I hadn't noticed those drains!
Are they really that close to the houses and pillars?
Is there no railing or protection?
For main streets, drains are typically dug out between the roadway and the covered walkway (exposed sidewalks are not common in built up areas of the town). Side streets need not include any sidewalks, so the drains along these roadways hug the sides of buildings or boundaries in each block. And yes, there are no railings. Pedestrians or vehicles CAN fall into the drain by accident. An exception to the rule may be municipal buildings, where concrete slabs may be placed over drains to cover up its unsightliness. Also, the drains will usually have to be substantially deep to handle excess rainwater. The climate here calls for rainy seasons which can trigger overflowing of nearby rivers, and flooding.
I'm having a hard time finding exact illustrations (given people here don't seem to have an interest in these things), but here is one that roughly depicts the type of design I'm aiming for:
Of course, the drain I would be using for this part of town will typically be much shallower (knee deep, the most) and narrower, and lack these support pillars. Also, the drains to be illustrated are meant to be made of from pre-fab concrete pieces, instead of the more elaborate rock-and-concrete construction pictured. However, the latter design may be used for wider and sturdier mainline drainage leading to rivers (the drainage route can be hammered out later).
