Fill slope erosion where the culvert was blocked with soil and debris washed downstream by the record December rains.
December 2015 saw some serious rainfall and storm events, far exceeding the previous record for precipitation in that month, and with that record rainfall came some major challenges to forest road infrastructure in northwest Oregon. During the most intense periods of rainfall, small landslides were a common occurrence on steep slopes, particularly where high cut-banks along roads became saturated. As small headwater streams became raging torrents, they sometimes overwhelmed culverts at stream crossings, particularly where soil and rock were being carried downstream and filling catch-basins. In such situations, the downhill side of the road fill is very vulnerable to erosion as the stream is flowing across the road and finding its way down the other side. Seen here is a picture of such a situation in the North Tualatin Mountains, west of Portland.
Of course, no one knows what the rest of the winter and spring holds in store for us, but the break in heavy rain we are experiencing now (minus the snow and ice) presents a good opportunity to get out and survey forest roads and culverts for damage and assess whether maintenance is needed to keep them functioning properly for the remainder of our rainy season.