The Mountain Runoff Cover Test

Rowan's Journal at Silver Fir Station

Rowan helps take measurements at Silver Fir weather station, high above a mountain town. Below the station, workers are repairing a short section of a water-pipeline access path. Loose soil from the repair area could wash downhill toward the town reservoir. The town water team wants to protect the reservoir from extra sediment. Sediment is soil carried by moving water. Too much sediment can make water cloudy and can collect in a reservoir. The team is considering a fiber mat that rests over the soil.

For a small test, workers prepared two similar runoff trays below the repair area. Each tray held the same kind and amount of soil and had the same slope. One tray had the fiber mat, and the other tray had bare soil. After rain, the team collected runoff from each tray and dried and weighed the sediment. Rowan recorded weather conditions at the station. The trays were reset in the same way before each new rain event.

The records below show four rain events recorded over several days. The sediment amounts came from the two trays, not from the whole reservoir. The town water team will use these records with other information before choosing a larger protection plan.

Each rain event is listed below with its rainfall, highest wind, sediment from the bare tray and sediment from the mat tray. Event 1: 8 mm of rain, highest wind 12 km/h, 18 g from the bare tray, 7 g from the mat tray. Event 2: 15 mm of rain, highest wind 20 km/h, 31 g from the bare tray, 11 g from the mat tray. Event 3: 4 mm of rain, highest wind 8 km/h, 9 g from the bare tray, 4 g from the mat tray. Event 4: 22 mm of rain, highest wind 26 km/h, 45 g from the bare tray, 16 g from the mat tray.