The processes which existed in intact chain of pond systems at the time of Euro settlement, and those described by Peter Andrews in Back from the Brink are evident in this roadside gutter.
In this case, a ‘leaky weir’ formed (spilt asphalt from roadworks), slowing the water enough for sediment to drop out. This provided a bed for a wetland (weeds and grasses) to establish in the channel, which in turn captured more sediment, growing larger wetlands and so on.
The moisture and organic matter trapped by the wetland create ideal composting conditions and beautiful black soil begins to develop (Good enough for these two worms to decide to start a family)
When the flow is obstructed by the vegetation in the ‘wetlands’, it’s forced from the channel onto the floodplain (road). As the flow spreads and slows on the rough, well vegetated surface (blue metal chunks), bulk biomass and fertility from the wetlands is deposited. Here, the biomass has accumulated on contour, similar to this other post.
Copyright Cam Wilson, Earth Integral 2012