration. Check: 30 − 17 − 3 = 10 L in this model.
Try it, then explain it.
Complete a short set without looking at the example. After each answer, explain which evidence or rule supports your decision and why the alternatives do not fit.
Sources & authorship
Original OpenExam explanations and examples. References support the concepts; they are not the source of copied questions. Independent educator review is pending.
USGS Surface Runoff and the Water Cycle