EARTH 2 Study Guide - Final Guide: Geologic Time Scale, Loess, Sedimentary Rock
Document Summary
Stream channels form by downcutting and lengthen by headward erosion. They carry water from sheetwash, lakes, springs, and melting snow or ice. Drainage networks carry water from a watershed to the sea and have a variety of geometries. Permanent streams flow all year, while ephemeral streams flow only intermittently. Stream discharge, the amount of water passing through a cross section of the stream in a given time, depends on such factors as watershed area and climate. Water velocity varies across a stream, and tends to be turbulent, so calculating average velocity is complicated. Streams erode by scouring, breaking and lifting, abrasion, and dissolution. They carry sediment as dissolved, suspended, or bed loads. Competence, the ability to carry sediment, depends on flow velocity. Stream erosion and deposition yield distinct landforms. Streams have steeper regional gradients in their headwaters, and carve canyons or valleys. Gradient decreases toward a stream"s mouth - the mouth can"t be lower than a base level.
