Why Thames has more water in it by the time it reaches London?

The Thames River has more water by the time it reaches London due to the cumulative effect of numerous tributaries and streams that feed into it as it flows southeast. Additionally, the river's course passes through various landscapes, including rural areas where rainfall and runoff contribute to its flow. As it approaches London, tidal influences from the North Sea also play a role, causing the river to swell during high tide. These factors combine to increase the volume of water in the Thames as it enters the capital.