Final answer:
Two factors that will increase the rate of a stream's flow are a steeper gradient or slope and an increased volume of water due to factors such as more rainfall or additional tributaries feeding into the stream.
Step-by-step explanation:
To answer which two factors will increase the rate of a stream's flow, one must consider the physical aspects that influence water movement. An increased gradient, meaning a steeper slope, will result in the water flowing more quickly due to gravity pulling it down the incline. Additionally, an increased volume of water entering the stream, such as through increased rainfall or additional tributaries, will cause the flow rate to rise as more water is pushed through the same channel. Other factors like the shape of the river channel and the roughness of the channel bed also affect the velocity of the stream flow.
According to fluid dynamics, as described in paragraph 21, when a liquid moves from a wider area to a smaller one, the speed of the flow increases. For streams, a narrowing of the channel can result in faster flow. The volume of water in a river is another key factor; more water entering a section of a river from tributaries leads to a higher flow rate, as referenced in the text discussing the increasing width of the channel due to more tributaries. This analogy corresponds to the behaviors of streams, where constriction can speed up water, and increased input boosts the overall flow.