Water quality can be severely impacted by increased sediment transport, particularly agriculturally-dominated systems like those found in central Illinois. Many low-gradient sediment studies focus on the fine material transported in suspension. However, coarse-material transport can be equally important for understanding sediment loads to surficial reservoirs for local drinking water. To address a general gap in knowledge of coarse-sediment transport through agricultural streams, seasonal changes and watershed differences in sediment transport were examined in a low-gradient system. This was accomplished through the installation of bedload traps, scour-fill markers, and bank erosion pins at two streams, Six Mile Creek and Money Creek located in different, but geographically similar, watersheds. After record-breaking amounts of precipitation in the early summer, it was found the two streams transported different mass of sediment and different grain sizes during the spring and summer. Six Mile Creek transported large grains (maximum d84 = 17.25 mm) while Money Creek was dominated by finer material(d84 = 3.35 mm). Overall, the two watersheds have different slopes and areas, and one stream cuts through a ground moraine and the other an end moraine. Changes in slope, parent material, and watershed area may result in dramatically different sediment transport in two geographically similar watersheds. In a system where fine material erosion and transport is considered the dominant process, this study shows how important bedload transport can be to sediment transport models.
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