What is the measure of the largest particles a stream can carry is it competence or capacity or discharge or gradient

Answer;

Competence

Competence is the measurement of the largest particles a stream can carry (increases with velocity).

Explanation;

A stream is defined as all channelized movement of water, including large movements of water in rivers, such as the Yangtze River and the Mississippi River

Stream competence is the size of sedimentary particle that can be carried, moved, transported in a channelized stream of water. Each stream has a competency for what size of sedimentary particle it can move by its force (volume and velocity). This competency may change as stream volume and flow of velocity change due to seasonal flooding and other factors of topography.

The difference between stream capacity and stream competence is that capacity measures quantity of sediment while competence measures size of particles comprising sediment.

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.