When a large block of ice is added to a hot cup of water then it won't melt the ice because mass of water is less. Therefore, heat released or given out by it will be less. Whereas lake is able to dissolve the large block of ice because lake has large mass and thus it will have more heat
If you are measuring the rate of water flow, which in other words, the speed of the water flow,
Then you need to divide the water quantity by time
What’s the rest of the question or is that it?