River Bandits

Ok, brief update to yesterday (I was too lazy to look this up at the time)... Chains have 10 hp and require a DC20 Strength check to break, and manacles 15 hp, DC20 Strength to break as well. Manacles can also be escaped with a successful DC20 Dexterity check, or the lock picked with thieves' tools on a DC15 Dexterity check.
On a side note, I offered the encounter yesterday with its setup and the intent of the party being taken prisoner, in the end assuming that was the outcome. It is entirely possible the party could defend themselves and not get taken prisoner, or that DM discretion would have to intercede and swarm the party with a never ending supply of bandits until they were defeated or surrendered to get the desired result. The best option would be a wand of sleep with several charges... but none exist in the DMG. Speaking of which, I thought a great option for taking the party by surprise would be tossing some dust of darkness into their fire... but nothing like that exists. Maybe its time to invent some magic items! I think there would be tiny glass balls or marbles that would have the dust inside them, smash them, and voila - darkness!
I digress. Back on track, the encounter with the bandits' ambush can end with party victory or party capture. Bandits are a basic NPC type, with bandit captains making worthy adversaries. For a first level party, the straight numbers might work fine, but if the party is second level, the bandits should probably be second level as well. Looking at their stats, just giving them an extra d8 hp might be enough to keep them a challenge.
Either way, at some point the party will be free of the bandits, but at the risk of encountering more. This section of river is perfect for them, with the easily accessible banks and gentle wooded hillsides concealing plenty of caves and secret dells for them to operate from. If the party is able to regain their boat and continue upriver afloat, they should expect repeated ambush attempts and outright assaults at other times. The bandits tend to operate in groups of 3-5, often with a bandit captain leading them.
If the party escapes and tries moving upriver on foot, the travel is slow, but it would allow them to become the hunter rather than the hunted, and let them ambush bandit groups or encounter their hideouts. This could be a nice way to gather a little coin, and the odd bit of weapon or magic. Bandit groups will have 2d4x10 gp, while a camp would have 3d6x10 gp, as well as extra swords or bows, shield, and the occasional magic item.
The bandits threaten about a 20 mile stretch of river around the first red dot on yesterday's map. Beyond this point, the river narrows and flows more rapidly, making it more difficult to travel on, and the mountain slopes are steeper and more rocky, with fewer trees and areas of cover. There are more caves, so the travel can be as dangerous or more, but the danger is that of orc and troglodyte, less of men.