If they are close to the ocean, fresh water is flowing into the ocean, so we"re losing fresh water to salt water: our water sources are lakes (surface water), aquifers (ground water) If you look at rivers, that"s usually where cities are set up because it"s easy access to fresh water. V7) and in some you will underestimate (ex. V4) accuracy: highest speed is closer to the surface of the stream but we want to know the average speed, not the fastest speed. If you go down to 60% of the depth, it"s a good average speed to measure for that rectangle. If water table higher than stream level, water flows into stream (like in diagram) If water table lower than stream, water flows from stream into groundwater. Discharge volume of water moving past a given point per unit time; product of cross section area and stream velocity.