Effects of urbanization on a small perennial stream: Second Creek in Knoxville, Tennessee

Little is known about the coarse load carried by streams in urban areas or the length of time needed for stream channel adjustments to urban conditions. In this study, I examine the history of urbanization in the basin of Second Creek, the status of the channel, and the sediment load of the creek in recent years.; Second Creek is a small perennial stream whose 18.6 km2 drainage basin is almost entirely contained within the City of Knoxville, Tennessee. Almost all of the drainage basin was developed more than 40 years ago, and is now urban and suburban in character.; If a channel is adjusted to present-day hydrologic and sediment load regimes, little net deposition or erosion is expected to take place, yet my examination of the channel of Second Creek reveals that both deposition and erosion have occurred in recent decades. Sediment deposits in the channel in several reaches are about 30 years old, but I find few signs of present-day deposition. Rather than deposition, much of the channel (where not lined with concrete or thick riprap) shows signs of recent erosion. Therefore, channel erosion appears to have replaced deposition as the dominant process in the last few years. From this I conclude that Second Creek has not adjusted to the urban conditions of its drainage basin, and that channel enlargement is occurring.; Impervious surfaces and lawns cover most potentially erodible soil in the drainage basin, so the suspended load is expected to be low, yet my measurements show it to be high. Channel erosion is likely to be contributing suspended sediment and coarse particles to the stream. Coarse particles are common in the streambed alluvium, yet my calculations of the volume of sediment in the reservoir at the stream outlet show the amount of bedload carried by the creek in the last 50 years to be low. The numbers and/or sizes of coarse anthropogenic particles are sufficient at some sites to alter mean particle diameters and, therefore, stream dynamics. Such particles should not be ignored in fluvial studies.