Bucket List: Arched Bridge

On a vacation a few years back in the Amani Mountains (sometimes called East Usambara Mtns)  we liked the place and ended up buying a few acres and this house at a price we couldnt pass up.  There is a spring down in a steep ravine. 

The problem is we need a bridge.  We have another plot further up the river and here is the bridge to get there.

Up by the house I have been collecting these stones, to make an arched bridge over the river in a narrow spot.  I want to make a stone arched bridge before i kick it.