EARTHSC 2GG3 Lecture : Earth Science - Lecture 35.docx

• School: McMaster University
• Department: Earth Sciences
• Course: EARTHSC 2GG3
• Professor: Sergei Basik

Document Summary

Early towns established along rivers for access to water and transportation. Severe alterations of landscape through urbanization, logging, grazing, forest fires. Increasing urbanization promotes increasing numbers of flash floods and higher flood levels. Wherever roads and buildings cover landscape, water is forced to run off rapidly into nearby streams (sometimes through concrete channels) Driving through flooded roadway can be dangerous (even fatal) because: force of water against car can wash it downstream, deep erosion may not be visible underwater, difficult to escape from submerged and sinking car. Deforestation of watershed by fire, heavy logging or overgrazing caused increased sediment load. Streams become choked with sediment, braided, steeper. Fire: removes soil protection, decreases soil permeability. Clear-cut logging: methods remove brush, form skid trails and logging roads that focus downslope drainage and add sediment to streams. Grazing: removes surface vegetation, increases soil erosion. Mining: can change sediment load, disrupts the structure of the channel.