Geology: Rivers
The borders of 100 Acres: The Virginia B. Fairbanks Art & Nature Park are defined primarily by two bodies of water—the White River and the canal. Have you ever walked along the path at the north end of the Park where the river bends to the west and wondered why it does that, rather than continuing south parallel to the canal? In the past, before the canal was built, the river might have done just that. However, rivers and the topology of the land change each other over time.
About 17,000 years ago, when the climate was much cooler in this region, the enormous Laurentide glacial ice sheet grew southwest into Indiana. As the massive glacier scraped along the terrain, it carved out the beginnings of the watershed that now feeds the White River. It then melted over a period of many centuries.
Fluvial Processes
The movement of glaciers determined the general path of the White River, but a river also affects the landscape that it runs though by eroding, suspending, transporting and depositing material. The way in which a river does this is dependent on the speed of the current within the stream. In places where the water is moving quickly, more erosion occurs and the river can suspend larger material. In places where the water moves slowly, suspended rocky material, also called alluvium, is deposited on the riverbed.
Over time, a straight stream develops meanders as the high velocity flow on the exterior of curves cuts away at the bank and the eroded material is deposited on point bars in the slow moving interiors of the curves. When dams slow the current of a river, sand or gravel bars can develop in the middle of a river as well, as can be seen in the White River south of 38th Street.
The image below on the left illustrates the velocity measurements taken in the White River by the USGS. The red regions indicate the areas where water is moving the fastest, while the blue regions mark the slowest moving currents. In the image on the right, color indicates depth, and various features created by the flow of the river are annotated.
