That bridge is a new one, which is similar to the one connecting Avignon to Villeneuve nowadays. Behind it, you can spot an old destroyed bridge, which is a reference to the actual Pont Saint-Bénézet.

To be honest, the main reason why I chose to change the topography is because it was fun to draw and I thought it looked interesting.

Lore-wise, I guess a great river would be an odd sight in the 41st millenium Terra. Centuries of conflict changed the face of the city which is now surrounded by a gigantic crater.