Environmental effects of aggregate extraction from river channels and floodplains
G. Mathias Kondolf
Abstract
River channels and floodplains are important sources of aggregate in many settings by virtue of the durability of river-worked gravels and their sorting by fluvial processes. Extraction of aggregate from rivers and floodplains involves a host of environmental effects that are distinct from, and in addition to, the environmental effects of upland quarries. Instream mining can result in channel instability through the direct disruption of preexisting channel geometry or through the effects of incision and related undercutting of banks. By analogy to incision from sediment starvation downstream of dams, incision from gravel mines can be expected to propagate farther in finer gravels and sands than in coarse gravels, because of armoring effects in the latter. By interrupting the continuity of sediment transport through the river system, mining can induce channel incision downstream and upstream. The change in sediment mass balance affected by instream gravel mining can be utilized as a tool for river control on aggrading rivers.