I collected soil samples from the local area, to include riverbed samples. I poured a set amount of water on each sample. I controlled the amount of time each soil was exposed to water. The water left on the top of the soil was poured off and measured as "run-off." The remainder of the water was calculated as absorbed.
Results showed that the higher the gravel content of a soil, the higher is its absoption; less water was collected as run-off in gravel samples. The higher the silt content of a soil, the lower is its absorption; more water was collected as run-off.
Results were not exactly what I'd expected. The sands in the riverbed were not the most absorbent soils in my trials. I had not given enough attention to gravel when I formulated my hypothesis. Gravel is the most absorbent soil material. However, it is not in great supply in riverbed samples because riverbeds experience greater erosion over time. As soil texture increases in size, so does its ability to absorb water. Because we depend on underground water sources in our desert, I thought that the sands in the riverbed would and act to absorb water quickly, allowing it to pass into underground aquifers. While the riverbed soil was not the fastest at absorbing water, neither was it the slowest. From my research, I also learned that this could be due in part to a natural filtering capability of graded sands. It would be necessary to have a moderate absorption rate to allow filtering to occur while maintaining water absorbency.
This project investigates as a soil increases in particle size, so does its ability to absorb water.
Science Fair Project done By Elizabeth Avalos