No, it increases as there is more water in the channel.
Because the Width and Depth both increase downstream. This means the wetted perimeter will also increase.
The greater the wetted perimeter, the more friction the water encounters with the bed and sides. This reduces the speed of the river.
Hydraulic Mean Radius = Cross sectional area of conduit divided by the inside (wetted) perimeter.
The Bradshaw model is a geographical model made in 1978, by Proffesor Michel Bradshaw, which describes how a river's characteristics vary between the upper course and lower course of a river. It shows that channel width, channel depth and the wetted perimeter increase downstream. The Bradshaw Model shows how certain elements of a river increase in size or amount in their journey downstream, while some decrease such as the load particle size.
In the lower course of a river, the channel is typically wider and deeper due to erosion and sediment transport, resulting in a greater wetted perimeter. This increased wetted perimeter allows for more water contact with the riverbed and banks, influencing flow dynamics and habitat availability. Additionally, the flow is often slower in the lower course, which can lead to a more pronounced interaction between the water and the surrounding environment.
Hydraulic Mean Radius = Cross sectional area of conduit divided by the inside (wetted) perimeter.
I'm trying to find out too :P But iv'e found this link :) http://www.geographyteachingtoday.org.uk/fieldwork/resource/fieldwork-techniques/rivers/cross-sections/ With wetted perimeter you simple use a measure tape and starting from one bank you run the tape along the sides and base of the channel including any bumps/holes you come across.
erosion :P
Decrease. The source of the river is usually in a mountainous area with a steep gradient.
The area will decrease but the perimeter can increase, stay the same or decrease depending upon how the piece was cut off.
Fine silt and mud are carried further downstream than heavier rocks and gravel. Which often results in muddy banks at the river mouth.
The hydraulic diameter for any cross section is: Dh= 4 * A / Wp Where Dh = hydraulic diameter A = cross sectional area Wp = wetted perimeter