What is the primary device used to estimate slope steepness in the field?

The primary device used to estimate slope steepness in the field is a clinometer. This instrument specifically measures angles of slope, elevation, or depression of a surface, making it especially useful in determining how steep a hill or terrain is. By using a clinometer, a user can directly read the angle of inclination, which allows for quick and accurate evaluations of slope steepness.

In contrast, other tools like a surveyor's level is primarily used for establishing a horizontal plane to ensure level measurements over a distance. While it can provide information relevant to slope, it does not measure the slope angle itself directly. A GPS device is focused on determining geographical locations and can provide elevation data, but it doesn't offer the immediate slope steepness reading that a clinometer does. Lastly, a water level, which uses the principle of hydraulic balance to show level differences, is effective for short distances but is not ideal for directly measuring slope angles in varying terrains. Thus, the clinometer remains the most appropriate choice for assessing slope steepness efficiently in field conditions.