Here's why:

* Gradient is the measure of how steep a slope is. It's calculated as the change in elevation over a certain distance.

* Shallow or no slope means there's a small change in elevation over a given distance.

* Therefore, a stream with a shallow or no slope will have a low gradient.

Example:

Imagine a stream flowing across a flat plain. The elevation change is very small, even over a long distance. This would result in a low gradient stream.

Contrast:

A stream flowing down a steep mountainside would have a high gradient due to the significant change in elevation over a short distance.