Name one thing about a river channel that would make its Manning's 'n' value (roughness) get higher.

The presence of dense, obstructive vegetation within the river channel would make its Manning's 'n' value get higher. Manning's 'n' is a crucial coefficient used in the Manning equation to quantify the resistance that the channel's boundary exerts on the flowing water. This value, often referred to as a roughness coefficient, directly reflects the channel's ability to impede flow; a higher 'n' value signifies greater resistance. When a river channel contains significant amounts of vegetation, such as aquatic plants, grasses, shrubs, or even fallen trees and debris along its bed and banks, these elements act as physical obstructions. These obstructions create friction and turbulence as water flows past them, directly impeding the water's movement. For example, dense stands of reeds or submerged weeds present a larger surface area for water to drag against, thereby increasing the overall resistance to flow. This increased resistance on the channel's wetted perimeter is directly represented by a higher Manning's 'n' value, indicating that the water will flow slower for a given channel slope and depth.