What is the age or stage of the Pecatonica River?
The Pecatonica river headwaters rise from the hills of southwestern Wisconsin, west of Cobb. The headwaters of the main branch do not come from a spring, but from runoff from the hills. This is typical of many rivers originating in the Driftless area. As the Pecatonica river continues its journey of 194 miles, it flows through rolling hills and valleys, farmlands, and wooded areas. It's journey ends when it flows into the Rock river near Rockton, Illinois. There are many tributaries that flow into the Pecatonica, including the Sugar river. The current is generally mild.
To determine any river's age, geologists primarily look at its landform characteristics like the steepness of its gradient, the presence of meanders, the size of its floodplain, the type of sediment it carries, and the overall shape of its valley, with older rivers typically having a flatter gradient, large meanders, wide floodplains, and a well-developed valley compared to young, steeper rivers.
The very interesting part of this study is that you will need to adjust your perception of time. In this study we aren’t evaluating the age compared to date. We are evaluating the stage based on where the river is in its length. Does this seem a bit weird... well, yes, it is. It’s like an evolution of a river so to speak, or the stage the river is in.
Young rivers, from a geological perspective, are typically in early stages of development, characterized by steep gradients and high-energy flow. These rivers are often found in mountainous or upland areas where the land is still being uplifted. The flow of water is fast and turbulent as it moves through narrow valleys, and the riverbed is usually rocky or uneven. The erosional power of the river is strong during this stage, as the water cuts deeply into the landscape, carving V-shaped valleys and often creating waterfalls or rapids. The water’s velocity is high enough to transport large sediments, such as rocks and boulders, downstream. These rivers are relatively straight.
Middle-aged rivers, often referred to as a mature rivers, are characterized by a more moderate gradient and a wider, flatter valley. By this stage, the river has slowed down, and the erosional focus shifts from vertical downcutting to lateral erosion, meaning the river starts to meander across its floodplain. This occurs because the land has become less steep, allowing the river to erode the banks more horizontally. The riverbed is typically made up of smaller sediments, like gravel and sand, which have been transported downstream over time. The moderate slope and energy of the river allow it to develop a more meandering course, forming oxbow lakes, natural levees, and broader floodplains. This shift happens due to a combination of factors, including the reduction in the energy of the flow and the relative maturity of the surrounding landscape.
Older rivers typically have a gentle slope with reduced erosive energy. The channels are generally broader, due to erosion.They tend to develope distinct curves and bends. These are known as meanders. Meanders can become so developed that the river cuts through the narrow neck, and makes a straight path . This leaves the old meander as a crescent shaped lake. These are called oxbow lakes. They are often surrounded by extensive floodplains with significant amounts of sediment deposited due to the slow flow.
Here is an illustration to help explain river stages:
Your mission today should you choose to accept it is to seek the viewpoint of the Pecatonica River at the access point where kayaks are launched and retrieved. Please send these answers to me.. Group answers are welcome. As you view the river answer these simple questions:
1. In your opinion what is the age of the river here?
2. Describe the banks and the flow at the time you are viewing it. How high are the top of the banks to the surface flow of the river?
Please share a photo of you at the top of the entrance to the ramp down to the river.