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SECTION 2 - HUMAN ACTIVITIES THAT ALTER STREAM CORRIDORS Channel Modification How Channels are Modified Humans modify channels in three fundamental ways: by straightening, armoring, or constricting them. • Straightening a channel involves replacing meandering reaches with straight reaches. • Armoring involves using large rocks, car bodies, or other heavy-duty materials to stabilize a channel to prevent it from eroding. • Constricting a channel involves placing a structure such as a bridge, levee, road, or culvert across or along a stream. How Channel Modification Alters Stream Corridors Boulder Creek after Restoration • Straightening channels reduces or eliminates meanders and reduces the ability of a channel to dissipate the energy of moving water. • Armoring channels interferes with the dynamic nature of stream channels. It greatly reduces the ability of water to erode small amounts of sediment from the outsides of meander bends and deposit this sediment on the insides of meander bends downstream. • Constricting channels can reduce stream access during floods to the floodplain, causing more severe floods downstream than would otherwise be the case. Effects of Channel Modification • Increased flooding and channel downcutting (entrenchment) down- stream caused by channel straightening upstream; downcutting lowers water tables and can dry out riparian areas and wetlands. • Loss of aquatic and riparian habitat due to elimination of meanders in the process of channel straightening. Lessening Our Negative Impact • Avoid building in the floodplain. • Don't straighten stream channels in the first place; maintain sinuosity. • Use trees and shrubs instead of rip-rap to partially stabilize eroding stream banks. • Replace undersized culverts and stream crossings with properly designed and installed structures. 24 Boulder Creek before Restoration