Streams carry sediment, like pebbles, in their flows. The pebbles can be in a variety of locations in the flow, depending on it's size, the balance between the upwards velocity on the pebble (drag and lift forces), and it's settling velocity.
1) The equivalent resistance of two resistors in parallel is given by:

so in our problem we have

and the equivalent resistance is

2) If we have a battery of 12 V connected to the circuit, the current in the circuit will be given by Ohm's law, therefore: