In the film The Lord of the Rings: The Two Towers, Faramir and his group of Rangers (with the captive Frodo, Sam and Gollum in tow) witness smoke rising from Osgiliath, which is under attack by Sauron's army. They are clearly on the eastern bank of the Anduin River since Minas Tirith (located west of Osgiliath) is visible on the horizon.
However, the subsequent scene shows the group on the western bank (in the western half of Osgiliath), desperately fending off arrows and catapult missiles from the Orcs who, according to Faramir's subordinate,
have taken the eastern shore. Their numbers are too many.
The tone of the conversation suggests that the group did not physically battle the enemy troops during their crossing of the River.
In a later scene (Extended Edition) Faramir shows the Hobbits (for the first time) the old sewers running under the river, with which to return to the east bank en route to Mordor.
In view of the above, how did the group initially cross the Anduin into West Osgiliath without using the sewers AND without battling an overwhelmingly large enemy force on the eastern bank?